Stimulus-responsive "smart" hydrogels as novel drug delivery systems

Recently, there has been a great deal of research activity in the development of stimulus-responsive polymeric hydrogels. These hydrogels are responsive to external or internal stimuli and the response can be observed through abrupt changes in the physical nature of the network. This property can be favorable in many drug delivery applications. The external stimuli can be temperature, pH, ionic strength, ultrasonic sound, electric current, etc. A majority of the literature related to the development of stimulus-responsive drug delivery systems deals with temperature-sensitive poly(N-isopropyl acrylamide) (pNIPAAm) and its various derivatives. However, acrylic-based pH-sensitive systems with weakly acidic/basic functional groups have also been widely studied. Quite recently, glucose-sensitive hydrogels that are responsive to glucose concentration have been developed to monitor the release of insulin. The present article provides a brief introduction and recent developments in the area of stimulus-responsive hydrogels, particularly those that respond to temperature and pH, and their applications in drug delivery.

Microspheres as floating drug-delivery systems to increase gastric retention of drugs

Gastric emptying is a complex process, which is highly variable and makes in vivo performance of the drug-delivery systems uncertain. In order to avoid this variability, efforts have been made to increase the retention time of the drug-delivery systems for more than 12 h. The floating or hydrodynamically controlled drug-delivery systems are useful in such applications. The present review addresses briefly the physiology of the gastric emptying process with respect to floating drug-delivery systems. In recent years, the multiparticulate drug-delivery systems are used in the oral delivery of drugs. One of the approaches toward this goal is to develop the floating microspheres so as to increase the gastric retention time. Such systems have more advantages over the single-unit dosage forms. The development of floating microspheres involves different solvent evaporation techniques to create the hollow inner core. The present review addresses the preparation and characterization of the floating microspheres for the peroral route of administration of the drug.

A comparison of solid sampler methods for the determination of hexamethylene-based isocyanates in spray-painting operations

A polyurethane foam sponge impregnated with 1-(2-methoxyphenyl) piperazine in dimethylsulfoxide was mounted in both cassette and inhalable organic monitor samplers and these were then compared with a dual-filter cassette. The samplers were used for the collection of hexamethylene diisocyanate (HDI) monomer and oligomers during actual spray-painting operations. The dual filter cassettes were positioned on a mannequin. The polyurethane foam cassette (PUF CAS) and polyurethane foam inhalable organic monitor (PUF IOM) samplers were positioned on a cart in the same maximum overspray area. Data from this pilot study suggest that there is no significant difference (P < 0.05, n = 6) in the amount of HDI monomer obtained with the PUF IOM sampler when compared with the amount obtained from the dual filter cassette. The data also suggest that the PUF IOM sampler yields a higher amount of HDI oligomer than either the dual filter cassette or the PUF CAS sampler, neither of which exhibited a significant difference (P < 0.05, n = 6) from each other.

In-vitro release kinetics of cefadroxil-loaded sodium alginate interpenetrating network beads

This paper reports the development of new interpenetrating polymeric networks of sodium alginate with gelatin or egg albumin cross-linked with a common cross-linking agent, glutaraldehyde, for the in-vitro release of cefadroxil. The beads formed were characterized by Fourier transform infra-red spectroscopy, scanning electron microscopy and differential scanning calorimetry. Swelling/drying experiments were performed to compute the diffusion coefficients and the molecular mass between cross-links of the beads. The release results were evaluated using an empirical equation to understand the transport mechanism. The extent of cross-linking was studied in terms of the size and release characteristics of the beads. The experimental and derived quantities have been used to study their dependencies on the nature of the polymeric beads, transport mechanism, encapsulation efficiency and drug diffusion, as well as the cross-linking abilities of the polymers.

Biodegradable polymeric nanoparticles as drug delivery devices

This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drug delivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surface modification methods as well as surface characterization are covered from 1990 through mid-2000.

Biodegradable polymeric nanoparticles as drug delivery devices

This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drug delivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surface modification methods as well as surface characterization are covered from 1990 through mid-2000.

