Modelação numérica em polarização neuronal transcraniana:aplicação clínica à epilepsia

Tese de doutoramento, Engenharia Biomédica e Biofísica, 2009, Universidade de Lisboa, Faculdade de CiênciasA polarização neuronal transcraniana (PN) é uma técnica não-invasiva, indolor, económicae portátil que permite modular a excitabilidade cortical. Recentemente, a investigação e aplicabilidadeda PN para o tratamento de várias doenças tem vindo a crescer. Contudo, de modo aoptimizar as aplicações clínicas deste método, é imprescindível conhecer a distribuição da densidadede corrente no cérebro.Primeiro, usando o Método de Elementos Finitos, mostramos que não existe uma relaçãolinear entre a intensidade de corrente, a área do eléctrodo e a densidade de corrente num pontofixo no cérebro. Em segundo lugar, comparamos a performance de modelos de PN através damedição da focalidade e distribuição da densidade de corrente (à superfície do cérebro e em profundidade)para várias montagens de eléctrodos esponja e eléctrodos EEG colocados no SistemaInternacional 10 ¡ 10.O nosso estudo introduz o uso de eléctrodos EEG na PN. Estes eléctrodos aumentam a focalidadedesta técnica, sobretudo quando um cátodo é usado em combinação com vários ânodos.Adicionalmente, a sua utilização requer menos corrente injectada, facilita a associação dasposições no escalpe com as zonas de representação do cérebro e permite a aplicação da PN concomitantementecom o registo do EEG.Por último, introduzimos um sistema experimental inédito, que combina o registo contínuodo EEG com a PN. Este sistema é mais seguro que os existentes, permitindo uma avaliação detalhadada actividade interictal na epilepsia humana durante a aplicação da PN. Permite tambémuma escolha optimizada da montagem de eléctrodos para diferentes focos epileptogénicos. Estesistema foi testado em dois pacientes com epilepsia focal refractária à terapia farmacológica.Notavelmente, a actividade paroxística interictal diminuiu em todos os casos estudados. Os resultadosencontrados são encorajadores e abrem perspectivas promissoras para o uso desta técnicana terapia da epilepsia humana.Transcranial direct current stimulation (tDCS) is a non invasive, painless, economic andportable technique that has been shown to modulate cortical excitability. Recently, research intDCS and its applications to the treatment of several pathologies have been expanding. However,to optimize the clinical applications of tDCS a reliable estimate of the current density in the brainis of outmost importance.First, using the Finite Element Method, we show that a non-linear relationship exists betweenthe injected current, the electrode area and the current density at a fixed target point in the brain.Second, we investigate the performance of tDCS models by studying the focality and the distributionof the current density (at the surface of the brain and in depth) using sponge and EEGelectrodes in the 10-10 international system coordinates.Our study introduces the use of EEG electrodes in tDCS. These electrodes increase the focalityof this technique, particularly when one cathode and several anodes are used in combination. Inaddition, we show that this montage requires less injected current, can be placed at scalp positionswith known relationship with the underlying cerebral cortex and further allows the use of tDCSand EEG recording concomitantly.We propose the first experimental system that combines continuous recording of the EEGsimultaneously with tDCS. This system improves safety and allows a detailed evaluation of theinterictal events. Furthermore, it permits the optimization of the montages of the electrodes fordifferent locations of the epileptogenic foci. To date, this system was tested in two epilepticpatients and we demonstrate that their interictal activity was reduced in all cases studied. Ourresults are encouraging and open doors for the application of tDCS in human epilepsy therapy

A Computer Tool for 3D Shape Recovery of Fruits

Characterizing a fruit’s mechanical behavior is an important step towards reducing economic losses due to bruising. Several 3D scanning technologies allow to obtain the external geometry of a fruit, but no easily accessible tools exist for the acquisition of the geometry of internal structures such as the core. We propose a low-cost destructive method for tomographic reconstruction of a fruit from scanned slices. A method for overcoming the difficulties in registering the different images is also presented.info:eu-repo/semantics/publishedVersio

