Key Engineering Materials Vols. 336-338

Abstract: The aim of the present study is to evaluate the biomineralization behavior of silk fibroin. The biomimetic mineralization was carried out in an alternative calcium/phosphate soaking solution (ACPS). The formation of calcium phosphate deposits was identified by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). A quick formation of well-crystallized apatite on the surface of the silk fibroin film indicates that biomineralization may be an effective approach to obtaining fibroin/HAP composites.

Abstract: Bone repair method has run to a new stage of bone tissue engineering. Doctors use bone scaffold to fill bone trauma and expect human regeneration ability to reconstruct bone trauma while bone is degrading. Scaffold is essential to bone tissue engineering. Scaffold should introduce new bone with scaffold’s conduction channel. But it’s still very difficult for scaffold to mimic fine structure of bone. Ideal scaffold should have similar component and microstructure to natural bone, which makes it more biocompatible and better to reconstructed bone. So we forward microCT aided design and preparation to solve this problem. MicroCT outputs both shape and three-dimensional internal density information. Then, we build computer model of scaffold with acquired microstructure. We fabricate scaffold that mimics natural bone by 3D rapid prototype machine.

Abstract: Ca3(PO4)2/ZrO2 dental composite ceramics using for CAD/CAM system were prepared and the effects of weak phases on microstructures and mechanical properties were studied. The results showed that intergranular spreads happened with the increasing Ca3(PO4)2 contents due to the discontinuity of weak interfaces between Zirconia and Calcium phosphate in matrix. So the flexural strength and hardness of the Ca3(PO4)2/ZrO2 composite ceramics were decreased effectively, which improved the machinability of the composites. On the other hand, strong interfaces between Zirconias increased the integrality of the ceramic structures. ZrO2 composite Ceramics with 15% Ca3(PO4)2 were sintered at 1350°C. The flexural strength is 300.44MPa, fracture toughness is 4.36 MPam1/2, and hardness is 6.69 GPa. The cutting exponent of the Ca3(PO4)2/ZrO2 composite ceramics is obviously lower than that of the common commercial Vita Mark II and Dicor MGC ceramics, which shows good mechanical properties and machinability.

Abstract: Crystallization behavior of ZrO2-ZnO-Al2O3-SiO2 glass has been studied by differential thermal analysis, X-ray diffraction analysis and scanning electronic microscope. ZrO2 doped in the glass induces the phase separation effectively. The crystal phases obtained are gahnite (ZnAl2O4) and a small amount of ZrO2 phase. SEM photographs show that the crystal phases distribute uniformly in the glass ceramics and the grain sizes of glass ceramics after different heat treatment are less than 60nm.

Abstract: 3Y-TZP ceramics were fabricated with the addition of 10wt% MgO-Al2O3-SiO2 glass additive by cold-isostatic pressing and afterwards liquid-phase sintering at 1200-1400°C for 2 h. The densities of samples sintered at 1300°C for 2 h reaches 99.1%, but further increase of sintering temperature results in the decrease of densities. XRD analysis showed that the cordierite crystals and a small amount of amorphous phase were presented at the grain junctions, and SEM observation indicated that the mean grain size of ZrO2 with round-shape ranged from 200 to 300 nm, which was below the critical transformation size, and the increase in sintering temperature was accompanied with an increase in the mean grain size. The strength and toughness of samples were kept in the range of 396-528 MPa, 4.4-5.8 MPa·m1/2 respectively, which could meet the need of clinical applications of all-ceramic dental materials.

Abstract: The effect of Si doping on the bioactivity and characteristics of hydroxyapatite/TiO2 composite films was investigated. Pure titanium plates were treated to form Ca, P and Si enriched titania-based films by using micro-arc oxidation (MAO). Then, some specimens were undergone a further hydrothermal treatment to produce a thin outermost layer of hydroxyapatite (HA). Experiments revealed that that the film, which was about 10μm thick, was composed of amorphous silicon dioxide, amorphous calcium phosphate, rutile and anatase. The film was porous and uneven, with the pore size of 1-4μm. No obvious cracks exist on the surface. In order to investigate the cytocompatibility of the films, periodontal ligament (PDL) cells were seeded onto the surface of the films. It was concluded that the Si ion did not influence the characters of MAO film but Si enriched hydroxyapatite/ TiO2 composite coatings exhibited an effect on cell attachment.

Abstract: The aim of this study was to analyze the microstructure and to observe the surface reactivity of a composite system composed of two kinds of zirconia/alumina (Z/A) composites and Vita alpha glass-ceramic, which would satisfy the biocompatibility and strength requirements for dental applications. Two zirconia/alumina composites defined as specimen A and B were used as the substrate of fixed partial denture, while commercial Vita alpha glass-ceramic as the coating-glass.
From the experiment we can find the following results. Zirconia particles migrated into grain boundaries and located at three or four grain junctions of alumina particles. The crack pattern is consistently transgranular for the zirconia grains, whereas it is intergranular for alumina grains. The mechanical properties of the composite with 66.6wt% zirconia was superior to that of 33.3wt% zirconia-composed composite, while the homogeneous bond between Vita alpha glass-ceramic and Z/A composites are distinct. Therefore, this system composed of Z/A composites and Vita alpha glass-ceramic would satisfy matching properties of dental requirements and it has a great future to be used as all-ceramic restoration materials.

Abstract: This study was conducted to evaluate the influence of surface roughness on anchoring strength between ceramic and coating glass. Commercial Vita alpha glass-ceramic was selected as the coating glass, while the zirconia/alumina (Z/A) composite as the substrate. Anchoring strength between substrate and coating-glass was tested, and microstructure of the junction was also observed. From the experiments we can find the following results. There was significant difference in the mean strength of different surface roughness groups and HF acid-etching also had a favorable effect on matching properties. The highest amount of anchoring strength was occurred at the high scope of roughness after HF acid-etching and surface roughness will also affect the microstructure of the junction. Therefore, we can draw the conclusions that with the limit of this research, roughness will influence matching properties between ceramic substrate and coating-glass, while hydrofluoric acid etching was also suggested in the matching procedure. Testing matching properties between ceramic substrate and coating-glass should consider the influence of surface roughness.

Abstract: The effect of carbon nanotubes (CNTs) on bending strength of calcium phosphate cement was investigated. The cement composite powders, containing 0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0wt% CNTs respectively, were prepared by ball milling. It was found that the presence of CNTs improved the bending strength of the cement from 6.6 MPa to the best 10.5 MPa. The reason for mechanical property improvement is related to the fibers (bars)-like microstructure of the reinforcing element, with CNT in the core and hydroxyapatite crystals growing on it.

Abstract: Unsintering macroporous calcium phosphate scaffolds with macropore sizes of 200∼400μm and hydroxyapatite nanofiber of in-situ growth were prepared by coating porous polyurethane templates with α-tricalcium phosphate bone cement (CPC) slurry, and their subsequent hydrolysis to calcium deficient hydroxyapatite (HAp) during the self-setting processes are presented. The effects of Sr2+ (SrNO3) on the nucleation, growth of the hydroxyapatite nanofiber and phase constitution were studied. The results show that the main component of the coating is HA after hydrolysis for 72h and the Sr2+ added could depress the growth of block or sheet HA crystal and promote the nanowhisker growth. This new processing technique can be used to improve the bioactivity of porous polymer template while maintaining its macroporous structure.