Abstract/Summary

Physically crosslinked cryogels can be prepared using linear polyethyleneimine (L-PEI) and a freeze-thawing technique. L-PEI was synthesized by hydrolysis of poly(2-ethyl-2-oxazoline) under acidic conditions. Dissolution of L-PEI in deionized water was achieved at 80 oC and resulted in a transparent solution, leading to an opaque gel forming upon freezing and subsequent thawing. The cryogels exhibited reversibility and after heating at 80 oC formed a clear solution due to the melting of the crystalline domains of L-PEI. The effects of different cooling temperatures and the use of various solvent compositions on L-PEI gelation were also studied. L-PEI cryogels were produced by freezing aqueous solutions to various temperatures (-196, -80, -30, and 0 °C) for 3 h and subsequent thawing at 25°C for 24 h. Gel rigidity correlated with the freezing temperature and was strongest when cooled to -196 oC, consistent with determinations of the degree of crystallinity in the gels, the enthalpy of fusion and rheological behaviour. The effect of solvent mixtures on the crystallinity and rheological properties of L-PEI cryogels was also investigated. Water/ethanol mixtures containing a higher proportion of ethanol significantly reduced the strength, viscosity and degree of crystallinity of the L-PEI cryogels. Thus, by controlling the freezing temperature or modifying the solvent, L-PEI cryogels can be designed with desired mechanical properties for applications ranging from cell immobilisation and tissue culture scaffolds to drug delivery systems or antimicrobial wound dressings.