individually designed implants can be performed in different ways. A production process as described above is possible, based on laser melting/sintering techniques from individual computer data (Rechtenwald et al. 2004; Schmidt et al. 2007).

PEEK is a fine powder and commercially available. Materials with low melting viscosity and a homogenous distribution of particle size are best suited for the laser sintering process. The average particle size varies between 50 and 150 mm with irregular, edged particles. The irregular particle size makes is necessary to sieve the material before laser sintering as layers of 100–150 mm seem to be ideal for the layer-by-layer sintering technique.

To improve the biological and physical properties of the material, other allogenic and xenogenic materials can be added. Addition of nano-sized carbon black improves the flow characteristics of PEEK for modeling the implant. Organic and inorganic biological materials can be added to improve the biological response of tissues on nondegradable polymers as ­in-vivo application of PEEK results in an ­encapsulation of the implant with fibrous tissues, isolating the material from the surrounding bone (Balani et al. 2007). It has been shown that addition of bioactive ceramics such as Bioglass and sintered hydroxylapatite enhances osteoblast proliferation. In-vivo experiments with biologically altered PEEK basis material resulted in bony ingrowths into the implants based on a bonelike apatite layer on the surface of the implant (Rodil et al. 2005; von Wilmowsky et al. 2008).

PEEK combines the excellent manufacturing properties of SLM-titanium implants with the advantages of an outstanding material with chemical and physical properties with a close resemblance to bone. The general problem of PEEK materials is fibrous encapsulation. As promising studies have shown, this might be overcome in the near future. Therefore, laser-sintered PEEK implants appear to be ideal as bone substitutes for various indications.

15.3.3  Outlook

Based on the experience with complex three-dimensional data sets, the development of implants with completely new features is close at hand. The features are:

•Well-defined porosity for improved bone ingrowth

•Adapted stiffness and elasticity close to that of bone

•Maximum reduction of allogenic material

The realization of these features requires the fol-

lowing work items:

•Dimensional accuracy £0.1 mm

•Fabrication of thin lattice structures with a detail resolution of 150–200 mm, made of titanium or polymers

•Smooth transfer of biomechanical loads from the natural bone into the metallic/polymeric implant based on Finite Element Method (FEM) implant design

•Fabrication of graded surface porosity

•Fabrication of surfaces with defined roughness (RZ = 15 mm up to 100 mm)

•Implant manufacture for all kinds of bone defects

The SLM technique, based on titanium and PEEK polymeric materials, is available for clinical use today. However, as described before, the technical process of transforming a virtual three-dimensional data set into real existing implants is challenging. The process chain demands a close cooperation between IT engineers, the manufacturing team and surgeons to guarantee a successful reconstruction. Today, this ideal setting is only available in a few medical centers.

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