Polysiloxanes as matrix materials for slow release of 2-pyridine aldoxime chloride

The efficacy of polysiloxanes and copolysiloxanes as matrix materials for the slow release of 2-pyridine aldoxime chloride (2-PAM-Cl) was investigated by in vitro studies using both slabs and microcapsules. The release rate of 2-PAM-Cl was determined in pH 7·4 phosphate buffer at 37°C. Transport parameters such as the Fickian coefficient, diffusion coefficient, and the polymer–2-PAM-Cl interaction parameter were calculated. The order of release and the time taken for 80% release were also calculated. © 1998 SCI.     

Preparation of polyethersulfone–alginate microcapsules for controlled release

In this study, polyethersulfone (PES)–alginate microcapsules were prepared for drug‐controlled release, and vitamin B₁₂ (VB₁₂), rifampicin (RFP), and bovine serum albumin (BSA) were used as model drugs. Different microcapsules were prepared by the variation of the crosslinking degree of alginate and the variation of the chemical components of the microcapsule membrane, including the PES and polyethylene glycol (PEG) contents. Systematic experiments were carried out to study their influences on the release profile of the model drugs. The results showed that with the increase of the crosslinking degree of the alginate, the drug release rate increased; whereas with the increase of the PES concentration used to prepare the microcapsule membrane, the drug release rate decreased. The contents of the PEG in the microcapsule membrane also affected the drug release. This study enriched the methodology of the fabrication of the microcapsules, and the microcapsules may have a potential use for controlled release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of biocompatible polyurethanes for controlled release of hydrophobic and hydrophilic drugs

Design of biocompatible and biodegradable polymer systems for sustained and controlled release of bioactive agents is critical for numerous biomedical applications. Here, we designed, synthesized, and characterized four polyurethane carrier systems for controlled release of model drugs. These polyurethanes are biocompatible and biodegradable because they consist of biocompatible poly(ethylene glycol) or poly(caprolactone diol) as soft segment, linear aliphatic hexamethylene diisocyanate or symmetrical aliphatic cyclic dicyclohexylmethane-4,4′-diisocyanate as hard segment, and biodegradable urethane linkage. They were characterized with Fourier transform infrared spectroscopy, atomic force microscope, and differential scanning calorimetry, whereas their degradation behaviors were investigated in both phosphate buffered saline and enzymatic solutions. By tuning polyurethane segments, different release profiles of hydrophobic and hydrophilic drugs were obtained in the absence and presence of enzymes. Such difference in release profiles was attributed to a complex interplay among structure, hydrophobicity, and degradability of polyurethanes, the size and hydrophobicity of drugs, and drug-polymer interactions. Different drug-polyurethane combinations modulated the distribution and location of the drugs in polymer matrix, thus inducing different drug release mechanisms. Our results highlight an important role of segmental structure of the polyurethane as an engineering tool to control drug release.     

Synthesis and characterization of polysiloxanes with pendant bicyclic fragments

Transparent poly vinyl alcohol (PVA) based coatings with antimicrobial activity against a wide range of microorganisms have been prepared. The films have been prepared by spincoating a mixture of PVA, ammonium dichromate and metal (zinc or silver) precursor from water solutions, and then rendered insoluble by crosslinking under UV illumination. Antimicrobial activity has been tested against different bacteria and fungi, such as Bacillus atrophaeus, Bacillus megaterium, Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, Salmonella enterica, Escherichia coli, Neurospora crassa, and Saccharomyces cerevisiae. It was found that combining the zinc and silver precursors resulted in films which had excellent antimicrobial activity and at the same time exhibited superior environmental stability compared to films containing prepared with single metal precursor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis,characterization and evaluation of novel methoxypolyethyleneglycol‐ grafted‐ poly(ester‐urethane)s for controlled release of repaglinide

Novel biodegradable aliphatic poly(ester‐urethane)s (PEUs) based on polycaprolactone diol (PCL) and methoxypolyethyleneglycol grafted onto trimethylol propane (mPEG‐g‐TMP) were synthesized by solution polymerization technique and characterized using a variety of techniques. Microspheres ranging in size from 7 to 25 μm were prepared by the solvent evaporation technique and loaded with repaglinide up to 71 to 96%. Increasing molar ratios of mPEG‐g‐TMP propane with respect to polycaprolactone diol gave increase in particle size along with increase in % encapsulation efficiency. Surface morphology and spherical nature of the microspheres were confirmed by scanning electron microscopy (SEM). The release of repaglinide varied, depending upon the molar ratios of mPEG‐g‐TMP moieties with respect to PCL. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of poly(N‐vinyl‐2‐pyrrolidone) grafted sodium alginate hydrogel beads for the controlled release of indomethacin

