K17 - Assessment of a Decellularized Matrix and Electrospun Fibers for Pediatric Heart Valve Replacements

Introduction: : Congenital heart defects are one of the most common birth defects in the world. Treatment, if possible, is dependent on the impacted anatomy and defect severity. In the case of congenital valve defects, treatment options are limited. Typical valve replacements use either a mechanical or bioprosthetic valve, which cannot support somatic growth- a key disadvantage for a pediatric population as it results in the child requiring multiple reoperations until adulthood. To address this unmet need, the field of tissue engineered heart valves emerged. In general tissue engineering, the interactions between cells, scaffold material, and the host must be considered. As valves are dynamic structures, the scaffold of choice is of critical importance as it will determine the resulting construct’s functionality. A multitude of materials have been investigated in tissue engineering heart valve studies. Our initial work looked at porcine small intestinal submucosa (PSIS), a decellularized matrix, as a potential scaffold material choice. However, we observed that extended culture periods cause the PSIS-based valve to become distensible and have inadequate hydrodynamic functionality. Our efforts have now shifted towards electrospinning polycaprolactone (PCL), a biocompatible and biodegradable polymer. Electrospinning is a fabrication method that allows us to obtain the desired construct geometry, fiber thickness, and alignment through the following optimized spinning parameters: polymer solution concentration, flow rate, needle tip-to-collector distance, voltage, and collector speed.

Materials and

Methods: : Hydrodynamic testing was conducted on three types of differently treated PSIS valves: raw PSIS (n=3), cultured PSIS (n=6), and dehydrated PSIS (n=2). In brief, to create the cultured PSIS valves, 14mm-diameter tubular PSIS scaffolds were seeded with human bone marrow-derived mesenchymal stem cells for 8 days in a rotator and then 14 days in a bioreactor with oscillatory flow. Valves were subsequently decellularized using a 1% Triton X-100 solution. Dehydrated valves underwent the same treatment with an additional dehydration step using a 57% glycerol solution. A mechanical valve was used as a control. The left heart pulse duplicator (ViVitro Pulse Duplicator, ViVitro Labs) was set to have a mean arterial pressure of 100mmHg, a heart rate of 70 beats/min, and a 35% systolic waveform. Each test consists of 10 simulated cardiac cycles and each sample was tested in triplicates. The following hydrodynamic parameters were calculated from the obtained data: regurgitant factor (RF), effective orifice area (EOA), transvalvular pressure (ΔP), and mean flow rate (Qrms).
Our electrospinning collector consists of a 3D-printed base and housing. The base holds a motor while the housing is used for insulating the motor. Attached to the motor is a segmented metal rod that acts as the scaffold mold. Proof-of-concept experiments showed that our collector design can successfully create tubular PCL scaffolds using the following spinning parameters: a 20% PCL-acetone solution, 20cm needle tip-to-collector distance, 0.30 ml/min flow rate, and 14 kV voltage.

Results, Conclusions, and Discussions:: Raw PSIS had an average RF of 47.63% ± 26.9, EOA of 0.99 cm2 ± 0.61, ΔP of 25.18 mmHg ± 13.97, and Qrms of 151.68 ml/s ± 82.40. Cultured PSIS had an average RF of 58.4% ± 12.33, EOA of 0.67 cm2 ± 0.49, ΔP of 26.37 mmHg ± 6.36, and Qrms of 108.05 ml/s ± 21.40. Dehydrated PSIS had an average RF of 36.41% ± 22.41, EOA of 0.65 cm2 ± 0.55, ΔP of 33.01 mmHg ± 10.16, and Qrms of 120.02 ml/s ± 96.55. The mechanical valve had an average RF of 6.21% ± 0.29, EOA of 3.26 cm2 ± 0.48, ΔP of 4.31 mmHg ± 1.53, and Qrms of 249.11 ml/s ± 8.12. All of the PSIS groups had high regurgitation and ΔP with low EOA and flow rates compared to the mechanical valve. The PSIS valves also had wide variability in their results, which aligns with the inconsistent and abnormal behavior observed during testing. Ultimately, PSIS has inadequate functionality and cannot serve as a scaffold material for valve applications.
In proof-of-concept experiments, we were able to successfully create tubular PCL scaffolds using a PCL-acetone solution and our collector design. While the overall geometry of the scaffolds was correct, fiber deposition was uneven and had surface abnormalities due to the deposition of PCL globules. These issues are likely due to the rapidly evaporating solvent used, which can hinder smooth fiber deposition. The experimental setup and spinning parameters need to be further optimized to get uniform tubular scaffolds. Once this is accomplished, the structural, mechanical, and functional properties of these PCL scaffolds can be assessed. Ultimately, this work contributes to the foundational understanding of what materials can be used specifically for tissue engineered heart valves.

Acknowledgements and/or References (Optional):: We’d like to thank the Florida Heart Research Foundation for funding this work.