Academic Appointments


Administrative Appointments


  • Editorial Board, Tissue Engineering (A, B, C) (2015 - 2018)
  • Session Editor of Biomaterials topic, Journal of Orthopedic Translation (2013 - Present)
  • Director-at-Large, International Association For Dental Research (IADR) Implantology Research Group (2010 - Present)
  • Voting member, U.S. Technical Advisory Group for ISO/TC 106 Dentistry (2008 - Present)
  • Editorial Board, Journal of Thermodynamics & Catalysis (2010 - Present)
  • Editorial Board, Journal of Cancer Science & Therapy (2010 - Present)
  • Editorial Board, The International Journal of Oral & Maxillofacial Implants (2007 - Present)

Honors & Awards


  • Research Award, National Institute of Health (2014-2019)
  • 2014 Defense University Research Instrumentation Program Award, Army Research Office (2014)
  • Coulter Translational Research Seed Grant, Stanford Coulter Program (2014)
  • Spark Seed Grant Award, Stanford Spark Program (2014)
  • Research Award, Foundation of Orthopedic Trauma (2014)
  • Research Diversity Supplement Award, National Institutes of Health (2012-2015)
  • Research Diversity Supplement Award, National Institutes of Health (2012-2014)
  • Research Award, NanoHealth Alliance (2011-2013)
  • Research Award, National Institutes of Health (2011-2015)
  • Wallace H. Coulter Fellow, Wallace H. Coulter Foundation (2011)
  • Dean’s Teaching Excellence Award in “Scholarship of Engagement and Collaboration”, the University of Texas Health Science Center at Houston (2011)
  • Congressional Briefing on translational research breakthroughs at Capitol Hill, the American Institute of Medical and Biological Engineering (2010)
  • Research Award, Department of Defense (2010-2014)
  • Research Award, National Institutes of Health (2010-2014)
  • Research Award, Airlift Research Foundation (2010-2012)
  • Early Career Translational Research Award Phase II, Wallace H Coulter Foundation (2009-2012)
  • Young Investigator Award, the University of Texas Health Science Center at Houston (2009)
  • Research Award, UTRF Technology Maturation Fund Program (2008-2009)
  • Aircast Award for Basic Science, AMERICAN ORTHOPAEDC SOCIETY FOR SPORTS MEDICINE (2008)
  • Research Award, Implant Dentistry Research and Education Foundation (2007-2009)
  • Early Career Translational Research Award Phase I, Wallace H Coulter Foundation (2007-2009)
  • Research Award, March of Dimes Foundation (2006-2010)
  • Research Award, Memphis Bioworks Foundation (2005-2006)

Professional Education


  • Postdoctoral Fellow, University of Texas Health Science Center at San Antonio, San Antonio, TX, Biomaterials (2003)
  • Postdoctoral Fellow, West China University of Medical Sciences, Chengdu, China, Biomaterials (1999)
  • Ph.D., Sichuan University, Chengdu, China, Biomedical Engineering (1997)
  • M.E., Sichuan University, Chengdu, China, Inorganic Materials (1995)
  • B.S., Sichuan University, Chengdu, China, Inorganic Materials (1992)

Current Research and Scholarly Interests


Our research interests are in the areas of biomaterials, implant devices, drug delivery, and musculoskeletal tissue engineering. In particular, we are interested in developing bio-inspired biomaterials and platform technologies to engineer tissues and organs. We aim to improve understanding of tissue-like chemistry and structure approaches of implant device design and fabrication, how these lead to tissue-like properties and functions, and the extent to which they can enhance clinical outcomes. Our research methodology includes concept design and development, characterization and evaluation, in vitro and in vivo validation of novel biomaterials and implant devices. Our current program comprises the following themes: Enabling technology for musculoskeletal tissue engineering, surface nanotechnology for osseointegrated implant devices, and naturally derived novel biomaterials for cancer treatment.

2014-15 Courses


Journal Articles


  • Vascularization in Bone Tissue Engineering Constructs. Annals of biomedical engineering Mercado-Pagán, Á. E., Stahl, A. M., Shanjani, Y., Yang, Y. 2015

    Abstract

    Vascularization of large bone grafts is one of the main challenges of bone tissue engineering (BTE), and has held back the clinical translation of engineered bone constructs for two decades so far. The ultimate goal of vascularized BTE constructs is to provide a bone environment rich in functional vascular networks to achieve efficient osseointegration and accelerate restoration of function after implantation. To attain both structural and vascular integration of the grafts, a large number of biomaterials, cells, and biological cues have been evaluated. This review will present biological considerations for bone function restoration, contemporary approaches for clinical salvage of large bone defects and their limitations, state-of-the-art research on the development of vascularized bone constructs, and perspectives on evaluating and implementing novel BTE grafts in clinical practice. Success will depend on achieving full graft integration at multiple hierarchical levels, both between the individual graft components as well as between the implanted constructs and their surrounding host tissues. The paradigm of vascularized tissue constructs could not only revolutionize the progress of BTE, but could also be readily applied to other fields in regenerative medicine for the development of new innovative vascularized tissue designs.

    View details for DOI 10.1007/s10439-015-1253-3

    View details for PubMedID 25616591

  • Engineering a vascularized collagen-β-tricalcium phosphate graft using an electrochemical approach. Acta biomaterialia Kang, Y., Mochizuki, N., Khademhosseini, A., Fukuda, J., Yang, Y. 2015; 11: 449-58

    Abstract

    Vascularization of three-dimensional large synthetic grafts for tissue regeneration remains a significant challenge. Here we demonstrate an electrochemical approach, named the cell electrochemical detachment (CED) technique, to form an integral endothelium and use it to prevascularize a collagen-β-tricalcium phosphate (β-TCP) graft. The CED technique electrochemically detached an integral endothelium from a gold-coated glass rod to a collagen-infiltrated, channeled, macroporous β-TCP scaffold, forming an endothelium-lined microchannel containing graft upon removal of the rod. The in vitro results from static and perfusion culture showed that the endothelium robustly emanated microvascular sprouting and prevascularized the entire collagen/β-TCP integrated graft. The in vivo subcutaneous implantation studies showed that the prevascularized collagen/β-TCP grafts established blood flow originating from the endothelium-lined microchannel within a week, and the blood flow covered more areas in the graft over time. In addition, many blood vessels invaded the prevascularized collagen/β-TCP graft and the in vitro preformed microvascular networks anastomosed with the host vasculature, while collagen alone without the support of rigid ceramic scaffold showed less blood vessel invasion and anastomosis. These results suggest a promising strategy for effectively vascularizing large tissue-engineered grafts by integrating multiple hydrogel-based CED-engineered endothelium-lined microchannels into a rigid channeled macroporous scaffold.

    View details for DOI 10.1016/j.actbio.2014.09.035

    View details for PubMedID 25263031

  • Novel osteoinductive photo-cross-linkable chitosan-lactide-fibrinogen hydrogels enhance bone regeneration in critical size segmental bone defects ACTA BIOMATERIALIA Kim, S., Bedigrew, K., Guda, T., Maloney, W. J., Park, S., Wenke, J. C., Yang, Y. P. 2014; 10 (12): 5021-5033
  • Biodegradable Photocrosslinkable Poly(depsipeptide-co-epsilon-caprolactone) for Tissue Engineering: Synthesis, Characterization, and In Vitro Evaluation JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Elomaa, L., Kang, Y., Seppala, J. V., Yang, Y. 2014; 52 (23): 3307-3315

    View details for DOI 10.1002/pola.27400

    View details for Web of Science ID 000344359500002

  • Fabrication, vascularization and osteogenic properties of a novel synthetic biomimetic induced membrane for the treatment of large bone defects BONE Ren, L., Kang, Y., Browne, C., Bishop, J., Yang, Y. 2014; 64: 173-182

    Abstract

    The induced membrane has been widely used in the treatment of large bone defects but continues to be limited by a relatively lengthy healing process and a requisite two stage surgical procedure. Here we report the development and characterization of a synthetic biomimetic induced membrane (BIM) consisting of an inner highly pre-vascularized cell sheet and an outer osteogenic layer using cell sheet engineering. The pre-vascularized inner layer was formed by seeding human umbilical vein endothelial cells (HUVECs) on a cell sheet comprised of a layer of undifferentiated human bone marrow-derived mesenchymal stem cells (hMSCs). The outer osteogenic layer was formed by inducing osteogenic differentiation of hMSCs. In vitro results indicated that the undifferentiated hMSC cell sheet facilitated the alignment of HUVECs and significantly promoted the formation of vascular-like networks. Furthermore, seeded HUVECs rearranged the extracellular matrix produced by hMSC sheet. After subcutaneous implantation, the composite constructs showed rapid vascularization and anastomosis with the host vascular system, forming functional blood vessels in vivo. Osteogenic potential of the BIM was evidenced by immunohistochemistry staining of osteocalcin, tartrate-resistant acid phosphatase (TRAP) staining, and alizarin red staining. In summary, the synthetic BIM showed rapid vascularization, significant anastomoses, and osteogenic potential in vivo. This synthetic BIM has the potential for treatment of large bone defects in the absence of infection.

    View details for DOI 10.1016/j.bone.2014.04.011

    View details for Web of Science ID 000337011500024

    View details for PubMedID 24747351

  • Engineering Vascularized Bone Grafts by Integrating a Biomimetic Periosteum and beta-TCP Scaffold ACS APPLIED MATERIALS & INTERFACES Kang, Y., Ren, L., Yang, Y. 2014; 6 (12): 9622-9633

    Abstract

    Treatment of large bone defects using synthetic scaffolds remain a challenge mainly due to insufficient vascularization. This study is to engineer a vascularized bone graft by integrating a vascularized biomimetic cell-sheet-engineered periosteum (CSEP) and a biodegradable macroporous beta-tricalcium phosphate (β-TCP) scaffold. We first cultured human mesenchymal stem cells (hMSCs) to form cell sheet and human umbilical vascular endothelial cells (HUVECs) were then seeded on the undifferentiated hMSCs sheet to form vascularized cell sheet for mimicking the fibrous layer of native periosteum. A mineralized hMSCs sheet was cultured to mimic the cambium layer of native periosteum. This mineralized hMSCs sheet was first wrapped onto a cylindrical β-TCP scaffold followed by wrapping the vascularized HUVEC/hMSC sheet, thus generating a biomimetic CSEP on the β-TCP scaffold. A nonperiosteum structural cell sheets-covered β-TCP and plain β-TCP were used as controls. In vitro studies indicate that the undifferentiated hMSCs sheet facilitated HUVECs to form rich capillary-like networks. In vivo studies indicate that the biomimetic CSEP enhanced angiogenesis and functional anastomosis between the in vitro preformed human capillary networks and the mouse host vasculature. MicroCT analysis and osteocalcin staining show that the biomimetic CSEP/β-TCP graft formed more bone matrix compared to the other groups. These results suggest that the CSEP that mimics the cellular components and spatial configuration of periosteum plays a critical role in vascularization and osteogenesis. Our studies suggest that a biomimetic periosteum-covered β-TCP graft is a promising approach for bone regeneration.

