Functional integration in implants through additive manufacturing technology and smart materials
Presentation held at European Forum on Rapid Prototyping; Rapid Prototyping & Manufacturing, 12.-14. Juni 2012, Paris
Funktionsintegration in Implantaten mittels generativen Fertigungsverfahren und intelligente Werkstoffe
At the current state of the art, endoprostheses are predominantly manufactured by cutting, forming or casting technologies. Another, rather new way of implant manufacturing is the Additive Manufacturing process called Beam Melting, using a Laser or Electron beam. In particular the customized production with no need for any type of tooling, combined with the unique freedom of design spark interest in this technology for implant manufacturing. The use of Beam Melting enables the fabrication of endoprostheses with almost any design of inner and outer geometries. Previous developments and research activities were focussing either on customized, patient specific implant designs with a production batch size of only one piece, or on structured surfaces of specific design for better bone ingrowth and improved stability of the implant-bone bonding. Both approaches have not yet reached a significant breakthrough for Additive Manufacturing as an adopted technology to produce (metal) implants, besides some niche applications, e. g. for individual cranial or jaw plates or some Electron Beam Melting series production of hip cups. This paper focuses on the integration of completely new features and functions into endoprostheses which give various added value opportunities to implants that where unthinkable before. Strategies from tooling applications of Additive Manufacturing were adopted which have proved very successful in giving added value to tools and dies by implementing complex inner cooling channels. The paper describes two innovative strategies to integrate new features and functions into standard implants, e. g. hip stems, by the creation of: - inner design features like functional channels and cavities and - surface and inner structures to integrate additional active components (e. g. shape memory alloys) The inner channels and cavities (inner design features) can fulfil various functions within the implant, e. g. local supply of bio-resorbable filler, prevention and treatment of implant loosening even years after implantation, post-operative medical treatment through a medication depot and supply channels, post-operative drainage of blood and wound oozing through the implant, endoscopic examination of implant-bone interface and surrounding tissue and easier and quicker explantation with less damage to the bone structure through local application of soluble. In non-cemented hip implants, stem loosening is mainly caused by a change in force application and insufficient load transmission between implant and osseous anchor bedding. The target is to achieve a homogeneous force distribution at the implant-bone interface by using shape-memory-alloys. The active components were integrated in hip stems with a new designed surface and inner structures. The results proved that the frictional connection between a stem prosthesis anchored without cement and the femur can be achieved using shape memory alloy elements. So there is a potential to stabilize the prosthesis and increase is useful life.