Compressive elasticity of three-dimensional nanofiber matrix directs mesenchymal stem cell differentiation to vascular cells with endothelial or smooth muscle cell markers.

The importance of mesenchymal stem cells (MSC) in vascular regeneration is becoming increasingly recognized. However, few in vitro studies have been performed to identify the effects of environmental elasticity on the differentiation of MSC into vascular cell types. Electrospinning and photopolymerization techniques were used to fabricate a three-dimensional (3-D) polyethylene glycol dimethacrylate nanofiber hydrogel matrix with tunable elasticity for use as a cellular substrate. Compression testing demonstrated that the elastic modulus of the hydrated 3-D matrices ranged from 2 to 15 kPa, similar to the in vivo elasticity of the intima basement membrane and media layer. MSC seeded on rigid matrices (8-15 kPa) showed an increase in cell area compared with those seeded on soft matrices (2-5 kPa). Furthermore, the matrix elasticity guided the cells to express different vascular-specific phenotypes with high differentiation efficiency. Around 95% of MSC seeded on the 3-D matrices with an elasticity of 3 kPa showed Flk-1 endothelial markers within 24h, while only 20% of MSC seeded on the matrices with elasticity >8 kPa demonstrated Flk-1 marker. In contrast, ∼80% of MSC seeded on 3-D matrices with elasticity >8 kPa demonstrated smooth muscle α-actin marker within 24h, while fewer than 10% of MSC seeded on 3-D matrices with elasticity <5 kPa showed α-actin markers. The ability to control MSC differentiation into either endothelial or smooth muscle-like cells based purely on the local elasticity of the substrate could be a powerful tool for vascular tissue regeneration.

Biohybrid nanofiber constructs with anisotropic biomechanical properties.

Synthetic implant materials often lack of the anisotropic mechanical properties and cell-interactive surface which are shown by natural tissues. For example, engineered vascular grafts need to be developed to address the mechanical and biological problems associated with the graft materials. This study has demonstrated a double-electrospinning fabrication process to produce a poly(ε-caprolactone)-fibroin multilayer composite which shows well-integrated nanofibrous structure, endothelial-conducive surface and anisotropic mechanical property, suitable as engineered vascular constructs. Electrospinning parameters such as voltage, solution concentration, feed rate, and relative humidity were optimized to obtain defect-free, uniform nanofibers. To mimic the different mechanical properties of natural vessels in the circumferential and longitudinal directions, a rotating cylinder was used as collector, resulting in the production of constructs with anisotropic properties. The combination of the collector shape and the collector rotation allows us to produce a tubular structure with tunable anisotropic mechanical properties. Fourier transform infrared spectroscopy, differential scanning calorimetry, and uniaxial tensile tests were used to characterize the electrospun constructs. Cell cultures with primary endothelial cells demonstrated that cells showed spread morphology and strong adhesion on fibroin richer surfaces. The platform for producing robust multilayer scaffolds with intermixing nanofiber structure, tunable anisotropy ratio, and surface with specific compositions may hold great potential in tissue engineering applications.