Key Engineering Materials Vols. 493-494

Abstract: Splitting problems at HA-coated implants are generally due to biological reasons. Bond-coatings were used to prevent the splitting problem of zirconia ceramics; this method can be widely seen in industrial applications. Two main groups were used; the first group consisted of spraying a bond layer of titania onto commercially pure titanium. This followed by a spray of HA with 5, 10 and 15 % zirconia (8 % yttria doped) as main layer onto the first bond-coating. For the second group, the samples were coated without bond-coating. Firstly, X-ray diffraction patterns of the starting powders were taken. Then x-ray diffraction patterns of the plasma sprayed samples were taken. In literature, it was seen that 20 % zirconia was sufficient for the transformation into a monoclinic structure for the bond-coated samples. For this study it was found that 10 % zirconia was sufficient to transform to the same structure of the desired crystalline phase transformation. The coating kept its crystal structure and relatively small amount of amorphous transformation was detected. A similar structure was produced using less zirconia. It was thought that the use of titanium-oxide bond-coating layer would play an important role as a third variable in the results. To further investigate these phenomena, more detailed researches must be conducted with using titanium-oxide yittria stabilized zirconia (8 wt %) hydroxyapatite bond-coatings with HA main coatings.

Abstract: Ti6Al4V alloy commonly used in human body for load bearing prosthesis was coated by micro arc oxidation (MAO) with magnesium rich TiO₂ oxide. Since the presence of magnesium in bone tissues is known to promote bone formation and proliferation in physiological environment, its integration with TiO₂ on implant surface could bring about a bioactivity for a fast bone formation and proliferation. The formation of a composite layer consisting of Mg integrated TiO₂ by MAO process was carried out in an electrolyte with different magnesium content. The characterization studies of these coatings were performed by using X-ray diffractometry (XRD), scanning electron microscopy (SEM) coupled with EDS analysis and XP2 surface profilometry.

Abstract: Many micropores were formed on the surface of a Ti-15Mo-5Zr-3Al alloy plate and a polyethylene terephthalate (PET) plate by sandblasting, Apatite Nuclei were precipitated in the pores, then bioactive Apatite Nuclei-precipitated composites were fabricated. In order to examine the bioactivity, the composites were soaked in SBF and it was observed that hydroxyapatite was induced on the whole surface within 1 d. The hydroxyapatite layer possessed high adhesive strength to the plate due to a mechanical interlocking effect between hydroxyapatite in the micropores and the plate.

Abstract: Alumina (α-Al₂O₃) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) are biocompatible ceramic materials. Alumina is described as “bioinert” while hydroxyapatite as “bioactive”. These ceramics can be used in production of orthopedic prostheses, dental implants and bone filling materials either separately or in composite form. Especially porous materials attract attention due to their supportive structure for cell and tissue growth/development.Alumina was derived via sol-gel method. Firstly, boehmite (AlOOH) sol was produced by hydrolyzing the starting material, aluminium iso-propoxide (AIP, Al(OC₃H₇)₃). Then this sol was mixed with hydroxyapatite powders (Bovine Hydroxyapatite, BHA) obtained from bovine bones. Subsequently, the mixture was gelated at 110 °C for 3 hours and the resulting gel mixture was heat treated at 1300 °C for 2 hours. BHA powders were not synthetic and added as 10 and 30 wt.% of AIP to the boehmite sol. Irregular shape of the powders produced after the heat treatment was interpreted as a sign of porosity.SEM-EDS and XRD characterization studies were performed on heat treated powders. XRD results showed that powders were composed of α-alumina and apatite based phases such as tricalcium phosphate and hydroxyapatite. SEM images of the composite powders indicated that neck bonds were not formed between α-alumina and apatite based phases. Comparison of SEM images and EDS results of pure BHA and composite powders revealed that pure BHA powders possess granular particle shape. Furthermore, needle shaped alumina particles were observed in the composite sample with 10 wt.% BHA. Finally, it has been found out that alumina particles were placed layer by layer in the composite powders with 30 wt.% BHA.

Abstract: Hybrids of hydroxyapatite (HAp) and poly(L-lactic co glycolic) (PLGA) have been fabricated, which can be expected to be a novel filler for bone grafting. The porous HAp ceramics with bimodal pore structure have been fabricated from apatite fibers synthesized by homogeneous precipitation method. Then, HAp/PLGA hybrids have been fabricated by introducing PLGA having high molecular-weight into the open pores of the porous HAp ceramics. Total porosities of the porous HAp ceramics slightly decreased from 71.5% down to 67.4% after infiltrating PLGA into the porous HAp ceramics. The bending strength of the HAp/PLGA hybrids was ~ 8.3 MPa. The value attained about 2 times that of the porous HAp ceramics.

Abstract: Siloxane-containing vaterite (SiV) / poly (lactic acid) hybrid (SiPVH) beads with the releasability of silicate and calcium ions were prepared with an electrospraying method. According to the increase in the silicon content of the SiV, the amount of silicate ion released from the resulting beads also increased. When the beads were soaked in a cell culture medium, proteins derived from fetal bovine serum were adsorbed on their surfaces. Cell adhesion tests were also performed on the beads with using mouse osteoblast-like cell line (MC3T3-E1) in vitro. After 5 days of culturing, the cells adhered and spread well to cover the surface of the beads. In the localized area, agglomerated cells were observed to combine with cauliflower-shaped calcium phosphate deposits.

