Effect of terminal functional groups of silane layers on adhesive strength between biomedical Ti-29Nb-13Ta-4.6Zr alloy and segment polyurethanes

Composite materials that consisted of a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with low Young's modulus and segment polyurethane (SPU) have been fabricated for application in biomedical devices. The effects of different kinds of terminal functional groups and the thickness of the silane layers (SIL) on the adhesive strength between TNTZ and SPU were investigated by means of shear bonding tests. The following silane coupling agents were employed in this study: 3-methacryloxypropyltrimethoxysilane (gamma-MPTS), aminopropyltriethoxysilane CAPS), and 3-mercaptopropyltrimethoxysilane (gamma-MPS). Furthermore, the shear bonding strength of the TNTZ/SIL/SPU interface was also characterized after immersion in water for 30 d. Silane coupling treatment produces a ten-fold increase in the shear bonding strength, independent of the type of terminal functional groups and the thickness of the silane layers. Scanning electron microscopic evaluation of the fracture surfaces of the TNTZ/SIL/SPU composites after the shear bonding tests coupled with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the TNTZ/SIL/SPU composites are partially fractured at the interfaces of the TNTZ/SIL while the rest of the fracture occurs at the interfaces of the SIL/SPU in single sample. The shear bonding strength decreases after immersion in water for 30 d when APS and gamma-MPS are used as the silane coupling agents, because stable chemical bonding is not achieved between the silane layer and SPU, whereas the bonding of the gamma-MPTS composite is not affected by exposure to water. (C) 2012 Elsevier B.V. All rights reserved.