外加剂对磷酸钙-水系统流动性能的影响

以无水碳酸钠、腐殖酸钠、鞣型减水剂（AST）作为磷酸钙-水系统外加剂,评价外加剂种类及用量对磷酸钙-水系统流动性能的影响。结果表明,随着外加剂用量的增加,磷酸钙-水系统的相对黏度均呈现先下降后升高的趋势,当外加剂用量为1%-1.5%时,均会明显降低磷酸钙-水系统相对黏度,进而提高磷酸钙-水系统的流动性。其中外加剂AST对提高磷酸钙-水系统的流动性较为显著,当AST用量为1.5%时,可使磷酸钙-水系统的相对黏度达到1.03 s/s,磷酸钙-水系统的流动性最佳。

Facile hydrothermal synthesis of TiO_2-Ca P nano-films on Ti6Al4V alloy

Ti6Al4V alloy was subjected to hydrothermal treatment in the concentrated Ca3(PO4)2, Ca HPO4 and Ca(H2PO4)2 solutions for bioactive surface modification. The treated samples are covered by films composed of nano-particles with the size of 60-240 nm. Such film can also be grown on the strut surface of a Ti6Al4 V scaffold prepared by electron beam melting(EBM) technology. XPS analysis indicates that Ti element on the surface presents as TiO2, and Ca and P elements are in the form of calcium phosphate. XRD and Raman analyses show that the surface layer is composed of anatase TiO2 and hydroxyapatite. Potentiodynamic polarization test in a Ca-free Hank's balanced solution demonstrates that the treated sample has markedly improved corrosion resistance compared with the polished sample. The present work provides a bioactive surface modification method that is easily-operated, low-temperature, less corrosion, and applicable to porous Ti6Al4 V alloy for biomedical applications.

Synthesis of Crystalline Hydroxyapatite from CaCO_3 and CaHPO_4·2H_2O by Mechanochemical Method

The mixture of CaHPO 4·2H 2O and CaCO 3 was ground in an aqueous system under appropriate conditions to investigate the mechanochemical reaction for the synthesis of crystalline hydroxyapatite (HA) powder. Hydroxyapatite of high crystallinity powder including trace Ca 10 (PO 4) 6CO 3(OH) and Ca 9HPO 4(PO 4) 6OH can be synthesized by mechanical activation without further thermal treatment at a high temperature. The synthesis reaction during the grinding process was almost completed within 1h. The as-ground powder exhibits a particle distribution of 20-100nm in size with a spherical or rodlike morphology. The composition and degree of crystallinity of the mechanochemical synthesized hydroxyapatite powders were coincident with the cement-type hydroxyapatite.

Effect of Additives on the Morphology of the Hydrated Product and Physical Properties of a Calcium Phosphate Cement

The morphology of a hydrated calcium phosphate cement （CPC） doped with several normally used additives was investigated by scanning electron microscopy （SEM） and the compressive strength of the cement was determined in this study. The hydrated products of CPC without additives was rod-like hydroxyapatite （HA） grains with around 2-5 μm in length and 100 nm in width. The addition of Sr obviously decreased the crystal size of the rod-like grains. CPCs containing carbonate, collagen and gelatin showed flake-like crystal morphology. Crylic acid-containing CPC presented flocculus-like structure. And malic acid-containing CPC exhibited oriented flake-like structure. The X-ray diffraction （XRD） analysis showed that the additives used in this study did not alter the hydration products of the cement. The compressive strength tests indicated that the compressive strength of the cement with rod-like morphology HA crystals was much higher than that of the cement with flake-like morphology HA crystals, and the cement with oriented flake-like morphology HA crystals exhibited the poorest compressive strength.

Microstructure and Mechanical Properties of Calcium Phosphate Cement/gelatine Composite Scaffold with Oriented Pore Structure for Bone Tissue Engineering

In this study,the macroporous calcium phosphate cement with oriented pore structure was prepared by freeze casting.SEM observation showed that the macropores in the porous calcium phosphate cement were interconnected aligned along the ice growth direction.The porosity of the as-prepared porous CPC was measured to be 87.6% by Archimede's principle.XRD patterns of specimens showed that poorly crystallized hydroxyapatite was the main phase present in the hydrated porous calcium phosphate cement.To improve the mechanical properties of the CPC scaffold,the 15% gelatine solution was infiltrated into the pores under vacuum and then the samples were freeze dried to form the CPC/gelatine composite scaffolds.After reinforced with gelatine,the compressive strength of CPC/gelatin composite increased to 5.12 MPa,around 50 times greater than that of the unreinforced macroporous CPC scaffold,which was only 0.1 MPa.And the toughness of the scaffold has been greatly improved via the gelatine reinforcement with a much greater fracture strain.SEM examination of the specimens indicated good bonding between the cement and gelatine.In conclusion,the calcium phosphate cement/gelatine composite with oriented pore structure prepared in this study might be a potential scaffold for bone tissue engineering.

