Reversibly Reconfigurable Cross-Linking Induces Fusion of Separate Chitosan Hydrogel Films

Regulating Supramolecular Assembly and Disassembly of Chitosan toward Efficiently Antibacterial Lubricous and Biodegradable Hydrogel Urinary Catheters

Urinary catheters serve as critical medical devices in clinical practice. However, the currently used urinary catheters lack efficient antibacterial and lubricating properties, often leading to discomfort with patients and even severe urinary infections. Herein, a new strategy of supramolecular assembly and disassembly of chitosan (Cs) is developed that enables efficient antibacterial lubricous and biodegradable hydrogel urinary catheters. Sodium lauryl sulfonate (SLS) is employed to induce supramolecular assembly on the surface of Cs film strips in an aqueous solution, resulting in the formation of hollow hydrogel catheters of Cs@SLS. Subsequent disassembly in a strong alkaline solution eliminates the SLS component, yielding neat Cs hydrogel catheters. The mechanical strength of these catheters reaches 16 MPa, exceeding that of similar devices made of plastics. The Cs hydrogel catheters are endowed with high antibacterial activity, capable of inhibiting the growth of Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Proteus mirabilis(P. mirabilis) on its surface, while these bacteria are found to proliferate rapidly on plastic catheters within 24 h. They also demonstrate excellent lubricity, with a friction coefficient approaching zero, and thus about 13 times lower than that of plastic catheters. In vivo tests further confirm the biodegradability of the catheters, highlighting their strong potential for clinical applications.

Biopolymer-based beads for the adsorptive removal of organic pollutants from wastewater: Current state and future perspectives

Among biopolymer-based adsorbents, composites in the form of beads have shown promising results in terms of high adsorption capacity and ease of separation from the effluents. This review addresses the potential of biopolymer-based beads to remediate wastewaters polluted with emerging organic contaminants, for instance dyes, active pharmaceutical ingredients, pesticides, phenols, oils, polyaromatic hydrocarbons, and polychlorinated biphenyls. High adsorption capacities up to 2541.76 mg g-1 for dyes, 392 mg g-1 for pesticides and phenols, 1890.3 mg g-1 for pharmaceuticals, and 537 g g-1 for oils and organic solvents have been reported. The review also attempted to convey to its readers the significance of wastewater treatment through adsorption by providing an overview on decontamination technologies of organic water contaminants. Various preparation methods of biopolymer-based gel beads and adsorption mechanisms involved in the process of decontamination have been summarized and analyzed. Therefore, we believe there is an urge to discuss the current state of the application of biopolymer-based gel beads for the adsorption of organic pollutants from wastewater and future perspectives in this regard since it is imperative to treat wastewater before releasing into freshwater bodies.

Progress in preparation and properties of chitosan-based hydrogels

Chitosan is a kind of natural polysaccharide biomass with the second highest content in nature after cellulose, which has good biological properties such as biocompatibility, biodegradability, hemostasis, mucosal adsorption, non-toxicity, and antibacterial properties. Therefore, hydrogels prepared from chitosan have the advantages of good hydrophilicity, unique three-dimensional network structure, and good biocompatibility, so they have received extensive attention and research in environmental testing, adsorption, medical materials, and catalytic supports. Compared with traditional polymer hydrogels, biomass chitosan-based hydrogels have advantages such as low toxicity, excellent biocompatibility, outstanding processability, and low cost. This paper reviews the preparation of various chitosan-based hydrogels using chitosan as raw material and their applications in the fields of medical materials, environmental detection, catalytic carriers, and adsorption. Some views and prospects are put forward for the future research and development of chitosan-based hydrogels, and it is believed that chitosan-based hydrogels will be able to obtain more valuable applications.

Electro-Biofabrication. Coupling Electrochemical and Biomolecular Methods to Create Functional Bio-Based Hydrogels

