title: Additive Manufacturing for Patient-specific Facial Prosthetics
Creators: name: Ward, Michael
Publisher: name: University of Liverpool Repository
Year: 2022

description: Additive manufacturing (AM) is a rapidly growing technology. Based on the technology’s intrinsic nature of being able to manufacture complex and organic shapes, at low production volumes, it is well suited to the medical industry. The amalgamation of both industries is already rapidly evolving, through devices such as limb prosthetics, surgical planning tools, surgical cutting guides, patient-specific implants, and burn masks. Research has been carried out involving the use of additive manufacturing for facial prosthetics, however primarily as one step in the process, with a continuation of conventional practices. The primary aim of facial prosthetics inherently revolves around the accuracy of aesthetics. Concealment of an ablation or disfigurement is the primary goal. This facet is imperative with regards to the patient’s wellbeing and social comfort. Currently prosthetics are produced in a very labour-intensive, linear fashion. The process is closer to a work of art, than a repeatable, anatomical model. Current prosthetics generally look highly realistic, visually, however the final product depends on the individual skill set of the prosthetist. Additive manufacturing may hold the potential for highly realistic, repeatable, and cost-effective prosthetic manufacturing. This study found there to be a significant difference between the mechanical properties of soft facial tissue, based on anatomical location. Bulk measurements found that skin from the ear of porcine samples was significantly stiffer than that of cheek and snout samples. Furthermore, macro scale testing showed that auricular cartilage was stiffer than septal. In terms of polymers, the study found that the printed materials had a lower ultimate tensile strength than the silicones, were stiffer and more viscoelastic. The study deemed that the mechanical properties of the photopolymers were robust enough for use within facial prosthetics. The study further found that the mechanical properties of the printed materials can be significantly altered through the use of graded lattice structures or multi-material blends. The linear elastic moduli of all tissue types were stiffer than that of all the polymers tested, however the printed polymers were most comparable. In terms of biocompatibility, the study suggests that the proposed AM material had an adverse effect on cells, most prominently beyond a 24h time period. However, the material did exhibit a comparable response to that of the biocompatible control photopolymer. Therefore, the study suggests that further research is required, regarding the effect of a wash-out phase, for printed materials aimed at use within a biocompatible environment. Overall the findings of the thesis suggest that AM materials show great potential for mimicking the biomechanics of biological tissue, and therefore show promise for use within facial prosthetics. Further biocompatibility testing is required, but the study believes that the proposed material still shows potential for short term skin contact. With this classification requiring further analysis, the mechanical study presented within this thesis still presents immediate value to the ever-increasing interest in medical phantoms.