    View details for DOI 10.1021/am502056q

    View details for Web of Science ID 000338184500088

    View details for PubMedID 24858072

  • Radiation combined injury models to study the effects of interventions and wound biomechanics. Radiation research Zawaski, J. A., Yates, C. R., Miller, D. D., Kaffes, C. C., Sabek, O. M., Afshar, S. F., Young, D. A., Yang, Y., Gaber, M. W. 2014; 182 (6): 640-52

    Abstract

    In the event of a nuclear detonation, a considerable number of projected casualties will suffer from combined radiation exposure and burn and/or wound injury. Countermeasure assessment in the setting of radiation exposure combined with dermal injury is hampered by a lack of animal models in which the effects of interventions have been characterized. To address this need, we used two separate models to characterize wound closure. The first was an open wound model in mice to study the effect of wound size in combination with whole-body 6 Gy irradiation on the rate of wound closure, animal weight and survival (morbidity). In this model the addition of interventions, wound closure, subcutaneous vehicle injection, topical antiseptic and topical antibiotics were studied to measure their effect on healing and survival. The second was a rat closed wound model to study the biomechanical properties of a healed wound at 10 days postirradiation (irradiated with 6 or 7.5 Gy). In addition, complete blood counts were performed and wound pathology by staining with hematoxylin and eosin, trichrome, CD68 and Ki67. In the mouse open wound model, we found that wound size and morbidity were positively correlated, while wound size and survival were negatively correlated. Regardless of the wound size, the addition of radiation exposure delayed the healing of the wound by approximately 5-6 days. The addition of interventions caused, at a minimum, a 30% increase in survival and improved mean survival by ∼9 days. In the rat closed wound model we found that radiation exposure significantly decreased all wound biomechanical measurements as well as white blood cell, platelet and red blood cell counts at 10 days post wounding. Also, pathological changes showed a loss of dermal structure, thickening of dermis, loss of collagen/epithelial hyperplasia and an increased density of macrophages. In conclusion, we have characterized the effect of a changing wound size in combination with radiation exposure. We also demonstrated that the most effective interventions mitigated insensible fluid loss, which could help to define the most appropriate requirements of a successful countermeasure.

    View details for DOI 10.1667/RR13751.1

    View details for PubMedID 25409125

  • Hemocompatibility evaluation of small elastomeric hollow fiber membranes as vascular substitutes. Journal of biomaterials applications Mercado-Pagán, Á. E., Ker, D. F., Yang, Y. 2014; 29 (4): 557-65

    Abstract

    One of the main challenges for clinical implementation of small diameter vascular grafts (SDVGs) is their limited hemocompatibility. Important design specifications for such grafts include features that minimize the long-term risks of restenosis, fouling, and thrombus formation. In our lab, we have developed elastomeric hollow fiber membranes (HFMs), using a phase inversion method, as candidates for SDVGs. Here, we present our results for in vitro hemocompatibility testing of our HFM under flow and static conditions. Our results showed that the polymer-based HFMs do not damage the integrity of human red blood cells (RBCs) as shown by their low hemolytic extent (less than 2%). When analyzed for blood cell lysis using lactate dehydrogenase (LDH) activity as an indicator, no significant differences were observed between blood exposed to our HFMs and uncoagulated blood. Analysis of protein adsorption showed a low concentration of proteins deposited on the surfaces of HFM after 24 h. Platelet adhesion profiles using human platelet-rich plasma (PRP) showed that a low level of platelets adhered to the HFMs after 24 h, indicating minimal thrombotic potential. Under the majority of conditions, no significant differences were observed between medical-grade polymers and our HFMs. Eventual optimization of hemocompatible elastomeric HFM vessel grafts could lead to improved tissue vascularization as well as vascularized, tissue-engineered scaffolds for organ repair.

    View details for DOI 10.1177/0885328214537541

    View details for PubMedID 24913612

  • Hydrogel bioprinted microchannel networks for vascularization of tissue engineering constructs LAB ON A CHIP Bertassoni, L. E., Cecconi, M., Manoharan, V., Nikkhah, M., Hjortnaes, J., Cristino, A. L., Barabaschi, G., Demarchi, D., Dokmeci, M. R., Yang, Y., Khademhosseini, A. 2014; 14 (13): 2202-2211

    Abstract

    Vascularization remains a critical challenge in tissue engineering. The development of vascular networks within densely populated and metabolically functional tissues facilitate transport of nutrients and removal of waste products, thus preserving cellular viability over a long period of time. Despite tremendous progress in fabricating complex tissue constructs in the past few years, approaches for controlled vascularization within hydrogel based engineered tissue constructs have remained limited. Here, we report a three dimensional (3D) micromolding technique utilizing bioprinted agarose template fibers to fabricate microchannel networks with various architectural features within photocrosslinkable hydrogel constructs. Using the proposed approach, we were able to successfully embed functional and perfusable microchannels inside methacrylated gelatin (GelMA), star poly(ethylene glycol-co-lactide) acrylate (SPELA), poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(ethylene glycol) diacrylate (PEGDA) hydrogels at different concentrations. In particular, GelMA hydrogels were used as a model to demonstrate the functionality of the fabricated vascular networks in improving mass transport, cellular viability and differentiation within the cell-laden tissue constructs. In addition, successful formation of endothelial monolayers within the fabricated channels was confirmed. Overall, our proposed strategy represents an effective technique for vascularization of hydrogel constructs with useful applications in tissue engineering and organs on a chip.

    View details for DOI 10.1039/c4lc00030g

    View details for Web of Science ID 000337096800008

    View details for PubMedID 24860845

  • Deletion of the Transforming Growth Factor beta Receptor Type II Gene in Articular Chondrocytes Leads to a Progressive Osteoarthritis-like Phenotype in Mice ARTHRITIS AND RHEUMATISM Shen, J., Li, J., Wang, B., Jin, H., Wang, M., Zhang, Y., Yang, Y., Im, H., O'Keefe, R., Chen, D. 2013; 65 (12): 3107-3119

    Abstract

    While transforming growth factor β (TGFβ) signaling plays a critical role in chondrocyte metabolism, the TGFβ signaling pathways and target genes involved in cartilage homeostasis and the development of osteoarthritis (OA) remain unclear. Using an in vitro cell culture method and an in vivo mouse genetic approach, we undertook this study to investigate TGFβ signaling in chondrocytes and to determine whether Mmp13 and Adamts5 are critical downstream target genes of TGFβ signaling.TGFβ receptor type II (TGFβRII)-conditional knockout (KO) (TGFβRII(Col2ER)) mice were generated by breeding TGFβRII(flox/flox) mice with Col2-CreER-transgenic mice. Histologic, histomorphometric, and gene expression analyses were performed. In vitro TGFβ signaling studies were performed using chondrogenic rat chondrosarcoma cells. To determine whether Mmp13 and Adamts5 are critical downstream target genes of TGFβ signaling, TGFβRII/matrix metalloproteinase 13 (MMP-13)- and TGFβRII/ADAMTS-5-double-KO mice were generated and analyzed.Inhibition of TGFβ signaling (deletion of the Tgfbr2 gene in chondrocytes) resulted in up-regulation of Runx2, Mmp13, and Adamts5 expression in articular cartilage tissue and progressive OA development in TGFβRII(Col2ER) mice. Deletion of the Mmp13 or Adamts5 gene significantly ameliorated the OA-like phenotype induced by the loss of TGFβ signaling. Treatment of TGFβRII(Col2ER) mice with an MMP-13 inhibitor also slowed OA progression.Mmp13 and Adamts5 are critical downstream target genes involved in the TGFβ signaling pathway during the development of OA.

    View details for DOI 10.1002/art.38122

    View details for Web of Science ID 000327692600014

    View details for PubMedID 23982761

  • Synthesis and characterization of novel elastomeric poly(D,L-lactide urethane) maleate composites for bone tissue engineering EUROPEAN POLYMER JOURNAL Mercado-Pagan, A. E., Kang, Y., Ker, D. F., Park, S., Yao, J., Bishop, J., Yang, Y. P. 2013; 49 (10): 3337-3349
  • The effect of rhBMP-2 and PRP delivery by biodegradable beta-tricalcium phosphate scaffolds on new bone formation in a non-through rabbit cranial defect model JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE Lim, H., Mercado-Pagan, A. E., Yun, K., Kang, S., Choi, T., Bishop, J., Koh, J., Maloney, W., Lee, K., Yang, Y. P., Park, S. 2013; 24 (8): 1895-1903

    Abstract

    This study evaluated whether the combination of biodegradable β-tricalcium phosphate (β-TCP) scaffolds with recombinant human bone morphogenetic protein-2 (rhBMP-2) or platelet-rich plasma (PRP) could accelerate bone formation and increase bone height using a rabbit non-through cranial bone defect model. Four non-through cylindrical bone defects with a diameter of 8-mm were surgically created on the cranium of rabbits. β-TCP scaffolds in the presence and absence of impregnated rhBMP-2 or PRP were placed into the defects. At 8 and 16 weeks after implantation, samples were dissected and fixed for analysis by microcomputed tomography and histology. Only defects with rhBMP-2 impregnated β-TCP scaffolds showed significantly enhanced bone formation compared to non-impregnated β-TCP scaffolds (P < 0.05). Although new bone was higher than adjacent bone at 8 weeks after implantation, vertical bone augmentation was not observed at 16 weeks after implantation, probably due to scaffold resorption occurring concurrently with new bone formation.

    View details for DOI 10.1007/s10856-013-4939-9

    View details for Web of Science ID 000321915300008

    View details for PubMedID 23779152

  • Modeling vascularized bone regeneration within a porous biodegradable CaP scaffold loaded with growth factors BIOMATERIALS Sun, X., Kang, Y., Bao, J., Zhang, Y., Yang, Y., Zhou, X. 2013; 34 (21): 4971-4981

    Abstract

    Osteogenetic microenvironment is a complex constitution in which extracellular matrix (ECM) molecules, stem cells and growth factors each interact to direct the coordinate regulation of bone tissue development. Importantly, angiogenesis improvement and revascularization are critical for osteogenesis during bone tissue regeneration processes. In this study, we developed a three-dimensional (3D) multi-scale system model to study cell response to growth factors released from a 3D biodegradable porous calcium phosphate (CaP) scaffold. Our model reconstructed the 3D bone regeneration system and examined the effects of pore size and porosity on bone formation and angiogenesis. The results suggested that scaffold porosity played a more dominant role in affecting bone formation and angiogenesis compared with pore size, while the pore size could be controlled to tailor the growth factor release rate and release fraction. Furthermore, a combination of gradient VEGF with BMP2 and Wnt released from the multi-layer scaffold promoted angiogenesis and bone formation more readily than single growth factors. These results demonstrated that the developed model can be potentially applied to predict vascularized bone regeneration with specific scaffold and growth factors.

