Chapter 10 Thermoforming processes for knitted-fabric-reinforced thermoplastics: New manufacturing techniques for load-bearing, anisotropic implants

In this chapter the application of specific thermoforming techniques for knitted carbon-fiber-reinforced thermoplastic composite materials to medical implants is described. In the first part of this chapter, the properties of the fiber architecture in knitted-fabric-reinforced composites and their influence on the mechanical properties are outlined in order to provide a basic understanding of the potential of knitted fabrics as reinforcement as well as their medical and engineering applications. Therefore, the influence of fiber orientation distribution, matrix and interphase properties on the mechanical behavior is discussed in detail. In a second part, a new net-shape bulk forming techniques is described in which the coherence of a knitted fabric was used to manufacture a typical load-bearing implant, in this case an osteosynthesis plate, using a single-step technique and, thereby, reinforcing the countersunk holes of the osteosynthesis plate which are the mechanically critical load induction and joining areas. The effect of a knittedfiber architecture on the mechanical properties and the homoelasticity of the plate, is compared to the behavior of a laminated and a stainless steel plate. In a third part, the forming behavior of knitted-fabric-reinforced organo-sheets is described for the application in diaphragm deep drawing. The influence of multiaxial drawability and coherence of knitted fabrics as well as of flow conditions on the structure-properties relations in the deep drawn part are discussed. In general, this chapter should be seen as an introduction in thermoforming techniques for knitted-fabric-reinforced thermoplastics with regard to structure-properties relations and failure characteristics.