Dr. Chen is an instructor in the Department of Ophthalmology at Stanford University. Her research focuses on materials science and engineering approaches to biological or biomedical problems. Specifically, she is dedicated to understanding the design principles and developing nanoscale and macroscale biomaterials for medical applications, experimental investigations of cell therapies, and integration across multiple disciplines including materials science, chemistry, medical imaging, and life science. Her ongoing projects are developing nanoparticles (funded by the NIH K99/R00 award) and hydrogels to treat various eye diseases. Dr. Chen has published over 30 peer-reviewed papers, contributed chapters to 2 books, given almost 30 presentations at professional conferences, and been included in 3 patents.
Before becoming an instructor, Dr. Chen was trained as a postdoc scholar at Stanford Ophthalmology Department. During this training, she invented several natural biopolymers based in situ forming hydrogels to promote corneal wound healing. She also established two corneal disease models in rodents and large animals with surgical tool-inner stopper trephines, which she invented to create consistent corneal defects in animal corneas. Her postdoctoral research in hydrogel and tissue engineering is complementary to her Ph.D. training in nanoparticles and cell tracking. Dr. Chen completed her Ph.D. in Materials Science and Engineering at UCSD, where she discovered several ultrasound-based contrast agents, revealed cytotoxicity and adsorption properties of various nanomaterials, and created a theranostic nanoparticle that improved the treatment efficacy of stem cell therapy for heart diseases. Beyond research, Dr. Chen has also served as a mentor, area safety coordinator, lab manager, animal protocol manager, and reviewer for multiple professional journals.
Honors & Awards
NIH K99/R00 Pathway to Independence Award, National Eye Institute (2023)
Finalist, Dean's Postdoctoral Fellowship, Stanford School of Medicine (2021)
Qais Farjo, MD Memorial Travel Grant, ARVO (2021)
MATS Dissertation Year Fellowships, UCSD (2019)
Rising Stars Women in Engineering, Asian Deans’ Forum 2019 (2019)
Chancellor’s Research Excellence Scholarship, UCSD (2018)
Nomination of Schmidt Science Fellows Program, UCSD (2018)
Travel Award: 256th ACS National Meeting & Exposition, GSA, UCSD (2018)
Travel Award: Xiangjiang Symposium for Global Young Scholars, CSU (2017)
Alumni Association Scholarship, Southeast University (2007)
Provincial Outstanding Student Leader, Jiangsu Province, China (2007)
Outstanding Student Leader, Southeast University (2006)
Outstanding Student Leader, School of Mater. Sci. & Eng. of Southeast University (2006)
10th ‘All-in-one Card’ Scholarship, China Merchants Bank Nanjing Branch (2005)
Boards, Advisory Committees, Professional Organizations
Member, SFB (2023 - Present)
Member, ARVO (2021 - Present)
Member, ACS (2016 - Present)
Ph.D., UC San Diego, Materials Science & Engineering (2019)
Master, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Materials Science (2012)
Bachelor, Southeast University, Materials Science & Engineering (2008)
David Myung, Fang Chen, Gabriella Fernandes-Cunha, Sarah Hull, Sarah Heilshorn, Christopher Lindsay, Christopher Madl, Hyun Jong Lee. "United States Patent WO2021222612A1, US20230263943A1 Hydrogels for in situ-forming tissue constructs", Leland Stanford Junior University, US Department of Veterans Affairs VA, Aug 24, 2023
Darren J. Lipomi, Charles Dhong, Samuel Edmunds, Fang Chen, Laure V. Kayser, Julian Ramirez, Jesse Jokerst. "United States Patent WO2019195618A1 Non-contact measurements of fluids, particles and bubbles", Oct 10, 2019
Jesse Jokerst, Fang Chen, Junxin Wang. "United States Patent US20190029637A1 A wearable sensor, and method, to monitor anti-coagulation therapy", University of California, Jan 31, 2019
Current Research and Scholarly Interests
Corneal regeneration via hydrogel-based cell scaffold and cell encapsulation
Nanoparticle-Based Tracking of Retinal Ganglion Cell Transplant, Stanford University (7/1/2023 - 6/30/2028)
Stanford, CA, US
- Fusogenic liposome-enhanced cytosolic delivery of magnetic nanoparticles RSC ADVANCES 2021; 11 (57): 35796-35805
Gold nanoparticles to enhance ophthalmic imaging.
The use of gold nanoparticles as diagnostic tools is burgeoning, especially in the cancer community with a focus on theranostic applications to both cancer diagnosis and treatment. Gold nanoparticles have also demonstrated great potential for use in diagnostic and therapeutic approaches in ophthalmology. Although many ophthalmic imaging modalities are available, there is still a considerable unmet need, in particular for ophthalmic molecular imaging for the early detection of eye disease before morphological changes are more grossly visible. An understanding of how gold nanoparticles are leveraged in other fields could inform new ways they could be utilized in ophthalmology. In this paper, we review current ophthalmic imaging techniques and then identify optical coherence tomography (OCT) and photoacoustic imaging (PAI) as the most promising technologies amenable to the use of gold nanoparticles for molecular imaging. Within this context, the development of gold nanoparticles as OCT and PAI contrast agents are reviewed, with the most recent developments described in detail.
View details for DOI 10.1039/d0bm01063d
View details for PubMedID 33057463
Simultaneous Interpenetrating Polymer Network of Collagen and Hyaluronic Acid as an In Situ-Forming Corneal Defect Filler.