Preparation of cross-linked sodium alginate microparticles using glutaraldehyde in methanol

Polymeric sodium alginate microparticles were prepared by precipitating sodium alginate in methanol, followed by cross-linking with glutaraldehyde. The extent of cross-linking was controlled by the time of exposure to glutaraldehyde. The topology of microparticles was characterized by scanning electron microscopy (SEM), which indicated smooth surfaces. The equilibrium swelling experiments were carried out in water to observe the effect of cross-linking and drug loading for better utility of microparticles. It was found that swelling decreased, but drug loading increased, with an increase in cross-linking of the matrix.

Determination of hexamethylene diisocyanate-based isocyanates in spray-painting operations. Part 2. Comparison of high performance liquid chromatography with capillary zone electrophoresis

A capillary zone electrophoresis (CZE) approach was developed for the determination of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. A comparison of CZE with high performance liquid chromatography (HPLC) indicates that the CZE separation completely isolates isocyanates from excess solvent, derivatizing reagent and pigment while offering a fivefold increase in sensitivity. The CZE approach allows for the quantification of HDI monomer and oligomer within a 1 min time window under the run conditions selected. For the determination of HDI-based oligomer, provided that the relative response with respect to HDI monomer is calculated, there is no significant difference (p < 0.05, n = 10) in the isocyanate air concentration when using either HPLC or CZE. The results are significant because they indicate that CZE has advantages for the determination of both HDI-based oligomer and HDI monomer generated during spray-painting operations.

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.

Evaluation of tryptamine in an impinger and on XAD-2 for the determination of hexamethylene-based isocyanates in spray-painting operations

Tryptamine was evaluated as a reagent for derivatizing hexamethylene diisocyanate (HDI) monomer and oligomers during actual spray-painting operations. In one side-by-side sampling study, an impinger filled with 1-(2-methoxyphenyl)piperazine in toluene was compared with a second impinger filled with tryptamine in dimethyl sulfoxide (DMSO). The amount of HDI monomer obtained was below the limit of quantification for both impingers. The amount of HDI oligomer obtained when using 1-(2-methoxyphenyl)piperazine in toluene was comparable to the amount obtained when using an impinger filled with tryptamine in DMSO. In a second side-by-side sampling study, a tryptamine-coated XAD-2 resin was used as a sorbent. The relative collection efficiency of the tryptamine-coated XAD-2 resin was on average 60% of the value obtained using an impinger filled with tryptamine in DMSO. The results indicate that using an impinger filled with tryptamine in DMSO gives higher concentrations of isocyanate than a tryptamine-coated XAD-2 sorbent for HDI monomer and oligomer.

Evaluation of 1-(9-anthracenylmethyl) piperazine for the analysis of isocyanates in spray-painting operations

A new reagent, 1-(9-anthracenylmethyl)piperzine (MAP), was used for the derivatization of airborne 1,6-hexamethylene diisocyanate (HDI) and polyisocyanates generated during spray-painting operations. The new reagent, which offers enhanced sensitivity and uniformity of response to both the monomeric and oligomeric forms of HDI, was compared directly with 1-(2-methoxyphenyl)piperazine (MOP), the currently employed derivatizing reagent used in the National Institute for Occupational Safety and Health Method 5521. Both the validity of the side-by-side sampling protocol and the efficacy of two derivatizing reagents were evaluated in field studies. The analytical results indicate that there is no significant difference at the 95% confidence level in the concentration of polyisocyanate in the aerosol as determined by two impingers containing MAP and a third containing MOP when these are positioned in a side-by-side-by-side arrangement.

The Raman spectra of selenomethionine and selenocystine

The trace element selenium is known to be a part of the enzyme glutathione peroxidase (glutathione-hydrogen peroxide oxidoreductase, E.C.1.11.1.9). Studies have shown that selenium in the enzyme exists in at least two forms or oxidation states. It is probable that selenium has been incorporated into the enzyme as the selenocysteine amino acid. In the present study, the Raman spectra of selenocystine and selenomethionine have been obtained, structural assignments have been verified, and the behavior of the two selenoamino acids have been monitored under varying conditions of oxidative stress. The assignments will assist in the interpretation of the spectrum of the actual enzyme.