Graft copolymers of sodium alginate (NaAlg) with N‐vinyl‐2‐pyrrolidone were prepared using azobisisobutyronitrile as initiator. The graft copolymers (NaAlg‐g‐PVP) were characterized with Fourier transform infrared spectroscopy, elemental analysis, and differential scanning calorimetry. Polymeric hydrogel beads of NaAlg and NaAlg‐g‐PVP were prepared by crosslinking method using glutaraldehyde (GA) as a crosslinker in the hydrochloric acid catalyst (HCl) and these beads were used to deliver anti‐inflammatory drug, indomethacin (IM). Chemical stability of the IM after encapsulation into beads was confirmed by FTIR. Preparation conditions of the NaAlg‐g‐PVP beads were optimized by considering the percentage entrapment efficiency, particle size, swelling capacity and their release data. In vitro release studies were performed in simulated gastric fluid (pH 1.2) for the initial 2 h, followed by simulated intestinal fluid (pH 7.4) for 4 h. Effects of GA concentration, exposure time to GA, drug/polymer (d/p) ratio, and concentration of HCl on the release of IM were discussed. It was observed that IM release from the beads decreased with increasing GA concentration and exposure time. IM release also decreases with increasing d/p ratio and HCl concentration. The highest IM release was obtained to be 77% for beads crosslinked with 0.027M GA. Swelling experiments were also performed to compute molecular mass between crosslinks of the beads. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

N-mPEG-O-季铵化壳聚糖微球的制备及其载药性能

将聚乙二醇单甲醚（mPEG）醛化改性后,通过西佛碱反应接枝到自制的O-季铵化壳聚糖的NH2上,硼氢化钠还原制得N-mPEG接枝O-季铵化壳聚糖（QACS-mPEG）,反相悬浮法制备二乙烯基砜交联QACS-mPEG微球。用FTIR、1 H NMR、EA和SEM对产物进行表征,并且以酮洛芬为模型药物研究微球的载药性能及释放行为。结果表明,mPEG和季铵盐基团的引入提高了N-mPEG-O-季铵化壳聚糖微球的载药量,为4.31mg/mg;载药N-mPEG-O-季铵化壳聚糖微球在模拟肠液的缓释效果优于胃液,微球释药具有pH响应性。     

可用于缓控释肥聚乙烯基吡咯烷酮（K32）的合成与表征

研究了可用于缓控释肥包膜材料的聚乙烯基吡咯烷酮（PVP K32）的合成.研究了通过水溶液自由基聚合法合成PVP K32的实验技术,研究了不同引发剂、聚合工艺等对合成PVP K32的相对分子质量及残留单体含量的影响.通过优化实验获得一种分子量分布窄、残单含量低的PVP K32的聚合工艺,并对样品进行了表征及成分分析.     

药物控释用智能水凝胶研究进展

智能水凝胶在药物控释方面具有智能化、效率高和安全方便等优点.近年来,研究开发药物控释用智能水凝胶非常活跃,展示了广阔的应用前景.本文综述了药物控释用温度、pH值、葡萄糖、电场、磁场及光敏感水凝胶的最新研究进展.     

肥料和农药缓释/控释技术研究

缓释/控释技术作为一项新兴技术越来越受到重视,它可以有效地解决活性制剂释放速度快、有效时间短等问题。针对目前肥料和农药利用效率低、环境污染严重等现实问题,主要从加工工艺和缓释材料两方面,简要介绍了缓释技术的基本原理、类型和途径,综述了它在肥料和农药方面的应用进展,并且讨论了其发展特点及趋势。     

Semi‐interpenetrating polymer network beads of crosslinked chitosan–glycine for controlled release of chlorphenramine maleate

Spherical, semi‐interpenetrating polymer network beads of chitosan and glycine, crosslinked with different concentrations of glutaraldehyde were prepared for controlled release of drugs. The structural and morphological studies of the beads were carried out with FTIR and SEM techniques. The swelling behavior of the beads at different time intervals was monitored in solutions of different pH. Structural changes of the beads in response to solution pH were put forward using the data obtained from IR/UV spectral analysis. The release experiments were performed in solutions of pH 2.0 and pH 7.4 at 37°C, using chlorphenramine maleate as a model drug. The results indicate that, chitosan might be useful as a vehicle for controlled release of drugs. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 672–683, 2000     

