Programmable Strain Gradients in 3D Hydrogels to Analyze and Direct Cell and Tissue Formation

Background: Biological tissues experience various stretch gradients in the body which act as mechanical signaling from the extra-cellular environment to cells. These mechanical stimuli are transferred to cell sensor proteins, triggering essential signaling cascades regulating cell migration, cell differentiation and tissue remodeling. Previous studies have successfully applied simple, uniform stretch to hydrogels in order to analyze the response of living cells, however, the ability to induce non-uniform strains in controlled gradients has proven challenging. Methods: In this study, we manipulated the geometry of 3D fibrin hydrogels embedded in punctured silicone rubber strips. The strips were then stretched using a dedicated stretching device [1] and imaged in real-time under confocal microscopy. The resulting strains and internal fiber alignment gradients were analyzed and compared to computer models. Results: Strain gradient control through geometric manipulation and external stretch was confirmed. A linear relationship between strain magnitude and fiber alignment in the stretch direction was found. These findings were verified by simulations conducted on 2D finite element models. Conclusion: The experimental and simulation data confirm our ability to custom design mechanical gradients in 3D hydrogels. This clearly offers a framework for the analysis of cell response to mechanically induced signaling, pushing the limits of bioengineering and providing a platform for programming the control of cellular behavior and differentiation.

[1] Avishy Roitblat Riba, Sari Natan, Avraham Kolel, Hila Rushkin, Oren Tchaicheeyan, Ayelet Lesman. Straining 3D hydrogels with uniform z-axis strains while enabling live microscopy imaging. Annals of Biomedical Engineering (2019), https://doi.org/10.1007/s10439-019-02426-7.