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Porous and dense TiNi alloys were successfully fabricated by powder metallurgy (P/M) method, and to further improve their surface biocompatibility, surface modification techniques including grind using silicon-carbide (SiC) paper, acid etching and alkali treatment were employed to produce either irregularly rough surface or micro-porous surface roughness. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) attached to SEM were used to characterize surface structure and the Ca-P coatings. Effects of the above surface treatments on the surface morphology, apatite forming ability were systematically investigated. Results indicate that all the above surface treatments increase the apatite forming ability of TiNi alloys in varying degrees when soaked in simulated body fluid (SBF). More apatite coatings formed on TiNi samples sintered at 1050° and 1100° due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation. Furthermore, more uniform apatite was fabricated on the sample sintered from the mixture of Ni and Ti powders. [ABSTRACT FROM AUTHOR]

Magneli phase titanium sub-oxide conductive ceramic TiO was used as the support for Pt due to its excellent resistance to electrochemical oxidation, and Pt/TiO composites were prepared by the impregnation-reduction method. The electrochemical stability of TiO was investigated and the results show almost no change in the redox region after oxidation for 20 h at 1.2 V (vs NHE) in 0.5 mol/L HSO aqueous solution. The catalytic activity and stability of the Pt/TiO toward the oxygen reduction reaction (ORR) in 0.5 mol/L HSO solution were investigated through the accelerated aging tests (AAT), and the morphology of the catalysts before and after the AAT was observed by transmission electron microscopy. At the potential of 0.55 V (vs SCE), the specific kinetic current density of the ORR on the Pt/TiO is about 1.5 times that of the Pt/C. The LSV curves for the Pt/C shift negatively obviously with the half-wave potential shifting about 0.02 V after 8000 cycles AAT, while no obvious change takes place for the LSV curves for the Pt/TiO. The Pt particles supported on the carbon aggregate obviously, while the morphology of the Pt supported on TiO remains almost unchanged, which contributes to the electrochemical surface area loss of Pt/C being about 2 times that of the Pt/TiO. The superior catalytic stability of Pt/TiO toward the ORR could be attributed to the excellent stability of the TiO and the electronic interaction between the metals and the support. [ABSTRACT FROM AUTHOR]

FeCrAl(f)/HA biological functionally gradient materials (FGMs) were successfully fabricated by the hot pressing technique. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and bending strength test machine were utilized to characterize the microstructure, component, mechanical properties and the formation of the Ca-deficient apatite on the surface of these materials. The results indicate that an asymmetrical FeCrAl(f)/HA FGM, consolidating powders prepared by mixing HA with 3%-15% (volume fraction) is successfully prepared. Both of the matrix and FeCrAl fiber are integrated very tightly and bite into each other very deeply. And counter diffusion takes place to some extent in two phase interfaces. The elemental compositions of the FeCrAl(f)/HA FGM change progressively. Ca and P contents increase gradually with immersion time increasing, and thereafter approach equilibrium. The bone-like apatite layer forms on the materials surface, which possesses benign bioactivity, and the favorable biocompatibility can provide potential firm fixation between FeCrAl(f)/HA asymmetrical FGM implants and human bone. [ABSTRACT FROM AUTHOR]

The steady and dynamic rheological behaviors of precipitated calcium carbonate (PCC) suspension in polyethylene glycol (PEG) were investigated on a TA AR2000ex rheometer. Under steady shear consistency index K and flow exponent N of suspensions with different volume fractions were determined. The shear-thinning and the discontinuous shear-thickening behavior were observed at different constant frequencies from 10 to 100 rad/s. The relationship between the complex viscosity and the constant frequency were determined. As the volume fraction increases, flow exponent N shows a rapid increase, and it increases dramatically when the discontinuous shear-thickening takes place, while consistency index K decreases. Dynamic oscillatory shear experiments were conducted at constant strain amplitude and constant frequency, respectively. For the frequency sweep, the system shows viscous property in entire range of the frequency investigated, and the complex viscosity shows discontinuous jump at a critical frequency of 10 rad/s. For the strain sweep, on the other hand, at low strain the elastic modulus is strongly dependent on the strain, and the viscous modulus is independent of the strain. But at the critical strain point both of the moduli show an abrupt jump and the system transits from elastic to viscous at a strain of 0.1. [ABSTRACT FROM AUTHOR]

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ (δ is the out-of-phase angle) vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region. [ABSTRACT FROM AUTHOR]

