Soft tissue modelling and facial movement simulation using the finite element method

This thesis presents a framework for soft tissue modelling, facial surgery simulation, and facial movement synthesis based on the volumetric finite element method. Assessment of facial appearance pre- and post-surgery is of major concern for both patients and clinicians. Pre-surgical planning is a prerequisite for successful surgical procedures and outcomes. Early computer-assisted facial models have been geometrically based. They are computationally efficient, but cannot give an accurate prediction for facial surgery simulation. Therefore, in this thesis, the emphasis is placed on physically-based methods, especially the finite element technique. To achieve realistic surgery simulation, soft tissue modelling is of crucial importance. Thus, in this thesis, considerable effort has been directed to develop constitutive equations for facial skeletal muscles. The skeletal muscle model subsequently developed is able to capture the complex mechanical properties of skeletal muscle, which are active, quasi-incompressible, fibre-reinforced and hyperelastic. In addition, to improve the characterisation of in-vivo muscle behaviour, a technique has been developed to visualise the internal fibre arrangement of skeletal muscle using the FEM-NURBS method, which is the combination of the finite element method and the non-uniform rational B-spline solid mathematical representation. Another principal contribution made in this thesis is the three-dimensional finite element facial model, which can be used for the simulations of facial surgery and facial movement. The procedure of one cranio-facial surgery is simulated by using this facial model and the numerical predictions show a good agreement with the patient post-surgical data. In addition, it would be very helpful to also simulate the facial movement and facial expressions. In this thesis, two facial expressions (smile and disgust) and the mouth opening are simulated to assess the post-surgical appearance and test the muscle-driven facial movement simulation method

Advanced Applications of Rapid Prototyping Technology in Modern Engineering

Rapid prototyping (RP) technology has been widely known and appreciated due to its flexible and customized manufacturing capabilities. The widely studied RP techniques include stereolithography apparatus (SLA), selective laser sintering (SLS), three-dimensional printing (3DP), fused deposition modeling (FDM), 3D plotting, solid ground curing (SGC), multiphase jet solidification (MJS), laminated object manufacturing (LOM). Different techniques are associated with different materials and/or processing principles and thus are devoted to specific applications. RP technology has no longer been only for prototype building rather has been extended for real industrial manufacturing solutions. Today, the RP technology has contributed to almost all engineering areas that include mechanical, materials, industrial, aerospace, electrical and most recently biomedical engineering. This book aims to present the advanced development of RP technologies in various engineering areas as the solutions to the real world engineering problems

Development of procedures for the design, optimization and manufacturing of customized orthopaedic and trauma implants: Geometrical/anatomical modelling from 3D medical imaging

