Photo-tunable hydrogel mechanical heterogeneity informed by predictive transport kinetics model
Callie I. Higgins, Jason P. Killgore, Frank W. DelRio, Stephanie J. Bryant, Robert R. McLeod
Mimicking the three-dimensional (3D) mechanical and chemical properties of distinctly different, adjacent biological tissues is crucial to study and to understand these regions. 3D printing is a technique often employed to spatially control the distribution of the biomaterials of interest, but it is difficult to print both mechanically robust (high modulus and toughness) and biocompatible (low modulus) in a single structure due to fast diffusion of mobile species within the cell-seeded hydrogels, which can result in cell death. Also due to the fast diffusion and nonequilibrium swelling conditions of low solids content hydrogels, it is challenging to form the high-fidelity structures required to mimic tissues due to diffusion and swelling during printing. Here we present a predictive transport and swelling model to characterize and ultimately compensate for these effects during printing. This model is then validated experimentally by photo-patterning spatially distinct hydrogel elastic moduli using a single photo-tunable poly(ethylene glycol) (PEG) pre- polymer or precursor solution via a sequential process of repeated precursor in-diffusion and patterned light exposures.