The viscoelastic properties of the suspension of monodisperse spherical silica produced by hydrolysis of tetraethoxysilane in alcohol solvent with ammonia as a catalyst in polyethylene glycol (PEG) were studied. The results show that the SiO2/PEG suspension possesses the reversible shear thinning and shear thickening behaviors. In the shear thinning region, the loss modulus ( G″) almost remains unchanged, whereas the storage modulus ( G′) decreases. In the shear thickening region, G″ and G′ increase for the formation of the “clusters”. The larger G″ over G′ in all the stress studied shows that the system mainly possesses the viscous property, and that the energy dissipated( E d) is larger than that stored. E d of this suspension is proportional to the maximum strain ( γ max) rising with the exponent of 1.92 under low shear stress; however, in the shear thickening region, E d is proportional to γ max rising with the exponent of 5.00. [ABSTRACT FROM AUTHOR]

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min-1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min-1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of Kg(II)/Kg(III) is 2.17 [Kg(II) = 6.025 × 105K2, Kg(III) = 1.307 × 106 K2]. [ABSTRACT FROM AUTHOR]

Porous sol-gel glass of CaO-SiO2-P2O5 system with macropores larger than 100 μm was prepared by adding stearic acid as pore former when the sintering was carried out at 700 °C for 3 h. The sol-gel porous glass shows an amorphous structure. The diameter of the pore created by pore former varies from 100 to 300 μm, and macroporous glass has a narrow and small pore size distribution in mesoporous scale. The porosity and pore size of macroporous bioactive glass can be controlled. [ABSTRACT FROM AUTHOR]

Poly-L-lactide(PLLA) was synthesized by ring-opening polymerization from high purity L-lactide with tin octoate as initiator, and characterized by means of infrared, and 1H-nuclear magnetic resonance. The influences of initiator concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of PLLA were investigated. The effects of different purification methods on the concentration of initiator and viscosity average molecular mass were also studied. PLLA with a viscosity average molecular mass of about 50.5×104 was obtained when polymerization was conducted for 24 h at 140 °C with the molar ratio of monomer to purification initator being 12 000. After purification, the concentration of tin octoate decreases; however, the effect of different purification methods on the viscosity average molecular mass of PLLA is different, and the obtained PLLA is a typical amorphous polymeric material. The crystallinity of PLLA decreases with the increase of viscosity average molecular mass. [ABSTRACT FROM AUTHOR]

The rheological behavior of fumed silica suspensions in polyethylene glycol(PEG) was studied at steady and oscillatory shear stress using AR 2000 stress controlled rheometer. The systems show reversible shear thickening behavior and the shear-thickening behavior can be explained by the clustering mechanism. The viscosity and the degree of shear-thickening of the systems strongly depend on the mass fraction of the silica, the molecular weigh of PEG and the frequency used in the rheological measurement. The silica volume fraction of the systems is 1.16%–3.62%, corresponding to the mass fraction of 4%–9%. The shear-thickening taking place in the low volume fraction may contribute to the fractal nature of the silica. At oscillatory shear stress, when the shear stress is less than the critical stress, the storage modulus decreases significantly, meanwhile the loss modulus and the complex viscosity almost remain unchanged; when the shear stress is larger than the critical stress, the storage modulus, the loss modulus and the complex viscosity increase with the increase of shear stress. The loss modulus is larger than the storage modulus in the range of stress studied and both moduli depend on frequency. [ABSTRACT FROM AUTHOR]

Poly(D,L-lactide) was synthesized by indirect method from D,L-lactic acid and characterized by infrared spectrum and proton nuclear magnetic resonance. The influences of monomer purity, initiator concentration, polymerization temperature and polymerization time on the relative molecular mass of poly(D, L-lactide) were investigated. The polylactide was made into porous materials by using solvent-casting particulate-leaching method. Under the optimized conditions, polylactides with a viscosity average molecular mass up to 1.82 × 105 are obtained and the results are fairly reproducible. Scanning electron microscope observation indicates that the sample is highly porous and well-distributed with good interconnections between pores and the pore size of porous materials is in the range from 200 µm to 500 µm and it can be used as scaffold for bone tissue engineering. [ABSTRACT FROM AUTHOR]

