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Multilayer thin films composed of phenylboronic acid (PBA)-modified poly(allylamine hydrochloride) (PAH), PBA-PAH, with different PBA contents were prepared to study the effect of PBA content on the stability of the films. An alternate deposition of PBA-PAH and poly(vinyl alcohol) (PVA) on the surface of a quartz slide afforded multilayer films through forming boronate ester bonds between PBA-PAH and PVA. The 10-layered (PBA-PAH/PVA) 10 films constructed using PBA-PAHs containing 16% and 26% PBA residues were stable in aqueous solutions over the range of pH 4.0–10.0, whereas the multilayer films composed of PBA-PAHs with 5.9% and 8.3% PBA decomposed at pH 8.0 or lower. The pH-sensitive decomposition of the films was rationalized based on the destabilization of the boronate ester bonds in neutral and acidic solutions. In addition, the (PBA-PAH/PVA) 10 films decomposed in glucose and fructose solutions as a result of competitive binding of sugars to PBA-PAH in the films. The sugar response of the films depended on the PBA content in PBA-PAH. The (PBA-PAH/PVA) 10 films consisting of 16% and 26% PBA-substituted PBA-PAHs are sensitive to physiological relevant level of glucose at pH 7.4 while stable in glucose-free solution, suggesting a potential use of the films in constructing glucose-induced delivery systems. [ABSTRACT FROM AUTHOR]

Insulin-containing microcapsules were prepared by a layer-by-layer (LbL) deposition of poly(allylamine hydrochloride) (PAH) and polyanions, such as poly(styrenesulfonate) (PSS), poly(vinyl sulfate) (PVS), and dextran sulfate (DS) on insulin-containing calcium carbonate (CaCO3) microparticles. The CaCO3 core was dissolved in diluted HCl solution to obtain insulin-containing hollow microcapsules. The microcapsules were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM) images and ζ-potential. The release of insulin from the microcapsules was faster at pH 9.0 and 7.4 than in acidic solutions due to the different charge density of PAH. In addition, insulin release was suppressed when the microcapsules were constructed using PAH with a lower molecular weight, probably owing to a thicker shell of the microcapsules. The results suggested a potential use of the insulin-containing microcapsules for developing insulin delivery systems. [ABSTRACT FROM AUTHOR]

Abstract: We present an overview of the recent progress in the development of layer-by-layer (LbL) assembled thin films and microcapsules for insulin delivery. The LbL deposition of insulin-containing thin films on the surfaces of flat substrates or microparticles has been investigated for orally administered insulin formulations. The amount of insulin in the LbL films can be precisely controlled by altering the number of layers in the films. As-prepared LbL films and microcapsules can be loaded with insulin by exposing the films and microcapsules to an insulin solution. The insulin can be released by pH-induced decomposition or permeability changes in the LbL films and microcapsules. Closed-loop insulin delivery systems that can release insulin in response to changes in glucose concentration have also been constructed with LbL films and microcapsules. Glucose-sensitive materials, such as glucose oxidase, concanavalin A, and phenylboronic acid, have been incorporated into insulin-containing LbL assemblies. In addition, LbL film-coated pancreatic islet cells have recently been developed as a bio-artificial pancreas, in which the islet cells are isolated from the recipient's immune system by the LbL coatings. Thus, LbL films and microcapsules could make a significant contribution to the further development of patient-friendly insulin delivery systems. [Copyright &y& Elsevier]

Abstract: Layer-by-layer (LbL) thin films containing insulin were prepared by alternately depositing insulin and poly(allylamine hydrochloride) (PAH) onto a solid surface at pH 7.4. The deposition behavior of the LbL films was studied using a quartz crystal microbalance, UV–vis absorption spectrometer, ζ-potential analyzer, and an atomic force microscope. The insulin-containing LbL films were stable in neutral pH media, but the films decomposed in solutions at pH 5.0 or lower. The decomposition of the LbL films can be rationalized on the basis of the loss of electrostatic interactions between insulin and PAH due to a shift in the net electric charge of insulin from negative to positive in acidic media. The films also decomposed to some extent in media at pH 9.0 and 10. A circular dichroism analysis showed that insulin retained its original conformation when released from LbL film into acidic solutions. [Copyright &y& Elsevier]