Chemistry of materials : a publication of the American Chemical Society
2020; 32 (12): 5208-5216
Timely treatment of corneal injuries injury can help to prevent corneal scarring, blindness, and the need for corneal transplantation. This work describes a novel hydrogel that can fill corneal defects and assist in corneal regeneration. This hydrogel is a simultaneous interpenetrating polymer network (IPN) composed of collagen cross-linked via strain-promoted azide-alkyne cycloaddition reaction and hyaluronic acid cross-linked via thiol-ene Michael click reaction. The formation of the IPN gel was confirmed via FTIR spectra, UV-vis spectra, and morphological changes. We compared the gelation time, mechanical properties, transmittance, and refractive index of the IPN gel to the collagen gel, hyaluronic acid gel, and semi-IPN gel. The IPN combined the advantages of collagen and hyaluronic acid gels and supported corneal epithelial cell growth on its surface. When applied to corneal stromal defects in vivo, the IPN avoided epithelial hyperplasia, decreased stromal myofibroblast formation, and increased tight junction formation in the regenerated epithelium.
View details for DOI 10.1021/acs.chemmater.0c01307
View details for PubMedID 33603277
View details for PubMedCentralID PMC7888987
Bio-orthogonally crosslinked hyaluronate-collagen hydrogel for suture-free corneal defect repair.
2020; 255: 120176
Biomaterials that mimic corneal stroma could decrease the need for donor corneal tissue and could decrease the prevalence of complications associated with corneal transplantation, including infection and rejection. We developed a bio-orthogonally crosslinked hyaluronate-collagen hydrogel which can fill corneal defects in situ without the need for any sutures, initiators, or catalysts. We studied the effects of biorthogonal crosslinking on the light transmittance of the hydrogel, which was greater than 97% water. The transmittance of the optimized hydrogel in the visible light range was over 94%. We also investigated the mechanical properties, refractive index, morphology, biocompatibility, and corneal re-epithelialization capacity of the hyaluronate-collagen hydrogel. Our in vitro, in vivo, and ex vivo results demonstrated that this bio-orthogonally crosslinked hyaluronate-collagen hydrogel has excellent potential as a biomaterial for cornea repair and regeneration.
View details for DOI 10.1016/j.biomaterials.2020.120176
View details for PubMedID 32559566
Increasing the Efficacy of Stem Cell Therapy via Triple-Function Inorganic Nanoparticles
2019; 13 (6): 6605–17
Stem cell therapy in heart disease is challenged by mis-injection, poor survival, and low cell retention. Here, we describe a biocompatible multifunctional silica-iron oxide nanoparticle to help solve these issues. The nanoparticles were made via an in situ growth of Fe3O4 nanoparticles on both the external surfaces and pore walls of mesocellular foam silica nanoparticles. In contrast to previous work, this approach builds a magnetic moiety inside the pores of a porous silica structure. These materials serve three roles: drug delivery, magnetic manipulation, and imaging. The addition of Fe3O4 to the silica nanoparticles increased their colloidal stability, T2-based magnetic resonance imaging contrast, and superparamagnetism. We then used the hybrid materials as a sustained release vehicle of insulin-like growth factor-a pro-survival agent that can increase cell viability. In vivo rodent studies show that labeling stem cells with this nanoparticle increased the efficacy of stem cell therapy in a ligation/reperfusion model. The nanoparticle-labeled cells increase the mean left ventricular ejection fraction by 11 and 21% and the global longitudinal strain by 24 and 34% on days 30 and 60, respectively. In summary, this multifunctional nanomedicine improves stem cell survival via the sustained release of pro-survival agents.
View details for DOI 10.1021/acsnano.9b00653
View details for Web of Science ID 000473248300046
View details for PubMedID 31188564
Cellular toxicity of silicon carbide nanomaterials as a function of morphology
2018; 179: 60–70
Silicon carbide has been shown to be biocompatible and is used as a coating material for implanted medical devices to prevent biofilms. Silicon carbide nanomaterials are also promising in cell tracking due to their stable and strong luminescence, but more comprehensive studies of this material on the nanoscale are needed. Here, we studied the toxicity of silicon carbide nanomaterials on human mesenchymal stem cells in terms of metabolism, viability, adhesion, proliferation, migration, oxidative stress, and differentiation ability. We compared two different shapes and found that silicon carbide nanowires are toxic to human mesenchymal stem cells but not to cancer cell lines at the concentration of 0.1 mg/mL. Control silicon carbide nanoparticles were biocompatible to human mesenchymal stem cells at 0.1 mg/mL. We studied the potential mechanistic effect of silicon carbide nanowires on human mesenchymal stem cells' phenotype, cytokine secretion, and gene expression. These findings suggest that the toxic effect of silicon carbide nanomaterials to human mesenchymal stem cells are dependent on morphology.
View details for DOI 10.1016/j.biomaterials.2018.06.027
View details for Web of Science ID 000441490200005
View details for PubMedID 29980075
View details for PubMedCentralID PMC6069971
Multifunctional nanomedicine with silica: Role of silica in nanoparticles for theranostic, imaging, and drug monitoring
JOURNAL OF COLLOID AND INTERFACE SCIENCE
2018; 521: 261–79
The idea of multifunctional nanomedicine that enters the human body to diagnose and treat disease without major surgery is a long-standing dream of nanomaterials scientists. Nanomaterials show incredible properties that are not found in bulk materials, but achieving multi-functionality on a single material remains challenging. Integrating several types of materials at the nano-scale is critical to the success of multifunctional nanomedicine device. Here, we describe the advantages of silica nanoparticles as a tool for multifunctional nano-devices. Silica nanoparticles have been intensively studied in drug delivery due to their biocompatibility, degradability, tunable morphology, and ease of modification. Moreover, silica nanoparticles can be integrated with other materials to obtain more features and achieve theranostic capabilities and multimodality for imaging applications. In this review, we will first compare the properties of silica nanoparticles with other well-known nanomaterials for bio-applications and describe typical routes to synthesize and integrate silica nanoparticles. We will then highlight theranostic and multimodal imaging application that use silica-based nanoparticles with a particular interest in real-time monitoring of therapeutic molecules. Finally, we will present the challenges and perspective on future work with silica-based nanoparticles in medicine.
