Qiaoling Hu

Gelation process visualized by aggregation-induced emission fluorogens

Alkaline-urea aqueous solvent system provides a novel and important approach for the utilization of polysaccharide. As one of the most important polysaccharide, chitosan can be well dissolved in this solvent system, and the resultant hydrogel material possesses unique and excellent properties. Thus the sound understanding of the gelation process is fundamentally important. However, current study of the gelation process is still limited due to the absence of direct observation and the lack of attention on the entire process. Here we show the entire gelation process of chitosan LiOH-urea aqueous system by aggregation-induced emission fluorescent imaging. Accompanied by other pseudo in situ investigations, we propose the mechanism of gelation process, focusing on the formation of junction points including hydrogen bonds and crystalline.

Orientation in multi-layer chitosan hydrogel: morphology, mechanism, and design principle.

Hydrogels with organized structure have attracted remarkable attentions for bio-related applications. Among the preparation of hierarchical hydrogel materials, fabrication of hydrogel with multi-layers is an important branch. Although the generation mechanism of layers had been fully discussed, sub-layer structure was not sufficiently studied. In this research, multi-layered chitosan hydrogel with oriented structure was constructed, and the formation mechanism of orientation was proposed, based on gelation behavior and entanglement of polymer chains in the hydrogel-solution system. Employing the layered-oriented characteristic, chitosan hydrogel materials with various shapes and structure can be designed and fabricated.

Using absorbable chitosan hemostatic sponges as a promising surgical dressing

As absorbable hemostatic dressings, chitosan with a deacetylation degree of 40% (CS-40) and 73% (CS-73) have been fabricated into sponges via a modified method. The hemostatic, biocompatible and biodegradable properties were evaluated through in vivo assays. In a hepatic hemorrhage model, the chitosan sponges, with excellent blood compatibility, achieved less blood loss than the gelation sponge (GS). In addition, CS-40 showed better hemostatic capability and biodegradability than CS-73. After implantation, a histological analysis indicated that CS-40 exhibited the best biodegradability, tissue regeneration and least tissue adhesion. By contrasting CS-40 and CS-73, the deacetylation degree is confirmed to be a key factor for the hemostatic effect, biodegradability, biocompatibility and tissue regeneration. Our overall results demonstrated the potential application of CS-40 for use in absorbable hemostatic dressings.

Preparation and characterization of bionic bone structure chitosan/hydroxyapatite scaffold for bone tissue engineering

Three-dimensional oriented chitosan (CS)/hydroxyapatite (HA) scaffolds were prepared via in situ precipitation method in this research. Scanning electron microscopy (SEM) images indicated that the scaffolds with acicular nano-HA had the spoke-like, multilayer and porous structure. The SEM of osteoblasts which were polygonal or spindle-shaped on the composite scaffolds after seven-day cell culture showed that the cells grew, adhered, and spread well. The results of X-ray powder diffractometer and Fourier transform infrared spectrometer showed that the mineral particles deposited in the scaffold had phase structure similar to natural bone and confirmed that particles were exactly HA. In vitro biocompatibility evaluation indicated the composite scaffolds showed a higher degree of proliferation of MC3T3-E1 cell compared with the pure CS scaffolds and the CS/HA10 scaffold was the highest one. The CS/HA scaffold also had a higher ratio of adhesion and alkaline phosphate activity value of osteoblasts compared with the pure CS scaffold, and the ratio increased with the increase of HA content. The ALP activity value of composite scaffolds was at least six times of the pure CS scaffolds. The results suggested that the composite scaffolds possessed good biocompatibility. The compressive strength of CS/HA15 increased by 33.07% compared with the pure CS scaffold. This novel porous scaffold with three-dimensional oriented structure might have a potential application in bone tissue engineering.

Design and formulation of trimethylated chitosan-graft-poly(ɛ-caprolactone) nanoparticles used for gene delivery

The ideal gene polyplexes should have a subtle balance between polyplex stability to protect DNA against nucleases, and polyplex instability to permit DNA dissociation inside cells. In this research, low molecular weight trimethylated chitosan was chemically modified with poly(ε-caprolactone). Owing to the amphiphilic character, trimethylated chitosan-graft-poly(ε-caprolactone) (TMC-g-PCL) formed nanoparticles in aqueous media. TMC-g-PCL nanoparticles could effectively condense pDNA into polyplexes about 200 nm in size. The TMC-g-PCL/DNA polyplexes were stable in physiological salt condition and showed high uptake efficiency probably due to the increasing cell membrane-carrier interaction as a result of hydrophobic modification. However, the high degree of quaternization influenced the buffer capacity of TMC-g-PCL and led to a reduction in the release from the lysosomes. By adding chloroquine to exclude the limitation of lysosome escape, the transfection efficiency of TMC-g-PCL/DNA polyplexes was similar to that of PEI/DNA polyplexes. This study demonstrated the potential of TMC-g-PCL/DNA nanoparticles as an efficient carrier for gene delivery.

A novel chitosan-based sponge coated with self-assembled thrombin/tannic acid multilayer films as a hemostatic dressing

In order to prepare a novel hemostatic dressing for uncontrolled hemorrhage, a porous chitosan sponge was coated with self-assembled (thrombin/tannic acid)n films, which were based on hydrogen bonding interactions between thrombin and tannic acid at physiologic pH. According to the whole blood clotting test, the coated chitosan sponges showed a significantly high rate of blood clotting due to the addition of thrombin. On the other hand, the storable half-life of immobilized thrombin is extended to 66.9 days at room temperature, which is 8.5 times longer than unfixed thrombin. It is because of the immobilization effect of, not only the porous structure of chitosan sponge but also the interactions between thrombin and tannic acid. In addition, the tannic acid has similar antibacterial effect to chitosan. Therefore, it is an excellent combination of chitosan, thrombin and tannic acid. Besides, all of materials in this research have been approved by the United States Food and Drug Administration (FDA). So the chitosan-based sponge is a promising candidate dressing for uncontrolled hemorrhage due to its storable, bio-safe and highly effective hemostatic properties.

