纳米羟基磷灰石的溶胶-凝胶制备及其特性研究

采用溶胶-凝胶法制备羟基磷灰石的前体物--无定形磷酸钙(ACP),并进行晶化处理得到纳米羟基磷灰石(HAP).在Ca/P＝1.67的条件下,Ca(OEt)2和H3PO4在乙醇溶液中发生反应,合成ACP凝胶体.采用化学滴定法、透射电镜(TEM),X射线衍射法(XRD),BET,傅立叶红外吸收光谱分析法(FTIR)对晶化处理前后的ACP粉料进行的性能测试表明:溶胶-凝胶法制备的HAP粉料具有粒度小、晶化处理活性高、相纯度和结晶度优良的特点.     

The Effect of pH Value on Phase Transformation of Calcium Phosphate Cement

The effects of various pH values of sodium phosphate buffer solution (PBS), 4.0, 6.0, 8.0, and 9.0 on calcium phosphate cement (CPC) prepared by mixing monocalcium phosphate monohydrate (MCPM), calcium carbonate, and PBS were studied. The phase evolution takes place in three steps: Firstly, the MCPM and calcium carbonate crystals dissolve in the PBS and precipitate in the form of DCPD crystals. Then, after 12 h, DCPD begins to convert to amorphous calcium phosphate (ACP). Finally, the metastable ACP phase converts into stable CDHA. With an increase in the pH of the PBS, the CDHA content in the CPC increased.     

Collagen modulating crystallization of apatite in a biomimetic gel system

Apatite crystals were formed at 37 °C in a biomimetic gel system with the presence and absence of collagen under pH 6.5, 7.0 and 7.5 respectively. X-ray diffraction, transmission electron microscope and selected area electron diffraction pattern were applied to characterize the crystals. The results indicated that collagen modulate crystallization of apatite both in composition and morphology. With the absence of collagen, the obtained crystals were ribbon-shaped octacalcium phosphate (OCP) at pH 6.5, the mixture of OCP and nanosize rod-shaped hydroxyapatite (HAP) at pH 7.0 and 7.5 respectively. OCP would be a precursor of HAP with the absence of collagen. With the presence of collagen, collagen acted more effectively in controlling crystallization of HAP than pH did in the system. Ribbon-shaped HAP was the main phase at pH 6.5, kept a very thin structure at pH 7.0 while the needle-shaped HAP with several nanometers in diameter was obtained at pH 7.5. It was discussed amorphous calcium phosphate would be an intermediate phase of HAP with the presence of collagen. Such understanding of collagen and pH control on biomineralization gives new insights on the controlled synthesis of apatite.     

Preparation of Nanostructured Hexagonal Boron Nitride Powder

In this communication, we describe an inexpensive and feasible method for the preparation of hexagonal boron nitride (h–BN) nanorods in the absence of metal catalyst. Tertiary calcium phosphate (Ca₃(PO₄)₂) and ammonium biborate hydrate (NH₄HB₄O₇·3H₂O) were selected as starting materials where calcium phosphate was used as a diluting agent to prevent the formation of bulk B₂O₃ during the thermolysis of ammonium biborate hydrate. The mixture was nitrided at 900°C in the flowing ammonia and was transformed into h–BN nanorods after subsequent crystallization. After crystallization at 1650°C for 2 h, the unique microstructure of h–BN nanorods was observed.     