View details for DOI 10.1016/j.jcis.2018.02.053
View details for Web of Science ID 000430526700029
View details for PubMedID 29510868
View details for PubMedCentralID PMC5899957
Organosilica Nanoparticles with an Intrinsic Secondary Amine: An Efficient and Reusable Adsorbent for Dyes
ACS APPLIED MATERIALS & INTERFACES
2017; 9 (18): 15566–76
Nanomaterials are promising tools in water remediation because of their large surface area and unique properties compared to bulky materials. We synthesized an organosilica nanoparticle (OSNP) and tuned its composition for anionic dye removal. The adsorption mechanisms are electrostatic attraction and hydrogen bonding between the amine on OSNP and the dye, and the surface charge of the OSNP can be tuned to adsorb either anionic or cationic dyes. Using phenol red as a model dye, we studied the effect of the amine group, pH, ionic strength, time, dye concentration, and nanomaterial mass on the adsorption. The theoretical maximum adsorption capacity was calculated to be 175.44 mg/g (0.47 mmol/g), which is higher than 67 out of 77 reported adsorbents. The experimental maximum adsorption capacity is around 201 mg/g (0.53 mmol/g). Furthermore, the nanoparticles are highly reusable and show stable dye removal and recovery efficiency over at least 10 cycles. In summary, the novel adsorbent system derived from the intrinsic amine group within the frame of OSNP are reusable and tunable for anionic or cationic dyes with high adsorption capacity and fast adsorption. These materials may also have utility in drug delivery or as a carrier for imaging agents.
View details for DOI 10.1021/acsami.7b04181
View details for Web of Science ID 000401307100039
View details for PubMedID 28422482
View details for PubMedCentralID PMC5443609
Exosome-like silica nanoparticles: a novel ultrasound contrast agent for stem cell imaging
2017; 9 (1): 402–11
Ultrasound is critical in many areas of medicine including obstetrics, oncology, and cardiology with emerging applications in regenerative medicine. However, one critical limitation of ultrasound is the low contrast of target tissue over background. Here, we describe a novel cup-shaped silica nanoparticle that is reminiscent of exosomes and that has significant ultrasound impedance mismatch for labelling stem cells for regenerative medicine imaging. These exosome-like silica nanoparticles (ELS) were created through emulsion templating and the silica precursors bis(triethoxysilyl)ethane (BTSE) and bis(3-trimethoxysilyl-propyl)amine (TSPA). We found that 40% TSPA resulted in the exosome like-morphology and a positive charge suitable for labelling mesenchymal stem cells. We then compared this novel structure to other silica structures used in ultrasound including Stober silica nanoparticles (SSN), MCM-41 mesoporous silica nanoparticles (MSN), and mesocellular foam silica nanoparticles (MCF) and found that the ELS offered enhanced stem cell signal due to its positive charge to facilitate cell uptake as well as inherently increased echogenicity. The in vivo detection limits were <500 cells with no detectable toxicity at the concentrations used for labelling. This novel structure may eventually find utility in applications beyond imaging requiring an exosome-like shape including drug delivery.
View details for DOI 10.1039/c6nr08177k
View details for Web of Science ID 000391739300049
View details for PubMedID 27924340
View details for PubMedCentralID PMC5179289
- Chitosan enclosed mesoporous silica nanoparticles as drug nano-carriers: Sensitive response to the narrow pH range MICROPOROUS AND MESOPOROUS MATERIALS 2012; 150 (1): 83–89
Collagen Gels Crosslinked by Photoactivation of Riboflavin for the Repair and Regeneration of Corneal Defects.
ACS applied bio materials
Bioengineered corneal tissue is a promising therapeutic modality for the treatment of corneal blindness as a substitute for cadaveric graft tissue. In this study, we fabricated a collagen gel using ultraviolet-A (UV-A) light and riboflavin as a photosensitizer (PhotoCol-RB) as an in situ-forming matrix to fill corneal wounds and create a cohesive interface between the crosslinked gel and adjacent collagen. The PhotoCol-RB gels supported corneal epithelialization and exhibited higher transparency compared to physically crosslinked collagen. We showed that different riboflavin concentrations yielded gels with different mechanical and biological properties. In vitro experiments using human corneal epithelial cells (hCECs) showed that hCECs are able to proliferate on the gel and express corneal cell markers such as cytokeratin 12 (CK12) and tight junctions (ZO-1). Using an ex vivo burst assay, we also showed that the PhotoCol-RB gels are able to seal corneal perforations. Ex vivo organ culture of the gels filling lamellar keratectomy wounds showed that the epithelium that regenerated over the PhotoCol-RB gels formed a multilayer compared to just a double layer for those that grew over physically cross-linked collagen. These gels can be formed either in situ directly on the wound site to conform to the geometry of a defect, or can be preformed and then applied to the corneal wound. Our results indicate that PhotoCol-RB gels merit further investigation as a way to stabilize and repair deep and perforating corneal wounds.
