Heterocyclic methacrylates for clinical applications-further studies of water sorption

The room temperature polymerizing system comprising poly(ethyl methacrylate)-tetra hydrofurfuryl methacrylate (PEM/THFMA) has potential in orthopaedic and dental applications, and earlier work has shown it to have unusual water absorption characteristics. This aspect has been studied in further detail, by studying the water absorption behaviour from some biological solutions, and the effect of the addition of an antibiotic (gentamicin). For comparison purposes, a parallel system whereby tetrahydrofuryl methacrylate was replaced by hydroxyethyl methacrylate (PEM/HEMA), was studied. In the case of PEM/THFMA, water uptake was substantially reduced when absorption was carried out from solutions (from about 30% in water to about 1.5% in solutions of higher concentrations), and the corresponding diffusion coefficient increased (by a factor of several hundred). The addition of gentamicin increased uptake, but the extent of increase also decreased in solutions. It was concluded that uptake was related to the osmolarity of the external solution, and also on the presence of osmotic sites within the polymer; hence the uptake process appears to be governed by chemical potential considerations. At the higher uptakes, there was evidence of water clusters. In marked contrast, the uptake by the PEM/HEMA system was independent of the osmolarity of the external solutions, presumably due to the hydrophilic nature of HEMA.