Effect of molecular weight and concentration of poly(acrylic acid) on the formation of a polymeric calcium phosphate cement

Previous investigations have noted that the tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA) apatite forming calcium phosphate cement (CPC) possesses many favorable properties from a biomaterials standpoint. Despite these positive properties various shortcomings have limited clinical usage of these materials and fostered investigations into the effect of numerous additives. The present study concerns the effect of poly(acrylic acid) (PAA) addition and the influence of factors such as molecular weight and concentration of the additive on the properties of the set cement. One-way ANOVA was conducted using all results obtained, to firstly derive the influence of concentration within each molecular weight group, and secondly to derive the influence of molecular weight within each concentration group. All investigated mechanical properties were influenced by both molecular weight and concentration of the additive. Higher molecular weights tended to result in cements with shorter setting times and higher compressive, diametral and biaxial flexural strengths than their lower molecular weight counterparts. The effect of concentration on the properties of the set cement however was somewhat more complex, a negative correlation was observed between the initial setting time and PAA concentration. In regards to the final setting time, any correlation with concentration was difficult to derive as a consequence of the highly brittle nature of cements made with low concentrations. In regard to mechanical properties, intermediate concentrations tended to give higher strengths than both their higher and lower counterparts, however the exact pattern was largely specific to the mechanical strength test employed. We conclude that molecular weight and concentration of PAA influence the setting behavior and final mechanical properties of the TTCP/DCPA cement, and that selection of an appropriate PAA solution can lead to the production of cements with properties superior to those formed in the absence of the polymer.     

Synthesis and in vitro characterization of a poly(acrylic acid)-homocysteine conjugate

It was the aim of this study to improve our knowledge on thiolated polymers by the synthesis and in vitro characterization of a poly(acrylic acid)-homocysteine conjugate. Mediated by a carbodiimide, homocysteine was therefore covalently attached to poly(acrylic acid) via the formation of an amide bond. The isolated conjugate displayed 930 micromol +/- 83 micromol sulfur atoms per gram polymer. Of these thiol groups, 80.1% were oxidized to disulfide bonds during the coupling reaction. In aqueous solutions the conjugate was rapidly oxidized by the formation of disulfide bonds at pH 8, whereas it remained stable at pH 7 and below during the observation period of 4 hours. Due to the immobilization of thiol groups on the polymer, the mucoadhesive and cohesive properties of poly(acrylic acid) were strongly improved. Furthermore, the thiolated polymer exhibited a significantly (p < 0.05) improved permeation enhancing effect in comparison to the unmodified polymer. Because of these features the poly(acrylic acid)-homocysteine conjugate seems to represent a promising novel tool, which might be useful in particular for aqueous formulations based on thiomers.     

Oral-based controlled release formulations using poly(acrylic acid) microgels

Aim: To investigate the release of hydrophobic and hydrophilic substances from tablets containing Pemulen and Carbopol as excipients. Method: The dissolution patterns of a hydrophobic (diazepam) and a hydrophilic active substance (midodrine-HCl) from different tablet formulations containing a nonmodified polyacrylic microgel (Carbopol 981 F) or a hydrophobically modified polyacrylic microgel (Pemulen®) have been studied. Possible differences in dissolution in phosphate buffer (pH 6.8) and in 0.1 M HCl between tablets produced using wet granulation and direct compression were also investigated. Results: Tablets produced by wet granulation had a greater effect on the release of active substance from the tablets. No major differences were observed in the release patterns of the hydrophilic substance midodrine-HCl from wet granulated tablets based on Carbopol and Pemulen. However, the release pattern of the more hydrophobic drug substance, diazepam, differed considerably between the two polymers. Wet granulation gave reproducible release patterns. The release patterns from the polymers differed considerably at pH 6.8 but were similar at low pH. Conclusions: The release of the diazepam from the hydrophobic polymer Pemulen was very slow, and the release was close to zero order.     

