Adhesion promotion via noncovalent interactions in self-healing polymers

Dimethylnorbornene ester (DNE) is successfully used as a noncovalent adhesion promoter. DNE was confirmed to copolymerize with dicyclopentadiene (DCPD) to yield a copolymer with better adhesion to an EPON 828 epoxy matrix relative to poly(DCPD) alone. The mechanical properties of the copolymer were comparable to that of poly(DCPD) alone. An optimized blend of the monomers was encapsulated using a urea-formaldheyde microencapsulation procedure and the resulting capsules were used for in situ self-healing experiments. Improved healing efficiency was observed for samples containing the DCPD/DNE capsules under conditions in which the monomers were efficiently polymerized.     

直流电位法检测高温合金的疲劳裂纹扩展性能

介绍了在高温下使用直流电位法测定疲劳裂纹长度的基本原理、试验方法及所需配置的仪器,并对有关影响因素进行了分析;并利用Johnson的分析型关系式,研究了一种适用于自动测定材料高温疲劳裂纹长度的直流电位法,该方法已成功应用于高温合金疲劳裂纹扩展试验,其测得的疲劳裂纹扩展速率da/dN-ΔK数据与长焦聚显微镜法测得的数据完全一致。     

介孔分子筛/聚双环戊二烯复合材料的制备

将负载催化剂的SBA-15型介孔分子筛(方法1)、偶联剂表面改性的SBA-15 (方法2)、偶联剂表面改性后负载催化剂的SBA-15 (方法3), 采用原位聚合法分别制备了SBA-15/聚双环戊二烯(PDCPD)复合材料。研究了不同制备方法对SBA-15/PDCPD力学性能的影响。结果表明, 对于方法2, 虽然偶联剂改性SBA-15可提高与PDCPD界面作用力, 但由于分子筛孔道中的双环戊二烯(DCPD)单体难以发生聚合反应, 导致复合材料的力学性能较PDCPD没有明显改善。采用方法1及方法3可使PDCPD分子链在SBA-15孔道中生成, 改善了PDCPD基体与SBA-15的界面作用力, 使复合材料的力学性能明显改善。采用方法1, SBA-15/PDCPD质量比为2∶100时, 复合材料拉伸强度较PDCPD提高了24.5%, 弯曲强度提高了24%。采用方法3制备的复合材料中偶联剂分子占据了SBA-15孔道空间, 导致孔道中生成聚合物分子链数量较方法1少, 使其力学性能提高幅度低于方法1, 但优于方法2。     

Effect of diluents on tablet integrity and controlled drug release

The objective of this study was to evaluate the effect of diluents and wax level on tablet integrity during heat treatment and dissolution for sustained-release formulations and the resultant effect on drug release. Dibasic calcium phosphate dihydrate (DCPD), microcrystalline cellulose (MCC), and lactose were evaluated for their effect on tablet integrity during drug dissolution and heat treatment in wax matrix formulations. A newly developed direct compression diluent, dibasic calcium phosphate anhydrous (DCPA), was also evaluated. Compritol® 888 ATO was used as the wax matrix material, with phenylpropanolamine hydrochloride (PPA) as a model drug. Tablets were made by direct compression and then subjected to heat treatment at 80°C for 30 min. The results showed that MCC, lactose, and DCPA could maintain tablets intact during heat treatment above the melting point of wax (70°C-75°C). However, DCPD tablets showed wax egress during the treatment. MCC tablets swelled and cracked during drug dissolution and resulted in quick release. DCPD and lactose tablets remained intact during dissolution and gave slower release than MCC tablets. DCPA tablets without heat treatment disintegrated very quickly and showed immediate release. In contrast, heat-treated DCPA tablets remained intact through the 24-hr dissolution test and only released about 80% PPA at 6 hr. In the investigation of wax level, DCPD was used as the diluent. The drug release rate decreased as the wax content increased from 15% to 81.25%. The dissolution data were best described by the Higuchi square-root-of-time model. Diluents showed various effects during heat treatment and drug dissolution. The integrity of the tablets was related to the drug release rate. Heat treatment retarded drug release if there was no wax egress.     