Tese de Doutoramento (Programa Doutoral em Engenharia Biomédica)The introduction of imaging techniques in 1970 is one of the most relevant historical milestones in modern medicine. Medical imaging techniques have dramatically changed our understanding of the Human anatomy and physiology. The ability to non-invasively extract visual information allowed, not only the three-dimensional representation of the internal organs and musculo-skeletal system, but also the simulation of surgical procedures, the execution of computer aided surgeries, the development of more accurate biomechanical models, the development of custom-made implants, among others. The combination of the most advanced medical imaging systems with the most advanced CAD and CAM techniques, may allow the development of custom-made implants that meet patient-speci c traits. The geometrical and functional optimization of these devices may increase implant life-expectancy, especially in patients with marked deviations from the anatomical standards. In the implant customization protocol from medical image data, there are several steps that need to be followed in a sequential way, namely: Medical Image Processing and Recovering; Accurate Image Segmentation and 3D Surface Model Generation; Geometrical Customization based on CAD and CAE techniques; FEA Optimization of the Implant Geometry; and Manufacturing using CAD-CAM Technologies. This work aims to develop the necessary procedures for custom implant development from medical image data. This includes the extraction of highly accurate three-dimensional representation of the musculo-skeletal system from the Computed Tomography imaging, and the development of customized implants, given the speci c requirements of the target anatomy, and the applicable best practices found in the literature. A two-step segmentation protocol is proposed. In the rst step the region of interest is pre-segmented in order to obtain a good approximation to the desired geometry. Next, a fully automatic segmentation re nement is applied to obtain a more accurate representation of the target domain. The re nement step is composed by several sub-steps, more precisely, the recovery of the original image, considering the limiting resolution of the imaging system; image cropping; image interpolation; and segmentation re nement over the up-sampled domain. Highly accurate segmentations of the target domain were obtained with the proposed pipeline. The limiting factor to the accurate description of the domain accuracy is the image acquisition process, rather the following image processing, segmentation and surface meshing steps. The new segmentation pipeline was used in the development of three tailor-made implants, namely, a tibial nailing system, a mandibular implant, and a Total Hip Replacement system. Implants optimization is carried with Finite Element Analysis, considering the critical loading conditions that may be applied to each implant in working conditions. The new tibial nailing system is able of sustaining critical loads without implant failure; the new mandibular endoprosthesis that allows the recovery of the natural stress and strain elds observed in intact mandibles; and the Total Hip Replacement system that showed comparable strain shielding levels as commercially available stems. In summary, in the present thesis the necessary procedures for custom implant design are investigated, and new algorithms proposed. The guidelines for the characterization of the image acquisition, image processing, image segmentation and 3D reconstruction are presented and discussed. This new image processing pipeline is applied and validated in the development of the three abovementioned customized implants, for di erent medical applications and that satisfy speci c anatomical needs.Um dos principais marcos da história moderna da medicina e a introdução da imagem médica, em meados da década de 1970. As tecnologias de imagem permitiram aumentar e potenciar o nosso conhecimento acerca da anatomia e fisiologia do corpo Humano. A capacidade de obter informação imagiológica de forma não invasiva permitiu, não são a representação tridimensional de órgãos e do sistema músculo-esquelético, mas também a simulação de procedimentos cirúrgicos, a realização de cirurgias assistidas por computador, a criação de modelos biomecânicos mais realistas, a criação de implantes personalizados, entre outros. A conjugação dos sistemas mais avançados de imagem medica com as técnicas mais avançadas de modelação e maquinagem, pode permitir o desenvolvimento de implantes personalizados mais otimizados, que vão de encontro as especificidades de cada paciente. Por sua vez, a otimização geométrica e biomecânica destes dispositivos pode permitir, quer o aumento da sua longevidade, quer o tratamento de pessoas com estruturas anatómicas que se afastam dos padrões normais. O processo de modelação de implantes a partir da imagem medica passa por um conjunto de procedimentos a adotar, sequencialmente, ate ao produto final, a saber: Processamento e Recuperação de Imagem; Segmentação de Imagem e Reconstrução tridimensional da Região de Interesse; Modelação Geométrica do Implante; Simulação Numérica para a Otimização da Geometria; a Maquinagem do Implante. Este trabalho visa o desenvolvimento dos procedimentos necessários para a criação de implantes personalizados a partir da imagem medica, englobando a extração de modelos ósseos geométricos rigorosos a partir de imagens de Tomografia Computorizada e, a partir desses modelos, desenvolver implantes personalizados baseados nas melhores praticas existentes na literatura e que satisfaçam as especificidades da anatomia do paciente. Assim, apresenta-se e discute-se um novo procedimento de segmentação em dois passos. No primeiro e feita uma pre-segmentação que visa obter uma aproximação iniciala região de interesse. De seguida, um procedimento de refinamento da segmentação totalmente automático e aplicada a segmentação inicial para obter uma descrição mais precisa do domínio de interesse. O processo de refinamento da segmentação e constituído por vários procedimentos, designadamente: recuperação da imagem original, tendo em consideração a resolução limitante do sistema de imagem; o recorte da imagem na vizinhança da região pre-segmentada; a interpolação da região de interesse; e o refinamento da segmentação aplicando a técnica de segmentação Level-Sets sobre o domínio interpolado. O procedimento de segmentação permitiu extrair modelos extremamente precisos a partir da informação imagiológica. Os resultados revelam que o fator limitante a descrição do domínio e o processo de aquisição de imagem, em detrimento dos diversos passos de processamento subsequentes. O novo protocolo de segmentação foi utilizado no desenvolvimento de três implantes personalizados, a saber: um sistema de fixação interna para a tíbia; um implante mandibular; e um sistema para a Reconstrução Total da articulação da Anca. A otimização do comportamento mecânico dos implantes foi feita utilizado o Método dos Elementos Finitos, tendo em conta os carregamentos críticos a que estes podem estar sujeitos durante a sua vida útil. O sistema de fixação interna para a tíbia e capaz de suportar os carregamentos críticos, sem que a sua integridade mecânica seja comprometida; o implante mandibular permite recuperar os campos de tensão e deformação observados em mandíbulas intactas; e a Prótese Total da Anca apresenta níveis de strain shielding ao longo do fémur proximal comparáveis com os níveis observados em dispositivos comercialmente disponíveis. Em suma, nesta tese de Doutoramento são investigados e propostos novos procedimentos para o projeto de implantes feitos por medida. São apresentadas e discutidas as linhas orientadoras para a caracterização precisa do sistema de aquisição de imagem, para o processamento de imagem, para a segmentação, e para a reconstrução 3D das estruturas anatómicas a partir da imagem medica. Este conjunto de linhas orientadoras é aplicado e validado no desenvolvimento de três implantes personalizados, citados anteriormente, para aplicações médicas distintas e que satisfazem as necessidades anatómicas específicas de cada paciente.Fundação para a Ciência e Tecnologia (FCT

