Zhongzheng Zhou

Biomaterials based on N,N,N-trimethyl chitosan fibers in wound dressing applications.

In the present work, N,N,N-trimethyl chitosan (TMC) fibers were synthesized successfully and the resulting quaternized materials were characterized by FTIR. The designed TMC fibers with different degree of quaternization achieved high water absorption capability. In antibacterial activity study, TMC fibers showed high antibacterial activity than chitosan fibers against the gram-negative bacteria Escherichia coli (>63%) and gram-positive bacteria Staphylococcus aureus (>99%). TMC fibers exhibited no obvious cytotoxicity to mouse embryo fibroblast cells with low extraction concentrations (<0.05g/mL). In animal wound healing test, TMC2 fibers could significantly enhance wound re-epithelialization and contraction compared with the control (chitosan fibers). In conclusion, TMC fibers have a potential to be used as wound dressing materials.

Preparation of composite hydroxybutyl chitosan sponge and its role in promoting wound healing

In this work, a composite sponge was produced by physically mixing hydroxybutyl chitosan with chitosan to form a porous spongy material through vacuum freeze-drying. Hydrophilic and macroporous composite hydroxybutyl chitosan sponge was developed via the incorporation of chitosan into hydroxybutyl chitosan. The composite sponge showed higher porosity (about 85%), greater water absorption (about 25 times), better softness and lower blood-clotting index (BCI) than those of chitosan sponge and hydroxybutyl chitosan sponge. The composite sponge with good hydrophilic could absorb the moisture in the blood to increase blood concentration and viscosity, and become a semi-swelling viscous colloid to clog the capillaries. Cytocompatibility tests with L929 cells and HUVEC cells demonstrated that composite sponge were no cytotoxicity, and could promote the growth of fibroblasts. It made up for the shortcomings of hydroxybutyl chitosan with unfavorable antibacterial effect to achieve a higher level of antibacterial (>99.99% reduction). Eventually, the vivo evaluations in Sprague-Dawley rats revealed that epithelial cells attached to the composite sponge and penetrated into the interior, in addition to this, it was also proved that the composite sponge (HC-1) had a better ability to promote wound healing and helped for faster formation of skin glands and re-epithelialization. The obtained data encourage the use of this composite sponge for wound dressings.

Different chemical groups modification on the surface of chitosan nonwoven dressing and the hemostatic properties

The hemostatic properties of surface modified chitosan nonwoven had been investigated. The succinyl groups, carboxymethyl groups and quaternary ammonium groups were introduced into the surface of chitosan nonwoven (obtained NSCS, CMCS and TMCS nonwoven, respectively). For blood clotting, absorbance value (0.105±0.03) of NSCS1 nonwoven was the smallest (CS 0.307±0.002, NSCS2 0.148±0.002, CMCS1 0.195±0.02, CMCS2 0.233±0.001, TMCS1 0.191±0.002, TMCS2 0.345±0.002), which indicated the stronger hemostatic potential. For platelet aggregation, adenosine diphosphate agonist was added to induce the nonwoven to adhered platelets. The aggregation of platelet with TMCS2 nonwoven was highest (10.97±0.16%). Further research of blood coagulation mechanism was discussed, which indicated NSCS and CMCS nonwoven could activate the intrinsic pathway of coagulation to accelerate blood coagulation. NSCS1 nonwoven showed the shortest hemostatic time (147±3.7s) and the lowest blood loss (0.23±0.05g) in a rabbit ear artery injury model. These results demonstrated that these surface modified chitosan nonwoven dressings could use as a promising hemostatic intervention, especially NSCS nonwoven dressing.

Systematic investigation of fabrication conditions of nanocarrier based on carboxymethyl chitosan for sustained release of insulin

pH-responsive nanoparticles (NPs) comprised of degradable carboxymethyl chitosan (CMCS) crosslinked with CaCl2 were simply prepared via ionic gelation. Fabrication conditions including insulin dosage, CMCS concentration, and crosslinking density were systematically investigated for insulin loading and release in vitro. The encapsulation efficiencies (EE), loading capacity (LC) and average size of the NPs decreased with the increasing insulin concentrations (<0.192mg/mL), while they notably increased as the insulin dosage was above 0.192mg/mL. When the concentration of CMCS increased from 0.5 to 2.0mg/mL, the EE of the NPs reduced while the size of the NPs increased. We further demonstrated that crosslinking density offered a simple method for tuning the properties of the NPs towards various insulin concentrations. The mass ratio 10:5 of CMCS to CaCl2 exhibited the optimal performance at higher insulin concentration, whereas a higher crosslinking density of 10:7 (m:m) gave the optimal performance at low insulin concentration. The cumulative release of insulin from insulin loaded NPs decreased with the elevating crosslinking density. These findings not only provided a better understanding of the synthesis of CMCS NPs but also contributed to the practical applications of insulin loading and release.

pH-Activated nanoparticles with targeting for the treatment of oral plaque biofilm

