Applications of cellulose and chitin/chitosan derivatives and composites as antibacterial materials: current state and perspectives.

The bacterial infections have always a serious problem to public health. Scientists are developing new antibacterial materials to overcome this problem. Polysaccharides are promising biopolymers due to their diverse biological functions, low toxicity, and high biodegradability. Chitin and chitosan have antibacterial properties due to their cationic nature, while cellulose/bacterial cellulose does not possess any antibacterial activity. Moreover, the insolubility of chitin in common solvents, the poor solubility of chitosan in water, and the low mechanical properties of chitosan have restricted their biomedical applications. In order to solve these problems, chemical modifications such as quaternization, carboxymethylation, cationization, or surface modification of these polymers with different antimicrobial agents, including metal and metal oxide nanoparticles, are carried out to obtain new materials with improved physiochemical and biological properties. This mini review describes the recent progress in such derivatives and composites with potential antibacterial applications.

Spatial correlation of confocal Raman scattering and secondary ion mass spectrometric molecular images of lignocellulosic materials.

A detailed chemical and structural understanding of pre-enzymatic processing of lignocellulosic materials (LCMs) is a key objective in the development of renewable energy. Efficient rendering of biomass components into fermentable substrates for conversion into biofuel feedstocks would benefit greatly from the development of new technologies to provide high-quality, spatially resolved chemical information about LCMs during the various processing states. In an effort to realize this important goal, spatially correlated confocal Raman and mass spectrometric images allow the extraction of three-dimensional information from the perennial grass, Miscanthus x giganteus. An optical microscopy-based landmark registry scheme was developed that allows samples to be transferred between laboratories at different institutions, while retaining the capability to access the same physical regions of the samples. Subsequent to higher resolution imaging via confocal Raman microscopy and secondary ion mass spectrometry (SIMS), laser desorption-ionization mass spectrometry was used to place these regions within the overall sample architecture. Excellent sample registry was evident in the highly correlated Raman and SIMS images. In addition, the correlation of vibrational Raman scattering with mass spectra from specific spatial locations allowed confirmation of the assignment of intracellular globular structures to hemicellulose-rich lignin complexes, an assignment which could only be made tentatively from either image alone.

Development and antibacterial activities of bacterial cellulose/graphene oxide-CuO nanocomposite films.

The absence of antibacterial activity of bacterial cellulose (BC) restricts its applications in the biomedical field. To introduce antimicrobial properties into BC, we studied the synthesis, structure, and antimicrobial properties of a novel nanocomposite film comprising BC, graphene oxide (GO), and copper-oxide (CuO) nanosheets. The nanocomposite film was synthesized by incorporating GO-CuO nanohybrids into BC matrix through homogenized blending. The CuO nanosheets, with a length range of 50 nm-200 nm and width range of 20 nm-50 nm, which were uniformly grown on the GO along with even distribution of GO-CuO nanohybrids on the surface of the cellulose fibers. The nanocomposites displayed better antibacterial activity against gram-positive than gram-negative bacteria. BC/GO-CuO nanocomposites showed higher antibacterial activity than BC/CuO. We also elucidated the mechanism of antibacterial activity of the nanocomposites. Further, the nanocomposites exhibited biocompatibility towards mice fibroblast cells. The nanocomposites might serve as an excellent source for development of antibacterial materials.

Preparation and antibacterial activity of silver-loaded poly(oligo(ethylene glycol) methacrylate) brush.

Herein, we report on a robust approach to fabricate antibacterial nanocomposite coating simply by immersing poly(oligo(ethylene glycol) methacrylate) (POEGMA) brush into a silver perchlorate solution without using any external reducing agents. The POEGMA brush of 48.3 nm in thickness is prepared via surface-initiated atom transfer radical polymerization method. Field-emission scanning electron microscope and Raman measurements indicate that silver nanoparticles of 14 ∼ 25 nm in diameter are successfully embedded into the POEGMA brush. Antibacterial activities of the resultant silver-loaded POEGMA brushes against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus are measured by zone of inhibition and colony-counting methods, respectively. The results show that the silver-loaded POEGMA coatings exhibit enhanced antibacterial efficiency compared to bare POEGMA brush. In order to elucidate their antibacterial mechanism, silver release behaviors of these silver-loaded POEGMA brushes are monitored via inductively coupled plasma mass spectrometry.

A facile construction of bacterial cellulose/ZnO nanocomposite films and their photocatalytic and antibacterial properties.

