A novel 3D-Printed preferential posterior mitral annular dilation device delineates regurgitation onset threshold in an ex vivo heart simulator.
Medical engineering & physics
Mitral regurgitation (MR) due to annular dilation occurs in a variety of mitral valve diseases and is observed in many patients with heart failure due to mitral regurgitation. To understand the biomechanics of MR and ultimately design an optimized annuloplasty ring, a representative disease model with asymmetric dilation of the mitral annulus is needed. This work shows the design and implementation of a 3D-printed valve dilation device to preferentially dilate the posterior mitral valve annulus. Porcine mitral valves (n=3) were sewn into the device and mounted within a left heart simulator that generates physiologic pressures and flows through the valves, while chordal forces were measured. The valves were incrementally dilated, inducing MR, while hemodynamic and force data were collected. Flow analysis demonstrated that MR increased linearly with respect to percent annular dilation when dilation was greater than a 25.6% dilation threshold (p<0.01). Pre-threshold, dilation did not cause significant increases in regurgitant fraction. Forces on the chordae tendineae increased as dilation increased prior to the identified threshold (p < 0.01); post-threshold, the MR resulted in highly variable forces. Ultimately, this novel dilation device can be used to more accurately model a wide range of MR disease states and their corresponding repair techniques using ex vivo experimentation. In particular, this annular dilation device provides the means to investigate the design and optimization of novel annuloplasty rings.
View details for DOI 10.1016/j.medengphy.2020.01.005
View details for PubMedID 32008935
Mitral chordae tendineae force profile characterization using a posterior ventricular anchoring neochordal repair model for mitral regurgitation in a three-dimensional-printed ex vivo left heart simulator.
European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery
OBJECTIVES: Posterior ventricular anchoring neochordal (PVAN) repair is a non-resectional technique for correcting mitral regurgitation (MR) due to posterior leaflet prolapse, utilizing a single suture anchored in the myocardium behind the leaflet. This technique has demonstrated clinical efficacy, although a theoretical limitation is stability of the anchoring suture. We hypothesize that the PVAN suture positions the leaflet for coaptation, after which forces are distributed evenly with low repair suture forces.METHODS: Porcine mitral valves were mounted in a 3-dimensional-printed heart simulator and chordal forces, haemodynamics and echocardiography were collected at baseline, after inducing MR by severing chordae, and after PVAN repair. Repair suture forces were measured with a force-sensing post positioned to mimic in vivo suture placement. Forces required to pull the myocardial suture free were also determined.RESULTS: Relative primary and secondary chordae forces on both leaflets were elevated during prolapse (P<0.05). PVAN repair eliminated MR in all valves and normalized chordae forces to baseline levels on anterior primary (0.37±0.23 to 0.22±0.09 N, P<0.05), posterior primary (0.62±0.37 to 0.14±0.05 N, P=0.001), anterior secondary (1.48±0.52 to 0.85±0.43 N, P<0.001) and posterior secondary chordae (1.42±0.69 to 0.59±0.17 N, P=0.005). Repair suture forces were minimal, even compared to normal primary chordae forces (0.08±0.04 vs 0.19±0.08 N, P=0.002), and were 90 times smaller than maximum forces tolerated by the myocardium (0.08±0.04 vs 6.9±1.3 N, P<0.001).DISCUSSION: PVAN repair eliminates MR by positioning the posterior leaflet for coaptation, distributing forces throughout the valve. Given extremely low measured forces, the strength of the repair suture and the myocardium is not a limitation.
View details for DOI 10.1093/ejcts/ezz258
View details for PubMedID 31638697
- Modeling conduit choice for valve-sparing aortic root replacement on biomechanics with a 3-dimensional-printed heart simulator JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY 2019; 158 (2): 392–403
- Bioengineered analog of stromal cell-derived factor 1 alpha preserves the biaxial mechanical properties of native myocardium after infarction JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS 2019; 96: 165–71
- Ex Vivo Biomechanical Study of Apical Versus Papillary Neochord Anchoring for Mitral Regurgitation ELSEVIER SCIENCE INC. 2019: 90–97
Ex vivo biomechanical study of apical versus papillary neochord anchoring for mitral regurgitation.