Preparation and characterization of a novel injectable strontium-containing calcium phosphate cement with collagen

Purpose： To develop a novel injectable strontium-containing calcium phosphate cement with collagen. Methods： A novel calcium phosphate bone cement （CPC） was prepared with the addition of strontium element, collagenl, and modified starch; the injectability, solidification time, microstructure, phase composition, compressive strength, anti-collapsibility and histological properties of material were evaluated. Results： The results showed that the material could be injected with an excellent performance; the modified starch significantly improved the anti-washout property of cement; with the liquid to solid ratio of 0.3, the largest compressive strength of cement was obtained （48.0 MPa _＋ 2.3 MPa）; histological examination of repair tissue showed that the bone was repaired after 16 weeks; the degradation of cement was consistent with the new bone growth. Conclusion： A novel injectable collagen-strontium-containing CPC with excellent compressive strength and suitable setting time was prepared, with addition of modified starch. The CPC showed a good anti-washout property and the degradation time of the cement met with the new bone growing. This material is supposed to be used in orthopedic and maxillofacial surgery for bone defects.

Delivering MC3T3-E1 cells into injectable calcium phosphate cement through alginate-chitosan microcapsules for bone tissue engineering

Objective： To deliver cells deep into injectable calcium phosphate cement（CPC） through alginate-chitosan（AC） microcapsules and investigate the biological behavior of the cells released from microcapsules into the CPC.Methods： Mouse osteoblastic MC3T3-E1 cells were embedded in alginate and AC microcapsules using an electrostatic droplet generator.The two types of cell-encapsulating microcapsules were then mixed with a CPC paste.MC3T3-E1 cell viability was investigated using a Wst-8 kit,and osteogenic differentiation was demonstrated by an alkaline phosphatase（ALP） activity assay.Cell attachment in CPC was observed by an environment scanning electron microscopy.Results： Both alginate and AC microcapsules were able to release the encapsulated MC3T3-E1 cells when mixed with CPC paste.The released cells attached to the setting CPC scaffolds,survived,differentiated,and formed mineralized nodules.Cells grew in the pores concomitantly created by the AC microcapsules in situ within the CPC.At Day 21,cellular ALP activity in the AC group was approximately four times that at Day 7 and exceeded that of the alginate microcapsule group（P0.05）.Pores formed by the AC microcapsules had a diameter of several hundred microns and were spherical compared with those formed by alginate microcapsules.Conclusions： AC microcapsule is a promising carrier to release seeding cells deep into an injectable CPC scaffold for bone engineering.

Movement of Phosphorus in a Calcareous Soil as Affected by Humic Acid

When humic acid (HA) and phosphorus (P) fertilizer are simultaneously applied to soil, HA may affect the movement of P. A laboratory incubation experiment was conducted to quantify the effects of a commercial HA product co-applied with monocalcium phosphate (MCP) on the distance of P movement and the concentration of P in various forms at different distances from the P fertilizer application site in a calcareous soil from northern China. Fertilizer MCP (at a rate equivalent to 26.6 kg P ha-1 ) was applied alone or in combination with HA (at 254.8 kg HA ha-1 ) to the surface of soil packed in cylinders (150 mm high and 50 mm internal diameter), and then incubated at 320 g kg-1 moisture content for 7 and 28 d periods. Extraction and analysis of each 2 mm soil layer in columns showed that the addition of HA to MCP increased the distance of P movement and the concentrations of water-extractable P, acid-extractable P and Olsen P in soil. The addition of HA to MCP could enhance P availability by increasing the distance of P movement and the concentration of extractable P in soil surrounding the P fertilizer.

Experimental study on the repair of tibial plateau defect

Objective： To evaluate the effect of autograft bone, allograft bone, calcium sulfate bone cement, and calcium phosphate bone cement on the repair of tibial plateau defect in rabbits. Methods： We used autograft bone, allograft bone, calcium sulfate bone cement, and calcium phosphate bone ce ment to repair tibial plateau defect in rabbits. Gross and histo logic observations, Xray examination, and biomechanical test were conducted at 1, 2, 4, 8 weeks after operation. Results： Xray examination found that the bone den sity was evidently reduced in calcium sulfate group at 8 weeks after operation; there were no marked changes in other groups. The maximal load measurements showed that autograft and allograft groups were greater than calcium sulfate and calcium phosphate groups at 1 and 2 weeks after operation. However at 4 and 8 weeks after operation, no significant difference was found among the four groups. In autograft and allograft groups, there was no significant difference in biomechanical intensity at 2, 4, and 8 weeks,but it was significantly higher than that at 1 week. In cal cium sulfate and calcium phosphate groups, the outcome was ranked in descending order as 1 week〈 2 week〈 4 week =8 week. Histologic examination found a great amount of new bones at 8 week in both autograft and allograft groups. In calcium sulfate group, calcium sulfate was almost absorbed and there were numerous bone trabeculations. There was a large amount of unabsorbed calcium phosphate in calcium phosphate group. Conclusion： At 12 weeks postoperatively, the biome chanical intensity is higher in autograft and allograft groups than calcium sulfate and calcium phosphate groups, but after 48 weeks, there is no significant difference among groups. At 12 weeks, the biomechanical intensity in all groups is increased, but at 48 weeks, there is no significant increase. The rates of absorption and bone formation are quicker in calcium sulfate group than calcium phosphate group.