View details for DOI 10.1021/acsabm.3c00015
View details for PubMedID 37126648
In Situ-Forming Collagen-Hyaluronate Semi-Interpenetrating Network Hydrogel Enhances Corneal Defect Repair.
Translational vision science & technology
2022; 11 (10): 22
Purpose: Millions worldwide suffer vision impairment or blindness from corneal injury, and there remains an urgent need for a more effective and accessible way to treat corneal defects. We have designed and characterized an in situ-forming semi-interpenetrating polymer network (SIPN) hydrogel using biomaterials widely used in ophthalmology and medicine.Methods: The SIPN was formed by cross-linking collagen type I with bifunctional polyethylene glycol using N-hydroxysuccinimide ester chemistry in the presence of linear hyaluronic acid (HA). Gelation time and the mechanical, optical, swelling, and degradation properties of the SIPN were assessed. Cytocompatibility with human corneal epithelial cells and corneal stromal stem cells (CSSCs) was determined in vitro, as was the spatial distribution of encapsulated CSSCs within the SIPN. In vivo wound healing was evaluated by multimodal imaging in an anterior lamellar keratectomy injury model in rabbits, followed by immunohistochemical analysis of treated and untreated tissues.Results: The collagen-hyaluronate SIPN formed in situ without an external energy source and demonstrated mechanical and optical properties similar to the cornea. It was biocompatible with human corneal cells, enhancing CSSC viability when compared with collagen gel controls and preventing encapsulated CSSC sedimentation. In vivo application of the SIPN significantly reduced stromal defect size compared with controls after 7 days and promoted multilayered epithelial regeneration.Conclusions: This in situ-forming SIPN hydrogel may be a promising alternative to keratoplasty and represents a step toward expanding treatment options for patients suffering from corneal injury.Translational Relevance: We detail the synthesis and initial characterization of an SIPN hydrogel as a potential alternative to lamellar keratoplasty and a tunable platform for further development in corneal tissue engineering and therapeutic cell delivery.
View details for DOI 10.1167/tvst.11.10.22
View details for PubMedID 36239965
Nanomedicine and drug delivery to the retina: current status and implications for gene therapy.
Naunyn-Schmiedeberg's archives of pharmacology
Blindness affects more than 60 million people worldwide. Retinal disorders, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma, are the leading causes of blindness. Finding means to optimize local and sustained delivery of drugs or genes to the eye and retina is one goal to advance the development of new therapeutics. Despite the ease of accessibility of delivering drugs via the ocular surface, the delivery of drugs to the retina is still challenging due to anatomic and physiologic barriers. Designing a suitable delivery platform to overcome these barriers should enhance drug bioavailability and provide a safe, controlled, and sustained release. Current inventions for posterior segment treatments include intravitreal implants and subretinal viral gene delivery that satisfy these criteria. Several other novel drug delivery technologies, including nanoparticles, micelles, dendrimers, microneedles, liposomes, and nanowires, are now being widely studied for posterior segment drug delivery, and extensive research on gene delivery using siRNA, mRNA, or aptamers is also on the rise. This review discusses the current state of retinal drug/gene delivery and highlights future therapeutic opportunities.
View details for DOI 10.1007/s00210-022-02287-3
View details for PubMedID 36107200
In Situ-forming Collagen Hydrogels Crosslinked by Multifunctional Polyethylene Glycol as a Matrix Therapy for Corneal Defects: 2-Month Follow-Up In Vivo.
PURPOSE: We recently showed that in situ-forming collagen gels crosslinked through multifunctional polyethylene glycol (PEG) supported corneal epithelialization 7 days after treatment of lamellar keratectomy wounds. In this study, we aimed to evaluate the longer-term regenerative effects of this gel in animals.METHOD: Corneal wound healing was assessed 60 days after lamellar keratectomy and gel treatment using slitlamp examination, optical coherence tomography (OCT), pachymetry, corneal topography, an ocular response analyzer, and tonometry. The corneas were evaluated for the presence of beta-tubulin, cytokeratin 3, zonula occludens-1, and alpha smooth muscle actin (SMA) markers. Gene expression of aldehyde dehydrogenase 3A1 (ALDH3A1), cluster of differentiation 31, CD163, alpha-SMA, hepatocyte growth factor, and fibroblast growth factor 2 (FGF-2) and protein expression of CD44 and collagen VI were evaluated.RESULTS: Intraocular pressure, corneal thickness, and hysteresis for the corneas treated with collagen-PEG gels did not significantly change compared with the saline group. However, placido disk topography revealed greater regularity of the central cornea in the gel-treated group compared to the saline group. The gel-treated group exhibited a lower degree of epithelial hyperplasia than the saline group. Immunohistochemical and gene expression analysis showed that the gel-treated corneas exhibited lower alpha-SMA expression compared with the saline group. CD163 and CD44 were found to be elevated in the saline-treated group compared with normal corneas.CONCLUSIONS: The in situ-forming collagen-PEG gel promoted epithelialization that improved central corneal topography, epithelial layer morphology, and reduced expression of fibrotic and inflammatory biomarkers after 60 days compared to the saline group.
View details for DOI 10.1097/ICO.0000000000003104
View details for PubMedID 35965399
Fusogenic liposome-enhanced cytosolic delivery of magnetic nanoparticles.
