Papers by Author: Yin Zhang

Abstract: This Magnesium-doped calcium polyphosphate (MCPP) porous bioceramics of different magnesium content were prepared by the method of solid reaction sintering. The effect of magnesium on the structure and density of magnesium-doped calcium polyphosphate bioceramics was studied. Phases, cross section morphologies and porosity of MCPP bioceramics were analyzed with X-ray diffraction(XRD) and scanning electron microscopy (SEM). The results show that MCPP ceramics were successfully prepared by the solid reaction sintering, and the bending strength of ceramics began to increase and then to decrease with increasing amounts of magnesium content apart with the improvement of the stability improved.

Abstract: Calcium metaphosphate (CMP) fine powders were produced by a chemical precipitation method. In order to produce the powders, CMP was prepared by the mixing of two precursors, such as calcium oxide (CaO) and phosphate acid (H3PO4). Sparingly soluble chemicals, the Ca/P ratio of the mixture was set to be 0.50 to produce stoichiometric CMP, were chemical agitated in phosphate acid solution. At least 3 hours of pre-hydrolysis of phosphorus precursor were required to obtain CMP phase. The CMP powders were dried in a drying oven at 60°C for 72 hours and then heat-treated at various temperatures at a ramp of 1°C /min in air for various hours. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA, Zeta Potential Meter, Specific Surface Area, and Particle Size Analyzer. The results showed that obtained CMP powders have a significantly powder characteristics.

Abstract: There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting macropores whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated flexural strength of bimodal porous apatite ceramics prepared using apatite slurry and its slurry synthesis was studied. Slips with different contents of HAp (K-HAp and T-HAp) and deflocculant were prepared by milling in a pot mill. The viscosity of slurries made of commercial T-HAp powder showed a drop after 3 hours’ milling, but the viscosity of slurry with high solid content of k-HAp and 2.0 wt% deflocculant increased with an increase of milling time after 2 hours’ milling. The porosity and flexural strength of the porous HAp prepared by heating the foam dipped in K-HAp slip with 2.0 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C were 62.4 % and 14.7 MPa, and those in T-HAp were 59.7 % and 15.2 MPa with 1.5 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C.

Abstract: Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and betatricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios was prepared. One kinds of HAp and one kind of β-TCP powders were used to produce porous BCP bioceramics with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20. A slip was obtained by adding a mixed powders of HAp and β-TCP to a solution 1.5% of deflocculant and 0.5 wt% of foaming agent. The optimum value for the minimum viscosity in these present slips with respect to its solid loading and the optimum amount of the deflocculant were investigated. The specimen obtained by casting a polyurethane foam with 1.5 wt% of deflocculant into a slip, and drying it under vacuum, was heated at 1150°C for 3 hours. The resultant porous BCP sintered body had large spherical pores of 300 /m with interconnecting rectangular voids. Many small pores in the size range of 2-3 /m or below were observed in the specimen obtained by heating at 1150°C for 3 hours. The dissolution test was done as follows. The obtained porous ceramics samples about 0.5g individually soaked into 30 mL of simulated body fluid (SBF) solution at 36.5°C. The calcium and phosphorous content of the SBF solution was analyzed by ICP. The porous body was dried, and characterized using SEM, XRD, and FT-IR.

Abstract: A bimodal porous hydroxyapatite (HAp) body with high flexural strength was prepared through slip casting. HAp fine powder used in this study was synthesized by wet milling, drying and heating of a mixture of calcium hydrogen phosphate di-hydrate and calcium carbonate. The synthesized HAp powder was 0.32
0.05 μm in size and 38.1
0.8m2/g in specific surface area. The slip was prepared by adding deflocculant and foaming reagent. The optimum value for the minimum viscosity in the present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were studied. The total porosity of the specimens obtained from a slip of 48 wt% HAp solid loading is in the range of 49 – 61vol %, and the resultant porous HAp sintered body had large spherical pores of 300 -m with interconnecting rectangular voids. Many small pores in the size range of 2-3 -m or below were observed in the specimen obtained by heating at 1100, and 1200 . The flexural strength of the bimodal porous HAp ceramics sintered at 1200 C showed a large value of 17.6 MPa, with a porosity of 60.5vol.

Abstract: Two kinds of tri-calcium phosphate ceramics, β-TCP, which have the same macrostructure and microstructure, but different special surface area and particle size, were used in porous ceramics. A slip was obtained by adding the powders to a solution 1.0 wt% of deflocculant, respectively. The specimen obtained by casting a polyurethane foam with 0.5wt% into a slip, and drying it under vacuum, was heated at 1150
, for 3 hours. The porous ceramics samples about 0.5g were individually soaked into 30 mL of phosphate buffer saline (PBS) at 20
for 1,3,7 and 10 days, respectively. The calcium content of the PBS solution was analyzed by (ICP). The porous bodies were filtered, dried, and characterized using SEM, XPD, and FT-IR.

Abstract: The preparation of hyperstructured hydroxyapatite (HAp) ceramics is reported. Mesoporous silica with nano size pore was coated on the bi-modal type porous HAp ceramics with pore size 100-200 µm and 1-2 µm. The mesoporous silica coating was done using two different procedures and the ceramics were characterized by XRD, N2 Sorption, SEM/EDX, and TEM. The results clearly showed the formation of mesoporous coating on the large pores of parent HAp ceramics. SEM images reveal that the mesoporous coatings consists of almost spherical particles with relatively uniform sizes of ~1 µm. Protein adsorption and release behavior on these mesoporous coated HAp ceramics was evaluated using UV-VIS spectrometry. The large pores are suitable for cell immobilization, and the mesopores several nm in size were found to enhance protein encapsulation ability.

Abstract: Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios were prepared from fine powders. Porous BCP ceramic materials with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20 were prepared. In this study, the bioactivity is reduced at a bigger HAp content rate, which is likely related to the high driving pore for the formation of a new phase, and the reaction rate was proportional to the β-TCP. The porous BCP ceramics having a bigger porosity rate can easily under up dissolution. The powder having a bigger β-TCP content rate can easily generate a new phase. The dissolution results confirmed that the biodegradation of calcium phosphate ceramics could be controlled by simply adjusting the amount of HAp or β-TCP in the ceramics and porosity rate.

Abstract: The effect of different particle sizes on the flexural strength and microstructure of three different types of hydroxyapatite (HAp) powders was studied. The powder characteristics of laboratory synthesized HAp powder (Lab1 and Lab2) were obtained through a wet milling method, and the median particle size and the specific surface area of powders are different with the dryness period. The median particle sizes of Lab1 and Lab2 are 0.34 µm and 0.74 µm, and the specific surface areas of Lab1 and Lab2 are 38.01 m2/g and 19.77 m2/g. The commercial HAp had median particle size of 1.13 µm and specific surface area of 11.62m2/g. The different powder characteristics affected the slip characteristics, and the flexural strength and microstructure of the sintered porous HAp bodies are also different. The optimum value for the minimum viscosity in these present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were investigated. The flexural strengths of the porous HAp ceramics prepared by heating at 1200°C for 3 hrs in air were 17.59 MPa for Lab1 with a porosity of 60.48％, 10.51 MPa for Lab2 with a porosity of 57.75％, and 3.92 MPa for commercial HAp with a porosity of 79.37％.