Key Engineering Materials Vols. 309-311

Abstract: Silicon-doped calcium carbonate / poly (lactic acid) composites (Si-CCPC) were estimated in cellular biocompatibility with culture tests using osteoblast-like cells (MC3T3-E1) and mesenchymal stem cells (MSC). The cellular biocompatibility of Si-CCPC was enhanced by coating with bone-like hydroxycarbonate apatite (b-HA) formed by simulated body fluid immersion. The b-HA was formed on Si-CCPC after 3-days of immersion and closely bonded with Si-CCPC. Numerous MC3T3-E1 and MSC showed good adhesion on the b-HA with extending their lamellipodia. The number of adhering MC3T3-E1 on Si-CCPC coated with the b-HA was higher than that on Si-CCPC. The b-HA has excellent biocompatibility and silicon is regarded to stimulate osteoblast and bone formation in vivo and vitro. The b-HA containing silicon on Si-CCPCis expected to enhance the cellular adheresion, proliferation and differentiation.

Abstract: There are still some existing problems that are common to all absorbable materials; 1) It cannot be subjected to radiosterilization, 2) Sufficient strength cannot be maintained until the complete bone union is obtained. To solve these problems, PLLA and PLLA/HA were mixed with cross-bridge supplementary agent, Triallyl Isocyanurate (TAIC). Using these materials in vivo, we created and tested γ-ray radiosterilized absorbable bone fixation materials.

Abstract: Fifteen different lithium-hydroxyapatite composites were tested in this work. LiHA were prepared using 0.25 %, 1 % and 2 % of lithium and five different sintering temperature 900, 1000, 1100, 1200 and 1300oC. Primary culture of osteoblasts were used to evaluate the biocompatibility of the samples, concerning to cell viability and alkaline phosphatase production. The 1% LiHA samples sintered at 1100, 1200 and 13000C showed the best results.

Abstract: Hydroxyapatite (HA) which has excellent biocompatibility and osteoconductivity is limited in the load-bearing repair because of its brittleness. Applying appropriate sintering additives for HA is a possible way to improve its mechanical properties. Systematic studies have has been performed to investigate the effect of LiCl as an additive on the microstructure and sinterability of HA and the relationship to its mechanical properties. The densification of HA containing different LiCl contents was completed through a special sintering process with the highest temperature of 1280°C. Microhardness was tested as a short cut to evaluate the changes of mechanical properties affected by the microstructure of HA doped with LiCl. The results of the experiment showed that LiCl is an effective sintering agent which causes neither decomposition of HA nor formation of other undesired phases with the increase of its microhardness.

Abstract: Silicon-containing apatite (Si-HAp) fibres were successfully synthesized by a homogeneous precipitation method. The resulting Si-HAp fibres were composed of carbonate-containing apatite fibres with preferred orientation in the c-axis. The Si contents in the Si-HAp fibres could be controlled by the Si concentration of the starting solutions. TEM observation indicated that the Si-HAp fibres were of single crystal. The Si-HAp fibres have potential as novel materials for high-performance biomedical devices.

Abstract: In this study, the osteoconductive properties of novel cyanoacrylate-based filling materials for bone defect were evaluated. A new filling material was prepared by mixing Histoacryl® and acid-treated
-tricalcium phosphate (
-TCP). Mixing weight ratio of acid-treated
-TCP to Histoacryl® was 5:1. 12 male Spraque-Dawley rats were used in this study. The animals were divided into 4 groups. Critical-sized calvarial defects (8 mm) were created in 9 animals, and then the defects were treated with dense pellet specimen, porous cement-like specimen, and untreated defect for surgical control group. Augmentation treatments were carried out in 3 animals. Histological analysis revealed excellent ostgeoconductive properties of new filling materials. But, some of
-TCP particle in the cement-like group were encapsulated by fibrous connective tissue. For the dense pellet group and augmentation treatment group, shape and stability were better maintained during the implantation time than cement like group. These results indicate that our novel
-TCP/Histoacryl® composite have the potential to serve as filling materials for bone defects in the dental and plastic surgery.

Abstract: Hydroxyapatite (HA) is one of the most promising biomaterials, which is on use since decades in biomedicine. Because of the known mechanical weakness of HA in load carrying situations, various dopants, like ceramic oxides and metallic particles, have been used to produce HA-composite materials. In this study, Ti powders were admixed with enamel derived HA at 5 and 10 wt %. After ball milling, the mixtures were uniaxially pressed into pellets of a cylindrical form. The composites were sintered at temperatures between 1000°C and 1300°C. Microhardness, compression strength, and density measurements together with X-ray diffraction analysis and SEM studies were performed. The best mechanical values were obtained for the samples sintered between 1100°C and 1300°C.

Abstract: Zirconia-hydroxyapatite (40-60 vol%) composites were sintered at different temperatures in air. The x-ray diffraction patterns of the sintered composites showed that hydroxyapatite began to decompose to tricalcium phosphate even below 950°C. The decomposition of hydroxyapatite also involved release of structural water, which was studied using thermogravimetric analysis. By reducing the loss of structural water from the hydroxyapatite, the phase stability of the hydroxyapatite could be increased. This allowed higher temperatures to be used during the densification process where dense composites without any detectable reactions where produced by hot isostatic pressing at 1200°C as well as with spark plasma sintering at 1100°C.

Abstract: The repeated-deformation processing technique was used in the preparation of layered tricalcium phosphate (TCP)/yttria partially stabilized tetragonal zirconia (Y-TZP) composites with ribbon-like microstructures. The fabrication technique involved repeated plastic deformation of layered green tapes, which are stacked together to form starting bi-material laminates, burn-out of the organic vehicle, and sintering at 1300°C. At this rather low sintering temperature, which was chosen to prevent the extensive diffusion of the calcium into the Y-TZP, the zirconia layers could not be fully densified. In spite of the relatively low fractional density (about 75% TD) of these layers, flexural strength values exceeding 100 MPa were achieved with these composites, 150% higher than the matrix material. During autoclaving in water at 200oC for 24 hours no t-m transformation of the zirconia phase took place, indicating full stability of the porous zirconia layers in these composites under the hydrothermal conditions used in this study.

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.