Jingyi Nie

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.

Chitosan Hydrogel Structure Modulated by Metal Ions

As one of the most important polysaccharide, chitosan (CS) has generated a great deal of interest for its desirable properties and wide applications. In the utilization of CS materials, hydrogel is a major and vital branch. CS has the ability to coordinate with many metal ions by a chelation mechanism. While most researchers focused on the applications of complexes between CS and metal ions, the complexes can also influence gelation process and structure of CS hydrogel. In the present work, such influence was studied with different metal ions, revealing two different kinds of mechanisms. Strong affinity between CS and metal ions leads to structural transition from orientation to multi-layers, while weak affinity leads to composite gel with in-situ formed inorganic particles. The study gave a better understanding of the gelation mechanism and provided strategies for the modulation of hydrogel morphology, which benefited the design of new CS-based materials with hierarchical structure and facilitated the utilization of polysaccharide resources.

Difference between Chitosan Hydrogels via Alkaline and Acidic Solvent Systems.

Chitosan (CS) has generated considerable interest for its desirable properties and wide applications. Hydrogel has been proven to be a major and vital form in the applications of CS materials. Among various types of CS hydrogels, physical cross-linked CS hydrogels are popular, because they avoided the potential toxicity and sacrifice of intrinsic properties caused by cross-linking or reinforcements. Alkaline solvent system and acidic solvent system are two important solvent systems for the preparation of physical cross-linked CS hydrogels, and also lay the foundations of CS hydrogel-based materials in many aspects. As members of physical cross-linked CS hydrogels, gel material via alkaline solvent system showed significant differences from that via acidic solvent system, but the reasons behind are still unexplored. In the present work, we studied the difference between CS hydrogel via alkaline system and acidic system, in terms of gelation process, hydrogel structure and mechanical property. In-situ/pseudo in-situ studies were carried out, including fluorescent imaging of gelation process, which provided dynamic visualization. Finally, the reasons behind the differences were explained, accompanied by the discussion about design strategy based on gelation behavior of the two systems.

Biomimetic multi-layered hollow chitosan–tripolyphosphate rod with excellent mechanical performance

In this work, chitosan–tripolyphosphate hydrogel and dry rods were prepared, which possessed biomimetic features, i.e. multi-layered and hollow features. The ratio of internal to external diameter could be designed and controlled. The relationship between the biomimetic hierarchical structure and mechanical performance was also explored in this research. The resulting rods with three-dimensional, organized structure and excellent mechanical performance have a great potential application in bone tissue engineering.

High strength chitosan rod prepared via LiOH/urea solvent through centrifugation induced orientation processing

Chitosan material is a promising candidate for bioabsorbable internal fixation devices, owing to its biocompatibility, biodegradability and versatility in orthopedic treatment. However, mechanical strength of existing chitosan rod materials is still unsatisfactory. In this study, chitosan rods with excellent mechanical performance had been prepared via a novel solvent, i.e. LiOH/urea solvent. The bending strength of chitosan rod prepared via LiOH/urea solvent could reach 450.2 MPa, which is over 300% higher than chitosan rods prepared via acidic solvent. Reasons behind the high bending strength of chitosan rods could be summarized in two aspects. Firstly, the gelation process of chitosan LiOH/urea solution is distinct from that of traditional acidic chitosan solution, which endows the material with homogeneous network structure. Secondly, due to the state of macromolecules in the solution, centrifugation processing can generate flow orientation in the material. Resulted from unique characteristics of chitosan LiOH/urea solution, the improvement of strength had made the novel chitosan rod a promising candidate of biomedical device for bone fracture internal fixation.

Construction of ordered structure in polysaccharide hydrogel: A review

Hydrogels are three-dimensional, hydrophilic, polymeric networks, held together by a variety of physical or chemical crosslinks. Among the numerous polymers that can be employed to fabricate hydrogel, polysaccharides have attracted enormous attention due to their peculiar properties that make them suitable for various applications. Compared with homogeneous hydrogels, hydrogels with ordered structures on various length scales are endowed with excellent properties and promising applications in materials science. In the present review, a wide range of techniques were introduced and discussed, which had been utilized to construct ordered hierarchical structures in polysaccharide hydrogels. These techniques focused on the construction of multi-layered and orientated structure, which are two typical and very important forms of hierarchical structure.

High strength chitosan rod reinforced by non-covalent functionalized multiwalled carbon nanotubes via an in situ precipitation method

Chitosan (CS) has been widely used as temporary mechanical supporter for the regeneration of bone, owing to its biocompatibility, biodegradability and versatility in orthopedic treatment. CS rod material is a promising candidate for internal fixation devices. However, the mechanical strength of existing CS rod materials is still unsatisfactory. In the present work, multiwalled carbon nanotubes (MWCNTs) were non-covalently functionalized by poly(p-aminophenylacetylene) (PaPA). CS/MWCNTs composite rods were subsequently fabricated via a unique in situ precipitation method. The resultant composite rods were studied in view of their microscopic morphology, crystallinity, mechanical strength, and biocompatibility. Results indicated that the composite rods showed great improvement in mechanical strength and exhibited good biocompatibility, which made the material a promising candidate for bone fracture internal fixation.