Furosemide microcrystals were encapsulated with polyions and gelatin to control the release of the drug in aqueous solutions. Charged linear polyions and gelatin were alternatively deposited on 5-mm drug microcrystals through layer-bylayer (LbL) assembly. Sequential layers of poly(dimethyldiallyl ammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS) were followed by adsorption of two to six gelatin /PSS bilayers with corresponding capsule wall thicknesses ranging from 45 to 115 nm. The release of furosemide from the coated microparticles was measured in aqueous solutions of pH 1.4 and 7.4. At both pH values, the release rate of furosemide from the encapsulated particles was reduced by 50-300 times (for capsules coated with two to six bilayers) compared to uncoated furosemide. The results provide a method of achieving prolonged drug release through self-assembly of polymeric shells on drug microcrystals.

The introduction of electrostatic layer-by-layer (LbL) self-assembly has shown broad biomedical applications in thin film coating, micropatterning, nanobioreactors, artificial cells, and drug delivery systems. Multiple assembly polyelectrolytes and proteins are based on electrostatic interaction between oppositely charged layers. The film architecture is precisely designed and can be ontrolled to 1-nm precision with a range from 5 to 1000 nm. Thin films can be deposited on any surface including many widely used biomaterials. Microencapsulation of micro/nanotemplates with multilayers enabled cell surface modification, controlled drug release, hollow shell formation, and nanobioreactors. Both in vitro and in vivo studies indicate potential applications in biology, pharmaceutics, medicine, and other biomedical areas.

A recently developed method for surface modification, layer-by-layer (LbL) assembly, has been applied to silicone, and its ability to encourage endothelial cell growth and control cell growth patterns has been examined. The surfaces studied consisted of a precursor, with alternating cationic polyethyleneimine (PEI) and anionic sodium polystyrene sulfonate (PSS) layers followed by alternating gelatin and poly-D-lysine (PDL) layers. Film growth increased linearly with the number of layers. Each PSS/PEI bilayer was 3 nm thick, and each gelatin/PDL bilayer was 5 nm thick. All layers were more hydrophilic than the unmodified silicone rubber surface, as determined from contact angle measurements. The contact angle was primarily dictated by the outermost layer. Of the coatings studied, gelatin was the most hydrophilic. A film of (PSS/PEI)4/(gelatin/PDL)4/gelatin was highly favorable for cell adhesion and growth, in contrast to films of (PSS/PEI)8 or (PSS/PEI)8/PSS. Cell growth patterns were successfully controlled by selective deposition of microspheres on silicone rubber, using microcontact printing with a silicone stamp. Cell adhesion was confined to the region of microsphere deposition. These results demonstrate that the LbL selfassembly technique provides a general approach to coat and selectively deposit films with nanometer thickness on silicone rubber. Furthermore, they show that this method is a viable technique for controlling cellular adhesion and growth.

Diblock copolymers of poly(q-caprolactone) (PCL) and monomethoxy poly(ethylene glycol) (MPEG) with various compositions were synthesized. The amphiphilic block copolymers self-assembled into nanoscopic micelles and their hydrophobic cores encapsulated doxorubicin (DOX) in aqueous solutions. The micelle diameter increased from 22.9 to 104.9 nm with the increasing PCL block length (2.5–24.7 kDa) in the copolymer composition. Hemolytic studies showed that free DOX caused 11% hemolysis at 200 Ag ml 1, while no hemolysis was detected with DOX-loaded micelles at the same drug concentration. An in vitro study at 37 JC demonstrated that DOX-release from micelles at pH 5.0 was much faster than that at pH 7.4. Confocal laser scanning microscopy (CLSM) demonstrated that DOX-loaded micelles accumulated mostly in cytoplasm instead of cell nuclei, in contrast to free DOX. Consistent with the in vitro release and CLSM results, a cytotoxicity study demonstrated that DOX-loaded micelles exhibited time-delayed cytotoxicity in human MCF-7 breast cancer cells. D 2004 Elsevier B.V. All rights reserved.

