Odilio B. G. Assis

A Review of the Antimicrobial Activity of Chitosan

Chitosan, a versatile hydrophilic polysaccharide derived from chitin, has a broad antimicrobial spectrum to which gram-negative, gram-positive bacteria and fungi are highly susceptible. In the current review, three possible and accepted antimicrobial mechanisms for chitosan are presented and briefly discussed. The activity dependence on polymeric molecular weight (MW) and degree of acetylation (DA) are described. The chitosan minimum inhibitory concentrations (MIC) are summarized according to recent data found in the literature. The potential to improve inhibitory growth of bacteria by using water soluble chitosan derivatives is also discussed. The data indicate that the effectiveness of chitosan varies and is dependent on species of target microorganisms.

Development of poly(lactic acid) nanostructured membranes for the controlled delivery of progesterone to livestock animals

Solution blow spinning (SBS) is a novel technology feasible to produce nanostructured polymeric membranes loaded with active agents. In the present study, nanofibrous mats of poly(lactic acid) (PLA) loaded with progesterone (P4) were produced by SBS at different P4 concentrations. The spun membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The in vitro releasing of P4 was evaluated using high-performance liquid chromatography (HPLC). Interactions between progesterone and PLA were confirmed by rheological measurements of the PLA/P4 solutions and in the spun mats by microscopy (SEM), thermal (DSC) and spectral (FTIR) analyses. SEM micrographs provided evidences of a smooth and homogeneous structure for nanostructured membranes without progesterone crystals on fiber surface. FTIR spectroscopy indicated miscibility and interaction between the ester of PLA and the ketone groups of the P4 in the nanofibers. X-ray analysis indicated that the size of PLA crystallites increased with progesterone content. Finally, by in vitro release experiments it was possible to observe that the progesterone releasing follows nearly first-order kinetics, probably due to the diffusion of hormone into PLA nanofibers.

AFM characterization of chitosan self-assembled films

Atomic force microscopy (AFM) was used to examine the surface structure of self-assembled films obtained from water-soluble chitosan rich solution precursor. The film was supported onto functionalized glass slides resulting in a mountain-and-valley structure. This feature is attributed as resulting of the experimental condition where agglomeration of molecules in solution may occur. The film height does not exceed 20 nm with medium pore size of approximately 12 nm. This range of porosity is suitable for nanofiltration applications.

Quaternary Salts of Chitosan: History, Antimicrobial Features, and Prospects

Recently, increasing attention has been paid to water-soluble derivatives of chitosan at its applications. The chemical characteristics and the antimicrobial properties of these salts can play significant role in pharmacological and food areas mainly as carriers for drug delivery systems and as antimicrobial packaging materials. In the current paper, a historical sequence of the main preparative methods, physical chemistry aspects, and antimicrobial activity of chitosan quaternized derivatives are presented and briefly discussed. In general, the results indicated that the quaternary derivatives had better inhibitory effects than the unmodified chitosan.

Some properties of protective sol–gel glass coatings on sintered stainless steels

Sol–gel SiO2 films are deposited onto sintered AISI 316 steel by dip-coating technique from TEOS (tetraethyl orthosilicate) precursor solution. Two different heating rates in the sintering step (800°C/2 h) were used, viz., 10 and 3°C/min. Analysis of the coatings were carried out by scanning electron microscopy and atomic force microscopy to determine the topographical features and the homogeneity of the films. Corrosion of coated and uncoated samples in H2SO4 was measured. Results indicate that the heating affects the homogeneity of a sintered film. A film prepared with a heating rate at 10°C/min is inhomogeneous when compared with a film prepared with a rate of 3°C/min; however the 3°C/min film had greater roughness (RMS) than the 10°C/min film (64.7 and 23.3 nm, respectively). For the corrosion data, a reduction in the passivation current, when compared with the non-coated steels is reported.

Chemical treatment and characterization of soybean straw and soybean protein isolate/straw composite films

This work investigated changes in the chemical composition and structure of soybean straw (SS) treated with alkali (NaOH 5% and 17.5%) and bleached with hydrogen peroxide (H2O2) or sodium hypochlorite (NaOCl). Removal of the amorphous constituents increased the degree of crystallinity and the content of cellulose fibers particularly after reaction with high concentrations of alkali. Treatment with NaOH 17.5% contributed to the allomorph transition from cellulose I to II regardless of the bleaching agent, but H2O2 as bleaching agent promoted more effective delignification. This work also evaluated the potential use of treated and non-treated SS as reinforcement filler in soy protein isolate film (SPI). Films added with treated SS presented higher mechanical resistance, lower elongation at break, and lower solubility in water. Addition of non-treated SS did not affect the properties of the SPI film significantly. The low solubility and the reasonable water vapor permeability of the composite films make them suitable packaging materials for fresh fruit and vegetables.

Caracterização estrutural e da capacidade de absorção de água em filmes finos de quitosana processados em diversas concentrações

Chitosan thin-films (medium molar mass) were produced from different concentration precursor solution and characterized regarding structure and water absorption capability. Films were obtained from direct dipping of glass slides previously functionalized into acid medium gels (self-assembly technique). Analysis of scanning electron and atomic force microscopy data revealed a film thickness of less than 25-30 nm with low dependence upon polymer concentration. All films were featured as a nano porous structure. The water affinity, however, varies exponentially (2ls) with the chitosan content. Comparison tests in buffer solution were also carried out pointing to different behavior from that found for water.

Immobilized lysozyme protein on fibrous medium: Preliminary results for microfiltration applications

The protein lysozyme was deposited onto a permeable support comprising chemically functionalized glass fiber. The main objective of this study was to set a stable organic net with no effect on the medium bed permeability and a preliminary test the activity of this enzyme under immobilized conditions. The film formation is followed by atomic force microscopy (AFM) surface imaging. The effect on the bacteria Escherichia coli was tested using a simple microfiltration column. The filtration results pointed around 75% removal of bacteria in the effluent when compared to the influent concentration. The removal mechanism is assumed as being essentially due biointeraction. The surface polarity characteristics of the formed film were also considered as playing an important role, suggesting an electrostatic interaction mechanism in the microorganism removal.

Alteração do caráter hidrofílico de filmes de quitosana por tratamento de plasma de HMDS

Alteration in hydrophilicity feature of chitosan films by hexamethyldisilazane (HMDS) cold-plasma treatment is evaluated. All treated films were colorless and transparent with no apparent textural changes. The effect on surfaces was characterized through contact angle measurements, degree of swelling and water vapor permeation. A significant reduction in all of the hydrophilicity parameters was observed. It is assumed that the HMDS treatment forms nonpolar silicone type structures. The goal is to investigate the formation of a stable hydrophobic barrier in order to increase the chitosan films usefulness in packaging applications.

Mechanical properties of N,N,N-trimethylchitosan chloride films

Films of chitosan and N,N,N-trimethylchitosan were cast from aqueous solutions. Chitosan was dissolved in 1% acetic acid while deionized water was the solvent for N,N,N-trimethylchitosan chloride. The resulting films presented different mechanical behaviors as evaluated by DMTA. The film of chitosan exhibited an elastic-type behavior while that of N,N,N-trimethylchitosan was typically viscous. No glass transition temperatures were observed; however, a discrete thermal transition was detected at 25 °C in the case of the N,N,N-trimethylchitosan.