Synthesis and characterization of biodegradable macroporous cryogels crosslinked by chitosan oligosaccharide-graft-acrylic acid

Abstract

Biodegradable macroporous hydrogels were prepared using a biodegradable crosslinker based on chitosan derivatives. The chitosan crosslinker was synthesized through the amidating reaction of amino groups in the chitosan oligosaccharide (CSO) chains and carboxyl groups in acrylic acid (AA) under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydro-chloride (EDC) and N-hydroxysuccinimide (NHS). The amidating reaction is able to provide polymerizable carbon–carbon double bonds for CSO. The chemical structure of the resulting compound chitosan oligosaccharide-graft-acrylic acid (CSO-g-AA) was characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The content of double bonds was measured by titration analysis. The measurement showed a grafting ratio of AA on CSO of about 3.5% (on average two acryoyl groups per CSO-g-AA chain) when the applied molar ratio of AA to CSO was 1.0. Polyacrylamide (PAM) cryogels were synthesized by the free radical polymerization of acrylamide using a modified freezing polymerization method crosslinked by CSO-g-AA. The obtained cryogels were macroporous hydrogels which could be degraded into solutions of linear polymer chains when treated with appropriate enzymes. Then we used snailase as a model enzyme to study the biodegradation process. The degradation was monitored by morphological studies using a confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM), mechanical strength, and swelling ratio. The duration of the degradation process was adjustable from one month to two months when using different concentrations of snailase solutions.