腐植酸/丙烯酸型吸水性树脂的合成及吸水性能研究

以腐植酸、丙烯酸为单体,丙三醇为交联剂,采用溶液聚合法合成了腐植酸/丙烯酸型吸水性树脂,并考察腐植酸加入量、中和度、交联剂、引发剂用量对吸水倍率的影响。结果表明,各组分含量对合成树脂的吸水倍率影响较大。     

The actuation of a biomimetic poly(vinyl alcohol)poly(acrylic acid) gel

Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as biomimetic actuators and "artificial muscles". In previous work, a thermodynamically consistent finite-elastic constitutive model has been developed to describe the mechanical and actuation behaviours of active polymer gels. The mechanical properties were characterized by a free-energy function, and the model uses an evolving internal variable to describe the actuation state. In this work, an evolution law for the internal variable is determined from free actuation experiments on a poly(vinyl alcohol)poly(acrylic acid) (PVAPAA) gel. The complete finite-elastic/evolution law constitutive model is then used to predict the response of the PVA-PAA gel to isotonic and isometric loading and actuation. The model is shown to give relatively good agreement with experimental results.     

Preparation of amorphous calcium carbonate nanoparticles from impure dolomitic marble with the aid of poly(acrylic acid) as a stabilizer

Nanomaterials of Precipitated Calcium Carbonate (PCC) such as Amorphous Calcium Carbonate (ACC) nanoparticles are highly demanded industrial products. These products are prepared in industrial scale, using pure CaCO₃ natural resources such as pure carbonate rocks, cockle shells, corals, and pearls. Such natural resources could be consumed rapidly due to their excessive use in PCC industries. Therefore, the development of novel procedures to prepare nanoparticles of PCC using impure minerals is desirable. Herein, we report a simple, novel and economical method to synthesize poly(acrylic acid) (PAA) stabilized ACC nanoparticles using extensively distributed impure dolomitic marbles in place of natural pure CaCO₃ raw materials. The yields of final ACC products are enhanced using a bubbling column which can produce small bubbles to improve bubbling efficiency. The average particle sizes of final calcium carbonate products are in the range 21–53 nm. The best conditions to produce ACC, among the conditions used in the proposed method, are temperature of 40 °C, pH of 4.5 and PAA concentration of 10⁻² M. One or more crystalline phase(s) of PCC is associated with ACC in each product and its nature depends on the conditions used in the synthesis of these products. The unstable vaterite form of PCC is formed when the PAA concentration is less than 0.5 M and at lower temperatures such as room temperature. The stability of the vaterite phase decreases when the temperature and the PAA concentration are increased. The synthesized ACC nanoparticles are in required purity and quality to be suitable for industrial applications.     

Luminescence enhancement of Eu3+-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand

This work reports on the photoluminescence enhancement of Eu³⁺-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand. The polymeric material was synthesized by polymerization in aqueous solution of the monomer partially neutralized with Eu₂O₃, containing 1,10-phenanthroline, and using potassium persulfate as initiator. The monomer modification and the coordination of antenna ligand to the Eu³⁺ ions were confirmed by ¹H-NMR. The doped polymer was characterized by luminescence spectroscopy. The excitation spectra show clear evidence of the coordination between the Eu³⁺ ions and the 1,10-phenanthroline ligands in the polymer matrix. On the other hand, the emission spectra show an inhomogeneous broadening and, together with the relative intensity of the ⁵D₀ → ⁷F_1,2 transitions of Eu³⁺, indicate that the dopant ions are uniformly distributed in low symmetry coordination sites. Besides, an enhancement in the intensity of the Eu³⁺ characteristic red emission by 1,10-phenanthroline addition is observed, and it is due to the antenna effect of the ligand, which acts as a sensitizer of the Eu³⁺ ions. An estimation of the increasing luminescence efficiency is presented.     

Preparation of nanoporous poly(methyl silsesquioxanes) films using PS-b-P4VP as template

Nanoporous poly(methyl silsesquioxane) (PMSSQ) film was prepared through the templating of an amphiphilic block copolymer, poly(styrene-4-vinyl pyridine) (PS-b-P4VP). The experimental and theoretical studies suggest that the intermolecular hydrogen bonding is existed between the PMSSQ precursor and PS-b-P4VP. The miscible hybrid and the narrow thermal decomposition of the PS-b-P4VP lead to nanopores in the prepared films from the results of TGA, AFM, and TEM. The effects of the loading ratio on the morphology and properties of the prepared nanoporous PMSSQ films were investigated. The TEM and AFM studies show that the uniform pore morphology with pore size 10-15 nm can be prepared from a modest porogen loading level for the optimum intermolecular hydrogen bonding. The refractive index and dielectric constant of the prepared nanoporous films decreases with an increase in PS-b-P4VP loading. On the other hand, the porosity increases with an increasing PS-b-P4VP loading. This study demonstrates a methodology to control pore morphology and properties of the nanoporous PMSSQ films through the templating of PS-b-P4VP.     

