Synthesis and characterization of in situ cross-linked hydrogel based on self-assembly of thiol-modified chitosan with PEG diacrylate using Michael type addition

Robot-Assisted Synthesis of Structure-Controlled Star-Cluster Hydrogels with Targeted Mechanophysical Properties for Biomedical Applications

Advancements in polymer chemistry have enabled the design of macromolecular structures with tailored properties for diverse applications. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a controlled technique for precise polymer design. Automation tools further enhance polymer synthesis by enabling the rapid, reproducible preparation of polymer libraries. This study utilizes an automated platform and a biologically friendly bio-Fenton RAFT synthesis method to create hydrogels with embedded star polymers derived from complex block copolymers with controlled block lengths and sequences. Automation improves the efficiency compared to manual methods, while the choice of prepolymer and polymerization techniques ensures biocompatibility. Hydrogels formed by cross-linking linear block copolymers exhibit tunable physical, chemical, and mechanical properties. By systematically altering the prepolymer block sequences, promising hydrogel candidates for enhanced cell biocompatibility and proliferation are identified. These synthetic hydrogels mimic cellular microenvironments and offer a robust platform for biomedical applications, paving the way for an efficient hydrogel design and synthesis.

Silicon-Enhanced PVA Hydrogels in Flexible Sensors: Mechanism, Applications, and Recycling

Hydrogels, known for their outstanding water absorption, flexibility, and biocompatibility, have been widely utilized in various fields. Nevertheless, their application is still limited by their relatively low mechanical performance. This study has successfully developed a dual-network hydrogel with exceptional mechanical properties by embedding amino-functionalized polysiloxane (APSi) networks into a polyvinyl alcohol (PVA) matrix. This hydrogel effectively dissipates energy through dense sacrificial bonds between the networks, allowing for precise control over its tensile strength (ranging from 0.07 to 1.46 MPa) and toughness (from 0.06 to 2.17 MJ/m3) by adjusting the degree of crosslinking in the polysiloxane network. Additionally, the hydrogel exhibits excellent conductivity (10.97 S/cm) and strain sensitivity (GF = 1.43), indicating its potential for use in wearable strain sensors. Moreover, at the end of its life (EOL), the sensor waste can be repurposed as an adsorbent material for metal ions in water treatment, achieving the recycling of hydrogel materials and maximizing resource utilization.

Synthesis and characterization of methacryl glycol chitosan as a novel functionally advanced thermogel for biomedical applications

Thermo-responsive hydrogels (thermogels), known for their sol-gel transition capabilities, have garnered significant interest for biomedical applications over recent decades. However, conventional thermogels are hindered by intrinsic physicochemical and functional limitations that impede their broader utility. This study introduces methacryl glycol chitosan (MGC) as a novel thermogel, offering enhanced functionality and addressing these limitations. MGCs, synthesized through N-methacrylation of glycol chitosan, exhibit tunable thermogelling and photo-crosslinking behaviors. The thermo-reversible sol-gel transition of MGCs occurs within a 21-54 °C range, adjustable by polymer concentration and methacryl substitution degree. Photo-crosslinking using UV light further enhances the mechanical properties of MGC thermogels, creating thermo-irreversible, chemically crosslinked hydrogels. MGCs show no cytotoxic effects and effectively support cell encapsulation. In vivo studies demonstrate stable crosslinking with minimal UV-induced skin damage. Due to their unique thermo-sensitivity, multi-functionality, and customizable properties, MGC thermogels are promising novel biomaterials for various biomedical applications, particularly injectable tissue engineering and cell encapsulation, thus overcoming the limitations of conventional thermogels.

Zinc Oxide/Carbon Material-Embedded Supramolecular Drug Delivery System with Photoswitching Properties for Highly Selective and Effective Chemotherapy

Phototherapy has become a hopeful procedure for the treatment of cancer. Nevertheless, the straightforward creation of a theranostic system that can achieve both tumor localization and production of oxygen species is greatly desired yet remains a challenging endeavor. In this study, we synthesized spherical nanostructures by decorating zinc oxide (ZnO) with peanut shell-based carbon (PNS-C) in an aqueous solution. The PNS-C-decorated ZnO (ZnO/PNS-C)-embedded supramolecular system exhibited spontaneous self-assembly. The nanogels that are produced have several desirable characteristics, including exceptional resistance to degradation by light, highly stable nanostructures that form spontaneously in biological environments, outstanding ability to prevent the destruction of red blood cells, and a high level of sensitivity to changes in pH and light. Under light irradiation, the addition of ZnO/PNS-C-incorporated supramolecular provided high reactive oxygen species production. Moreover, in vitro cellular assays demonstrated ZnO/PNS-C-incorporated supramolecular exhibited highly selective and induced phototoxicity into cancer cells and no effect on the viability of normal cells both before and after irradiation. Overall, the ZnO/PNS-C-incorporated supramolecular system has the potential to stimulate advancements in phototherapy by utilizing highly tumor-selective therapeutic molecules. This can lead to a more effective targeted therapy for cancers.

