Pengjian Li

Current Progress in Bioactive Ceramic Scaffolds for Bone Repair and Regeneration

Bioactive ceramics have received great attention in the past decades owing to their success in stimulating cell proliferation, differentiation and bone tissue regeneration. They can react and form chemical bonds with cells and tissues in human body. This paper provides a comprehensive review of the application of bioactive ceramics for bone repair and regeneration. The review systematically summarizes the types and characters of bioactive ceramics, the fabrication methods for nanostructure and hierarchically porous structure, typical toughness methods for ceramic scaffold and corresponding mechanisms such as fiber toughness, whisker toughness and particle toughness. Moreover, greater insights into the mechanisms of interaction between ceramics and cells are provided, as well as the development of ceramic-based composite materials. The development and challenges of bioactive ceramics are also discussed from the perspective of bone repair and regeneration.

Fabrication and Characterization of Porous 45S5 Glass Scaffolds via Direct Selective Laser Sintering

A porous 45S5 bioactive glass-ceramic scaffold has been designed and fabricated via direct selective laser sintering (SLS). The scaffolds sintered over a range of laser powers from 6.0 to 30.0 W were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Their mechanical properties were tested with Vickers hardness tester. The testing results showed that the 45S5 glass in an initial amorphous state was transformed into the favorable crystallization phase Na2Ca2Si3O9 by inhibiting other phase transformation due to the rapid heating and cooling of laser. The 45S5 particles began to soften and fuse together with the increased laser power during the sintering process. At a proper range of laser power (around 15.0 W), the sample became denser and had higher degree of crystallinity with superior fracture toughness. Further increasing the laser power, the 45S5 glass powders were melted, and there are the undesired holes or even sinking emerged on the surface of the sample. So, the scaffold with the superior fracture toughness and degree of crystallinity has been obtained under the laser power of 15.0 W.

Bioactivity Improvement of Forsterite-Based Scaffolds with nano-58S Bioactive Glass

Forsterite-based composite scaffolds with interconnected pore architecture were successfully manufactured via selective laser sintering. The nano-58S bioactive glass (BG) was added to forsterite for purpose of improving the bioactivity of the composite scaffolds. The effect of nano-58S BG contents on the biological behavior and mechanical properties was investigated. The results showed that the composite scaffolds could induce the formation of apatite compared with the pure forsterite scaffolds. Moreover, with increasing nano-58S BG, the scattered spherical apatite particles accumulated continuously and covered the whole surface. At last the apatite layer became sponge-like shape. The presence of apatite was confirmed with scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. In addition, MG-63 cells adhesion was enhanced with increase in the amount of the nano-58S BG. Besides, the maximum compressive strength was 43.9 ± 1.1 MPa when the nano-58S BG was 20.0 wt%. This study indicated that the composite scaffolds have a potential for bone tissue engineering.

Novel forsterite scaffolds for bone tissue engineering: selective laser sintering fabrication and characterisation

Abstract The interconnected porous forsterite scaffolds were prepared by selective laser sintering at laser power from 4 to 10 W. The microstructure and composition of the scaffolds were analysed by scanning electron microscopy and X-ray diffraction. The mechanical properties were investigated with a universal testing system and a Vickers microindenter. The results showed that the sintering degree increased with increasing the laser power until a critical laser power had been reached (8 W). With the further increase of laser power, a few irregular cracks and voids occurred. It was attributed to the rapid outward expansion of the gas inside the powder layer, which was caused by the acute rising of temperature resulting from high laser power. The optimum compressive strength, elastic moduli and fracture toughness were 28·70±1·24 MPa, 154·72±6·95 MPa and 1·93±0·24 MPa m1/2 respectively. It was shown that MG-63 cells adhered, spread and grew well on the forsterite scaffolds, suggesting that the forsterite scaffolds might be appropriate for bone tissue engineering applications.

Optimize Structure Dimension of Spacer-Free Nozzle of Aluminum Roll Casting Using Orthogonal Experiment Design

Optimization of nozzle was crucial process to improve quality of production of roll casting, and nozzle without spacer should be pre-designed before placing spacer in it. Using orthogonal experiment design, three main structure dimensions and the speed of roll casting sheet were chosen as 4 factors, to make orthogonal array of 3 levels for simulation of nozzle. It was concluded that an optimal combination of factors and levels could be provided by orthogonal experiment, which might achieve optimum of good distributing of velocity and temperature of flow fluid in nozzle. The optimized result would be used as the original condition of integrated design of nozzle and spacers.

FABRICATION OPTIMIZATION OF NANOHYDROXYAPATITE ARTIFICIAL BONE SCAFFOLDS

Serious microcracks often occur on the surface of nanohydroxyapatite (n-HAP) artificial bone scaffolds prepared by selective laser sintering (SLS) technology. In this study, we found that appropriate preheating before sintering can reduce and attenuate the cracks. The microstructure and morphology of sintered n-HAP were tested at different preheating temperature and laser sintering speed with scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The experiments showed that the cracks gradually reduced and then disappeared when the preheating temperature increased from 0°C to 600°C while other parameters remain unchanged. The n-HAP particles gradually fused and grew up, while the grain size of sintered n-HAP will be attenuated with the increase of preheating temperature. As the thermal conductivity of n-HAP increases with increased preheating temperature, the temperature drops quickly, inhibiting greatly the grain growth of n-HAP. We obtained a group of optimum parameters when the sintered n-HAP still maintains nanostructure and possesses the optimal comprehensive performances, that is, laser power is 26 W, spot diameter is 4 mm, sintering speed is 200 mm/min, layer thickness is 0.4 mm, layer density is 852 kg/m3, and optimized preheating temperature is 600°C. These data illustrated that the cracks of sintered n-HAP can be eliminated at appropriate preheating temperature and sintering speed. This provided experimental optimal condition for the preparation of artificial bone scaffolds with nanohydroxyapatite ceramics.

Pre-design and Analysis of Flow Field of Spacer-Free Nozzle of Aluminum Roll-Casting

To optimize the design of flow field of nozzle in aluminum roll-casting, a coupled fluid-thermal finite element analysis using ANSYS software, was performed to explore the distributing of velocity and temperature of melt aluminum in spacer-free nozzle by MATLAB. Curve of velocity was gently sloping but curve of temperature was steep at outlet of spacer-free nozzle. It was explored that geometrical sizes of nozzle should be pre-designed to get better curves of velocity and temperature before placing spacers into nozzle.

An Optimization Scheme of Single-Spacer Nozzle of Aluminum Roll Casting Using Coupled Fluid-Thermal Finite Element Analysis

To optimize shape of single-spacer nozzle, width of single spacer was chosen to be the only optimized parameter to discover its influence on distribution of velocity and temperature of nozzle’s flow fluid. According to results of coupled fluid-thermal finite element analysis with four different widths of single spacer in nozzle, it was discovered that the greater width was, the more uneven of distribution of velocity and temperature of flow fluid at outlet of nozzle would be.

Quantitative Analysis of Orthogonal Experiment on Simulation of Fluid Field in Spacer-Free Nozzle in Aluminum Roll-Casting

Conventional analysis of orthogonal experimental results was applied to optimize structure of spacer-free nozzle in aluminum roll-casting. Weighting factors of velocity and temperature were determined in analysis with extreme deviation. It was concluded that good distributing of flow fluid’s velocity and temperature, would come with bigger width of outlet, modest thickness of entrance, and smaller thickness of outlet. The main effects in order of priority were investigated and advices on improving performance were given for industrial experiments.