Hua Zheng

Conductive PPY/PDLLA conduit for peripheral nerve regeneration

The significant drawbacks and lack of success associated with current methods to treat critically sized nerve defects have led to increased interest in neural tissue engineering. Conducting polymers show great promise due to their electrical properties, and in the case of polypyrrole (PPY), its cell compatibility as well. Thus, the goal of this study is to synthesize a conducting composite nerve conduit with PPY and poly(d, l-lactic acid) (PDLLA), assess its ability to support the differentiation of rat pheochromocytoma 12 (PC12) cells in vitro, and determine its ability to promote nerve regeneration in vivo. Different amounts of PPY (5%, 10%, and 15%) are used to synthesize the conduits resulting in different conductivities (5.65, 10.40, and 15.56 ms/cm, respectively). When PC12 cells are seeded on these conduits and stimulated with 100 mV for 2 h, there is a marked increase in both the percentage of neurite-bearing cells and the median neurite length as the content of PPY increased. More importantly, when the PPY/PDLLA nerve conduit was used to repair a rat sciatic nerve defect it performed similarly to the gold standard autologous graft. These promising results illustrate the potential that this PPY/PDLLA conducting composite conduit has for neural tissue engineering.

A novel in situ-formed hydrogel wound dressing by the photocross-linking of a chitosan derivative

In situ photopolymerized hydrogel dressings create minimally invasive methods that offer advantages over the use of preformed dressings such as conformability in any wound bed, convenience of application, and improved patient compliance and comfort. Here, we report an in situ‐formed hydrogel membrane through ultraviolet cross‐linking of a photocross‐linkable azidobenzoic hydroxypropyl chitosan aqueous solution. The hydrogel membrane is stable, flexible, and transparent, with a bulk network structure of smoothness, integrity, and density. Fluid uptake ability, water vapor transmission rate, water retention, and bioadhesion of the thus resulted hydrogel membranes (0.1 mm thick) were determined to range from 97.0–96.3%, 2,934–2,561 g/m2/day, 36.69–22.94% (after 6 days), and 4.8–12.3 N/cm2, respectively. These data indicate that the hydrogel membrane can maintain a long period of moist environment over the wound bed for enhancing reepithelialization. Specifically, these properties of the hydrogel membrane were controllable to some extent, by adjusting the substitution degree of the photoreactive azide groups. The hydrogel membrane also exhibited barrier function, as it was impermeable to bacteria but permeable to oxygen. In vitro experiments using two major skin cell types (dermal fibroblast and epidermal keratinocyte) revealed the hydrogel membrane have neither cytotoxicity nor an effect on cell proliferation. Taken together, the in situ photocross‐linked azidobenzoic hydroxypropyl chitosan hydrogel membrane has a great potential in the management of wound healing and skin burn.

Encapsulation and controlled release of hydrophilic pesticide in shell cross-linked nanocapsules containing aqueous core.

In this study, amphiphilic biocopolymers, synthesized by mixing azidobenzaldehyde (Az) and an aqueous solution of carboxymethyl chitosan (CMCS), which self-assemble into nanocapsules with a aqueous core (ACN) in aqueous media followed by photo-cross-linking to obtain shell cross-linked nanocapsules, were used to develop a controlled release pesticide system. The system was characterized by TEM and DLS. Its encapsulation efficiency was determined. The obtained result showed that it is efficient to encapsulate methomyl reaching encapsulation efficiency as high as 90% in an aqueous medium at pH 4.0, which is mainly attributed to the hydrogen bonding adsorption between methomyl molecules and the inner surface of nanocapsules. Release profiles of methomyl from methomyl-loaded nanocapsules in an aqueous solution at pH 6.0 were shown to be diffusion controlled with a half-release time (t(½)) of 36.3-69.5h from different samples. The shell cross-linking and its degree of cross-linking are assumed to be responsible for this diffusion behavior. The insecticidal activity test in laboratory showed that the control efficacy of methomyl-loaded nanocapsules against the armyworm larvae was significantly superior to the original. The relative control efficacy still maintained 100% over 7 days.