Physically Based Forehead Modelling and Animation including Wrinkles

There has been a vast amount of research on the production of realistic facial models and animations, which is one of the most challenging areas of computer graphics. Recently, there has been an increased interest in the use of physically based approaches for facial animation, whereby the effects of muscle contractions are propagated through facial soft-tissue models to automatically deform them in a more realistic and anatomically accurate manner. Presented in this thesis is a fully physically based approach for efficiently producing realistic-looking animations of facial movement, including animation of expressive wrinkles, focussing on the forehead. This is done by modelling more physics-based behaviour than current computer graphics approaches. The presented research has two major components. The first is a novel model creation process to automatically create animatable non-conforming hexahedral finite element (FE) simulation models of facial soft tissue from any surface mesh that contains hole-free volumes. The generated multi-layered voxel-based models are immediately ready for simulation, with skin layers and element material properties, muscle properties, and boundary conditions being automatically computed. The second major component is an advanced optimised GPU-based process to simulate and visualise these models over time using the total Lagrangian explicit dynamic (TLED) formulation of the FE method. An anatomical muscle contraction model computes active and transversely isotropic passive muscle stresses, while advanced boundary conditions enable the sliding effect between the superficial and deep soft-tissue layers to be simulated. Soft-tissue models and animations with varying complexity are presented, from a simple soft-tissue-block model with uniform layers of skin and muscle, to a complex forehead model. These demonstrate the flexibility of the animation approach to produce detailed animations of realistic gross- and fine-scale soft-tissue movement, including wrinkles, with different muscle structures and material parameters, for example, to animate different-aged skin. Owing to the detail and accuracy of the models and simulations, the animation approach could also be used for applications outside of computer graphics, such as surgical applications. Furthermore, the animation approach can be used to animate any multi-layered soft body (not just soft tissue)

Unveiling the prospects of point-of-care 3D printing of Polyetheretherketone (PEEK) patient-specific implants