The Annals of thoracic surgery
BACKGROUND: Neochordoplasty is an important repair technique, though optimal anchoring position is unknown. While typically anchored at papillary muscles, new percutaneous devices anchor the chordae at or near the ventricular apex, which may have an effect on chordal forces and the long-term durability of the repair.METHODS: Porcine mitral valves (n=6) were mounted in a left heart simulator that generates physiological pressure and flow through the valves while chordal forces were measured using Fiber Bragg Grating strain gauge sensors. Isolated mitral regurgitation was induced by cutting P2 primary chordae and the regurgitant valve was repaired using PTFE neochord with apical anchoring, followed by papillary muscle fixation for comparison. In both cases, the neochord was anchored to a customized force-sensing post positioned to mimic the relevant in vivo placement.RESULTS: Echocardiographic and hemodynamic data confirmed that the repairs restored physiologic hemodynamics. Forces on the chordae and neochord were lower for papillary fixation than the apical (p=0.003). Additionally, the maximum rate of change of force was higher for the chordae and neochord for apical fixation when compared to papillary (p=0.028).CONCLUSIONS: Apical point of anchoring results in higher forces on the chordae and neochord stitch as well as an increased rate of loading on the neochord when compared to the papillary muscle fixation. These results suggest the papillary fixation repair may have superior durability.
View details for PubMedID 30836099
Development and ex vivo validation of novel force-sensing neochordae for measuring chordae tendineae tension in the mitral valve apparatus using optical fibers with embedded Bragg gratings.
Journal of biomechanical engineering
Few technologies exist that can provide quantitative data on forces within the mitral valve apparatus. Marker-based strain measurements can be performed, but chordal geometry and restricted optical access are limitations. Foil-based strain sensors have been described and work well, but the sensor footprint limits the number of chordae that can be measured. We instead utilized Fiber Bragg Grating (FBG) sensors-optical strain gauges made of 125µm diameter silica fibers- to overcome some limitations of previous methods of measuring chordae tendineae forces. Using FBG sensors, we created a force-sensing neochord that mimics the natural shape and movement of native chordae. FBG sensors reflect a specific wavelength of light depending on the spatial period of gratings. When force is applied, the gratings move relative to one another, shifting the wavelength of reflected light. This shift is directly proportional to force applied. The FBG sensors were housed in a protective sheath fashioned from a 0.025" flat coil, and attached to the chordae using polytetrafluoroethylene suture. The function of the force-sensing neochordae was validated in a 3D-printed left heart simulator, which demonstrated that FBG sensors provide highly sensitive force measurements of mitral valve chordae at a temporal resolution of 1000 Hz. As ventricular pressures increased, such as in hypertension, chordae forces also increased. Overall, FBG sensors are a viable, durable, and high-fidelity sensing technology that can be effectively used to measure mitral valve chordae forces and overcome some limitations of other such technologies.
View details for DOI 10.1115/1.4044142
View details for PubMedID 31253992
Rapid and durable photochemical bonding of cartilage using the porphyrin photosensitizer verteporfin.
Osteoarthritis and cartilage
To evaluate the effectiveness of verteporfin as a photosensitizer to photochemically bond articular cartilage tissues and determine bond durability in vitro.Bond strength induced by verteporfin over a range of concentrations and light exposure conditions was investigated using a disk-annulus model and a pushout test. Exposure was parameterized by varying either irradiance or irradiation time. Bond robustness in a cell-mediated degeneration environment was examined by exposing newly bonded samples to interleukin-1 alpha for the first 4 days of a 7-day culture period, followed by mechanical testing and biochemical and cellular viability assays.Photochemical bonding using verteporfin produced high bonding shear strengths at relatively low photosensitizer concentrations. Low exposures produced by either low irradiance or short irradiation time were sufficient to produce shear strengths comparable to those previously produced with phthalocyanine photosensitizers with substantially higher light exposure. Photochemically produced bonds were resistant to cell-mediated degeneration in vitro with no evident differences in cell viability among treatments.Verteporfin offers distinct advantages as a photosensitizer for photochemical bonding of articular cartilage due to the production of strong, durable bonds at relatively low light exposures. Further exploration may lead to clinically feasible strategies to augment cartilage repair techniques.
