Self-assembly of human serum albumin (HSA) and L-alpha-dimyristoylphosphatidic acid (DMPA) microcapsules for controlled drug release

Human serum albumin (HSA) and L-alpha-dimyristoylphosphatidic acid (DMPA) were applied as a pair to encapsulate ibuprofen microcrystals by means of a technique based on the layer-by-layer (LbL) assembly of oppositely charged species, for the purpose of controlling drug release. The successful adsorption of HSA and DMPA multilayers onto ibuprofen crystals was confirmed by optical microscopy. The drug release process, in a solution of pH 7.4, was monitored by optical microscopy and UV spectroscopy. The results revealed that the rate of release of ibuprofen from HSA/DMPA microcapsules decreased as the capsule wall thickness and drug crystal size increased, indicating that the permeability of the microcapsules can be controlled by simply varying the number of HSA/DMPA deposition cycles.     

A controlled-release anti-inflammatory drug

A procedure to obtain a controlled-release microencapsulated anti-inflammatory drug based on a solvent evaporation method is described. The present method makes use of ethylcellulose as the polymer and methylene chloride as solvent. The evaporation of solvent is controlled by means of an air stream. Variations in the preparative procedure and their effects on capsule dimensions and permeabilities were studied. The release behavior of the drug is determined, and two different diffusion constants are also determined: 7.0×10⁻¹⁰ cm²/s and 1.2×10⁻¹⁰ cm²/s, corresponding to low and high release time. Based on these results it is proposed that these microcapsules have a nonhomogeneous polymeric wall, and are more porous in the outer surface. This model might be applicable to the microcapsules obtained by means of the solvent evaporation method.     

Rose bengal-grafted biodegradable microcapsules: singlet-oxygen generation and cancer-cell incapacitation

Rose bengal-grafted chitosan (RB-CHI), synthesized through dehydration between amino and carboxyl functional groups under mild conditions, was coated onto the outer layer of preformed biodegradable microcapsules consisting of sodium alginate and chitosan. The fabricated photosensitive microcapsules were characterized by optical microscopy, scanning electron microscopy, and confocal laser scanning microscopy. The assembled materials maintained intact spherical morphology and thus showed good ability to form thin films. Electron spin resonance spectroscopy allowed direct observation of the generation of singlet oxygen ((1)O(2)) from photosensitive microcapsules under light excitation at about 545 nm. Furthermore, with increasing light radiation, the content of (1)O(2) increased, as detected by a chemical probe. In vitro cellular toxicity assays showed that RB-CHI-coated photosensitive microcapsules exhibit good biocompatibility in darkness and high cytotoxicity after irradiation, and could provide new photoresponsive drug-delivery vehicles.     

Tramadol Release from a Delivery System Based on Alginate‐Chitosan Microcapsules

Alginate‐chitosan microcapsules to control the release of Tramadol‐HCl were prepared using two different methods. In the two‐stage procedure (Variant I) alginate was first pumped into a CaCl₂/NaCl solution and then transferred into a chitosan solution. In the one‐stage procedure (Variant II) alginate was directly pumped into a chitosan/CaCl₂ solution, and different behavior could be noted in each case. The microcapsules were spherical in both variants and they swelled to a greater extent in a basic medium as compared to an acid one. The drug release profile of Tramadol from microcapsules in simulated gastric fluid and simulated intestinal fluid was also studied. The maximum release of Tramadol at 24 h was 64% and 86% for Variant I and II, respectively, in simulated intestinal fluid. Release was adjusted using the power law of the semi‐empirical Peppas equation in order to gain information about the release mechanism. In both cases the values of the exponent were found to be between 0.53 and 0.84 for swellable microcapsules in simulated gastric and intestinal fluids, respectively, indicating anomalous drug transport for both variants. The good results obtained with alginate‐chitosan microcapsules are comparable to those of the best products so far described in the scientific bibliography and in addition, chitosan is useful in pharmacy.

Surface morphology of Tramadol‐loaded microcapsule.     

Microencapsulation of astiban acid for the treatment ofSchistosomiasis mansoni

Schistosomiasis is among the top five diseases in the world in terms of morbidity, affecting perhaps 200 million people in tropical and subtropical countries. Antischistosomal drugs are toxic and rapidly metabolized. Hence, they must be given in a number of spaced doses. In spite of this there are severe side effects leading to poor patient compliance. This is an ideal situation for the application of sustained drug release to avoid the toxic peak concentration of drug. This study was carried out using Astiban acid, an antimonial drug that is effective againstS. mansoni. Unfortunately, the drug is sufficiently soluble that 50 mg will dissolve in 100 mL water in less than a minute. To permit sustained release of intramuscularly injected drug, microcapsules of astiban acid in poly(d,l-lactic acid) were formed by coacervation. Release studies show that an appreciable fraction of the drug is available at the surface for rapid solution. After this surface drug dissolves, the remaining drug is released slowly with half-times of many hours. After the initial burst, the release of drug follows Higuchi’s equation up to approximately 80% release, with exponentially decreasing release rates thereafter.     