Grafting of poly(ethylene glycol) onto poly(acrylic acid)-coated glass for a protein-resistant surface

The surface of solid glass supports for samples in optical microscopy and for biosensors needs to be protein-resistant. A coating of a poly(ethylene glycol) monomethyl ether (mPEG) on the surface of the glass is one promising method for preventing the nonspecific adsorption of proteins. In this study, we have developed a novel technique for achieving an optimal coverage of a glass surface with mPEG to prevent protein adhesion. A clean glass substrate previously treated with (3-aminopropyl)dimethylethoxysilane (APDMES) was treated sequentially with poly(acrylic acid) and subsequently a primary amine derivative of mPEG in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The resultant glass surface was demonstrated to be highly protein-resistant, and the adsorption of bovine serum albumin decreased to only a few percentage points of that on a glass surface treated with APDMES alone. Furthermore, to extend the present method, we also prepared a glass substrate on which biotinylated poly(ethylene glycol) was cografted with mPEG, and biotinylated myosin subfragment-1 (biotin-S1) was subsequently immobilized on this substrate by biotin/avidin chemistry. Actin filaments were observed to glide on the biotin-S1-coated glass surface in the presence of ATP, and thus, the method is capable of immobilizing the protein specifically without any loss in its biological function.     

蒙脱土/海藻酸钠接枝丙烯酸高吸水性复合物的制备及吸附性能研究

以过硫酸胺(APS)为引发剂,N,N-亚甲基双丙烯酰胺(MBA)为交联剂,采用插层聚合法制备了蒙脱土/海藻酸钠接枝丙烯酸(MMT/SA-g-PAA)高吸水性复合物。通过红外光谱(FT-IR)、扫描电镜(SEM)、热重分析(TGA)对MMT/SA-g-PAA的结构和性能进行了表征。研究了MMT/SA-g-PAA对重金属离子的吸附性能,结果表明室温下MMT/SA-g-PAA对Pb2+、Cu2+、Ni 2+的最大吸附量分别为968.9、231.0及236.0mg/g,其中对Pb2+和Cu2+的吸附符合Langmuir吸附模型,而对Ni 2+的吸附符合Freundlich吸附模型。     

聚乳酸-羟基乙酸共聚物/磷酸钙骨水泥多孔复合支架的制备

利用定向冰晶-冷冻干燥法制备了具有定向孔隙结构的磷酸钙骨水泥支架材料, 将两种具有不同降解速率的聚乳酸-羟基乙酸共聚物(PLGA) 与磷酸钙骨水泥多孔支架进行多次浸润复合, 以改善支架的力学性能。结果表明: PLGA 与支架材料复合可大大提高复合支架材料的抗压强度, 经过PLGA 二次复合后, 复合支架抗压强度可达6. 37 MPa ±0. 54 MPa 。经过PLGA 复合的支架材料保持了复合前的孔隙结构, 在孔的轴向方向上具有定向排列的开口孔隙, 这些开口孔隙的存在有利于植入初期新生组织的长入。覆盖在骨水泥基体表面的PLGA 膜可以增强基体的强度并弥补基体表面的缺陷, 充填在孔隙内部的PLGA 泡沫体可以很好地承受外加载荷, 使复合支架材料具有较好的强度和韧性。      

Mechanical and rheological properties and injectability of calcium phosphate cement containing poly (lactic-co-glycolic acid) microspheres

