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Titanium and titanium alloys for medical applications: opportunities and challenges
Feature article: PIM International, Vol.2 No. 2 June 2008, pages 21-30, 4615 words
Abt. Pulvertechnologie WTP, GKSS-Forschungszentrum Geesthacht GmbH, Max-Planck-Straße 1, D-21502 Geesthacht, Germany
Introduction
Titanium parts produced by powder injection moulding are now produced by a number of companies around the world. Yet despite the current level of knowledge and the availability of powders and feedstock, penetration of the medical sector is at an early stage. Dr. Thomas Ebel, from the GKSS Forschungszentrum Geesthacht GmbH, Germany, looks at the opportunities and challenges ahead.
For many years titanium and its alloys have been recognised as ideal materials for use in medical devices and long-term implants thanks to their unique combination of excellent biocompatibility and high strength to density ratio. Surgical instruments, hip implants, parts of artificial heart valves, bone nails and screws and spinal fusion devices are only a few examples that titanium materials are used for. However, even if titanium is most often the optimal choice for a medical application, its actual use is limited due to the relative high costs of the raw material and processing. Manufacturing components with complex geometries from titanium materials requires specialist knowledge. Titanium’s high affinity to oxygen excludes warm processing such as forging or casting and requires significant post-treatment of the surface.
The increasing demand for cost reduction in the public health sector has led to an often unsatisfactory situation with regards to the functionality of medical products, especially long-term implants. Either a cheaper but less biocompatible material is used, which is easier to shape, or the geometry of a part is simplified at the expense of functionality - often at the expense of anatomically important features.
Such a situation could be improved through the use of manufacturing techniques which avoid waste material and simultaneously provide the possibility to shape parts to complex geometries at lower costs. Metal injection moulding (MIM) generally offers these benefits and, thus, could help to overcome such problems.
Further sections of this article include:
- Titanium in medicine
- Why MIM?
- Developments
- MIM of shape memory alloys
- Micro MIM
- Dental implants
- Challenges
- Investments
- Acceptance
- Data
- Missing standards
- Summary
- References
Figures and Tables:Fig. 1 Prototype of anatomically shaped aortic heart valve prosthesis made from TiAl6Nb7 by MIM Fig. 2 Prototype of an implantable bone screw for dens-axis repair, made from TiAl6V4 by MIM Fig. 3 Endoscopical instrument. The three parts marked by a yellow arrow are made by MIM from Ti Grade 4 feedstock Fig. 4 A knife socket weighing 60g Fig. 5 Part of an electric driller used in medicine made by MIM from Ti Grade 4 feedstock Fig. 6 Part of a sleep apnea device made by MIM from Ti Grade 4 feedstock Fig. 7 Housing and catheter fixation of an implantable port system made by MIM from TiAl6V4 ELI feedstock Fig. 8 Main plate of an implantable drug delivery device made by MIM from TiAl6V4 ELI feedstock Fig. 9 Micrographs of the surface region of a MIM manufactured part from TiAl6V4 powder. a) as sintered, b) shot peened. Fig. 10 Port system housings, surface treated by barrel finishing and anodic oxidation Fig. 11 NiTi-specimen produced from NiTi powder by means of micro- MIM Fig. 12 Stirrup of the middle ear as an example for an implant made by micro MIM from Ti-powder Fig. 13 Prototype of a dental implant made by MIM from Ti Grade 1, coated with foam-like highly-porous titanium. Left: fully machined implant. Right: CT-scans of the MIM-produced part, with and without coating Table 1 Typical tensile test properties for three titanium materials |