Synthesis of polysiloxanes with pendant methoxy‐substituted aromatic fragments

The synthesis of new polysiloxanes was performed via hydrosilylation reactions of polymethylhydrosiloxane with 4‐allyl‐1‐methoxybenzene and 4‐allyl‐1,2‐dimethoxybenzene in the presence of Karstedt's catalyst {Pt₂[(VinSiMe₂)₂O]₃} and platinum hydrochloric acid (0.1M solution in tetrahydrofuran). The hydrosilylation reactions were carried out at 60°C. The molar ratio of ?Si? H groups to the allylic compound was 1 : 1.2. The synthesized oligomers were characterized with ¹H‐NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and gel permeation chromatography. In the presence of platinum hydrochloric acid, not all active ?Si? H bonds took part in hydrosilylation, and because of this, gelation took place and the molecular masses of the extracted parts increased 7–8 times; in contrast to this, in the presence of Karstedt's catalyst, all active ?Si? H bonds participated in hydrosilylation, and an increase in the molecular masses did not occurs. The influence of substituted methoxy groups on the glass‐transition temperatures was studied. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008     

Glutaraldehyde‐crosslinked chitosan beads for controlled release of diclofenac sodium

An inexpensive and simple method was adopted for the preparation of chitosan beads, crosslinked with glutaraldehyde (GA), for the controlled release of diclofenac sodium (DS). The beads were prepared by varying the experimental conditions such as pH, temperature, and extent of crosslinking. The absence of any chemical interaction among drug, polymer, and the crosslinking agent was confirmed by FTIR and thermal analysis. The beads were characterized by microscopy, which indicated that the particles were in the size range of 500–700 μm and SEM studies revealed smooth surface and spherical shape of beads. The beads produced at higher temperature and extended exposure to GA exhibited lower drug content, whereas increased drug loading resulted in enhanced drug release. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 211–217, 2007     

环氧改性硅油的制备与表征及应用进展

重点阐述了环氧改性硅油的各种合成方法(如硅氢化加成法、本体聚合法和乳液聚合法等)以及它们各自的特点,概述了环氧改性硅油的表征方法。环氧改性硅油兼具聚硅氧烷和环氧基的双重性质,从而使其具有链段柔顺、耐热,并具反应性、吸附性等特点。介绍了环氧改性硅油在纤维整理、树脂改性、光固化防黏隔离剂、涂料添加剂等方面的应用。最后展望了环氧改性硅油的应用前景。     

pH-sensitive hydrogels based on polyvinylpyrrolidone–polyacrylic acid (PVP–PAA) semi-interpenetrating networks (semi-IPN): Swelling and controlled release

Complexes of polyvinylpyrrolidone–polyacrylic acid (PVP–PAA) photopolymerized from a mixture of PVP and acrylic acid (AA) were characterized by means of differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectrometry. The swelling of PVP–PAA semi-interpenetrating network (semi-IPN) films was studied in various pH media. The results showed that swelling in 0.1N HCl solution and pH 3.0 phosphate buffer was strikingly different from that in the pH 6.0 phosphate buffer. Caffeine release rate from the semi-IPN film followed Fick's Law. The rate of release was higher in dissolution media having pH above a critical value of about 3.8. Control of caffeine release from the semi-IPN film was realized by changing cyclically the pH of dissolution medium between 0.1N HCl solution and pH 6.0 phosphate buffer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 921–930, 1998     

pH‐sensitive acrylic‐based copolymeric hydrogels for the controlled release of a pesticide and a micronutrient

Acrylic‐based copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) have been prepared by solution and bulk polymerization techniques using benzoyl peroxide (BPO) as an initiator. Three polymers were prepared with a varying ratio of MMA/MAA. In an effort to increase the hydrophilicity of the matrix, one MMA/MAA polymer was prepared by adding an additional amount of 2‐hydroxy ethyl methacrylate (HEMA). All the polymers were crosslinked in situ by ethylene glycol dimethacrylate (EGDMA). These polymers were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Viscous flow characteristics were determined from solution viscosity and rheological measurements. Dynamic and equilibrium swelling experiments were carried out under varying pH conditions (i.e., 0.1N NaOH, 0.1N HCl, and double‐distilled water). Partially crosslinked hydrogels show varying hydrophilicity because of the presence of carboxylic acid groups making them pH‐responsive. Swelling increased with an increasing number of —COOH groups on the polymer backbone and the hydrophilicity varied with changing pH. Cypermethrin, a widely used pesticide, and cupric sulfate, a model micronutrient, were loaded into these pH‐sensitive hydrogels to investigate their controlled release characteristics. The in vitro release rates of both compounds have been carried out under static dissolution conditions at 30°C. Release data have been fitted to an empirical relation to estimate transport parameters. The release results have been discussed in terms of the varying hydrophilicity of the hydrogel network polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 394–403, 2003     

