(240g) Effect of the Mechanical Environment on Connective Tissue Development in Fiber/Hydrogel Composite Meshes

Mechanical cues are one of several stimuli which influence stem cell proliferation, differentiation, and development into organized tissue structures.  Indeed, aligned topographic features and anisotropic mechanical properties can guide the development of aligned spindle shaped cells that may be suited for muscle and connective tissue regeneration, while soft isotropic gels lacking in topographic features may be better suited for regenerating cartilage and fat tissues.  We have recently developed a process for fabricating cellularized composite meshes consisting of an elastomeric network of electrospun polyurethane (PU) fibers and an electrosprayed collagen gel, where the mechanical properties of the composite are dictated by the fabrication conditions.  In this study we suspended mesenchymal stem cells (MSCs) in 0.3 to 0.7 wt% solutions of collagen and incorporated them into randomly oriented PU fiber meshes.  Resultant composites were cultured for up to 8 days slack or under uniaxial static tension.

Analysis of composite meshes indicated that collagen content, composite thickness, and water weight increased with increasing collagen concentration.  Under slack conditions, MSCs organized into spherical clusters and proliferated best in materials with a low collagen content.  In contrast, inclusion of at least 0.5 wt% collagen was critical for cell survival under a 10% static uniaxial load, and permitted cell spreading and alignment parallel to the load axis.  Poor survival of MSCs at lower collagen contents suggest that the collagen gel affords the cells protection from the PU fibers under tensile loads.  PCR and confocal imaging – to probe how the mechanical environment affects differentiation toward a connective tissue phenotype – are underway.  Nevertheless, the data show that fiber/hydrogel composite meshes can be prepared with different mechanical properties, and that these properties can affect MSC viability and morphology.