Yudong Zheng

In situ synthesis of silver-nanoparticles/bacterial cellulose composites for slow-released antimicrobial wound dressing.

Bacterial cellulose has attracted increasing attention as a novel wound dressing material, but it has no antimicrobial activity, which is one of critical skin-barrier functions in wound healing. To overcome such deficiency, we developed a novel method to synthesize and impregnate silver nanoparticles on to bacterial cellulose nanofibres (AgNP-BC). Uniform spherical silver nano-particles (10-30 nm) were generated and self-assembled on the surface of BC nano-fibers, forming a stable and evenly distributed Ag nanoparticles coated BC nanofiber. Such hybrid nanostructure prevented Ag nanoparticles from dropping off BC network and thus minimized the toxicity of nanoparticles. Regardless the slow Ag(+) release, AgNP-BC still exhibited significant antibacterial activities with more than 99% reductions in Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Moreover, AgNP-BC allowed attachment and growth of epidermal cells with no cytotoxicity emerged. The results demonstrated that AgNP-BC could reduce inflammation and promote wound healing.

Silver nanoparticle/bacterial cellulose gel membranes for antibacterial wound dressing: investigation in vitro and in vivo

Bacterial cellulose (BC) has attracted increasing attention as a novel wound dressing material, but its antimicrobial activity, which is one of the critical skin-barrier functions in wound healing, is not sufficient for use in practical applications. To overcome such a deficiency, silver nanoparticles were generated and self-assembled on the surface of BC nanofibers, forming a stable and evenly distributed Ag nanoparticle coated BC nanofiber (AgNP-BC). The performance of AgNP-BC was systematically studied in terms of antibacterial activities, cytocompatibility and effects on wound healing. The results showed that AgNP-BC exhibited significant antibacterial activity against Staphylococcus aureus. Moreover, AgNP-BC allowed attachment, and growth of rat fibroblasts with low cytotoxicity emerged. Based on these advantages, AgNP-BC samples were applied in a second-degree rat wound model. Wound flora showed a significant reduction during the healing. The fresh epidermal and dermis thicknesses with AgNP-BC samples were 111 and 855 µm respectively, higher than 74 and 619 µm for BC groups and 57 and 473 µm for untreated control wounds. The results demonstrated that AgNP-BC could reduce inflammation and promote scald wound healing.

Impregnation of silver sulfadiazine into bacterial cellulose for antimicrobial and biocompatible wound dressing.

Silver sulfadiazine (SSD) is a useful antimicrobial agent for wound treatment. However, recent findings indicate that conventional SSD cream has several drawbacks for use in treatments. Bacterial cellulose (BC) is a promising material for wound dressing due to its outstanding properties of holding water, strength and degradability. Unfortunately, BC itself exhibits no antimicrobial activity. A combination of SSD and BC is envisaged to form a new class of wound dressing with both antimicrobial activity and biocompatibility, which has not been reported to date. To achieve antimicrobial activity, SSD particles were impregnated into BC by immersing BC into SSD suspension after ultrasonication, namely SSD-BC. Parameters influencing SSD-BC impregnation were systematically studied. Optimized conditions of sonication time for no less than 90 min and the proper pH value between 6.6 and 9.0 were suggested. The absorption of SSD onto the BC nanofibrous network was revealed by XRD and SEM analyses. The SSD-BC membranes exhibited significant antimicrobial activities against Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus evaluated by the disc diffusion method. In addition, the favorable biocompatibility of SSD-BC was verified by MTT colorimetry, epidermal cell counting method and optical microscopy. The results demonstrate the potential of SSD-BC membranes as a new class of antimicrobial and biocompatible wound dressing.

Thiol/Acrylate-Modified PEO-PPO-PEO Triblocks Used as Reactive and Thermosensitive Copolymers

The reactive thermal-sensitive hydrogels, which combined the reversible thermosensitive and mild reactive property, were designed based on thiol-ene reaction in physiological conditions between thiol and acrylate capped thermosensitive Poloxamer 188. The modified P188A, P188SH, and their reactivity were characterized by (1)H NMR, FT-IR, GPC, DSC, Ellman method, and Rheometer. It was found that the thiol-ene reaction was pH and thermal-sensitive. There was 77.7% SH involved into the reaction at 37.0 degrees C and pH 7.4 within the first 30 min. The most of molecules reacted as CC/SH mol ratio was 1.5. The exothermic thiol-ene reaction was mild, with about DeltaH = -91.18 J/g changes. The multiblocks or network structure limited the dissolution of hydrogel, correspondingly the gels duration and the release time of methylene blue were prolonged to 124 h. The experimental results indicated the reactive thermal-sensitive hydrogels potential applications in drug delivery, tissue engineering, and cell encapsulation.

Influence of dialdehyde bacterial cellulose with the nonlinear elasticity and topology structure of ECM on cell adhesion and proliferation

Bacterial cellulose (BC) has attracted much attention as a novel biomaterial recently. In this work, the special chemical structure, topology structure and mechanical behavior of C2, 3-oxidized dialdehyde BC (DBC) were investigated. The DBC was prepared from the selective-oxidation of BC with sodium periodate. DBC membranes show obvious shrinkage in 2D direction with no significant changes in thickness. Similar to elastins, DBC exhibits a typical nonlinear elasticity, it can return to its original shape as soon as the deformation force is removed. Similarly to elastin, DBC exhibits a typical nonlinear elastic behavior. It can return to its original shape as soon as the deformation force is removed, and this nonlinear elastic behavior is typical for fiber networks in general. DBC has a nano-fiber network topology structure that is similar to the extracellular matrix. Moreover, the reaction between cell-surface proteins and aldehydes of DBC is conducive to the adhesion and proliferation of cells within the DBC networks. In general, the nonlinear elasticity, topology structure and cell adhesion of DBC were similar to the extracellular matrix. This demonstrates the potential of using DBC as a material in the repair process of injured tissues.

