Gradient Chitosan Hydrogels Modified with Graphene Derivatives and Hydroxyapatite: Physiochemical Properties and Initial Cytocompatibility Evaluation

In this study, we investigated preparation of gradient chitosan-matrix hydrogels through a novel freezing-gelling-thawing method. The influence of three types of graphene family materials (GFM), i.e., graphene oxide (GO), reduced graphene oxide (rGO), and poly(ethylene glycol) grafted graphene oxide (GO-PEG), as well as hydroxyapatite (HAp) on the physicochemical and biological properties of the composite hydrogels was examined in view of their potential applicability as tissue engineering scaffolds. The substrates and the hydrogel samples were thoroughly characterized by X-ray photoelectron spectroscopy, X-ray diffractometry, infrared spectroscopy, digital and scanning electron microscopy, rheological and mechanical analysis, in vitro chemical stability and bioactivity assays, as well as initial cytocompatibility evaluation with human umbilical cord Wharton's jelly mesenchymal stem cells (hUC-MSCs). We followed the green-chemistry approach and avoided toxic cross-linking agents, using instead specific interactions of our polymer matrix with tannic acid, non-toxic physical cross-linker, and graphene derivatives. It was shown that the most promising are the gradient hydrogels modified with GO-PEG and HAp.

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.

Chitosan nanoparticles as alternative anti-staphylococci agents: Bactericidal, antibiofilm and antiadhesive effects

Chitosan is a biocompatible, bioactive, non-toxic polymer that due to these characteristics has been widely used as a carrier for targeted delivery of bioactive molecules. In recent years, and considering that chitosan has a strong antimicrobial potential, the scientific community's focus has shifted onto the possible antimicrobial activity of chitosan nanoparticles. With this in mind, the aim of this work was to produce low molecular weight chitosan nanoparticles, through the ionic gelation method and characterize their potential biological activity against three staphylococci (MSSA, MRSA and MRSE) in planktonic and sessile environments. The chitosan nanoparticles produced had an average size of 244±12nm, an average charge of 17.3±1.4mV and had a MIC of 1.25mg/mL for all tested microorganisms. Bactericidal activity was only registered for MSSA and MRSA with the time-inhibition curves showing bactericidal activity within 1h. Assays regarding chitosan nanoparticles' impact upon sessile populations showed that they were effective in preventing MRSE adhesion and highly effective in reducing MRSA and MSSA biofilm formation.

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.

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.

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.

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

High strength CS/MWCNTs composite rods preparedvia in situprecipitation & PaPA functionalization, with a 3D sophisticated structure and uniformly dispersed MWCNTs.

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

High strength chitosan rod prepared via LiOH/urea solvent utilizing the unique centrifugation induced orientation method.

Preparation and characterization of N-phthaloyl-chitosan-g-(PEO–PLA–PEO) as a potential drug carrier

Synthesis of N-phthaloyl-chitosan-g-(PEO–PLA–PEO) and its drug loading capacities and drug release profiles of IMC.