Key Engineering Materials Vols. 396-398

Abstract: Wear of the articulation partners in artificial joints for hip or knee is known to influence the in vivo survival rate of the implants. Wear amount can be strongly increased if third body wear occurs in the joint gap. Alumina ceramic is noted for a good wear resistance even under these worst case conditions. We tested the wear behaviour of the new dispersion ceramics ZTA (Zirconia Toughened Alumina) and ATZ (Alumina Toughened Zirconia) in comparison to alumina for the couplings ceramic on PE and ceramic on ceramic in a hip joint simulator in presence of third body particles.

Abstract: Pure b-tricalcium phosphate (bTCP) and Si-substituted b-tricalcium phosphate powders with compositions ranging from x = 0.01 to 0.20 were synthesized using a wet precipitation method. The results showed that the addition of Si decreased the maturation time of single-phase Si-substituted bTCP. For longer maturation time, other phases were observed such as hydroxyapatite (HA) and a-tricalcium phosphate (aTCP). The Si incorporation was confirmed by X-ray diffraction with Rietveld refinement, indicating an increase of the lattice volume from 3524.88 Å3 for pure bTCP to 3527.41 Å3 with increasing Si content.

Abstract: Phosphorus containing biopolymers have been synthesized and studied as polymeric candidates for potential tissue engineering applications. The presence of phosphorus in the polymeric structure may improve the biocompatibility of polymers by enhancing their tissue contact. One aim of this study was to examine the chain extending reaction of poly(ε-caprolactone), PCL, using ethyldichlorophosphate as a coupling agent. A preliminary survey was done to find out whether the presence of phosphoester units in a rapidly degradable polymeric structure improves the Ca phosphate formation on PCL. Another aim of this study was to synthesize one kind of polyphosphazene, i.e. poly[bis(methacrylate)]phosphazene, PMAP. In addition, a preliminary biomineralization study for PMAP polymer was carried out. The results of the biomineralization studies indicated some bioactivity of both biopolymers.

Abstract: The aim of this paper is to evaluate using ICP/MS (inductively coupled plasma mass spectrometry method ) the small amount of heavy metal existing in temporary teeth of children from area with high environmental risk regarding heavy metals, and to correlate this amount with the state of degradation of such teeth, taking into account that teeth are biological archive.

Abstract: The osseointegration of porous titanium implants was evaluated in the present work. Implants were fabricated from ASTM grade 2 titanium by a powder metallurgy method. Part of these implants were submitted to chemical and thermal treatment in order to deposit a biomimetic coating, aiming to evaluate its influence on the osseointegration of the implants. The implants were characterized by Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy. Three coated and three control (uncoated) implants were surgically inserted into thirty albino rabbits’ left and right tibiae, respectively. Tibiae samples were submitted to histological and histomorphometric analyses, utilizing SEM, optical microscopy and mechanical tests. EDS results indicated calcium (Ca) and phosphorous (P) at the surface and Raman spectra exhibited an intense peak, characteristic of hydroxyapatite (HA). Bone neoformation was detected at the bone-implant interface and inside the pores, including the central ones. The mean bone neoformation percentage in the coated implants was statistically higher at 15 days, compared to 30 and 45 days. The mechanical tests showed that coated implants presented higher resistance to displacement, especially after 30 and 45 days.

Abstract: Six mechanisms have been identified, which control how Ca-aluminate materials are integrated onto tissue; 1) Main reaction, the hydration step of CA, 2) Apatite formation in presence of phosphate ions in the biomaterial, 3) Apatite formation in the contact zone in presence of body liquid, 4) Transformation of hydrated Ca-aluminate into apatite and gibbsite, 5) Biological induced integration and ingrowth, i.e. bone formation at the contact zone, and 6) Mass increase reaction, especially important when un-hydrated CA is used as coatings or as augmentation pastes. These six mechanisms affect the integration differently depending on a) what type of tissue the biomaterial is in contact with, b) in what state (un-hydrated or hydrated) the CA is introduced, and c) what type of application is aimed at (cementation, dental fillings, endodontic fillings, sealants, coatings and augmentation products). Both a pure nanostructural mechanically controlled integration, and a chemically induced integration seem plausible.