Low swelling hyperbranched poly(amine-ester) hydrogels for pH-modulated differential release of anticancer drugs

Hydrogels composed of hyperbranched poly(amine-ester) (HPAE) macromers with 36% of terminal CC groups were prepared as a pH-sensitive multi-drug release system with low swelling ratios (4.2% for the lowest one). Anticancer drugs including doxorubicin hydrochloride (Dox), 5-fluorouracil (5FU) and hydroxycamptothecin (HPT) were separately encapsulated in HPAE macromers before hydrogel formation and their release can be controlled by the conformational change of HPAE macromers under different pH conditions, fast when pH > 7 and slow when pH < 7. Furthermore, this system allows a combination release of multiple drugs and the release behavior of each drug was relatively independent with no interference from each other. This is different from traditional pH-sensitive hydrogel systems which control the drug release by a swelling-shrinking mechanism. HPAE hydrogels exhibited pH-controllable drug release properties with a relatively constant volume, because the swelling of hydrogel is limited due to the unique globe like structure of HPAE molecules. These findings show the great promise of HPAE hydrogels as a smart release system for controlled delivery of single or multiple drugs in combined therapy, and where a constant volume of the release system is required.

Dual stimulus responsive drug release under the interaction of pH value and pulsatile electric field for a bacterial cellulose/sodium alginate/multi-walled carbon nanotube hybrid hydrogel

A novel hybrid hydrogel composed of sodium alginate (SA), bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs) was synthesized using CaCl2 as a crosslinking agent. The hydrogel (BC/SA/MWCNTs) was proposed as a pH and electric field dual-stimulus responsive drug delivery system. Various amounts of MWCNTs were doped into the BC/SA in order to obtain the highest electric sensitivity of the composite hydrogel. The releasing profile of the drug from the hybrid hydrogels demonstrated the dual pH-/electric-sensitive property of the composite hydrogel. The amount of drug released, which was found to be dependent on the applied electric current strength, was greater under the electrical stimulus compared with that under passive diffusion. The electric-enhanced releasing behaviour was selective to the pH value of the surrounding culture. In neutral conditions, release curves under an electric voltage showed obvious electric-sensitivity. In acidic or alkaline conditions, release curves with or without an applied electric voltage showed little difference. A pulsatile pattern of drug release was observed by switching “on and off” the electric stimulus. In neutral conditions, drug release from the hydrogel showed a significant pulsatile characteristic. The overall performance of the BC/SA/MWCNTs hybrid hydrogel demonstrated that MWCNTs as additives played a synergistic role in the control release performance of the drug delivery system.

Photoswitched Protein Adsorption on Electrostatically Self‐Assembled Azobenzene Films

Photoresponsive polymeric films fabricated by a facile electrostatic self-assembly technique are utilized to switch protein adsorption by light irradiation. The introduction of SiO(2) nanoparticles on the substrate results in a large reversible change of both wettability and protein adsorption.

Performance of novel bioactive hybrid hydrogels in vitro and in vivo used for artificial cartilage

The long-term fixation of poly(vinyl alcohol) PVA hydrogels cartilage implants on ambient tissue is a difficult problem, which is one of the obstacles for PVA hydrogels to be used as articular cartilage implants. In this work, a novel bioactive PVA/HA hydrogel was prepared by the in situ sol-gel synthesis method. Simulated experiments were performed to evaluate and compare the bioactive ability and properties of the hydrogels in simulated body fluid (SBF). Gradual-structure PVA/HA cartilage implants were developed and used to repair articular cartilage defects in rabbit knees. In vitro bioactive evaluation showed that PVA/HA hydrogels could be bio-mineralized to form bone-like hydroxyl-carbonate-apatite deposit in SBF solution. The macroscopic and histological observation of animal experiments displayed that the implanted hydrogels combined tightly with ambient tissues, and some bone-like tissue grew into the bottom of the implants from the base bone to form more deep-set binding between replacement and cartilage tissues.

Protein adsorption behaviors of carboxymethylated bacterial cellulose membranes.

Carboxymethylated bacterial cellulose (CBC) membranes with different degrees of substitution (DS) were prepared by surface carboxymethylation of bacterial cellulose, which were characterized by FTIR, contact angles and zeta potential. Both the contact angels and zeta potentials increased with the increase of degrees of carboxymethylation. Protein adsorption behaviors of CBC membranes were investigated with bovine serum albumin (BSA) as model protein and the adsorption quantity increased gradually with the increase of the DS. The protein adsorption was not only governed by the chemical structure of CBC, but also by the electrostatic interaction between CBC and BSA. The protein was found to be adsorbed on CBC membrane at pH lower its isoelectric point (pI) while no protein was adsorbed at pH above its pI. The protein adsorption on the CBC membranes was also characterized by scanning electron microscopy (SEM).