Yi Nie

Structure and properties of nano-hydroxypatite scaffolds for bone tissue engineering with a selective laser sintering system

In this study, nano-hydroxypatite (n-HAP) bone scaffolds are prepared by a homemade selective laser sintering (SLS) system based on rapid prototyping (RP) technology. The SLS system consists of a precise three-axis motion platform and a laser with its optical focusing device. The implementation of arbitrary complex movements based on the non-uniform rational B-Spline (NURBS) theory is realized in this system. The effects of the sintering processing parameters on the microstructure of n-HAP are tested with x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The particles of n-HAP grow gradually and tend to become spherical-like from the initial needle-like shape, but still maintain a nanoscale structure at scanning speeds between 200 and 300 mm min(-1) when the laser power is 50 W, the light spot diameter 4 mm, and the layer thickness 0.3 mm. In addition, these changes do not result in decomposition of the n-HAP during the sintering process. The results suggest that the newly developed n-HAP scaffolds have the potential to serve as an excellent substrate in bone tissue engineering.

The microstructure evolution of nanohydroxapatite powder sintered for bone tissue engineering

Nanotechnology has been widely used to overcome the brittleness of coarse ceramics. Laser sintering is an effective approach for the preparation of nanoceramics due to the laser properties such as high energy density and rapid heating. In this study, the nanohydroxypatite (HAP) was used to prepare for artificial bone scaffold using a home-made selective laser sintering (SLS) system. The microstructure and the properties of the sintered nanoHAP are tested with scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. We found that the shape of nanoHAP particle changes from long needle-like to spherical or ellipsoidal after sintering, and the HAP particles grow up until they merge together with the increasing temperature. The tendency of preferred orientation reduces and the degree of crystallinity increases with the growth of nanoHAP. HAP dehydroxylation occurs during sintering. HAP decomposes to tetracalcium phosphate and β-calcium phosphate when the sintering temperature is over 1354°C (the laser power is 8.75 W). Sintered nanoHAP maintains a high degree of crystalline and nanometre scale when the laser power is 7.50 W, spot radius 2 mm, sintering time 4 s and thickness of the layer is 0.2 mm. This study presented the optimised technology parameters for the preparation of nanoceramics with a novel SLS system and demonstrated that the nanoceramics with nanosize scale can be obtained by this system.

Performance improvement of optical fiber coupler with electric heating versus gas heating

Gas heating has been widely used in the process of fused biconical tapering. However, as the instability and asymmetric flame temperature of gas heating exist, the performance of the optical devices fabricated by this method was affected. To overcome the problems resulting from gas combustion, an electric heater is designed and manufactured using a metal-ceramic (MoSi(2)) as a heating material. Our experimental data show that the fused-taper machine with an electric heater has improved the performance of optical devices by increasing the consistency of the extinction ratio, excess loss, and the splitting ratio over that of the previous gas heating mode. Microcrystallizations and microcracks were observed at the fused region of the polarization-maintaining (PM) fiber coupler and at the taper region with scanning electron microscopy and atomic force microscopy respectively. The distribution of the microcrystallizations and microcracks are nonuniform along the fiber with gas heating, while their distribution is rather uniform with electric heating. These findings show that the novel optical fiber coupler with an electric heater has improved the performance of optical fiber devices by affecting the consistency of the optical parameters and micromorphology of the surface of PM fiber.

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.

Control Software Development of a Novel Rapid Prototype Laser Sintering System for Fabricating Artificial Bone

An open motion control software for a novel selective laser sintering system has been developed to fabricate a three-dimensional porous artificial bone with complex shape. It adopts the library functions provided by a motion control card in Delphi 2006. It focuses on the realizations of control for ‘sintering a dot’, ‘sintering a line’ and ‘sintering a surface’ aiming at the characteristics of selective laser sintering. A problem that the transmission length of interpolation commands can not exceed certain value at a time due to constriction by the register capacity of the motion control card has been resolved. The control software has been successfully used in the experiment of laser sintering for fabricating artificial bone. The results show that the selective laser sintering system has high stability and accuracy.

Structural Analysis and Design Optimization of a Selective Laser Sintering System

A three dimensional geometric model of a homemade selective laser sintering (SLS) system is simplified and imported into Ansys Finite Element Software for static and modal analysis. The analysis results show that the supporting base that holds up the laser system undergoes large deformations. The machining accuracy can hardly meet the high-precision requirements of sintered parts with complex internal and external geometries. A method is put forward for the structural optimization of the SLS system. The calculation results show that the bending deformation of the supporting base decreases by 73.2%, and the maximum stress also decreases significantly. It indicates that the high precision manufacturing can be achieved with the improved SLS system.

Movement Realization of a Novel Fused Biconical Taper System Based on Electrical Heater

A novel fused biconical taper system is developed based on electrical heating system. Its movement platforms are designed. The main drawing movement platform, heater movement platform and packaging movement platform are focused on analysis. Motion control program is developed based on Delphi 2006 according to its technological requirements. The experimental results show that the movement of the novel fused biconical taper system is very stable, and the optical fiber couplers fabricated with the novel system have the good optical performance and the good consistency in particular.