Abstract: Layer-by-layer (LbL) thin films containing insulin were deposited on the surface of biodegradable poly(lactic acid) (PLA) microbeads and the pH-triggered release of insulin was studied. The LbL films were successfully prepared by the alternate deposition of insulin and poly(vinyl sulfate) (PVS) or dextran sulfate (DS) at pH 4.0 through the electrostatic force of attraction between positively charged insulin and polyanions. The loading of insulin on the microbeads was dependent on the number of insulin layers and the type of polyanions used; higher insulin loading was observed for thicker films and when PVS was used as the polyanion. Insulin was released from the microbeads when they were exposed to neutral solution (pH 7.4) due to a loss of electrostatic attraction between the insulin and polyanions in the films, which in turn was caused by the charge reversal of insulin from positive to negative in the neutral medium. The pH threshold for insulin release was found to be pH 5.0–6.0. The released insulin retained its original secondary structure as evidenced by circular dichroism spectra. The insulin loaded on the microbeads was satisfactorily stable even in the presence of a digestive enzyme (pepsin) at pH 1.5. These results suggest a potential future use for insulin-loaded microbeads in the oral delivery of insulin. [Copyright &y& Elsevier]

Sugar-sensitive microcapsules containing insulin were prepared by a layer-by-layer (LbL) deposition of alginic acid (AGA) and phenylboronic acid-modified poly (allylamine) (PBA-PAH) on the surface of a calcium carbonate (CaCO3) microparticle in which insulin had been embedded, followed by dissolution of the CaCO3 core. The microcapsules thus prepared were stable at pH 7.0-9.0. In the presence of 10-100 mM fructose or glucose, the release of insulin was significantly enhanced depending on solution pH and sugar concentration. The sugar-triggered release of insulin was explained on the basis of decomposition of the microcapsules, which in turn was caused by competitive binding of added sugar to the phenylboronic acid moieties in the LbL film. [ABSTRACT FROM AUTHOR]

Abstract: Layer-by-layer (LbL) thin films composed of fluorescein-modified poly(allylamine) (F-PAH) and poly(styrenesulfonic acid) (PSS) were prepared on the surface of an indium–tin oxide (ITO) electrode and the electrode potential-dependent colorimetric response of the LbL films was studied in the presence of hydrogen peroxide (H2O2). The LbL films were prepared by an alternate deposition of F-PAH and PSS on the surface through an electrostatic force of attraction. The LbL films exhibited a UV–visible absorption band around 500nm originating from fluorescein residues in the film and the intensity of the absorption band depended on the pH of the solution to which the LbL film is exposed. The absorbance of the film was higher at neutral pH than that in weakly acidic solutions. The intensity of the absorption band decreased when an electrode potential higher than 0.6V was applied in the presence of H2O2, while virtually no response was observed at lower electrode potential. The colorimetric response was suppressed in solutions with higher buffer capacity. The results were rationalized on the basis of the changes in local pH at the vicinity of the electrode surface, which in turn was induced by electrolysis of H2O2 on the electrode surface. A possible application of the system for colorimetric sensing of H2O2 was discussed. [Copyright &y& Elsevier]

Thin films were prepared using layer-by-layer (LbL) deposition of Nafion (NAF) and polycations such as poly(allylamine hydrochloride) (PAH), poly(ethyleneimine) (PEI), and poly(diallydimethylammonium chloride) (PDDA). Insulin was then adsorbed on the NAF-polycation LbL films by immersion in an insulin solution. The NAF-polycation LbL films were characterized using a quartz crystal microbalance and an atomic force microscope. The release of insulin from the LbL films was characterized using UV-visible adsorption spectroscopy and fluorescence emission spectroscopy. The greatest amount of insulin was adsorbed on the NAF-PAH LbL film. The amount of insulin adsorbed on the (NAF/PAH)5NAF LbL films by immersion in a 1 mg mL−1 insulin solution at pH 7.4 was 61.8 µg cm−2. The amount of insulin released from the LbL films was higher when immersed in insulin solutions at pH 2.0 and pH 9.0 than at pH 7.4. Therefore, NAF-polycations could be employed as insulin delivery LbL films under mild conditions and as an insulin release control system according to pH change. [ABSTRACT FROM AUTHOR]