Dafu Wei

Damage of Escherichia coli membrane by bactericidal agent polyhexamethylene guanidine hydrochloride: micrographic evidences

Aims:  The purpose of this study was to provide micrographic evidences for the damaged membrane structure and intracellular structure change of Escherichia coli strain 8099, induced by polyhexamethylene guanidine hydrochloride (PHMG).

Investigation of extensional rheological behaviors of polypropylene for foaming

This study investigated the relationship between the extensional rheological behaviors and the foamability of polypropylenes (PPs). Both the shear and extensional rheological properties of four types of PPs with different molecular structures (linear PP, linear PP with high-molecular component, long-chain-branched PP, and cross-linked PP) were tested by rheometers and the PPs were foamed by batch process with supercritical carbon dioxide as foam agent. It was found that when the PP showed strain-hardening behavior at certain strain rates (on the order of 1 s−1), the obtained foams had high expansion ratio and fine cell structures. Otherwise, the strain-hardening behavior of PP had limited effects on the foamability. In addition, a theoretical analysis suggested that the strain-hardening behavior provided higher melt strength and simultaneously changed the rupture behavior of the melt, thus the gas bubble could be stable during expansion step and the cellular structure was generated. The foamability of PPs can be predicted from the extensional properties without considering their molecular structures.

Synthesis and Characterization of Antimicrobial Polyvinyl Pyrrolidone Hydrogel as Wound Dressing

Novel antimicrobial PVP-GP hydrogels were prepared by polycondensation of hexamethylenediamine and guanidine hydrochloride, followed by cross-linking reaction using N-vinyl pyrrolidone (NVP) and N,N’-methylene bisacrylamide (MBAm). The products were characterized by 1H NMR, FTIR, SEM, and their performances for wound dressing applications were also evaluated. Swelling study showed that the water absorptivity of the hydrogels decreased as the cross-linking density increased either in water or in physiological saline solution. Both PVP and PVP-GP hydrogels possessed excellent mechanical strength which could address the requirements for wound dressing. The water vapor transmission rates (WVTR) of PVP and PVP-GP hydrogels were in the range of 1727–2320 g/m2/day, indicating that the prepared hydrogels were suitable for wound dressings without dehydrating the wound surface or accumulating exudates. Kirby-Bauer inhibition zone test and microbe penetration assay proved that the PVP-GP hydrogels had high antimicrobial activity.

Condensation between guanidine hydrochloride and diamine/multi-amine and its influence on the structures and antibacterial activity of oligoguanidines

Abstract The polycondensation of guanidine hydrochloride and diamine leads to various types of oligoguanidines, including linear and branched/cyclic types, which constitutes the mixture of oligoguanidines exhibiting efficient biocidal activities. In the present work, a series of polyhexamethylene guanidine hydrochloride (PHMG) were prepared by varying the mole ratio of hexamethylenediamine to guanidine hydrochloride and the reaction conditions, and their antibacterial activities were investigated. The contents of linear and branched/cyclic types in the mixture varied with different reaction conditions, and more branched/cyclic types led to more efficient antibacterial activity. Other oligoguanidines PDMG and PMXMG were synthesized using guanidine hydrochloride and decamethylenediamine and 1,3- benzenedimethanamine, respectively. Their chemical structures were similar to PHMG’s while the antibacterial activities were slightly different from PHMG’s. Further when the polycondensation were conducted between guanidine hydrochloride and multi-amine, such as diethylenetriamine or trithylenetetramine, the chemical structures of products were completely different from the above oligoguanidines. A new five-membered ring structure was observed, and the fivemembered ring structure further decreased the antibacterial activities.

Permanent antimicrobial cotton fabrics obtained by surface treatment with modified guanidine

Antimicrobial cotton fabrics received much attention for the demand of health and hygiene fields. In this work, an antimicrobial copolymer was prepared via a reaction between polyhexamethylene guanidine hydrochloride and polypropylene glycol diglycidyl ether. The copolymer has amphiphilic characteristic and excellent antimicrobial properties. When the copolymer was adhered onto cotton fabrics through physical adsorption and chemical bonding using dipping-drying method, the resultant cotton fabrics had excellent and durable antimicrobial properties. The antimicrobial rates against Escherichia coli and Staphylococcus aureus were higher than 99.99% when the adsorption amount of the copolymer was above 35.5mg/g. The antimicrobial cotton fabrics remained the excellent antimicrobial properties even after laundered with detergent solution.

Study of Stimuli-Sensitivities of Amphiphilic Modified Star Poly[N,N-(Dimethylamino)ethyl Methacrylate] and Its Ability of DNA Complexation

Cationic star polymers as drug/gene carriers have attracted increasing attention. Herein, environmental sensitivities and star-shaped architecture were combined into a well-defined gene carrier system, and further amphiphilic modification was conducted. The thermo- and pH-sensitive behaviors of poly[N,N-(dimethyl amino)ethyl methacrylate] (PDMAEMA) star polymers before and after amphiphilic modification in aqueous solutions were investigated. The observed lower critical solution temperature (LCST) increased with increasing arm length due to the increase of hydrophilicity. A significant decrease of the LCSTs with increasing pH and ionic-strength of the solution was found. The incorporation of MMA and BA lipophilic moieties decreased the LCST of the cationic star polymer due to enhanced hydrophobic interaction. As a potential gene carrier, the performance of star polymers on binding DNA was primarily evaluated via particle size, zeta potential, and gel retardation measurements. All the complexes formed stable small particles with diameter of 100∼150 nm at N/P ratio higher than 3.0. The electrostatic screening effect and facilitation for the interaction of complexes with cell membrane induced by the incorporation of lipophilic units were expected to enhance the gene transfection efficiency.