alpha-Helical polypeptide microcapsules formed by emulsion-templated self-assembly

alpha-Helical peptide microcapsules were prepared by the emulsion-templated self-assembly of amphiphilic poly(gamma-benzyl L-glutamate)s (PBLG) 1. By mixing solutions of 1 in dichloromethane (in the form of a sodium salt) with water, oil-in-water emulsions were obtained. Spontaneous stripping of the dichloromethane phase caused a decrease in the diameter of the microdroplets and finally stable microcapsules formed. The microcapsules contain an inner aqueous phase as observed by confocal laser scanning microscopy (CLSM). Binding of hydrophobic pyrene molecules to the polypeptide shell was also demonstrated. The present polypeptide microcapsules are stable even after drying in air and they would serve as supramolecular vehicles for both hydrophobic and water-soluble molecules.     

十八烷/聚(St-MMA)相变微胶囊制备及表征

采用乳液聚合的方法,分别选取聚苯乙烯(PS)、聚甲基丙烯酸甲酯(PMMA)或苯乙烯和甲基丙烯酸甲酯的共聚物为壁材,正十八烷为芯材,十二烷基苯磺酸钠(SDBS)为乳化剂,制作相变储能微胶囊。用粒径分析仪、透射电子显微镜(TEM)、热重分析仪(TG)和示差扫描量热测试仪(DSC)对微胶囊的形貌、相变热性能和热稳定性分别进行表征。结果表明:壁材选取两者共聚物,当两种单体的比例为St∶MMA=1∶5,SDBS用量为1.5g(总质量的3%)时,微胶囊粒径大小均匀,粒子分散性好,壁材的包裹性好。微胶囊的放热峰为起始温度为27.3℃,终止温度为31.9℃,相变温度为28.9℃,相变焓为48.4J/g。TG表明长期使用温度不能超过131℃。IR分析微胶囊中含有芯材和壁材。这种十八烷/聚(St-MMA)相变微胶囊可以用于诸能材料。     

Near‐Infrared‐Activated Nanocalorifiers in Microcapsules: Vapor Bubble Generation for In Vivo Enhanced Cancer Therapy

Photothermal therapy based on gold nanostructures has been widely investigated as a state‐of‐the‐art noninvasive therapy approach. Because single nanoparticles cannot harvest sufficient energy, self‐assemblies of small plasmonic particles into large aggregates are required for enhanced photothermal performance. Self‐assembled gold nanorods in lipid bilayer‐modified microcapsules are shown to localize at tumor sites, generate vapor bubbles under near‐infrared light exposure, and subsequently damage tumor tissues. The polyelectrolyte multilayer enables dense packing of gold nanorods during the assembly process, which leads to the formation of vapor bubbles around the excited capsules. The resulting vapor bubbles achieve a high efficiency of suppressing tumor growth compared to single gold nanorods. In vivo experiments demonstrated the ability of soft‐polymer multilayer microcapsules to cross the biological barriers of the body and localize at target tissues.     

Reconfigurable Photonic Capsules Containing Cholesteric Liquid Crystals with Planar Alignment

Cholesteric liquid crystals (CLCs) reflect selected wavelengths of light owing to their periodic helical structures. The encapsulation of CLCs leads to photonic devices that can be easily processed and might be used as stand‐alone microsensors. However, when CLCs are enclosed by polymeric membranes, they usually lose their planar alignment, leading to a deterioration of the optical performance. A microfluidics approach was employed to integrate an ultrathin alignment layer into microcapsules to separate the CLC core and the elastomeric solid membrane using triple‐emulsion drops as the templates. The thinness of the alignment layer provides high lubrication resistance, preserving the layer integrity during elastic deformation of the membrane. The CLCs in the microcapsules can thus maintain their planar alignment, rendering the shape and optical properties highly reconfigurable.     

Surface Modification of Poly(urea-formaldehyde) Microcapsules and the Effect on the Epoxy Composites Performance

The surfaces of poly(urea-formaldehyde) (PUF) were modified by γ -glycidoxypropyltrimethoxy silane (KH560) in order to improve the interfacial bonding between self-healing PUF microcapsules and epoxy matrix. The modification mechanism between PUF microcapsules and KH560 was studied. X-ray photoelectron spectra (XPS) analyses showed that the silane coupling agent molecular binds strongly to the surfaces of PUF microcapsules. Chemical bond (Si–O–C) and hydrogen bond were formed at interface by the reaction between Si–OH and the hydroxyl group of PUF microcapsules surface. The tensile and impact resistance tests revealed that strength and toughness of the composites was improved significantly. Furthermore, scanning electronic microscopy (SEM) photographs of the fractured surface confirmed that the silane coupling agent plays an important role in improving the interfacial performance between microcapsules and resin matrix.