    View details for DOI 10.1016/j.biomaterials.2013.03.015

    View details for Web of Science ID 000319630000008

    View details for PubMedID 23566802

  • Osteogenic and angiogenic potentials of monocultured and co-cultured human-bone-marrow-derived mesenchymal stem cells and human-umbilical-vein endothelial cells on three-dimensional porous beta-tricalcium phosphate scaffold ACTA BIOMATERIALIA Kang, Y., Kim, S., Fahrenholtz, M., Khademhosseini, A., Yang, Y. 2013; 9 (1): 4906-4915

    Abstract

    The use of biodegradable beta-tricalcium phosphate (?-TCP) scaffolds holds great promise for bone tissue engineering. However, the effects of ?-TCP on bone and endothelial cells are not fully understood. This study aimed to investigate cell proliferation and differentiation of mono- or co-cultured human-bone-marrow-derived mesenchymal stem cells (hBMSCs) and human-umbilical-vein endothelial cells (HUVECs) on a three-dimensional porous, biodegradable ?-TCP scaffold. In co-culture studies, the ratios of hBMSCs:HUVECs were 5:1, 1:1 and 1:5. Cellular morphologies of HUVECs, hBMSCs and co-cultured HUVECs/hBMSCs on the ?-TCP scaffolds were monitored using confocal and scanning electron microscopy. Cell proliferation was monitored by measuring the amount of double-stranded DNA (dsDNA) whereas hBMSC and HUVEC differentiation was assessed using the osteogenic and angiogenic markers, alkaline phosphatase (ALP) and PECAM-1 (CD31), respectively. Results show that HUVECs, hBMSCs and hBMSCs/HUVECs adhered to and proliferated well on the ?-TCP scaffolds. In monoculture, hBMSCs grew faster than HUVECs on the ?-TCP scaffolds after 7 days, but HUVECs reached similar levels of proliferation after 14 days. In monoculture, ?-TCP scaffolds promoted ALP activities of both hBMSCs and HUVECs when compared to those grown on tissue culture well plates. ALP activity of cells in co-culture was higher than that of hBMSCs in monoculture. Real-time polymerase chain reaction results indicate that runx2 and alp gene expression in monocultured hBMSCs remained unchanged at days 7 and 14, but alp gene expression was significantly increased in hBMSC co-cultures when the contribution of individual cell types was not distinguished.

    View details for DOI 10.1016/j.actbio.2012.08.008

    View details for Web of Science ID 000313376900047

    View details for PubMedID 22902820

  • Directed endothelial cell morphogenesis in micropatterned gelatin methacrylate hydrogels BIOMATERIALS Nikkhah, M., Eshak, N., Zorlutuna, P., Annabi, N., Castello, M., Kim, K., Dolatshahi-Pirouz, A., Edalat, F., Bae, H., Yang, Y., Khademhosseini, A. 2012; 33 (35): 9009-9018

    Abstract

    Engineering of organized vasculature is a crucial step in the development of functional and clinically relevant tissue constructs. A number of previous techniques have been proposed to spatially regulate the distribution of angiogenic biomolecules and vascular cells within biomaterial matrices to promote vascularization. Most of these approaches have been limited to two-dimensional (2D) micropatterned features or have resulted in formation of random vasculature within three-dimensional (3D) microenvironments. In this study, we investigate 3D endothelial cord formation within micropatterned gelatin methacrylate (GelMA) hydrogels with varying geometrical features (50-150 ?m height). We demonstrated the significant dependence of endothelial cells proliferation, alignment and cord formation on geometrical dimensions of the patterned features. The cells were able to align and organize within the micropatterned constructs and assemble to form cord structures with organized actin fibers and circular/elliptical cross-sections. The inner layer of the cord structure was filled with gel showing that the micropatterned hydrogel constructs guided the assembly of endothelial cells into cord structures. Notably, the endothelial cords were retained within the hydrogel microconstructs for all geometries after two weeks of culture; however, only the 100 ?m-high constructs provided the optimal microenvironment for the formation of circular and stable cord structures. Our findings suggest that endothelial cord formation is a preceding step to tubulogenesis and the proposed system can be used to develop organized vasculature for engineered tissue constructs.

    View details for DOI 10.1016/j.biomaterials.2012.08.068

    View details for Web of Science ID 000310721900011

    View details for PubMedID 23018132

  • Cytokine combination therapy prediction for bone remodeling in tissue engineering based on the intracellular signaling pathway BIOMATERIALS Sun, X., Su, J., Bao, J., Peng, T., Zhang, L., Zhang, Y., Yang, Y., Zhou, X. 2012; 33 (33): 8265-8276

    Abstract

    The long-term performance of tissue-engineered bone grafts is determined by a dynamic balance between bone regeneration and resorption. We proposed using embedded cytokine slow-releasing hydrogels to tune this balance toward a desirable final bone density. In this study we established a systems biology model, and quantitatively explored the combinatorial effects of delivered cytokines from hydrogels on final bone density. We hypothesized that: 1) bone regeneration was driven by transcription factors Runx2 and Osterix, which responded to released cytokines, such as Wnt, BMP2, and TGF?, drove the development of osteoblast lineage, and contributed to bone mass generation; and 2) the osteoclast lineage, on the other hand, governed the bone resorption, and communications between these two lineages determined the dynamics of bone remodeling. In our model, Intracellular signaling pathways were represented by ordinary differential equations, while the intercellular communications and cellular population dynamics were modeled by stochastic differential equations. Effects of synergistic cytokine combinations were evaluated by Loewe index and Bliss index. Simulation results revealed that the Wnt/BMP2 combinations released from hydrogels showed best control of bone regeneration and synergistic effects, and suggested optimal dose ratios of given cytokine combinations released from hydrogels to most efficiently control the long-term bone remodeling. We revealed the characteristics of cytokine combinations of Wnt/BMP2 which could be used to guide the design of in vivo bone scaffolds and the clinical treatment of some diseases such as osteoporosis.

    View details for DOI 10.1016/j.biomaterials.2012.07.041

    View details for Web of Science ID 000310401000008

    View details for PubMedID 22910219

  • The osteogenic differentiation of human bone marrow MSCs on HUVEC-derived ECM and beta-TCP scaffold BIOMATERIALS Kang, Y., Kim, S., Bishop, J., Khademhosseini, A., Yang, Y. 2012; 33 (29): 6998-7007

    Abstract

    Extracellular matrix (ECM) serves a key role in cell migration, attachment, and cell development. Here we report that ECM derived from human umbilical vein endothelial cells (HUVEC) promoted osteogenic differentiation of human bone marrow mesenchymal stem cells (hMSC). We first produced an HUVEC-derived ECM on a three-dimensional (3D) beta-tricalcium phosphate (?-TCP) scaffold by HUVEC seeding, incubation, and decellularization. The HUVEC-derived ECM was then characterized by SEM, FTIR, XPS, and immunofluorescence staining. The effect of HUVEC-derived ECM-containing ?-TCP scaffold on hMSC osteogenic differentiation was subsequently examined. SEM images indicate a dense matrix layer deposited on the surface of struts and pore walls. FTIR and XPS measurements show the presence of new functional groups (amide and hydroxyl groups) and elements (C and N) in the ECM/?-TCP scaffold when compared to the ?-TCP scaffold alone. Immunofluorescence images indicate that high levels of fibronectin and collagen IV and low level of laminin were present on the scaffold. ECM-containing ?-TCP scaffolds significantly increased alkaline phosphatase (ALP) specific activity and up-regulated expression of osteogenesis-related genes such as runx2, alkaline phosphatase, osteopontin and osteocalcin in hMSC, compared to ?-TCP scaffolds alone. This increased effect was due to the activation of MAPK/ERK signaling pathway since disruption of this pathway using an ERK inhibitor PD98059 results in down-regulation of these osteogenic genes. Cell-derived ECM-containing calcium phosphate scaffolds is a promising osteogenic-promoting bone void filler in bone tissue regeneration.

    View details for DOI 10.1016/j.biomaterials.2012.06.061

    View details for Web of Science ID 000308269600010

    View details for PubMedID 22795852

  • Vascularized Bone Tissue Engineering: Approaches for Potential Improvement TISSUE ENGINEERING PART B-REVIEWS Nguyen, L. H., Annabi, N., Nikkhah, M., Bae, H., Binan, L., Park, S., Kang, Y., Yang, Y., Khademhosseini, A. 2012; 18 (5): 363-382

    Abstract

    Significant advances have been made in bone tissue engineering (TE) in the past decade. However, classical bone TE strategies have been hampered mainly due to the lack of vascularization within the engineered bone constructs, resulting in poor implant survival and integration. In an effort toward clinical success of engineered constructs, new TE concepts have arisen to develop bone substitutes that potentially mimic native bone tissue structure and function. Large tissue replacements have failed in the past due to the slow penetration of the host vasculature, leading to necrosis at the central region of the engineered tissues. For this reason, multiple microscale strategies have been developed to induce and incorporate vascular networks within engineered bone constructs before implantation in order to achieve successful integration with the host tissue. Previous attempts to engineer vascularized bone tissue only focused on the effect of a single component among the three main components of TE (scaffold, cells, or signaling cues) and have only achieved limited success. However, with efforts to improve the engineered bone tissue substitutes, bone TE approaches have become more complex by combining multiple strategies simultaneously. The driving force behind combining various TE strategies is to produce bone replacements that more closely recapitulate human physiology. Here, we review and discuss the limitations of current bone TE approaches and possible strategies to improve vascularization in bone tissue substitutes.

    View details for DOI 10.1089/ten.teb.2012.0012

    View details for Web of Science ID 000309516500003

    View details for PubMedID 22765012

  • Sequential delivery of BMP-2 and IGF-1 using a chitosan gel with gelatin microspheres enhances early osteoblastic differentiation ACTA BIOMATERIALIA Kim, S., Kang, Y., Krueger, C. A., Sen, M., Holcomb, J. B., Chen, D., Wenke, J. C., Yang, Y. 2012; 8 (5): 1768-1777

    Abstract

    The purpose of this study was to develop and characterize a chitosan gel/gelatin microsphere (MSs) dual delivery system for sequential release of bone morphogenetic protein-2 (BMP-2) and insulin-like growth factor-1 (IGF-1) to enhance osteoblast differentiation in vitro. We made and characterized the delivery system based on its degree of cross-linking, degradation, and release kinetics. We also evaluated the cytotoxicity of the delivery system and the effect of growth factors on cell response using pre-osteoblast W-20-17 mouse bone marrow stromal cells. IGF-1 was first loaded into MSs, and then the IGF-1-containing MSs were encapsulated into the chitosan gel which contained BMP-2. Cross-linking of gelatin with glyoxal via Schiff bases significantly increased thermal stability and decreased the solubility of the MSs, leading to a significant decrease in the initial release of IGF-1. Encapsulation of the MSs into the chitosan gel generated polyelectrolyte complexes by intermolecular interactions, which further affected the release kinetics of IGF-1. This combinational delivery system provided an initial release of BMP-2 followed by a slow and sustained release of IGF-1. Significantly greater alkaline phosphatase activity was found in W-20-17 cells treated with the sequential delivery system compared with other treatments (P<0.05) after a week of culture.

