**5. Biological testing and validation**

In addition to good mechanical behaviour, material produced by EBM has good biological response as well. Thomsen et al (Thomsen, 2009) have performed a study of surface characterization and early response of porous EBM material in rabbits. According to this

<sup>1</sup> Data for EBM porous Ti64 with pore size of 504 μm 2 Data for Ti foam

<sup>3</sup> Data for tantalum foam

<sup>4</sup> Estimated value upon the results of samples with smaller and bigger pore size

Additive Manufacturing Solutions for Improved Medical Implants 161

study the as-produced EBM Ti6Al4V implants had increased surface roughness but similar surface chemical composition compared with machined, wrought Ti6Al4V implants. Also, the general tissue response was similar with a high degree of bone-to-implant contact for all implant types. The results show that the surface properties of EBM Ti6Al4V display biological short-term behavior in bone equal to that of conventional wrought titanium alloy. Furthermore, the bone ingrowth of EBM scaffolds in rabbits has been evaluated as well (Petrovic, 2011). For evaluation of bone ingrowth, EBM samples were compared to the samples provided by two medical device manufacturers, BIO-VAC and Eckermann. Five samples of each type were implanted in the femur of rabbits (Figure 14b). The control period was 8 weeks. The results show that after 8 weeks between 64 and 86% of void space was filled by the bone tissue. In addition, no adverse effect (infection, inflammation, rejection,

As explained in Supply Chain section, AM technologies manufacture directly from digital information of the part (digital files with 3D geometry) and do not need any kind of auxiliary tooling during the manufacturing process. Normally, the use of tooling (moulds, machining tools, etc) makes crucial influence on the product geometry, since desirable

These manufacturing constraints are not present in AM processes. Using AM processes, designers are not limited or conditioned by conventional manufacturing constraints and can focus only on the optimum design of the product according to its application. AM technologies permit greater freedom in product design, enabling the manufacturing of much more complex geometries and in many cases, geometries that are impossible to manufacture

As a matter of fact, EBM has few manufacturing constraints, in terms of producing complex geometries and scaffolds structures and also offers the highest production speed (AIMME, 2009). Its high productivity makes economically viable the fabrication of high added value implants. Although it must be said that due to high processing temperature in EBM process, unfused powder is sintered around the part or scaffold. In certain geometrical features the cleaning process may be difficult, especially in large scaffolds with very small pore size. The main advantages of using EBM as a Manufacturing technology for implants consist in: Full customization. Implant geometry can be customized to the anatomy of the patient and to its specific injury or pathology and fabricated by EBM, with its inherent benefits. Controlled and designed porosity. The inclusion of porous regions on the surface of the

For the time being, three titanium (Ti64, Ti64 ELI and Ti grade 2) and one cobalt chromium (CoCr ASTM F75) alloys are being commercialized by the EBM technology provider and widely used for medical implants. There is a big number of case studies of customized implants that have been implanted in human body. There are also standard implants with added value certified for sale in EU and worldwide. In this section, the authors demonstrate

implant improves the bone osteo-integration in the patient body.

the advantages of AM through different types of application, such as:

etc.) was noticed in animals submitted to this study.

product features cannot be produced.

with another fabrication method.

**6. Applications** 

Fig. 14. Results of bone ingrowth testing of porous Ti64 in New Zealand rabbits (Courtesy of Instituto de Biomecánica de Valencia): a) excised sample for pull-out test; b) CT image of EBM sample; micro CT reconstruction of EBM (c) and conventional (d) Ti64 sample.

study the as-produced EBM Ti6Al4V implants had increased surface roughness but similar surface chemical composition compared with machined, wrought Ti6Al4V implants. Also, the general tissue response was similar with a high degree of bone-to-implant contact for all implant types. The results show that the surface properties of EBM Ti6Al4V display biological short-term behavior in bone equal to that of conventional wrought titanium alloy.

Furthermore, the bone ingrowth of EBM scaffolds in rabbits has been evaluated as well (Petrovic, 2011). For evaluation of bone ingrowth, EBM samples were compared to the samples provided by two medical device manufacturers, BIO-VAC and Eckermann. Five samples of each type were implanted in the femur of rabbits (Figure 14b). The control period was 8 weeks. The results show that after 8 weeks between 64 and 86% of void space was filled by the bone tissue. In addition, no adverse effect (infection, inflammation, rejection, etc.) was noticed in animals submitted to this study.