L-lactide was prepared from L-lactic acid with stannous octoate as the catalyst. The effects of reaction temperature and pressure on the ingredient of crude lactide were investigated. The results show that the mass fraction of meso-lactide increases with the increasing reaction temperature. Crude lactide containing 85.4% L-lactide is obtained when the reaction temperature is 200 °C. High purity of L-lactide with a yield of 40.6% is obtained by synthetic purifying method. The properties of L-lactide are characterized by optical purity, infrared spectrum and gas chromatogram/mass spectrum. The L-lactide samples purified by recrystallization and synthetic purifying methods are polymerized with the catalyst of stannous octoate, and the corresponding viscosity average relative molecular masses of poly(L-lactide) are 2.85×105 and 5.05×105, respectively. This indicates that the optical purity of L-lactide has great influence on the relative molecular mass of poly(L-lactide). [ABSTRACT FROM AUTHOR]

Sintering shrinkage, compressive strength, bending strength, metallurgical morphology, microstructure and chemical composition diffusion of hydroxyapatite-316L stainless steel (HA-316L SS) composites were investigated. The results show that the sintering shrinkage of HA-316L SS composites decreases from 27.38% to 8.87% for cylinder sample or from 27.18% to 8.62% for cuboid sample with decreasing the volume ratio of HA to 316L SS, which leads to higher sintering activity of HA compared with that of 316L SS. The compressive strength of HA-316L SS composites changes just like parabolic curve (245.3→126.3→202.8 MPa) with reducing the volume ratio of HA to 316L SS. Bending strength increases from 86.3MPa to 124.2 MPa with increasing the content of 316L SS. Furthermore, comprehensive mechanical properties of 1.0:3.0 (volume ratio of HA to 316L SS) composite are optimal with compressive strength and bending strength equal to 202.8 MPa and 124.2 MPa, respectively. The microstructure and metallurgical structure vary regularly with the volume ratio of HA to 316L SS. Some chemical reaction takes place at the interface of the composites during sintering. [ABSTRACT FROM AUTHOR]

Exclusion and inflammation in the clinic are observed for various reasons including material chemical composition, physical properties as well as macro- and micro-structure of the implants, surface condition of the implants, and also patient dependent factors. Cytotoxicity expression of cells is a central issue in current biocompatibility to screen the potential implant materials and drugs. This study was aimed at investigation reaction between the potential implant materials and surround tissue. Cytotoxicity of human and rat osteoblast in the material extracts was determinated by testing standards such as GHS assay, MTT assay, alkaline phosphatase activity assay, LDH assay, and Lowry assay. Research results demonstrated that compared with the control condition polystyrene culture plate both human and rat osteoblast cells have normal phenotypic expression in hydroxyapatite extract, and this expression was statistically restricted in hydroxyapatite-spinel extract. However, this restrict, e.g. cytotoxicity could be partially eliminated by immersion treatment of the materials in culture medium. [ABSTRACT FROM AUTHOR]

DNA synthesis and collagen formations on the implant material by cell culture in vitro are the most important phenotypical expression to estimate the biocompatibility. In this part, DNA synthesis and collagen formation on implant materials were quantitatively and qualitatively estimated by radioactive isotope H+ -thymidine to incorporate into DNA chains, H+ -proline to incorporate into type I collagen proteins followed by scintillation counting and antibody-antigen immunocytochemistry staining, respectively. Research results demonstrate that hydroxyapatite (HA) stimulates DNA synthesis and collagen formation on the material whereas this stimulation is restricted by adding spinel to the materials. There are statistical differences between the influences of material components on both DNA synthesis and collagen formation. It is supposed that porous materials can supply more platforms for cell anchoring, and more DNA and collagen are synthesised on the porous materials. Immersion in culture medium results in new HA crystal formation on the porous HA materials. [ABSTRACT FROM AUTHOR]

The biocompatibility evaluation of calcium phosphate based biomaterials is performed by tissue culture in vitro model. Three kinds of bioceramic materials which are potential to deal with bone trauma and/or conduct tissue growth are recommodated. The biological research results show that human and animal osteoblast cells anchor the materials surface in two hours in culture. Confocal laser scanning microscopy (CLSM) demonstrated the normal cell distribution and proliferation on both of dense and porous biomaterials. Hydroxyapatite and tricalcium phosphate stimulate cell proliferation. However, DNA and protein synthesis were considerably limited and the apoptosis phenomenon would be present on the hydroxyapatite (HA) materials by adding Al, Mg elements. Several important methods of biocompatibility evaluation of implant materials are described and the related biological molecular techniques such as tissue culture, cell transfection, cellular DNA stain, and Lowry assay are involved in the present research. [ABSTRACT FROM AUTHOR]