Additive manufacturing (AM) or three-dimensional (3D) printing is rapidly gaining acceptance in the healthcare sector. With the availability of low-cost desktop 3D printers and inexpensive materials, in-hospital or point-of-care (POC) manufacturing has gained considerable attention in personalized medicine. Material extrusion-based [Fused Filament Fabrication (FFF)] 3D printing of low-temperature thermoplastic polymer is the most commonly used 3D printing technology in hospitals due to its ease of operability and availability of low-cost machines. However, this technology has been limited to the production of anatomical biomodels, surgical guides, and prosthetic aids and has not yet been adopted into the mainstream production of patient-specific or customized implants. Polyetheretherketone (PEEK), a high-performance thermoplastic polymer, has been used mainly in reconstructive surgeries as a reliable alternative to other alloplastic materials to fabricate customized implants. With advancements in AM systems, prospects for customized 3D printed surgical implants have emerged, increasing attention for POC manufacturing. A customized implant may be manufactured within few hours using 3D printing, allowing hospitals to become manufacturers. However, manufacturing customized implants in a hospital environment is challenging due to the number of actions necessary to design and fabricate the implants. The focus of this thesis relies on material extrusion-based 3D printing of PEEK patient-specific implants (PSIs). The ambitious challenge was to bridge the performance gap between 3D printing of PEEK PSIs for reconstructive surgery and the clinical applicability at the POC by taking advantage of recent developments in AM systems. The main reached milestones of this project include: (i) assessment of the fabrication feasibility of PEEK surgical implants using material extrusion-based 3D printing technology, (ii) incorporation of a digital clinical workflow for POC manufacturing, (iii) assessment of the clinical applicability of the POC manufactured patient-specific PEEK scaphoid prosthesis, (iv) visualization and quantification of the clinical reliability of the POC manufactured patient-specific PEEK cranial implants, and (v) assessment of the clinical performance of the POC manufactured porous patient-specific PEEK orbital implants. During this research work, under the first study, we could demonstrate the prospects of FFF 3D printing technology for POC PEEK implant manufacturing. It was established that FFF 3D printing of PEEK allows the construction of complex anatomical geometries which cannot be manufactured using other technologies. With a clinical digital workflow implementation at the POC, we could further illustrate a smoother integration and faster implant production (within two hours) potential for a complex-shaped, patented PEEK patient-specific scaphoid prosthesis. Our results revealed some key challenges during the FFF printing process, exploring the applicability of POC manufactured FFF 3D printed PEEK customized implants in craniofacial reconstructions. It was demonstrated that optimal heat distribution around the cranial implants and heat management during the printing process are essential parameters that affect crystallinity, and thus the quality of the FFF 3D printed PEEK cranial implants. At this stage of the investigation, it was observed that the root mean square (RMS) values for dimensional accuracy revealed higher deviations in large-sized cranial prostheses with “horizontal lines” characteristics. Further optimization of the 3D printer, a layer-by-layer increment in the airflow temperature was done, which improved the performance of the FFF PEEK printing process for large-sized cranial implants. We then evaluated the potential clinical reliability of the POC manufactured 3D printed PEEK PSIs for cranial reconstruction by quantitative assessment of geometric, morphological, and biomechanical characteristics. It was noticed that the 3D printed customized cranial implants had high dimensional accuracy and repeatability, displaying clinically acceptable morphologic similarity concerning fit and contours continuity. However, the tested cranial implants had variable peak load values with discrete fracture patterns from a biomechanical standpoint. The implants with the highest peak load had a strong bonding with uniform PEEK fusion and interlayer connectivity, while air gaps and infill fusion lines were observed in implants with the lowest strength. The results of this preclinical study were in line with the clinical applicability of cranial implants; however, the biomechanical attribute can be further improved. It was noticed that each patient-specific reconstructive implant required a different set of manufacturing parameters. This was ascertained by manufacturing a porous PEEK patient-specific orbital implant. We evaluated the FFF 3D printed PEEK orbital mesh customized implants with a metric considering the design variants, biomechanical, and morphological parameters. We then studied the performance of the implants as a function of varying thicknesses and porous design constructs through a finite element (FE) based computational model and a decision matrix based statistical approach. The maximum stress values achieved in our results predicted the high durability of the implants. In all the implant profile configurations, the maximum deformation values were under one-tenth of a millimeter (mm) domain. The circular patterned design variant implant revealed the best performance score. The study further demonstrated that compounding multi-design computational analysis with 3D printing can be beneficial for the optimal restoration of the orbital floor. In the framework of the current thesis, the potential clinical application of material extrusion-based 3D printing for PEEK customized implants at the POC was demonstrated. We implemented clinical experience and engineering principles to generate a technical roadmap from preoperative medical imaging datasets to virtual surgical planning, computer-aided design models of various reconstructive implant variants, to the fabrication of PEEK PSIs using FFF 3D printing technology. The integration of 3D printing PEEK implants at the POC entails numerous benefits, including a collaborative team approach, quicker turnaround time of customized implants, support in pre-surgical and intraoperative planning, improved patient outcomes, and decreased overall healthcare cost. We believe that FFF 3D printing of customized PEEK implants could become an integral part of the hospitals and holds potential for various reconstructive surgery applications

Use of 3-Dimensional Miniplate in Mandibular Angle Fracture Fixation: A Clinical and Finite Element Study

SUMMARY & CONCLUSION: Our results suggest that 3- Dimensional plating system is a suitable method for fixation of simple mandibular angle fractures. The 3- D design incorporates more implant material and the vertical bars resist torque forces, which favours stability. Post-operatively, no infection or wound dehiscence developed in the patients. Hence, the morbidity associated with the use of the plate is very low. But it is difficult to adapt than a conventional miniplate, which lead to increased operative time. 3-D plate is unfavourable to use in cases of angle fractures with lingual splaying and those involving the mental nerve. However, another study with a larger sample size would give definitive results. Finite element analysis, originally used in structural analysis has revolutionized dental biomedical research. It can make clinically relevant predictions about mandibular loading with various plating systems. It is also useful in evaluation of different types of fractures and fracture sites, as evident with our study results and those in the literature. The advantage of configuration of 3-D plating system is that the stress distribution to bone, both cortical and cancellous is minimal as the plate takes up and imbibes maximum stress and load, which allows optimum physiologic bone growth and healing. Hence, new plating systems can be designed and experimented virtually where the metallurgy and physical properties of plate is biologically compatible to the properties of bone. This will save a lot of time and material on animal experiments. FEA can provide an insight into the complex biomechanical behavior of the craniofacial complex and mandible. But it is technique sensitive, requires expensive softwares and skilled analysist. Thus simultaneous evaluation of 3-D miniplate, both clinically and by finite element analysis delineates that the plate provides adequate stability and is useful for fixation of mandibular angle fracture

