Effect of Texture on Success Rates of Implants

Abstract

The aim of the present study was to study the interface implant-bone by synchrotron radiation and neutron diffraction, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium alloy (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to have good mechanical properties at the interface with the implant. Therefore, we studied the texture of the reconstituted bone crystals at the interface applying two non-destructive diffraction methods, as well as the influence of the coating on crystallinity index. The required high spatial resolution was achieved utilizing high-energy synchrotron radiation on ID15 at ESRF in Grenoble, France, and the second method was done by neutron diffraction, the high-intensity with two-axis diffractometer was used, equipped with variable resolution: D20, at Institut Max von LauePaul Langevin (ILL) in Grenoble, France. In orthopaedic surgery, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance. Bone is a composite material whose components are primarily collagen and HAp. The c-axes of the apatite crystallites and the collagen fibres are preferentially oriented, e.g., in the long bones in the directions of the stresses that the bones need to withstand. HAp crystallizes in the hexagonal system and its unit cell parameters are a=9,4 A and c=6,8 A its space group is P63/m. Bone occurs in two principal structural forms: cortical, or compact bone, which forms a dense matrix, and spongy bone. We use cortical bone in this work. The long-term success of biomedical implants largely depends on the stable fixation of the implant to bones. Composite materials, in which metals have coated with ceramics, have been extensively reported as an alternative to plain materials in favour of a long-term fixation. The development of bioactive ceramic-alloy structures for implants has focused by the idea of combining the bioactivity of ceramics with the mechanical properties of selected metallic alloys. Ti-6Al-4V presents good mechanical proprieties and is biocompatible. HAp has low mechanical strength, but has a very good osteointegration and biocompatibility. The idea is to combine these two materials in order to have mechanical strength and good osteointegration proprieties at the interface. Plasma spraying is the most popular method for coating implant parts with HAp. In order to improve these coatings, it is necessary to investigate the texture and crystallinity evolutions of the bone’s crystal structure, as a function of the distance from the implant-interface.