Graduate student University of Missouri - Columbia, United States
Introduction:: Valvular heart diseases (VHD) predominantly result from leaflet malfunction. Tissue engineering of functional heart valves requires the development of leaflet substrates that accurately mimic the trilayer extracellular matrix (ECM), high flexibility, and mechanical anisotropy of human native heart valve leaflets to avoid VIC activation and maladaptive remodeling. In this study, we produced electrospun trilayer polycaprolactone (PCL)/poly(trimethylene carbonate) (PTMC) substrates using PCL, poly(trimethylene carbonate-co-l-lactide) (PTMC-LA), and poly(trimethylene carbonate-co-caprolactone) (PTMC-CL) polymer blends. The tensile properties, anisotropicity, and fiber orientations of these substrates were similar to human native aortic leaflets.
Materials and Methods:: The substrates were produced through electrospinning. The crystallinity, hydrophobicity, structure, tensile, and flexural properties of the trilayer PCL/PTMC substrates were evaluated and compared to trilayer PCL substrates (control). The trilayer PCL and PCL/PTMC substrates were seeded with valvular interstitial cells (VICs) and cultured in vitro to produce the trilayer PCL and PCL/PTMC cell-cultured constructs. Cell proliferation, viability, ECM production, mechanical properties, calcification resistance, and gene expression of the cell-cultured constructs were assessed.
Results, Conclusions, and Discussions:: The random and radial layers of the trilayer PCL/PTMC were produced from PCL/PTMC-CL. Also, the circumferential layer of the trilayer PCL/PTMC substrate was electrospun from PCL/PTMC-LA (Figure: a-c). The crystallinity and hydrophobicity of the PCL/PTMC substrates were lower than that of the PCL substrates. Collectively, the tensile modulus and strength anisotropic ratios of the PCL/PTMC substrates (7.97 ± 0.32 and 6.94 ± 0.22) were significantly higher than that of the PCL substrate (3.61 ± 0.87 and 2.11 ± 0.31) and similar to human native leaflets (15.05 MPa and 2.49 MPa) (Figure: e-f). PCL/PTMC constructs had a 17% higher cell number, 41% more collagen, and 33% more GAG than the PCL constructs (Figure: e-g). The higher gene expression of vimentin, smooth muscle actin, collagen type I, and transforming growth factor beta-3 by the PVICs in the PCL/PTMC constructs than in the PCL constructs suggested that more cells were in a growth state.
The electrospun trilayer PCL/PTMC substrates developed in this study exhibited structural, tensile, and anisotropic properties similar to human native aortic valve leaflets. The lower hydrophobicity of the PCL/PTMC substrates contributed to better cell adhesion than the PCL substrates. The PCL/PTMC cell-cultured constructs maintained similar mechanical anisotropy and flexural properties compared to the PCL/PTMC original substrate. Further, the PCL/PTMC cell-cultured constructs had more cell proliferation, infiltration, ECM material production, and superior PVIC gene expression than the PCL cell-cultured constructs.
