Beihai He

Synthesis of modified guanidine-based polymers and their antimicrobial activities revealed by AFM and CLSM.

Modified guanidine-based polymers with chain extension were synthesized by condensation and cross-linking polymerizations in an attempt to increase molecular weight and charge density of the antimicrobial polymers. The antimicrobial activity and the corresponding mechanisms were investigated by several approaches. The results indicated that the antimicrobial activities of the modified guanidine-based polymer, based on the minimum inhibition concentration (MIC) against E.coli, varied with alkyl monomer ratios. UV absorption at 260 nm further quantified the amount of intracellular components leaked into bacteria suspension. The UV absorption measurements were also used to monitor inhibition processes dynamically. It was found that the modified guanidine-based polymer inhibited the growth of bacteria by causing membrane compromised and intracellular leaked. Dual fluorescent dyes were used to stain all bacteria including the dead ones, which enabled us to utilize CLSM to visualize the viability of bacteria in the presence of various modified guanidine-based polymers without causing any damage. The morphologies of bacteria untreated and treated with modified guanidine-based polymer were observed using an atomic force microscope (AFM), which further demonstrated the damage of E.coli membrane and the leakage of intracellular component induced by the modified guanidine-based polymers.

Synergistic effects of chitosan-guanidine complexes on enhancing antimicrobial activity and wet-strength of paper.

Chitosan-guanidine complexes were prepared by reacting chitosan and polyhexamethylene guanidine hydrochloride or crosslinked polyhexamethylene guanidine hydrochloride in the presence of sodium tripolyphosphate as a crosslinking agent. The complexes, used as functional additives for paper, synergistically improved wet-strength and antimicrobial activities. In comparison with the control sample, the wet/dry strength ratio of hand-sheets treated with the complexes was increased from 2.65% up to 23.3%. The MIC values of the chitosan-PHGH and chitosan-PHGHE complexes against Escherichia coli were 15.6 and 31.2 microg mL(-1), respectively, thus demonstrating excellent antimicrobial activity. Hand-sheets treated with the complexes exhibited antibacterial activity against E. coli and Staphylococcus aureus. The release of the guanidine polymers included in the complexes was dynamically monitored using UV and the results showed the amount released exceeded 80%. Atomic force microscopy images indicated that the antimicrobial mechanism of the complexes was likely due to membrane damage.

Immobilization of pectinase and lipase on macroporous resin coated with chitosan for treatment of whitewater from papermaking

Anionic residues and pitch deposits in whitewater negatively impact the operation of paper-forming equipment. In order to remove these substances, a macroporous resin based on a methyl acrylate matrix was synthesized and coated with chitosan of various molecular weights through glutaraldehyde cross-linking. Pectinase from Bacillus licheniformis and lipase from Thermomyces lanuginosus were immobilized on the resin coated with chitosan by a Schiff base reaction. The highest hydrolysis activities of the immobilized enzymes were achieved by using chitosan with 10×10(5)DaMW for coating and 0.0025% glutaraldehyde for cross-linking chitosan. The cationic demand and pitch deposits in whitewater were reduced by 58% and 74%, respectively, when treating whitewater with immobilized dual-enzymes for 15min at 55°C and pH 7.5. This method is useful for treatment of whitewater in the papermaking industry.

Immobilization of pectinase on oxidized pulp fiber and its application in whitewater treatment.

Modified pulp fiber was originally used as a new type of carrier for pectinase immobilization. Pulp fiber was oxidized by sodium periodate to produce aldehyde groups for covalently binding with amino groups of pectinase. Results showed that the enzymatic activity of immobilized pectinase on pulp fiber reached 65 μgg(-1)min(-1) when immobilization pH value, temperature and time were of 7.0, 20 °C and 15 min, respectively. The immobilized pectinase showed higher thermo stability in a wider temperature range of 40-70 °C than its free type and its optimal pH shifted from 8.0 to 8.8. Furthermore, the immobilized pectinase exhibited good operational stability. When employed in whitewater treatment of papermaking industry, it still efficiently decreased the cationic demand after operating repeatedly for six batches. The results obtained demonstrate a promising route to prepare available, cheap and biodegradable carrier for immobilizing enzymes with potential application in wastewater treatment in papermaking industry.

Polyelectrolyte complex containing antimicrobial guanidine-based polymer and its adsorption on cellulose fibers

Abstract Polyelectrolyte (PE) complexes (PECs) are formed by the electronic interaction between cationic and anionic PEs, and a number of factors influence the forming pattern and characteristic of the PECs. In this work, a guanidine-based polymer with high cationic charge density (CD) and low molecular weight (MW) was applied for interacting with anionic carboxymethylcellulose (CMC) with low CD and high MW. To reveal the self-assembly pattern of the PEC, the turbidity of PEC and layer-by-layer (LBL) film, along with its adsorption on cellulose fibers, was characterized. The antimicrobial activity of the handsheet containing the PEC was also investigated. The charge ratio of anionic PE to cationic PE was found to be critical to the PEC stability. The roughness of the LBL film was increased and then decreased with more bilayers assembled. The isothermal adsorption indicated that the amount of adsorbed cationic PE on cellulose fibers was increased significantly by interacting with anionic CMC. The inhibition of the cationic PE on bacterial growth was not impaired by the formation of the complex. The CMC with high MW in the complex could maintain or even improve the antimicrobial efficiency of the guanidine-based polymer in handsheet.

