Key Engineering Materials Vols. 342-343

Abstract: To combine the bioinert titanium with the biological active coating of hydroxyapatite [HA, Ca10(PO4)6(OH)2] a new pulsed laser deposition(PLD) method was applied. The initial osteoblast-like MC3T3-E1 cell response to this thin HA coated(<1μm) surface was compared with non-coated surfaces. Cell responses on four different pure titanium surfaces, such as smooth titanium, HA coated smooth titanium, rough titanium and HA coated rough titanium, were compared. Cell morphology and attachment were examined by scanning electron microscopy after 6, 24 and 72 hrs of culture, cell proliferation by MTS assay after 3, 7 and 14 days. The differentiation of the cells was analyzed by real time PCR up to 21 days. The cells were well spread and attached on all surfaces and showed more irregular shapes on the HA coated specimens. They proliferated continuously on all specimens up to 14 days. Smooth surface specimens showed better cell proliferation than rough ones after 7 days, and the HA coated specimens demonstrated slightly greater MTS activity than the non-coated groups after 14 days. The surface topography affected cell proliferation initially however; there was no significant difference afterwards. Thin HA coating influenced the expression of some genes related with cell differentiation.

Abstract: OH groups on hydroxyapatite (HA) and calcium metaphosphate (CMP) were evaluated by grafting tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethyloxysilane (3-APTES) which can bond covalently with OH group of ceramic biomaterials. The prepared HA and CMP disks were soaked in pH 2 and 5 of acidic water and ethanol solution respectively, where pH change of each solution was measured during soaking of samples. After grafting TEOS and 3-APTES on HA and CMP disks, samples were ultrasonically cleaned in distilled water and soaked in pH 5 of ethanol solution, and pH measurement was carried out in the same manner. The pH value of HA and CMP in aqueous solution at pH 2 increased with time continuously, resulting from dissolution of HA and CMP by acidic condition on surface. At pH 5 in aqueous solution, it was the same though the pH increase was smaller. In case of ethanol at pH 5 with HA, though pH value went up slightly, the curve became saturated with time, while there was no change in pH with CMP. After grafting TEOS and 3-APTES, pH values were stabilized with few changes, indicating that there was no direct chemical reaction between the acidic media and the surface of samples due to covalently grafted TEOS and 3-APTES layer. In conclusion, it was confirmed that OH group on the surface of HA was crystallographic and chemical one rather than physically adsorbed one by grafting TEOS or 3-APTES and it will serve an effective binding site for calcium and phosphate ions, or minerals.

Abstract: To eliminate thermal stress during laser cladding and to raise the bonding strength between substrate and coating, composition gradient coatings are designed and fabricated by using wideband laser cladding technique on a Ti alloy. And mechanical properties on coating is studied. The experimental results indicate that the bonding strength between coating and substrate is fairly high, above 38.8MPa. The highest microhardness is obtained for coating containing 0.6wt.% Y2O3 1062HV0.1 and 1405HV0.1, respectively at bioceramic coating and alloyed transition layer. The average tensile strength, bending strength, and elastic modules of coatings are 767.83MPa, 1671.65MPa, and 13.98GPa, respectively.

Abstract: In this study, microstructure and biocompatibility of gradient bioceramic composite coating fabricated by Wide-Band Laser Cladding is investigated. The experimental results indicate that the coating consists of an alloyed transition layer and the bioceramic coating. The bioceramic coating is mainly comprised of HA, CaTiO3, CaO, α-TCP, β-TCP and TiO. The coral-shaped structure and short-rod piled structure existing on the surface of coating. After the implantation of the bioceramic coatings into dogs’ femur for 6, 12, and 24 weeks, hypersusceptibility, rejection and pathological changes are not found. No fiber cyst, necrosis of bone tissue and chronic inflammation obviously appear through slice observation of hard tissues. The bioceramic coating with different ratios of Ca : P have different abilities to induce osteogenesis. At Ca: P=1.4 and 0.6wt.% Y2O3 (No.3 sample), the bioceramic coating is of best bioactivity and biocompatibility.

