Cranial implants are highly intricate and must be manufactured to the highest standards. Once such patient in Argentina, who needed a particularly large implant after cerebrovascular surgery, required an implant to be the best fit possible, with good tolerance of the implant by the body and integration with biological functions. Novax DMA, based in Buenos Aires, was assigned the challenge to develop and manufacture a perfectly-fitting implant for the cranial area - able to accommodate permeability to liquids and heat dissipation.
The body is very tolerant of titanium but, as it is a metal, there is a danger to patients exposing themselves to the sun and too much heat being transmitted into the body. In addition, a titanium structure would not be permeable for tissue fluid from the brain. For this patient, the procedure required special secondary process added to the specification. By including a secondary treatment after manufacturing - in this case ‘cleaning’ - made it possible to use a 3D printed part for this challenge. The importance of cleaning is vital because adherent particles are released from the body by the slightest movement, which can lead to infection or rejection. So a completely germ-free environment is a key criterion for the successful acceptance of an implant by the body.
It is important for an implant in the cranium-brain area to support - or at least not hinder - the recovery process. The first requirement is as perfect as fit as possible. This is one of the major benefits of additive manufacturing: the layer-by-layer manufacturing by a laser - in this case with titanium - hardened on a piece-by-piece basis; lends itself to maximum customisation of shape and size.
As well as the need for a perfect fit, there were more challenges along the way for Novax DMA, who partnered by Protolabs, during the challenge to create the perfect part. Due to the size of the patient’s hole in the cranial bone, the solution included integrating the biological function of the implant while minimising heat transfer into the brain tissue.
After Novax DMA and Protolabs experts pulled together and evaluated all aspects of the challenge, they came to the conclusion that only a porous structure would exhibit the required properties. The result involved a grill-shaped implant with integrated fixing lugs for the cranial bone. This will allow liquids to permeate it and enables growth of the bone. In addition, this design has an insulating effect, so the conduction of heat into the interior of the cranium is minimised. The dimensions: The pinholes themselves are approx. 1mm wide, the grill width being around 0.2mm. After the basic structure was confirmed, the medical technology specialists took over.
Daniel Fiz, Chief Executive Officer of Novax DMA, remembers: “Time was of the essence for this work. Patients need to receive their implant as quickly as possible. After we received the final information about dimensions, we started work on the construction and manufacture of the implant with Protolabs.”
The result: a perfectly cut implant tailored to the specific requirements of the patient's condition. Porosity reaches 95% so that liquids can flow with as little resistance as possible, so the bone tissue is able to penetrate the outer edges of the implant, again with as little resistance as possible, and grow with it. The material is also stable enough to enable the patient to lead a normal life; the standard grill structure allows for the required heat transfer properties - so the patient can enjoy time in the sunshine without problems.
Amongst all the possibilities for perfecting the process, one factor in particular was critical. Time-to-market is key in an industrial environment and plays to the strengths of additive manufacturing, particularly in the medical sector: the implant was in the operating theatre within just three weeks. The biggest log jam in the system was transport, which took around a week. Preparing the data and manufacturing were done in about 2 1/2 days, and the rest of the time was taken up with various procedures to do with logistics and coordination.
The two companies could verify the degree of cleanliness through a range of tests. Christoph Erhardt’s team were able to carry out particle and cytotoxicity tests amongst other things. There was also analysis using gas chromatography. “All the investigations confirmed that the additively manufactured implant fulfilled the necessary requirements for the long-term stability and protection of the patient’s skullcap.
The 90-minute-long operation was completed without incident in 2014. The patient was able to leave the clinic after 2 days, and the wound healed after 3 weeks. To date, the patient has experienced no complications after the operation.
Thanks to processes and projects such as this, 3D printing can significantly assist contribute towards patients with cranial injuries lead a full life.