Toward Backbone-Degradable Hydrogels with Enhanced Mechanical Performances via Step-Growth Polymerization

Hydrogels, polymer networks with water, have been widely used in biomedical applications including drug delivery, wound healing and tissue engineering due to their similarity with our body. However, conventional hydrogels have insufficient mechanical properties, which limit their use in physiological mechanical environment. To overcome this problems, various studies have been done to improve mechanical properties of hydrogels for recent 15-20 years. Nevertheless, many tough hydrogels are synthesized with chain-growth polymerization, which contain nondegradable polymer backbonbes. For temporary biomedical applications such as drug delivery or tissue engineering, backbone degradability is particularly desirable after its usage.
In this study, we developed a degradable network with enhanced mechanical properties via step-growth polymerization. We incorporated hydrolyzable ester bond in polymer backbone through thiol-ene michael addition for degradability. In order to improve mechanical properties, we induced polymer entanglement with low cross-linker concentration and high monomer concentration in addition to reversible physical bonding for energy dissipation and recovery. In the dry state, the resulting gel exhibited an elastic modulus of up to 1.8MPa, elongation of up to 10 times its initial length and hysteresis ratio of 60%. In addition, the loading-unloading curve for successive cycles nearly overlapped, indicating repeated energy dissipation and recovery. The gel also degraded under alkaline aqueous conditions, which demonstrates its potential for hydrolytic degradation.

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