Abstract: Hydroxylapatite, titania and Bioglass 45S5 are the components generally used for the production of bioactive biomaterials for years. In literature, although the binary composites with the permutation of three components exist, a ternary composite has not yet been tried. Primarily, Bioglass 45S5 was cast, its thermal analysis (Differential thermal analysis (DTA), dilatometric analysis), phase analysis (X-Ray Diffraction (XRD) ), microstructural characterization (Scanning Electron Microscopy (SEM) ) were performed. Then Bioglass 45S5 powder was ground to fine powder to make its particle size closer to the hydroxylapatite and the titania powders. The particle size of the powders were determined using the laser particle sizer. The DTAs of the 3 components, separately and mixed, were performed. They were then mixed, and ball-milled during 24 hours for a better homogenization. Following drying for 24 hours, pellets of 1 inch diameter were obtained using unaxial manuel press and sintered at 1000, 1100, 1200 °C. Mechanical testing (compression and microhardness), porosity measurement (The Archimèdes Method), phase determination (XRD) and microstructural characterization (SEM) of the composites were then performed. As a conclusion, when sintering temperature was increased, the porosity in the structure was decreased. Between 1100 °C and 1200 °C, a phase transformation occurred. The results of microhardness ( 24.6, 38.99, 316.2 HV (500gf for 15 sec) for the composites sintered at 1000, 1100, 1200 °C, respectively) and subsequent compression tests (93.023±10.5, 298.14±78.074, 371.9684±38.36 MPa, respectively) approved the possible phase transformation between 1100 °C and 1200 °C along with the XRD results.

Abstract: Both natural and synthetic materials have been utilized to provide three dimensional scaffold environments ideal for bone repair. The biomechanical and biocompatibility characteristics of these scaffolds play a vital role in successful tissue engineering constructs. Polymer/carbonate apatite (CHA) composites have shown to improve cell adhesion and proliferation on the scaffold as well as increase elastic modulus, toughness and strength. The aim of this study is to prepare CHA- polylactic-co-glycolide (PLGA) composites in the form of microsphere, scaffold and disc and evaluate their physico-chemical properties, mechanical properties and in vitro bioactivity. 3-D porous cylindrical composite scaffolds were prepared using PLGA/CHA composites with varying PLGA/CHA ratios (30:70 and 50:50). The CHA was prepared by hydrolysis method and characterized using x-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR). The physico-chemical and mechanical properties of the composite scaffolds were evaluated using scanning electron microscopy (SEM), micro-computed tomography (μCT), XRD, FTIR, and thermogravimetry (TGA). Flexural strength was determined using Instron. In vitro bioactivity was determined by the formation of apatite on composite disc surfaces after immersion in simulated body fluid (SBF). SEM and μCT analyses showed high porosity and interconnectivity between microspheres in the composite scaffolds. In vitro bioactivity was observed by the development of an apatite layer on the surfaces of the composite scaffolds after immersion in simulated body fluid. The mechanical strength of the scaffolds was to be dependent on the PLGA-CHA ratio. The elastic modulus, toughness and strength values obtained for the composites were similar to those of reported bone substituted materials. Results from this study provided information on the fabrication of PLGA-CHA scaffolds and their properties that may be useful for their potential application in bone repair and as scaffolds in tissue engineering for bone regeneration.

Abstract: Damages to articular cartilage that are caused by trauma, age-related diseases (arthritis, arthrosis) and/or physical stress pose major medical problems. A possible solution is to introduce a biodegradable sponge-like scaffold containing cartilage-forming cells. In the current work we developed a model for a partially calcified functional biomedical membrane with a gradient of calcium phosphate crystal density to form the interface between bone and a sponge-like cell containing scaffold for cartilage regeneration. The membrane consists of a biocompatible, biodegradable, partially calcified hydrogel, in our case gelatin was used. One part is an organic-inorganic nanocomposite consisting of nanocrystalline calcium phosphate particles, formed in situ within the hydrogel, while the other part is the hydrogel without inorganic crystals. The experimental method used was one-dimensional single diffusion. Gelatin gels containing calcium or phosphate ions, respectively, were exposed from the upper side to a solution of the other constituent ion (i.e. a sodium phosphate solution was allowed to diffuse into a calcium containing gel and vice versa). Scanning electron microscopy (E-SEM), EDX, XRD and ATR-FTIR spectroscopy confirmed the existence within the gel of a density gradient of carbonate apatite crystals, with a dense top layer extending several microns into the gel. Ca/P atomic ratios were in the range characteristic of calcium deficient apatites. The effect of different experimental parameters on the calcification process within the gelatin membranes is discussed.

Abstract: In this study, nanocomposites based on of β-tri calcium phosphate (β-TCP) and 2.5-10 wt% merwinite nanoparticles were prepared and sintered at 1100-1300°^c. The mechanical properties were investigated by measuring compressive strength and fracture toughness. Structural properties were evaluated by XRD, TEM and SEM analysis, and the in vitro bioactivity was studied by soaking the samples in simulated body fluid (SBF). The mechanical strength of the sintered samples were increased, by increasing the amount of merwinite phase up to 5 wt%, whereas it decreased when the samples were sintered at 1100 and 1200°^c. Nanostructured calcium phosphate layer was formed on the surfaces of the nanocomposites within 1 day immersion in simulated body fluid. Because of appropriate mechanical properties the composite is suggested to be used as substitute for hard tissue.