Ionic liquids functionalized chitosan: An effective, rapid and green adsorbent for gold recovery

Thiosulfate has been considered as a more environmentally-friendly alternative to cyanide salts for the extraction of gold from gold ores and the development of affordable, green and efficient adsorbents for the isolation of gold-thiosulfate complex (Au(S2O3)23-) from the leaching solution remains a significant challenge. To address this issue, chitosan, a natural macromolecule, was selected as a carrier and chemically modified with ionic liquids. The ionic liquids modified chitosan showed greater adsorption capacity towards Au(S2O3)23- compared with pristine chitosan. The adsorption of Au(S2O3)23- on ionic liquid modified chitosan followed Freundlich isotherm and pseudo-second order kinetic models, involving an anion-exchange mechanism with liquid film diffusion as the rate-limiting step. The chitosan modified with butylimidazolium-based ionic liquid had an adsorption capacity of 5.0 mg g-1 for gold (10 mg L-1 of gold, pH 6, 2 g L-1 of adsorbent dosage), outperforming other reported adsorbents. The ionic liquid modified chitosan showed a high adsorption efficiency of up to 96.7 % for Au(S2O3)23- in an actual thiosulfate leaching solution with a desorption efficiency of 98.4 %, suggesting that the ionic liquid modified chitosan has the potential to be a eco-friendly, biocompatible and effective adsorbent for the recovery of Au(S2O3)23-.

Natural Polymer-Based Hydrogel Dressings for Wound Healing

Significance: Acute wounds such as severe burns and chronic wounds like diabetic ulcers present a significant threat to human health. Wound dressings made from natural polymers offer inherent properties that effectively enhance wound healing outcomes and reduce healing time. Recent Advances: Numerous innovative hydrogels are being developed and translated to the clinic to successfully treat various wound types. This underscores the substantial potential of hydrogels in the future wound care market. Economically, annual sales of wound care products are projected to reach $15-22 billion by 2024. Critical Issues: While chitosan-, cellulose-, and collagen-based hydrogel dressings are currently commercially available, scaling-up and manufacturing hydrogels for commercial products remain a challenging process. In addition, ensuring the sterility and stability of the chemical or biological components comprising the hydrogel is a critical consideration. Future Directions: In light of the persistent increase in wound fatalities and the resulting economic and social impacts, as well as the importance of educating the public about dietary health and disease, there should be increased investment in new wound care dressings, particularly hydrogels derived from natural products. With numerous researchers dedicated to advancing preclinical hydrogels, the future holds promise for more innovative and more personalized hydrogel wound dressings.

Multifunctional hydrogels with spatially controlled light activation with photocaged oligonucleotides

Recreating tissue environments with precise control over mechanical, biochemical, and cellular organization is essential for next-generation tissue models for drug discovery, development studies, and the replication of disease environments. However, controlling these properties at cell-scale lengths remains challenging. Here, we report the development of printing approaches that leverage polyethylene glycol diacrylate (PEGDA) hydrogels containing photocaged oligonucleotides to spatially program material characteristics with non-destructive, non-ultraviolet light. We further integrate this system with a perfusion chamber to allow us to alter the composition of PEGDA hydrogels while retaining common light-activatable photocaged DNAs. We demonstrate that the hydrogels can capture DNA functionalized materials, including cells coated with complementary oligonucleotides with spatial control using biocompatible wavelengths. Overall, these materials open pathways to orthogonal capture of any DNA functionalized materials while not changing the sequences of the DNA.

Engineering superstable islets-laden chitosan microgels with carboxymethyl cellulose coating for long-term blood glucose regulation in vivo

Islet transplantation to restore endogenous insulin secretion is a promising therapy for type 1 diabetes in clinic. However, host immune rejection seriously limits the survival of transplanted islets. Despite of the various encapsulation strategies and materials developed so far to provide immune isolation for transplanted islets, long-term blood glucose regulation is still difficult due to the inherent defects of the encapsulation materials. Herein, a novel islet-encapsulation composite material with low immunogenicity, good biocompatibility and excellent stability is reported. Specifically, chitosan (CS) microgels (diameter: ∼302 μm) are prepared via Michael addition reaction between maleimide grafted chitosan (CS-Mal) and thiol grafted chitosan (CS-NAC) in droplet-based microfluidic device, and then zwitterionic surface layer is constructed on CS microgel surface by covalent binding between maleimide groups on CS and thiol groups on thiol modified carboxymethyl cellulose (CMC-SH). The as-formed carboxymethyl cellulose coated chitosan (CS@CMC) microgels show not only long-term stability in vivo owing to the non-biodegradability of CMC, but also fantastic anti-adsorption and antifibrosis because of the stable zwitterionic surface layer. As a result, islets encapsulated in the CS@CMC microgels exhibit high viability and good insulin secretion function in vivo, and long-term blood glucose regulation is achieved for 180 days in diabetic mice post-transplantation.

