Novel magnetic stimulation methodology for low-current implantable medical devices

Recent studies highlight the ability of inductive architectures to deliver therapeutic magnetic stimuli to target tissues and to be embedded into small-scale intracorporeal medical devices. However, to date, current micro-scale biomagnetic devices require very high electric current excitations (usually exceeding 1 A) to ensure the delivery of efficient magnetic flux densities. This is a critical problem as advanced implantable devices demand self-powering, stand-alone and long-term operation. This work provides, for the first time, a novel small-scale magnetic stimulation system that requires up to 50-fold lower electric current excitations than required by relevant biomagnetic technology recently proposed. Computational models were developed to analyse the magnetic stimuli distributions and densities delivered to cellular tissues during in vitro experiments, such that the feasibility of this novel stimulator can be firstly evaluated on cell culture tests. The results demonstrate that this new stimulative technology is able to deliver osteogenic stimuli (0.1-7 mT range) by current excitations in the 0.06-4.3 mA range. Moreover, it allows coil designs with heights lower than 1 mm without significant loss of magnetic stimuli capability. Finally, suitable core diameters and stimulator-stimulator distances allow to define heterogeneity or quasi-homogeneity stimuli distributions. These results support the design of high-sophisticated biomagnetic devices for a wide range of therapeutic applications.This work was funded by the Portuguese Foundation for Science and Technology (FCT), through the grant references SFRH/BPD/117475/2016, SFRH/BD/129340/2017 and IF/01089/2015, and by the European Structural and Investment Funds, through the project reference POCI-01-0145-FEDER-031132 and POCI-01-0145-FEDER-007679. It was also support by the TEMA - Centre for Mechanical Technology & Automation (UID/EMS/00481/2013-FCT and CENTRO-01-0145-FEDER-022083) and CICECO - Aveiro Institute of Materials (UID /CTM /50011/ 2013).in publicatio

Using reaction-diffusion equations to model and simulate the interaction of bone cells with electrical stimulation

Electrical stimulation is being used clinically to promote bone ingrowth on implant surfaces and bone healing after complicated fractures. The osseointegration of biomaterials in bone requires complex biological interactions between different bone cells types and electrical stimulation. This work addresses modeling and simulation of the interactions between bone cells and electrical stimulation.Die elektrische Stimulation wird klinisch eingesetzt, um das Einwachsen von Knochen auf Implantatoberflächen sowie die Knochenheilung nach komplizierten Frakturen zu fördern. Die Osseointegration von Biomaterialien im Knochen unterliegt dabei komplexen biologischen Interaktionen zwischen Knochenzellen und der elektrischen Stimulation. Im Rahmen dieser Arbeit erfolgte daher die Modellierung und Simulation der Wechselwirkungen zwischen Knochenzellen und elektrischer Stimulation mit Hilfe eines konstruierten In-vitro-Systems, um elektrotaktische Experimente an Osteoblasten durchzuführen

Mechanical bone growth stimulation by magnetic fibre networks obtained through a competent finite element technique.

Fibre networks combined with a matrix material in their void phase make the design of novel and smart composite materials possible. Their application is of great interest in the field of advanced paper or as bioactive tissue engineering scaffolds. In the present study, we analyse the mechanical interaction between metallic fibre networks under magnetic actuation and a matrix material. Experimentally validated FE models are combined for that purpose in one joint simulation. High performance computing facilities are used. The resulting strain in the composite's matrix is not uniform across the sample volume. Instead we show that boundary conditions and proximity to the fibre structure strongly influence the local strain magnitude. An analytical model of local strain magnitude is derived. The strain magnitude of 0.001 which is of particular interest for bone growth stimulation is achievable by this assembly. In light of these findings, the investigated composite structure is suitable for creating and for regulating contactless a stress field which is to be imposed on the matrix material. Topics for future research will be the advanced modelling of the biological components and the potential medical utilisation

Um novo modelo de conceito para implantes ortopédicos instrumentados ativos

Doutoramento em Engenharia MecânicaTotal hip replacement (THR) is one of the most performed surgical procedures around the world. Millions of THR are carried out worldwide each year. Currently, THR revision rates can be higher than 10%. A significant increase of the number of primary and revision THRs, mainly among patients less than 65 years old (including those under 45 years old) has been predicted for the forthcoming years. A worldwide increase in the use of uncemented fixation has also been reported, incidence caused mainly by the significant increase of more active and/or younger patients. Besides the significant breakthroughs for uncemented fixations, they have not been able to ensure long-term implant survival. Up to date, current implant models have shown evidences of their inability to avoid revision procedures. The performance of implants will be optimized if they are designed to perform an effective control over the osseointegration process. To pursue this goal, improved surgical techniques and rehabilitation protocols, innovative bioactive coatings (including those for controlled delivery of drugs and/or other bio-agents in the bone-implant interface), the concepts of Passive Instrumented Implant and Active Instrumented Implant have been proposed. However, there are no conclusive demonstrations of the effectiveness of such methodologies. The main goal of this thesis is to propose a new concept model for instrumented implants to optimize the bone-implant integration: the self-powered instrumented active implant with ability to deliver controlled and personalized biophysical stimuli to target tissue areas. The need of such a new model is demonstrated by optimality analyses conducted to study the performance of instrumented and non-instrumented orthopaedic implants. Promising results on the potential of a therapeutic actuation driven by cosurface-based capacitive stimulation were achieved, as well as for self-powering instrumented active implants by magnetic levitation-based electromagnetic energy harvesting.A artroplastia total da anca (THR) é um dos procedimentos cirúrgicos mais realizados à escala global. Milhões de THRs são realizadas todos os anos em todo o mundo. Atualmente, as taxas de revisão destas artroplastias podem ser superiores a 10%. O número de THRs primárias e de revisão têm aumentado e estima-se que cresçam acentuadamente nos próximos anos, principalmente em pacientes com idades inferiores a 65 anos (incluindo aqueles com menos de 45 anos). Também se tem verificado uma tendência generalizada para o uso de fixações não cimentadas, incidência principalmente causada pelo aumento significativo de pacientes mais jovens e/ou activos. Embora se tenham realizado avanços científicos no projeto de implantes não cimentados, têm-se verificado o seu insucesso a longo-prazo. Encontram-se evidências da ineficácia dos modelos de implantes que têm sido desenvolvidos para evitar procedimentos de revisão. O desempenho dos implantes será otimizado se estes foram projetados para controlarem eficazmente o processo de osseointegração. Para se alcançar este objetivo, têm sido propostas a melhoria das técnicas cirúrgicas e dos protocolos de reabilitação, a inovação dos revestimentos (onde se incluem os revestimentos ativos projetados para a libertação controlada de fármacos e/ou outros bio-agentes) e os conceitos de Implante Instrumentado Passivo e Implante Instrumentado Ativo. Contudo, não existem demonstrações conclusivas da eficácia de tais metodologias. O principal objetivo desta tese é propor um novo modelo de conceito para implantes instrumentados para se otimizar a integração osso-implante: o implante instrumentado ativo, energeticamente auto-suficiente, com capacidade de aplicar estímulos biofísicos em tecidos-alvo de forma controlada e personalizada. A necessidade de um novo modelo é demonstrada através da realização de análises de otimalidade ao desempenho dos implantes instrumentados e não-instrumentados. Foram encontrados resultados promissores para o controlo otimizado da osseointegração usando este novo modelo, através da atuação terapêutica baseada na estimulação capacitiva com arquitetura em co-superfície, assim como para fornecer energia elétrica de forma autónoma por mecanismos de transdução baseados em indução eletromagnética usando configurações baseadas na levitação magnética