    View details for DOI 10.1016/j.actbio.2012.01.009

    View details for Web of Science ID 000302989700012

    View details for PubMedID 22293583

  • Effect of Coadministration of Vancomycin and BMP-2 on Cocultured Staphylococcus aureus and W-20-17 Mouse Bone Marrow Stromal Cells In Vitro Antimicrob. Agents Chemother A. H. Nguyen, S. Kim, W. J. Maloney, J. C. Wenke, Y. Yang 2012; 56 (7): 3776-3784
  • In vitro evaluation of an injectable chitosan gel for sustained local delivery of BMP-2 for osteoblastic differentiation. Journal of biomedical materials research. Part B, Applied biomaterials Kim, S., Tsao, H., Kang, Y., Young, D. A., Sen, M., Wenke, J. C., Yang, Y. 2011; 99 (2): 380-390

    Abstract

    We investigated the effect of sustained release of bone morphogenetic protein-2 (BMP-2) from an injectable chitosan gel on osteoblastic differentiation in vitro. We first characterized the release profile of BMP-2 from the gels, and then examined the cellular responses of preosteoblast mouse stromal cells (W-20-17) and human embryonic palatal mesenchymal (HEPM) cells to BMP-2. The release profiles of different concentrations of BMP-2 exhibited sustained releases (41% for 2 ng/mL and 48% for 20 ng/mL, respectively) from the chitosan gels over a three-week period. Both cell types cultured in the chitosan gels were viable and significantly proliferated for 3 days (p < 0.05). Chitosan gels loaded with BMP-2 enhanced ALP activity of W-20-17 by 3.6-fold, and increased calcium mineral deposition of HEPM by 2.8-fold at 14 days of incubation, compared to control groups initially containing the same amount of BMP-2. In addition, schitosan gels loaded with BMP-2 exhibited significantly greater osteocalcin synthesis of W-20-17 at seven days, and of HEPM at both 7 and 14 days compared with the control groups (p<0.05). This study suggests that the enhanced effects of BMP-2 released from chitosan gels on cell differentiation and mineralization are species and cell type dependent.

    View details for DOI 10.1002/jbm.b.31909

    View details for PubMedID 21905214

  • Creation of bony microenvironment with CaP and cell-derived ECM to enhance human bone-marrow MSC behavior and delivery of BMP-2 BIOMATERIALS Kang, Y., Kim, S., Khademhosseini, A., Yang, Y. 2011; 32 (26): 6119-6130

    Abstract

    Extracellular matrix (ECM) comprises a rich meshwork of proteins and proteoglycans, which not only contains biological cues for cell behavior, but is also a reservoir for binding growth factors and controlling their release. Here we aimed to create a suitable bony microenvironment with cell-derived ECM and biodegradable ?-tricalcium phosphate (?-TCP). More specifically, we investigated whether the ECM produced by bone marrow-derived mesenchymal stem cells (hBMSC) on a ?-TCP scaffold can bind bone morphogenetic protein-2 (BMP-2) and control its release in a sustained manner, and further examined the effect of ECM and the BMP-2 released from ECM on cell behaviors. The ECM was obtained through culturing the hBMSC on a ?-TCP porous scaffold and performing decellularization and sterilization. SEM, XPS, FTIR, and immunofluorescent staining results indicated the presence of ECM on the ?-TCP and the amount of ECM increased with the incubation time. BMP-2 was loaded onto the ?-TCP with and without ECM by immersing the scaffolds in the BMP-2 solution. The loading and release kinetics of the BMP-2 on the ?-TCP/ECM were significantly slower than those on the ?-TCP. The ?-TCP/ECM exhibited a sustained release profile of the BMP-2, which was also affected by the amount of ECM. This is probably because the ?-TCP/ECM has different binding mechanisms with BMP-2. The ?-TCP/ECM promoted cell proliferation. Furthermore, the BMP-2-loaded ?-TCP/ECM stimulated reorganization of the actin cytoskeleton, increased expression of alkaline phosphatase and calcium deposition by the cells compared to those without BMP-2 loading and the ?-TCP with BMP-2 loading.

    View details for DOI 10.1016/j.biomaterials.2011.05.015

    View details for Web of Science ID 000292904100018

    View details for PubMedID 21632105

  • SAM-based Cell Transfer to Photopatterned Hydrogels for Microengineering Vascular-Like Structures Biomaterials N. Sadr, M. Zhu, T. Osaki, T. Kakegawa, Y. Yang, M. Moretti, J. Fukuda, A. Khademhosseini 2011; 32: 7479-7490
  • Enhanced mechanical performance and biological evaluation of a PLGA coated ?-TCP composite scaffold for load-bearing applications. European polymer journal Kang, Y., Scully, A., Young, D. A., Kim, S., Tsao, H., Sen, M., Yang, Y. 2011; 47 (8): 1569-1577

    Abstract

    Porous ?-tricalcium phosphate (?-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the application of ?-TCP has been limited by its brittleness. Here, we demonstrated that an interconnected porous ?-TCP scaffold infiltrated with a thin layer of poly (lactic-co-glycolic acid) (PLGA) polymer showed improved mechanical performance compared to an uncoated ?-TCP scaffold while retaining its excellent interconnectivity and biocompatibility. The infiltration of PLGA significantly increased the compressive strength of ?-TCP scaffolds from 2.90 MPa to 4.19 MPa, bending strength from 1.46 MPa to 2.41 MPa, and toughness from 0.17 MPa to 1.44 MPa, while retaining an interconnected porous structure with a porosity of 80.65%. These remarkable improvements in the mechanical properties of PLGA-coated ?-TCP scaffolds are due to the combination of the systematic coating of struts, interpenetrating structural characteristics, and crack bridging. The in vitro biological evaluation demonstrated that rat bone marrow stromal cells (rBMSCs) adhered well, proliferated, and expressed alkaline phosphatase (ALP) activity on both the PLGA-coated ?-TCP and the ?-TCP. These results suggest a new strategy for fabricating interconnected macroporous scaffolds with significantly enhanced mechanical strength for potential load-bearing bone tissue regeneration.

    View details for PubMedID 21892228

  • A chitosan/beta-glycerophosphate thermo-sensitive gel for the delivery of ellagic acid for the treatment of brain cancer BIOMATERIALS Kim, S., Nishimoto, S. K., Bumgardner, J. D., Haggard, W. O., Gaber, M. W., Yang, Y. 2010; 31 (14): 4157-4166

    Abstract

    We report here the development of a chitosan/beta-glycerophosphate(Ch/beta-GP) thermo-sensitive gel to deliver ellagic acid (EA) for cancer treatment. The properties of the Ch/beta-GP gels were characterized regarding chemical structure, surface morphology, and viscoelasticity. In vitro EA release rate from the EA loaded Ch/beta-GP gel and chitosan degradation rate were investigated. The anti-tumor effect of the EA loaded Ch/beta-GP gel on brain cancer cells (human U87 glioblastomas and rat C6 glioma cells) was evaluated by examining cell viability. Cell number and activity were monitored by the MTS assay. The Ch/beta-GP solution formed a heat-induced gel at body temperature, and the gelation temperature and time were affected by the final pH of the Ch/beta-GP solution. The lysozyme increased the EA release rate by 2.5 times higher than that in the absence of lysozyme. Dialyzed chitosan solution with final pH 6.3 greatly reduced the beta-GP needed for gelation, thereby significantly improving the biocompatibility of gel (p < 0.001). The chitosan gels containing 1% (w/v) of ellagic acid significantly reduced viability of U87 cells and C6 cells compared with the chitosan gels at 3 days incubation (p < 0.01, and p < 0.001, respectively).

    View details for DOI 10.1016/j.biomaterials.2010.01.139

    View details for Web of Science ID 000276541300045

    View details for PubMedID 20185170

  • Novel template-casting technique for fabricating beta-tricalcium phosphate scaffolds with high interconnectivity and mechanical strength and in vitro cell responses. Journal of biomedical materials research. Part A Liu, Y., Kim, J., Young, D., Kim, S., Nishimoto, S. K., Yang, Y. 2010; 92 (3): 997-1006

    Abstract

    A novel template-casting method was developed to produce completely interconnected, macroporous biodegradable beta-tricalcium phosphate (beta-TCP) scaffolds, whose architecture and chemistry can be fully manipulated by varying the templates and casting materials. The processing route includes preparation of beta-TCP slurry; casting and shaping into preformed templates comprised of paraffin beads; solidifying, drying; and sintering. Structural, chemical, and mechanical properties of the prepared macroporous scaffolds were characterized using micro computed tomography, scanning electron microscopy, x-ray diffractometry, Fourier transform infrared spectroscopy, and mechanical testing. Human embryonic palatal mesenchymal cells were used to evaluate cell proliferation within the scaffolds in vitro. The scaffolds consisted of interconnected macropores and solid struts, leading to a reticular network. Two groups of scaffolds with larger pores, approximately 600-800 microm and smaller pores approximately 350-500 microm, were demonstrated. The interconnected windows between neighboring macropores were 440 +/- 57 microm in diameter for the larger-pored scaffolds, and 330 +/- 50 microm for the smaller-pored scaffolds. The scaffolds were highly crystallized and composed dominantly of beta-tricalcium phosphate (beta-TCP) accompanied by minor phase of hydroxyapatite (HA). The hydroxyl group was clearly detected by FTIR on the scaffolds. High mechanical strength (9.3 MPa) was demonstrated by the completely interconnected scaffolds with approximately 79% porosity. The human embryonic palatal mesenchymal (HEPM) cells proliferated well on the smaller-pored and larger-pored scaffolds, exhibiting a significantly higher level of proliferation in the first 11 days of culture on the smaller pored scaffolds. High levels of differentiation were also evidenced in both pore sizes of scaffolds.

    View details for DOI 10.1002/jbm.a.32443

    View details for PubMedID 19296544

  • Anodic Oxidized Nanotubular Titanium Implants Enhance Bone Morphogenetic Protein-2 Delivery J Biomed Mater Res In-Ho Bae, Kwi-Dug Yun, Hyun-Seung Kim, Byung-Chul Jeong, Hyun-Pil Lim, Sang-Won Park, Kwang-Min Lee, Young-Chai Lim, Kyung-Ku Lee, Yun-Zhi Yang, Jeong-Tae Koh. 2010; 93B: 484-491
  • Effect of growth factors in combination with injectable silicone resin particles on the biological activity of dermal fibroblasts: a preliminary in vitro study. Journal of biomedical materials research. Part B, Applied biomaterials Jennings, J. A., Crews, R. M., Robinson, J., Richelsoph, K., Cole, J. A., Bumgardner, J. D., Yang, Y., Haggard, W. O. 2010; 92 (1): 255-260

    Abstract

    Injections of silicone fluid have been clinically evaluated to treat and prevent foot ulcers due to diminished plantar fat-pad in neuropathic diabetics. The objective of this study was to determine preliminary in vitro effects of an injectable form of silicone resin particles in combination with growth factors to determine the suitability of this potential therapy for prevention of diabetic foot ulcers. Basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and platelet-derived growth factor (PDGF-BB) were added to monolayer culture along with silicone resin particles (12 microm average diameter). Growth factors were also combined as follows: bFGF+PDGF-BB, EGF+PDGF-BB, and bFGF+EGF. Growth factors alone and in combination increased fibroblast proliferation, but the presence of particles did not significantly affect cellular proliferation. The addition of particles significantly increased fibronectin production 117% in the control group and 151% in the PDGF only group. Collagen production was increased with exposure to EGF and growth factor combinations, but the presence of particles did not lead to any significant differences, except an 81% increase in the bFGF group. These preliminary results suggest that a combination of PDGF and bFGF may be effective in stimulating proliferation and matrix production around injectable silicone resin particles to generate a fibrous tissue pad to alleviate the abnormal distribution of high pressures that contribute to diabetic foot ulcer formation.