Recent advances of magnetic chitosan hydrogel: Preparation, properties and applications

Magnetic chitosan hydrogels are organic-inorganic composite material with the characteristics of both magnetic materials and natural polysaccharides. Due to its biocompatibility, low toxicity and biodegradability, chitosan, a natural polymer has been widely used for preparing magnetic hydrogels. The addition of magnetic nanoparticles to chitosan hydrogels not only improves their mechanical strength, but also endows them with magnetic thermal effects, targeting capabilities, magnetically-sensitive release characteristics, easy separation and recovery, thus enabling them to be used in various applications including drug delivery, magnetic resonance imaging, magnetothermal therapy, and adsorption of heavy metals and dyes. In this review, the physical and chemical crosslinking methods of chitosan hydrogels and the methods for binding magnetic nanoparticles in hydrogel networks are first introduced. Subsequently, the properties of magnetic chitosan hydrogels were summarized including mechanical properties, self-healing, pH responsiveness and properties in magnetic fields. Finally, the potential for further technological and applicative advancements of magnetic chitosan hydrogels is discussed.

Enzymatic co-crosslinking of star-shaped poly(ethylene glycol) tyramine and hyaluronic acid tyramine conjugates provides elastic biocompatible and biodegradable hydrogels

A combination of the viscoelastic properties of hyaluronic acid (HA) and the elastic properties of star shaped 8-arm poly(ethylene glycol) (8-arm PEG) was used to design in-situ forming hydrogels. Hydrogels were prepared by the enzymatic crosslinking of a partially tyramine modified 8-arm PEG and a tyramine conjugated HA using horseradish peroxidase in the presence of hydrogen peroxide. Hydrogels of the homopolymer conjugates and mixtures thereof were rapidly formed within seconds under physiological conditions at low polymer and enzyme concentrations. Elastic hydrogels with high gel content (≥95%) and high storage moduli (up to 22.4 kPa) were obtained. An in vitro study in the presence of hyaluronidase (100 U/mL) revealed that with increasing PEG content the degradation time of the hybrid hydrogels increased up to several weeks, whereas hydrogels composed of only hyaluronic acid degraded within 2 weeks. Human mesenchymal stem cells (hMSCs) incorporated in the hybrid hydrogels remained viable as shown by a PrestoBlue and a live-dead assay, confirming the biocompatibility of the constructs. The production of an extracellular matrix by re-differentiation of encapsulated human chondrocytes was followed over a period of 28 days. Gene expression indicated that these highly elastic hydrogels induced an enhanced production of collagen type II. At low PEG-TA/HA-TA ratios a higher expression of SOX 9 and ACAN was observed. These results indicate that by modulating the ratio of PEG/HA, injectable hydrogels can be prepared applicable as scaffolds for tissue regeneration applications.

Silva-Filho E, Estevinho LM. Antibacterial and Healing Effect of Chicha Gum Hydrogel (Sterculia striata) with Nerolidol

Chicha gum is a natural polymer obtained from the Sterculia striata plant. The hydroxyl groups of its structure have a chemical affinity to form hydrogels, which favors the association with biologically active molecules, such as nerolidol. This association improves the biological properties and allows the material to be used in drug delivery systems. Chicha gum hydrogels associated with nerolidol were produced at two concentrations: 0.01 and 0.02 g mL-1. Then, the hydrogels were characterized by thermogravimetry (TG), Fourier Transform Infrared spectroscopy (FTIR), and rheological analysis. The antibacterial activity was tested against Staphylococcus aureus and Escherichia coli. The cytotoxicity was evaluated against Artemia salina. Finally, an in vivo healing assay was carried out. The infrared characterization indicated that interactions were formed during the gel reticulation. This implies the presence of nerolidol in the regions at 3100-3550 cm-1. The rheological properties changed with an increasing concentration of nerolidol, which resulted in less viscous materials. An antibacterial 83.6% growth inhibition effect was observed using the hydrogel with 0.02 g mL-1 nerolidol. The in vivo healing assay showed the practical activity of the hydrogels in the wound treatment, as the materials promoted efficient re-epithelialization. Therefore, it was concluded that the chicha hydrogels have the potential to be used as wound-healing products.

Thiolated Polymeric Hydrogels for Biomedical Applications: A Review

Hydrogels are a three-dimensional (3D) network of hydrophilic polymers. The physical and chemical crosslinking of polymeric chains maintains the structure of the hydrogels even when they are swollen in water. They can be modified with thiol by thiol epoxy, thiol-ene, thiol-disulfide, or thiol-one reactions. Their application as a matrix for protein and drug delivery, cellular immobilization, regenerative medicine, and scaffolds for tissue engineering was initiated in the early 21st century. This review focuses on the ingredients, classification techniques, and applications of hydrogels, types of thiolation by different thiol-reducing agents, along with their mechanisms. In this study, different applications for polymers used in thiolated hydrogels, including dextran, gelatin, polyethylene glycol (PEG), cyclodextrins, chitosan, hyaluronic acid, alginate, poloxamer, polygalacturonic acid, pectin, carrageenan gum, arabinoxylan, carboxymethyl cellulose (CMC), gellan gum, and polyvinyl alcohol (PVA) are reviewed.

