Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 174

As noted earlier, prior to implantation in the physiological environment, the surface of most polymers is normally covered with physically adsorbed water molecules. In comparison, most metals and ceramics have a surface composed of OH groups attached to the outermost metal atoms, on top of which are physically adsorbed H₂O molecules. The physiological fluid in vivo, on the other hand, can be approximated as an aqueous medium of homeostatic temperature 37.4 °C and pH 7.4, which contains a variety of ions, small molecules such as amino acids, macromolecules such as proteins, and substances released by cells. Upon implantation, the surface of a biomaterial acquires a positive or negative charge due to adsorption of ions or molecules from the aqueous medium or dissociation of certain surface functional groups, depending on the surface chemistry of the biomaterial.