Microstructural evolution in external callus of human long bone

Accurate knowledge of bone fracture healing process is of clinical and theoretical importance in bone repair and regeneration, and biomineralization. It is well known that the histological healing occurs via the formation of hematoma, fibrocartilage, bony callus and bone modeling/remodeling. However, the detailed process from fracture to healing at the microstructural level remains unclear. In the present study, an evolutionary model of external callus is proposed, in which five representative stages are presented in terms of the organization of collagen and minerals during the formation of bony callus. The first stage is the formation of loose, disordered collagen fibrils, which is followed by mineralization on some of these individual microfibrils. Then the matrix is characterized by the fusion of mineralized individual fibrils into bundles. In the third stage, the absorption of disordered matrix occurs. This is gradually replaced by ordered collagen in stage four. Finally, completely ordered mineralized tissue is formed. The proper sequence of the process plays an important role in deciding the success of healing.In addition to the common mineral phase of hydroxyapatite (HA), dicalcium phosphate dihydrate (DCPD) phase was also found in early stage of healing, especially in rapid healing (children's callus). It vanished in the following process of healing. The deposition of DCPD is supposed to be brought about by some non-collagenous protein.     

半缩聚法合成双环戊二烯型不饱和聚酯的工艺研究

本文用半缩聚法合成双环戊二烯型不饱和聚酯树脂。研究结果表明,合成反应的最佳工艺条件为总酸酐丙二醇DCPD=11.10.10～0.15;加成温度为120～140℃;加成反应时系统酸值为120～140mgKOH/g;加成反应时间为2小时。      

Synthesis and characterization of nano-crystalline calcium phosphates with EDTA-assisted hydrothermal method

This study aims to prepare the biologically important hydroxyapatite (HA), dicalcium phosphate dihydrate (DCPD) and dicalcium phosphate anhydrous (DCPA) phases in simple EDTA – assisted hydrothermal method. X-ray diffraction results showed that pure DCPD, DCPA and HA nano-crystals were obtained in the Ca–EDTA/PO₄ solutions at 120 °C, 180 °C and 210 °C, respectively. Thermal gravimetric analysis of the DCPD precipitates revealed that phase transformations of DCPD to DCPA and DCPA to HA occurred at 139 °C and 195 °C, respectively, which resulted in the different Ca–P phases during hydrothermal synthesis at different temperature ranges.     

Composition-dependent fracture toughness of ROMP-based Dilulin/dicyclopentadiene copolymers

The fracture toughness of a series of ring-opening metathesis polymerization-based Dilulin/dicyclopentadiene (DCPD) copolymers was evaluated by utilizing the essential work of fracture method and the structure-fracture property relationship was thoroughly analyzed. Both dynamic mechanical analyzer and scanning electron microscope demonstrated a reaction-induced phase separation in the copolymers. The copolymers’ composition-dependent morphologies showed a significant effect on their fracture behavior. The maximum value for the essential work of fracture was found with Dil30DCPD70, which may be explained by their less heterogeneous structure and high cross-link density. The highest non-essential work of fracture was observed with samples made from Dil40DCPD60, which is possibly a consequence of the formation of a rigid DCPD-phase.     

Simultaneous crystallization of calcium phosphate and calcium oxalate in the presence of ascorbic acid under physiological conditions

Ascorbic acid (AA—Vitamin C) plays a vital role in human body to preserve optimal health. However, high intake may cause the formation of pathological calcium oxalate stones. Calcium oxalate and calcium phosphates are the major crystalline constituents of the urinary calculi and commonly found together. The effect of AA on the crystallization of calcium phosphate was studied in gel matrix under physiological conditions. Calcium phosphates such as hydroxyapatite (HAp), brushite (DCPD) and calcium oxalate dihydrate (COD—Weddellite) were found to crystallize simultaneously in the gel matrix. The formation of HAp is accelerated by AA. A possible reaction scheme for the formation of COD by the metal induced conversion of AA is proposed.     

