Fabrication of PEG–carboxymethylcellulose hydrogel by thiol-norbornene photo-click chemistry

Both poly(ethylene glycol) (PEG) and carboxymethylcellulose (CMC) are biocompatible polymers, which have been widely utilized in biomedical fields. In this study, we demonstrated the fabrication of pH-sensitive PEG–CMC hydrogels based on thiol-norbornene photo-click reaction and characterized their properties, such as swelling ratio, stiffness, degradation, and protein drug release. For the hydrogel fabrication, tetra-arm PEG and CMC were functionalized with norbornene groups and thiol groups, respectively. The hydrogels fabricated with varying concentration (0–3%) of CMCSH and a fixed concentration (4%) of PEG4NB by orthogonal step-growth photopolymerization showed high gel fractions (∼0.85). The presence of CMCSH in hydrogel did not affected gel point (∼4 s) but significantly prolonged completion time of gelation. Swelling ratios of PEG–CMC increased from ∼32 to ∼60 and the shear elastic modulus decreased from ∼3000 to ∼600 Pa with an increase of CMCSH content (0–3%). PEG–CMC hydrogel containing more CMCSH not only underwent slower hydrolytic bulk degradation but also showed a slower BSA release in acidic condition. These results indicate thiol-norbornene PEG–CMC hydrogel has potential as pH-sensitive protein drug carrier.