Key Engineering Materials Vols. 330-332

Abstract: Poly(vinyl alcohol) (PVA) was introduced during in situ synthesis of hydroxyapatite (HA) in neutral collagen (COL) solution and final PVA-COL-HA nanohybrids were achieved via sequential steps including gelation by fibrillogenesis, freezing-thawing physical crosslinking, removal of unreacted residues and dehydration. This method is expected to endow the pure PVA with good bioactivity and meanwhile the presence of elastic PVA would improve the properties of COL-HA composites. The phase, microstructure and possible molecular interactions of the achieved PVA-COL-HA nanohybrids were analyzed by using X-ray diffraction, Fourier transform infra-red spectroscopy and scanning electron microscopy. The results indicate that the inorganic phase is poorly crystallized apatite with a nanometer size due to the confinement of organic macromolecules which forms a network structure.

Abstract: This research was aimed at the construction and characterization of nano-FHA bioceramic coating on titanium surface. Nano-FHA coating was constructed on the surface of commercially pure titanium by sol-gel route. X-ray diffraction (XRD), scanning electromicroscope (SEM) and dissolution test was employed to characterize the obtained coating. In vitro cellular responses of osteoblasts to the coating were also evaluated by MTT assay, ALP assay and SEM observation. Conventional HA coatings and commercially pure titanium (cpTi) were taken as control. Results show the nano-FHA bioceramic coating has good crystallization and homogeneous, nano-scale surface morphology. The dissolution rate of the coating is favorable. The in vitro osteoblasts culture exhibits satisfactory bioactivity.

Abstract: Zirconia ceramics were introduced in the seventhies for use as structural biomaterials after laboratory tests and simulator studies. However, nowadays concerns remain about their reliability in vivo, despite published clinical studies have already established the safety and the good tribological performance of these materials. It is still unclear what level of reliability can be achieved in ceramic biomaterials and how much their toughness level can be enhanced by microstructural design. The polycrystalline nature of ceramic materials may make both the observed properties and performance very scattered. In particular, the grain size and other microstructural features likely play a fundamental role in the mechanical behavior of the material. In this paper, we propose a set of fracture mechanics assessments, aimed to establish the quantitative amount of toughness achievable in a zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite), and in situ confocal Raman spectroscopy to visualize toughening mechanisms, including polymorph transformation and residual stress fields stored around the crack path.

Abstract: A composite of needle-like nano-Hydroxyapatite / silk fibroin (n-HA/SF) with strong interfacial bonding was successfully prepared from calcium chloride (CaCl2) and diammonium phosphate ((NH4)2HPO4) as starting materials of HA in the presence of SF powders dissolved in a ternary solvent system of CaCl2-C2H5OH-H2O (1:2:8 in molar ration) at 80 °C for 30 min prior to preparation of n-HA/SF composite. The n-HA crystals in the composite were poorly crystallized and uniformly distributed in the composite with a crystal size of 4~6 nm in diameter and 20~40 nm in length, which was smaller than that of pure nano-HA. Molecular interaction and strong chemical bonds were formed between n-HA and SF in the composite, which were revealed by Fourier transform infrared spectrometric analysis (FTIR). The synthetic n-HA/SF composite had a good homogeneity and preferential orientation along c-axis and would have a great potential for bone tissue engineering.

Abstract: In the present study, hydroxyapatite (HA) /silk fibroin (SF) nanocomposite containing 40 wt % of SF, was synthesized in an aqueous solution of CaCl2/(NH4)2HPO4 system containing SF to mimic bone structure of nano HA crystallites in organic matrix. The experimental results show that SF promotes the preferential growth of nano HA crystallites along the plane (002) which indicates the interaction between nano HA crystallites and SF. The nanocomposite with nano HA crystallites dispersed homogeneously in SF matrix possesses a compression strength of 97.6 MPa higher than that of woven bone. The methodology has a great potential for designing and engineering of biomaterials with improved biological properties. The novel nanocomposite may be used as bone substitutes and tissue engineering scaffolds.