2021; 11 (57): 35796-35805
Magnetic nanoparticles (MNPs) are widely used in cell sorting, organelle selection, drug delivery, cell delivery, and cell tracking applications. However, organelle manipulation in living cells has been limited due to the endocytic uptake and sequestration of MNPs. Here, we introduce a method for modifying MNPs with fusogenic liposomes that facilitate MNP passage directly into the cytosol. MNPs were enclosed in fusogenic liposomes that exhibit a core-shell structure under a transmission electron microscope (TEM). The lipid-to-MNP ratio was optimized for one layer of liposome coating around each MNP, so that MNPs were delivered to the cytosol without endosomal or liposomal coatings. After incubation with the retinal pigment epithelial cell line ARPE-19, single-layer liposome-coated MNPs exhibited the highest MNP delivery efficiency. Although uncoated MNPs are taken up through endocytosis, less than 15% of the fusogenic liposome-coated MNPs co-localized with early endosomes. MNPs delivered by fusogenic liposomes showed cytosolic localization early on and increased lysosomal localization at later time points. The movement of intracellular MNPs could be manipulated with an external magnet to estimate cytosolic viscosity. Bypassing endocytosis in this way allowed efficient delivery of MNPs to the cytosol, potentially allowing for the targeting of specific organelles and controlling their motion in living cells.
View details for DOI 10.1039/d1ra03094a
View details for PubMedID 35492766
View details for PubMedCentralID PMC9043121
A Simple Inner-Stopper Guarded Trephine for Creation of Uniform Keratectomy Wounds in Rodents.
Journal of ophthalmic & vision research
2021; 16 (4): 544-551
Creating controllable, reproducible keratectomy wounds in rodent corneas can be a challenge due to their small size, thickness, and the lack of usual tools available for human eyes such as a vacuum trephine. The purpose of this work is to provide a consistent, reproducible corneal stromal defect in rats using a simple, economical, and customized inner-stopper guarded trephine.The inner-stopper guarded trephine is used to induce a circular wound in rat corneas. After trephination, the corneal flap can be removed by manual dissection using a blunt spatula. We used optical coherence topography (OCT) to measure the defect wound depth induced in ex vivo rat eyes.Despite a minor learning curve, this simple device enables depth control, reduces variability of manual keratectomy wound depth in rats, and decreases the risk for corneal perforation during keratectomy. Corneal defect creation was highly reproducible across different researchers and was independent of their surgical training.This inner-stopper guarded trephine can be utilized and applied to pre-clinical testing of a wide range of corneal wound healing therapies, including but not limited to biotherapeutics, corneal prosthetics, and regenerative technologies.
View details for DOI 10.18502/jovr.v16i4.9743
View details for PubMedID 34840676
View details for PubMedCentralID PMC8593534
- A Simple Inner-Stopper Guarded Trephine for Creation of Uniform Keratectomy Wounds in Rodents JOURNAL OF OPHTHALMIC & VISION RESEARCH 2021; 16 (4): 544-551
Supramolecular host-guest hyaluronic acid hydrogels enhance corneal wound healing through dynamic spatiotemporal effects.
The ocular surface
Large abrasions and deeper ulcers of the cornea can lead to corneal scarring, ulceration and thinning if not promptly and adequately treated. Hyaluronic acid (HA) has been investigated for the treatment of corneal wounds due to its remarkable biocompatibility, transparency and mucoadhesive properties. However, intact linear HA has low retention time on the cornea and chemical crosslinkers to synthesize HA hydrogels can cause toxicity limiting their clinical ocular applications. Here, we used supramolecular HA hydrogels formed by non-covalent host-guest interactions between HA-cyclodextrin and HA-adamantane to evaluate the impact of the hydrogels on corneal wound healing. Supramolecular HA hydrogels facilitated adhesion and spreading of encapsulated human corneal epithelial cells ex vivo and improved corneal wound healing in vivo as an in situ-formed, acellular therapeutic membrane. The HA hydrogels were absorbed within the corneal stroma over time, modulated mesenchymal cornea stromal cell secretome production, reduced cellularity and inflammation of the anterior stroma, and significantly mitigated corneal edema compared to treatment with linear HA and untreated control eyes. Taken together, our results demonstrate supramolecular HA hydrogels as a promising and versatile biomaterial platform for corneal wound healing.
View details for DOI 10.1016/j.jtos.2021.09.002
View details for PubMedID 34537415
Bio-orthogonally Crosslinked Matrix Therapies for Corneal Defect Repair
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690761100026
In vitro characterization of a novel in situ-forming semi-interpenetrating polymer network of crosslinked collagen and glycosaminoglycans for corneal defect repair
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690760500859
Collagen gels crosslinked by photoactivation of riboflavin for corneal defect repair
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690760500751
In situ-forming semi-interpenetrating network hydrogels for corneal regeneration: in vivo biological response
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690760500744
In situ forming collagen-PEG hydrogel as a matrix therapy for corneal defects: 2 month in vivo response
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690760500752
Magnetic nanoparticles for subcellular organelle manipulation
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021
View details for Web of Science ID 000690761600204
3D Printable, Modified Trephine Designs for Consistent Anterior Lamellar Keratectomy Wounds in Rabbits.
Current eye research
Purpose: Our goal is to develop a low-cost tool that can be used to create consistent, partial-thickness defects in rabbit and other large animals with minimal surgical training and that can facilitate pre-clinical testing of lamellar and in situ-forming biosynthetic matrix materials for corneal repair. Materials & Methods: In this study, three modified trephines were designed to create deep corneal wound defects with consistent depth in large animals. The modified trephines incorporated either 3D-printed parts made from photopolymerizable resins, or custom-cut commercially available Teflon sheets. Wound defects were imaged with optical coherence tomography (OCT), and the depth was analyzed based on the OCT images. Results: The results revealed that an inner-stopper guard trephine had the best performance in creating consistent and precise wound defect depth compared to modified vacuum trephine and custom guard vacuum trephine. A 75% ± 10% cut of the cornea was achieved with the inner-stopper guard trephine. The wound defect depth by created by the inner-stopper guard trephine was independent of the corneal thickness or size of the globes. Although the cut depth of the inner-stopper guard trephine differed by the experience-level of its users, the consistency (standard deviation) of the depth was independent of experience. Conclusions: Our studies provided three cost-efficient animal trephines that can create corneal wounds of consistent depth by lab researchers without extensive training in keratectomy.