Abstract: Poly-L-lactide/β-tricalcium phosphate (PLLA/β-TCP) porous scaffold fabricated by freeze shrinking/particulate leaching was studied. The scaffold was immersed into simulated body fluid (SBF) for 1, 2, 3 and 4 weeks and analyzed by the SEM, XRD and FT-IR spectroscopy. The ability of inducing Ca-P formation was compared among the scaffolds with different content of β- TCP. SEM shows a typical feature of apatite precipitation. Diffraction peak of new crystal structure was detected by x-ray diffraction (XRD). IR Spectrum in which absorption bands arise from newly formed groups of carbonate apatite can be seen. At the same testing point, higher density of Ca-P crystal can be observed by SEM in scaffold with high content of β-TCP than in low group. Until 3 weeks, Ca-P individual crystal started on the wall of inner pore of pure PLLA. Porous PLLA/β-TCP composite scaffolds also indicate good ability of Ca-P formation in vitro, the ability of which to form apatite was enhanced by addition of each other that has different degradable mechanism.

Abstract: Previously, various surface treatments have been used to enhance the ability of titanium surfaces to induce calcium phosphate (Ca-P) formation in simulated body fluid (SBF). However, there were no systematic investigations on the key factors of the surface treatments to control such ability. In this work, three factors are studied for their roles in controlling Ca-P precipitation in SBF: surface roughness, surface chemistry and surface energy. Four kinds of single-step chemical treatments on Ti surfaces were carried out, including alkali treatment (AT), nitric acid treatment (NT), hydrogen peroxide treatment (HPT), and heat treatment. The experimental results show that the surface energy is the most likely controlling factor of Ca-P formation ability.

Abstract: Osseointegrated titanium implants have been widely used in clinics for replacement of missing teeth. However, sensory perception thresholds of implants were 10 to 100 times higher than those of natural teeth. The purpose of this study was to evaluate the effect of the ceramic coating generated by microarc oxidation (MAO) on sensory reconstruction around dental implants. The MAO coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning probe microscope (SPM). Moreover, the chemical composition was analyzed with an energy dispersive spectroscope (EDS). Using smooth titanium discs as a control, Schwann cell responses to the coating were evaluated by SEM, MTT assay, total protein content and leakage of cytosolic lactate dehydrogenase (LDH) activity. In addition, the amount of brain-derived neurotrophic factor (BDNF) secreted by Schwann cells was measured by Enzyme-Linked Immunosorbent Assay (ELISA). It was observed that the porous coating had separated and homogeneous micropores in the diameter of 1-2 μm. The concentrations of Ca and P in the layer were 8.63% and 5.23% respectively. The cell morphology, proliferation and secretion of BDNF were unaffected. The results indicated that the MAO ceramic coating developed on the surface of pure titanium had good biocompatibility with Schwann cells for sensory reconstruction around dental implants.

Abstract: Bioactivity of hydroxyapatite reinforced ultrahigh molecular weight polyethylene (HA/UHMWPE) nanocomposites with HA volume content of 10~50 % was evaluated by simulated body fluid (SBF) immersion. The effect of HA content on the capability for calcium phosphate (Ca- P) induction was studied. It was found that Ca-P deposition covered the whole surface of the composite with 30 vol. % of HA after immersion for 1 day and the layer grew to around 10 0m thick in one-week immersion, while there was few nucleus formed for composites with HA content lower than 30 vol. % after one-week immersion. The Ca-P structure was identified as octacalcium phosphate (OCP) by SEM, TEM, and ToF-SIMS.

Abstract: The hydrogels composed of chitosan and carboxylmethyl-β-cyclodextrin (CMCD) were prepared to enhance and sustain the antioxidant activities. The carboxylic groups of CMCD were directly grafted and cross-linked on the amino groups of chitosan. The swelling rate decreased with increasing the CMCD contents in the hydrogel and the swelling ratio of CMCD-grafted chitosan hydrogels was improved due to breaking the crystallinity of chitosan caused by introducing the bulky group such as cyclodextrin. The scavenging activity of the tested hydrogels increased with CMCD contents, because antioxidants entrapped in the CMCD were potent free radical terminators.

Abstract: The research of stress distributions and the structural deformation at the sliding core in artificial intervertebral disc under the dorsiflexion is becoming more significant. This research analyzes the finite element model of sliding core and evaluates the effect of radius of curvature and the friction coefficient at the sliding core on von-Mises stress and the contact pressure. New Models of the artificial intervertebral disc are suggested by the results of the sliding core is evaluated by the comparison of that of SB Charité III. Based on the above facts, the optimized radius curvature of the sliding core is also suggested.