Effect of Chemical Structure and Composition of the Resin Phase on Vinyl Conversion of Amorphous Calcium Phosphate-filled Composites

The objective of this study was to elucidate the effect of chemical structure and composition of the polymer matrix on the degree of vinyl conversion (DC) of copolymers (unfilled resins) and their amorphous calcium phosphate (ACP) composites attained upon photo-polymerization. The DC can also be an indicator of the relative potential of these polymeric materials to leach out into the oral environment un-reacted monomers that could adversely affect their biocompatibility. The following resins were examined: 1) 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) (1:1 mass ratio; BT resin) combined with hydroxyethyl methacrylate (HEMA; BTH resin) and with HEMA and zirconyl dimethacrylate (BTHZ resin), 2) urethane dimethacrylate (UDMA)/HEMA resins, and 3) pyromellitic glycerol dimethacrylate (PMGDMA)/TEGDMA (PT resin). To make composite specimens, resins were mixed with a mass fraction of 40 % zirconia-hybridized ACP. Copolymers and their composites were evaluated by near infra-red spectroscopy for DC after 1 d and 28 d post-cure at 23 °C. Inclusion of HEMA into the BT and UDMA resins yielded copolymers and composites with the highest DCs. The significantly lower DCs of PT copolymers and their composites are attributed to the rigid aromatic core structure, tetra-vinyl functionality and limited methacrylate side-chain flexibility of the surface-active PMGDMA monomer. There was, however, an increase in the 28 d DC for the PT materials as there was for the BTHZ system. Surprisingly, the usual decrease observed in DC in going from unfilled polymer to composite was reversed for the PT system.     

Purification of L-asparaginase II by crystallization

Here a case study of L-asparaginase II out of a recombinant Escherichia coli is presented. The target protein was obtained by simple cell disintegration and acetone precipitation. The L-asparaginase II has been crystallized in three different forms in the following microbatch crystallization. The rod-shaped crystals (~400 μm edge length) were obtained at either 8°C or 22°C after 17 h by addition of PEG₆₀₀₀. The rectangular-shaped crystals were obtained after further recrystallization of the rod-shaped crystals. The rhombic-shaped crystals formed at 8°C after 12 days when cold ethanol was used instead of PEG₆₀₀₀. All crystallizations were performed in tris-acetate buffer (50 mmol·L^-1, pH 5.1). By crystallization, the specific activity of L-asparaginase II has increased 5-fold. The protein content and the purity of the crystals were evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The more concentrated L-asparaginase II out of an extract mixture and the presence of only less minor proteins after crystallization demonstrates that crystallization is an effective and mild method to purify the target protein. The single crystal X-ray diffraction pattern reveals that the crystals are proteins and the X-ray powder diffraction (XRPD) pattern shows clearly that the crystals forming in PEG₆₀₀₀ and ethanol have different crystal structures.     

Thermal crystallisation of amorphous calcium phosphate to α-tricalcium phosphate

Dehydration and thermal change in amorphous calcium phosphate (ACP) have been studied by thermogravimetry, differential thermal analysis and X-ray diffractometry. ACP retained water up to about 773 K. Immediately after the dehydration, a high-temperature form of calcium phosphate, α —Ca₃(PO₄)₂ (α -TCP), was obtained by ignition of ACP precipitated from the solution with a high degree of supersaturation. The kinetics of thermal crystallisation of α-TCP from ACP were also studied.     

酪蛋白溶解与酶解行为的动态光散射

采用动态光散射技术,以磷酸盐为缓冲液,研究了温度、离子强度和酶解行为对酪蛋白胶束平均流体力学半径(Rh)的影响规律. 结果表明,Rh值在升温过程中发生不可逆减小;随着离子强度增大,Rh值先减小再增大;酪蛋白在胰蛋白酶作用下,溶液光散射强度对应于分子量大小先急剧下降,再逐渐趋于平缓,而Rh值的变化规律与之相反;并推测了酪蛋白胶束酶解过程的结构变化模型,即由原始致密的球状体逐渐舒展为松散而规则的毛束状蛋白肽链.     

Preparation of Nanohydroxyapatite by a Sol–Gel Method Using Alginic Acid as a Complexing Agent

Single-phase calcium hydroxyapatite (HAP) was synthesized by a sol–gel route using calcium nitrate solution and ammonium dihydrogen phosphate solution as Ca and P sources and alginic acid as a chelating agent. The dried gel was heat-treated at different temperatures in the range of 110°–900°C. Structural evolution from sol to gel and from the gel to HAP was studied by the powder X-ray diffraction method, Infrared spectroscopy, and thermal analyses. The formation temperature of HAP was confirmed to be ∼300°C. Examination of the product obtained at 300°C under TEM suggested the development of hexagonal-shaped nanoparticles, with the average particle size in the range of 50–100 nm.     