Microstructure evolution and corrosion mechanism of dicalcium phosphate dihydrate coating on magnesium alloy in simulated body fluid

Dicalcium phosphate dihydrate (DCPD) coating was deposited on the substrate surface of magnesium alloy with solution treatment. The microstructures and corrosion behaviors of the DCPD-coated samples before and after immersion in simulated body fluid (SBF) for different times were investigated. It is important to note that DCPD was not only transformed into hydroxyapatite (HA) but also induced HA precipitation after immersion in SBF. An HA-like coating was generated on the substrate surface in a two step process involving an initial coating with DCPD, resulting in the corrosion resistance increasing along with the corrosion mechanism changing with increase to soaking time.     

A Comparison of Trehalose Dihydrate and Mannitol as Stabilizing Agents for Dicalcium Phosphate Dihydrate Based Tablets

This study investigated the possible utility of trehalose dihydrate (TD) as a tablet stabilizing agent. Acetylsalicylic acid was used as the model hydrolyzable drug and dicalcium phosphate dihydrate (DCPD) as the base excipient, because it is well documented that ASA/DCPD tablets are unstable during storage at low temperature and high relative humidity; DCPD is usually combined with mannitol in order to improve tablet stability.

Tablets comprising DCPD, 10% ASA, and 0%, 10%, or 20% w/w of TD were prepared by direct compression and stored at 35°C and 82.9% relative humidity for 6 months. Additionally, control tablets with DCPD and ASA, only, or with DCPD, ASA and 20% mannitol, were also evaluated. At predetermined time intervals, formulations were tested for drug content, mechanical, microstructural, and drug dissolution properties. Additionally, thermal analyses and ASA solution stability studies were carried out. Results reveal that both TD and mannitol significantly reduce degradation of ASA included in DCPD-based tablets, but neither effectively protects against the marked decline in tablet mechanical properties on aging. The ASA stabilization effects of TD and mannitol were also observed in solution, indicating an interaction between these sugars and ASA.     

Hydrolysis of dicalcium phosphate dihydrate to hydroxyapatite

Dicalcium phosphate dihydrate (DCPD) was hydrolysed in water and in 1 M Na2HPO4 solution at temperatures from 25–60°C. Hydrolysis was incomplete in water. At 25 °C, DCPD partially hydrolysed to hydroxyapatite (HAp). Formation of HAp is indicative of incongruent DCPD dissolution. At the higher temperatures, hydrolysis to HAp was more extensive and was accompanied by the formation of anhydrous dicalcium phosphate (DCP). Both of these processes are endothermic. When hydrolysis was carried out in 1 M Na2HPO4 solution, heat absorption was greater at any given temperature than for hydrolysis in water. Complete hydrolysis to HAp occurred in this solution. The hydrolysis of DCPD to HAp in sodium phosphate solution was also endothermic. The complete conversion of DCPD to HAp in sodium phosphate solution would not be expected if the only effect of this solution was to cause DCPD dissolution to become congruent. Because of the buffering capacity of a dibasic sodium phosphate solution, DCPD hydrolysed completely to HAp. Complete conversion to HAp was accompanied by the conversion of dibasic sodium phosphate to monobasic sodium phosphate. The formation of DCP was not observed indicating that the sodium phosphate solution precluded the DCPD-to-DCP dehydration reaction. In addition to affecting the extent of hydrolysis, reaction in the sodium phosphate solution also caused a morphological change in the HAp which formed. HAp formed by hydrolysis in water was needle-like to globular while that formed in the sodium phosphate solution exhibited a florette-like morphology. © 1998 Chapman & Hall     

双环戊二烯催化开环移位聚合研究进展

环烯的开环移位聚合已经成为高分子工程领域的一个研究热点.其中,双环戊二烯由于具有来源方便、价格低廉,聚合后力学性能优异等优点而成为开环移位聚合热点研究对象之一.许多过渡金属化合物都可以作为双环戊二烯开环移位聚合的催化剂,通过采用不同的催化体系,可以得到不同结构的聚合物.介绍了双环戊二烯移位聚合反应机理及催化体系的研究进展.     