Abstract: Hydroxyapatite/collagen composites were prepared in-situ synthesis. The composites were finally achieved by dehydration including air-drying and freeze-drying methods. FTIR, XPS and DSC were employed to investigate the composites dehydrated by two methods. The air-dried composites had better mechanical properties than those of the composites dried by freeze drying. Air-drying of the composite induced more bond formation and crosslink between collagen fibers and HA crystals compared with freeze-drying of the composite, as indicated by the shifting of amide A and I bands to the lower wavenumber and by the changes in the binding energy of O1s, Ca2p, and P2p, leading to the increase of the peak temperature of the composites. Collagen crosslink and bond formation in the air-dried composites were key factors to increase the bending strength of the composites. The results of this study confirm that in situ synthesis and air-dry method are effective ways to obtain nanoHA/COL composites with high mechanical properties.

Abstract: The effect of sandblasting and heat treatment on biaxial flexure strengths of the zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) was evaluated in comparison to that of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The disc-shaped specimens of the nanocomposite and Y-TZP were sandblasted with 70)m alumina powder. After sandblasting, half of the specimens were heated at 1000°C for 5 min. The biaxial flexure strengths of Y-TZP were independent on the sandblasting, but decreased with the heat treatment. On the other hand, the biaxial flexure strength of the nanocomposite increased with the sandblasting and significantly decreased with the heat treatment. The content of monoclinic ZrO2 of Y-TZP and the nanocomposite increased with the sandblasting pressure and dramatically decreased with the heat treatment. These results suggest that the stress-induced transformation from tetragonal to monoclinic of the nanocomposite occurs more easily than Y-TZP.

Abstract: Magnetic hydroxyapatite/chitosan nanocomposites were prepared via in situ hybridization strategy in the ambient condition. Magnetic hydroxyapatite/chitosan nanocomposites were investigated by XRD, SQUID and TEM. XRD results indicated that the inorganic phases dispersed in chitosan matrix were composed of magnetite and hydroxyapatite. The magnetic hydroxyapatite/chitosan shown the behavior of superparamagnetism determined by SQUID, which indicated the size of magnetite crystal were less than 30nm. The inorganic nanoparticles with size of 30-50nm were dispersed chitosan matrix homogeneously. In situ hybridization strategy provided a simple and efficient route to synthesize the magnetic chitosan/hydroxyapatite nanocomposites in the mild condition. The most important of in situ hybridization is that the processes of precipitation of chitosan, synthesis of magnetite and hydroxyapatite, and compositing between three components were completed in single step.

Abstract: Thick coatings of bone morphogenetic protein (BMP)-calcium phosphate nano-composite were prepared by a biomimetic process, in which substrates were immersed in modified simulated body fluid containing rh-BMP2 at room temperature and pressure. In vitro analyses showed that the calcium phosphate and BMP formed stable and uniform coating of composite on surface of substrate, and that the composite derive significant improvement in tissue formation, suggesting an osteoinductive bioactive surface.

Abstract: Nano-hydroxyapatite/polyamide66 (n-HA/PA66) composite scaffolds are prepared using phase separation and phase separation in combination with particle leaching, and both the composite powder and paste are used as starting materials. The composite is characterized by IR and XRD. The micro-architecture of the scaffolds is observed by SEM, and the mechanisms that the formation of the porous structure follows have been investigated preliminarily. The results show that scaffold prepared by phase separation in combination with particle leaching method using composite powder as starting material possesses controllable porosity and interconnectivity, as well as good mechanical strength comparable to human cancellous bone, suitable for being the tissue-engineered scaffold for load-bearing bone repair. Furthermore, scaffold made by phase separation using composite paste as starting material exhibits an anisotropy both in morphology and mechanical properties, which indicates the potential of guiding cell seeding, distribution and new tissue formation in preferential direction.