Ferroferric oxide/chitosan scaffolds with three-dimensional oriented structure

A facile approach to construct ferroferric oxide/chitosan composite scaffolds with three-dimensional oriented structure has been explored in this research. Chitosan and ferroferric oxide are co-precipitated by using an in situ precipitation method, and then lyophilized to get the composite scaffolds. XRD indicated that Fe3O4 was generated during the gel formation process, and increasing the content of magnetic particles could destruct the crystal structure of chitosan. When the content of magnetic particles is lower than 10%, the layer-by-layer structure and wheel spoke structure are coexisting in the scaffolds. Increasing the content of magnetic particles, just layer-by-layer structure could be observed in the scaffolds. Ferroferric oxide particles were uniformly distributed in the matrix, the size of which was about 0.48 μm in diameter, 2 μm in length. Porosity of magnetic chitosan composite scaffolds is about 90%. When the ratio of ferroferric oxide to chitosan is 5/100, the compressive strength of the material is 0.4367 MPa, which is much higher than that of pure chitosan scaffolds, indicating that the layer-by-layer and wheel spokes complex structure is beneficial for the improvement of the mechanical properties of chitosan scaffolds. However, increasing the content of ferroferric oxide, the compressive strength of scaffolds decreased, because of the decreasing of chitosan crystallization and aggregation of magnetic particles as stress centralized body. Another reason is that the layer-by-layer and wheel spokes complex structure makes bigger contributions for the compressive strength than the layer-by-layer structure does. Three-dimensional ferroferric oxide/chitosan scaffolds could be used as hyperthermia generator system, improving the local circulation of blood, promoting the aggradation of calcium salt and stimulating bone tissue regeneration.

Monitoring layer-by-layer self-assembly process of natural polyelectrolytes by fluorescent bioconjugate with aggregation-induced emission characteristic

A novel chitosan-based fluorescent bioconjugate (TPE-CS) with aggregation-induced emission (AIE) characteristic is synthesized and used as a fluorescent probe for monitoring layer-by-layer self-assembly process of natural polyelectrolytes. QCM results and contact angle measurement indicate that this AIE active TPE-CS bioconjugate can be assembled with alginate (ALG) through layer-by-layer deposition. Ellipsometry and fluorescence (FL) spectroscopy show an exponential growth of the TPE-CS/ALG multilayer films. Moreover, the exponential relationship between the FL intensity and the number of bilayers, which is in accordance with the thickness variation of multilayer films, provides solid evidence for its capacity to monitor the layer-by-layer self-assembly process.

Catechol-Functional Chitosan/Silver Nanoparticle Composite as a Highly Effective Antibacterial Agent with Species-Specific Mechanisms

In this study, silver nanoparticles (Ag NPs) coated with catechol-conjugated chitosan (CSS) were prepared using green methods. Interestingly, we uncovered that CSS-coated Ag NPs (CSS-Ag NPs) exhibited a higher toxicity against gram-negative Escherichia coli (E. coli) bacteria than against gram-positive Staphylococcus aureus (S. aureus) bacteria. The differences revealed that the CSS-Ag NPs killed gram bacteria with distinct, species-specific mechanisms. The aim of this study is to further investigate these underlying mechanisms through a series of analyses. The ultrastructure and morphology of the bacteria before and after treatment with CSS-Ag NPs were observed. The results demonstrated the CSS-Ag NPs killed gram-positive bacteria through a disorganization of the cell wall and leakage of cytoplasmic content. In contrast, the primary mechanism of action on gram-negative bacteria was a change in membrane permeability, induced by adsorption of CSS-Ag NPs. The species-specific mechanisms are caused by structural differences in the cell walls of gram bacteria. Gram-positive bacteria are protected from CSS-Ag NPs by a thicker cell wall, while gram-negatives are more easily killed due to an interaction between a special outer membrane and the nanoparticles. Our study offers an in-depth understanding of the antibacterial behaviors of CSS-Ag NPs and provides insights into ultimately optimizing the design of Ag NPs for treatment of bacterial infections.

Redox-triggered intracellular dePEGylation based on diselenide-linked polycations for DNA delivery

Extracellular stability to protect DNA against nucleases and stimulus-triggered intracellular DNA release are key factors in designing non-viral gene vectors. In this study, the diselenide-linked polycation mPEG-SeSe-PEI was developed as a new type of PEG-detachable gene vector for redox-responsive gene delivery. The corresponding stable analog mPEG-PEI and the disulfide-linked polycation mPEG-SS-PEI were synthesized as controls. The results showed that all the PEGylated polycations could condense DNA into tightly packed spherical nanoparticles about 80 nm in size, which showed excellent stability under physiological conditions. The results of zeta-potential measurements, stability tests and DNA release ability assay indicated that at a GSH concentration of 0.3 mM, the diselenide bonds were more easily cleaved than disulfide bonds, which facilitated dePEGylation and DNA release. Meanwhile, it was interestingly found that mPEG-SeSe-PEI/DNA polyplexes showed higher gene expression than mPEG-SS-PEI/DNA polyplexes in both HEK293T and HepG2 cells. Confocal laser scanning microscope (CLSM) images revealed that mPEG-SeSe-PEI/DNA polyplexes showed more efficient endosomal escape ability than mPEG-SS-PEI/DNA polyplexes. Based on these results, the diselenide bonds as a novel strategy are more suitable to address the challenging problem of extracellular stability and intracellular DNA release.