Phase Evolution during the Formation of α-Tricalcium Phosphate

The formation of α-tricalcium phosphate from monobasic ammonium phosphate and calcium carbonate was investigated using a number of complementary techniques. Differential thermal analysis showed five distinct thermal events attributed to melting of the ammonium phosphate, decomposition of acidic calcium orthophosphate into an amorphous calcium metaphosphate, crystallization of β-calcium metaphosphate, crystallization of β-calcium pyrophosphate, and calcination of calcium carbonate. X-ray diffraction analyses as a function of temperature supported the evolution of these events and phases and also showed the formation of other intermediates, including an amorphous phase, apatite, lime, and β-tricalcium phosphate. Thermal gravimetric analysis (TGA) showed a large weight loss occurring between 150° and 250°C due to reaction between the acidic phosphate liquid and the calcium carbonate. This resulted in an amorphous intermediate with a Ca/P ratio between 0.5 and 1.0 from which both β-calcium metaphosphate and β-calcium pyrophosphate crystallized. Mass spectroscopy indicated that the ammonia and carbon dioxide were evolved in four different steps, while water was evolved in at least five steps. These decomposition steps correlated with those observed by TGA. Scanning electron microscopy indicated the formation of an intermediate phase that coated the calcium carbonate by 250°C. The proposed mechanistic reaction path to alpha-tricalcium phosphate involves the formation and consumption of the following sequence of intermediates: an acidic amorphous condensed phosphate; β-calcium metaphosphate and β-calcium pyrophosphate; lime, apatite, and β-tricalcium phosphate.     

Europium-doped amorphous calcium phosphate porous nanospheres: preparation and application as luminescent drug carriers

Calcium phosphate is the most important inorganic constituent of biological tissues, and synthetic calcium phosphate has been widely used as biomaterials. In this study, a facile method has been developed for the fabrication of amorphous calcium phosphate (ACP)/polylactide-block-monomethoxy(polyethyleneglycol) hybrid nanoparticles and ACP porous nanospheres. Europium-doping is performed to enable photoluminescence (PL) function of ACP porous nanospheres. A high specific surface area of the europium-doped ACP (Eu³⁺:ACP) porous nanospheres is achieved (126.7 m²/g). PL properties of Eu³⁺:ACP porous nanospheres are investigated, and the most intense peak at 612 nm is observed at 5 mol% Eu³⁺ doping. In vitro cytotoxicity experiments indicate that the as-prepared Eu³⁺:ACP porous nanospheres are biocompatible. In vitro drug release experiments indicate that the ibuprofen-loaded Eu³⁺:ACP porous nanospheres show a slow and sustained drug release in simulated body fluid. We have found that the cumulative amount of released drug has a linear relationship with the natural logarithm of release time (ln(t)). The Eu³⁺:ACP porous nanospheres are bioactive, and can transform to hydroxyapatite during drug release. The PL properties of drug-loaded nanocarriers before and after drug release are also investigated.     

