SCANNING AND TRANSMISSION ELECTRON-MICROSCOPY OF POLY 2-HYDROXYETHYL METHACRYLATE-BASED BIOMATERIALS

Hydrogels, especially poly 2-hydroxyethyl methacrylate, or pHEMA, have received increased attention for numerous biomedical applications. We have prepared several pHEMA-based biomaterials suitable as bone subst itutes; alkaline phosphatase, for example, when immobilized in pHEMA i n a copolymerization technique at 4 degrees C retains its biological a ctivity. When pellets of the biomaterial were placed in synthetic body fluids or tissue culture medium containing organic phosphates, numero us calcified nodules formed spontaneously. Osteoblast-like cells harve sted on pHEMA or pHEMA/alkaline phosphatase materials can spread and e stablish direct contacts. However, the hydrophilicity of pHEMA is a re al handicap for preparing scanning and transmission electron microscop ic analyses. We have found that 2-propanol was an excellent dehydratin g preparing for scanning electron microscopy before critical point dry ing. HEMA itself was found to dehydrate the transmission electron micr oscopy blocks because it can copolymerize with the methacrylate-based embedding resin Lowicryl K4M. These 2 preparation techniques have allo wed us to study calcium-phosphate crystal growth and cellular response s in vitro on these hydrogel biomaterials.