title: Mechanism for converting Al2O3-containing borate glass to hydroxyapatite in aqueous phosphate solution.
abstract: The effect of replacing varying amounts (0-2.5 mol.%) of B2O3 with Al2O3 in a borate glass on (1) the conversion of the glass to HA in an aqueous phosphate solution and (2) the compressive strength of the as-formed HA product was investigated. Samples of each glass (10 x 10 x 8 mm) were placed in 0.25 M K2HPO4 solution at 60 degrees C, and the conversion kinetics to HA were determined from the weight loss of the glass and the pH of the solution. The structure and composition of the solid reaction products were characterized using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. While the conversion rate of the glass to HA decreased considerably with increasing Al2O3 content, the microstructure of the HA product became denser and the compressive strength of the HA product increased. The addition of SiO2 to the Al2O3-containing borate glass reversed the deterioration of the conversion rate, and produced a further improvement in the strength of the HA product. The compressive strength of the HA formed from the borate glass with 2.5 mol.% Al2O3 and 5 mol.% SiO2 was 11.1 +/- 0.2 MPa, which is equal to the highest strengths reported for trabecular bone. The results indicated that simultaneous additions of Al2O3 and SiO2 could be used to control the bioactivity of the borate glass and to enhance the mechanical strength of the HA product. Furthermore, the HA product formed from the glass containing both SiO2 and Al2O3 could be applied to bone repair.
authors.affiliation: Institute of Bioengineering and Information Technology Materials, Center for Advanced Materials & Nano-Biomedicine, Tongji University, Shanghai 200092, China.
authors.forename: Di
authors.initials: D
authors.lastname: Zhao
authors.forename: Wenhai
authors.initials: W
authors.lastname: Huang
authors.forename: Mohamed N
authors.initials: MN
authors.lastname: Rahaman
authors.forename: Delbert E
authors.initials: DE
authors.lastname: Day
authors.forename: Deping
authors.initials: D
authors.lastname: Wang
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D001881:Borates / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D010710:Phosphates / Q000737:chemistry*; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D014961:X-Ray Diffraction
chemical_list: D001881:Borates; D010710:Phosphates; D012996:Solutions; D017886:Durapatite; D000537:Aluminum Oxide