Influence of degree of substitution and folic acid coinitiator on pullulan-HEMA hydrogel properties crosslinked under visible-light initiating system

Hydroxyethyl methacrylate-derivative pullulan (pullulan-HEMA) was synthesized by activation of HEMA followed by catalyzed reaction for adjusting the degree of substitution (DS) of copolymer. Pullulan-HEMA was photocrosslinked using new three-components photoinitiating system composed of carboxylated camphorquinone-folic acid-iodonium salt under visible light. Folic acid was employed as new coinitiator for improving the entire hydrogel properties and avoiding harms of traditional used tertiary amine coinitiators. Pullulan-HEMA hydrogels were characterized by swelling, crosslinking density, and degree of conversion. It was observed that the increase of crosslinking density, T-g, degree of conversion are owing to increasing the DS of copolymer. However, water uptake of hydrogel decreased with increasing the DS value and folic acid concentrations, owing to increasing the crosslinking densities of hydrogels. Also, increasing DS of copolymer and folic acid improved sharply hydrogel surface morphology and prolonged the required time for enzymatic degradation. Notably, the alteration in DS of copolymer converted the in vitro release profile of dexamethasone from rapid and big burst release into sustained and low release behavior. Meanwhile, we could obtain progressive and tunable storage modulus ranged ca. 2.0-10 KPa when DS of copolymer was altered from 0.025 to 0.086, showing that pullulan-HEMA hydrogels are promising biomaterial candidate for biomedical applications. (C) 2018 Elsevier B.V. All rights reserved.