Structural Characterization, Chain Conformation, and Morphology of a β-(1→3)-d-Glucan Isolated from the Fruiting Body of Dictyophora indusiata

A water-soluble glucan, namely, PD3, was isolated from the fruiting body of Dictyophora indusiata as the method reported previously. Its chemical structure was characterized by GC, FTIR, and (13)C NMR. The results indicated that PD3 is a (1-->3)-beta-D-glucan, with (1-->6)-beta-glucopyranoside side branches. The chain conformation and morphology of PD3 in aqueous solution were investigated by viscometry, rheometer, and laser light scattering (LLS) measurements, atomic force microscopy (AFM), and transmission electron microscopy (TEM), respectively. The weight-average molecular mass (M(w)), radius of gyration (R(g)), hydrodynamic radius (R(h)), and intrinsic viscosity ([eta]) of PD3 in water were determined to be 5.1 x 10(5), 141 nm, 44 nm, and 1440 cm(3) g(-1), respectively, by LLS and viscometry. The structural parameter rho (Rg/Rh) of PD3 was calculated to be 3.4, and the [eta] dependence of C(NaOH) of PD3 is similar to that of triple helical polysaccharides Scleroglucan and Lentinan, suggesting that PD3 exists as a triple helical chain in water. This conclusion was further proved by rheological measurement and AFM observation. Interestingly, the [eta] of PD3 dramatically decreased in a narrow range concentration of NaOH between 0.18 and 0.22 M, higher than that of Scleroglucan and Lentinan (both less than 0.1 M), indicating the helix-coil conformation transition of PD3 is more difficult than that of Scleroglucan and Lentinan. Moreover, with the increase of concentration, PD3 trends to self-assemble to fibrous aggregates in aqueous solution as measured by TEM.

pH/redox responsive core cross-linked nanoparticles from thiolated carboxymethyl chitosan for in vitro release study of methotrexate.

A novel amphiphilic thiolated carboxymethyl chitosan was synthesized. It self-assembled into disulfide bond cross-linked nanoparticles in deionized water. The TEM showed that these nanoparticles had a core-shell structure with an average diameter of 160 nm. Dynamic light scattering showed that the nanoparticles were stable in water solution. The particle size changed with pH values and GSH concentrations, and reached a maximum diameter at pH 7.0 and 20mM GSH respectively, exhibiting an obvious pH/redox responsibility. Methotrexate was encapsulated in nanoparticles reaching encapsulation efficiency as much as 43.4%. Release profiles of methotrexate showed a release rate of 19 wt% in pH 7.4 buffer containing 10 μM GSH, whereas as high as 93 wt% in pH 5.0 buffer containing 20mM GSH, indicating that the nanoparticles may be used for tumor-specific drug release. The anticancer activity test in vitro showed that the inhibition rate of methotrexate-loaded nanoparticles against HeLa cells reached 90%.

Finding the Lost Open-Circuit Voltage in Polymer Solar Cells by UV-Ozone Treatment of the Nickel Acetate Anode Buffer Layer

Efficient polymer solar cells (PSCs) with enhanced open-circuit voltage (Voc) are fabricated by introducing solution-processed and UV-ozone (UVO)-treated nickel acetate (O-NiAc) as an anode buffer layer. According to X-ray photoelectron spectroscopy data, NiAc partially decomposed to NiOOH during the UVO treatment. NiOOH is a dipole species, which leads to an increase in the work function (as confirmed by ultraviolet photoemission spectroscopy), thus benefitting the formation of ohmic contact between the anode and photoactive layer and leading to increased Voc. In addition, the UVO treatment improves the wettability between the substrate and solvent of the active layer, which facilitates the formation of an upper photoactive layer with better morphology. Further, the O-NiAc layer can decrease the series resistance (Rs) and increase the parallel resistance (Rp) of the devices, inducing enhanced Voc in comparison with the as-prepared NiAc-buffered control devices without UVO treatment. For PSCs based on the P3HT:PCBM system, Voc increases from 0.50 to 0.60 V after the NiAc buffer layer undergoes UVO treatment. Similarly, in the P3HT:ICBA system, the Voc value of the device with a UVO-treated NiAc buffer layer increases from 0.78 to 0.88 V, showing an enhanced power conversion efficiency of 6.64%.

