Redox and pH responsive hydrogels were synthesized, which can serve as matrices for smart drug delivery systems exploiting the redox and pH gradients in the human body. Water soluble thiolated poly(aspartic acid), a biocompatible synthetic polymer, enables us to crosslink in water with a non-cleavable cross-linker, poly(ethylene glycol) diglycidyl ether. The permanent cross-linker establishes stable polymer hydrogels regardless of the redox environment, thus the gels swell but do not dissolve upon redox stimuli. The reversible response upon redox stimulus was induced by thiol-disulphide transformation inside the hydrogel. The degree of swelling and the stiffness of the macroscopic hydrogels were controlled by their chemical composition including thiol content and cross-linking ratio as well as the redox state of the hydrogels. The degree of swelling of the hydrogels showed strong pH dependence due to the polyelectrolyte nature of the polymer network. Release of a macromolecular model drug was considerably faster in reducing than in oxidising environment, which indicates the potential use of the synthesized hydrogels as redox responsive drug delivery systems. Nanogels were prepared in water-in-oil emulsion and displayed redox-responsive properties. The hydrodynamic diameter of the nanogels strongly increased upon the cleavage of the disulphide linkages in reducing solution without the disruption of the gels.
Several types of promising cell-based therapies for tissue regeneration have been developing worldwide. However, for successful therapeutical application of cells in this field, appropriate scaffolds are also required. Recently, the research for suitable scaffolds has been focusing on polymer hydrogels due to their similarity to the extracellular matrix. The main limitation regarding amino acid-based hydrogels is their difficult and expensive preparation, which can be avoided by using poly(aspartamide) (PASP)-based hydrogels. PASP-based materials can be chemically modified with various bioactive molecules for the final application purpose. In this study, dopamine containing PASP-based scaffolds is investigated, since dopamine influences several cell biological processes, such as adhesion, migration, proliferation, and differentiation, according to the literature. Periodontal ligament cells (PDLCs) of neuroectodermal origin and SH-SY5Y neuroblastoma cell line were used for the in vitro experiments. The chemical structure of the polymers and hydrogels was proved by 1H-NMR and FTIR spectroscopy. Scanning electron microscopical (SEM) images confirmed the suitable pore size range of the hydrogels for cell migration. Cell viability assay was carried out according to a standardized protocol using the WST-1 reagent. To visualize three-dimensional cell distribution in the hydrogel matrix, two-photon microscopy was used. According to our results, dopamine containing PASP gels can facilitate vertical cell penetration from the top of the hydrogel in the depth of around 4 cell layers (~150 μm). To quantify these observations, a detailed image analysis process was developed and firstly introduced in this paper.
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