PMMA‐based microgels for controlled release of an anticancer drug

Methyl methacrylate (MMA), methoxy poly(ethylene glycol) monomaleate (MPEG), and acrylamidoglycolic acid (AGA) terpolymeric microgels (MGs) have been synthesized by free‐radical surfactant‐free emulsion polymerization. MPEG was synthesized from maleic anhydride and methoxy poly(ethylene glycol). The MGs were crosslinked with ethylene glycol dimethacrylate, and the chemical crosslinking was confirmed by Fourier transform infrared spectroscopy. 5‐Fluorouracil (5‐FU), a model anticancer drug, has been loaded into the MGs by in situ and adsorption methods. Empty as well as drug‐loaded MGs were then characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). DSC and XRD studies indicated a molecular level dispersion of the drug in PMMA MGs during in situ loading. TEM images showed the formation of spherical MGs. In vitro release of 5‐FU from the crosslinked poly(MMA‐co‐AGA‐co‐MPEG) MGs were investigated at both pH 7.4 and 1.2 buffer medium that controlled release of the drug up to ～ 18 h. Both the encapsulation efficiency and the release patterns were dependent on the amount of crosslinking agent and the amount of drug loaded. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of liquid crystalline polysiloxanes

Most studies on the structure-property relationship of liquid crystalline polysiloxanes are focused on the side-chain-type polymers bearing calamitic or discotic side groups decoupled from the backbone via a flexible spacer. However, main-chain liquid crystalline polymers have been obtained by combining flexible siloxane segments with rigid rod-type mesogens. The synthesis and properties of these two types of liquid crystalline polysiloxanes are examined. One of the most widely used methods of preparation is the hydrosilylation of unsaturated mesogens. However, this reaction is not always as clean and clear-cut as would be necessary for the obtention of polymers with reproducible characteristics. This point is discussed and specific examples of side reactions are given. Some data concerning liquid crystalline polysiloxanes with no mesogenic groups as well as liquid crystalline elastomers are presented. Potential applications of these polymers and future developments are discussed.This review is from the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.     

Synthesis and characterization of fluorine‐containing liquid crystalline polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens

Several novel side‐chain liquid crystalline (LC) polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric LC monomer cholesteryl 3‐(4‐allyloxy‐phenyl)‐acryloate and a fluoro‐containing LC monomer 4‐[2‐(3‐trifluoromethyl‐phenoxy)‐acetoxy]‐phenyl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques, such as FTIR, ¹H‐NMR, ¹³C‐NMR, TGA, DSC, POM, and XRD. The temperatures at which 5% weight loss occurred were greater than 300°C for all the polymers, and the residue weight near 600°C increased slightly with increase of the trifluoromethyl‐substituted mesogens in the fluorinated polymer systems. The samples containing mainly cholesteryl cinnamate mesogens showed chiral nematic phase when they were heated and cooled, but the samples containing more trifluoromethyl‐substituted mesogens exhibited chiral smectic A mesophase. The glass transition temperature of the series of polymers increased slightly with increase of trifluoromethyl‐substituted mesogens in the polymer systems, but mesophase–isotropic phase transition temperature did not change greatly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of trifluoromethyl‐substituted mesogens in the fluorinated polymers systems, indicating that the smectic order derived from trifluoromethyl‐substituted mesogens should be strengthened. These results should be due to the fluorophobic effect between trifluoromethyl‐substituted mesogens and the polymer matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermo‐ and pH‐responsive microgels for controlled release of insulin

Microgel particles were prepared, made of hydroxypropylcellulose‐graft‐(acrylic acid) (HPC‐g‐AA) and acrylic acid(AA). The particles undergo reversible volume phase transitions in response to both pH and temperature changes while keeping the inherent properties of PAA and HPC‐g‐AA. Dynamic light scattering measurements reveal that the average hydrodynamic radius and hydrodynamic radius distributions of the microgel particles depend on temperature and pH. The microgels exhibit excellent pH sensitivity and a higher swelling ratio at higher pH in aqueous solution. In vitro release study shows that the amount of insulin released from the microgels is less at pH = 1.2 than at pH = 6.8. The results indicate that the resultant microgels seem to be of great potential for intelligent oral drug delivery. Copyright © 2012 Society of Chemical Industry