Oral plaque biofilms are highly resilient microbial assemblies that are challenging to eradicate. Herein, we describe the synthesis and study of pH-positive, doxycycline (DOX)-loaded nanocarriers to combat pathogenic biofilms. The mixed shell-core nanoparticles consisted of quaternary ammonium chitosan (TMC) as a positively charged section, which targeted nanoparticles to negatively charged biofilm surfaces. In addition liposomes were used as a DOX loading tool to eradicate the multidrug-resistant biofilm. In a drug release test, DOX release was pH-dependent with t1/2 = 0.75 h and 2.3 h for release at pH 4.5 and 6.8, respectively. Furthermore, TMC-Lip-DOX NPs could adhere to the biofilm and efficiently remove the biofilm from the hydroxyapatite (HA) surface. Furthermore, TMC-Lip-DOX NPs had biocomaptible properties and were non-toxic to MC3T3-E1 cells. This constitutes a highly effective pathway to control oral plaque biofilms and has a good potential use for dental biofilm therapies.

Sodium carboxymethylation-functionalized chitosan fibers for cutaneous wound healing application

A water absorption biomaterial, sodium carboxymethylation-functionalized chitosan fibers (Na-NOCC fibers) were prepared, applied for cutaneous wound repair, and characterized by FTIR and NMR. The water absorption of Na-NOCC fibers increased significantly with substitution degree rising, from 3.2 to 6.8 g/g, and higher than that of chitosan fibers (2.2 g/g) confirmed by swelling behavior. In the antibacterial action, the high degree of substitution of Na-NOCC fibers exhibited stronger antibacterial activities against E. coli (from 66.54% up to 88.86%). The inhibition of Na-NOCC fibers against S. aureus were above 90%, and more effective than E. coli. The cytotoxicity assay demonstrated that Na-NOCC2 fibers were no obvious cytotoxicity to mouse fibroblasts. Wound healing test and histological examination showed that significantly advanced granulation tissue and capillary formation in the healing-impaired wounds treated with Na-NOCC fibers, as compared to those treated with gauze, which demonstrated that Na- NOCC fibers could promote skin repair and might have great application for wound healing.

Optimization of the preparation conditions of thermo-sensitive chitosan hydrogel in heterogeneous reaction using response surface methodology

A thermo-sensitive hydroxybutyl chitosan (HBC) hydrogel was prepared by using 1,2‑butene oxide as an etherification modifying agent. To obtain the maximum yield of HBC, response surface methodology (RSM) was applied to optimize its preparation conditions. Key factors were chosen firstly by Plackett-Burman design (PBD) experiments, such as the concentration of NaOH, the ratio of isopropanol to water and reaction temperature. Steepest ascent experiments were employed to reach the top region of the response and determine the appropriate levels of three key factors. A three-level-three-variable Box-Behnken design (BBD) was used to further optimize the synthesis parameters. The results indicated that when the concentration of NaOH and the ratio of isopropyl alcohol to water were 40.65% and 2.68:1 at reaction temperature of 59 °C, respectively, the yield of HBC production was 5.897 ± 0.112 g and close to the predicted value (6.002 g), which demonstrated that the effectiveness of BBD model and the controllability for the yield of HBC in the heterogeneous reaction system.

The green and stable dissolving system based on KOH/urea for homogeneous chemical modification of chitosan

The novel solvent (0.25 M KOH/0.01 M urea alkaline solution) was used to successfully dissolve chitosan without freezing-thawing cycles, for the first time. The results from XRD, FTIR, and 13CNRM proved that KOH/urea solution could destroy the hydrogen bonds between chitosan chains more efficiently than NaOH/urea solution. The dynamic light scattering, rheology, viscosity and elemental analysis confirmed that the KOH/urea hydrogen-bonded chitosan complex had a better thermal stability at 40 °C, and no obvious deacetylation and degradation appeared in dissolution process. Subsequently, the homogeneous chemical modification of chitosan based on KOH/urea dissolution system solution was conducted at 25 °C. The FTIR and microscopic observation indicated that the carboxymethyl chitosan, N,N,N-trimethyl chitosan and hydroxyl butyl chitosan were synthetized successfully. This work provided a green and stable solvent for homogeneous chemical modification of chitosan.

Reinforcement of thermoplastic chitosan hydrogel using chitin whiskers optimized with response surface methodology

To strengthen the mechanical strength of thermo-sensitive hydroxybutyl chitosan (HBC) hydrogel, chitin whiskers were used as sticker to fabricate reinforced HBC (HBCW) hydrogel by using response surface methodology. Unlike the intrinsic network of HBC hydrogel, HBCW hydrogel showed a laminar shape with firm structure. The preparation condition was optimized by three-factor-three-level Box-Behnken design. The maximum mechanical strength (1011.11 Pa) was achieved at 50 °C, when the concentrations of HBC and chitin whiskers were 5.1 wt% and 2.0 wt%, respectively. The effects of temperature, pH value and NaCl concentration on mechanical strength of HBCW hydrogels were investigated via the oscillatory stress sweeps. The results showed that HBCW hydrogel could reach the maximum stiffness (∼1126 Pa) at 37 °C pH 12.0. Low pH and high salty ions could decrease the stability of hydrogel, while chitin whiskers could increase the stress tolerance and related ruptured strain of HBCW hydrogels.