Amorphous calcium phosphate composites with improved mechanical properties

Hybridized zirconium amorphous calcium phosphate (ACP)-filled methacrylate composites make good calcium and phosphate releasing materials for anti-demineralizing/remineralizing applications with low mechanical demands. The objective of this study was to assess the effect of the particle size of the filler on the mechanical properties of these composites. Photo-curable resins were formulated from ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate. Camphorquinone and ethyl-4-N,N-dimethylaminobenzoate were utilized as components of the photoinitiator system. After 2 h of mechanical milling in isopropanol, an approximate 64 % reduction in the median particle diameter was observed [27.48 μm vs. 9.98 μm] for unmilled and milled wet ACP, respectively. Dry ACP showed a 43 % reduction in particle size from pre- to post-milling. As well as dry composites, those that had been immersed in aqueous media were evaluated for their Young's Modulus, water sorption, biaxial tensile, three-point flexural and diametral tensile strength. Mechanically milling the filler increased the volume of fine particles in the composite specimens, resulting in a more homogeneous intra-composite distribution of ACP and a reduction in voids. In turn, less water diffused into the milled composites upon aqueous exposure, and they showed a marked improvement in biaxial flexure strength and a moderate improvement in flexural strength over composites with unmilled ACP. The demonstrated improvement in the mechanical stability of milled Zr-ACP composites may help in extending their dental applicability.     

Preparation and Sustained-Release Property of Triblock Copolymer/Calcium Phosphate Nanocomposite as Nanocarrier for Hydrophobic Drug

The P123/ACP nanocomposite with sizes less than 100 nm consisting of triblock copolymer P123 and amorphous calcium phosphate (ACP) has been prepared by using an aqueous solution containing CaCl₂, (NH₄)₃PO₄, and P123 at room temperature. The P123/ACP nanocomposite is used as the nanocarrier for hydrophobic drug ibuprofen, based on the combined advantages of both amphiphilic block copolymer and calcium phosphate delivery system. The P123/ACP nanocomposite has a much higher ibuprofen loading capacity (148 mg/g) than the single-phase calcium phosphate nanostructures. The drug release percentage of the P123/ACP nanocomposite in simulated body fluid reaches about 100% in a period of 156 h, which is much slower than that of single-phase calcium phosphate nanostructures. It is expected that the P123/ACP nanocomposite is promising for the application in the controlled delivery of hydrophobic drugs.     

Synthesis and thermal stability of potassium substituted hydroxyapatites and hydroxyapatite/β-tricalciumphosphate mixtures

Hydroxyapatite (HAP) and biphasic ceramics of two different HAP and β-tricalcium phosphate (β-TCP) proportions with substituted potassium were prepared through the aqueous precipitation method. The prepared powders were characterized using XRD, FT-IR and elemental analysis. The results have shown that potassium added during the synthesis was found present in the apatite structure even after calcination at 1300 °C without showing any significant change in the phase behaviour of resultant apatites. The substitution of potassium in the calcium deficient apatites was accompanied by the formation of biphasic mixture of HAP and β-TCP ceramics, upon calcination beyond 700 °C and the resultant mixtures were dependent on the initial Ca/P ratios of the precursors. The calculated cell constant values for potassium substituted apatites have shown contraction in a-axis and irregular changes in the c-axis relative to those of pure HAP prepared under the same experimental conditions.     

从糠饼中生产干酪素联产磷酸氢钙新工艺

提出了利用糠饼生产干酪素联产磷酸氢钙的新工艺 ,实验确定了最佳工艺条件和影响产品收率的主要因素。所得产品质量稳定 ,干酪素收率达 16.5 % ,副产品磷酸氢钙收率 7.5 %。     

牛奶中酪蛋白和乳糖的分离方法研究

用蛋白质等电沉淀法从牛奶中分离酪蛋白和乳糖。酪蛋白分离的最佳工艺参数为:提取温度40℃,pH值4.8,乙醇用量20 mL/100 mL牛奶;乳糖分离的最佳工艺参数为:pH值4.8,碳酸钙用量2.5 g/100 mL牛奶,结晶时间4 d。温度对乳糖得率的影响不大。     

Phase transformation on bone cement: Monocalcium phosphate monohydrate into calcium-deficient hydroxyapatite during setting