Customizing nano-chitosan for sustainable drug delivery

Chitosan is a natural polymer with acceptable biocompatibility, biodegradability, and mechanical stability; hence, it has been widely appraised for drug and gene delivery applications. However, there has been no comprehensive assessment to tailor-make chitosan cross-linkers of various types and functionalities as well as complex chitosan-based semi- and full-interpenetrating networks for drug delivery systems (DDSs). Herein, various fabrication methods developed for chitosan hydrogels are deliberated, including chitosan crosslinking with and without diverse cross-linkers. Tripolyphosphate, genipin and multi-functional aldehydes, carboxylic acids, and epoxides are common cross-linkers used in developing biomedical chitosan for DDSs. Methods deployed for modifying the properties and performance of chitosan hydrogels, via their composite production (semi- and full-interpenetrating networks), are also cogitated here. In addition, recent advances in the fabrication of advanced chitosan hydrogels for drug delivery applications such as oral drug delivery, transdermal drug delivery, and cancer therapy are discussed. Lastly, thoughts on what is needed for the chitosan field to continue to grow is also debated in this comprehensive review article.

Engineering Hydrogels for Modulation of Material-Cell Interactions

Hydrogels are a recurrent platform for Tissue Engineering (TE) strategies. Their versatility and the variety of available methods for tuning their properties highly contribute to hydrogels' success. As a result, the design of advanced hydrogels has been thoroughly studied, in the quest for better solutions not only for drugs- and cell-based therapies but also for more fundamental studies. The wide variety of sources, crosslinking strategies, and functionalization methods, and mostly the resemblance of hydrogels to the natural extracellular matrix, make this 3D hydrated structures an excellent tool for TE approaches. The state-of-the-art information regarding hydrogel design, processing methods, and the influence of different hydrogel formulations on the final cell-biomaterial interactions are overviewed herein. This article is protected by copyright. All rights reserved.

Low-cost luminescent scaffolds-based on thiol chitosans by microwave radiation for vertebral disc repair/theragnostic

This study introduces a new 3D scaffold based on thiolated chitosans with luminescence by microwave radiation using cysteine (Chi_CT_Cys) and 11-mercaptoundecanoic acid (Chi_CT_MUA) for vertebral disc regeneration/theragnostic. These scaffolds were characterized by Raman, PL spectroscopy, swelling, gel-fraction, and morphologies. Cytocompatibility and mechanical behavior were evaluated. Raman showed that disulfide bonds improved the grafting degree (Chi_CT_Cys (1072 ± 136) μmol·g^-1 and Chi_CT_MUA (3245 ± 105) μmol·g^-1). Morphologies showed interesting characteristics. Swelling behavior showed that Chi_CT_MUA presented a slight minor swelling (2101 ± 251) % compared to Chi_CT_Cys (2589 ± 188) %. Differently, gel-fraction showed that the chemical stability of Chi_CT_Cys was worse (29 ± 4) % than Chi_CT_MUA (15 ± 3) %. PL showed a possibility to use theragnostic evaluation of points of greater compression in a vertebral disc. The mechanical behavior of Chi_CT_MUA presented better results ((70 ± 3) MPa) than Chi_CT_Cys ((37 ± 3) MPa). Cytocompatible showed that the scaffolds presented cell viability >90%. Thusly, these 3D scaffolds presented an incredible potential for tissue engineering applications.

Complementary Nucleobase Interactions Drive Co-Assembly of Drugs and Nanocarriers for Selective Cancer Chemotherapy

A new concept in cooperative adenine-uracil (A-U) hydrogen bonding interactions between anticancer drugs and nanocarrier complexes was successfully demonstrated by invoking the co-assembly of water soluble, uracil end-capped polyethylene glycol polymer (BU-PEG) upon association with the hydrophobic drug adenine-modified rhodamine (A-R6G). This concept holds promise as a smart and versatile drug delivery system for the achievement of targeted, more efficient cancer chemotherapy. Due to A-U base pairing between BU-PEG and A-R6G, BU-PEG has high tendency to interact with A-R6G, which leads to the formation of self-assembled A-R6G/BU-PEG nanogels in aqueous solution. The resulting nanogels exhibit a number of unique physical properties, including extremely high A-R6G-loading capacity, well-controlled, pH-triggered A-R6G release behavior, and excellent structural stability in biological media. Importantly, a series of in vitro cellular experiments clearly demonstrated that A-R6G/BU-PEG nanogels improved the selective uptake of A-R6G by cancer cells via endocytosis and promoted the intracellular release of A-R6G to subsequently induce apoptotic cell death, while control rhodamine/BU-PEG nanogels did not exert selective toxicity in cancer or normal cell lines. Overall, these results indicate that cooperative A-U base pairing within nanogels is a critical factor that improves selective drug uptake and effectively promotes apoptotic programmed cell death in cancer cells.

