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  • 1
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In this study hydroxyapatite plasma-sprayed Ti-6Al-4V was characterized by X-ray diffraction (XRD) after being cyclically loaded, while immersed in two different testing environments: Hank's balanced salt solution (HBSS) and an isotonic saline solution (0.15 m NaCl). An original method was developed to test these systems under cyclic bending, while immersed in the testing solution. The crystallinity of the coating was calculated, before and after testing. Crystallinity changes were related to coating dissolution rates, measured by atomic absorption spectroscopy (AAS) and by a photocolourimetric method using ascorbic acid. Structural changes induced either by the plasma-spraying procedure or due to corrosion-fatigue tests, namely a preferential dissolution of the coating's amorphous phase, were also found in X-ray diffraction patterns. Long-term immersion tests, without any applied load, were carried out for assessing cyclic loading effects. An immersion for 2 years in static conditions was found to be equivalent to a cyclic test of 27.8 h in the same solution, as measured by the changes on the coating structure and by the amount of coating material lost to the solution.
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This work describes the influence of surface pretreatments over the nucleation and growth of an apatite layer, formed by a biomimetic process, on which a bioactive glass is used as a precursor of the calcium-phosphate (Ca-P) formation on the materials surface. SEVA-C, a corn starch-based biodegradable blend, was used as substrate. The surfaces were pretreated during various periods by: (i) physical methods, namely ultraviolet radiation (u.v.), and over exposure to ethylene oxide sterilization (EtO); and (ii) chemical methods, namely potassium hydroxide (KOH) and acetic anhydride (CH3CO)2 etchings. The surface modifications, performed before the production of the biomimetic coatings, resulted in a faster formation of Ca-P nuclei during the first stages of SBF immersion, particularly in the case of the KOH etching. In this case, it was possible to observe a decrease in the average surface roughness, as measured by laser profilometry, and an increase of the hydrophilicity of the material, which was evident from a clear increment in the water-uptake ability and quantified by contact angle measurements. With this treatment it was possible not only to reduce the induction period for the formation of a well defined and dense apatite-like layer, as observed by scanning electron microscopy (SEM), but also to improve the adhesion of the Ca-P layer to the substrate, as confirmed by the adhesion strength tests. For all the studied pre-treatments, the composition of the films, analyzed by energy dispersive spectroscopy (EDS) and identified by thin-film X-ray diffraction (TF-XRD), seems to be very similar to that of human bone apatites.
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  • 3
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Phosphate- and silicate-based glasses were added to hydroxyapatite in order to improve its mechanical properties and to fabricate composites with different degrees of bioactivity. A strong chemical bonding was obtained between hydroxyapatite and the phosphate-based glasses leading to samples approaching theoretical density, according to density measurements and scanning electron microscopy. Bioglass® additions led to the formation of a complex calcium phosphate silicate which hampered the reinforcement process. The fracture toughness of the hydroxyapatite-glass composites was shown to be within the 1.1–1.2 MPam1/2 range, which is double that determined for sintered hydroxyapatite. A 2 μm thick apatite layer was observed on the surface of the hydroxyapatite-glass composites after 48 h immersion in a simulated human blood plasma, whereas only a few apatite crystals were detected on sintered hydroxyapatite after 7 days immersion. From the results obtained we anticipate that the composites might show a higher rate of bone bonding, leading to enhanced bioactivity.
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  • 4
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In this work, a bioactive glass is used as a percusor of calcium-phosphate (Ca-P) film deposition onto several polymer-based materials. Both bioinert (high molecular weight polyethylene, HMWPE), and biodegradable (corn starch-based blends, SEVA-C) polymers, unreinforced or reinforced with hydroxylapatite (HA), were coated by the very simple proposed route. Also polyurethane (PU) foams, with an open-cell structure, were mineralized by the proposed method. In fact, it was possible to induce the growth of the Ca-P films not only at the surface, but also in the bulk of the PU foam. These cellular materials are intended for cancellous bone replacement applications. The morphology of the formed films was strongly dependent on the used substrate, its polar character, and on the presence of HA in its composition, as observed by SEM. Nevertheless, a well defined needly like structure was observed in all samples at high magnifications. The Ca:P ratios of the films were between 1.5 and 1.7, i.e. in the range of tricalcium phosphate-hydroxylapatite. Raman spectroscopy and thin-film x-ray diffraction (XRD) evidenced the formation of mostly amorphous calcium-phosphate films. After scraping the coating from the polymer surface and heat-treating the resulting powder at 1000°C for 1 h, HA and β-tricalcium phosphate (TCP) typical peaks were found on XRD patterns.
