Papers by Author: Kui Cheng

Abstract: Aluminum phosphate is one of the best inorganic binders, and the addition of chromium oxide can improve the properties of the binder. In this work, the phase evolutions in chromium phosphate system and aluminum-chromium-phosphate system during heat-treatment were investigated. The initial binder solutions were prepared by dissolving Al(OH)3 and Cr2O3 in aqueous H3PO4 solution. The binder solutions consolidated at 100°C. The as-consolidated products were heated at different temperature. The experimental results showed the phase evolution of the consolidated products as: amorphous phase in 300~800°C, Cr(PO3)3 and Cr4(P2O7)3 in 900~1200°C for chromium phosphate system binder; amorphous phase in 300~1000°C, Cr(PO3)3 and AlPO4 in 1100°C, Cr4(P2O7)3 and AlPO4 in 1200°C for aluminumchromium- phosphate system binder. The addition of chromium oxide demonstrates to strengthen amorphous network, which further improves the thermal stability.

Abstract: The effect of Mn on the protein adsorption of calcium phosphate coatings is investigated in this work. Mn containing β-tricalcium phosphate (Mn-TCP) is first prepared through a coprecipitation based methods. Then Mn-TCP is dispersed into the fluoridated hydroxyapatite (FHA) precursor sol. Mn-TCP/FHA biphasic coatings are prepared with these sols. After cell culture, it is found the amount of protein adsorbed on the coatings following this rule: Mn-TCP/FHA > β-TCP/FHA > FHA. That is ascribed to two reasons: a) Ca and PO4 releasing can promote the activity of cells; b) Mn releasing promotes protein activation even at quite low concentration.

Abstract: Bone-Like Microstructured β-TCP/Collagen Layer on Fluoridated Hydroxyapatite Coating, which could able to create a biodegradation layer with enhancing bone formation, was prepared in wet synthesis. The formation of the layer was characterized and discussed.

Abstract: Two starting collagens, sponge and floc collagen, were used to prepare collagen/tricalcium phosphate (TCP) composites. The resulting composites were porous and had 200μm pore size. However, there was a difference in the microstructure of the pore walls for the composites derived from the two collagens, the pore walls in sponge collagen/TCP composite were still porous and had 200 nm micropores size, TCP particles were trapped in collagen matrices. While floc collagen/TCP composite had smooth and dense walls in which TCP particles were embedded. The difference could be attributed to the starting collagen with different status. Sponge collagen has a soft structure, which easily becomes disassembled fibrils during alkali treatment, the disassembled fibrils are integrated again to form a dense morphology for pore walls after freeze-drying. While floc collagen has already a low disassembly degree, the alkali treatment could not be able to separate the fibrils, this remains as micropores in pore walls after freeze-drying. Both porous composites are significant in bone tissue engineering or regeneration. MTT test results showed the two composites had good cytocompatibility, and sponge collagen/TCP composite was somewhat better than floc collagen/TCP composite, which could result from that micropores derived roughness in pore walls of sponge collagen/TCP composite is suitable for cell growth.

Abstract: Porous β-tricalcium phosphate (β-TCP)/ Poly L-lactic acid (PLLA) composites were prepared by thermally induced phase separation method. The results showed that the composite had an interconnected pore structure with ～200μm macropores. The inorganic particle content in the composites varied from 50% to 80% and these particles were homogeneously dispersed in PLLA matrix. The composites obtained in this study could act as a promising scaffold for bone tissue engineering because of the pore structure and the mechanical properties.

Abstract: In this work, nano-sized strontium containing tricalcium phosphate (SrTCP) particles with different strontium content were prepared using co-precipitation method in an ice-water bath and then 800°C calcination. The AAS results show that the relative Sr/(Sr+Ca) ratios are consistent with the amount of strontium added in the initial solution but larger than the designed molar percentage. The TEM micrographs demonstrate the size of the SrTCP particles is in the region of 150-400 nm while the pure TCP particle is about 500nm. The SEM photographs show the morphology of the particles before and after incorporation of strontium and it is obvious that the particle size of SrTCP decrease with the increasing of strontium content.

Abstract: Stearic acid was utilized to modify biphasic alpha-tricalcium phosphate (α-TCP)/hydroxyapatite (HA) powders in the ethanol. The results showed that the dispersion of biphasic α-TCP/HA powders (BCPs) in non-polar matrix improved. And the released content of Ca2+ and PO4 3- of the BCPs soaked in the NaAc-HAc buffer solution (pH 5.0) was almost same as that before modification. Stearic acid could modify the suface properties of BCPs and would not obviously affect their biological characteristics, which affords a good groundwork of application of calcium phosphates powders.

Abstract: Biphasic α-tricalcium phosphate/hydroxyapatite (α-TCP/HA) calcium phosphate (BCP) is prepared through a modified slip casting based method: α-TCP powders are dispersed in the HA precursor solutions to form castable slurries, then the slurries are poured into round mold. After curing, the slurries turn into cakes. Room temperature curing leads the cakes to contain α-TCP and HA phases. Higher temperature heat treatment will result in the increase of HA content, while even higher temperature will leads the cakes to be triphasic. Low temperature derived BCP have particular microstructure with HA covers the surface of α-TCP powders, and these powders further agglomerate into large blocks. After higher temperature treatment, β-TCP dominates the cake and microporous structure is resulted.

Abstract: In order to optimize the dissolution resistance, cell attachment and Ca and P releasing ability of the calcium phosphate coatings, Hydroxyapatite/fluorapatite (HA/FA) biphasic coatings are prepared and characterized. Ultrasonically dispersing of HA powders in the mixed ethanol solution of Ca(NO3)2, P2O5 and HPF6, to form a “colloidal sol” for dip coating. The coatings are prepared on Ti6Al4V substrate by dip coating, 150oC drying and 600oC firing. The coatings are characterized by X-ray Diffractometer for the crystalline phase, X-ray Photoelectron Spectroscopy for chemical composition and Scanning Electron Microscopy for the surface morphology. The results show biphasic HA/FA coatings with homogenous distribution of HA particle in the FA matrix can be obtained. The nominal F content of the coatings decreases with the increasing amount of HA, and the surface morphology is rough. These demonstrate the obtained biphasic HA/FA coatings are suitable to response to cells, accelerating bone formation.

Abstract: β-tricalcium phosphate (β-TCP)/collagen composites are in the limelight for their biomedical applications. It is believed that joint status of β-TCP particles with collagen fibrils plays key roles in both osteoconductivity and biodegradability of composites. In this work, the influence of acidity during synthesis on the joint status between nano-sized β-TCP particles and collagen fibrils is investigated. The composites are characterized by X-ray diffractometer and Field Emission Scanning Electron Microscope. The results show that the joint status of nano-sized β-TCP particles with collagen fibrils in the composites depends on the acidity in collagen suspensions. A desired joint status with obvious disassembled collagen fibril, good particle dispersion and strong boding between the particles and the fibrils could be obtained when acidity of the collagen suspension is pH 2.