View details for DOI 10.1016/j.joca.2019.05.022
View details for PubMedID 31229683
Bioengineered analog of stromal cell-derived factor 1α preserves the biaxial mechanical properties of native myocardium after infarction.
Journal of the mechanical behavior of biomedical materials
2019; 96: 165–71
Adverse remodeling of the left ventricle (LV) after myocardial infarction (MI) results in abnormal tissue biomechanics and impaired cardiac function, often leading to heart failure. We hypothesized that intramyocardial delivery of engineered stromal cell-derived factor 1α analog (ESA), our previously-developed supra-efficient pro-angiogenic chemokine, preserves biaxial LV mechanical properties after MI. Male Wistar rats (n = 45) underwent sham surgery (n = 15) or permanent left anterior descending coronary artery ligation. Rats sustaining MI were randomized for intramyocardial injections of either saline (100 μL, n = 15) or ESA (6 μg/kg, n = 15), delivered at four standardized borderzone sites. After 4 weeks, echocardiography was performed, and the hearts were explanted. Tensile testing of the anterolateral LV wall was performed using a displacement-controlled biaxial load frame, and modulus was determined after constitutive modeling. At 4 weeks post-MI, compared to saline controls, ESA-treated hearts had greater wall thickness (1.68 ± 0.05 mm vs 1.42 ± 0.08 mm, p = 0.008), smaller end-diastolic LV internal dimension (6.88 ± 0.29 mm vs 7.69 ± 0.22 mm, p = 0.044), and improved ejection fraction (62.8 ± 3.0% vs 49.4 ± 4.5%, p = 0.014). Histologic analysis revealed significantly reduced infarct size for ESA-treated hearts compared to saline controls (29.4 ± 2.9% vs 41.6 ± 3.1%, p = 0.021). Infarcted hearts treated with ESA exhibited decreased modulus compared to those treated with saline in both the circumferential (211.5 ± 6.9 kPa vs 264.3 ± 12.5 kPa, p = 0.001) and longitudinal axes (194.5 ± 6.5 kPa vs 258.1 ± 14.4 kPa, p < 0.001). In both principal directions, ESA-treated infarcted hearts possessed similar tissue compliance as sham non-infarcted hearts. Overall, intramyocardial ESA therapy improves post-MI ventricular remodeling and function, reduces infarct size, and preserves native LV biaxial mechanical properties.
View details for PubMedID 31035067
Modeling conduit choice for valve-sparing aortic root replacement on biomechanics with a 3-dimensional-printed heart simulator.
The Journal of thoracic and cardiovascular surgery
OBJECTIVE: The optimal conduit for valve-sparing aortic root replacement is still debated, with several conduit variations available, ranging from straight tubular grafts to Valsalva grafts. Benefits of neosinus reconstruction include enhanced flow profiles and improved hemodynamics. Curiously, however, some clinical data suggest that straight grafts may have greater long-term durability. In this study, we hypothesized that straight tubular grafts may help maintain the native cylindrical position of the aortic valve commissures radially, resulting in preserved leaflet coaptation, reduced stresses, and potentially improved valve performance.METHODS: Using 3D printing, a left heart simulator with a valve-sparing root replacement model and a physiologic coronary circulation was constructed. Aortic valves were dissected from fresh porcine hearts and reimplanted into either straight tubular grafts (n=6) or Valsalva grafts (n=6). Conduits were mounted into the heart simulator and hemodynamic, echocardiographic, and high-speed videometric data were collected.RESULTS: Hemodynamic parameters and coronary blood flow were similar between straight and Valsalva grafts, although the former were associated with lower regurgitant fractions, less peak intercommissural radial separation, preserved leaflet coaptation, decreased leaflet velocities, and lower relative leaflet forces compared with Valsalva grafts.CONCLUSIONS: Valsalva grafts and straight grafts perform equally well in terms of gross hemodyanics and coronary blood flow. Interestingly, however, the biomechanics of these 2 conduits differ considerably, with straight grafts providing increased radial commissural stability and leaflet coaptation. Further investigation into how these parameters influence clinical outcomes is warranted.
View details for PubMedID 30745047