To enhance tissue ingrowth and promote rapid resorption, efforts were made to build macropores into calcium phosphate cement (CPC); however, this led to a decrease in its mechanical properties. In this study, poly (lactic-co-glycolic acid) (PLGA) microspheres were incorporated into CPC to impart macroporosity and maintain early strength. The influences of the content of PLGA microspheres on the mechanical strength, rheological properties, injectability, setting time, and microstructure of CPC were also systematically investigated. At the PLGA to CPC mass ratios of 20/80 and 30/70, the compressive strength of the composites was similar to that of CPC without PLGA microspheres. The rheological results indicated that PLGA microspheres/CPC pastes showed plastic and shear-thinning behaviors. The addition of PLGA microspheres to CPC resulted in the increase of viscosity and yield stress of the pastes. Simultaneously, the injectability of the pastes decreased with the addition of PLGA microspheres. When the PLGA to CPC ratio was 20/80, the injectability of the paste was still higher than 95%. The calcium phosphate cement containing 20 wt.% PLGA microspheres exhibited excellent injectability and satisfactory setting time without strength degradation. Obviously, such an in situ macropores-generable CPC should have potential prospects for the wider applications in orthopedics, oral, and maxillofacial surgery.     

In vitro and in vivo evaluation of the biocompatibility of a calcium phosphate/poly(lactic-co-glycolic acid) composite

This study assess the effects of bioceramic and poly(lactic-co-glycolic acid) composite (BCP/PLGA) on the viability of cultured macrophages and human dental pulp fibroblasts, and we sought to elucidate the temporal profile of the reaction of pulp capping with a composite of bioceramic of calcium phosphate and biodegradable polymer in the progression of delayed dentine bridge after (30 and 60 days) in vivo. Histological evaluation of inflammatory infiltrate and dentin bridge formation were performed after 30 and 60 days. There was similar progressive fibroblast growth in all groups and the macrophages showed viability. The in vivo study showed that of the three experimental groups: BCP/PLGA composite, BCP and calcium hydroxide (Ca(OH)₂) dentin bridging was the most prevalent (90 %) in the BCP/PLGA composite after 30 days, mild to moderate inflammatory response was present throughout the pulp after 30 days. After 60 days was observed dentine bridging in 60 % and necrosis in 40 %, in both groups. The results indicate that understanding BCP/PLGA composite is biocompatible and by the best tissue response as compared to calcium hydroxide in direct pulp capping may be important in the mechanism of delayed dentine bridge after 30 and 60 days.     

丙烯酸(钠)-壳聚糖吸水树脂的合成

以丙烯酸和壳聚糖为原料,硝酸铈铵为引发剂,N,N-亚甲基双丙烯酰胺为交联剂,在醋酸溶液中合成了丙烯酸壳聚糖吸水树脂。研究了氯化钠、引发剂硝酸铈铵、丙烯酸与壳聚糖配比及交联剂N,N-亚甲基双丙烯酰胺对产物吸水性能的影响,采用正交实验对工艺条件进行了优化。结果表明:氯化钠0.6g、硝酸铈铵96mg、丙烯酸与壳聚糖比例为14.5∶1.5及N,N-亚甲基双丙烯酰胺48mg时合成树脂吸水率最高。     

聚丙烯酸改性膨润土吸附铜离子性能研究

用硫酸酸化钙基膨润土为原料,通过丙烯酸原位聚合制备了聚丙烯酸改性膨润土(PAA/HB)无机/有机高分子改性剂.采用IR、TG、XRD、SEM对其结构与形貌进行了表征,发现膨润土与丙烯酸很好地复合,呈现出层状结构和粗糙的表面.考察了该新型吸附剂对Cu2+的吸附性能,最佳条件下对Cu2+去除率可达98%以上.并探讨了PAA...     

分子自组装型水性丙烯酸改性环氧聚酯纳米乳液的合成

利用分子自组装技术采用两嵌段聚合物或共聚物制备出了水性丙烯酸改性环氧聚酯纳米乳液.合成出的聚合物纳米乳液的粒径随反应温度的升高而逐渐减小,当温度升高到100℃时,聚合物纳米乳液的粒径随温度升高逐渐增大.乳液粒径随引发剂浓度的升高和水含量的升高而逐渐减小.研究了相对于某一分散介质(例如水),这些聚合物形成球状胶束(纳米尺度内,50～90nm),在这种胶束中极性链段构成胶束的壳,而非极性链段构成胶束的核,所以乳液体系得以分散稳定.该乳液在正相反相的转变过程中经过一种特殊的双连续结构,在连续的转相过程中体系始终保持各向同性.该纳米级聚合物乳液平均粒径尺寸可达72nm.可用做水性工业漆的成膜材料.