Figure 7. Computational models predict strain fields of heterogenous fibrin gels.

A $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ gel with a 4 $\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ elliptical inclusion was stretched by applying a $3000\mu \mathrm{m}$ displacement on one end, and its deformation was tracked based on a photo-bleached grid (a). Unidirectional extension of the heterogeneous gel led to non-uniform strain $E_{xx}$, with larger strains in the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ region with respect to the $4\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ inclusion (b). A corresponding finite element model was created to replicate the geometry of the gel in the experiment, including the photo-bleached grid (c). Unidirectional extension of the finite element model using the average material parameters for the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ and $4\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ homogeneous gels also showed heterogeneous strains, with larger strains in the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ domain compared to the inclusion (d). A $4\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ gel with a $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ inclusion was also constructed (e), and its strain measured by tracking a phot-bleached grid of quadrilaterals. The gel with the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ inclusion showed more homogeneous strain transfer, with moderately larger strains in the inclusion with respect to the surrounding domain (f). A finite element simulation matching the gel geometry was run for the gel with the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ inclusion (g). Finite element simulations showed greater variation in strain across domains compared to experiments, but showed larger strains in the $2\mathrm{m}\mathrm{g}/\mathrm{m}\mathrm{L}$ region, similar to experiments (h).