    View details for DOI 10.1002/jbm.b.31512

    View details for PubMedID 19904740

  • Effect of nanotubular-micro-roughened titanium surface on cell response in vitro and osseointegration in vivo Materials Science and Engineering Yun, K., Yang, Y., Lim, H., Oh, G., Koh, J., Bae, I., Kim J., Lee, K., Park, S. 2010; 30C: 27-33
  • The inhibition of glioma growth in vitro and in vivo by a chitosan/ellagic acid composite biomaterial BIOMATERIALS Kim, S., Gaber, M. W., Zawaski, J. A., Zhang, F., Richardson, M., Zhang, X. A., Yang, Y. 2009; 30 (27): 4743-4751

    Abstract

    This study has developed a chitosan-based delivery system to locally administer ellagic acid for brain cancer treatment. We fabricated chitosan/ellagic acid composite films with various concentrations of ellagic acid. In vitro release study was performed by using a UV spectrophotometer, and enzymatic degradation rate was determined by analyzing the increased free amino groups. Viability of brain cancer cells (human U87 glioblastomas and rat C6 glioma cells) was measured via direct and indirect cell culture on the films by MTS assay. Caspase-3 activation, Western blot for p53, and anti-angiogenesis assays were also examined. In the in vivo study, GFP-tagged rat C6 glioma cells were implanted subcutaneously at the right flank region of nude mice and treatments were initiated by implanting the films subcutaneously. Tumor growth was evaluated by measuring tumor volume using a caliper, an ultrasound machine, and an optical imaging system. The chitosan/ellagic acid composite films were enzymatically degradable and exhibited a sustained slow release of ellagic acid. These materials could inhibit the cancer cell growth in an ellagic acid concentration-dependent manner by inducing apoptosis of cancer cells as well as suppressing angiogenesis. These materials also significantly suppressed tumor tissue growth in vivo.

    View details for DOI 10.1016/j.biomaterials.2009.05.010

    View details for Web of Science ID 000269330400036

    View details for PubMedID 19501395

  • Development of chitosan-ellagic acid films as a local drug delivery system to induce apoptotic death of human melanoma cells. Journal of biomedical materials research. Part B, Applied biomaterials Kim, S., Liu, Y., Gaber, M. W., Bumgardner, J. D., Haggard, W. O., Yang, Y. 2009; 90 (1): 145-155

    Abstract

    This study was designed to develop a local chemotherapy device using chitosan as a local drug carrier and ellagic acid (EA) as an anticancer drug. We fabricated chitosan-ellagic acid (Ch-EA) films with concentrations of 0, 0.05, 0.1, 0.5, and 1% (w/v) of EA and examined the films using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurement. The WM115 human melanoma cell line as a skin cancer model was used to evaluate cell response to the films with the MTS assay and apoptosis assay, and HS68 human newborn fibroblast cell line as a control. With the increase in the concentration of the EA, the composite films exhibit increasing amide and ester groups and diffraction peaks of the crystallized EA and greater surface roughness and hydrophilicity. The chitosan films with 0.5 and 1% (w/v) of EA were found to have a potent antiproliferative effect on the melanoma cells by inducing apoptotic cell death. Localized effect of composites on cell behaviors has been clearly demonstrated. Our study demonstrated that the novel Ch-EA film can be potentially used in local chemotherapy.

    View details for DOI 10.1002/jbm.b.31266

    View details for PubMedID 18985785

  • Lyophilization to improve drug delivery for chitosan-calcium phosphate bone scaffold construct: a preliminary investigation. Journal of biomedical materials research. Part B, Applied biomaterials Reves, B. T., Bumgardner, J. D., Cole, J. A., Yang, Y., Haggard, W. O. 2009; 90 (1): 1-10

    Abstract

    Lyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of an antibiotic and a growth factor from a composite scaffold would be beneficial for treatment of complex fracture sites, such as comminuted fractures and segmental bone defects. The aim of this investigation was to increase the loading capacity of the composite by taking advantage of the increased porosity, due to lyophilization, and to produce an extended elution profile using a secondary chitosan-bead coating. The physiochemical properties of the composite were investigated, and loading and elution studies were performed with alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and amikacin. Lyophilization was found to increase the surface area of scaffolds by over 400% and the porosity of scaffolds by 50%. Using ALP as a model protein, the loading capacity was increased by lyophilization from 4.3 +/- 2.5 to 24.6 +/- 3.6 microg ALP/mg microspheres, and the elution profile was extended by a supplemental chitosan coating. The loading capacity of BMP-2 for composite microspheres was increased from 74.4 +/- 3.7 to 102.1 +/- 8.0 microg BMP-2/g microspheres with lyophilization compared with nonlyophilized microspheres. The elution profiles of BMP-2 and the antibiotic amikacin were not extended with the supplemental coating. Additional investigations are planned to improve these elution characteristics for growth factors and antibiotics.

    View details for DOI 10.1002/jbm.b.31390

    View details for PubMedID 19441116

  • Design and characterization of a novel chitosan/nanocrystalline calcium phosphate composite scaffold for bone regeneration. Journal of biomedical materials research. Part A Chesnutt, B. M., Viano, A. M., Yuan, Y., Yang, Y., Guda, T., Appleford, M. R., Ong, J. L., Haggard, W. O., Bumgardner, J. D. 2009; 88 (2): 491-502

    Abstract

    To meet the challenge of regenerating bone lost to disease or trauma, biodegradable scaffolds are being investigated as a way to regenerate bone without the need for an auto- or allograft. Here, we have developed a novel microsphere-based chitosan/nanocrystalline calcium phosphate (CaP) composite scaffold and investigated its potential compared to plain chitosan scaffolds to be used as a bone graft substitute. Composite and chitosan scaffolds were prepared by fusing microspheres of 500-900 microm in diameter, and porosity, degradation, compressive strength, and cell growth were examined. Both scaffolds had porosities of 33-35% and pore sizes between 100 and 800 . However, composite scaffolds were much rougher and, as a result, had 20 times more surface area/unit mass than chitosan scaffolds. The compressive modulus of hydrated composite scaffolds was significantly higher than chitosan scaffolds (9.29 +/- 0.8 MPa vs. 3.26 +/- 2.5 MPa), and composite scaffolds were tougher and more flexible than what has been reported for other chitosan-CaP composites or CaP scaffolds alone. Using X-ray diffraction, scaffolds were shown to contain partially crystalline hydroxyapatite with a crystallinity of 16.7% +/- 6.8% and crystallite size of 128 +/- 55 nm. Fibronection adsorption was increased on composite scaffolds, and cell attachment was higher on composite scaffolds after 30 min, although attachment rates were similar after 1 h. Osteoblast proliferation (based on dsDNA measurements) was significantly increased after 1 week of culture. These studies have demonstrated that composite scaffolds have mechanical properties and porosity sufficient to support ingrowth of new bone tissue, and cell attachment and proliferation data indicate composite scaffolds are promising for bone regeneration.

    View details for DOI 10.1002/jbm.a.31878

    View details for PubMedID 18306307

  • Fabrication and characterization of Functionally Graded Nano-Micro Porous Titanium Surface by Anodizing. J Biomed Mater Res HS Kim, Y Yang, JT Koh, KK Lee, DJ Lee, KM Lee, SW park 2009; 88B: 427-435
  • Development of Sputtered Nanoscale Dense Titanium Oxide Coating on Osseointegrated Implant Devices and Biological Evaluation Vacuum Y Yang, Y Liu, Park S, Lee K, Kim, H Koh, H Ji, X Wang, J Ong. 2009; 83: 569-574
  • Plasma surface modification of poly(D,L-lactic acid) as a tool to enhance protein adsorption and the attachment of different cell types. Journal of biomedical materials research. Part B, Applied biomaterials Alves, C. M., Yang, Y., Marton, D., Carnes, D. L., Ong, J. L., Sylvia, V. L., Dean, D. D., Reis, R. L., Agrawal, C. M. 2008; 87 (1): 59-66

    Abstract

    We have studied the influence of oxygen radio frequency glow discharge (RfGD) on the surface and bulk properties of poly(D,L-lactic acid) (PDLLA) and the effect of this surface modification on both protein adsorption and bone cell behavior. PDLLA films were characterized before and after plasma surface modification by water contact angle, surface energy, and adhesion tension of water as well as by scanning electron microscopy (SEM), X-ray electron spectroscopy (XPS), and Fourier transform infra-red (FTIR) spectroscopy. RfGD-films showed an increase in hydrophilicity and surface energy when compared with untreated films. Surface morphological changes were observed by SEM. Chemical analysis indicated significant differences in both atomic percentages and oxygen functional group. Protein adsorption was evaluated by combining solute depletion and spectroscopic techniques. Bovine serum albumin (BSA), fibronectin (FN), vitronectin (VN), and fetal bovine serum (FBS) were used in this study. RfGD-treated surfaces adsorbed more BSA and FN from single specie solutions than FBS that is a more complex, multi-specie solution. MG63 osteoblast-like cells and primary cultures of fetal rat calvarial (FRC) cells were used to assess both the effect of RfGD treatment and protein adsorption on cell attachment and proliferation. In the absence of preadsorbed proteins, cells could not distinguish between treated and untreated surfaces, with the exception of MG63 cells cultured for longer periods of time. In contrast, the adsorption of proteins increased the cells' preference for treated surfaces, thus indicating a crucial role for adsorbed proteins in mediating the response of osteogenic cells to the RfGD-treated PDLLA surface.

    View details for DOI 10.1002/jbm.b.31068

    View details for PubMedID 18360882

  • The effect of titanium surface roughening on protein absorption, cell attachment, and cell spreading INTERNATIONAL JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS Nishimoto, S. K., Nishimoto, M., Park, S., Lee, K., Kim, H., Koh, J., Ong, J. L., Liu, Y., Yang, Y. 2008; 23 (4): 675-680

    Abstract

    The purpose of this study was to compare properties of roughened and polished titanium with respect to their ability to attach to cells and bind to protein as well as their cell spreading behavior.Three different titanium surface treatments were compared for their ability to support cell attachment and spreading: sandblasted and acid-etched, resorbable blast media, and machine-polished titanium. The surface of the materials was characterized for surface roughness, surface energy, and surface chemistry. Osteoblast-like MG-63 cells were tested for in vitro attachment and spreading in the presence of serum proteins. Cell attachment was assessed by direct counting, dye binding, and microculture titanium assays. Cell spreading was determined by measuring area/cell in phalloidin-AlexaFluor 488 stained cells. Absorption of bovine serum albumin was determined by assay.Scanning electron micrography and x-ray diffractometry confirmed increased surface roughness of the roughened materials. All 3 materials had similar albumin binding kinetics. Three different methods confirmed that roughened surfaces enhance early cell attachment to titanium in the presence of serum. Cells spread better on smoother machined surfaces than on the roughened surfaces.Roughened titanium surfaces exhibited better early cell attachment than smooth surfaces in the presence of serum. The cells attached to roughened titanium were less spread than those attached to machined titanium. Although albumin binding was not different for roughened surfaces, it is possible that roughened surfaces preferentially bound to serum adhesive proteins to promote early cell attachment.