Fabrication of hydrophobic biocomposite by combining cellulosic fibers with polyhydroxyalkanoate

Due to increasing environmental concerns related to bio-persistence of petroleum based polymers, and the fact that most biopolymers such as polysaccharides or bio-polyesters are hydrophilic, hydrophobic biodegradable composite consisting of natural cellulosic fiber matrix and bio-derived polyhydroxyalkanoate (PHA) were fabricated by dip-coating, in which PHA was grafted using maleic anhydride to improve its compatibility with cellulosic fibers. It was found that there was a balance between the hydrophobicity of the complex and the grafting degree of MA on PHA. The composite film reached the highest contact angle of 130° at the grafting degree of 0.05% and the ratio of biopolymer to fibers 15%, and it was found to withstand the time aging without loss of hydrophobicity. The tensile strength of the composite film was greatly improved as a result of the introduction of PHA. This hydrophobic composite can potentially be used as a substitute for synthetic polymer/cellulose composite materials.

Surface modification of natural fibers by plasma for improving strength properties of paper sheets

Abstract Fibers of aspen chemi-thermomechanical pulp (CTMP), spruce CTMP, bleached kraft pulp (BKP), and kraft pulp were treated by low-temperature plasma (air) aiming at the detection of the relationship between chemical components on the surface and the properties of sheets. The effects of plasma treatment were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The results show that the strength properties of sheets, especially the wet-tensile strength, were significantly improved, while optical properties were scarcely affected. Aspen and spruce CTMPs with abundant lignin and extractives were sensitive to plasma treatment in that the O/C ratio increased and lignin or extractive contents decreased. However, the crystallinity of BKP evidently decreased after plasma treatment owing to carbohydrate enrichment on the surface. Compared to the partial removal of noncarbohydrates through a laccase/mediator system, plasma treatment did not remove them in large amounts but created more carboxyl and hydroxyl groups, which improved the strength properties of paper sheets.

Preparation of Novel Nano-Sized Hydrogel Microcapsules via Layer-By-Layer Assembly as Delivery Vehicles for Drugs onto Hygiene Paper

Hydrogel microcapsules are improved transplantation delivery vehicles for pharmaceuticals by effectively segregating the active ingredients from the surroundings and delivering them to a certain target site. Layer-by-layer (LbL) assembly is an attractive process to fabricate the nano-sized hydrogel microcapsules. In this study, nano-sized hydrogel microcapsules were prepared through LbL assembly using calcium carbonate nanoparticles (CaCO3 NPs) as the sacrificial inorganic template, sodium alginate (SA) and polyethyleneimine (PEI) as the shell materials. Ciprofloxacin was used to study the encapsulation and release properties of the hydrogel microcapsules. The hydrogel microcapsules were further adsorbed onto the paper to render antimicrobial properties. The results showed that the mean size of the CaCO3 template was reduced after dispersing into sodium n-dodecyl sulfate (SDS) solution under sonication. Transmission electron microscope (TEM) and atomic force microscope (AFM) revealed that some hydrogel microcapsules had a diameter under 200 nm, typical creases and collapses were found on the surface. The nano-sized PEI/SA hydrogel microcapsules showed high loading capacity of ciprofloxacin and a sustained release. PEI/SA hydrogel microcapsules rendered good antimicrobial properties onto the paper by the adsorption of hydrogel microcapsules, however, the mechanical properties of the hygiene paper were decreased.

Novel Wearable Electrodes Based on Conductive Chitosan Fabrics and Their Application in Smart Garments

Smart garments, which can capture electrocardiogram signals at any time or location, can alert others to the risk of heart attacks and prevent sudden cardiac death when people are sleeping, walking, or running. Novel wearable electrodes for smart garments based on conductive chitosan fabrics were fabricated by electroless plating of silver nanoparticles onto the surfaces of the fibers. The electrical resistance, which is related to the silver content of the composite fabrics, can be as low as 0.0332 ± 0.0041 Ω/sq due to the strong reactivity between amine groups and silver ions. After washing these fabrics eight times, the electrical resistance remained below 1 Ω/sq. The conductive chitosan fabrics were applied to smart garments as wearable electrodes to capture electrocardiogram signals of the human body in static state, jogging state, and running state, which showed good data acquisition ability and sensitivity.

Microwave Assisted Preparation of Antimicrobial Chitosan with Guanidine Oligomers and Its Application in Hygiene Paper Products

Guanidinylated chitosan (GCS) was prepared by grafting guanidine oligomers onto chitosan under microwave irradiation. The structure of GCS characterized by FT-IR and 1H NMR verified the covalent bonding between the guanidine oligomers and chitosan; the effects of molar ratio, reaction temperature, and time were investigated and the degree of substitution of GCS reached a maximum of 25.5% under optimized conditions in this work. The resulting GCS showed significantly enhanced antimicrobial activities. The results obtained from the dynamic UV absorption of Escherichia coli (E. coli) and atomic force microscopy (AFM) revealed that the deactivation of E. coli by GCS was due to the destructing of the cell membrane and the prompt release of cytoplasm from the bacterial cells. The adsorption of GCS onto cellulose fibers and the antimicrobial efficiency of the hygiene papers with GCS were also investigated. Microwave irradiation as a green assisted method was applied to promote this reaction. This facile approach allowed chitosan to be guanidinylated without tedious preparation procedures and thus broadened its application as a biocompatible antimicrobial agent.