Unique gelation of chitosan in an alkali/urea aqueous solution

3D printing of 'green' thermo-sensitive chitosan-hydroxyapatite bone scaffold based on lyophilized platelet-rich fibrin

The critical bone defect is still an urgent problem in the field of bone repair. Here, we reported a new type of chitosan (CS)-hydroxyapatite (HAP) scaffolds based on lyophilized platelet-rich fibrin (L-PRF) for releasing abundant growth factors to realize their respective functions. It also has strong mechanical properties to maintain the stability of the bone repair environment. However, acid-soluble CS hydrogels often contain toxic and organic solvents. Moreover, chemical agents may be used for cross-linking for better mechanical properties, further increasing cytotoxicity. In this study, we used an alkali/urea dissolution system to dissolve CS, which improved its mechanical properties and made it thermo-sensitive. Finally, the L-PRF-CS-HAP (P-C-H) composite scaffold was constructed by extrusion-based printing. The results showed that the printing ink had desirable printability and temperature sensitivity. The compressive properties of the scaffolds exhibited a trend of decline with L-PRF content increasing, but all of them could meet the strength of cancellous bone. Meanwhile, the scaffolds had high hydrophilicity, porosity, and could be degraded stablyin vitro. The antibacterial properties of the scaffolds were also verified, greatly reducing the risk of infection during bone repair. It was also demonstrated that the release time of growth factor from L-PRF was significantly prolonged, and growth factor could still be detected after 35 d of sustained release. The capacity of cells to proliferate increased as the number of L-PRF components increased, indicating that L-PRF still exhibited biological activity after 3D printing.

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

Hydrogels, as interconnected networks (polymer mesh; physically, chemically, or dynamic crosslinked networks) incorporating a high amount of water, present structural characteristics similar to soft natural tissue. They enable the diffusion of different molecules (ions, drugs, and grow factors) and have the ability to take over the action of external factors. Their nature provides a wide variety of raw materials and inspiration for functional soft matter obtained by complex mechanisms and hierarchical self-assembly. Over the last decade, many studies focused on developing innovative and high-performance materials, with new or improved functions, by mimicking biological structures at different length scales. Hydrogels with natural or synthetic origin can be engineered as bulk materials, micro- or nanoparticles, patches, membranes, supramolecular pathways, bio-inks, etc. The specific features of hydrogels make them suitable for a wide variety of applications, including tissue engineering scaffolds (repair/regeneration), wound healing, drug delivery carriers, bio-inks, soft robotics, sensors, actuators, catalysis, food safety, and hygiene products. This review is focused on recent advances in the field of bioinspired hydrogels that can serve as platforms for life-science applications. A brief outlook on the actual trends and future directions is also presented.

Husk of Agarwood Fruit-Based Hydrogel Beads for Adsorption of Cationic and Anionic Dyes in Aqueous Solutions

Hydrogel beads based on the husk of agarwood fruit (HAF)/sodium alginate (SA), and based on the HAF/chitosan (CS) were developed for the removal of the dyes, crystal violet (CV) and reactive blue 4 (RB4), in aqueous solutions, respectively. The effects of the initial pH (2–10) of the dye solution, the adsorbent dosage (0.5–3.5 g/L), and contact time (0–540 min) were investigated in a batch system. The dynamic adsorption behavior of CV and RB4 can be represented well by the pseudo-second-order model and pseudo-first-order model, respectively. In addition, the adsorption isotherm data can be explained by the Langmuir isotherm model. Both hydrogel beads have acceptable adsorption selectivity and reusability for the study of selective adsorption and regeneration. Based on the effectiveness, selectivity, and reusability of these hydrogel beads, they can be treated as potential adsorbents for the removal of dyes in aqueous solutions.

Functionalized Graphene Oxide-Reinforced Chitosan Hydrogel as Biomimetic Dressing for Wound Healing

A novel chitosan composite hydrogel by combining functionalized graphene oxide (CGO) is fabricated. The introduction of CGO significantly improves the mechanical property of CS hydrogel owing to the enhanced interaction between chitosan and CGO sheets. In comparison to the CS-GO composite hydrogel, the compressive stress of the CS-CGO composite hydrogel increases from 1.9 MPa at strain of 70.4% to 4.2 MPa at strain of 78.4%, the tensile stress and strain improve from 141.2 kPa and 134.6% to 300.2 kPa and 165.9%, respectively. An interconnected porous structure is formed in the CS-CGO composite hydrogel and the pore size decreases as the CGO loading increases, which is desirable in improving its mechanical property. Furthermore, the cytotoxicity tests indicate that the CS-CGO composite hydrogel possesses an excellent biocompatibility and can promote the adhesion and proliferation of fibroblasts. In vivo evaluation on full-thickness excision wounds in experimental rat shows that the CS-CGO composite hydrogel significantly accelerates wound healing, and the wound closure rate reaches up to 92.2% after 21 days. A feasible strategy to fabricate an enhanced chitosan composite hydrogel for application in wound healing is offered.