Tailoring Bioengineered Scaffolds for Regenerative Medicine

The vision to unravel and develop biological healing mechanisms based on evolving molecular and cellular technologies has led to a worldwide scientific endeavor to establish regenerative medicine. This is a multidisciplinary field that involves basic and preclinical research and development on the repair, replacement, and regrowth or regeneration of cells, tissues, or organs in both diseases (congenital or acquired) and traumas. A total of over 63,000 patients were officially placed on organs’ waiting lists on 31 December 2013 in the European Union (European Commission, 2014). Tissue engineering and regenerative medicine have emerged as promising fields to achieve proper solutions for these concerns. However, we are far from having patient-specific tissue engineering scaffolds that mimic the native tissue regarding both structure and function. The proposed chapter is a qualitative review over the biomaterials, processes, and scaffold designs for tailored bioprinting. Relevant literature on bioengineered scaffolds for regenerative medicine will be updated. It is well known that mechanical properties play significant effects on biologic behavior which highlight the importance of an extensively discussion on tailoring biomechanical properties for bioengineered scaffolds. The following topics will be discussed: scaffold design, biomaterials and scaffolds bioactivity, biofabrication processes, scaffolds biodegradability, and cell viability. Moreover, new insights will be pointed out

How to correctly estimate the electric field in capacitively coupled systems for tissue engineering: a comparative study

Capacitively Coupled (CCoupled) electric fields are used to stimulate cell cultures in Tissue Engineering. Knowing the electric field (E-Field) magnitude in the culture medium is fundamental to establish a relationship between stimulus strength and cellular effects. We analysed eight CCoupled studies and sought to corroborate the reported estimates of the E-Field in the culture medium. First, we reviewed the basic physics underlying CCoupled stimulation and delineated three approaches to estimate the E-field. Using these approaches, we found that the reported values were overestimated in five studies, four of which were based on incorrect assumptions. In all studies, insufficient information was provided to reproduce the setup exactly. Creating electrical models of the experimental setup should improve the accuracy of the E-field estimates and enhance reproducibility. For this purpose, we developed a free open-source tool, the E-field Calculator for CCoupled systems, which is available for download from an internet hosting platform.info:eu-repo/semantics/publishedVersio

Electrical Stimulation Optimization in Bioreactors for Tissue Engineering Applications

We review here the current research status on bioreactors for tissue engineering with cell electrical stimulation. Depending on the cell types, electrical stimulation has distinct objectives: 1) being employed both to mimic and enhance endogenous electricity measured in the natural regeneration of living organisms and 2) to mimic strain working conditions for contractible tissues (for instance muscle and cardiac tissues). Understanding the distinct parameters involved in electrical stimulation is crucial to optimize its application. The results presented in the literature and reviewed here reveal that the application of electrical stimulation can be essential for tissue engineering applications.info:eu-repo/semantics/publishedVersio

Comprehensive Review on Full Bone Regeneration through 3D Printing Approaches

Over the last decades, the number of work accidents associated with bone fractures has increased leading to a growing concern worldwide. Currently, autografts, allografts, and xenografts are used for bone regeneration. However, their application has associated risks. Tissue engineering (TE) has brought solutions to address these problems, through the production of temporary supports, providing mechanical support to the formation of new bone tissue and biocompatible and biodegradable scaffolds, which allow cell adhesion and proliferation to ensure bone formation. The combination of materials and structure with the technique to be used will directly influence their physical and chemical properties and, consequently, their action in contributing to bone regeneration. Thus, the focus of this chapter is to perform an exhaustive literature review and a critical analysis of the state of the art in bone TE and present a proposal of an optimized temporary support geometry for bone regeneration in case of large bone defects. For this, it was listed and identified the best choice of biomaterials, fabrication method, cell type and their culture conditions (static vs. dynamic), and/or the inclusion of growth factors for the repair of large bone defects

Biomechanical Outcomes Related with Gait in Children with Cerebral Palsy Using Ankle-Foot Orthotic - A Systematic Review