    View details for Web of Science ID 000258914700012

    View details for PubMedID 18807564

  • Chitosan-coated stainless steel screws for fixation in contaminated fractures CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Greene, A. H., Bumgardner, J. D., Yang, Y., Moseley, J., Haggard, W. O. 2008; 466 (7): 1699-1704

    Abstract

    Stainless steel screws and other internal fixation devices are used routinely to stabilize bacteria-contaminated bone fractures from multiple injury mechanisms. In this preliminary study, we hypothesize that a chitosan coating either unloaded or loaded with an antibiotic, gentamicin, could lessen or prevent these devices from becoming an initial nidus for infection. The questions investigated for this hypothesis were: (1) how much of the sterilized coating remains on the screw with simulated functional use; (2) is the unloaded or loaded chitosan coating bacteriostatic and biocompatible; and (3) what amount and rate does an antibiotic elute from the coating? In this study, the gentamicin eluted from the coating at a detectable level during 72 to 96 hours. The coating was retained at the 90% level in simulated bone screw fixation and the unloaded and loaded chitosan coatings had encouraging in vitro biocompatibility with fibroblasts and stem cells and were bacteriostatic against at least one strain of Staphylococcus aureus. The use of an antibiotic-loaded chitosan coating on stainless steel bone screws and internal fixation devices in contaminated bone fracture fixation may be considered after optimization of antibiotic loading and elution and more expanded in vitro and in vivo investigations with other organisms and antibiotics.

    View details for DOI 10.1007/s11999-008-0269-5

    View details for Web of Science ID 000256658900027

    View details for PubMedID 18443893

  • Novel fabrication of nano-rod array structures on titanium and in vitro cell responses JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE Liu, Y., Chen, W., Yang, Y., Ong, J. L., Tsuru, K., Hayakawa, S., Osaka, A. 2008; 19 (7): 2735-2741

    Abstract

    Nano-scale rod arrays of titania were fabricated on titanium surface by a glass phase topotaxy growth (GPT) method, which was featured by an interfacial reaction between sodium tetraborate coating and the preheated metallic titanium at elevated temperature. The samples were characterized by thin-film X-ray diffraction (XRD), scanning electron microscope (SEM), profilometer and contact angle measurement. Thin-film XRD analysis indicated that the nano-rod arrays were composed of pure rutile titania phase. SEM images showed that these rutile rods were 100-200 nm wide and 1-2 microm long. The nano-rod arrays had significantly higher average roughness (P < 0.05) and greater hydrophilicity (P < 0.05) compared to the control. Human embryonic palatal mesenchymal (HEPM) cells were grown to evaluate in vitro cell responses to the nano-rod array structures in terms of cell attachment and proliferation. An equivalent high attachment rate of 94% was observed after 4-h incubation, but a lower proliferation rate was observed on the nano-rod array after 12-day culture compared to the control (P < 0.05).

    View details for DOI 10.1007/s10856-008-3396-3

    View details for Web of Science ID 000255879100027

    View details for PubMedID 18305905

  • Characterization of biomimetic calcium phosphate on phosphorylated chitosan films JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A Chesnutt, B. M., Yuan, Y., Brahmandam, N., Yang, Y., Ong, J. L., Haggard, W. O., Bumgardner, J. D. 2007; 82A (2): 343-353

    Abstract

    This study examined the effect of chitosan degree of deacetylation (DDA), concentration of simulated body fluid (SBF), and mineralization time on the composition, structure, and crystallinity of calcium phosphate (CaP) biomimetically deposited on chitosan and on osteoblast cell growth. Phosphorylated chitosan films of 92.3%, 87.4%, and 80.6% DDA were soaked in SBF (1.0x or 1.5x) for 7, 14, or 21 days. Scanning electron microscopy revealed that CaP precipitated from 1.5x SBF had a porous, granular morphology; while the coatings precipitated in 1.0x SBF were smoother and more uniform. X-ray diffraction showed that films mineralized in 1.0x SBF were amorphous, while films mineralized in 1.5x SBF for 21 days exhibited crystalline peaks similar to hydroxyapatite, with the most crystalline peaks seen on 92.3% DDA chitosan. When mineralized films were placed in cell media for 14 days, more calcium phosphate precipitated onto all films, and the most calcium phosphate was found on 92.3% DDA films mineralized in 1.5x SBF. After seven days of osteoblast culture, there were approximately three times as many cells (based on DNA measurements, p < 0.05) on 92.3% DDA films soaked in 1.0x SBF for seven or 21 days than on 80.6% DDA films soaked in 1.0x SBF for any length of time or any films soaked in 1.5x SBF. The DDA of chitosan, concentration of SBF and mineralization time affect the structure of and biological response to chitosan/biomimetic CaP films, and these factors must be considered when designing new materials to be used in orthopaedic and dental/craniofacial implant applications.

    View details for DOI 10.1002/jbm.a.31070

    View details for Web of Science ID 000247836600010

    View details for PubMedID 17295230

  • The integration of chitosan-coated titanium in bone: An in vivo study in rabbits IMPLANT DENTISTRY Bumgardner, J. D., Chesnutt, B. M., Yuan, Y., Yang, Y., Appleford, M., Oh, S., McLaughlin, R., Elder, S. H., Ong, J. L. 2007; 16 (1): 66-79

    Abstract

    Much research is directed at surface modifications to enhance osseointegration of implants. A new potential coating is the biopolymer, chitosan, the deacetylated derivative of the natural polysaccharide, chitin. Chitosan is biocompatible, degradable, nontoxic, and exhibits osteogenic properties. The aim of this research was to investigate the hypothesis that chitosan-coated titanium supports bone formation and osseointegration.Chitosan (1 wt% of 92.3% deacetylated chitosan in 1% acetic acid) was solution cast and bonded to rough ground titanium pins (2-mm diameterx4-mm long) via silane reactions. Calcium phosphate sputter-coated titanium and uncoated titanium pins were used as controls. Two chitosan-coated pins, and 1 each of calcium phosphate coated and uncoated pins were implanted unilaterally in the tibia of 16 adult male New Zealand white rabbits. At 2, 4, 8, and 12 weeks, undecalcified sections were histologically evaluated for healing and bone formation.Histological evaluations of tissues in contact with the chitosan-coated pins indicated minimal inflammatory response and a typical healing sequence of fibrous, woven bone formation, followed by development of lamellar bone. These observations were similar to those for tissues interfacing the control calcium phosphate-coated and uncoated titanium implants. Quantitative comparisons of the bone-implant interface were not possible since 31% of the implants migrated into the tibial marrow space after implantation due to insufficient cortical bone thickness to hold pins in place during healing.These data support the hypothesis that chitosan-coatings are able to develop a close bony apposition or the osseointegration of dental/craniofacial and orthopedic implants.

    View details for DOI 10.1097/ID.0b013e3180312011

    View details for Web of Science ID 000249965300010

    View details for PubMedID 17356373

  • Effect of genipen crosslinking on degradation and protein release from chitosan microspheres Carbohydrate polymers Y Yuan, BC Chesnutt, G Utturkar, J Ong, Y Yang, W haggard, J Bumgardner 2007; 68: 561-567
  • Modulating bone cells response onto starch-based biomaterials by surface plasma treatment and protein adsorption BIOMATERIALS Alves, C. M., Yang, Y., Carnes, D. L., Ong, J. L., Sylvia, V. L., Dean, D. D., Agrawal, C. M., Reis, R. L. 2007; 28 (2): 307-315

    Abstract

    The effect of oxygen-based radio frequency glow discharge (rfGD) on the surface of different starch-based biomaterials (SBB) and the influence of proteins adsorption on modulating bone-cells behavior was studied. Bovine serum albumin, fibronectin and vitronectin were used in single and complex protein systems. RfGD-treated surfaces showed to increase in hydrophilicity and surface energy when compared to non-modified SBB. Biodegradable polymeric blends of cornstarch with cellulose acetate (SCA; 50/50wt%), ethylene vinyl alcohol (SEVA-C; 50/50wt%) and polycaprolactone (SPCL; 30/70wt%) were studied. SCA and SCA reinforced with 10% hydroxyapatite (HA) showed the highest degree of modification as result of the rfGD treatment. Protein and control solutions were used to incubate with the characterized SBB and, following this, MG63 osteoblast-like osteosarcoma cells were seeded over the surfaces. Cell adhesion and proliferation onto SCA was found to be enhanced for non-treated surfaces and on SCA+10%HA no alteration was brought up by the plasma modification. Onto SCA surfaces, BSA, FN and VN single solutions improved cell adhesion, and this same effect was found upscaled for ternary systems. In addition, plasma treated SEVA-C directed an increase in both adhesion and proliferation comparing to non-treated surfaces. Even though adhesion onto treated and untreated SPCL was quite similar, plasma modification clearly promoted MG63 cells proliferation. Regarding MG63 cells morphology it was shown that onto SEVA-C surfaces the variation of cell shape was primarily defined by the protein system, while onto SPCL it was mainly affected by the plasma treatment.

    View details for DOI 10.1016/j.biomaterials.2006.09.010

    View details for Web of Science ID 000242310500018

    View details for PubMedID 17011619

  • Bone cell attachment and growth on well-characterized chitosan films Polymer International V Hamilton, Y Yuan, DA Rigney, BM Chesnutt, AD Puckett, JL Ong, Y Yang, WO Haggard, SH Elder, JD Bumgardner 2007; 56: 641-647
  • Microstructure, mechanical properties, and biological response to functionally graded HA coatings Mater Sci and Eng Afsaneh Rabiei, Travis Blalock, Brent Thomas, Jerry Cuomo, Y. Yang, Joo Ong 2007; 27C: 529-533
  • Characterization of chitosan films and effects on fibroblast cell attachment and proliferation JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE Hamilton, V., Yuan, Y., Rigney, D. A., Puckett, A. D., Ong, J. L., Yang, Y., Elder, S. H., Bumgardner, J. D. 2006; 17 (12): 1373-1381

    Abstract

    Chitosan has been researched for implant and wound healing applications. However, there are inconsistencies in reports on the tissue and fibroblast responses to chitosan materials. These inconsistencies may be due to variations in chitosan material characteristics. The aim of this study was to correlate fibroblast responses with known chitosan material characteristics. To achieve this aim, chitosan was characterized for degree of deacetylation (DDA), molecular weight (MW), residual protein and ash contents, and then solution cast into films and characterized for hydrophilicity by water contact angle. The films were seeded with normal human dermal fibroblasts and the number of attached cells was evaluated for after 30 min. Cell proliferation was evaluated over 5 days. This study found no relationship between DDA, contact angle, cell attachment, and or proliferation. General trends were observed for increasing proliferation with increasing residual ash content and decreasing residual protein. These data indicate that chitosan characteristics other than DDA may be important to their biological performance.

    View details for DOI 10.1007/s10856-006-0613-9

    View details for Web of Science ID 000242511100023

    View details for PubMedID 17143770

  • Enhancement of osseointegration using surface modified titanium implants Journal of Minerals, Metals, and Materials Yang, Y., N. Oh, Y. Liu, W. Chen, S. Oh, M. Appleford, S. Kim, K. Kim, S. Park, J. Bumgardner, W. Haggard, J Ong 2006; 58: 71-76
  • Preparation and characterization of anodized titanium surfaces and their effect on osteoblast responses. journal of oral implantology Kim, K., Kwon, T., Kim, S., Kang, I., Kim, S., Yang, Y., Ong, J. L. 2006; 32 (1): 8-13

    Abstract

    In this study, titanium (Ti) surface was modified by anodizing with a mixture of beta-glycerophosphate sodium and calcium (Ca) acetate, and the anodized surfaces were characterized by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. In vitro osteoblast response to anodized oxide was also evaluated. The anodic oxide produced was observed to have interconnected pores (0.5-2 microm in diameter) and intermediate roughness (0.60-1.00 microm). In addition, anodic oxide was observed to have amorphous and anatase oxide. Calcium and phosphorus ions were deposited on the Ti oxide during anodization. Osteoblast differentiation, as indicated by alkaline phosphatase production, was enhanced on anodized surfaces. It was thus concluded from this study that Ca phosphate can be deposited on Ti surfaces by anodization. It was also concluded that the phenotypic expression of osteoblast was enhanced by the presence of Ca phosphate and higher roughness on anodized Ti surfaces.

