The influence of stem surface in micromobility and cement bone stresses

Cemented hip prostheses have produced excellent clinical results and THR is at that moment one of the most successful surgical techniques, with good success rates. Cemented fixation represents 87% of the total number of replacements according to the Swedish orthopedic register. Therefore, it is important to reduce revisions and understand why revision happens. The purpose of this study was to access the micro mobility and stresses developed in a cemented hip replacement. An in vitro cemented Lubinus SPII stem replacement was performed in synthetic femurs and sectioned. Section 5 was analyzed after fatigue test and was observed to be the most critical in crack incidence. A CAD model of this section was built considering bone and cement boundary geometry. The finite element model was built and the influences of different interface conditions of the cement interfaces (bone and stem) were analyzed. The interface stiffness associated with stresses for interface failure was used to simulate different surface roughness and time after surgery. The surface roughness associated with the interface strength did not present significant influence relatively to cement interface stresses and micro mobility of the stem. The type if interface changes the stress and strain distribution of bone and the most severe factor is friction at the cement/bone interfaces. The cement/bone interface debonding increase the bone strains and suggests pain

Fabrico rápido de implantes ósseos personalizados

Actualmente existem situações clínicas específicas relacionadas com perdas ou correcções ósseas significativas, cuja solução dificilmente poderá ser alcançada com implantes ou próteses disponíveis comercialmente, sendo necessário o recurso a soluções personalizadas (ditas customizadas), isto é, implantes que são concebidos e fabricados em função das especificidades do paciente. Neste sentido, o desenvolvimento de uma nova metodologia que permita o fabrico rápido de implantes ósseos em simultâneo com o acto cirúrgico poderá apresentar vantagens significativas, pois permite ao cirurgião corrigir ou alterar a geometria do implante em função de uma qualquer ocorrência anómala detectada já durante a cirurgia. A abordagem neste trabalho passou pelo desenvolvimento de uma aplicação informática que permitisse integrar numa única plataforma um conjunto de ferramentas como scanner 3D, sistema de fabrico assistido por computador (CAM) e fabrico em máquinas controladas por computador (CNC) para assim fabricar de forma rápida um implante adaptado à anatomia do paciente. O método estabelecido assentou em quatro etapas essenciais: a primeira consiste na captação da geometria do implante, realizada localmente pelo cirurgião e não envolve meios computacionais. A segunda consiste na obtenção do modelo virtual da geometria do implante, realizada a partir do levantamento de forma do modelo obtido na etapa anterior, utilizando um scanner 3D por laser. A terceira etapa consiste na utilização de um sistema CAM para a elaboração do programa de maquinagem do implante. Na quarta e última etapa materializa- se o fabrico do implante numa fresadora CNC. O sistema desenvolvido permitiu integrar recursos e tecnologias cuja utilização exige conhecimentos muito especializados, mas inseridos num ambiente amigável para o utilizador possibilita que estes possam ser utilizados por pessoas não profundamente conhecedoras das tecnologias integradas. A solução implementada revelou-se mais acessível ao nível dos custos de aquisição das tecnologias de suporte e da facilidade de utilização quando comparada com outros processos de fabrico de implantes customizados, nomeadamente os obtidos a partir de informação gerada por tomografia computorizada (TAC)

