Key Engineering Materials Vols. 336-338

Abstract: Porous hydroxyapatite bioceramics were obtained by impregnating the polyurethane sponge with rheologically optimized slurry. 6wt% bioglass was doped into hydroxyapatite to act as a sintering additive. Thermal analysis was used to study the pyrolysis process of the polyurethane sponge. Phase component and surface morphology were characterized by X-ray diffraction and scanning electron microscopy, respectively. It was found that hydroxyapatite was the main phase composition of the porous ceramics sintered at 1250°C. The porous bodies prepared had an open, uniform and interconnected structure with pore size of 200-400μm. The porous ceramics possessed high porosity of 70-80% and compressive strength of 2.3MPa. The precipitates formed on the surface of the porous ceramics might be bone-like apatite after immersion in a simulated body fluid for various periods.

Abstract: This work has achieved a novel self-setting biphase porous calcium phosphate cement (CPC). This biphase porous CPC is mainly formed by α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). The influence of the weight percent (wt%) of β-TCP of the powder was studied. The setting time is mainly 10-30min, and increasing with the weight percent of β-TCP. Powder ray diffraction (XRD) analysis showed that most α-TCP have turned to low-crystallinized HA after immersed in Simulated Body Fluid (SBF) of 37°C for 7 days. SEM observation showed that the resultants are mainly formed with micropores and microcrystallites, and more micropores turned out in cements with more β-TCP after immersed in SBF for 8 weeks.

Abstract: The porous structure of calcium phosphate ceramics is one of the essential conditions resulting in bone formation. The porous structure of biphasic HA/β-TCP ceramics was improved by adding microporous porosifer and the porous characteristics such as porosity, pore size and pore size distribution were determined by the mercury intrusion porosimetry, the cell culture in vitro and the animal experiment. By means of SEM and fluorescence decoration, cells were observed firstly attaching the edge of macropores of specimens and the wall of the macropores with micropores when co-cultured with HA/β-TCP ceramics. The specimens were also implanted in dorsal muscles of healthy dogs for 1.5and 3 months. More bone formation in the specimen with microporous porosifer was found by histological observation after taking out. It suggested that the micropores in the walls of macropores of bioceramics had important effect upon their osteoinduction.

Abstract: Calcium phosphate cement (CPC) is a kind of promising materials used in dental and orthopeadic restoration. Nowadays, CPC is of special interest due to its self-setting behavior when mixed with an aqueous liquid phase. In this study, α-tricalcium phosphate (α-TCP) and tetracalcium phosphate (TeCP) were served as the solid component of the cement, and the liquid component was consisted of sodium phosphate dibasic dedocahydrate (SPDD, Na2HPO4·12H2O), and/or citric acid. The cement’s properties as compressive strength and porosity were measured. The effects of preparing conditions, such as liquid-to-powder ratio (L/P) and liquid composition, on compressive strength of calcium phosphate were investigated. The results show that the compressive strength increases with the decreasing of pH value. There is a premium L/P in which the compressive strength gains its maxim. The compressive strength reached 21.69 MPa at the condition of L/P = 0.30mL/g and pH =5.

Abstract: The in vivo study was performed to evaluate the biocompatibility and osteogenous ability of injectable fast-setting calcium phosphate cement (CPC). Eighteen four-week-old New Zealand white rabbits were divided into six groups randomly, three in each group. According to the principle of selfcontrast at the same time, cavities of 5mm in diameter and 6mm in depth were drilled in femoral condyle of rabbits. The materials were implanted into cavities of the left leg, the right leg as the blank control group. Rabbits were sacrificed at 2, 4, 8, 12, 16 and 24 weeks after surgery. The microstructure of specimens was observed using ESEM. The results showed that injectable fast-setting CPC had good fluidity and plasticity; it could be injected into bone defects and fast-set in situ. The start setting time was 5-8 min and the compressive strength was 25-30 MPa. The CPC had good biocompatibility and osteoconductivity, and benefited to the repair of bone defects.

