M. A. Del Nobile

Poly(Ethylene oxide) (PEO) and different molecular weight PEO blends monolithic devices for drug release

An interpretation of the drug release from monolithic water-swellable and soluble polymer tablets is presented. A convenient parameter, alpha, which compares the drug-diffusive conductance in the gel layer with the swelling and dissolving characteristics of the unpenetrated polymer was used to describe the release behaviour of beta-hydroxyethyl-theophylline (etofylline) from compression-moulded tablets of hydrophilic pure semicrystalline poly(ethylene oxides) of mol wt 600,000 and 4,000,000 and of two blends of the two molecular weights of poly(ethylene oxides). The water swelling and dissolution characteristics of two polymers and two blends were analysed, monitoring the thickness increase of the surface-dissolving layer and the rates of water swelling and penetration in the tablets. The drug diffusivities in the water-penetrated polymer gels were measured by carrying out permeation tests. Finally, drug release tests were performed to investigate the release kinetics of the different systems in an aqueous environment at 37 degrees C. The drug release from the high molecular weight poly(ethylene oxide) is principally related to the material swelling rather than polymer dissolution, leading to a progressive decrease of the drugs diffusive conductance in the growing swollen layer, and hence to a non-constant release induced by the prevailing diffusive control. Conversely, drug release from the low molecular weight poly(ethylene oxide) is strictly related to the polymer dissolution mechanism. The achievement of stationary conditions, in which the rate of swelling equals the rate of dissolution, ensures a constant release rate, even in the case of very low drug-diffusive conductance in the external gel layer. Intermediate behaviours were detected in the case of the two blends.

Vapor sorption in emptied clathrate samples of syndiotactic polystyrene

The analysis of chloroform vapor sorption at 35°C in semicrystalline syndiotactic polystyrene samples shows remarkably different sorption isotherms, depending on the crystalline form of the samples. In particular, “emptied” clathrate (“emptied” δ form) samples are characterized by higher equilibrium sorption levels and the differences are particularly relevant for low vapor activities. Moreover, sorption kinetics detected at a vapor activity equal to 0.5 show that in the case of “emptied” δ form samples the sorption rate is much higher than for the other semicrystalline samples. The larger sorption equilibrium uptakes and sorption rates of the “emptied” δ form samples are essentially due to their ability to absorb chloroform, already for low activities, by clathration in the crystalline phase. The measured equilibrium uptakes and sorption kinetics suggest that “emptied” δ form samples of syndiotactic polystyrene could be suitable for removing polluting chlorinated compounds from vapor and liquid streams.

Immobilization of lysozyme on polyvinylalcohol films for active packaging applications.

A new technique for the immobilization of lysozyme onto the surface of polyvinylalcohol films is presented. The active compound was sprayed along with a suitable bonding agent onto the surface of the cross-linked polymeric matrix. Active compound release tests determined the amount of lysozyme immobilized on the film surface. With the use of Micrococcus lysodeikticus, the antimicrobial activity of the films was determined and the results correlated with the amount of immobilized lysozyme. This new technique was effective for immobilizing the enzyme, and the developed films were active against the test microorganism. Results were compared with those obtained with a different immobilizing technique, in which the active compound was bound into the bulk of the polymeric film. As expected, the surface-immobilized lysozyme films have a higher antimicrobial activity than bulk-bound films.

Water sorption in cellulose-based hydrogels

Sorption of distilled water in a cellulose-based hydrogel is presented. The examined system is based on a mixture of sodium salt of carboxymethylcellulose and hydroxyethylcellulose, crosslinked with divinilsulphone. The effect of chemical composition, manufacturing procedures, as well as desiccation protocols on equilibrium water uptake was investigated. Experimental results were interpreted in terms of crosslinking density, presence of ionic groups on the backbone, as well as macroscopic sample morphology detected by electron scanning microscopy. The reported results evidence the possibility to bias the process parameters in order to obtain hydrogels characterized by the desired water sorption levels.

Active systems based on silver-montmorillonite nanoparticles embedded into bio-based polymer matrices for packaging applications.

Silver-montmorillonite (Ag-MMT) antimicrobial nanoparticles were obtained by allowing silver ions from nitrate solutions to replace the Na(+) of natural montmorillonite and to be reduced by thermal treatment. The Ag-MMT nanoparticles were embedded in agar, zein, and poly(ε-caprolactone) polymer matrices. These nanocomposites were tested in vitro with a three-strain cocktail of Pseudomonas spp. to assess antimicrobial effectiveness. The results indicate that Ag-MMT nanoparticles embedded into agar may have antimicrobial activity against selected spoilage microorganisms. No antimicrobial effects were recorded with active zein and poly(ε-caprolactone). The water content of the polymeric matrix was the key parameter associated with antimicrobial effectiveness of this active system intended for food packaging applications.