Bacterial cellulose (BC) has numerous excellent properties but the absence of antibacterial activity restricts its applications in biomedical field. Therefore, in order to introduce the antibacterial characteristics into BC; herein, a facile method for incorporation of ZnO nanoparticles (ZnO-NPs) is presented. BC films were first immersed in zinc nitrate solution, followed by treating with NaOH solution, the BC loaded ZnO nanocomposite films were dried by a sheet former instrument at 80 °C for 20 min. The obtained BC/ZnO nanocomposites were characterized by different techniques. XRD results showed the hexagonal wurtzite structure of ZnO-NPs while FE-SEM results displayed the particle size of ZnO-NPs was ranging from 70 to 100 nm. Thermogravimetric study revealed the thermal stability of nanocomposite films. The nanocomposite exhibited photocatalytic activity and revealed 91% degradation of methyl orange (MO) under UV-irradiation within 2 h. Moreover, the nanocomposites demonstrated significant UV-blocking properties and showed antibacterial activities against tested Gram-positive and Gram-negative bacterial strains. This work provides a simple and novel method for the synthesis of BC/ZnO nanocomposite as a functional biomaterial.

Development of bacterial cellulose/chitosan based semi-interpenetrating hydrogels with improved mechanical and antibacterial properties.

In the present work, novel bacterial cellulose (BC) and chitosan (CS) semi-interpenetrating network (semi-IPN) hydrogels were prepared via blending the slurry of BC with CS solution followed by cross-linking with glutaraldehyde. The structure and properties of BC-CS hydrogels were characterized by different techniques including; FTIR, XRD, FE-SEM, TGA and rotational rheometry. The results indicated cross-linking of chitosan chains by glutaraldehyde while BC was physically connected to network forming semi-IPN hydrogels. Microscopic study of cross-sectional freeze-dried hydrogels showed microporous openings. BC-CS hydrogels exhibited higher thermal stability than pure BC film or CS hydrogel alone. The rheological results presented significant mechanical properties of semi-IPN hydrogels. Moreover, the hydrogels showed antibacterial properties against tested Gram-positive and Gram-negative bacteria. The antibacterial properties were dependent on the ratio of BC to CS. Hydrogels with 20% BC to CS reduced the viable colonies by ~88%. The development of this new class of BC-CS antibacterial, mechanically strong and stable soft-material could be a promising candidate for antibacterial applications.

Reusable ternary PVA films containing bacterial cellulose fibers and ε-polylysine with improved mechanical and antibacterial properties.

The combination of high mechanical properties, antibacterial activity and a green synthesis of the polyvinyl alcohol (PVA) based films remains challenging. This study presents a ternary system of PVA films containing bacterial cellulose (BC) and epsilon-polylysine (ε-PL) by a green solution casting method. The prepared composite films showed more than 99% antibacterial properties against both Staphylococcus aureus and Escherichia coli bacteria. Moreover, the films were collected after a single use and were reused twice, which still exhibited strong antibacterial activity. The films showed thermal stability and higher mechanical properties as compared to pure PVA films. In addition, the cytotoxicity of the films was evaluated by MTT assay against NIH 3T3 mouse fibroblast cells. The results showed no toxicity of the films towards tested cells. We believe that these antibacterial films may find applications in active food packaging and biomedical fields.

Plasma polymerized epoxide functional surfaces for DNA probe immobilization.

The development of functional surfaces for the immobilization of DNA probe is crucial for a successful design of a DNA sensor. In this report, epoxide functional thin films were achieved simply by pulsed plasma polymerization (PP) of glycidyl methacrylate (GMA) at low duty cycle. The presence of epoxide groups in the resulting ppGMA films was confirmed by Fourier transform infrared spectroscopy. The ppGMA coatings were found to be resistant to the non-specific adsorption of DNA strands, while the epoxide groups obtained could react with amine-modified DNA probes in a mild basic environment without any activation steps. A DNA sensor was made, and was successfully employed to distinguish different DNA sequences with one base pair mismatch as seen by surface plasmon enhanced fluorescence spectroscopy (SPFS). The regeneration of the present DNA sensor was also discussed. This result suggests that surface modification with ppGMA films is very promising for the fabrication of various DNA sensors.

Preparation and characterization of a photocatalytic antibacterial material: Graphene oxide/TiO2/bacterial cellulose nanocomposite.

