Accelerated electrophoretic loading of proteins for hydrogel wound dressings : uptake, release and biocompatibility testing

Abstract

Rapid and efficient loading of hydrogels with therapeutic proteins for topical delivery for wound healing is required without compromising the biological activity of the protein or biocompatibility of the hydrogel. From studies of polyacrylamide gels crosslinked with bisacrylamide (either chemically or by γ-irradiation) the electrophoretic loading of the model protein, cytochrome c, is ~2000 times more efficient than sorption from solution. Because of temperature rises of up to 30°C, the current must be restricted to 8 mA or less. UV-Vis spectra of reduced cytochrome c before and after loading and release show that the bioactivity of the protein was maintained after release. The protein loading properties are independent of the crosslink density but the desorption kinetics depend on the mesh size particularly for chemically crosslinked gels. The mechanism of protein release from the hydrogel is anomalous diffusion (ie. the process was non-Fickian). The biocompatibility of polyacrylamide hydrogels was assessed by a three- dimensional de-epidermised dermis-human skin equivalent (DED-HSE) model and a wounded DED-HSE model that is inherently sensitive to cytotoxic and apoptotic agents as assessed by histology of the exposed HSE and immuno-chemical assay. The gels are found to produce some thinning of the artificial epidermis but neither detachment from the membrane nor inhibition of regrowth from a wound bed. Together, these results highlight the potential use of loading therapeutic protein into hydrogels by a rapid electrophoretic method and the use of the DED-HSE and, in particular, the wounded DED-HSE models for testing biocompatibility of hydrogels.