Hydrogen Bond Strength-Mediated Self-Assembly of Supramolecular Nanogels for Selective and Effective Cancer Treatment

This study provides a significant contribution to the development of multiple hydrogen-bonded supramolecular nanocarrier systems by demonstrating that controlling the hydrogen bond strength within supramolecular polymers represents a crucial factor to tailor the drug delivery performance and enhance the effectiveness of cancer therapy. Herein, we successfully developed two kinds of poly(ethylene glycol)-based telechelic polymers Cy-PEG and UrCy-PEG having self-constituted double and quadruple hydrogen-bonding cytosine (Cy) and ureido-cytosine (UrCy) end-capped groups, respectively, which directly assemble into spherical nanogels with a number of interesting physical characteristics in aqueous solutions. The UrCy-PEG nanogels containing quadruple hydrogen-bonded UrCy dimers exhibited excellent long-term structural stability in a serum-containing biological medium, whereas the double hydrogen-bonded Cy moieties could not maintain the structural integrity of the Cy-PEG nanogels. More importantly, after the drug encapsulation process, a series of in vitro experiments clearly confirmed that drug-loaded UrCy-PEG nanogels induced selective apoptotic cell death in cancer cells without causing significant cytotoxicity to healthy cells, while drug-loaded Cy-PEG nanogels exerted nonselective cytotoxicity toward both cancer and normal cells, indicating that increasing the strength of hydrogen bonds in nanogels plays a key role in enhancing the selective cellular uptake and cytotoxicity of drugs and the subsequent induction of apoptosis in cancer cells.

Copper metal-organic framework embedded carboxymethyl chitosan-g-glutathione/polyacrylamide hydrogels for killing bacteria and promoting wound healing

Bacterial infection and its induced oxidative stress as major clinical challenge during wound healing call for an urgent response for the development of medical dressings with multi-functions, such as antioxidant and antibacterial. To meet this demand, copper metal organic framework nanoparticles (HKUST NPs) and carboxymethyl chitosan-g-glutathione (CMCs-GSH) were synthesized and characterized. By embedding HKUST NPs into PAM/CMCs-GSH hydrogel (AOH), we developed a novel hydrogel dressing (HKUST-Hs) with dual effects of antibacterial and antioxidant. The morphology, swelling behavior, oxidation resistance and antibacterial properties of HKUST-Hs were investigated as well as the slow-release behavior of copper ions. Full-thickness cutaneous wound model of rats was created to assess the promoting effect of HKUST-Hs on wound healing. We found that HKUST NPs could be well dispersed in HKUST-Hs by shielding the positive charge of copper ions, and thus copper ions released were uniformly distributed and chelated with CMCs-GSH to promote the swelling stability of HKUST-Hs. Also, HKUST-Hs exhibited good free radical scavenging ability in vitro antioxidant assay. Meanwhile, a gradient sustained-release system of copper ions was formed in HKUST-Hs owing to the inhibition of HKUST NPs to copper release and the chelation of CMCs-GSH, which effectively inhibited the explosive release of copper ions and prolonged the release period, thereby reducing cytotoxicity. In vitro antibacterial test demonstrated there was synergistic antibacterial effect between the slow-released copper ions and CMCs-GSH, which improved the antibacterial activity and antibacterial persistence of HKUST-Hs. Finally, HKUST-Hs accelerated wound healing in vivo by continuously killing bacteria and inhibiting oxidative stress.

3D sponges of chemically functionalized chitosan for potential environmental pollution remediation: biosorbents for anionic dye adsorption and 'antibiotic-free' antibacterial activity