In this study, bacterial cellulose (BC) was used as a matrix to synthesize graphene oxide/Titanium dioxide (GOTiO2)-based hybrid materials. It was indicated by X-ray diffraction and selected area electron diffraction that the crystal structure of GOTiO2 was a mixed phase containing anatase and rutile. TiO2 nanoparticles were of 10-30nm diameters and densely anchored on graphene oxide sheets. Superior photocatalytic performance of the GOTiO2 was achieved under near UV excitation. The photocatalytic efficiency was optimized through controlling an appropriate calcined temperature. The obtained GOTiO2 nanoparticles were filled into porous BC matrix (GOTiO2/BC), and the photocatalytic properties of GOTiO2 nanoparticles were well maintained. Consistent with photocatalytic performance of TiO2, GOTiO2/BC generated reactive oxygen species after near ultraviolet irradiation. No dark cytotoxicity was observed at the long incubation time. In parallel, following exposure of Staphylococcus aureus cells to GOTiO2 and irradiation, a significant decrease in cell viability, as well as an increased production of reactive oxygen species was observed, which induced cellular death. The results indicated that GOTiO2/BC possess an excellent photodynamic antibacterial activity.

Improvement of antimicrobial activity of graphene oxide/bacterial cellulose nanocomposites through the electrostatic modification.

Graphene oxide (GO) has an attracting and ever-growing interest in various research fields for its fascinating nanostructures. In this study, bacterial cellulose (BC) was used as a matrix to synthesize GO-based materials by a mechanical mixing method. The modification of GO with PEI significantly improved the bonding force between GO nanofillers and BC matrix. The morphology of the nanocomposites had a significant effect on the mechanical properties, hydrophilic properties as well as the antibacterial activity. After the modification, the GO-PEI/BC showed a strong antimicrobial effect on Saccharomyces cerevisiae due to the effective direct contacts between the nanofillers of the composites and the cell surfaces. This study demonstrates that the morphology of the nanocomposites has a great effect on physiochemical properties and the interactions between the microorganism and the nanocomposites.

Base-induced delignification of Miscanthus x giganteus studied by three-dimensional confocal Raman imaging.

Confocal raman microscopy has been used to monitor the structural and chemical changes upon NaOH treatment of Miscanthus x giganteus, a potential energy crop and a model lignocellulosic material. Longitudinal and transversal-section images of the parenchyma cells in raw miscanthus samples reveal that lignin and cellulose are collocated in the cell wall and that a globular structure, composed predominantly of hemicellulose and lignin is associated with the interior cell wall. NaOH treatment results in the complete removal of lignin at long processing time but leaves the cellulose largely undisturbed as evidenced by the lack of conversion from type I to type II cellulose. Depth profiling images of partially processed (short exposure time) parenchyma cells reveal that lignin is removed preferentially from the interior surface of the cell wall as indicated by the anisotropic distribution of lignin and cellulose across the cell wall in partially processed samples. These spatially resolved chemical changes are important, because they illustrate how even simple pre-processing protocols can develop complex molecular profiles by differential rates of attack on the major components of the cell wall.

Plasma polymerized non-fouling thin films for DNA immobilization.

Development of DNA sensors has been an issue of great interest, owing to their potential applications in different fields, such as the diagnosis of infectious diseases, food quality control, or for environmental monitoring. Most DNA sensors involved the immobilization of single-stranded oligonucleotides, so-called DNA probes, onto the sensor surfaces. Here we report on a new approach for DNA probe immobilization using the streptavidin-biotin assembly coupled with a non-fouling thin film. Pulsed plasma polymerization of di(ethylene glycol) monovinyl ether (ppEO2) will result in non-fouling thin films, which are employed to immobilize streptavidin. By careful control of the thickness and the chemistry of ppEO2 films, the embedded streptavidin are able to bind the biotinylated oligonucleotides. The resulting DNA sensors show good resistance towards adsorption of both BSA and fibrinogen, and are employed to discriminate different DNA sequences from protein-containing sample solutions, as seen by surface plasmon enhanced fluorescence spectroscopy (SPFS). This result suggests that the present sensor is very promising for the detection of a DNA sequence from a complex solution.

Stabilization of plasma-polymerized allylamine films by ethanol extraction.

The effect of ethanol extraction on plasma-polymerized allylamine (PPAA) films was investigated by measuring their thickness change using surface plasmon resonance (SPR) spectroscopy and optical waveguide spectroscopy (OWS). It was found that much of the freshly deposited PPAA films is lost upon ethanol treatment. The decrease in PPAA thickness is related to the plasma input power, the monomer vapor pressure, and the thickness of the deposited films. Despite the relatively high loss in film thickness, the densities of the amine groups in the extracted PPAA are comparable to those of fresh films, as seen by Fourier transform infrared (FT-IR) spectroscopy. The results of this study are of specific importance with respect to the biomedical application of plasma-polymerized functional thin films, in which the stability of a plasma polymer in contact with aqueous media is essential.