Browsing by Author "Nogueira, Elisabete"
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- Acoustic Emission Studies in Hip Arthroplasty – Peak Stress Impact In Vitro Cemented ProsthesisPublication . Gueiral, Nuno; Nogueira, ElisabeteEngineering has a very important role in the development of non-destructive monitoring of orthopaedical systems allowing the evaluation of its integrity. Sir John Charnley revolutionized the field of joint arthroplasty in the 1960s with the development of the total hip replacement. He replaced the diseased hip joint with a steel femoral component and a plastic acetabular socket cup combination, both fixed into the bone using a self-curing acrylic cement, polymethylmethacrylate (PMMA) (Browne et al, 2005). That way, he has restored some of the most problematic joints in the human body. The placement of the metal implant in the channel open in the femoral bone without using cement or by mechanical attack, called a non cemented arthroplasty, came into use in an effort to solve the problem.
- Diffusion characteristics of ethylene glycol in skeletal musclePublication . Oliveira, Luís; Carvalho, Maria; Nogueira, Elisabete; Tuchin, ValeryPart of the optical clearing study in biological tissues concerns the determination of the diffusion characteristics of water and optical clearing agents in the subject tissue. Such information is sufficient to characterize the time dependence of the optical clearing mechanisms—tissue dehydration and refractive index (RI) matching. We have used a simple method based on collimated optical transmittance measurements made from muscle samples under treatment with aqueous solutions containing different concentrations of ethylene glycol (EG), to determine the diffusion time values of water and EG in skeletal muscle. By representing the estimated mean diffusion time values from each treatment as a function of agent concentration in solution, we could identify the real diffusion times for water and agent. These values allowed for the calculation of the correspondent diffusion coefficients for those fluids. With these results, we have demonstrated that the dehydration mechanism is the one that dominates optical clearing in the first minute of treatment, while the RI matching takes over the optical clearing operations after that and remains for a longer time of treatment up to about 10 min, as we could see for EG and thin tissue samples of 0.5 mm.
- Glucose diffusion in colorectal mucosa—a comparative study between normal and cancer tissuesPublication . Carvalho, Sónia; Gueiral, Nuno; Nogueira, Elisabete; Henrique, Rui; Oliveira, Luís; Tuchin, ValeryColorectal carcinoma is a major health concern worldwide and its high incidence and mortality require accurate screening methods. Following endoscopic examination, polyps must be removed for histopathological characterization. Aiming to contribute to the improvement of current endoscopy methods of colorectal carcinoma screening or even for future development of laser treatment procedures, we studied the diffusion properties of glucose and water in colorectal healthy and pathological mucosa. These parameters characterize the tissue dehydration and the refractive index matching mechanisms of optical clearing (OC). We used ex vivo tissues to measure the collimated transmittance spectra and thickness during treatments with OC solutions containing glucose in different concentrations. These time dependencies allowed for estimating the diffusion time and diffusion coefficient values of glucose and water in both types of tissues. The measured diffusion times for glucose in healthy and pathological mucosa samples were 299.2+/-4.7 s and 320.6+/-10.6 s for 40% and 35% glucose concentrations, respectively. Such a difference indicates a slower glucose diffusion in cancer tissues, which originate from their ability to trap far more glucose than healthy tissues. We have also found a higher free water content in cancerous tissue that is estimated as 64.4% instead of 59.4% for healthy mucosa.
- O impacto da pandemia COVID-19 na aprendizagem de estudantes de Engenharia: Taxa de aprovação em 6 anos consecutivos: Pré e pós pandemiaPublication . Gueiral, Nuno; Nogueira, Elisabete; Coelho, FátimaEste artigo analisa o impacto da pandemia COVID-19 nos estudantes que terminaram o ensino secundário (onde a frequência foi maioritariamente online) e ingressaram em cursos de engenharia presencial no ensino superior. Os resultados deste estudo poderão ser úteis para entender como a pandemia afetou o desempenho académico dos estudantes de engenharia e identificar estratégias para melhorar o ensino em ambientes STEM (Science, Technology, Engineering and Mathematics) nos pós pandemia.
- Optical clearing mechanisms characterization in musclePublication . Oliveira, Luís; Carvalho, M. Inês; Nogueira, Elisabete; Tuchin, Valery V.Optical immersion clearing is a technique that has been widely studied for more than two decades and that is used to originate a temporary transparency effect in biological tissues. If applied in cooperation with clinical methods it provides optimization of diagnosis and treatment procedures. This technique turns biological tissues more transparent through two main mechanisms — tissue dehydration and refractive index (RI) matching between tissue components. Such matching is obtained by partial replacement of interstitial water by a biocompatible agent that presents higher RI and it can be completely reversible by natural rehydration in vivo or by assisted rehydration in ex vivo tissues. Experimental data to characterize and discriminate between the two mechanisms and to find new ones are necessary. Using a simple method, based on collimated transmittance and thickness measurements made from muscle samples under treatment, we have estimated the diffusion properties of glucose, ethylene glycol (EG) and water that were used to perform such characterization and discrimination. Comparing these properties with data from literature that characterize their diffusion in water we have observed that muscle cell membrane permeability limits agent and water diffusion in the muscle. The same experimental data has allowed to calculate the optical clearing (OC) efficiency and make an interpretation of the internal changes that occurred in muscle during the treatments. The same methodology can now be used to perform similar studies with other agents and in other tissues in order to solve engineering problems at design of inexpensive and robust technologies for a considerable improvement of optical tomographic techniques with better contrast and in-depth imaging.