This study evaluated the phase transformation of calcium phosphate cement (CPC) using a mixture of monocalcium phosphate monohydrate (MCPM) and CaCO₃ as the solid phase and either water or a sodium phosphate buffer (SPB) solution (pH=7.0) as the liquid phase. The synthetic CPC was characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The setting reaction in the SPB solution involved three phase transformations. Firstly, MCPM and CaCO₃ reacted with sodium phosphate immediately to form dicalcium phosphate dehydrate (DCPD) which continued to dissolve. Secondly, meanwhile, an intermediate amorphous calcium phosphate (ACP) was formed. Finally, ACP transformed into calcium-deficient hydroxyapatite (CDHA). In contrast, the reaction stopped at the first stage in water. Consequently, the SPB solution not only caused the dissolution of DCPD but also provided the buffering capacity to induce the conversion of the starting materials to CDHA.     

Crystallization and coalescence of block copolymer micelles in semicrystalline block copolymer/amorphous homopolymer blends

Crystallization of two oxyethylene/oxybutylene block copolymers (E₇₆B₃₈ and E₁₅₅B₇₆) from micelles in block copolymer/amorphous homopolymer blends was studied by differential scanning calorimetry (DSC) and time-resolved small angle X-ray scattering (SAXS). Unlike the simultaneous crystallization and formation of superstructure in crystallization from an ordered structure, crystallization of block copolymer from micelles can be divided into two steps. The core of the micelles firstly crystallizes individually, with first-order crystallization kinetics and homogeneous nucleation mechanism. The SAXS revealed that crystallization-induced deformation occurs for the micelles, which strongly depends on microstructure of the block copolymers. For the shorter block copolymer E₇₆B₃₈, larger deformation induced by crystallization was observed, leading to coalescence of the micelles after crystallization, while for the longer block copolymer E₁₅₅B₇₆ the micelles show little deformation and the morphology of micelle is retained after crystallization.     

Formation of Apatite Coatings on an Artificial Ligament Using a Plasma- and Precursor-Assisted Biomimetic Process

A plasma- and precursor-assisted biomimetic process utilizing plasma and alternate dipping treatments was applied to a Leed-Keio artificial ligament to produce a thin coating of apatite in a supersaturated calcium phosphate solution. Following plasma surface modification, the specimen was alternately dipped in calcium and phosphate ion solutions three times (alternate dipping treatment) to create a precoating containing amorphous calcium phosphate (ACP) which is an apatite precursor. To grow an apatite layer on the ACP precoating, the ACP-precoated specimen was immersed for 24 h in a simulated body fluid with ion concentrations approximately equal to those in human blood plasma. The plasma surface modification was necessary to create an adequate apatite coating and to improve the coating adhesion depending on the plasma power density. The apatite coating prepared using the optimized conditions formed a thin-film that covered the entire surface of the artificial ligament. The resulting apatite-coated artificial ligament should exhibit improved osseointegration within the bone tunnel and possesses great potential for use in ligament reconstructions.     

Crystallization Study and Comparative in Vitro-in Vivo Hydrolysis of PLA Reinforcement Ligament

In the present work, the crystallization behavior and in vitro-in vivo hydrolysis rates of PLA absorbable reinforcement ligaments used in orthopaedics for the repair and reinforcement of articulation instabilities were studied. Tensile strength tests showed that this reinforcement ligament has similar mechanical properties to Fascia Latta, which is an allograft sourced from the ilio-tibial band of the human body. The PLA reinforcement ligament is a semicrystalline material with a glass transition temperature around 61 °C and a melting point of ~178 °C. Dynamic crystallization revealed that, although the crystallization rates of the material are slow, they are faster than the often-reported PLA crystallization rates. Mass loss and molecular weight reduction measurements showed that in vitro hydrolysis at 50 °C initially takes place at a slow rate, which gets progressively higher after 30-40 days. As found from SEM micrographs, deterioration of the PLA fibers begins during this time. Furthermore, as found from in vivo hydrolysis in the human body, the PLA reinforcement ligament is fully biocompatible and after 6 months of implantation is completely covered with flesh. However, the observed hydrolysis rate from in vivo studies was slow due to high molecular weight and degree of crystallinity.