ITO electrode/photoactive layer interface engineering for efficient inverted polymer solar cells based on P3HT and PCBM using a solution-processed titanium chelate

We report efficient inverted polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) using alcohol-soluble titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD) as an electron selective layer between the indium tin oxide (ITO) electrode and the photoactive layer. The thermally annealed TIPD layer is highly transparent in the visible range and shows effective electron collection ability. By optimizing the electron-collecting layer, the photoactive layer and the hole-collecting layer, the power conversion efficiency (PCE) of the inverted device with the structure ITO/TIPD/P3HT : PCBM/MoO3/Ag reaches 4.10% under the illumination of AM1.5G, 100 mW cm −2 , which is among the highest values for inverted PSCs based on P3HT : PCBM. The PCE of the inverted device is improved in comparison with the conventional device (3.77%) under the same experimental conditions. (Some figures may appear in colour only in the online journal)

Preparation of carboxymethyl cellulose sulfates and its application as anticoagulant and wound dressing

Tissue engineering is aiming to build an artificial environment or biological scaffold material that imitates the living environment of cells in the body. In this work, carboxymethyl cellulose sulfates were prepared by reacting carboxymethyl cellulose with N(SO3Na)3 which was synthesized by sodium bisulfite and sodium nitrite in aqueous solution. The reaction conditions affected the degree of substitution (DS) were measured by the barium sulfate nephelometry method. And the anticoagulant activity of carboxymethyl cellulose sulfates with different DS, concentration and molecular weights were investigated by the activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT). In addition, the effect of carboxymethyl cellulose sulfates on wound healing had been evaluated by the rate of wound healing and the histological examinations. The results indicated that the introduction of sulfate groups into the carboxymethyl cellulose sulfates improved its anticoagulant activity, and the wound dressings treated with carboxymethyl cellulose sulfates obviously promoted wound healing.

Preparation, characterization and in vitro release study of a glutathione-dependent polymeric prodrug Cis-3-(9H-purin-6-ylthio)-acrylic acid-graft-carboxymethyl chitosan.

In this work, an amphiphilic polymeric prodrug Cis-3-(9H-purin-6-ylthio)-acrylic acid-graft-carboxymethyl chitosan (PTA-g-CMCS) was designed and synthesized. In aqueous solution, this grafted polymer can self-assemble into spherical micelles with a size ranging from 104 to 285 nm and zeta potential ranging from -12.3 to -20.1 mV. For the release study, less than 24% of 6-Mercaptopurine (6-MP) was released from PTA-g-CMCS1 in the media containing 2 and 100 μM glutathione (GSH), whereas 37%, 54% and 75% of 6-MP was released from the media with GSH of 1, 2 and 10mM, respectively. Besides, pH and drug content of the polymeric prodrug only presented slight influence on the 6-MP release. MTT assay demonstrated that this system had higher inhibition ratio on HL-60 cells (human promyelocytic leukemia cells) in the presence of GSH and lower cytotoxicity on mouse fibroblast cell line (L929). Therefore, this nano-sized system is glutathione-dependent, and it can be employed as a potential carrier for the controlled release of 6-MP.

Preparation and anticoagulant activity of N-succinyl chitosan sulfates

In order to develop a promising substitute for heparin, N-succinyl chitosan (NSC) was chemically modified by sulfating agent N(SO(3)Na)(3), which were synthesized with sodium bisulfite and sodium nitrite in aqueous solution. The N-succinyl chitosan sulfates (NSCS) products were characterized by infrared spectroscopy (FT-IR) and (13)C NMR. The degree of substitution (DS) of NSCS depended on the ratio of sulfating agent to N-succinyl chitosan, reaction temperature, reaction time and pH of sulfation agent. N-succinyl chitosan sulfates with DS of 1.97 were obtained under optimal conditions. The in vitro coagulation assay of NSCS was determined by activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) assays. The results showed that NSCS obviously prolonged APTT. The anticoagulant activity strongly depended on DS, molecular weight (M(w)) and concentration of NSCS. The anticoagulant activity of NSCS promoted with the increase of DS and concentration, and NSCS exhibited the best anticoagulant activity with the M(w) of 1.37×10(4).