A life cycle thinking approach applied to novel micromobility vehicle

While the production of cars has high environmental costs, producing and maintaining micromobility vehicles might consume fewer resources. Likewise, replacing the car with active mobility transportation modes reduces noise and air pollution. The Life Cycle Assessment (LCA) methodology contributes to study such environmentally sustainable solutions. We present a "cradle-to-grave" analysis by tracking the activity from the extraction of raw materials until the product's life ends. The goal is to carry out an LCA of a novel micromobility vehicle under a life cycle thinking perspective. The LCA tool - Good to Go? Assessing the Environmental Performance of New Mobility, developed by the International Transport Forum - was used to model the baseline and alternative scenarios. The vehicle’s materials, primary energy sources for battery charging, use of the vehicle as a shared mobility mode, among other factors, were changed to assess the energy use and greenhouse gases (GHG) emissions during the entire life cycle chain. The LCA results at the baseline scenario for the micromobility device, the Ghisallo vehicle, are similar to the values of other micromobility vehicles. Energy consumption (Mega Joule [MJ]) and GHG emissions (grams of equivalent CO2) per vehicle-kilometer are 0.36 [MJ/v-km] and 29 [g CO2 eq/v-km], respectively. For this personal mobility vehicle, it is a conclusion that most GHG emissions are due to production (42% of the total). Air transport from production to sales site increases the impact by 10%. Finally, we present measures to decrease the energy and GHG emissions impact of a micromobility device life cycle.in publicatio

A biomimetic tissue engineering scaffold for repairing the injured spinal cord: proof of concept

Sem resumo disponível.publishe

Multi–layered electrospinning and electrospraying approach: effect of polymeric supplements on chondrocyte suspension

Articular cartilage was expected to be one of the first tissues to be successfully engineered, but replicating the complex fibril architecture and the cellular distribution of the native cartilage has proven difficult. While electrospinning has been widely used to reproduce the depth–dependent fibre architecture in 3D scaffolds, the chondrocyte-controlled distribution remains an unsolved problem. To incorporate cells homogeneously through the depth of scaffolds, a combination of polymer electrospinning and cell seeding is necessary. A multi-layer approach alternating between polymer electrospinning with chondrocyte electrospraying can be a solution. Still, the success of this process is related to the survival rate of the electrosprayed chondrocytes embedded within the electrospun mesh. In this regard, the present study investigated the impact of the multi-layered process and the supplementation of the electrospray chondrocyte suspension with different concentrations of Gelatin and Alginate on the viability of electrosprayed chondrocytes embedded within a Polycaprolactone/Gelatin electrospun mesh and on the mechanical properties of the resulting meshes. The addition of Gelatin in the chondrocyte suspension did not increase significantly (p > 0.05) the percentage of viable electrosprayed chondrocytes (25 %), while 3 wt% Alginate addition led to a significant (p < 0.05) increase in chondrocyte viability (50 %) relative to the case without polymer supplement (15 %). Furthermore, the addition of both polymer supplements increased the mechanical properties of the multi–layer construct. These findings imply that this multi-layered approach can be applied to cartilage TE allowing for automated chondrocyte integration during scaffolds creation.publishe

Femoral revision knee Arthroplasty with Metaphyseal sleeves: the use of a stem is not mandatory of a structural point of view

Purpose Metaphyseal sleeves are an option for patients with severe metaphyseal bony defects requiring TKA revision. Although sleeves are usually used with stems, little is known about the exact contribution/need of the stem for the initial sleeve-bone interface stability, particularly in the femur, if the intramedullary canal is deformed or bowed. It is hypothesised that diaphyseal-stem addition increases the sleeve-femur interface stability and the strain-shielding effect on the metaphyseal femur relatively to the stemless condition. Material and methods Synthetic-femur was used to measure cortex strain behaviour and implant cortex micromotions for three techniques: only femoral-component, stemless-sleeve and stemmed-sleeve. Paired t-tests were performed to evaluate the statistical significance of the difference between mean principal strains and implant-cortex micromotions. Finite-element models were developed to assess the cancellous-bone strain behaviour and sleeve-bone interface micromotions; these models were validated against the measurements. Results Cortex strains are reduced significantly (p<0.05) in 83% of strain gauges on stemmed-sleeve, which compares with 33% in stemless condition. Both techniques presented a cancellous bone strain reduction of 50% at the distal region and an increase of nearly four times at the sleeve proximal region relative to the model only with the femoral component. Both techniques presented sleeve-bone micromotions amplitude below 50-150μm, suitable for bone ingrowth. Conclusions The use of a supplemental diaphyseal-stem potentiates the risk of cortex bone resorption compared with the stemless-sleeve condition; however, the stem is not vital for increasing the initial sleeve-bone stability and has a minor effect on the cancellous-bone strain behaviour. Of a purely structural point view, appears that the use of a diaphyseal-femoral-stem with the metaphyseal sleeve is not mandatory in the revision TKA which is particularly relevant in cases where the use of stems is impracticable.publishe