In this work, it was developed three-dimensional (3D) porous hydrogel sponges produced by the freeze-dried process using chitosan polymer functionalized by 11-mercaptoundecanoic acid (MUA). These chitosan-based sponges were used as cationic adsorbents for the removal of anionic methyl orange (MO) dye, simulating a model organic pollutant in aqueous medium. Moreover, these porous 3D constructs were also evaluated as 'antibiotic-free' antibacterial materials against gram-negative and gram-positive bacteria, Pseudomonas aeruginosa and Staphylococcus aureus, respectively, which were used as model pathogens possibly found in contaminated hospital discharges. These 3D hydrogels were comprehensively characterized through morphological methods such as scanning electron microscopy and X-ray micro-computed tomography techniques, combined with FTIR, Raman, and UV-visible spectroscopy analyses. Additionally, the surface area, the degree of swelling, and the adsorption profiles and kinetics of these scaffolds were systematically investigated. The chemically thiolated chitosan (CHI-MUA) hydrogels were successfully produced with a supramolecular polymeric network based on hydrogen bonds, disulfide bonds, and hydrophobic interactions that resulted in higher stability in aqueous medium than hydrogels of pristine chitosan. CHI-MUA exhibited sponge-like three-dimensional structures, with highly interconnected and hierarchical pore size distribution with high porosity and surface area. These architectural aspects of the 3D sponges favoured the high adsorption capacity for MO dye (∼388 mg.g^-1) in water with removal efficiency greater than 90% for MO solutions (from 20 mg.L^-1-1200 mg.L^-1). The adsorption data followed a pseudo-second-order kinetic model and adsorption isotherm analysis and spectroscopy studies suggested a multilayer behaviour with coexistence of adsorbent-adsorbate and adsorbate-adsorbate interactions. Additionally, the in vitro evaluation of toxicity (MTT and LIVE-DEAD® assays) of 3D-sponges revealed a non-toxic response and preliminary suitability for bio-related applications. Importantly, the 3D-sponges composed of chitosan-thiolated derivative proved high antibacterial activity, specificity against P. aeruginosa (model hazardous pathogen), equivalent to conventional antibiotic drugs, while no lethality against S. aureus (reference commensal bacteria) was observed.

Unsaturated and thiolated derivatives of polysaccharides as functional matrixes for tissue engineering and pharmacology: A review

This review examines investigations into the functionalization of polysaccharides by substituents containing multiple (CC) bonds and thiol (SH) groups that are prone to (co)polymerization in the presence of thermal, redox and photoinitiators or Michael addition reactions. A comparative analysis of the approaches to grafting the mentioned substituents onto the polysaccharide macromolecules was conducted. The use of the modified polysaccharides for the design of the 3D structures, including for the development of the pore bearing matrixes of cells or scaffolds utilized in regenerative medicine was examined. These modified polymers were also examined toward the design of excipient matrixes in pharmacological compositions, including with controllable release of active pharmaceuticals, as wel as of antibacterial and antifungal agents and others. In addition, a few examples of the use of modified derivatives in other areas are given.

An injectable double cross-linked hydrogel adhesive inspired by synergistic effects of mussel foot proteins for biomedical application

Hydrogel adhesives with high tissue adhesion, biodegradability and biocompatibility are benefit for promoting surgical procedures and minimizing the pain and post-surgical complications of patients. In this paper, an injectable mussel inspired double cross-linked hydrogel adhesive composed of thiolated mussel inspired chitosan (CSDS) and tetra-succinimidyl carbonate polyethylene glycol (PEG-4S) was designed and developed. CSDS was synthesized with thiol and catechol groups inspired by the synergistic effect of mussel foot proteins (mfps). The double cross-linked hydrogel was first formed by the addition of sodium periodate (or Fe³⁺) and then double cross-linked with PEG-4S. The results showed that the mechanical and adhesion properties of the double cross-linked hydrogels were significantly improved by the synergistic effects of the functional groups. And the prepared hydrogels showed good cytocompatibility which evaluated by determining the viability of L929 cells and human umbilical vein endothelial cells (HUVECs). Additionally, the biodegradability and biocompatibility in vivo were further confirmed by subcutaneous implantation in mice model, and the histological analysis results identified that the prepared hydrogels were in vivo biocompatible. This work presents an injectable mussel inspired double cross-linked hydrogels that can use as a potential hydrogel adhesive for biomedical application.

Fabrication of silver nanoparticles/gelatin hydrogel system for bone regeneration and fracture treatment

The present work aims to examine the effect of gelatin on the stabilization of silver nanoparticles (AgNPs) and their use in healing the bone fracture. AgNPs-loaded Gel hydrogels (AgNPs/Gel) were fabricated under sunlight using gelatin (Gel) as stabilizing agent. The characterization of the synthesized hydrogels was performed with the help of techniques such as UV-visible spectroscopy (UV-Vis) and high-resolution transmission electron microscopy (HR-TEM). Furthermore, the results of cell cytotoxicity confirmed that the AgNPs/Gel hydrogels are nonhazardous to osteoblasts. The outcome of cell fixation with AgNPs/Gel hydrogels after an incubation period of five days exposed the improved survival and spreading of osteoblasts cells on the prepared AgNPs/Gel hydrogels. Moreover, the AgNPs/Gel hydrogel nanostructures displayed their ability in modulating bone fracture healing, which suggests their potential use in nursing care.

