Papers by Author: S. De Aza

Abstract: This document describes and discusses the non-isothermal devitrification process of the wollastonite-tricalcium phosphate (W-TCP) eutectic glass. This eutectic glass has been studied in situ, from room temperature up to 1375 °C, by Neutron Diffractometry (ND) in vacuum. The data obtained were complemented and compared with those performed on ambient atmosphere by Differential Thermal Analysis (DTA) and with those of samples fired in air, at selected temperatures, and then cooled down and subsequently studied by laboratory X-ray Powder Diffraction (LXRD) and Field Emission Scanning Electron Microscopy (FE-SEM) fitted with Energy X-Ray Dispersive Spectroscopy (EDS). Selected samples have been investigated by quantitative full-phase analysis (including the amorphous content) using the Rietveld method. The experimental evidence indicates that the devitrification of W-TCP eutectic glass, begins at ~870°C, with the crystallization of a Ca-deficient apatite phase (Ca9.92(P5.85O23.54)(OH)2.03 (H2O)2.194) followed by wollastonite-2M (-CaSiO3) crystallization at 1006°C. At 1375°C the bio glassceramic is comprised of quasi-rounded colonies formed by a homogeneous mixture of pseudowollastonite (-CaSiO3) and -tricalcium phosphate (-Ca3(PO4)2). This microstructure corresponds to irregular eutectic structures and is similar to that of Bioeutectic® W-TCP material obtained previously, via controlled slow solidification of the eutectic composition, by some of the present authors. It has also been found that from the eutectic composition of the wollastonite – tricalcium phosphate binary system is possible to obtain a wide range of bio glass-ceramics through appropriate design of thermal treatments.

Abstract: In this study a ceramic composite with nominal composition 40 wt% Ca3(PO4)2 – 60 wt% CaMg(SiO3)2 was obtained by solid state sintering of compacts of both synthetic fine powders. The ceramic composite showed a fine grained and homogeneous microstructure consisting of CaMg(SiO3)2 and b-Ca3(PO4)2 grains. The results of X-ray diffraction and scanning electron microscopy demonstrated that, during soaking in SBF, the grains of β-Ca3(PO4)2 dissolved preferably than those of CaMg(SiO3)2, leaving a porous surface layer rich in CaMg(SiO3)2. Subsequently, partial dissolution of the remaining CaMg(SiO3)2 occurred and the porous surface of the b-Ca3(PO4)2-CaMg(SiO3)2 ceramic became coated by a bone-like apatite layer after 7 days in SBF.

Abstract: The biological response following subcutaneous and bone implantation of β-wollastonite(β-W)-doped α-tricalcium phosphate bioceramics in rats was evaluated. Tested materials were: tricalcium phosphate (TCP), consisting of a mixture of α- and β-polymorphs; TCP doped with 5 wt. % of β-W (TCP5W), composed of α-TCP as only crystalline phase; and TCP doped with 15 wt. % of β-W (TCP15), containing crystalline α-TCP and β-W. Cylinders of 2x1 mm were implanted in tibiae and backs of adult male Rattus norvegicus, Holtzman rats. After 7, 30 and 120 days, animals were sacrificed and the tissue blocks containing the implants were excised, fixed and processed for histological examination. TCP, TCP5W and TCP15W implants were biocompatible but neither bioactive nor biodegradable in rat subcutaneous tissue. They were not osteoinductive in connective tissue either. However, in rat bone tissue β-W-doped α-TCP implants (TCP5W and TCP15W) were bioactive, biodegradable and osteoconductive. The rates of biodegradation and new bone formation observed for TCP5W and TCP15W implants in rat bone tissue were greater than for non-doped TCP.

Abstract: Wollastonite bioceramics prepared from synthetic and natural precursors were implanted in rats in bone and subcutaneous tissues. The implant sites were excised after 7, 30 and 120 days, fixed, dehydrated, embedded in paraffin wax for serial cutting and examined under transmitted light microscope. It was found a very similar behavior for both wollastonite bioceramics. They were biocompatible, bioactive and biodegradable when implanted in rat bone. The synthetic ceramic was more reabsorbable than the one from natural powder. When implanted in subcutaneous rat tissue, both materials elicited a mild initial inflammatory reaction that practically disappeared after 120 days. Both materials were encapsulated with a very thin fibrous capsule and slightly reabsorbed at their surfaces. None of the materials induced ectopic osteogenesis. According to the results, the studied materials seem to be able for manufacturing reabsorbable bone implants.

Abstract: In this work a new kind of CaSiO3-doped α-Ca3(PO4)2 ceramic materials, with compositions lying outside the field of the Ca3(PO4)2 solid solution in the system Ca3(PO4)2- CaSiO3, were obtained and some of their properties, relevant for bone repairing, were studied in vitro. Crystalline α-Ca3(PO4)2 solid solution and minor amounts of non-equilibrium residual glass were the only phases in the materials containing 2 and 5 wt% of CaSiO3. α-Ca3(PO4)2, crystalline eutectic-like phase and residual glass were observed for sample containing 15 and 20 wt% of CaSiO3. The mechanical strength improved for all the doped ceramics with regard to un-doped Ca3(PO4)2. The release of ionic Ca and Si in simulated physiological conditions increased with the content of CaSiO3 and favored α-Ca3(PO4)2 surface transformation. The soluble components extracted from the CaSiO3-doped α-Ca3(PO4)2 bioceramics were not cytotoxic to human fibroblastlike cells. Initial cell adhesion onto the surface of the materials seemed to be partially hindered by surface reactivity and remodeling, however those cells adhered to the experimental bioceramics were viable and proliferated normally.

Abstract: Synthetic pseudowollastonite (psW) and a nanostructured copolymer made of a biostable component, Poly(ethylmethacrylate) (PEMA) and a bioresorbable component, vinylpyrrolidone (VP) are used in this work for the preparation of a new family of bone substitutes that allow osseointegration and mechanical stability. Composites are prepared by bulk polymerization of the desired composition in 15 mm diameter cylindrical plastic moulds. Polymerization was induced thermally at 50°C using 1wt% azobis(isobutyronitrile) (AIBN) as free-radical initiator. The moulds were filled to a height of 100 mm and 1 mm height discs were cut with a diamond saw. Specimens with a ceramic/polymer ratio 58/42, 33/67,17/83 and 0/100 were obtained. Compression stress in the range 39-59 MPa and elastic modulus between 2.64 and 4.14 GPa are obtained where the greater values correspond to the specimens prepared with a 60% ceramic load. Degradation in SBF produces a porous nanostructure in the polymeric component indicating microdomains of different solubility and the formation of an apatite-like layer on the surface of the wollastonite component. All the compositions assayed present a biocompatibility at least of the level or even superior than the Thermanox® control used.