Abstract: Calcium phosphate cements (CPCs) are well-known orthopedic materials for filling bone. However, CPC pastes tend to disintegrate immediately when contacting with blood or other aqueous (body) fluids, which is a main limitation of its clinical applications in bone repairing, reconstruction and augmentation. To improve the anti-washout performance of CPC, modified starches such as pre-gelatinized starch, etherified starch, and esterified starch were added to the liquid phase of CPC in this work. CPC with good anti-washout performance was prepared and the effects of the modified starches on the properties of CPC were investigated. The results showed that the CPC with the modified starches were more stable in simulated body fluid than that without modified starch, especially the CPC with the etherified starch (II). X-ray diffraction analysis revealed that the modified starches did not inhibit CPC components from converting to hydroxyapatite. Furthermore, the anti-washout mechanism of the modified starches in CPC was discussed. It is concluded that the addition of the modified starches such as pre-gelatinized starch, etherified starch, and esterified starch to CPC can improve its anti-washout performance and should be of value in clinical surgery where the cement is exposed to blood.

Abstract: Electrically conducting polymer containing calcium phosphate coating (ppy/brushite) was made on the Ti-6Al-4V surface by means of electrochemically assisted co-precipitation. This study examined the effects of the electrically conducting polymer on electrochemically assisted co-precipitation of ppy/ brushite onto titanium alloys. Electrochemically assisted co-precipitation of ppy/ brushite coatings resulted in an increase in the thickness and adhesion of coatings compared to those of coatings of single calcium phosphate at the same deposition conditions. The surface morphology of coatings characterized by SEM showed that the morphology of ppy/ brushite was superior to that of brushite. XRD indicated that ppy did not change the phase of brushite. Thus, this electrochemically assisted co-precipitation technique provides an effective method of polypyrrole incorporation at physiological temperature, which can offer excellent thickness, adhesion and structure of coatings, with a potential for sustained release of therapeutic agents as required for metallic implant fixation.

Abstract: CaSO4/β-TCP composite powders were prepared by mixing CaSO4 and β-TCP. The CaSO4 /β-TCP (VS: VP) values were varied from 3:2 to 0:1. The composites were sintered at different temperatures. Tris was used to evaluate degradation behavior of the composites. The morphologies of composites before and after degradation were studied by SEM. The results show that degradation was increased with the increasing of VS: VP and decreased with the increasing of sintered temperatures.

Abstract: The purpose of this study is to explore the osteoinductivity of the composite materials (calcium phosphate ceramics/PLA or collagen composites) with similar physical character of osteoinductive calcium phosphate ceramics and the influence of the chemical composition of the composite materials on osteoinductivity, and also to provide an experimental evidence for optimizing the design of the composite materials. Two kinds of composite materials were prepared. One (BCP/PLA) is fabricated with different ratio of BCP (biphasic calcium phosphate) ceramics powder and PDLLA powder through the particulateleaching technique. The other (BCP/collagen) is that BCP ceramics sintered at 1250oC and modified with collagen. The porous materials cylinders with Φ 5×8 mm were prepared. SEM was used to observe the microstructure and physical morphology of the composite materials. The two groups of composite materials cylinders were implanted in the dorsal muscles of four dogs. Six samples of each group were implanted in each dog respectively. The specimens were harvested at 2, 4, 12 and 24 weeks post operation, and thin decalcified sections were prepared for light microscopy (LM) analysis to evaluate their osteoinductivity and compare the capability of osteoinduction. The fibro-tissue and bone-like tissue were observed in the two composites, but no obvious bone formation was found in the tested periods. The results indicated that the composite materials could modify the mechanical property of ceramics. However, if the composite materials were biodegraded soon, new bone could not form into the scaffold, and the calcium phosphate should be the major component of osteoinductive materials.

Abstract: The β-TCP granules with the range of diameter from 314μm to 800μm were prepared. The β-TCP/HAP composite bioceramics were prepared by dipping β-TCP discs made from the granules in HAP sol. The component and morphology of the ceramics were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The compressive strength of specimens was tested by Testometric M350-20KN. The results show that the samples can be calcined at 1150°C without phase transformation of β-TCP to α-TCP by doping the β-TCP with 1wt% MgO. And the compressive strength of the composite ceramics reaches 24MPa.