July 1, 2016 by admin 0 Comments

Development of design and manufacturing methodology to create preformed custom prostheses for cranioplasty applications

Natalia Leon, Leandro I. Martínez, Rafael R. Torrealba, Samuel B. Udelman
Polymethyl methacrylate (PMMA) preformed custom implants for cranioplasty applications have two main purposes: to restore the protection normally given by the cranium to the brain, and to improve the appearance of head surface after a traumatism or malformation. These implants have advantage such as material cost decrease, compared with other materials as titanium, hard tissue replacement (HTR) and polyether ether ketone (PEEK), and risk reduction related to tissue necrosis and residual monomer release to the bloodstream, as consequence of “in vivo” reactions. The aim of this work is to implement a process to create PMMA preformed custom implants, as an accessible alternative in the venezuelan economic context, made possible by applying a suitable design and manufacturing methodology. In Venezuela, the majority of cranioplasties are made either by implantation of titanium meshes or via “in vivo” reactions with PMMA. In such sense, we are introducing a more holistic methodology which not only creates the PMMA implant, but also establishes the key channels between a highly technical engineering staff and the medical system of our country, mainly the neurosurgeons that execute the cranioplasties, looking to adapt the implants design to the medical requirements as much as possible, and as a consequence, reducing the surgical time compared with prosthetic implants molded during the surgery. This process is designed as follows: first, the patient medical data is obtained from the computed tomography (CT) images processed in Mimics® and 3-matic® to generate the bone structure to be treated and design the corresponding implant to meet the neurosurgeon’s specific requirements. Then, the implant positive mold is 3D-printed in polylactic acid (PLA) using fused deposition modeling (FDM) technology, which reduces costs in comparison with others rapid prototyping processes and builds more accurate pieces. Using this positive mold, a negative mold is created based on a silicone rubber that cures at room temperature, with negligible shrinkage to avoid changes on the mold dimensions. This silicone was chosen to guarantee an exact reproduction of the positive implant details. The 3D-printed implant is removed from the mold cavity and filled with a PMMA based bone cement to generate the final implant. Compared with other two-steps methods for mold fabrication, the one presented here allows getting the most accurate thickness for the implant. After the PMMA cement has cured into such a silicone mold, the customized PMMA implant must be sterilized with ethylene oxide and is ready to be fitted and secured on the patient cranium during the cranioplasty