Abstract: The requirements for scaffolds for bone tissue engineering include appropriate chemistry, morphology and structure to promote cell adhesion and synthesis of new bone matrix. Silk fibroin (SF) represents an important biomaterial for biomedical application, due to its suitable mechanical properties, biodegradability, biocompatibility, and versatility in processing. Our group has developed a new method to obtain a porous SF membrane, and the study of its potential for use as a scaffold for bone regeneration was the aim of this study. Porous membranes were obtained from SF solution, through the compression of a material generated by phase separation. For in vitro calcification experiments, porous SF membrane samples were immersed in SBF at pH 7.4 placed in polyethylene flasks. The experiments were carried out for seven days, at 36.5±0.5 °C. After 48 and 96h, the solutions were changed for fresh SBF with the ion concentration 1.5-fold higher than that of the standard one, to accelerate the calcification process. The characterization of morphology and composition of samples was performed by using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The SEM micrographs indicated that the porous SF membranes presented calcium phosphate deposits after undergoing in vitro calcification. These results were confirmed by EDS spectra, which showed a stoichiometric molar Ca/P ratio ranging from 1.27 to 1.52. This fact may suggest that calcification deposits consisted of mixtures of HAP (Ca/P ratio = 1.67) and transient HAP precursor phases, such as octacalcium phosphate (Ca/P = 1.33) and dicalcium phosphate dehydrate (Ca/P = 1), indicating early stage mineralization. The porous silk fibroin membrane analysed in the current study is a promising material to be used as scaffolds for bone regeneration.

Abstract: Pathologic calcification can lead to failure or deterioration of cardiac valves. Several researchers have tried alternatives to construct these devices, such as the incorporation or utilization of new biomaterials able to inhibit or decrease the calcification process. In vitro calcification tests can be used to screen new biomaterials regarding their potential to calcify in vivo. However, the mechanisms involved in both cases are not completely understood. In order to collect more information about the calcification process of implanted materials, morphology and elemental analyses of calcified cardiac valve fragments explanted from different patients were investigated and compared to previous reports of in vitro calcification tests. Scanning Electron Microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses indicated that the calcium phosphate deposits from both bovine pericardium and human cardiac valves calcified in vivo were similar to the deposits obtained from in vitro calcification samples as previously reported in the literature.

Abstract: Mineralization of the proteic matrix composed mostly of collagen type I is controlled by specific interactions of ions Ca2+ and PO43-, present in the biological fluid, with the matrix, and by the diffusion of these ions. The specific interactions and the diffusion of ions combined; result in the nucleation and formation of calcium phosphate particles. Moreover, they control the morphology, size, crystallinity and composition of the particles In this work, precipitation of calcium phosphate particles in a collagen matrix type I was carried out through impregnation of the matrix with a Ca2+ and PO43- solution, with Ca/P ratio 1.67 and pH 2.5. Precipitation of particles associated with matrix structuring was carried out by adsorption of gaseous ammonia.

Abstract: On this study the influence of silicon dopping on the properties of the final calcium phosphate cement were analysed and compared to the ones of the conventional Si and Mg-free α-TCP cement. In spite of silicon doping, Si-α-TCP calcination temperature (1400°C) was higher than the one used for conventional α-TCP (1300°C) as a result of Mg contamination on the commercial precursor used on the Si-α-TCP synthesis. Because of the high temperature used, Si-α-TCP sample was difficult to mill. Even after 1 week milling, the particle size achieved was 12µm while Si-free α-TCP reached 7.7µm. Consequently, the reactivity of both powders was different. In conclusion, the properties of Si-α-TCP cement were not satisfactory for clinical application. In order to do it so, it is essential to enhance the powder reactivity by reducing Mg contamination, lowering the sintering temperature and reducing the particle size to, then, achieve the desired reactivity and compressive strength.