Systematic Evaluation of the Mesh Size of Poly(ethylene glycol)-based Hydrogels for Biomedical Applications

Poly(ethylene glycol) (PEG) hydrogels are one of the most widely utilized biomaterial systems, thanks to their intrinsic resistance to protein adsorption and the ability to be covalently linked to multiple functional moieties. This opens a wide range of design options for the synthesis of substrates with tunable chemistry and bioactivity. Moreover, the hydrogel mesh size can be finely controlled to regulate the molecular trafficking within the polymer matrix. The primary objective of this work was to explore the mesh size of poly(ethylene glycol) diacrylate (PEGDA)-based hydrogels obtained by photo- crosslinking. Aqueous solutions differing for polymer concentration and type of photoinitiator were crosslinked by ultraviolet (UV) expo- sure for different time lengths. Free swelling and uniaxial compression measurements were performed to evaluate the hydrogel mesh size, based on classical theoretical models of swelling and rubber elasticity. The calculated values of mesh size were then experimentally validated by protein diffusion studies. Further aim of this work was to assess the gradual increase of the mesh size resulting from hydrolytic degradation, upon incubation at 37°C for 10 weeks. The experimental results showed that, for the hydrogel formulations tested, the mesh size could be reliably estimated by both swelling and mechanical measurements. Remarkably, the evaluation of the mesh size following hydrolysis al- lowed detection of significant differences in the degradation rate of the samples, while providing pivotal information on the dynamic change of their diffusive properties. Such a systematic evaluation of the mesh size allows the careful design of PEG-based hydrogels for medium to long- term biomedical applications