**3.1 Implant reconstruction / design**

As mentioned before, AM process can be understood as 3D printing of solid models. There are two different ways to obtain medical models:

 *Designing the model in some 3D modelling software.* Based on the statistic information about patients (age, weight, physical constitution, etc.), implants are designed together with tooling for the surgical operation (Synthes, 2007). This is a commonly used way to make standard implants in different sizes. When implanted, the osseous zone is adjusted so that the implant fits to properly repair the damaged zone. The model can be manufactured by a variety of processes (forging, CNC machining, etc.). However,

Fig. 5. Some of biomedical parts as produced on the machine (osteosynthesis plates

In comparison with other AM processes, EBM has three major advantages very relevant for

*Substantially higher nominal speed* which makes viable a serial production of medical

*Processing under vacuum* - the processed material has very high purity resulting in

*High processing temperature* (for Ti64 around 650ºC) - less thermal stresses and less

Supply chain for medical implants fabricated by AM consists of six steps (Figure 6). Four of them belong to the fabrication process while the others are common to all medical device

As mentioned before, AM process can be understood as 3D printing of solid models. There

 *Designing the model in some 3D modelling software.* Based on the statistic information about patients (age, weight, physical constitution, etc.), implants are designed together with tooling for the surgical operation (Synthes, 2007). This is a commonly used way to make standard implants in different sizes. When implanted, the osseous zone is adjusted so that the implant fits to properly repair the damaged zone. The model can be manufactured by a variety of processes (forging, CNC machining, etc.). However,

manufacturing processes (medical post-treatment and surgical intervention).

Courtesy of CIMA).

medical implants manufacturing:

warpage in processed material.

**3.1 Implant reconstruction / design** 

are two different ways to obtain medical models:

higher properties and better biocompatibility.

implants (Figure 5).

**3. Supply chain flow** 

additive technologies introduce one important advantage: porous surface for better bone ingrowth (Figure 7). This *controlled* porous coating is designed in a specific software (in the case shown on Figure 7, it was Magics® by Materialise) and exported as a model coupled with the solid hip stem.

Fig. 6. Supply chain flow for medical implants.

Fig. 7. Example of femoral hip stem: a) 3D model of hip stem with superficial porous zone, b) hip stem coupled with femur bone (model) and c) Ti64 hip stem coupled with polyacrilic bone replica.

Additive Manufacturing Solutions for Improved Medical Implants 155

Fig. 9. Comparison by light digitalization: a) deviation of real vertebra vs reconstructed STL model, b) deviation of polyacrilic bone replica made on Stereolithography vs reconstructed

After completing the scan-to-part, in Additive Manufacturing the model is sliced virtually and then built layer by layer. This fact allows the fabrication of very complex shapes and forms. In biomedical applications, it allows the fabrication of near net-shape implants

The same solutions of gradual porosity mentioned previously can be applied to customized

The planning of manufacturing process of implants in Additive Manufacturing consists of

 Implant model is *properly oriented on the build platform* for layer-by-layer fabrication in order to optimize surface quality, support structure, build time, build cost, etc. If necessary, the support structure is generated and optimized. As much implants as possible are packed for more efficient fabrication (Figure 10). For the time being this is done manually, but some tools for automatic assessment are being developed for

 *Implant and support structure are sliced for fabrication.* Slices are stored into a sliced file which is uploaded to the machine (Figure 11). The machine uses specific software to interpret the file and to send commands to print layers into a solid part. The same build,

stored in the sliced file, can be build again without any pre-processing.

knowledge assisted part orientation (Petrovic, 2010).

STL model.

implants.

two steps:

customized to the patient's data.

**3.2 Implant pre-processing** 

 *Reconstruction of model upon patients CT images.* For customized implants, the common path is to reconstruct the model via *scan-to-part*: a cloud of points is reconstructed upon CT images and subsequently converted into a 3D model. The model can then be manufactured in chosen technology (Figure 8). As in each process of reverse engineering, there is an error that is introduced during the reconstruction. In the scan-to-part process, the maximum introduced deviation was 1.4 mm - the majority of the model points have deviation comprehended between 0.45 and 0.65 mm (Figure 9, left). On the other hand, the fabrication process reproduces the model with the deviation inferior to 0.15mm in more than 80% of points (Figure 9, right) (AIMME, 2009).

Fig. 8. Example of spinal vertebra: a) real bone, b) reconstructed model and c) polyacrilic bone replica made on Stereolithography.

 *Reconstruction of model upon patients CT images.* For customized implants, the common path is to reconstruct the model via *scan-to-part*: a cloud of points is reconstructed upon CT images and subsequently converted into a 3D model. The model can then be manufactured in chosen technology (Figure 8). As in each process of reverse engineering, there is an error that is introduced during the reconstruction. In the scan-to-part process, the maximum introduced deviation was 1.4 mm - the majority of the model points have deviation comprehended between 0.45 and 0.65 mm (Figure 9, left). On the other hand, the fabrication process reproduces the model with the deviation inferior to 0.15mm in more than 80% of points (Figure 9, right) (AIMME,

Fig. 8. Example of spinal vertebra: a) real bone, b) reconstructed model and c) polyacrilic

2009).

bone replica made on Stereolithography.

Fig. 9. Comparison by light digitalization: a) deviation of real vertebra vs reconstructed STL model, b) deviation of polyacrilic bone replica made on Stereolithography vs reconstructed STL model.

After completing the scan-to-part, in Additive Manufacturing the model is sliced virtually and then built layer by layer. This fact allows the fabrication of very complex shapes and forms. In biomedical applications, it allows the fabrication of near net-shape implants customized to the patient's data.

The same solutions of gradual porosity mentioned previously can be applied to customized implants.