Platelets were coated with 78-nm silica nanoparticles, 45-nm fluorescent nanospheres, or bovine immunoglobulin G (IgG) through layer-by-layer assembly by alternate adsorption with oppositely charged linear polyions. Sequential deposition on platelet surfaces of cationic poly(dimethyldiallylammonium chloride) and anionic poly(styrene sulfonate) was followed by adsorption of nanoparticles or immunoglobulins. Nanoorganized shells of platelets were demonstrated by transmission electron microscopy and fluorescence microscope images. Bovine IgG was assembled on platelets, as verified with anti-bovine IgG-FITC labeling. Localized targeting of anti-IgG shelled platelets was also demonstrated. An ability to coat blood cells with nano-organized shells can have applications in cardiovascular research and targeted drug delivery.

Furosemide microcrystals were encapsulated with polyions and gelatin to control the release of the drug in aqueous solutions. Charged linear polyions and gelatin were alternatively deposited on 5-mm drug microcrystals through layer-bylayer (LbL) assembly. Sequential layers of poly(dimethyldiallyl ammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS) were followed by adsorption of two to six gelatin /PSS bilayers with corresponding capsule wall thicknesses ranging from 45 to 115 nm. The release of furosemide from the coated microparticles was measured in aqueous solutions of pH 1.4 and 7.4. At both pH values, the release rate of furosemide from the encapsulated particles was reduced by 50–300 times (for capsules coated with two to six bilayers) compared to uncoated furosemide. The results provide a method of achieving prolonged drug release through self-assembly of polymeric shells on drug microcrystals.

We describe the development of multifunctional polymeric micelles with cancer-targeting capability via rvâ3 integrins, controlled drug delivery, and efficient magnetic resonance imaging (MRI) contrast characteristics. Doxorubicin and a cluster of superparamagnetic iron oxide (SPIO) nanoparticles were loaded successfully inside the micelle core. The presence of cRGD on the micelle surface resulted in the cancer-targeted delivery to rvâ3-expressing tumor cells. In vitro MRI and cytotoxicity studies demonstrated the ultrasensitive MRI imaging and rvâ3-specific cytotoxic response of these multifunctional polymeric micelles.

Low water solubility, rapid phagocytic and renal clearance, and systemic toxicity represent three major barriers that limit the therapeutic use of many hydrophobic antitumor agents such as doxorubicin (DOXO) and paclitaxel.[1] Various drugdelivery systems, among which polymeric micelles have emerged as a very important system, have been developed to overcome these limitations and deliver various drugs with remarkable in vitro and in vivo success.[2, 3] Polymeric micelles are nanoscopic (10 to 100 nm) colloidal particles self-assembled from amphiphilic block or graft copolymers in aqueous media. The hydrophobic core of the micelles is a carrier compartment that accommodates antitumor drugs, and the shell consists of a brushlike protective corona that stabilizes the nanoparticles in aqueous solution.[4] The basic requirements for polymeric micelles in drug-delivery applications include high drug-loading capacity, biodegradability, long blood circulation times, and controllable drug-release profiles. Research on micelles has been greatly advanced in the Scheme 1. Synthesis of MAL-PEG-PCL copolymer and preparation of cRGD-functionalized, DOXO-loaded micelles.

Layer-by-layer self-assembled polyelectrolyte shells are a new class of micro/nanocapsules with unique physicochemical properties for potential applications in drug/gene delivery. The objective of this study was to investigate the interactions of polyelectrolyte shells (1 min diameter) with MCF-7 breast cancer cells and identify key parameters that affect such interactions. Tailoring of surface properties of polyelectrolyte shells was achieved by choosing different outermost layer materials, including cationic polymers, anionic polymers, and lipid bilayers. Different surface compositions led to a wide range of electrostatic potentials from 46 to 47mv in phophate-buffered saline buffer. Confocal microscopy studies showed that the polyelectrolyte shells were internalized into the cell cytoplasm, but not into the nuclei. Correlation of cell uptake with shell surface compositions was complicated by the adsorption of serum proteins on the surface of polyelectrolyte shells, particularly polycation-coated shells. To prevent protein adsorption, poly(ethylene glycol) (PEG) grafted poly(ethyleneimine) (PEI) copolymers (1:1, 1:5, 1:10 graft ratios) were synthesized and introduced on the shell surface. Shells coated with PEI-PEG copolymers effectively reduced protein adsorption whereas PEI-PEG copolymers with lower graft ratios achieved higher cell uptake efficiency after 24 h of incubation with MCF-7 cells.