Key Engineering Materials Vol. 631

Abstract: The use of ceramics bearings in total hip joint replacement (THR) has increased markedly in the last ten years thanks to the optimum wear behaviour of ceramic-on-ceramic bearings and of the high biological safety of ceramic wear debris. As the number of ceramic THR bearings is increasing, also the number of implants that experience off-normal working conditions, e.g. edge loading, third bodies in the joint, soft tissues laxity, dislocation/subluxation of the joint, increases. Under all such conditions the surface of the bearing can be damaged to variable extent, leading eventually to a limitation of the expected performances of the implant.

Abstract: The apatite-forming ability of zirconia ceramics subjected to various surface treatments was investigated. Zirconia samples (Y-TZP) in the form of disks and rods were sandblasted and chemically etched in strong acids (HF, H₃PO₄, H₂SO₄) and/or in NaOH solution at an elevated temperature. The surface properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), wettability and roughness measurement. The ability to form bone-like apatite on the surface was evaluated by immersion of the sample in simulated body fluid, which has ion concentrations nearly equal to the inorganic part of human blood plasma. The effect of applied surface treatment on mechanical properties was investigated. Sandblasting resulted in significant increase of roughness. Chemical etching in H₃PO₄ and H₂SO₄ caused reduction of contact angle but this effect was lost when subsequent alkali treatment was applied. Etching in NaOH, H₂SO₄ and two-step treatment combining H₂SO₄ or H₃PO₄ with NaOH resulted in the formation of bone-like apatite after immersion in simulated body fluid. These results indicate that sandblasted and chemically etched zirconia may be capable of direct bonding with living bone through an apatite layer created on its surface in a human environment. To avoid possible mechanical failure sandblasting conditions need further optimization.

Abstract: Zirconia-based ceramics have gained considerable interest for several applications (e.g. solid electrolytes in fuel cells and in oxygen sensors, thermal barrier coatings and biomaterials for dental and orthopaedic applications) due to their high mechanical strength, improved fracture toughness and easy affordability. We constructed both a manual and an automated electrophoretic deposition set-ups, which allowed us to obtain multilayers of alternating tetragonal and cubic phases by layering nanometric sized powders of yttria doped zirconia (Y-TZP) with different mol percentages of yttria (3 % and 8 %). The rationale behind the design of these multilayer constructs was to optimize the properties of the final ceramic by combining the high mechanical toughness of the tetragonal phase of zirconia together with the high ionic conductivity of its cubic phase. These multilayered constructs were proved to have good mechanical integrity and a clearly defined interface between the cubic zirconia grains layer and the tetragonal zirconia grains layer.

Abstract: Low temperature degradation free Zirconia toughened alumina (ZTA) has been developed. It is reported that ZTA has higher mechanical strength compared to alumina due to the stress induced transformation and spontaneously transformation of zirconia phase on some ZTA have been occurred. For achieving the higher reliability of artificial joint prosthesis alternative to alumina and other ceramic materials, it is necessary to improve and validate the both mechanical characteristics and phase stability at the same time. We evaluated that microstructure, mechanical characteristics and phase stability of newly developed ZTA (BIOCERAM^® AZUL). It was confirmed that four-point bending strength and weibull modulus were extreamly high, and ZTA has higher reliability. There were no significant changes and deterioration in four-point bending strength, crystal structure and wear property with and without accelerated aging test. Newly developed ZTA not only with high mechanical characteristics but also with phase stability could be quite useful as bearing materials in artificial joints for longer clinical use.

