Abílio P. Silva

Bioactive polymeric-ceramic hybrid 3D scaffold for application in bone tissue regeneration.

The regeneration of large bone defects remains a challenging scenario from a therapeutic point of view. In fact, the currently available bone substitutes are often limited by poor tissue integration and severe host inflammatory responses, which eventually lead to surgical removal. In an attempt to address these issues, herein we evaluated the importance of alginate incorporation in the production of improved and tunable β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) three-dimensional (3D) porous scaffolds to be used as temporary templates for bone regeneration. Different bioceramic combinations were tested in order to investigate optimal scaffold architectures. Additionally, 3D β-TCP/HA vacuum-coated with alginate, presented improved compressive strength, fracture toughness and Youngs modulus, to values similar to those of native bone. The hybrid 3D polymeric-bioceramic scaffolds also supported osteoblast adhesion, maturation and proliferation, as demonstrated by fluorescence microscopy. To the best of our knowledge this is the first time that a 3D scaffold produced with this combination of biomaterials is described. Altogether, our results emphasize that this hybrid scaffold presents promising characteristics for its future application in bone regeneration.

Oxide Inclusions in Steel Welds of Car Body

The goal of this research is to choose the proper method of car body welding. Properties of weld metal deposits depend on many conditions. First of all, this paper attempts to study the role of oxide inclusion sites on the transformation of austenite to acicular ferrite in steel weld metal deposits and their toughness. Safety and exploitation conditions of welded steel structure depend on many factors. The most significant of those factors are connected with materials, welding technology, state of stress and temperature. Because of that a good selection of steel and welding method is crucial to obtain proper steel structure. Car body elements of higher durability are made of low carbon and low alloy steel, very often with small amount of carbon and the amount of alloy elements such as Ni, Mn, Mo, Cr and V in low alloy steel and their welds. In the terms of the kind of steel it is used a proper welding method and adequate filler materials. In the present paper the influence of Mn, Ni, Mo, in WMD on the behaviour of steel structure for low temperature service was tested.

Mechanical Characterization of Composites with Embedded Optical Fibers

The purpose of this investigation is to evaluate quantitatively and comparatively the effect of embedding optical fibers (OF) on the mechanical behavior of a carbon fiber-epoxy composite in order to verify whether their presence can possibly degrade the mechanical performance of the host material. The existing literature on this subject is not conclusive about the nature and intensity of this effect. Adding more reliable data to our systematic study contributes to this discussion favoring the conclusion about a harmful influence as a consequence of optical fiber embedment. Three kinds of mechanical tests have been performed in this work: impact tests, static flexural tests, and fatigue tests. The results of some experiments point to a possible detrimental influence related to the presence of the OF, being it different in nature and intensity for each of these tests. The mechanical behavior in static loading conditions seems to be not significantly affected as a consequence of the presence of the OF, while that in impact and fatigue tests are strongly affected, even though this influence being physically distinct from each other. Based on these results, some discussion is made about the possible failure mechanisms that can explain the detected differences.

Hygrothermal Effect on the Impact Response of Carbon Composites with Epoxy Resin Enhanced by Nanoclays

This paper presents the results of the hygrothermal effect on the impact response of carbon/epoxy composites and the benefits gained from doping the epoxy resin with nanoclays previously subjected to a silane treatment appropriate for the resin. The nanoclay reinforcement increased the maximum load and the elastic recovery of the composites. The thermal degradation caused by exposure to 60°C for 10 days was insignificant, while the immersion in water at 60°C for 30 days led to a continuous reduction in the maximum load and the elastic recovery. Multiple impacts resulted in a continuous and nearly linear degradation of the impact response both of dry and environmentally assisted specimens.

MPT Influence on the Rheological Behaviour of Self-Flow Refractory Castables

The success of a refractory castable is largely due to the quality of its properties and ease of application. Self-flow refractory castables (SFRC), with high flowability index (>130%), can be easily accommodated in a mould without the application of external energy, being ideal for the manufacture of monolithic linings. SFRC castables without cement require a matrix of very fine particles, which guarantees improved rheological behaviour and performs the role of the binder in the absence of the refractory cement. The presence of the aggregate (coarse particles) hinders the flowability index, but improves the castable mechanical strength and reduces firing shrinkage, and also contributes to the reduction of the castable costs. The control of the maximum paste thickness (MPT) allows the reduction of the coarse particles interference, minimizing the number of contact points among the grains and avoiding the formation of an aggregate skeleton that impairs the flowability of the mixture. In the present work, 100% alumina SFRCs without cement were produced with a fixed matrix of fine particles, whose particle size distribution was optimized using statistical techniques (mixtures design and triangular response surfaces). Different aggregate particle size distributions were used, with several MPT values, with the objective of evaluating which was the mean distance that maximized the flowability index, simultaneously ensuring good mechanical strength for the refractory castable. Ensuring a minimum surface area of 2.22m2/g, the mixtures reach the self-flow turning point with a minimum water content and the maximum flowability is obtained for an aggregate particle size distribution modulus of q=0.22, and consequently an optimized MPT value. SFRC with high mechanical strength (>60MPa) were obtained.

