Programmable Strain Gradients in 3D Hydrogels for Guiding Complex Tissue Architecture

Abstract

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, differentiation and tissue remodeling. Previous studies have successfully applied simple, uniform stretch to 2D elastic substrates in order to analyze the response of living cells. However, the ability to induce non-uniform strains in controlled gradients, particularly in 3D hydrogels, has proven challenging.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 [1,2] and imaged in real-time under confocal microscopy. The resulting strains and internal fiber alignment gradients were analyzed and compared to finite element simulations. Strain gradient control through geometric manipulation and external stretch was confirmed with a linear relationship between strain magnitude and fiber alignment in the stretch direction. Additionally, fibroblast cells embedded in the fibrin gels were found to align along the stretch direction in a gradient manner that correlate to the developed strain gradients. The experimental and simulation data confirm our ability to custom design mechanical gradients in 3D hydrogels and control cell alignment, offering a framework for further elucidation of cell response to mechanically induced signaling and providing a platform for programming cellular behavior and differentiation. [1] A. Roitblat Riba, S. Natan, A. Kolel, H. Rushkin, O. Tchaicheeyan, A. 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. [2] A. Kolel, A. Roitblat Riba, S. Natan, O. Tchaicheeyan, E. Saias, A. Lesman. Controlled Strain of 3D Hydrogels under Live Microscopy Imaging. Journal of Visualized Expirements. (Pending Publication). e61671. In-press (2020).