Cellular interactions with hydrogels

Abstract

An efficient means of evaluating potential biomaterials is to use the in vitro fibroblast cell culture model. However, the chemistry which influences cell adhesion on polymer substrates is poorly understood. The work in this thesis aims to rationalise several theories of current opinion and introduce new chemical techniques that may predict cellular behaviour. The keratoprosthesis is a typical example of the need to be able to manipulate cell adhesion of materials since both adhesive and non adhesive sections are needed for proper integration and optical function. Calcein AM/ethidium homodimer-1 and DAPI assays were carried out using 3T3 and EKl.BR cells. Poly(HEMA) was found to be the most cell adhesive hydrogel tested. The reactivity of monomers and the resulting sequence distribution were found to affect surface properties and this may explain the poor levels of cell adhesion seen on NVP/MMA copolymers. Surface free energy is shown to be dependent on the polar and non polar groups present along the backbone chain of the polymers. Dehydrated and hydrated contact angle measurements show the effect of rotation of surface groups around the backbone chain. This effect is most apparent on hydrogels containing methacrylic acid. Dynamic contact angle measurements confirm sequence distribution irregularities and demonstrate the mobility of surface groups. Incorporation of NVI or DEAEMA into the hydrogels does not affect the mobility of the surface groups despite their bulkiness. Foetal calf serum was used for the first time as a test solution in an attempt to mimic a biological environment during surface experiments. A Vroman effect may be present, and may involve different surface proteins for each material tested. This interdisciplinary study combines surface characterisation and biological testing to further the knowledge of the biomaterial/host interface. Surface chemistry techniques appear to be insufficiently sensitive to predict cellular behaviour. The degree of ionisation of hydrogels containing ionic groups depends on the nature of the functional groups as well as the concentration and this is an important parameter to consider when comparing charged materials.