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  • 5
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The development of new biodegradable hydrogels, based on corn starch/cellulose acetate blends, produced by free-radical polymerization with methyl methacrylate monomer (MMA) and/or an acrylic acid monomer (AA), is reported. The polymerization was initiated by a redox system consisting of a benzoyl peroxide and 4-dimethlyaminobenzyl alcohol at low temperature. These hydrogels may constitute an alternative to the materials currently used as bone cements or drug-delivery carriers. Swelling studies were carried out, as a function of pH and temperature, in buffered solutions. The xerogels were further characterized by Fourier transform–infrared spectroscopy. Tensile and compression tests, and dynamic mechanical thermal analysis were used to assess the mechanical performance of the developed materials. The fracture surfaces were observed by scanning electron microscopy. The developed materials are sensitive to the pH, showing a clear reversible transition in a relatively narrow interval of pH, which is just in the range of physiological conditions. These properties make the materials developed in this study very promising for biomedical applications. Fickian-type diffusion is the mechanism predominant in these systems, except for the composition with a higher concentration of AA, that corresponds to the most desirable kinetical behavior for controlled release (case II-transport mechanism). Furthermore, the results obtained in the mechanical tests are in the range of those reported for typical PMMA bone cements, showing that it is possible to develop partially degradable cements with an adequate mechanical behavior. © 1998 Kluwer Academic Publishers
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  • 6
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract It has been shown that blends of starch with a poly(ethylene-vinyl-alcohol) copolymer, EVOH, designated as SEVA-C, present an interesting combination of mechanical, degradation and biocompatible properties, specially when filled with hydroxyapatite (HA). Consequently, they may find a range of applications in the biomaterials field. This work evaluated the influence of HA fillers and of blowing agents (used to produce porous architectures) over the viscoelastic properties of SEVA-C polymers, as seen by dynamic mechanical analysis (DMA), in order to speculate on their performances when withstanding cyclic loading in the body. The composite materials presented a promising performance under dynamic mechanical solicitation conditions. Two relaxations were found being attributed to the starch and EVOH phases. The EVOH relaxation process may be very useful in vivo improving the implants performance under cyclic loading. DMA results also showed that it is possible to produce SEVA-C compact surface/porous core architectures with a mechanical performance similar to that of SEVA-C dense materials. This may allow for the use of these materials as bone replacements or scaffolds that must withstand loads when implanted.
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  • 7
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The aim of this research was to study the stability of plasma-sprayed eoated metal systems and to evaluate their susceptibility to the occurrence of corrosion fatigue. Hydroxylapatite plasma-sprayed coated samples of Ti−6AI−4V were studied under cyclic bending. During fatigue testing samples were immersed in a simulated physiological solution and mechanical and electrochemical degradation were monitored. Applied loads were intended to crack the ceramic coating and not the metal substrate. Electrochemical impedance spectroscopy was used to further characterize the electrochemical behaviour. No increase in tendency to corrode was detected in open-circuit corrosion fatigue testing. It appears as if the coating cracking does not increase metal substrate corrosion susceptibility. The coating integrity has been seriously affected, with marked decrease in thickness, due to the synergistic effect of load and presence of simulated body fluids environment. Impedance results, however, show a general tendency to an increase in corrosion kinetics after corrosion fatigue testing.
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: An extensive characterization of two biodegradable polymers that may constitute an alternative, if one is aiming at orthopaedic applications, to the currently used poly(glicolic acid), poly(lactic acid) or polyhydroxybutyrate was carried out. A cellulose acetate and three different grades of a novel starch based polymer were studied. The characterization included: tensile and instrumented impact tests, rheological measurements, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR), differential scanning calorimetry (DSC), and long-term degradation trials in Hank's solution. The results show that both polymers, specially the starch based one, present a great potential for biomedical applications, on which adequate mechanical properties associated to a controlled degradation rate are required.
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  • 9
    Publication Date: 2019
    Description: 〈p〉Awareness that traditional two-dimensional (2D) in vitro and nonrepresentative animal models may not completely emulate the 3D hierarchical complexity of tissues and organs is on the rise. Therefore, posterior translation into successful clinical application is compromised. To address this dearth, on-chip biomimetic microenvironments powered by microfluidic technologies are being developed to better capture the complexity of in vivo pathophysiology. Here, we describe a "tumor-on-a-chip" model for assessment of precision nanomedicine delivery on which we validate the efficacy of drug-loaded nanoparticles in a gradient fashion. The model validation was performed by viability studies integrated with live imaging to confirm the dose-response effect of cells exposed to the CMCht/PAMAM nanoparticle gradient. This platform also enables the analysis at the gene expression level, where a down-regulation of all the studied genes (〈i〉MMP-1〈/i〉, 〈i〉Caspase-3〈/i〉, and 〈i〉Ki-67〈/i〉) was observed. This tumor-on-chip model represents an important development in the use of precision nanomedicine toward personalized treatment.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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