Advanced Materials Forum VI

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Authors: I. Aleixo, A.C. Vale, M. Lúcio, P.M. Amaral, L.G. Rosa, J. Caetano-Lopes, A. Rodrigues, H. Canhão, J.E. Fonseca, M. Fatima Vaz
Abstract: We addressed the importance of defining a mechanical testing methodology for the compression of human trabecular bone specimens. In fact, currently there are several protocols to test trabecular bone, but a single, standard and validate method has not been accepted yet. In our work, human femoral epiphyses collected from patients with osteoporosis (fragility fractures) and hip osteoarthritis, submitted to total hip replacement surgery, were used. The aims of our work were to develop a mechanical testing methodology for the compression of trabecular bone specimens taking into account the optimization of bone extrinsic and intrinsic variables, in order to establish a patient bone sample database with clinical, structural and mechanical information. Extrinsic variables, such as the effect of specimen preparation, with particular focus on the dimensions of test specimens, and others associated with the compression test, such as the method employed to determine specimen deformation, and hence strain, were evaluated. Also, a new device used to withhold the specimens was developed and tested by the present authors. Although each specimen showed a unique behaviour, even when comparing compression curves between patients from the same disease group, implicating additional complexity and difficulty in the data analysis, the authors managed to assemble the results in two groups related with a possible difference in the deformation mechanisms occurring after yielding.
Authors: Bruno Henriques, Filipe Silva, Delfim Soares
Abstract: The purpose of this work was to perform a chemical and mechanical characterization of a preoxidized CoCrMo alumina blasted surface. This is a commonly performed surface treatment used in metal-porcelain systems for dental restorations to remove oxides formed during preoxidation heat treatment from the metal’s surface. CoCrMo dental alloy’s specimens produced by lost wax process were examined in terms of chemical composition using X-Ray fluorescence spectroscopy (XRF), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS); in terms of mechanical characteristics through the means of a microhardness test and in terms of surface roughness using a profilometer. It was investigated the chemical composition of various surface conditions: non-preoxidized, preoxidized, ground oxidized surface and sandblasted oxidized surface. After alumina blasting, the oxides level on metal’s surface remained high. Alumina blasting treatment (Ø110 µm) produced an 84% increase of CoCrMo surface hardening and an increase in surface roughness (Ra=0.58 µm). It was found alumina contaminants on the metal’s surface. Therefore, it was concluded that alumina blasting do not entirely removes the oxide layer formed during preoxidation heat treatment. It produced a chemical and mechanical surface modification that can influence the metal-ceramic bond strength.
Authors: Barbara Szaraniec
Abstract: In this work prototypes of internal fixation plates of acetabular fractures were developed and manufactured. The injection moulding was used to produce polymeric and composite samples. The plates and paddle-like beam samples made of polylactide and the polymer composite modified with 7 wt. % of tricalcium phosphate were produced. The samples were incubated in physiological fluids for 8 months. During the in vitro tests their durability and mechanical properties were determined. In comparison to the pure polylactide the addition of TCP accelerated degradation process. The degradation of the composite started after about 100 days of incubation, whereas the initial polymer began to degrade about 50 days later. The obtained biodegradable plates revealed sufficient mechanical properties for internal fixation of acetabular fractures for bone joining.
Authors: Pedro Teixeira, António Pontes, Elsa Henriques
Abstract: This research work intended to study the effect of the main injection moulding parameters in the final properties of biopolymers mouldings. An experimental procedure was carried out in which four biopolymers containing different composition percentages of poly-lactic acid (PLA) and plasticized starch (PLS) were compared with polypropylene (PP). For each material the effect of the processing conditions (mould temperature, injection temperature and holding pressure) on the final properties was discussed and the possibility of using biopolymers as a substitute of PP in household utility products was evaluated.
Authors: Bogdan Neagu, Eugen R. Neagu, Rui Igreja, C.J. Dias
Abstract: Information about the spatial distribution of the electric field can be obtained by measuring the electrode impedance as a function of the diameter of the electrolyte surrounding the electrode. The non-uniform distribution of the electric field around the electrode is supported by the variation of the geometry factor (GF) with the electrical conductivity and geometry of the volume conductor. A comparison of the values obtained for the GF from experimental data, from model calculations and simulations help to understand the non-uniform distribution of the electric field. The GF calculated from four-electrode-measurements is significantly higher. GF should be used with caution in calculations of the deep brain stimulation (DBS) electrode impedance.