Further Studies on the Anionic Copolymerization of Styrene and Glycidyl Methacrylate in Toluene

Sequential anionic copolymerization of styrene and glycidyl methacrylate (GMA) was performed with the protection of argon under normal pressure, where styrene, GMA, toluene, THF, n-butyllithium and a small amount of lithium chloride (LiCl) were used as first monomer, second monomer, solvent, polar reagent, initiator and additive, respectively. Polystyrene-b-poly(glycidyl methacrylate) diblock copolymers (PS-b-PGMA) with well-defined structure and narrow molecular weight distribution were prepared by the copolymerization reaction of poly(styryl)lithium with GMA under certain temperatures. The copolymers were characterized using gel permeation chromatography (GPC), 1H-NMR, 13C-NMR, thin layer chromatography (TLC) and hydrochloric acid-dioxane argentimetric methods. The effects of additives, copolymerization temperature and THF dosage on the copolymerization were studied. No chain transfer reaction of anionic polymerization of styrene in toluene was observed. Slightly broader molecular weight distribution of PS-b-PGMA was observed with the increase the GMA repeat units. Using THF/toluene blend solvent could reduce the polydispersity index (M w /M n ) and dissolve the copolymer better than toluene alone. Lower temperature (< -40°C) and LiCl are required to prepare PS-b-PGMA with narrower molecular weight distribution.

Design and fabrication of vapor-induced superhydrophobic surfaces obtained from polyethylene wax and silica nanoparticles in hierarchical structures

The present work reported a simple and effective approach to fabricate a low-cost, self-cleaning and mechanically durable superhydrophobic coating. The coating was prepared by dip-coating certain substrates in an ethyl acetate suspension of silica nanoparticles (SiO2), hydroxyl acrylic resin, cross-linking agent and polyethylene wax (PEW). Through the control of the cooling and drying process, vapor-induced PEW micro-clusters were formed on the surfaces during the evaporation of ethyl acetate, and uniform carpet-like hierarchical structures were finally obtained by properly adjusting the dosage of PEW. Under the synergistic effect of hydrophobic SiO2 nanoparticles and PEW micro-clusters, the composite coating exhibited a remarkable superhydrophobicity with a contact angle of 163° ± 5° with 25 wt% content of PEW, as well as preeminent self-cleaning properties against various food liquids. Moreover, the coating still maintained its surface cleanliness when immersed in the cyclohexane or hexadecane, indicating a superior self-cleaning property against solvent-contamination. The mechanical durability test showed that the coating still kept its excellent water repellency after fairly intensive knife-scratching, tape peeling and 25 cycles of sandpaper abrasion under 100 g of loading, indicating a quite admirable mechanical durability. The facile preparation and high-performance of the coating make it quite suitable for manufacture on a large scale, which is favorable for the development of superhydrophobic coatings.

Hydrogen-Bond Assembly of Poly(vinyl alcohol) and Polyhexamethylene Guanidine for Nonleaching and Transparent Antimicrobial Films

The combination of transparency, antimicrobial activities, nonleaching of antimicrobial component and green preparation for poly(vinyl alcohol) (PVA) films is of importance for practical applications in industry. However, until now it remains a challenge. Herein, a facile antimicrobial PVA films containing polyhexamethylene guanidine (PHMG) is reported via a green solution casting method. Such PVA films show high transparency of 91%, above 99.99% of antimicrobial rates against Escherichia coli and Staphylococcus aureus, and nonleaching characteristic of PHMG due to the hydrogen-bond (H-bond) interaction between PHMG and PVA. The thermal stability and mechanical properties of the PVA films are further improved compared to neat PVA film. These antimicrobial films are expected to find promising applications in tissue engineering and packaging fields, which opens up a methodology to prepare nonleaching antimicrobial polymeric materials via H-bond.

Branching and cross-linking of poly(ethylene terephthalate) and its foaming properties

The branching and cross-linking of poly(ethylene terephthalate) were investigated using two chain extenders: glycidyl methacrylate-styrene copolymer (GS) and poly(butylene terephthalate)-GS (PBT-GS) in order to improve the melt viscosity and melt strength of poly(ethylene terephthalate). An obvious increase in torque evolution associated with chain extending, branching and cross-linking was observed during the process. The properties of modified poly(ethylene terephthalate) were characterized by intrinsic viscosity and insoluble content measurements, rheological and thermal analysis. The intrinsic viscosity and rheological properties of modified PET were improved significantly when using PBT-GS, indicating that PBT-GS should be a better chain extender. Good foaming of poly(ethylene terephthalate) materials were obtained using supercritical CO2 as blowing agent. The average cell diameter and cell density were 61 μm and 1.8 × 108 cells/cm3, respectively.