**6.2 Scaffolds with controlled designed porosity**

As exposed previously, EBM technology enables one-step manufacturing of prostheses that combine solid and porous zones (scaffolds). By means of 3D CAD software, these scaffolds can be designed with the desired pore size, morphology, well-interconnected porosity and gradual transition from solid (body implant) to porous (scaffold), as shown on Figure 24. Designers can control the implant design and have freedom in the design of scaffolds (multiple geometrical solutions) for different pathologies. Only AM technologies are able to manufacture this kind of 3D geometries. For the time being, implants are coated with additional post-processes as plasma spray, microspheres sintering, etc. In contrast with EBM

Additive Manufacturing Solutions for Improved Medical Implants 171

different products in the market. They manufacture acetabular cups with different 3D scaffolds which offer better response in the human body. These products have obtained the

Fig. 25. Acetabular cup implants made on EBM by Italian companies: Cotile Fixa Ti-Por® by Adler Ortho® (left & middle) and DELTA-TT® Cup by Limacorporate (right) are already

EBM technology can also be used for the production of small/medium series of implants with a competitive price, since it offers an interesting alternative to other manufacturing processes where previous investment in tooling is necessary. A variety of industrial sectors use tooling for manufacturing of large series (millions of units) where the cost of the tooling is included in the final price of each produced part. The larger the production, the smaller the cost fraction included in each part. This is not economically viable in the case of small-medium series, since the cost fraction derived from tooling increases as the number of parts decreases. The case of a

Fig. 26. Comparison of the cost per part using manufacturing processes with tooling and

**6.4 Production of small/medium series of value-added biomedical products** 

customized implant is the low end of small series production (Figure 26).

CE Mark and are being implanted in humans (Figure 25).

available on the market.

AM technologies.

technology, these coatings are not able to produce regular or controlled scaffolds and provide less freedom in design (Ratner, 2004).

In bimetallic implants, there is a substantial risk of galvanic corrosion generated when materials with different electronegativity are placed in the same solution (Ratner, 2004), (Pedeferri, 2007). Conventionally made implants are usually coated with different methods and materials (plasma-sprayed titanium, Ti wire mesh, porous coatings made of CoCr or Ti, etc) for creating rough surfaces for encouraging bone ingrowth and proper fixation. With these conventional methods different metals might be combined and risk of galvanic corrosion may appear. In EBM, there isn't such a risk, due to the fact that part and scaffold are manufactured in the same material in one-step process (Figures 1 and 24).

Porous regions in contact with the bone tissue promote osseointegration (direct structural and functional connection between living bone and the surface of a load-bearing artificial implant), creating better fixation between the prosthesis and the bone. Due to the fact that scaffolds provide void space for bone ingrowth (Figure 14), this bone ingrowth will enhance the fixation of the implant. Scaffolds also contribute to transferring loads between the implant and the bone, avoiding the previously mentioned effect of stress shielding.

Fig. 24. Porous cranial implant (Courtesy of Arcam), customized acetabular cup (Courtesy of Arcam) and hip stem (FABIO Project) (Delgado, 2010).

EBM technology enables manufacturing of implants with different kind of scaffolds. These scaffolds can be placed in different regions of the same implant and each scaffold could have different features (pore size, morphology, etc) if the application requires. In addition, it is possible to manufacture totally porous implant (Figure 24).

Summarizing, EBM enables the manufacturing of implants with scaffolds, designed by means of CAD 3D tools (controlled porosity), which enhances the development of a new typology of high added value implants that are designed and manufactured according to the needs of the patient and not the other way around. This is possible because the EBM process doesn't have constraints imposed by traditional manufacturing processes. So as to illustrate above mentioned discussion, in the next paragraphs several kind of applications and high added value implants are going to be presented.