Authors: Rui R. Costa, Artur J. Ribeiro, José C. Rodríguez-Cabello, João F. Mano
Abstract: In the present work, chitosan (CHI) and elastin-like recombinamers (ELRs) were used to conceive nanostructured thin films driven by sequential electrostatic layer-by-layer (LbL), a simple and versatile technique that discards the use of harmful reagents. Two similar ELRs were engineered to contain negatively charged aminoacids and organized and a single monoblock or a triblock. The buildup of the films was monitored in real time using a quartz-crystal microbalance with dissipation monitoring (QCM-D). Wettability transitions were observed from a moderate hydrophobic surface to an extremely wettable upon increasing the temperature to 50 °C, accompanied by topography changes at the nanoscale as assessed by atomic force microscopy (AFM). Furthermore, the dependence on time for the surface molecular rearrangement was studied for the films with each ELR. The potential of this technology may stimulate the development of devices and biomaterials for biomedical applications in the near future, such as surfaces with tunable and patterned cell adhesion, while the use of ELRs will allow developing polypeptides with biological significance.
Authors: Ewa Stodolak-Zych, Magdalena Szumera, Marta Blazewicz
Abstract: Bone defect is one of the most important problem in orthopaedic therapy in which application of a biomaterial filling is necessary. Such material should be biocompatible, osteoconductive and porous as well as bioactive and compatible with the bone tissue. Subject of the work was investigations on nanocomposite membrane materials which consisted on synthetic polymer – poly-e-caprolactone (PCL) matrix and ceramic nanoparticles; tricalcium phosphate (TCP) and silica (SiO2) as a nano-filler. The nanocomposite membrane materials were produced by two-step dispersion of the nanoparticles in the biopolymer matrix. Characteristic of nanoparticles were made using transmission electron microscope (TEM), distribution of nanoparticles size (DLS) and specific surface area (BET). The morphology of nanocomposites and homogenous distribution of nanoadditives were made using scanning electron microscope with EDS analysis. Introduction of the nanofillers into the polymer matrix was monitored by thermal analysis method (TG-DCS). It was shown that the TCP nanoparticles affected stronger pore size and distribution but also the polymer structure (crystallity, physicochemical properties of the surface). Treatment of the nanocomposite samples in the simulated body fluid (SBF) induced some changes on the surface of the material containing bioactive ceramic nanoparticles. The results of the tests with SBF showed that the material is able to produce apatite structure on its surface (EDS analysis)
Authors: Constancio González-Obeso, Wen Long Song, Miguel A. Rodríguez-Pérez, João F. Mano
Abstract: Biodegradable and biocompatible materials have gained increased attentions because of their applications in biomedicine and tissue engineering. Among them, poly(3-hydroxybutyrate) (PHB), a natural origin polymer, has been employed in biomedical applications as a suitable substitute of synthetic polymers for preparing scaffolds and other devices. In this context it is relevant to understand the interactions between the cells and PHB surfaces, which are governed by aspects such as surface topography and chemical composition. Both, surface topography and chemistry determine surface wettability. The aim of this work is to process PHB surfaces exhibiting extreme wettablility properties, ranging from superhydrophobic (surface contact angle higher than 150º) to superhydrophilic (surface contact angle lower than 5º). A simple phase inversion method was used to fabricate surperhydrophobic PHB surface. Chloroform was used as solvent, and a mixture of water and ethanol as the coagulation bath. The water contact angle was found to be 154.3±2.9º. Furthermore the surface was treated by argon plasma for different times, permitting the control of wettability of the PHB surface from the superhydrophobic to superhydrophilic regime.
Authors: Marcia Adriana Tomaz Duarte, Larissa Coppini, C. Lucchesi, Marcelo Macedo, Eliana Aparecida De Rezende Duek
Abstract: The use of bioabsorbable polymers in biomedical application has increased greatly in recent years due to their good compatibility and bio-reabsorption. To obtain a polymeric material suitable for medical applications, the obtention and characterization of copolymer poly (L-co-DL lactic acid) (PLDLA) with the addition of poly (caprolactone triol) (PCL-T) was studied. PLDLA/PCL-T membranes were prepared by solvent casting in the 100/0, 90/10 and 70/30 (w/w) compositions. The membranes were characterized by Atomic Force Microscopy (AFM), Cellular Adhesion and Energy Dispersed Spectroscopy (EDS). Using MFA it was observed that an addition of PCL-T contributes to rough morphology and greater porosity. Increased cell adhesion on 90/10 and 70/30 membranes compared to 100/0 composition and controls was observed. From these results, it was observed that PCL-T improved cellular adhesion of the PLDLA membrane when compared to membranes without PCL-T. The PLDLA/PCL-T membrane is indicated for use in medical devices which do not require long implantation time, such as support for cell culture, dressings for skin ulceration and guided regeneration in periodontics.

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