Controlled release of antimicrobial compounds from highly swellable polymers

The suitability of antimicrobial release films made from highly swellable polymers for use in food packaging was evaluated. The possibility of modulating the release kinetics of active compounds either by regulating the degree of cross-link of the polymer matrix or by using multilayer structures was addressed. The release kinetics of lysozyme, nisin, and sodium benzoate (active compounds with different molecular weights) were determined at ambient temperature (25 degrees C). The effectiveness of the proposed active films in inhibiting microbial growth was addressed by determining the antimicrobial efficiency of the released active compounds. Micrococcus lysodeikticus, Alicyclobacillus acidoterrestris, and Saccharomyces cerevisiae were used to test the antimicrobial efficiency of released lysozyme, nisin, and sodium benzoate, respectively. Results indicate that the release kinetics of both lysozyme and nisin can be modulated through the degree of cross-link of the polymer matrix, whereas multilayer structures need to be used to control the release kinetics of sodium benzoate. All the active compounds released from the investigated active films were effective in inhibiting microbial growth.

A Study on the Antimicrobial Activity of Thymol Intended as a Natural Preservative

A quantitative investigation on the inhibitory activity of thymol against some microorganisms that could represent a potential spoilage risk both in acid and mild thermally treated foods is presented in this work. In order to assess potential biostatic or biocidal activity of thymol, both the growth kinetics and dose-response profiles were obtained and analyzed. A suitable macrodilution methodology based on a turbidimetric technique was adopted to produce inhibitory data used for characterizing microbial susceptibility against thymol at sub-MIC levels. Microbial growth was monitored through absorbance measurements at 420 nm as a function of contact time with the active compound. Moreover, for each tested microorganism, the noninhibitory concentration (NIC) and the MIC were quantified. Results prove that thymol can exert a significant antimicrobial effect on each phase of the growth cycle. The microbial susceptibility and resistance were found to be nonlinearly dose related. It is worth noting that significant biostatic effects were observed at sub-MIC levels.

Anomalous diffusion in poly-ether-ether-ketone

Poly-ether-ether-ketone (PEEK) is a thermoplastic tough polymer used as a matrix for advanced composite materials in aeronautic applications. The investigation of its resistance to humid environment and to exposure to organic and chlorinated solvents is extremely important. A series of integral sorption experiments were performed on PEEK with three different kinds of penetrant, namely water, methylene chloride and methylene chloride—n-heptane mixtures. Coupled diffusion and relaxation phenomena were observed to occur in most of the adopted experimental conditions. Moreover, for the case of methylene chloride sorption at medium and high activities a solvent-induced crystallization phenomenon was also detected. The sorption behavior was found to range from ideal Fickian diffusion (where the molecular mobility is not affected by the penetrant concentration) to so-called anomalous diffusion. In the latter case the penetrant mobility is a complex function of penetrant concentration, time and temperature. An overview of theoretical models reported in the literature to describe such phenomena is also presented with the aim of interpreting the experimental results obtained.

Antimicrobial activity of immobilized lysozyme on plasma-treated polyethylene films.

In this study we tested the antimicrobial activity of polyethylene films modified by means of plasma processes that were followed by the chemical immobilization of lysozyme, an antimicrobial enzyme. To chemically immobilize the enzyme in its active form at the surface of polyethylene, substrates that had been plasma treated under different experimental conditions were soaked in lysozyme solutions at different concentrations. The immobilization of the enzyme was checked, and the antimicrobial activity of the films was investigated by observing the death rate of Micrococcus lysodeikticus cells suspended in phosphate buffer in contact with the films. The results clearly indicate that plasma-treated films loaded with lysozyme are active against the selected microorganism. A modified version of the Gompertz equation was used to quantitatively valuate the dependence of the antimicrobial activity of the films under both plasma treatment conditions and lysozyme concentrations.

Cellulose-based hydrogels as body water retainers

In this work the possibility of using hydrogels as body water retainers for a therapeutic aid in pathologies such as oedemas of various origins was explored. For such a purpose, the material requires a good compatibility and a controlled swelling capacity without altering the body electrolyte homeostasis. The hydrogel was designed to meet the swelling requirements with the physiological constraints and its biocompatibility was assessed either in vitro or in vivo. Absorption tests were performed in order to define the swelling behavior by varying the pH and ion content of the external solution. The hydrogel swelling capacity was assessed in the presence of various solvents, in order to evaluate its absorption capacity in solutions similar to biological fluids. In addition, the capacity of the gel to modify electrolyte homeostasis by adsorbing ions such as calcium, potassium and sodium was tested. In order to assess the gel biocompatibility after contact of the hydrogel with intestinal cells, arachidonic acid relase was determined. No significant intracellular increase of free arachidonic acid was found in the cells after up to 2 h of contact with the gel. The results suggest that, as far as brief periods are concerned, the gel does not cause an inflammatory response in intestinal cells. ©2000 Kluwer Academic Publishers