UC San Diego

Degradable polymers and hydrogels are promising classes of soft materials that have sparked the interest of the research community for many years due to their unique properties.

Firstly, we investigate the viscoelastic properties of hydrogels through stress relaxation experiments to gain a better understanding of the force-dependent dynamics of these materials with the aspiration of expanding their application envelope within the biomedical field and beyond.

We experimentally studied the viscoelastic behavior of 4 different types of hydrogels: covalently crosslinked polyacrylamide (PAAm), covalently crosslinked PAAm network immersed in a viscous alginate solution, ionically crosslinked alginate along with crosslinked PAAm-alginate double network.

Through our investigations, we demonstrate that we can tailor the viscoelasticity of a covalently bonded PAAm network by tuning the viscosity of the solution in the gel. Moreover, based on the stress relaxation test of ionically crosslinked alginate gel and the double network gel, we have revealed the quantitative correlation between the ionic bond dissociation and force-dependent viscoelastic behavior of gels containing ionic crosslinks.

Secondly, we conducted a systematic investigation on stress-assisted erosion of the photocurable and degradable elastomer poly (glycerol sebacate) acrylate (PGSA). Without external stress, we confirmed that the elastomer undergoes surface erosion in an aqueous environment.

Upon the application of mechanical stress, our results revealed that the surface erosion rate was dramatically accelerated. By studying the stress corrosion cracking (SCC) phenomena, we demonstrated that the crack growth speed depends on the applied load and is significantly faster than the surface erosion rate of the elastomer.

We have further shown that with decreasing the crosslink density of the elastomer, the crack growth speed during SCC can be slowed down due to the increased viscoelasticity of the material.

With these reported discoveries, we hope to provide the scientific community with multiple methodologies to develop advanced polymers with tunable mechanical properties while highlighting the importance of time-dependent behavior and how it is correlated to microscopic mechanisms that take place within the polymer network including ionic debonding in hydrogels and the ester bond dissociation in PGSA.