Prevalence and Predictive Factors of Exclusive Breastfeeding in the First Six Months of Life

info:eu-repo/semantics/publishedVersio

Why are tapes better than wires in knotless rotator cuff repairs? An evaluation of force, pressure and contact area in a tendon bone unit mechanical model

Knotless repairs have demonstrated encouraging performance regarding retear rate reduction, but literature aiming at identifying the specific variables responsible for these results is scarce and conflictive. The purpose of this paper was to evaluate the effect of the material (tape or wire suture) and medial tendon passage (single or double passage) on the contact force, pressure and area at the tendon bone interface in order to identify the key factors responsible for this repairs´ success.info:eu-repo/semantics/publishedVersio

Development of a planar multi-body model of the human knee joint

The aim of this work is to develop a dynamic model for the biological human knee joint. The model is formulated in the framework of multibody systems methodologies, as a system of two bodies, the femur and the tibia. For the purpose of describing the formulation, the relative motion of the tibia with respect to the femur is considered. Due to their higher stiffness compared to that of the articular cartilages, the femur and tibia are considered as rigid bodies. The femur and tibia cartilages are considered to be deformable structures with specific material characteristics. The rotation and gliding motions of the tibia relative to the femur can not be modeled with any conventional kinematic joint, but rather in terms of the action of the knee ligaments and potential contact between the bones. Based on medical imaging techniques, the femur and tibia profiles in the sagittal plane are extracted and used to define the interface geometric conditions for contact. When a contact is detected, a continuous non-linear contact force law is applied which calculates the contact forces developed at the interface as a function of the relative indentation between the two bodies. The four basic cruciate and collateral ligaments present in the knee are also taken into account in the proposed knee joint model, which are modeled as non-linear elastic springs. The forces produced in the ligaments, together with the contact forces, are introduced into the system’s equations of motion as external forces. In addition, an external force is applied on the center of mass of the tibia, in order to actuate the system mimicking a normal gait motion. Finally, numerical results obtained from computational simulations are used to address the assumptions and procedures adopted in this study.Fundação para a Ciência e a Tecnologia (FCT

Microfabrication of a biomimetic arcade-like electrospun scaffold for cartilage tissue engineering applications

Designing and fabricating hierarchical geometries for tissue engineering (TE) applications is the major challenge and also the biggest opportunity of regenerative medicine in recent years, being the in vitro recreation of the arcade-like cartilaginous tissue one of the most critical examples due to the current inefficient standard medical procedures and the lack of fabrication techniques capable of building scaffolds with the required architecture in a cost and time effective way. Taking this into account, we suggest a feasible and accurate methodology that uses a sequential adaptation of an electrospinning-electrospraying set up to construct a system comprising both fibres and sacrificial microparticles. Polycaprolactone (PCL) and polyethylene glycol were respectively used as bulk and sacrificial biomaterials, leading to a bi-layered PCL scaffold which presented not only a depth-dependent fibre orientation similar to natural cartilage, but also mechanical features and porosity compatible with cartilage TE approaches. In fact, cell viability studies confirmed the biocompatibility of the scaffold and its ability to guarantee suitable cell adhesion, proliferation and migration throughout the 3D anisotropic fibrous network. Additionally, likewise the natural anisotropic cartilage, the PCL scaffold was capable of inducing oriented cell-material interactions since the morphology, alignment and density of the chondrocytes changed relatively to the specific topographic cues of each electrospun layer.publishe