    View details for PubMedID 16526576

  • Characterization and development of bioactive hydroxyapatite coatings. J ournal of Minerals, Metals, and Materials J. Ong, M. Appleford, S. Oh, Yang, Y., W. Chen, J.D. Bumgardner, W. Haggard. 2006; 58: 67-70
  • Enhancement of osseointegration using surface modified titanium implants Journal of Minerals, Metals, and Materials Yang, Y., N. Oh, Y. Liu, W. Chen, S. Oh, M. Appleford, S. Kim, K. Kim, S. Park, J. Bumgardner, W. Haggard, J Ong 2006; 58: 71-76
  • A study on functionally graded HA coatings processed using ion beam assisted deposition with in-situ heat treatment Surface and coating technology Rabiei A, Narayan TR, Cuomo, J, Yang, Y, Ong, J.L. 2006; 200: 6111-6116
  • Effects of applied voltages on hydroxyapatite coating on titanium by electrophoretic deposition J Biomed Mater Res Meng X.,, Kwon, T.; Yang, Y.; Ong, J.L.; Kim, K. 2006; 78B: 373-377
  • Enhancement of osseointegration using surface modified titanium implants Journal of Minerals, Metals, and Materials Yang, Y., N. Oh, Y. Liu, W. Chen, S. Oh, M. Appleford, S. Kim, K. Kim, S. Park, J. Bumgardner, W. Haggard, J Ong 2006; 58: 71-76
  • The effect of sputtered calcium phosphate coatings of difference crystallinity on osteoblast differentiation JOURNAL OF PERIODONTOLOGY Berube, P., Yang, Y. Z., Carnes, D. L., Stover, R. E., Boland, E. J., Ong, J. L. 2005; 76 (10): 1697-1709

    Abstract

    Coating titanium implants with hydroxyapatite (HA) has been suggested to increase osseointegration by stimulating early osteoblast function. The goal of this study was to determine the extent to which the crystalline content of the HA surface affected osteoblast function in vitro.Osteoblasts were isolated from fetal rat calvaria. Titanium coupons were sputter coated and analyzed. Mineralized nodule formation on plastic using von Kossa staining was compared to tetracycline and procion dye labeling. Cell proliferation, adhesion, alkaline phosphatase activity, morphology and spreading, and cytoskeletal arrangement were analyzed. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of mRNA for specific proteins.The percent crystallinity of coatings was 0% (HA1), 1.9% +/- 0.4% (HA2), and 66.4% +/- 2.8% (HA3). The nodule formation and cell number were greatest on titanium and HA3 compared to HA1 and HA2 (P < 0.01). At weeks 2 to 4, all samples showed strong alkaline phosphatase, osteocalcin, monocyte-colony stimulating factor (M-CSF), and receptor activator of nuclear factor kappa B ligand (RANKL) expression, but the specific activity of alkaline phosphatase decreased. Cell adherence was greater than 60% of applied cells for all surfaces except HA3. The cells were significantly more elongated on titanium, with no difference on the HA-coated surfaces. Actin filaments were arranged peripherally at 5 hours but arranged parallel to the long axis of the cell at 20 hours.Procion labeling is a valid method for evaluating mineralized nodule formation on opaque surfaces. There were no major differences in osteoblast function using titanium or high-crystalline coatings, and most functions were decreased on amorphous or low-crystalline coatings.

    View details for Web of Science ID 000232511500011

    View details for PubMedID 16253092

  • In vivo evaluation of hydroxyapatite coatings of different crystallinities INTERNATIONAL JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS Oh, S., Tobin, E., Yang, Y. Z., Carnes, P. L., Ong, J. L. 2005; 20 (5): 726-731

    Abstract

    The influence of calcium phosphate (CaP) and hydroxyapatite (HA) crystallinity on bone-implant osseointegration is not well established. In this study, the effect of HA crystallinity and coating method on bone-implant osseointegration was investigated using a rat tibia model.HA coatings 1 to 5 microm thick were produced using a supersonic particle acceleration (SPA) technology. The HA crystallinities used for this study were weight ratios of 30%, 50%, 70%, and 90%. A total of 128 HA-coated implants were placed into the tibiae of 64 male Sprague-Dawley rats. Bone-implant interfaces were evaluated using histology and push-out strength testing at 3 and 9 weeks after implantation.The 70% crystalline coatings exhibited significantly greater interfacial strength (5 implants/time point/treatment) than the 30%, 50%, and 90% crystalline coatings at 3 and 9 weeks following implantation. The implants with coatings of 70% crystallinity also had the greatest bone contact length. In addition, the HA coatings produced with SPA demonstrated greater interfacial strength and bone contact length than plasma-sprayed HA coatings (except for the HA coating with 30% crystallinity).HA coatings of different crystallinities exhibited different dissolution and re-precipitation properties which may enhance early bone formation and bone bonding.This study suggested that coating crystallinity and coating methods can influence the bone-implant interface.

    View details for Web of Science ID 000232455400008

    View details for PubMedID 16274146

  • Effect of heat-treated titanium surfaces on protein adsorption and osteoblast precursor cell initial attachment. Implant dentistry Kern, T., Yang, Y., Glover, R., Ong, J. L. 2005; 14 (1): 70-76

    Abstract

    The clinical success of dental implants is governed in part by surface properties of implants and their interactions with the surrounding tissues. The objective of this study was to investigate the effect of heat-treated titanium surfaces on protein adsorption and osteoblast precursor cell attachment in vitro. Passivated titanium samples used in this study were either non heat treated or heat treated at 750 degrees C for 90 minutes. It was observed that the contact angle on heat-treated titanium surfaces was statistically lower compared with the non-heat-treated titanium surfaces. The non-heat-treated titanium surface was also observed to be amorphous oxide, whereas heat treatment of titanium resulted in the conversion of amorphous oxide to crystalline anatase oxide. No significant difference in albumin and fibronectin adsorption was observed between the heat-treated and non-heat-treated titanium surfaces. In addition, no significant difference in initial cell attachment was observed between the two groups. It was concluded that heat treatment of titanium resulted in significantly more hydrophilic surfaces compared to non-heat-treated titanium surfaces. However, differences in oxide crystallinity and wettability were not observed to affect protein adsorption and initial osteoblast precursor cell attachment.

    View details for PubMedID 15764948

  • Protein adsorption and osteoblast precursor cell attachment to hydroxyapatite of different crystallinities INTERNATIONAL JOURNAL OF ORAL & MAXILLOFACIAL IMPLANTS Yang, Y. Z., Dennison, D., Ong, J. L. 2005; 20 (2): 187-192

    Abstract

    The effect of hydroxyapatite (HA) crystallinity on protein adsorption and osteoblast precursor cell attachment to HA was investigated.Different weight ratios of 100% crystalline HA and 100% amorphous calcium phosphate powders were mixed and pressed into disks (0.5 g) of different crystallinities--either 0% (HAO), 30% (HA30), 50% (HA50), 70% (HA70), or 100% (HA100).X-ray diffraction indicated differences in HA crystallinities. In addition, dissolution of the HA was dependent on its crystallinity, with an increase in phosphorus dissolution as the degree of crystallinity was decreased. No significant difference in albumin adsorption and initial osteoblast precursor cell attachment was observed in the range of HA0 to HA70 surfaces. However, a significantly lower albumin adsorption and initial osteoblast precursor cell attachment were observed on HA100.It was suggested that changes in ionic interactions as a result of a change in crystallinity affect the amount of calcium ion ligands readily available to electrostatically bind to proteins.It was thus concluded from this study that HA crystallinity affects the amount of albumin adsorbed and initial osteoblast attachment.

    View details for Web of Science ID 000228312500003

    View details for PubMedID 15839111

  • Review on calcium phosphate coatings produced using a sputtering process - an alternative to plasma spraying BIOMATERIALS Yang, Y. Z., Kim, K. H., Ong, J. L. 2005; 26 (3): 327-337

    Abstract

    New promising techniques for depositing hydroxyapatite (HA) and calcium phosphate (CaP) coatings on medical devices are continuously being investigated. Given the vast number of experimental deposition process currently available, this review will focus only on CaP and/or HA coatings produced using the sputtering process. This review will discuss the characterization of sputtered CaP coatings before and after post-deposition treatments and tissue responses to some of the characterized coating surfaces. From the studies observed in the literature, current research on sputtered CaP coatings has shown some promises that may eliminate some of the problems associated with the plasma-spraying process. It has been generally accepted that sputtered HA and CaP coatings improve bone strength and initial osseointegration rate. However, optimal coating properties required to achieve maximal bone response are yet to be reported. As such, the use of well-characterized sputtered CaP and/or HA surfaces in the evaluation of biological responses should be well documented to avoid controversial results. In addition, future investigations of the sputtering process should include clinical trials, to continue the understanding of bone responses to coated-implant surfaces of different properties, and the possibility of coupling sputtered HA and CaP coatings with growth factors.

    View details for DOI 10.1016/j.biomaterials.2004.02.029

    View details for Web of Science ID 000224014400010

    View details for PubMedID 15262475

  • Ectopic osteoinduction and eraly degradation of recombinant human bone morphogenetic protein-2 loaded porous beta-tricalcium phosphate in mice Biomaterials Liang, G., Yang, Y. Oh, S, Ong, J.L., Zheng, C, Ran, J, Yin, G, Zhou, D. 2005; 26 (20): 4265-4271
  • Effects of dissolved calcium and phosphorous on osteoblast responses. journal of oral implantology Ma, S., Yang, Y., Carnes, D. L., Kim, K., Park, S., Oh, S. H., Ong, J. L. 2005; 31 (2): 61-67

    Abstract

    The dissolution behavior of hydroxyapatite (HA) and its effect on the initial cellular response is of both fundamental and clinical importance. In this study, plasma-sprayed HA coatings were characterized by X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Calcium (Ca) and inorganic phosphorous (Pi) ions released from plasma-sprayed HA coatings within 3 weeks were measured by flame atomic absorption and colorimetrically molybdenum blue complex, respectively. To investigate the effect of dissolution of HA coatings on osteoblast response, additional Ca and Pi were added into the cell culture media to simulate the dissolution concentrations. Human embryonic palatal mesenchyme cells, an osteoblast precursor cell line, were used to evaluate the biological responses to enhanced Ca and Pi media over 2 weeks. Osteoblast differentiation and mineralization were measured by alkaline phosphatase-specific assay and 1,25 (OH)2 vitamin D3 stimulated osteocalcin production. The coatings exhibited an HA-type structure. FTIR indicated the possible presence of carbonates on the coatings. A dissolution study indicated a continual increase in Ca and Pi over time. In the cell culture study, enhanced osteoblast differentiation occurred in the presence of additional Ca concentration in the cell culture media. However, additional Pi concentration in the cell culture media was suggested to slow down osteoblast differentiation and mineralization.