Bioinspired Anisotropic Chitosan Hybrid Hydrogel

Natural soft tissues such as cartilage, tendon, and ligament have well-ordered hierarchical structures, which are crucial for their mechanical and biological functions. Inspired by the aligned fibrous structure, an anisotropic chitosan hybrid hydrogel (ACHH) is developed by combining the oriented chitosan nanofibers with the ductile polyacrylamide network. The resulting ACHH demonstrates outstanding mechanical properties: tensile strength and elastic modulus up to 25.6 and 218.2 MPa, which are comparable to those of natural cartilage and ligament. In addition, the ACHH also exhibits excellent biocompatibility and can promote the adhesion and proliferation of myoblasts. This work offers a facile method to fabricate an anisotropic, strong, and biocompatible chitosan-based hydrogel for potential biomaterials and tissue-engineering applications.

3D printing of high-strength chitosan hydrogel scaffolds without any organic solvents

Here, a novel direct ink printing method was developed to print high-strength chitosan hydrogel scaffolds without any organic solvents.

Dual pH/thermal-dependent coloring polymeric dye through Mannich reaction of chitosan: Synthesis and characterization

A novel polymeric dye was synthesized by one-pot Mannich reaction of chitosan (CS) and phenolphthalein (PHP). The grafting onto side chain of CS derivatives was confirmed by UV-vis, FT-IR, ¹H NMR techniques. The degree of substitution (DS) calculated by ¹H NMR and elemental analysis was revealed to increase with increasing mole ratio of formaldehyde and PHP. XRD analysis showed that the grafting through Mannich reaction was caused to amorphous structure in the derivatives. Covalent grafting of PHP onto CS made the grafted products showing pink color in basic conditions without leaching of dye and color fading after several weeks. Moreover, the derivatives dissolved in LiOH/urea systems could showed darker pink after heating. The results suggested that the novel CS derivatives with dual pH/thermal-dependent coloring property could potentially be prepared as pH/thermal-responsive biomaterial in a wide range of applications.

Rice husk derived double network hydrogel as efficient adsorbent for Pb(II), Cu(II) and Cd(II) removal in individual and multicomponent systems

In this study, lignin extracted from rice husk was used to synthesis double network hydrogel adsorbent, named RH-CTS/PAM gel. RH-CTS/PAM gel exhibited macroporous structure and high buried water content, which gave rise to the exceptional adsorption performance. As results, in individual systems, the equilibrium time of Pb(II), Cu(II) and Cd(II) with initial concentration of 200 mg/L could be reached within 10 min, with the theoretical maximum adsorption capacity of 374.32, 196.68 and 268.98 mg/g, respectively. The adsorption rate and capacity of Pb(II), Cu(II) and Cd(II) in multicomponent systems were lower than that of individual systems. However, in a few cases of ternary system, higher adsorption rate and capacity was observed compare to binary systems. Adsorption mechanism indicated that both oxygen-containing and nitrogen-containing functional groups played a dominant role during the adsorption process, and mainly through chemical interaction along with a small amount of physical interaction.

The thiolated chitosan: Synthesis, gelling and antibacterial capability

Chitosan-1-(mercaptomethyl)-cyclopropane acetic acid (CS-MCA) copolymer was synthesized by amino linkage. The obtained copolymer was characterized by FTIR, ¹H NMR, XRD, TGA and SEM. Porous and reticulate morphologies were found on the CS-MCA surface. The effects of pH on the rheological properties of CS-MCA were investigated. On the one hand, the apparent viscosity of CS-MCA indicated a shear-thinning behavior. The graft of MCA enhanced the moduli and the maximum elastic properties were observed at pH = 7.00. The addition of dithiothreitol reduced the viscosity and modulus of CS-MCA hydrogel, and the gelation time, temperature and frequency were obtained in dynamic oscillatory tests. The antibacterial effect of CS-MCA against E. coli was investigated for the inhibition zone and bacterial growth curve. These results showed that CS-MCA had better antibacterial ability than chitosan without modification. Therefore, the rheological behavior and functional activities can be applied for the hydrocolloid gels in food and pharmaceutical applications.

Chitosan enhances calcium carbonate precipitation and solidification mediated by bacteria

Formation of the biominerals in living organisms is mainly associated with organic macromolecules. These organic materials play an important role in the nucleation, growth, and morphology controls of the biominerals. Current study mimics this concept of organic matrix- mediated biomineralization by using microbial induced carbonate precipitation (MICP) method in combination with the cationic polysaccharide chitosan. CaCO₃ precipitation was performed by the hydrolysis of urea by the ureolytic bacteria Pararhodobacter sp. SO1 in the presence of CaCl₂, with and without chitosan. The crystal polymorphism and morphology of oven-dried samples were analyzed by X-ray diffraction and scanning electron microscopy. The amount of precipitate obtained was higher in the presence of chitosan. The precipitate included both of the CaCO₃ and the chitosan hydrogel. Rhombohedral crystals were dominant in the precipitate without chitosan and distorted crystal agglomerations were found with chitosan. Sand solidification experiments were conducted in the presence of chitosan under different experimental conditions. By adding chitosan, more strongly cemented sand specimens could be obtained than those from conventional method. All of these results confirm the positive effect of chitosan for the CaCO₃ precipitation and sand solidification.