Cytocompatibility of titanium metal injection molding with various anodic oxidation post-treatments

Structure and Properties of Co-Cr-Mo Alloy Manufactured by Powder Injection Molding Method

Cobalt-chromium-molybdenum alloys samples were obtained by the powder injection molding method (PIM). PIM is dedicated to the mass production of components and can manufacture several grades of dental screws, bolts, stabilizers, or implants. As a skeleton component, ethylene-vinyl acetate (EVA copolymer) with a low temperature of processing and softening point was used. The choice of a low-temperature binder made it necessary to use a coarse ceramic powder as a mechanical support of the green sample during sintering. The injection-molded materials were thermally degraded in N2 or Ar-5%H2 and further sintered in N2-5%H2 or Ar-5%H2 at 1300 or 1350 °C for 30 min. The structure of the obtained samples was characterized by X-ray diffraction and electron microscopy. Mechanical properties, including hardness and three-point bending tests, confirmed that a nitrogen-rich atmosphere significantly increases the bending strength compared to the material manufactured in Ar-5%H2. This is due to the precipitation of numerous fine nitrides and intermetallic phases that strengthen the ductile γ-phase matrix.

Porous Titanium Scaffolds Fabricated by Metal Injection Moulding for Biomedical Applications

Biocompatible titanium scaffolds with up to 40% interconnected porosity were manufactured through the metal injection moulding process and the space holder technique. The mechanical properties of the manufactured scaffold showed a high level of compatibility with those of the cortical human bone. Sintering at 1250 °C produced scaffolds with 36% porosity and more than 90% interconnected pores, a compressive yield stress of 220 MPa and a Young's modulus of 7.80 GPa, all suitable for bone tissue engineering. Increasing the sintering temperature to 1300 °C increased the Young's modulus to 22.0 GPa due to reduced porosity, while reducing the sintering temperature to 1150 °C lowered the yield stress to 120 MPa, indicative of insufficient sintering. Electrochemical studies revealed that samples sintered at 1150 °C have a higher corrosion rate compared with those at a sintering temperature of 1250 °C. Overall, it was concluded that sintering at 1250 °C yielded the most desirable results.

Biocompatibility of Advanced Manufactured Titanium Implants-A Review

Titanium (Ti) and its alloys may be processed via advanced powder manufacturing routes such as additive layer manufacturing (or 3D printing) or metal injection moulding. This field is receiving increased attention from various manufacturing sectors including the medical devices sector. It is possible that advanced manufacturing techniques could replace the machining or casting of metal alloys in the manufacture of devices because of associated advantages that include design flexibility, reduced processing costs, reduced waste, and the opportunity to more easily manufacture complex or custom-shaped implants. The emerging advanced manufacturing approaches of metal injection moulding and additive layer manufacturing are receiving particular attention from the implant fabrication industry because they could overcome some of the difficulties associated with traditional implant fabrication techniques such as titanium casting. Using advanced manufacturing, it is also possible to produce more complex porous structures with improved mechanical performance, potentially matching the modulus of elasticity of local bone. While the economic and engineering potential of advanced manufacturing for the manufacture of musculo-skeletal implants is therefore clear, the impact on the biocompatibility of the materials has been less investigated. In this review, the capabilities of advanced powder manufacturing routes in producing components that are suitable for biomedical implant applications are assessed with emphasis placed on surface finishes and porous structures. Given that biocompatibility and host bone response are critical determinants of clinical performance, published studies of in vitro and in vivo research have been considered carefully. The review concludes with a future outlook on advanced Ti production for biomedical implants using powder metallurgy.

Progress in Titanium Metal Powder Injection Molding

Metal powder injection molding is a shaping technology that has achieved solid scientific underpinnings. It is from this science base that recent progress has occurred in titanium powder injection molding. Much of the progress awaited development of the required particles with specific characteristics of particle size, particle shape, and purity. The production of titanium components by injection molding is stabilized by a good understanding of how each process variable impacts density and impurity level. As summarized here, recent research has isolated the four critical success factors in titanium metal powder injection molding (Ti-MIM) that must be simultaneously satisfied-density, purity, alloying, and microstructure. The critical role of density and impurities, and the inability to remove impurities with sintering, compels attention to starting Ti-MIM with high quality alloy powders. This article addresses the four critical success factors to rationalize Ti-MIM processing conditions to the requirements for demanding applications in aerospace and medical fields. Based on extensive research, a baseline process is identified and reported here with attention to linking mechanical properties to the four critical success factors.