Selective laser melting (SLM) is a novel technique being increasingly used for the production of porous structures with a high degree of precision and near net shape. These porous materials are finding their use in the biomedical industry for implants. In this thesis, the effect of post-processing using hot isostatic pressing (HIP) and surface modification techniques, such as chemical etching and sandblasting on the developed microstructure and mechanical properties is studied. Cylindrical porous samples with a diamond unit cell were produced by the vector based approach from Ti6Al4V ELI powder using the SLM process. The samples were tested in the as-processed and post-processed condition for compression and fatigue life. A comparison between the as-processed vector approach and Stereo Lithography (STL) approach was also studied and discussed in detail. The post-processing was found to have a positive influence on the microstructure and mechanical properties of the Ti6Al4V lattice structures. The HIP treatment showed the best post-processing step allowing to relieve residual stress, reduce the process induced porosity and obtain the optimal lamellar (α+β) microstructure. The HIP post-processing resulted in a significant improvement of the fatigue life of the studied porous structures. HIP followed by surface treatment using sandblasting technique was found to be promising for further fatigue life improvement without any reduction in strength as compared to HIP and as-processed conditions. Chemical etching showed improved fatigue life at lower stress levels but decreased strength due to a reduction in relative density. Additionally, the comparison between the vector and STL approach confirmed the importance of process parameter optimization required to improve the as-processed properties. In this study a combination of HIP and sandblasting methods allowed to improve fatigue properties of vector based samples, making them superior to STL as-processed condition. Thus, the application of the studied post-processing techniques can be further applied to other porous metallic structures in order to improve their mechanical performance.

The goal of this master thesis is to design an instrument which is able to insert an implant called a spinal cage, designed by M. Ahmadi, between two vertebrae. The spinal cage is of a new hinged, and spring loaded design, requiring a new insertion instrument, since no existing instruments are able to place the implant. The implant is used in a PLIF (Posterior Lumbar Interbody Fusion) surgery. The goal of this surgery is to relieve patients from their symptoms when suffering from a hernia. The new applicator is designed to have a workflow which induces a low workload. To gain information on the current surgery, two observations in the operating theatre are made and a workflow analysis is performed. After the initial analysis a lean startup process is used to create iterations of the new spinal cage applicator. This method is used because it is found to better suit the already largely defined context of the project. A test with the first design shows that the multi-segment spinal cage was difficult to load into the applicator, therefore a solution is found by creating a cartridge which contains the spinal cage and allows for a quick and easy insertion. A connection between the spinal cage and the part which pushes the implant into the body is added as well to allow for a controlled insertion. The second design is tested on a simulated anatomical setup. This user test shows that the connection between spinal cage and pusher, and markings indicating the correct insertion orientation requires improvement. The third design is tested to evaluate the workflow. It is found that the workflow induces a low to moderate workload. It is found that the applicator still blocks the surgical view too much. The final design, called ClearFix, is a disposable applicator made from clear polycarbonate to increase the surgeons view on the surgical area. Surgeons state that the ClearFix is easy and intuitive to use, and would use the ClearFix if it were available.

Selective laser melting (SLM) is an additive manufacturing technique, which is currently on the rise of being used for manufacturing bone implants. Spinal cage, dental and hip implants can for example be manufactured using SLM. Ti6Al4V lattice structures, categorised as metamaterials, can be printed by SLM with mechanical properties close to bone tissue. Due to the lattice structure the stiffness of the Ti6Al4V is decreased, by which stress shielding can be reduced. The lattice structures enhance bone ingrowth which in turn improves the implant’s integration into bone tissue. In light of this potential, this research is focused on biomechanical properties of additively manufactured Ti6Al4V metamaterials. The current research is aimed at improving the fatigue resistance and wettability of diamond lattice structured Ti6Al4V by applying different microstructural designs and surface engineering through hot isostatic pressing (HIP), sand blasting (SB) and chemical etching (CE). Furthermore a comparison is made between the two SLM processes in terms of continuous and pulsed laser scanning. In order to verify the developed herein post treatment procedures, the tests were also upscaled to actual spinal cage implants. Furthermore, surface modifications affect its wettability which can be linked to cell adhesion and ultimately healing time of the implant. Hence Sessile drop tests were performed to assess the wettability and compare the effect of the various surface modifications. For both SLM methods it was found that HIP reduces porosity of Ti6Al4V metamaterials, which reduces crack initiation sites and it also serves as a heat treatment increasing the b-phase fraction and thus increasing ductility and fatigue resistance. SB and CE were found to reduce surface indiscrepancies, which decrease the effect of stress concentration and fatigue initiation sites. Finally SB induces compressive residual surface stresses which means the surface is work hardened, increasing the overall mechanical properties. For continuous SLM samples an increase in yield strength from 89 MPa up to 115 MPa was found by applying HIP treatment. It should be noted, however, that static mechanical properties were not affected by SB and CE treatments. Fatigue resistance, both low cycle (LCF) and high cycle fatigue (HCF), was significantly improved by a combination of HIP, SB and CE. The observed trend was similar for both pulsed and continuous SLM samples. It is worth noting that SLM samples manufactured with pulsing laser were found in general to be inferior to the continuous laser SLM, both in terms of static and dynamic properties. The difference is likely attributed to the nature of the laser scanning process, where for pulsing laser method each bead interconnection serves as stress concentration, while for continues laser it is rather the strut interconnections that act as weakest points. Furthermore, for the continuous SLM a preferred grain growth direction was observed which indicates anisotropy. This was not observed for pulsed SLM samples. For the wettability results it was observed that SB decreases and CE increases the contact angle. A decrease in contact angle means the surface has become more hydrophilic, hence the in this study developed SB modification could be considered as more favourable for osseointergration. The upscaled spinal cage implants post treatment procedure showed a decrease in yield strength and an increase in fatigue resistance for the HIP+SB+CE as compared to as-processed implants. The rather limited post treatment improvement on implants was linked to the post process treatment method, which should be modified to account for the complex geometry of these structures.