Impact Of Laser Powder Bed Fusion Process Defects On Mechanical Properties Of Ti6Al4V Mandible Implants

DissertationEach year millions of patients’ quality of life is improved through surgical procedures involving medical implanted devices. The need for new implants, treatments and prostheses, as well as prolonging the life span of current implants has increased; the global prosthetics and orthotics market size is expected to reach $11.7 billion by 2025, as indicated in Healthcare Market Report (2020). Additive manufacturing (AM) was implemented in the medical field fairly recently. Despite the enormous contribution medical devices have made to the public health, there is a fear of possible liability exposure in the event of device malfunction or failure. Efficient quality control of implants produced by new AM technologies is an important task for suppliers in order to be in full compliance with existing regulations and certification of such implants. If any defects occur, implant strength will directly influence the part’s mechanical properties and performance, leading to the redistribution of stress and change in displacements affecting attached bone tissue and mineral matrix of the bone, resulting in implant failure. For wide applications in the medical industry, it is crucial that AM implants comply with international standards with regard to their mechanical properties. Three point bending tests (TPB) were carried out in this work on AM Ti6Al4V ELI specimens. TPB is a common tool used to characterize bone material properties and mechanical performance of biomaterials. Powder bed fusion is the unique AM method to produce metal objects with complex geometries and internal structures; it permits the manufacture of complex-shaped functional 3D objects such as customized implants. The benefits of AM in bone reconstruction using metal alloys are unquestionable in terms of customization of implants and production time. Comprehensive analysis of the laser powder bed fusion (LPBF) process together with functional anatomy biomechanics of the human mandible was done in this work. Some case studies on defects found in LPBF implants were evaluated. Based on biomechanics of the human mandible, LPBF Ti6Al4V ELI samples were designed. Experiments and numerical simulations of samples with sizes and placements of artificial pores were done. All samples were tested perpendicular to the vertical building direction and showed no signs of failure at a single loading pattern. Defects were designed and induced in the additive manufacturing of test samples of titanium, with different size and placement. Results indicate that defects of 1000 μm×300 μm×210 μm and 1000 μm×500 μm×420 μm at various depth to the neutral axis had no significant outcome on the mechanical performance of the samples with size of 100 mm 15 mm 2.5 mm when it was tested statically at loading of 800, 900 and 1500 N, representing a maximum biting force. This approach is a promising method of setting up a critical pore size to failure tolerance for AM implants with some defects

In Vivo Mechanics of Cam-Post Engagement in Fixed and Mobile Bearing TKA and Vibroarthrography of the Knee Joint

The objective of this dissertation was to determine the mechanics of the cam-post mechanism for subjects implanted with a Rotating Platform (RP) PS TKA, Fixed Bearing (FB) PS TKA or FB Bi-Cruciate Stabilized (BCS) TKA. Additionally, a secondary goal of this dissertation was to investigate the feasibility of vibroarthrography in correlating in-vivo vibrations with features exhibited in native, arthritic and implanted knees. In-vivo, 3D kinematics were determined for subjects implanted with nine knees with a RP-PS TKA, five knees with a FB-PS TKA, and 10 knees with a FB-BCS TKA, while performing a deep knee bend. Distance between the cam-post surfaces was monitored throughout flexion and the predicted contact map was calculated. A forward dynamic model was constructed for 3 test cases to determine the variation in the nature of contact forces at the cam-post interaction. Lastly, a different set of patients was monitored using vibroarthrography to determine differences in vibration between native, arthritic and implanted knees. Posterior cam-post engagement occurred at 34° for FB-BCS, 93o for FB-PS and at 97° for RP-PS TKA. In FB-BCS and FB-PS knees, the contact initially occurred on the medial aspect of the tibial post and then moved centrally and superiorly with increasing flexion. For RP-PS TKA, it was located centrally on the post at all times. Force analysis determined that the forces at the cam-post interaction were 1.6*body-weight, 2.0*body-weight, and 1.3*body-weight for the RP-PS, FB-BCS and FB-PS TKA. Sound analysis revealed that there were distinct differences between native and arthritic knees which could be differentiated using a pattern classifier with 97.5% accuracy. Additionally, vibrations from implanted knees were successfully correlated to occurrences such as lift-off and cam-post engagement. This study suggests that mobility of the polyethylene plays a significant role in ensuring proper cam-post interaction in RP-PS TKA. The polyethylene insert rotates axially in accord with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the FB-BCS and FB-PS TKAs