Particle Distribution Design in a Self-Flow Alumina Refractory Castable without Cement

A self-flow refractory castable (SFRC) without cement requires a matrix of fine particles and a broad size distribution of coarse particles (aggregate). The matrix ensures the rheological behaviour and performs the binding role of the absent refractory cement. The presence of the aggregate coarse particles hinders the flowability index (FI), but improves the castable mechanical strength and reduces firing shrinkage. A new methodology of SFRC particle distribution design was developed, using response surface statistical modelling and commercial alumina powders (reactive and tabular). First, the composition of the fine matrix was optimised, seeking minimum water content and maximum IF. To this matrix, various aggregate distributions, combining six tabular alumina size fractions and with different Andreasen distribution modulus, q, between 0.18 to 0.28, were added, to identify the composition with maximum FI. The results obtained show that a minimum specific surface area (SSA) of 2.22m2/g is necessary to reach the self-flow turning point, after which the largest FI requires the maximisation of the aggregate maximum paste thickness (MPT), corresponding to a distribution with q=0.22. The optimised castable composition presents high mechanical strength (>60MPa) and low shrinkage.

Design of the Particle Size Composition of an Alumina Powder Matrix for Maximum Flowability and Minimum Water Content

In this work, commercial alumina fine powders were used as raw materials, namely two tabular alumina fractions (–500 mesh and –230 mesh) and a reactive alumina. Statistical modelling and the Response Surface Methodology (Statistica, Mixtures Designs and Triangular Surfaces module) were applied to three-component mixtures and used to calculate the various property-composition surfaces. To that aim, the various mixtures were prepared, cast, dried, fired and characterised. The particle size distribution modulus, q, was determined for all mixtures using the software LISA. The various response surfaces were then combined, so that the water content in the mixture could be minimised and the matrix flowability maximised. The properties of the resulting test-bricks (linear shrinkage, mechanical strength, apparent density and porosity) were also modelled and response surfaces were obtained. Combined results enabled the definition of an optimised particle size composition range, which guarantees the presence of a low water flow-bed that enables the aggregate self-flow.

3D scaffolds coated with nanofibers displaying bactericidal activity for bone tissue applications

ABSTRACT Bone-limited capacity to fully repair large defects requires the development of new implants. In this context, new approaches have been used to promote bone regeneration and also to avoid the side effects associated with the therapeutics currently used in the clinic. Herein, 3D tricalcium phosphate/alginic acid scaffolds were produced and then coated with an electrospun mesh loaded with two different antibacterial agents, silver nanoparticles, and salicylic acid. The obtained results showed that the produced scaffolds have suitable mechanical properties, swelling, biodegradation, biomineralization activity, enhanced cellular adhesion/proliferation and bactericidal activity, and features essential for bone regeneration. GRAPHICAL ABSTRACT

Influence of Surface Area on the Flowability Behaviour of Self-Flow Refractory Castables

Alumina, with high melting point (2050°C), high hardness and mechanical strength, and excellent abrasion resistance, is one of the most common raw materials used in self-flow refractory castables (SFRC) for monolithic linings and is commercially available in various fine to coarse size classes. However, the performance of the refractory lining depends not only on the properties of its ingredients but also on its easy installation (good flowability). The aim of this work was to evaluate the relationship between the flowability index (FI) of fresh castable and the specific surface area (SSA) of its particles, which is mostly determined by the finer particles content. The results obtained showed that, by controlling the proportion between matrix and aggregate, it is possible to control the SSA of the refractory castable and find a mathematical relationship between the specific surface area and the minimum flowability index required to obtain a self-flow refractory castable. It is, thus, possible to optimize the refractory castable size composition and obtain an estimate for FI as a function of SSA. Using a minimum 45 wt.% matrix content in the castable mixture, a SSA value above 2.215 m2/g is obtained, which leads to FI ≥ 80%, the recommended value for self-flow.

Characterization of the mechanical and biological properties of a new alumina scaffold

Purpose In this work, an alumina scaffold was produced through a new method to be used in a near future as a bone substitute. Methods In vitro and in vivo studies were performed in order to characterize the mechanical and biological properties of the scaffold. Results The results obtained showed that this scaffold has high mechanical resistance and a porous surface that allows human osteoblast cells to adhere and proliferate. The in vivo studies revealed no systemic reaction. Conclusions The alumina scaffold produced herein has the mechanical and biological properties that are compatible with its application in bone therapy.