Modelling of Biomaterials: Molecular Recognition at the Surfaces of Bioactive Glasses

Among biomaterials, the Hench Bioglass® 45S5 of 46.1% SiO2, 26.9% CaO, 24.4% Na2O and 2.6% P2O5 molar composition is of great interest in medical applications since, in the presence of body fluids and depending upon the rate of ion release and re-sorption, it creates chemical gradients which promote the formation of a layer of biologically active bone-like hydroxyapatite at the implantation interface. Osteoblasts can preferentially proliferate on the hydoxyapatite layer, and differentiate to form new bone that binds strongly to the implant surface. Hydroxyapatite [HA, Ca10(PO4)6(OH)2] is the main constituent of the mineral phase in mammalian bones and teeth enamel. For this reason, HA is widely applied as an orthopaedic and dental biomaterial, both per se and together with other classes of materials, in the form of coating for metal alloys, in composites with polymers and so on. In this work quantum mechanical simulations carried out at B3LYP level within periodic boundary conditions as encoded in the CRYSTAL06 code to model bulk HA [1] and its main surfaces [2] as well as the Hench Bioglass® will be reported. For bioglass, structure, electronic and vibrational features of the bulk will be discussed [3]. For HA, structure and vibrational features of the bulk as well as the electrostatic features of the most important crystallographic surfaces will be discussed. For these latter, interaction with H2O [4] and with five aminoacids (Gly, Ser, Lys, Gln and Glu) will be described in terms of most stable adsorbed structures and interaction energies. For the case of glycine [5] a detailed study of the role of co-adsorbed water will be addressed. The above results have allowed us to model the process of conformational stabilization of a short poly-glycine (12 residues) induced by the adsorption on the HA (001) surface as a function of mutations in the chain. This study is believed to be the first attempt to model by an ab-initio approach the interaction of biological relevant molecules with HA being the most important interface at the surface of bioglasses. [1] Corno M., Busco C., Civalleri B., Ugliengo P., PhysChemChemPhys, 2006, 8, 2464. [2] Corno M., Orlando R., Civalleri B., Ugliengo P., Eur. J. Mineral., 2007, 19, 757. [3] Corno M., Pedone A., Dovesi R., Ugliengo P., Chem. Mater., 2008, 20, 5610. [4] Corno M., Busco C., Bolis V., Tosoni S., Ugliengo P., Langmuir, 2009, 25, 2188. [5] Rimola A., Corno M., Zicovich-Wilson C.M., Ugliengo P., J. Am. Chem. Soc., 2008, 130, 16181.