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Enginyeria mecànica (2)
This doctoral thesis has been focused on the challenge to obtain, using Additive Manufacturing (AM), models for surgical planning, under the premise that the equipment to obtain them should be accessible to the hospital field. The objective is to spread the use of prototypes as a surgical training tool, upgrading medical practice in the same way that technologies which enhanced radiographs at the time. The reason for using AM, instead of more traditional technologies, is its capacity to materialise, in a straight way, the digital data of the patient anatomy coming from three-dimensional scanning systems, making it possible to achieve personalised models. The results are basically the generation of new knowledge in order to create accessible multi-material 3D printing machines that would allow to obtain models mimicking living tissues. Related to the will to spread this technology, research has focused on open source technologies, mainly Fused Filament Fabrication (FFF), and similar technologies based on catalitzable liquids. This research is aligned with the development work related to AM at CIM UPC, and in this special field there is a close cooperation with Hospital Sant Joan de Déu in Barcelona (HSJD). The first section of the thesis includes a description of the state of the art, including the existing technologies and their application within the medical field. For the first time, basis have been laid for the characterisation of living tissues – primarily soft tissues – to support the selection of materials mimicking them in an AM process, so as to improve the surgical planning experience. The stiffness linked to most of the materials commonly used in 3D printing, makes them unhelpful to simulate tumours and other anatomic references. Then, parameters like density, viscoelasticity, soft materials industry characterisation, soft tissues and vessels elastic modulus, its hardness, mimicking blood and sterilisation requirements, are successively treated. The second section starts exploring FFF 3D printing. Processes are classified from the point of view of multi-materiality, a key factor for surgical planning models, telling multi-nozzle solutions from mixing printheads solutions. A study about probable useful materials (both filaments and liquids) to mimic soft tissues is included. It is stated how liquids, compared to filaments, are more demanding related to additive manufacturing processes, and different ways to print very soft materials are detailed. Finally, six real cases – in which the doctorate has participated in these last years –, involving collaboration with HSJD, are reported. In the origin it can be found the difficulty to perform tumour resection surgeries to children, like neuroblastoma type, and the initiative of Dr. Lucas Krauel. Finally, Section 3 is devoted to the exploration of many concepts (up to 8), activity performed along the last five years thanks to the technical resources of CIM UPC and the academic activity of the UPC students, related to their final degree thesis, therefore reaching the construction of several machines and mechanisms to test them. The wide and systematic research about these concepts makes closer the day to reach a desktop 3D printing multimaterial solution. It is found that the best way to progress is having a plurality of independent printheads in order to enable a 3D printer to integrate some of the researched concepts, thus materialising a possible solution. To sum up, it is raised how a 3D printer for surgical training models should be like, for the purpose of serving as a basis for new developments. (1)