Acknowledgments: This research was supported by COMPETE 2020, from Agência Nacional de Inovação (ANI) – Projectos ID&T Empresas em Copromoção, Programas Operacionais POCI and by the Fundação para a Ciência e a Tecnologia (FCT) and Centro2020 through the Project references: UID/Multi/04044/2013; PAMI - ROTEIRO/0328/2013 (Nº 022158) and NEXT.parts - Next- Generation of Advanced Hybrid Parts with the reference n. º 17963.Gait in children with cerebral palsy (CP) is often affected by motor impairments which limit the patient's ability to walk. To improve gait and reduce walking limitations, children with CP need to use ankle foot orthoses. An orthosis is an externally applied device that is designed and fitted to the body to achieve one or more of the following goals: a) Control biomechanical alignment. b) Correct or accommodate deformity, and 3) Protect and support an injury. This systematic review aims to describe research evidence supporting the use of ankle-foot orthoses to improve gait biomechanical outcomes among individuals with CP. Literature search was pursued from PubMed database. Studies were included if (1) they evaluated an outcome measure related with gait using ankle-foot orthotic (AFO) in children (2) considered children with a diagnosis of CP and have a (3) GMFCS classification of I, II or III. Papers were excluded if they evaluated (1) other population besides CP, (2) the use of orthoses other than AFOs and (3) gait analysis procedure was not presented. All the included studies have analyzed spatiotemporal parameters, the step length (m), stride length (m) and cadence (steps/minute) were the most frequently reported. Our findings showed that several studies have investigated the effects of AFOs, all of which have reported positive influences on at least one gait parameter, as well as positive changes in joint kinematics and kinetic in children with CP.info:eu-repo/semantics/publishedVersio

Aerodynamics of a wheelchair sprinter racing at the 100m world record pace by CFD

The aim of this study was to analyze aerodynamics in a racing position of a wheelchair-racing sprinter, at the world record speed. The athlete and wheelchair were scanned at the beginning of the propulsive phase position (hands near the handrims at 12h) for the 3D model acquisition. Numerical simulation was run on Fluent, having as output the pressure, viscosity and total drag force, and respective coefficients of drag at the world record speed in T-52 category. Total drag was 7.56N and coefficient of drag was 1.65. This work helped on getting a deeper insight about the aerodynamic profile of a wheelchair-racing athlete, at a 100m world record speed.info:eu-repo/semantics/publishedVersio

Multifunctional bacterial cellulose-chitosan tape: an innovative substitute for PVC

Synthetic polymers, generically named plastics, are manufactured from non-renewable sources, such as fossil fuels [1]. In 2020, 367 million metric tons of plastic were produced worldwide, and, only in 2018, global plastic waste volume reached 342.6 million metric tons [2,3]. One of the most used plastics is polyvinyl chloride (PVC), which is not environmentally friendly. The goal of this study was to achieve an eco-friendly substitute for PVC tapes while mimicking their properties and applications. In this way, bacterial cellulose (BC) and chitosan (CH) tapes in different concentrations, 1% and 2%, were developed. Mechanical properties, thickness, bonds between BC and CH and degradation tests were assessed in water and under different temperatures. Mechanical testing showed that the combination of the two polymers resulted in better mechanical performances when compared to BC tape (8.52 ± 1.11 MPa); this may be related to the stronger chemical bonds created between the BC and CH. In addition, BC–CH at 1% revealed closer values of strength compared to PVC tapes (703.19 ± 16.18 MPa and 516.92 ± 22.0 MPa, respectively). Moreover, with the present study we were able to conclude that the incorporation of CH increases tape porosity. Interestingly, higher porosities (BC and CH at 2%) resulted in better mechanical properties upon tensile testing (1344 ± 52.87 MPa). Upon contact with water, the BC–CH mixture at 1% proved to be more resistant and not mechanically affected over time, like PCV tape. Thermally, both tapes with CH revealed to be more resistant than the PVC tape. However, the BC–CH tape at 1% was the most stable over time at all temperatures tested. This preliminary study opens new possibilities to the use of these tapes in sport areas, packaging and pharmaceutical or biomedical fields.This research was funded by the Fundação para a Ciência e a Tecnologia FCT/MCTES (PIDDAC) and Centro2020 through the following Projects: UIDB/04044/2020; UIDP/04044/2020; Associate Laboratory ARISE LA/P/0112/2020; PAMI-ROTEIRO/0328/2013 (Nº 022158).info:eu-repo/semantics/publishedVersio