A study of brushite crystallization from calcium-phosphate solution in the presence of magnesium under the action of a low magnetic field

The paper discusses the crystallization of dicalcium phosphate dehydrate (DCPD) with subsequent transformation to nanocrystalline hydroxyapatite (НA) under the permanent magnetic field in the presence of magnesium. It was found that the presence of magnesium in the initial solution in concentrations of 0.01–0.03 g/l decreased the crystallinity of calcium-phosphates. The precipitation of DCPD under the magnetic field of 0.3 T was carried out in proximity of the north and south magnetic poles. The differences in the particle morphology and structure of precipitates with the same phase composition (DCPD) were observed in the neighborhood of the north and the south pole. Lattice parameters of DCPD precipitates obtained biomimetically near opposite magnet poles were calculated using XRD results. It was found that the increased crystallization time (more than 3 days) leads to a complete attenuation of DCPD peaks, whereas НА peaks are still present.     

A comparison of trehalose dihydrate and mannitol as stabilizing agents for dicalcium phosphate dihydrate based tablets

This study investigated the possible utility of trehalose dihydrate (TD) as a tablet stabilizing agent. Acetylsalicylic acid was used as the model hydrolyzable drug and dicalcium phosphate dihydrate (DCPD) as the base excipient, because it is well documented that ASA/DCPD tablets are unstable during storage at low temperature and high relative humidity; DCPD is usually combined with mannitol in order to improve tablet stability. Tablets comprising DCPD, 10% ASA, and 0%, 10%, or 20% w/w of TD were prepared by direct compression and stored at 35 degrees C and 82.9% relative humidity for 6 months. Additionally, control tablets with DCPD and ASA, only, or with DCPD, ASA and 20% mannitol, were also evaluated. At predetermined time intervals, formulations were tested for drug content, mechanical, microstructural, and drug dissolution properties. Additionally, thermal analyses and ASA solution stability studies were carried out. Results reveal that both TD and mannitol significantly reduce degradation of ASA included in DCPD-based tablets, but neither effectively protects against the marked decline in tablet mechanical properties on aging. The ASA stabilization effects of TD and mannitol were also observed in solution, indicating an interaction between these sugars and ASA.     

“Fabrication of arbitrarily shaped carbonate apatite foam based on the interlocking process of dicalcium hydrogen phosphate dihydrate”

Carbonate apatite (CO₃Ap) foam with an interconnected porous structure is highly attractive as a scaffold for bone replacement. In this study, arbitrarily shaped CO₃Ap foam was formed from α-tricalcium phosphate (α-TCP) foam granules via a two-step process involving treatment with acidic calcium phosphate solution followed by hydrothermal treatment with NaHCO₃. The treatment with acidic calcium phosphate solution, which is key to fabricating arbitrarily shaped CO₃Ap foam, enables dicalcium hydrogen phosphate dihydrate (DCPD) crystals to form on the α-TCP foam granules. The generated DCPD crystals cause the α-TCP granules to interlock with each other, inducing an α-TCP/DCPD foam. The interlocking structure containing DCPD crystals can survive hydrothermal treatment with NaHCO₃. The arbitrarily shaped CO₃Ap foam was fabricated from the α-TCP/DCPD foam via hydrothermal treatment at 200?°C for 24?h in the presence of a large amount of NaHCO₃.     

