3,4-Dihydroxy-L-Phenylalanine as a Novel Covalent Linker of Extracellular Matrix Proteins to Polyacrylamide Hydrogels with a Tunable Stiffness.

Cells acquire mechanical information from their surrounding and convert this into biochemical activity. The concept and mechanism behind this cellular mechanosensing and mechanotransduction are often studied by means of two-dimensional hydrogels. Polyacrylamide hydrogels (PAAMs) offer chemical, mechanical, and optical advantages but due to their inert surface do not allow protein and cell adherence. Several cross-linkers have been used to functionalize the surface of PAAMs with extracellular matrix (ECM) proteins to enable cell culture. However, the most commonly used cross-linkers are either unstable, expensive, or laborious and often show heterogeneous coating or require PAAM modification. Here, we introduce 3,4-dihydroxy-l-phenylalanine (L-DOPA) as a novel cross-linker that can functionalize PAAMs with ECM without the above-mentioned disadvantages. A homogenous collagen type I and fibronectin coating was observed after L-DOPA functionalization. Fibroblasts responded to differences in PAAMs' stiffness; morphology, cell area, and protein localization were all affected as expected, in accordance with literature where other cross-linkers were used. In conclusion, L-DOPA can be used as a cross-linker between PAAMs and ECM and represents a novel, straightforward, nonlaborious, and robust method to functionalize PAAMs for cell culture to study cell mechanosensing.