Macromolecules, Vol.40, No.21, 7625-7632, 2007
Synthesis and properties of poly[poly(ethylene glycol)-co-cyclic acetal] based hydrogels
The objective of this work is to synthesize and characterize a biomedical hydrogel based on the polyether-acetal, poly [poly(ethylene glycol)-co-cyclic acetal] (PECA). This hydrogel has been designed to possess two significant properties, a hydrolytically degradable cyclic acetal segment and a hydrophilic poly(ethylene glycol) (PEG) segment. The chemical structure of the synthesized PECA was analyzed by H-1 NMR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry, while the weight average molecular weight (M.) was measured by size exclusion chromatography. Results confirmed that PECA with M-w of 5000-44 000 g/mol was synthesized from a cyclic acetal and PEG, whose Mw ranged from 200 to 2000 g/mol. Differential scanning calorimetry confirmed that crystallization temperature and melting temperature increased as the Mw of PEG increased. After diacrylation of both hydroxyl terminal groups of the PECA chain, PECA hydrogels were prepared by cross-linking using redox initiators, ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine, and then characterized. The effects of polymer concentration and initiator concentration for cross-linking upon sol fraction and swelling degree were then investigated. Both sol fraction and swelling degree were found to be highly influenced by polymer concentration, while swelling degree and swelling rate were also influenced by Mw of PEG. Degradation kinetics of cyclic acetal segments were investigated in excessive acidic condition as well as simulated physiological conditions. Degradation rates of PECA in excessive acidic condition were significantly influenced by pH and temperature. Furthermore, the pH of buffer remained constant while the PECA hydrogel lost approximately 30% of its dry weight after 5 months of in vitro incubation. The ease of control over properties such as swelling degree and degradation rate indicates that the newly synthesized hydrogel is a promising material as a matrix for drug delivery and tissue engineering applications.