View details for DOI 10.1080/02713683.2020.1868010
View details for PubMedID 33474996
Bioengineered, In Situ-Crosslinked Collagen Gels for Suture-Free Stromal Defect Reconstruction of the Cornea
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2020
View details for Web of Science ID 000554528301263
Optimization of an in situ-forming interpenetrating polymer network of collagen and hyaluronic acid hydrogel independently and simultaneously crosslinked by click chemistries
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2020
View details for Web of Science ID 000554495700138
In situ-forming bio-orthogonally crosslinked collagen-hyaluronate co-polymeric hydrogel to treat deep corneal stromal defects: in vivo biological response
ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2020
View details for Web of Science ID 000554495702200
In situ-forming collagen hydrogel crosslinked via multi-functional PEG as a matrix therapy for corneal defects.
2020; 10 (1): 16671
Visually significant corneal injuries and subsequent scarring collectively represent a major global human health challenge, affecting millions of people worldwide. Unfortunately, less than 2% of patients who could benefit from a sight-restoring corneal transplant have access to cadaveric donor corneal tissue. Thus, there is a critical need for new ways to repair corneal defects that drive proper epithelialization and stromal remodeling of the wounded area without the need for cadeveric donor corneas. Emerging therapies to replace the need for donor corneas include pre-formed biosynthetic buttons and in situ-forming matrices that strive to achieve the transparency, biocompatibility, patient comfort, and biointegration that is possible with native tissue. Herein, we report on the development of an in situ-forming hydrogel of collagen type I crosslinked via multi-functional polyethylene glycol (PEG)-N-hydroxysuccinimide (NHS) and characterize its biophysical properties and regenerative capacity both in vitro and in vivo. The hydrogels form under ambient conditions within minutes upon mixing without the need for an external catalyst or trigger such as light or heat, and their transparency, degradability, and stiffness are modulated as a function of number of PEG arms and concentration of PEG. In addition, in situ-forming PEG-collagen hydrogels support the migration and proliferation of corneal epithelial and stromal cells on their surface. In vivo studies in which the hydrogels were formed in situ over stromal keratectomy wounds without sutures showed that they supported multi-layered surface epithelialization. Overall, the in situ forming PEG-collagen hydrogels exhibited physical and biological properties desirable for a corneal stromal defect wound repair matrix that could be applied without the need for sutures or an external trigger such as a catalyst or light energy.
View details for DOI 10.1038/s41598-020-72978-5
View details for PubMedID 33028837
Stem Cell Tracking with Nanoparticle-Based Ultrasound Contrast Agents.
Methods in molecular biology (Clifton, N.J.)
2020; 2126: 141–53
Cell therapy is revolutionizing modern medicine. To promote this emerging therapy, the ability to image and track therapeutic cells is critical to monitor the progress of the treatment. Ultrasound imaging is promising in tracking therapeutic cells but suffers from poor contrast against local tissues. Therefore, it is critical to increase the ultrasound contrast of therapeutic cells over local tissue at the injection site. Here, we describe a method to increase the ultrasound intensity of therapeutic cells with nanoparticles to make the injected therapeutic cells more visible.
View details for DOI 10.1007/978-1-0716-0364-2_13
View details for PubMedID 32112386
Non-invasive Staging of Pressure Ulcers Using Photoacoustic Imaging.
Wound repair and regeneration : official publication of the Wound Healing Society [and] the European Tissue Repair Society
Ulcers including pressure ulcers and diabetic foot ulcers damage the skin and underlying tissue in people with compromised blood circulation. They are classified into four stages of severity and span from mild reddening of the skin to tissue damage and muscle/bone infections. Here, we used photoacoustic imaging as a non-invasive method for detecting early tissue damage that cannot be visually observed while also staging the disease using quantitative image analysis. We used a mouse model of pressure ulcers by implanting sub-dermal magnets in the dorsal flank and periodically applying an external magnet to the healed implant site. The magnet-induced pressure was applied in cycles, and the extent of ulceration was dictated by the number of cycles. We used both laser- and LED-based photoacoustic imaging tools with 690 nm excitation to evaluate the change in photoacoustic signal and depth of injury. Using laser-based photoacoustic imaging system, we found a 4.4-fold increase in the photoacoustic intensity in stage I versus baseline (no pressure). We also evaluated the depth of injury using photoacoustics. We measured a photoacoustic ulcer depth of 0.38 ± 0.09 mm, 0.74 ± 0.11 mm, 1.63 ± 0.4 mm, and 2.7 ± 0.31 mm (n=4) for stages I, II, III, and IV, respectively. The photoacoustic depth differences between each stage were significant (p < 0.05). We also used an LED-based photoacoustic imaging system to detect early stage (stage I) pressure ulcers and observed a 2.5-fold increase in photoacoustic signal. Importantly, we confirmed the capacity of this technique to detect dysregulated skin even before stage I ulcers have erupted. We also observed significant changes in photoacoustic intensity during healing suggesting that this approach can monitor therapy. These findings were confirmed with histology. These results suggest that this photoacoustic-based approach might have clinical value for monitoring skin diseases including pressure ulcers. This article is protected by copyright. All rights reserved.
