Cell Response to Stiffness Gradients in Alginate Hydrogels

Directed cell migration is an important aspect in many physiological and pathological processes including cancer metastasis. Cells take in and process many signals including the mechanical signal of tissue stiffness. Durotaxis is the process in which cells migrate towards stiffer regions of the extracellular matrix. Alginate, which comes from brown algae, is commonly used hydrogels due to its biocompatibility and capability to retain large amounts of water. Using stencils to control diffusion, alginate hydrogels can be crosslinked with calcium to create 2D stiffness gradients imprinted into a 3D gel. These gels can be used to engineer an environment that mimics the extracellular matrix, providing insight into how cancer cells migrate and respond to mechanical signals. To make the gels cell adhesive, collagen was incorporated into the gel using two different functionalization methods, bulk functionalization and surface functionalization. Two different behaviors are observed under these conditions. Surface functionalization shows gradients in cell number and spread cells, which could be cause either by durotaxis or stiffness-dependent proliferation. Under bulk functionalization, we show that cells invade into the gel. By fixing and staining cells, invasion can be investigated using confocal microscopy to determine how far into the gels cells move. Future work is geared towards aligning fibers within the gel to create complex multi-cue environments to understand how cells respond when multiple cues are present.