Adjustment of physical properties and pH-responsive behavior of cryogels based on two- and three-armed poly(2-oxazoline) cross-linkers with functional side chains

In this study, we demonstrate the synthesis of an array of cryogels utilizing functional poly(2-oxazoline) (POx) cross-linkers. These differ in terms of number and type of polymerizable end groups, as well as in the functional groups present in the side chains (ethyl, active amine or ester groups). All of the cryogels were produced solely based on the respective cross-linkers, as well as by the addition of N,N-dimethylacrylamide (DMAAm) as comonomer. The chemical structure of the gels was verified using solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Scanning electron microscopy (SEM) and confocal laser-scanning microscopy (CLSM) were employed to examine the porous structure of the dried and hydrated gels, respectively. Thermogravimetric analysis (TGA) demonstrated that all gels would withstand an autoclaving process, which is important for potential cell assays. Mechanical and swelling properties exhibited a pronounced dependency on the cross-linker used. The incorporation of DMAAm as a comonomer resulted in the ability to adjust the stiffness of the resulting cryogels. As the storage modulus were ranging from 200 and 4,000 Pa the obtained cryogels can be used as models to mimic soft tissue properties such as those found in the breast, lung, pancreas, kidney or brain. The pH-dependent swelling tests reveal a stimuli responsive behavior of selected gels, with the bifunctional amine-containing cryogels displaying the most pronounced response.