A microstructure based mechanical model for planar fibrous scaffolds.

Cardiac valve and myocardium tissue regeneration has consistently raised interest for cell-seeded/microintegrated planar fibrous scaffolds. Electrospun constructs, decellularized tissues and collagen/fibrin gels often show a similar microstructure mainly characterized by the fibrous network topology. Microstructure based mechanical modeling enable fabrication parameters and scaffolds morphology to be related to mesomacro mechanical response. A novel approach to (1) characterize the material fibers network microarchitecture, (2) reproduce stochastically equivalent fiber network models, and (3) predict the mechanical response at meso-macro level is presented in this work. Electron micrographs (SEM) of electrospun poly (ester urethane) urea (PEUU) scaffolds were analyzed using a custom made software [D’Amore et al Biomat 2010; 31:(20) 5345-5354]. Two scaffolds families with isotropic and anisotropic structure (orientation index: 0.5, 0.65 respectively) were studied. The following architectural descriptors have identified for each scaffold family: fiber angle distribution, connectivity, fiber intersection density, fiber diameter. Stochastically equivalent scaffolds models (250x250 μm) were generated minimizing the differences in the above mentioned parameters between the real fiber networks and the simulated ones. The nodes and rods models were imported into the ANSYS environment as beam elements with axial and bending stiffnesses. A simple linear relation was adopted as constitutive model, thus structure mechanical non-linearity was dictated entirely by network topology. FEA analysis was performed simulating equibiaxial stretch conditions, the single fiber mechanical stiffness was the only parameter required to fit the equi-biaxial experimental data. At the macro level the bulk mechanical response agreed well with the experimental biaxial mechanical data, single fiber mechanical stiffness was ~380 kPa. At meso level under applied deformation, the simulated fiber networks showed, as expected, that the fibers aligned in the scaffold cross preferred direction carry higher forces. Fabrication parameters were connected to the material structure throughout image analysis and the material architecture was connected in turn to the mechanical behavior by FEA. The latter concept in conjunction with the multi-scale prediction capability of the adopted approach provides evidence of its potential in guiding cardiac tissue engineering constructs design and fabrication.