Synthesis of Network Polymers by Means of Addition Reactions of Multifunctional-Amine and Poly(ethylene glycol) Diglycidyl Ether or Diacrylate Compounds

Addition reactions of multi-functional amine, polyethylene imine (PEI) or diethylenetriamine (DETA), and poly(ethylene glycol) diglycidyl ether (PEGDE) or poly(ethylene glycol) diacrylate (PEGDA), have been investigated to obtain network polymers in H2O, dimethyl sulfoxide (DMSO), and ethanol (EtOH). Ring opening addition reaction of the multi-functional amine and PEGDE in H2O at room temperature or in DMSO at 90 °C using triphenylphosphine as a catalyst yielded gels. Aza-Michael addition reaction of the multi-functional amine and PEGDA in DMSO or EtOH at room temperature also yielded corresponding gels. Compression test of the gels obtained with PEI showed higher Young's modulus than those with DETA. The reactions of the multi-functional amine and low molecular weight PEGDA in EtOH under the specific conditions yielded porous polymers induced by phase separation during the network formation. The morphology of the porous polymers could be controlled by the reaction conditions, especially monomer concentration and feed ratio of the multi-functional amine to PEGDA of the reaction system. The porous structure was formed by connected spheres or a co-continuous monolithic structure. The porous polymers were unbreakable by compression, and their Young's modulus increased with the increase in the monomer concentration of the reaction systems. The porous polymers absorbed various solvents derived from high affinity between the polyethylene glycol units in the network structure and the solvents.

A bio-inspired injectable hydrogel as a cell platform for real-time glycaemic regulation

Frequent subcutaneous insulin injection and islet transplantation are promising therapeutic options for type 1 diabetes mellitus. However, poor patient compliance, insufficient appropriate islet β cell donors and body immune rejection limit their clinical applications. The design of a platform capable of encapsulating insulin-secreting cells and achieving real-time blood glucose regulation, is a so far unmet need. Herein, inspired by the natural processes of regulating blood glucose in pancreatic islet β cells, we developed a poly(N-isopropylacrylamide-co-dextran-maleic acid-co-3-acrylamidophenylboronic acid) (P(AAPBA-Dex-NIPAM)) hydrogel as a cell platform with glucose responsiveness and thermo-responsiveness for the therapy of diabetes. This platform showed good biocompatibility against insulin-secreting cells and presented glucose-dependent insulin release behaviour. The bioinspired P(AAPBA₆-Dex-NIPAM₆₄) hydrogel had a positive effect on real-time glycaemic regulation, as observed by intraperitoneal glucose tolerance tests. The non-fasting blood glucose of diabetic rats was restored to a normal level during the period of treatment. Additionally, the inflammatory response did not occur after administration of the platform. Collectively, we expected that the bio-mimetic platform combined with an insulin-secreting capability could be a new diabetic treatment strategy.

Synthesis and Applications of Hydrogels in Cancer Therapy

Hydrogels are water-insoluble, hydrophilic, cross-linked, three-dimensional networks of polymer chains having the ability to swell and absorb water but do not dissolve in it, that comprise the major difference between gels and hydrogels. The mechanical strength, physical integrity and solubility are offered by the crosslinks. The different applications of hydrogels can be derived based on the methods of their synthesis, response to different stimuli, and their different kinds. Hydrogels are highly biocompatible and have properties similar to human tissues that make it suitable to be used in various biomedical applications, including drug delivery and tissue engineering. The role of hydrogels in cancer therapy is highly emerging in recent years. In the present review, we highlighted different methods of synthesis of hydrogels and their classification based on different parameters. Distinctive applications of hydrogels in the treatment of cancer are also discussed.

Injectable microfluidic hydrogel microspheres based on chitosan and poly(ethylene glycol) diacrylate (PEGDA) as chondrocyte carriers

Chitosan/PEGDA double-network hydrogel microspheres prepared by microfluidic method as chondrocyte carriers for bottom-up cartilage tissue engineering.

Dynamic plant-derived polysaccharide-based hydrogels

Plant-derived polysaccharides are widely used to fabricate hydrogels because of their ease of gelation and functionalization, plus exceptional biological properties. As an example, nanocellulose is a suitable candidate to fabricate hydrogels for tissue engineering applications due to its enhanced mechanical and biological properties. However, hydrogels are prone to permanent failure whilst under load without the ability to reform their networks once damaged. Recently, considerable efforts are being made to fabricate dynamic hydrogels via installation of reversible crosslinks within their networks. In this paper, we review the developments in the design of dynamic hydrogels from plant-derived polysaccharides, and discuss their applications in tissue engineering, sensors, bioelectronics devices, etc. The main goal of the paper is to elucidate how the network design of hydrogels can influence their dynamic properties: self-healing and self-recovery. Complementary to this, current challenges and prospects of dynamic plant-derived hydrogels are discussed.