    View details for PubMedID 15871524

  • Interaction of hydroxyapatite-titanium at elevated temperature in vacuum environment BIOMATERIALS Yang, Y. Z., Kim, K. H., Agrawal, C. M., Ong, J. L. 2004; 25 (15): 2927-2932

    Abstract

    In this study, the interaction between hydroxyapatite (HA) and titanium (Ti) at elevated temperature in vacuum environment was investigated. The 80 wt% HA-20 wt% Ti powder mixtures and 90 wt% HA-10 wt% Ti powder mixtures were dry pressed and heat-treated at 1100 degrees C in vacuum environment. HA powders and the commercially pure Ti powders were used as controls. The heat-treated samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscope (SEM) and energy disperse spectra. XRD and SEM indicated densification of metallic Ti specimens during the in-vacuum heat treatment. Heat treatment of HA specimens in vacuum resulted in the loss of hydroxyl groups as well the formation of a secondary beta-tricalcium phosphate phase. Metallic Ti was not observed in the in-vacuum heat-treated HA-Ti specimens. However, alpha-tricalcium phosphate, tetracalcium phosphate and calcium titanium oxide were observed for the in-vacuum heat-treated HA-Ti specimens. It was concluded that the in-vacuum heat-treatment process completely converted the metal-ceramics composites to ceramic composites.

    View details for DOI 10.1016/j.biomaterials.2003.09.072

    View details for Web of Science ID 000189221600003

    View details for PubMedID 14967524

  • Protein adsorption on titanium surfaces and their effect on osteoblast attachment. Journal of biomedical materials research. Part A Yang, Y., Cavin, R., Ong, J. L. 2003; 67 (1): 344-349

    Abstract

    The objective of this study was to investigate the adsorption of albumin and fibronectin on titanium (Ti) surfaces and the effect of preadsorbed albumin and fibronectin on osteoblast attachment in vitro. Bovine serum albumin and bovine fibronectin were used in this study. Maximum adsorption of bovine serum albumin and fibronectin on Ti surfaces was observed to occur after 180-min incubation. In the presence of preadsorbed proteins, osteoblast attachment on Ti surfaces was observed to be enhanced compared to control Ti surfaces. However, cell attachment was affected by the types of protein adsorbed. Preadsorbed albumin was observed to have no significant effect on the amount of osteoblast cells attached. In comparison to control Ti surface and Ti surfaces preadsorbed with albumin, Ti surfaces preadsorbed with fibronectin for 15 min was observed to significantly increase osteoblast cell attachment, whereas Ti surfaces preadsorbed with fibronectin for 180 min did not affect cell attachment. In addition, cell morphology of the attached cells on protein preadsorbed Ti surfaces was not affected by the type of protein used in this study. It was concluded from this study that the concentration of fibronectin adsorbed on Ti surfaces was higher compared to albumin. In addition, it was also concluded that the concentration of fibronectin on Ti surfaces plays a role in governing cell attachment.

    View details for PubMedID 14517894

  • Influence of post-deposition heating time and the presence of water vapor on sputter-coated calcium phosphate crystallinity JOURNAL OF DENTAL RESEARCH Yang, Y., Kim, K. H., Agrawal, C. M., Ong, J. L. 2003; 82 (10): 833-837

    Abstract

    Extensive research suggested that calcium phosphate (CaP) coatings on titanium implants are essential for early bone response. However, the characterization of CaP crystallinity and the means to control coating crystallinity are not well-established. In this study, the effect of a 400 degrees C heat treatment for 1, 2, or 4 hours, and in the presence or absence of water vapor, on CaP crystallinity was investigated. Scanning electron microscopy indicated dense as-sputtered coatings. Increase in coating crystallinity was observed to be consistent with the increasing number of PO(4) peaks observed as a result of different heat treatments. In addition, x-ray diffraction analyses indicated amorphous as-sputtered coatings, whereas crystalline CaP coatings in the range of 0-85% were observed after different post-deposition heat treatments. It was concluded that the presence of water vapor and post-deposition heat treatment time significantly affect the crystallinity of CaP coatings, which may ultimately affect bone healing.

    View details for Web of Science ID 000185608500014

    View details for PubMedID 14514766

  • Osteoblast precursor cell attachment on heat-treated calcium phosphate coatings JOURNAL OF DENTAL RESEARCH Yang, Y., Bumgardner, J. D., Cavin, R., Carnes, D. L., Ong, J. L. 2003; 82 (6): 449-453

    Abstract

    The influence of properties of calcium phosphate (CaP) coatings on bone cell activity and bone-implant osseointegration is not well-established. This study investigated the effects of characterized CaP coatings of various heat treatments on osteoblast response. It was hypothesized that heat treatments of CaP coatings alter the initial osteoblast attachment. The 400 degrees C heat-treated coatings were observed to exhibit poor crystallinity and significantly greater phosphate or apatite species compared with as-sputtered and 600 degrees C heat-treated coatings. Similarly, human embryonic palatal mesenchyme (HEPM) cells, an osteoblast precursor cell line, seeded on 400 degrees C heat-treated coatings, exhibited significantly greater cell attachment compared with Ti surfaces, as-sputtered coatings, and 600 degrees C heat-treated coatings. The HEPM cells on Ti surfaces and heat-treated coatings were observed to attach through filopodia, and underwent cell division, whereas the cells on as-sputtered coatings displayed fewer filopodia extensions and cell damage. Analysis of the data suggested that heat treatment of CaP coatings affects cell attachment.

    View details for Web of Science ID 000183066700009

    View details for PubMedID 12766197

  • Deposition of highly adhesive ZrO2 coating on Ti and CoCrMo implant materials using plasma spraying BIOMATERIALS Yang, Y. Z., Ong, J. L., Tian, J. 2003; 24 (4): 619-627

    Abstract

    ZrO(2) (4% CeO(2)) and ZrO(2) (3% Y(2)O(3)) coatings were deposited on titanium (Ti) and CoCrMo implants using plasma spraying and the adhesive, morphological and structural properties of the plasma-sprayed coatings were evaluated. Characterization of these coatings was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness, hardness, and adhesive strength. XRD patterns showed that both the coatings appeared to be primitive tetragonal phase. SEM observations showed that both the ZrO(2) coatings appeared to be rough, porous and melted. The cross-section surface morphology of the coatings, coating-substrate interfaces and substrates without acid etching was very dense and smooth. After acid etching, as compared to the dense ZrO(2) coating-CoCrMo substrate interfaces, the thin gaps appeared within the ZrO(2) coating-Ti substrate interfaces. It is suggested that plasma spraying probably formed an amorphous Ti layer in the coating-Ti substrate interface that can be removed by acid etching. The average surface roughness of ZrO(2) (3% Y(2)O(3)) and ZrO(2) (4% CeO(2)) coatings was correlated to the starting powder size and substrates. No significant difference between the hardness of all coatings and substrates was observed. The adhesive strengths of ZrO(2) (4% CeO(2)) coating to Ti and CoCrMo substrates were higher than 68MPa and significantly greater than that of ZrO(2) (3% Y(2)O(3)) coatings.

    View details for Web of Science ID 000179561600010

    View details for PubMedID 12437956

  • Contact angle, protein adsorption, and osteoblast attachment to chitosan coatings bonded to titanium J Biomater Sci: Polymer Edition JD Bumgardner, R Jouett, Y Yang, JL Ong 2003; 14: 1401-1410
  • Fibronectin adsorption on titanium surfaces and its effect on osteoblast precursor cell attachment Colloids and Surfaces B: Interfaces Yang, Y., Glover, R., Ong, J.L. 2003; 30B: 291-297
  • Bond strength, compositional and structural properties of HA coating on Ti substrate, ZrO2-coated Ti substrate, and TPS-coated Ti substrate J Biomed Mater Res Yang, Y., Ong, J.L. 2003; 64A: 509-516
  • Morphological behavior of osteoblast-like cells on surface-modified titanium in vitro BIOMATERIALS Yang, Y. Z., Tian, J. M., Deng, L., Ong, J. L. 2002; 23 (5): 1383-1389

    Abstract

    In recent papers, we reported the results of a study on the graded porous titanium coatings on titanium by plasma spraying and amino-group ion implantation. The paper is to preliminarily evaluate the biocompatibility of surface-modified titanium through 2, 5 and 7 days cell culture in vitro. Cell morphology was observed by a scanning electron microscope. Cell proliferation and type I collagen synthesis were measured by 3(4.5-dimethyl-thiazole-2-yl)2,5-diphenyl tetrazolium bromide (MTT) and enzyme-linked immunosorbent assay (ELISA), respectively. Our experimental results showed that osteoblast-like cells attached and spread well on surface-modified titanium. Cells were observed to grow into the pores and form extracellular matrix. MTT and ELISA results showed no detrimental effect on the development of cell. These studies support the biocompatibility of surface-modified titanium.

    View details for Web of Science ID 000173220100013

    View details for PubMedID 11804294

  • Rapid sintering of hydroxyapatite by microwave processing Journal of Materials Science Letter Yang, Y., J.L. Ong, J. Tian 2002; 21: 67-69
  • In vivo evaluation of modified titanium implant surfaces using a hybrid plasma sparying processing Mater Sci and Eng Yang, Y., J.L. Ong, J. Tian 2002; 120C: 117-124
  • Surface modification of titanium through amino group implantation JOURNAL OF BIOMEDICAL MATERIALS RESEARCH Yang, Y. Z., Tian, J. M., Tian, J. T., Chen, Z. Q. 2001; 55 (3): 442-444

    Abstract

    We modified Ti surfaces by implantation of amino (NH(2+)) groups at 10(16) and 10(17) cm(-2). The implanted surfaces were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning Auger electron spectroscopy (AES), and second ion mass spectroscopy (SIMS). The experimental results showed that the implanted Ti specimens were covered by a dominant hydrocarbon overlayer due to contamination and the surface oxide layer of implanted specimens became thicker. XPS, AES, and SIMS depth profiles showed that implanted elements had a typical ion implantation distribution and that titanium nitride (TiN) was formed.

    View details for Web of Science ID 000167677200022

    View details for PubMedID 11255199

  • Preparation of graded porous titanium coatings on titanium implant materials by plasma spraying JOURNAL OF BIOMEDICAL MATERIALS RESEARCH Yang, Y. Z., Tian, J. M., Tian, J. T., Chen, Z. Q., Deng, X. J., Zhang, D. H. 2000; 52 (2): 333-337

    Abstract

    Graded porous titanium coatings have been deposited on titanium substrates for dental implants by plasma spraying in an argon atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness measurement, and tensile strength tests were performed on graded porous coatings. The results showed that Ti(3)O(5) was formed in the outermost surface of the porous coatings due to oxidation. The graded porous coatings consisted of three layers. The outer layer was full of macropores with a surface roughness of approximately 100 microm. The diameter of many macropores reached and even surpassed 150 microm, which could be beneficial for tissue to grow into the coating. The middle layer consisted of a mixture of micropores and macropores. The inner layer was a very dense and tight interface layer that included mechanical, physical, and metallurgical bonding. In tensile strength tests, testing bars peeled off the coatings, because the adhesive agent fractured, but the coatings remained intact.

    View details for Web of Science ID 000088812900012

    View details for PubMedID 10951372