Synthesis of fiber Bragg grating parameters from experimental reflectivity: a simplex approach and its application to the determination of temperature-dependent properties

A simple, accurate, and fast method to synthesize the physical parameters of a fiber Bragg grating numerically from its reflectivity is proposed and demonstrated. Our program uses the transfer matrix method and is based on a Nelder-Mead simplex optimization algorithm. It can be applied to both uniform and nonuniform (apodized and chirped) fiber Bragg gratings. The method is then used to synthesize a uniform Bragg grating from its reflectivity taken at different temperatures. It gives a good estimate of the thermal expansion coefficient and the thermo-optic coefficient of the fiber.     

Influence of dicalcium phosphate dihydrate coating on the <Emphasis Type="Italic">in vitro</Emphasis> degradation of Mg-Zn alloy

To reduce the degradation rate and further to improve the biocompatibility of magnesium alloy, dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) has been fabricated on a kind of magnesium-zinc alloy by way of electrodeposition method. The experimental results of XRD, SEM and EDS showed that the electrodeposited coating on the Mg-Zn alloy mainly contains the flake-like DCPD, along with some octacalcium phosphate (Ca₈(HPO₄)₂(PO₄)₄·4H₂O, OCP). After the in vitro degradation of the coated alloy in modified-simulated body fluid (m-SBF), it was proved that the coating could reduce the degradation rate effectively, and the samples were covered by calcium phosphate salts with a higher Ca/P ratio. Therefore, it indicates that compared with the bare alloy, the DCPD coating rendered a more biocompatible surface, and is a promising coating candidate for biomedical magnesium materials.     

Fabrication of mineralized electrospun PLGA and PLGA/gelatin nanofibers and their potential in bone tissue engineering

Surface mineralization is an effective method to produce calcium phosphate apatite coating on the surface of bone tissue scaffold which could create an osteophilic environment similar to the natural extracellular matrix for bone cells. In this study, we prepared mineralized poly(d,l-lactide-co-glycolide) (PLGA) and PLGA/gelatin electrospun nanofibers via depositing calcium phosphate apatite coating on the surface of these nanofibers to fabricate bone tissue engineering scaffolds by concentrated simulated body fluid method, supersaturated calcification solution method and alternate soaking method. The apatite products were characterized by the scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffractometry (XRD) methods. A large amount of calcium phosphate apatite composed of dicalcium phosphate dihydrate (DCPD), hydroxyapatite (HA) and octacalcium phosphate (OCP) was deposited on the surface of resulting nanofibers in short times via three mineralizing methods. A larger amount of calcium phosphate was deposited on the surface of PLGA/gelatin nanofibers rather than PLGA nanofibers because gelatin acted as nucleation center for the formation of calcium phosphate. The cell culture experiments revealed that the difference of morphology and components of calcium phosphate apatite did not show much influence on the cell adhesion, proliferation and activity.     

Calcium–phosphate–silicate composite bone cement: self-setting properties and in vitro bioactivity

In this study, a novel low temperature setting calcium phosphate–silicate cement was obtained by mixing CaHPO₄ · 2H₂O (DCPD) and Ca₃SiO₅ (C₃S) with 0.75 M sodium phosphate buffers (pH = 7.0) as liquid phase. The self-setting properties of the obtained DCPD/C₃S paste with liquid to powder ratio (L/P) of 0.6 ml/g, such as setting times, injectability, degradability and compressive strength were investigated and compared with that of DCPD/CaO cement system. The results indicated that, with the weight ratio of C₃S varied from 20% to 40%, the workable DCPD/C₃S pastes could set within 20 min, and the hydrated cement showed significantly higher compressive strength (around 34.0 MPa after 24 h) than that of the DCPD/CaO cement system (approximately 10.0 MPa). Furthermore, the in vitro pH value of the cements was investigated by soaking in simulated body fluid (SBF) for 12 h, and the result indicated that the DCPD/C₃S did not induce significant increase or decrease of pH value in SBF. Additionally, the composite cement possesses better ability to support and stimulate cell proliferation than the DCPD/CaO cement. With good hydraulic properties, improved biocompatibility and moderate degradability, the novel DCPD/C₃S bone cement may be a potential candidate as bone substitute.