Evaluation of in situ gelling chitosan-PEG copolymer for use in the spinal cord

The goal of the present work was to characterize a hydrogel material for localized spinal cord delivery. To address spinal cord injuries, an injectable in situ gelling system was tested utilizing a simple, effective, and rapid cross-linking method via Michael addition. Thiolated chitosan material and maleimide-terminated polyethylene glycol material were mixed to form a hydrogel and evaluated in vitro and in vivo. Three distinct thiolated chitosan precursors were made by varying reaction conditions; a modification of chitosan with Traut's reagent (2-iminothiolane) displayed the most attractive hydrogel properties once mixed with polyethylene glycol. The final hydrogel chosen for animal testing had a swelling ratio (Q) of 57.5 ± 3.4 and elastic modulus of 378 ± 72 Pa. After confirming low cellular toxicity in vitro, the hydrogel was injected into the spinal cord of rats for 1 and 2 weeks to assess host reaction. The rats displayed no overt functional deficits due to injection following initial surgical recovery and throughout the 2-week period after for both the saline-injected sham group and hydrogel-injected group. The saline and hydrogel-injected animals both showed a similar response from ED1+ microglia and GFAP overexpression. No significant differences were found between saline-injected and hydrogel-injected groups for any of the measures studied, but there was a trend toward decreased affected area size from 1 to 2 weeks in both groups. Access to the central nervous system is limited by the blood-brain barrier for noninvasive therapies; further development of the current system for localized drug or cellular delivery has the potential to shape treatments of spinal cord injury.

Rapid in situ cross-linking of hydrogel adhesives based on thiol-grafted bio-inspired catechol-conjugated chitosan

In this paper, a novel chitosan derivative, thiol-grafting bio-inspired catechol-conjugated chitosan was synthesized. The chemical structure of the synthesized catechol-conjugated chitosan was verified by ¹H NMR, and its contents of thiol group and catechol group were determined by UV-vis spectrum. Four percent of catechol-conjugated chitosan aqueous solution could form hydrogels rapidly in situ in 1 min or less with the addition of sodium periodate. Rheological studies showed that the mechanical properties depend on the concentrations of catechol-conjugated chitosan and the molar ratio of sodium periodate to catechol groups. Additionally, the adhesive properties of the resulting adhesives were evaluated, and the adhesion strength of obtained adhesives was as high as 50 kPa because of the complex and multiple interactions, especially the anti-oxidation mechanism of thiol group. The in vitro cytotoxicity assays demonstrated an excellent biocompatibility of the catechol-conjugated chitosan hydrogels. Benefiting from the in situ fast cured, desired mechanical strength, biocompatibility and relatively high adhesion performance, these properties suggested that catechol-conjugated chitosan hydrogel adhesives have potential applications as tissue adhesive for soft tissues.

Strengthening injectable thermo-sensitive NIPAAm-g-chitosan hydrogels using chemical cross-linking of disulfide bonds as scaffolds for tissue engineering

In the present study, we fabricated non-toxic, injectable, and thermo-sensitive NIPAAm-g-chitosan (NC) hydrogels with thiol modification for introduction of disulfide cross-linking strategy. Previously, NIPAAm and chitosan copolymer has been proven to have excellent biocompatibility, biodegradability and rapid phase transition after injection, suitable to serve as cell carriers or implanted scaffolds. However, weak mechanical properties significantly limit their potential for biomedical fields. In order to overcome this issue, we incorporated thiol side chains into chitosan by covalently conjugating N-acetyl-cysteine (NAC) with carbodiimide chemistry to strengthen mechanical properties. After oxidation of thiols into disulfide bonds, modified NC hydrogels did improve the compressive modulus over 9 folds (11.4 kPa). Oscillatory frequency sweep showed a positive correlation between storage modulus and cross-liking density as well. Additionally, there was no cytotoxicity observed to mesenchymal stem cells, fibroblasts and osteoblasts. We suggested that the thiol-modified thermo-sensitive polysaccharide hydrogels are promising to be a cell-laden biomaterial for tissue regeneration.

Acrylated Chitosan Nanoparticles with Enhanced Mucoadhesion

The aim of this study was to investigate the effect of acrylate modification on the mucoadhesion of chitosan at the nanoscale. Nanoparticles were fabricated from acrylated chitosan (ACS) via ionic gelation with tripolyphosphate and were characterized in terms of size, zeta potential, stability, and nanoparticle yield. Chitosan (CS) nanoparticles, serving as a control, were fabricated using the same procedure. The mucoadhesion of the nanoparticles was evaluated using the flow-through method after different incubation periods. The retention percentages of ACS nanoparticles were found to be significantly higher than those of CS nanoparticles, for all studied time intervals. An additional indication for the increased mucoadhesion of ACS nanoparticles was the increase in particle size obtained from the mucin particle method, in which mucin and nanoparticles are mixed at different ratios. NMR data verified the presence of free acrylate groups on the ACS nanoparticles. Thus, the improved mucoadhesion could be due to a Michael-type addition reaction between the nanoparticles and thiol groups present in mucin glycoprotein, in addition to entanglements and hydrogen bonding. Overall, ACS nanoparticles exhibit enhanced mucoadhesion properties as compared to CS nanoparticles and could be used as vehicles for drug delivery systems.