Although OEG-OPG-OEG triblocks are known for their micellization, which could hamper polymer network formation, reactive OEG-OPG-OEG triblock oligomers could be successfully polymerized into hydrogel networks. The degree of swelling of these hydrogels depends on their molecular weight and on the oligomer concentration used for hydrogel preparation. In combination with the temperature sensitivity of the ABA triblock copolymers, it is assumed that such hydrogels might be beneficial for future medical applications - e.g., removable drug release systems.

Oligo(ethylene glycol)-based hydrogel samples (OEG hydrogels) of varying cross-link densities and degrees of swelling were characterized through dynamic nanoindentation testing. Experiments were performed using a non-standard nanoindentation method which was validated on a standard polystyrene sample. This method maximizes the capability of the instrument to measure the stiffness and damping of highly compliant, viscoelastic materials.Experiments were performed over the frequency range of 1 to 50 Hz, using a 1 mm diameter flat punch indenter. A hydration method was adopted to avoid sample dehydration during testing. Values of storage modulus ‫)'ܧ(‬ ranged from 3.5 to 8.9 MPa for the different OEGhydrogel samples investigated. Samples with higher OEG concentrations showed greater scatter in the modulus measurements and it is attributed to inhomogeneities in these materials.The ‫'ܧ‬ values did not show a strong variation over frequency for any of the samples. Values of loss modulus ‫)''ܧ(‬ were two orders of magnitude lower than the storage modulus, resulting in very low values of loss factor ‫'ܧ/''ܧ(‬ < 0.1). These are characteristics of strong gels, which present negligible viscous properties.

The protein adsorption and immuno-compatibility of hydrogels largely influence the clinical outcome in biomedical application scenarios. In this study photo-crosslinked 2-isocyanate ethyl methacrylate-functionalized oligo(ethylene glycol)-oligo(propylene glycol)-oligo(ethylene glycol) (IEMA-OEG-OPG-OEG-IEMA)-based polymer hydrogel films were explored with respect to endotoxin contaminations, intrinsic immuno-modulatory features, and protein adsorption of human fibronectin as well as serum albumin. Therefore three different hydrogel films were prepared from aqueous solutions of dimethacrylated OEG-OPG-OEG triblock copolymers (M n = 12,700 g mol À1 , 70 mol% OEG content) with varying wt% of the macromonomer (10 to 30%) resulting in polymeric networks, which differ in their crosslinking density and accordingly their physical properties. It could be shown that all three hydrogel film compositions do not cause complement and immune cell activation. The films were protein repellent, but reversible protein diffusion in and out of the hydrogel network, depending on the mesh size of the network, could be observed. In conclusion, the hydrogels can be considered as immuno-compatible, which qualifies them for biomedical applications such as drug release systems.