- Optical measurements of rat muscle samples under treatment with ethylene glycol and glucosePublication . Oliveira, Luís; Carvalho, Maria Inês; Nogueira, Elisabete; Tuchin, Valery V.With the objective to study the variation of optical properties of rat muscle during optical clearing, we have performed a set of optical measurements from that kind of tissue. The measurements performed were total transmittance, collimated transmittance, specular reflectance and total reflectance. This set of measurements is sufficient to determine diffuse reflectance and absorbance of the sample, also necessary to estimate the optical properties. All the performed measurements and calculated quantities will be used later in inverse Monte Carlo (IMC) simulations to determine the evolution of the optical properties of muscle during treatments with ethylene glycol and glucose. The results obtained with the measurements already provide some information about the optical clearing treatments applied to the muscle and translate the mechanisms of turning the tissue more transparent and sequence of regimes of optical clearing.
- Skeletal muscle dispersion (400-1000 nm) and kinetics at optical clearingPublication . Oliveira, Luís; Carvalho, Maria Inês; Nogueira, Elisabete; Tuchin, ValerySkeletal muscle dispersion and optical clearing (OC) kinetics were studied experimentally to prove the existence of the refractive index (RI) matching mechanism of OC. Sample thickness and collimated transmittance spectra were measured during treatments with glucose (40%) and ethylene glycol (EG; 99%) solutions and used to obtain the time dependence of the RI of tissue fluids based on the proposed theoretical model. Calculated results demonstrated an increase of RI of tissue fluids and consequently proved the occurrence of the RI matching mechanism. The RI increase was observed for the wavelength range between 400 and 1000 nm and for the 2 probing molecules explored. We found that for 30 min treatment with 40% glucose and 99% EG, RI of sarcoplasm plus interstitial fluid was increased at 800 nm from 1.328 to 1.348 and from 1.328 to 1.369, respectively.
- Software development for estimation of optical clearing agent’s diffusion coefficients in biological tissuesPublication . Peixoto, Pedro; Oliveira, Luís; Carvalho, Maria; Nogueira, Elisabete; Tuchin, Valery V.The study of chemical diffusion in biological tissues is a research field of high importance and with application in many clinical, research and industrial areas. The evaluation of diffusion and viscosity properties of chemicals in tissues is necessary to characterize treatments or inclusion of preservatives in tissues or organs for low temperature conservation. Recently, we have demonstrated experimentally that the diffusion properties and dynamic viscosity of sugars and alcohols can be evaluated from optical measurements. Our studies were performed in skeletal muscle, but our results have revealed that the same methodology can be used with other tissues and different chemicals. Considering the significant number of studies that can be made with this method, it becomes necessary to turn data processing and calculation easier. With this objective, we have developed a software application that integrates all processing and calculations, turning the researcher work easier and faster. Using the same experimental data that previously was used to estimate the diffusion and viscosity of glucose in skeletal muscle, we have repeated the calculations with the new application. Comparing between the results obtained with the new application and with previous independent routines we have demonstrated great similarity and consequently validated the application. This new tool is now available to be used in similar research to obtain the diffusion properties of other chemicals in different tissues or organs.
- Total Hip Arthroplasty modelling and load simulation in COMSOL multiphysicsPublication . Gueiral, Nuno; Nogueira, ElisabeteIn total hip arthroplasty (THA), has been over time, an exponential growth of studies with Finite Element Method (FEM) computational simulation in order to obtain the prosthesis with a longer life duration, however just a few in COMSOL Multiphysics software. The main goal of this study was to perform stress and strain studies under different load conditions for the titanium and cobalt-chromium alloys in cementless prostheses. In software COMSOL Multiphysics, 3D models of a femur and a Lubinus SPII implant with two different alloys, were tested. Two COMSOL studies were carried out, one stationary and the other dynamic (time-dependent) for both material’s prostheses. In a stationary study for walking activity, the titanium alloy implant showed an equivalent von Mises stress maximum level of 0.9 × 108 Pa at the contact between the implant and the bone, having been found a similar value by other investigators ( Prasad, Karthika, et al. “Metallic biomaterials: current challenges and opportunities.“ Materials 10.8 (2017): 884.). In the Co-Cr alloy prosthesis, the equivalent von Mises stress for walking activity was like titanium alloy. The shear stress and normal stress of the two prostheses were compared. In the dynamic study for climbing stair activity the equivalent von Mises stress was greater 7.5 times than in walking activity for Co-Cr alloy implant. The maximum stress (stationary and dynamic) of the titanium alloy implant is slightly higher than the Co-Cr alloy implant, which indicates that Co-Cr prostheses react better when subjected to loads.
- Wavelength dependence of the refractive index of human colorectal tissues: comparison between healthy mucosa and cancerPublication . Carvalho, Sónia; Henrique, Rui; Gueiral, Nuno; Nogueira, Elisabete; Oliveira, Luís; Tuchin, ValeryBiological tissues have individual optical properties that may be used as an identity card. The refractive index in particular, which can be measured directly, is very significant for the improvement or development of optical technologies in clinical practice. With the objective of verifying if healthy and pathological tissues can be discriminated from refractive index measurements, we have studied human colorectal mucosa. By using the total internal reflection method to measure the refractive index from healthy and pathological colorectal mucosa tissues at different wavelengths, it was possible to calculate the dispersion curves for both types of tissues. It was observed a decaying refractive index with wavelength, both for healthy and pathological tissues, which were fitted with curves described by Cornu’s equation for wavelengths between ultraviolet and near-infrared range. Experimental results show higher refractive index values for the pathological mucosa for all wavelengths. By performing measurements at wavelengths near 850 nm, we have detected non-monotonic behavior for the refractive index of both healthy and pathological tissues. Such abnormal wavelength dependence is evidence of lipids in both tissues. The acquired experimental data demonstrated that it is possible to discriminate between healthy and pathological tissues from refractive index measurements. Similar studies can be made for different biological tissues. By using lasers with different wavelengths it might be possible to identify other tissue components.