Abstract: Various kinds of bioactive materials are developed as bone substitutes. Bioactive materials may affect attachment, proliferation and differentiation of cells and the subsequent integration in a host tissue. In this research 21%CaO–5%P₂O₅–64%SiO₂–5%ZnO-5%B₂O₃ and 16%CaO–5%P₂O₅–64%SiO₂–5%ZnO-10%B₂O₃ bioactive glasses were successfully synthesized by the sol–gel technique. Then the prepared bioactive glasses were soaked into simulated body fluid. Then the prepared samples were characterized using X-ray diffraction (XRD) and Scanning electron microscopy (SEM). It was seen that addition of boron to the structure remarkably enhances the formation of hydroxyapatite on the surface of the bioactive glass and subsequently improves the bioactivity. The obtained results from SEM and XRD were in good agreement with each other. Besides, effect of boron on atomic arrangement of the prepared bioactive glass was studies and compared with previous researches. It was shown that by increasing the boron content, more crystalline domains would be observed.

Abstract: Bioactive glass of the type CaO–SrO–P₂O₅–SiO₂ was obtained by the sol-gel processing method. Three samples containing 0 mol%, 5 mol% and 10 mol% of SrO were synthesized. The obtained bioactive glasses were characterized by the techniques such as, X-ray diffraction (XRD) and scanning electron microscope (SEM) and the effect of SrO/CaO substitution on in vitro biological properties of the synthesized glasses were evaluated and biocompatibility of the samples was measured using MTT assay. The results showed that incorporation of Sr in the obtained glass network did not result in any structural alteration of it due to the similar role of SrO compared with that of CaO. In vitro experiments with human osteosarcoma cell lines (MG-63) and MTT assay indicated that bioactive glass incorporating 5 mol% of Sr in the composition is non-toxic and revealed good biocompatibility.

Abstract: In this work, attention was paid to the understanding of the chemical modifications occurring in xerogeis of 58S bioglass (60% mol SiO₂; 36%mol CaO; 4%mol P₂O₅), during the 58S bioglass synthesis, prepared by the sol-gel (SG) and sol-gel self-propagating combustion (SGSPC) methods using citric acid as reductant/fuel. The chemical modifications of the xerogels were evaluated in the temperature range 70-920°C. Characteristic functional groups were evidenced by Fourier transform infrared spectroscopy (FTIR), and the thermal behaviour was evidenced by thermal gravimetric (TG) and differential thermal (DSC) analysis, the transition from glass to glass ceramic was also followed by X-ray diffraction.

Abstract: An innovative, resorbable and injectable composite cement (Spine-Ghost) to be used for augmentation and restoration of fractured vertebrae was developed. Type III α-calcium sulfate hemihydrate (CSH) was selected as the bioresorbable matrix, while spray-dried mesoporous bioactive particles (SD-MBP, composition 80/20% mol SiO₂/CaO), were added to impart high bioactive properties to the cement; a glass-ceramic containing zirconia was chosen as a second dispersed phase, in order to increase the radiopacity of the material. After mixing with water, an injectable paste was obtained. The developed cement proved to be mechanically compatible with healthy cancellous bone, resorbable and bioactive by soaking in simulated body fluid (SBF), cytocompatible through in-vitro cell cultures and it could be injected in ex-vivo sheep vertebra. Comparisons with a commercial control were carried out.

Abstract: Transparent bioceramics have great potential for applications in the biomedical field as they facilitate direct observation of the interactions at biomaterial – cell / tissue interfaces. Thus far, sintering of transparent hydroxyapatite (HA) usually involves application of extraordinarily high pressure and / or long duration. This study attempts to fabricate transparent HA by a direct and fast Spark Plasma Sintering (SPS) process using three different types of raw powder: micro-spheres (MS), nanorods (NR) and nanospheres (NS). The optical and mechanical properties of the sintered pellets were examined and compared. The highest total forward transmittance (TFT) showed by sintered MS pellet (~2 mm thick) was 85% in the visible spectrum, whereas sintered NR and NS pellets were either translucent or opaque. Although lowest degree of transparency was observed for NS pellets, they demonstrated highest Young’s modulus (E), hardness (H) and fracture toughness (K_IC). The eminent K_IC of NS pellets benefited mainly from its self-toughened microstructure.