Tunable microfabricated hydrogels - A study in protein interaction and diffusion

Hydrogels have been explored as robust engineering materials for sensors and actuators in microsystems. For hydrogels to successfully interact with a biological environment, characteristics such as mechanical strength, biomolecules storage and diffusion rate in a hydrogel matrix must be understood. The ability to easily tune the fabrication of a hydrogel for varying degrees of interaction or non-interaction with biomolecules would be advantageous. To this end, we fabricated pH-responsive hydrogels of various swelling ratios. Furthermore, the hydrogels were exposed to protein solutions and measured the mechanical strength of the same in the presence of bovine serum albumin (BSA), showing that BSA had no influence on the mechanical strength of the hydrogel. We then measured protein diffusion characteristics of BSA in the hydrogel by comparing relative fluorescence intensity across a range of swelling ratios. Higher swelling ratio gels exhibited higher fluorescence intensity and thus more storage capability. Finally, we explored the use of fluorescence recovery after photobleaching (FRAP) to characterize the diffusion constant of BSA, lysozyme, and monoclonal antibody in the studied hydrogels. Results show three distinct types of diffusion behavior: protein interaction with the hydrogel matrix, pH dependence of protein diffusion, and the observance of diffusion overshot.