Computational and experimental assessment of additively manufactured mesh-type Ti6Al4V structures for cranial implants

Susanne Lewin1, Ingmar Fleps2, Jonas Åberg1, Stephen J. Ferguson2, Håkan Engqvist1, Caroline Öhman-Mägi1, Benedikt Helgason2, Cecilia Persson1

1Uppsala University, Uppsala, Sweden; 2Institute for Biomechanics, ETH Zurich, Switzerland


Advances in additive manufacturing (AM) have resulted in major improvements for various biomedical applications. One example is the successful implementation and clinical use of  patient specific titanium-reinforced calcium phosphate (CaP–Ti) implants for cranial reconstructions [1]. Currently, the mesh-type Ti6Al4V structure of the implant is additively manufactured using laser beam powder bed fusion (L-PBF). Nevertheless, an electron-beam (E-PBF) process could potentially increase productivity due to higher deposition rate and increased possibility for stacking [2]. This study aimed to compare the geometrical accuracy and mechanical response of thin titanium structures manufactured by L-PBF (HIPed) and E-PBF (as-printed) [3]. Tensile test (ø = 1.2 mm) and implant specimens were manufactured. 
Measurements by μCT revealed a deviation in cross-sectional area as compared to the designed geometry: 13–35% for E-PBF and below 2% for L-PBF. A superior mechanical strength was obtained for the L-PBF specimens, both in the tensile test and the implant compression tests. The global peak load in the implant test was 457 ± 9 N and 846 ± 40 N for E-PBF and L-PBF, respectively. Numerical simulations demonstrated that geometrical deviation was the main factor in implant performance and enabled quantification of this effect: 34–39% reduction in initial peak force based on geometry, and only 11–16% reduction based on the material input. In conclusion, the use of E-PBF in this application requires a redesign by upscaling the dimensions and/or further post-processing of the as-printed surfaces, in order to reach a strength similar to the HIPed L-PBF structures. This study supports the importance of evaluating the AM process in the dimensions and printing directions of the final application. 

[1] Engstrand et al., Journal of neurosurgery, 2012. 
[2] Liu and Shin, Materials & Design, 2019. 
[3] Lewin et al., Materials & Design, 2021.