View details for DOI 10.1111/wrr.12751
View details for PubMedID 31301258
Listening for the therapeutic window: Advances in drug delivery utilizing photoacoustic imaging.
Advanced drug delivery reviews
The preclinical landscape of photoacoustic imaging has experienced tremendous growth in the past decade. This non-invasive imaging modality augments the spatiotemporal capabilities of ultrasound with optical contrast. While it has principally been investigated for diagnostic applications, many recent reports have described theranostic delivery systems and drug monitoring strategies using photoacoustics. Here, we provide an overview of the of the progress to date while highlighting work in three specific areas: theranostic nanoparticles, real-time drug monitoring, and stem cell ("living drug") tracking. Additionally, we discuss the challenges that remain to be addressed in this burgeoning field.
View details for DOI 10.1016/j.addr.2019.07.003
View details for PubMedID 31295522
- Gadolinium Doping Enhances the Photoacoustic Signal of Synthetic Melanin Nanoparticles: A Dual Modality Contrast Agent for Stem Cell Imaging CHEMISTRY OF MATERIALS 2019; 31 (1): 251–59
Photoacoustic Imaging Quantifies Drug Release from Nanocarriers via Redox Chemistry of Dye-Labeled Cargo.
Angewandte Chemie (International ed. in English)
We report a new approach to monitor drug release from nanocarriers via a paclitaxel-methylene blue conjugate (PTX-MB) with redox activity. This construct is in a photoacoustically silent reduced state inside poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PTX-MB@PLGA NPs). During release, PTX-MB is spontaneously oxidized to produce a concentration-dependent photoacoustic signal. An in vitro drug-release study showed an initial burst release (25 %) between 0-24 h and a sustained release between 24-120 h with a cumulative release of 40.6 % and a 670-fold increase in photoacoustic signal. An in vivo murine drug release showed a photoacoustic signal enhancement of up to 649 % after 10 hours. PTX-MB@PLGA NPs showed an IC50 of 78 μg mL-1 and 44.7±4.8 % decrease of tumor burden in an orthotopic model of colon cancer via luciferase-positive CT26 cells.
View details for DOI 10.1002/anie.201914120
View details for PubMedID 31840357
A Mechanistic Investigation of Methylene Blue and Heparin Interactions and Their Photoacoustic Enhancement
2018; 29 (11): 3768–75
We recently reported a real-time method to measure heparin in human whole blood based on the photoacoustic change of methylene blue (MB). Intriguingly, the MB behaved unlike other "turn on" photoacoustic probes-the absorbance decreased as the photoacoustic signal increased. The underlying mechanism was not clear and motivated this study. We studied the binding mechanism of MB and heparin in water and phosphate buffer saline (PBS) with both experimental and computational methods. We found that the photoacoustic enhancement of the MB-heparin mixture was a result of MB-heparin aggregation due to charge neutralization and resulting sequestration of MB in these aggregates. The sequestration of MB in the MB-heparin aggregates led to decreased absorbance-there was simply less free dye in solution to absorb light. The highest photoacoustic signal and aggregation occurred when the number of negatively charged sulfate groups on heparin was approximately equal to the number of positively charged MB molecule. The MB-heparin aggregates dissociated when there were more sulfated groups from heparin than MB molecules because of the electrostatic repulsion between negatively charged sulfate groups. PBS facilitated MB dimer formation regardless of heparin concentration and reprecipitated free MB in aggregates due to ionic strength and ionic shielding. Further molecular dynamics experiments found that binding of heparin occurred at the sulfates and glucosamines in heparin. Phosphate ions could interact with the heparin via sodium ions to impair the MB-heparin binding. Finally, our model found 3.7-fold more MB dimerization upon addition of heparin in MB solution confirming that heparin facilitates MB aggregation. We conclude that the addition of heparin in MB decreases the absorbance of the sample because of MB-heparin aggregation leading to fewer MB molecules in solution; however, the aggregation also increases the PA intensity because the MB molecules in the MB-heparin aggregate have reduced degrees of freedom and poor heat transfer to solvent.
View details for DOI 10.1021/acs.bioconjchem.8b00639
View details for Web of Science ID 000451496400029
View details for PubMedID 30281976
Optics-Free, Non-Contact Measurements of Fluids, Bubbles, and Particles in Microchannels Using Metallic Nano-Islands on Graphene
2018; 18 (8): 5306–11
Despite the apparent convenience of microfluidic technologies for applications in healthcare, such devices often rely on capital-intensive optics and other peripheral equipment that limit throughput. Here, we monitored the transit of fluids, gases, particles, and cells as they flowed through a microfluidic channel without the use of a camera or laser, i.e., "optics-free" microfluidics. We did this by monitoring the deformation of the side walls caused by the analyte passing through the channel. Critically, the analyte did not have to make contact with the channel walls to induce a deflection. This minute deformation was transduced into a change in electrical resistance using an ultrasensitive piezoresitive film composed of metallic nano-islands on graphene. We related changes in the resistance of the sensor to the theoretical deformation of the channel at varying flow rates. Then, we used air bubbles to induce a perturbation on the elastomeric channel walls and measured the viscoelastic relaxation of the walls of the channel. We obtained a viscoelastic time constant of 11.3 ± 3.5 s-1 for polydimethylsiloxane, which is consistent with values obtained using other techniques. Finally, we flowed silica particles and human mesenchymal stem cells and measured the deformation profiles of the channel. This technique yielded a convenient, continuous, and non-contact measurement of rigid and deformable particles without the use of a laser or camera.
