A patient in Argentina required a particularly large cranial implant after stroke-related surgery, placing stringent requirements on the manufacture of the prosthetic. Naturally it needed to fit precisely, but in this case it also had to be permeable to allow brain fluid to pass through. Minimal heat conduction to the cerebral tissue was important, especially in a sunny climate. Additionally, biocompatibility was needed to allow the bone to grow into the edges of the implant.
A titanium alloy lattice structure secured by screws directly into the skull was deemed to be ideal. It was additively manufactured layer by layer from metal powder in a machine produced by German firm EOS.
Time was of the essence in producing the implant. The process was started by Novax DMA in Buenos Aires, which specialises in developing and supplying medical implants for traumatology, orthopaedics and craniofacial surgery. For the 3D design of the implant, software was employed from UK company Within, which allowed the basic form and porous structure to be defined quickly.
As soon as the CAD work was completed, Alphaform AG, near Munich, manufactured the implant in a matter of hours in an EOSINT M 280 metal additive manufacturing machine from EOS. Several stringent mechanical requirements had to be met to ensure a successful result and technological advances in additive manufacturing allowed them to be achieved. The pores in the implant are approximately 1 mm across, while the links are about 0.2 mm thick, resulting in 95 per cent porosity. To achieve such a fine mesh in a rigid structure to tight dimensional and profile tolerances would be impracticable using conventional, subtractive production techniques.
The implant was in the operating theatre less than three weeks later, with transportation consuming one-third of that time. The one-and-a-half-hour surgical procedure was carried out successfully in May last year (2014).