Functionalizing Polyacrylamide Hydrogels for Renal Cell Culture Under Fluid Shear Stress

A functional renal tubule bioreactor needs to reproduce the reabsorption and barrier functions of the renal tubule. Our prior work has demonstrated that primary human renal tubule cells respond favorably when cultured on substrates with elasticity similar to healthy tissue and when subjected to fluid shear stress. Polyacrylamide (PA) is widely used in industrial processes such as water purification because it is electrically neutral and chemically inert. PA is a versatile tool as the concentration and mechanical properties of the gel are easily adjusted by varying the proportions of monomer and crosslinker. Control of mechanical properties is attractive for preparing cell culture substrates with tunable stiffness, but PA's inert chemical properties require additional steps to prepare PA for cell attachment, such as chemical reactions to bind extracellular matrix proteins. Methods based on protein functionalization for cell attachment work well in the short term but fail to provide sufficient attachment to withstand the mechanical traction of fluid shear stress. In our present work, we tested the effects of subjecting primary renal tubule cells to fluid shear stress on an elastic substrate by developing a simple method of incorporating N-(3-Aminopropyl) methacrylamide hydrochloride (APMA) into PA hydrogels. Integration of APMA into the PA hydrogel formed a nondegradable elastic substrate promoting excellent long-term cell attachment despite the forces of fluid shear stress. Impact statement Cell culture on artificial materials requires the presence of ligands on the surface to which extracellular matrix receptors on the cell can bind. Simple nonspecific adsorption or covalent linkage of plasma or extracellular matrix proteins only suffices for short-term static culture. Prolonged culture may result in degradation of the original protein such that linkage is severed but new proteins secreted by the cell are blocked from adsorbing to the artificial scaffold. This results in detachment and loss of cell mass, as well as defects in monolayers. We present a simple technique to integrate amine moeities into a polyacrylamide hydrogel that resist degradation and support long-term culture.