View details for DOI 10.1021/acs.nanolett.8b02292
View details for Web of Science ID 000441478300094
View details for PubMedID 30024767
View details for PubMedCentralID PMC6174088
- Development of a Trimodal Contrast Agent for Acoustic and Magnetic Particle Imaging of Stem Cells ACS APPLIED NANO MATERIALS 2018; 1 (3): 1321–31
Photoacoustic Imaging for Noninvasive Periodontal Probing Depth Measurements
JOURNAL OF DENTAL RESEARCH
2018; 97 (1): 23–30
The periodontal probe is the gold standard tool for periodontal examinations, including probing depth measurements, but is limited by systematic and random errors. Here, we used photoacoustic ultrasound for high-spatial resolution imaging of probing depths. Specific contrast from dental pockets was achieved with food-grade cuttlefish ink as a contrast medium. Here, 39 porcine teeth (12 teeth with artificially deeper pockets) were treated with the contrast agent, and the probing depths were measured with novel photoacoustic imaging and a Williams periodontal probe. There were statistically significant differences between the 2 measurement approaches for distal, lingual, and buccal sites but not mesial. Bland-Altman analysis revealed that all bias values were < ±0.25 mm, and the coefficients of variation for 5 replicates were <11%. The photoacoustic imaging approach also offered 0.01-mm precision and could cover the entire pocket, as opposed to the probe-based approach, which is limited to only a few sites. This report is the first to use photoacoustic imaging for probing depth measurements with potential implications to the dental field, including tools for automated dental examinations or noninvasive examinations.
View details for DOI 10.1177/0022034517729820
View details for Web of Science ID 000418548700003
View details for PubMedID 28880116
View details for PubMedCentralID PMC5755810
Photoacoustic Imaging of Human Mesenchymal Stem Cells Labeled with Prussian Blue-Poly(L-lysine) Nanocomplexes
2017; 11 (9): 9022–32
Acoustic imaging is affordable and accessible without ionizing radiation. Photoacoustic imaging increases the contrast of traditional ultrasound and can offer good spatial resolution when used at high frequencies with excellent temporal resolution. Prussian blue nanoparticles (PBNPs) are an emerging photoacoustic contrast agent with strong optical absorption in the near-infrared region. In this study, we developed a simple and efficient method to label human mesenchymal stem cells (hMSCs) with PBNPs and imaged them with photoacoustic imaging. First, PBNPs were synthesized by the reaction of FeCl3 with K4[Fe(CN)6] in the presence of citric acid and complexed with the cationic transfection agent poly-l-lysine (PLL). The PLL-coated PBNPs (PB-PLL nanocomplexes) have a maximum absorption peak at 715 nm and could efficiently label hMSCs. Cellular uptake of these nanocomplexes was studied using bright field, fluorescence, and transmission electron microscopy. The labeled stem cells were successfully differentiated into two downstream lineages of adipocytes and osteocytes, and they showed positive expression for surface markers of CD73, CD90, and CD105. No changes in viability or proliferation of the labeled cells were observed, and the secretome cytokine analysis indicated that the expression levels of 12 different proteins were not dysregulated by PBNP labeling. The optical properties of PBNPs were preserved postlabeling, suitable for the sensitive and quantitative detection of implanted cells. Labeled hMSCs exhibited strong photoacoustic contrast in vitro and in vivo when imaged at 730 nm, and the detection limit was 200 cells/μL in vivo. The photoacoustic signal increased as a function of cell concentration, indicating that the number of labeled cells can be quantified during and after cell transplantations. In hybrid ultrasound/photoacoustic imaging, this approach offers real-time and image-guided cellular injection even through an intact skull for brain intraparenchymal injections. Our labeling and imaging technique allowed the detection and monitoring of 5 × 104 mesenchymal stem cells in living mice over a period of 14 days.
View details for DOI 10.1021/acsnano.7b03519
View details for Web of Science ID 000411918200050
View details for PubMedID 28759195
View details for PubMedCentralID PMC5630123
A Nanoscale Tool for Photoacoustic-Based Measurements of Clotting Time and Therapeutic Drug Monitoring of Heparin.
2016; 16 (10): 6265-6271
Heparin anticoagulation therapy is an indispensable feature of clinical care yet has a narrow therapeutic window and is the second most common intensive care unit (ICU) medication error. The active partial thromboplastin time (aPTT) monitors heparin but suffers from long turnaround times, a variable reference range, limited utility with low molecular weight heparin, and poor correlation to dose. Here, we describe a photoacoustic imaging technique to monitor heparin concentration using methylene blue as a simple and Federal Drug Administration-approved contrast agent. We found a strong correlation between heparin concentration and photoacoustic signal measured in phosphate buffered saline (PBS) and blood. Clinically relevant heparin concentrations were detected in blood in 32 s with a detection limit of 0.28 U/mL. We validated this imaging approach by correlation to the aPTT (Pearson's r = 0.86; p < 0.05) as well as with protamine sulfate treatment. This technique also has good utility with low molecular weight heparin (enoxaparin) including a blood detection limit of 72 μg/mL. We then used these findings to create a nanoparticle-based hybrid material that can immobilize methylene blue for potential applications as a wearable/implantable heparin sensor to maintain drug levels in the therapeutic window. To the best of our knowledge, this is the first use of photoacoustics to image anticoagulation therapy with significant potential implications to the cardiovascular and surgical community.
View details for DOI 10.1021/acs.nanolett.6b02557
View details for PubMedID 27668964
View details for PubMedCentralID PMC5623117