Twenty years ago, this journal published a review entitled "Biofabrication with Chitosan" based on the observations that (i) chitosan could be electrodeposited using low voltage electrical inputs (typically less than 5 V) and (ii) the enzyme tyrosinase could be used to graft proteins (via accessible tyrosine residues) to chitosan. Here, we provide a progress report on the coupling of electronic inputs with advanced biological methods for the fabrication of biopolymer-based hydrogel films. In many cases, the initial observations of chitosan's electrodeposition have been extended and generalized: mechanisms have been established for the electrodeposition of various other biological polymers (proteins and polysaccharides), and electrodeposition has been shown to allow the precise control of the hydrogel's emergent microstructure. In addition, the use of biotechnological methods to confer function has been extended from tyrosinase conjugation to the use of protein engineering to create genetically fused assembly tags (short sequences of accessible amino acid residues) that facilitate the attachment of function-conferring proteins to electrodeposited films using alternative enzymes (e.g., transglutaminase), metal chelation, and electrochemically induced oxidative mechanisms. Over these 20 years, the contributions from numerous groups have also identified exciting opportunities. First, electrochemistry provides unique capabilities to impose chemical and electrical cues that can induce assembly while controlling the emergent microstructure. Second, it is clear that the detailed mechanisms of biopolymer self-assembly (i.e., chitosan gel formation) are far more complex than anticipated, and this provides a rich opportunity both for fundamental inquiry and for the creation of high performance and sustainable material systems. Third, the mild conditions used for electrodeposition allow cells to be co-deposited for the fabrication of living materials. Finally, the applications have been expanded from biosensing and lab-on-a-chip systems to bioelectronic and medical materials. We suggest that electro-biofabrication is poised to emerge as an enabling additive manufacturing method especially suited for life science applications and to bridge communication between our biological and technological worlds.

Antifatigue Hydration-Induced Polysaccharide Hydrogel Actuators Inspired by Crab Joint Wrinkles

Joint wrinkles in animals facilitate frequent bending and contribute to the duration of the joint. Inspired by the morphology and function of joint wrinkles, we developed a bionic hydration-induced polymeric actuator with constructed wrinkles at the selected area. Specifically, we adopt electrical writing to create defined single and double cross-linking regions on chitosan (CS) hydrogel. The covalent cross-linking network was constructed by electrical writing-induced covalent cross-linking between CS chains and epichlorohydrin. Subsequent treatment of sodium dodecyl sulfate allows electrostatic cross-linking at the unwritten area with the simultaneous formation of surface wrinkles. The resulting single and double cross-linking hydrogel demonstrates spontaneous deformation behaviors by the influx and efflux of H₂O to the electrostatic cross-linking domain under different ion concentrations. Importantly, the wrinkle structure endows the hydrogel with extraordinary antifatigue bending performance. By regulating the surface morphology and spatial cross-linking, we can design novel biomimetic polysaccharide hydrogel actuators with fascinating functions.

Structure and properties of chitosan/sodium dodecyl sulfate composite films

In this study, we investigated the effect of sodium dodecyl sulfate (SDS) content on the structure and properties of chitosan films. It is found that the binding of SDS to chitosan was realized through the interactions between -SO4 - and -NH3 +, forming an ionically cross-linked film. Structural analysis revealed that the crystallization was greatly hindered by introducing SDS. With an increase of SDS content, the glass transition temperatures (T g) of chitosan films increased due to the formation of crosslinks. Compared to pure chitosan film, the composite films had lower content of moisture and possessed better thermal stability. In addition, the mechanical properties of the as-obtained composite films were closely related to the content of SDS, and were significantly improved in the biopolymer films with moderate SDS content. These results indicate that the microstructure as well as properties of the chitosan films can be regulated by adding SDS.

Temperature-programmable and enzymatically solidifiable gelatin-based bioinks enable facile extrusion bioprinting

The development of exceptional bioinks with excellent printability, high fidelity, and excellent cell viability maintenance for extrusion bioprinting remains a major challenge. Gelatin is an ideal candidate bioink due to its biocompatibility, biodegradability, and non-immunogenicity. However, its inherently low viscosity and unstable physical gelation under physiological conditions make it unsuitable for direct extrusion bioprinting of tissue-like gelatin constructs with high fidelity. Herein, sequential chemical modification using reversible quadruple-hydrogen-bonded ureido-pyrimidinone (UPy) and enzyme-responsive tyramine moieties (Tyr) were devloped to endow the gelatin with a temperature-programmable viscosity and enzyme-controlled solidification, thus realizing enhanced printability and superior fidelity. As demonstrated in a proof-of-concept study, various cell-laden constructs were built based on our modified gelatin, including two-dimensional human bone marrow mesenchymal stem cell (hBMSC)-laden patterns, three-dimensional interconnected hBMSC-laden scaffolds, a reversible twisting-tension human-scale hBMSC-laden ear, a bicellular tibia-like construct containing hBMSCs and endothelial cells and a hexagonal prism-shaped hepatocyte-laden scaffold. The loaded cells in the construct have high viability of over 90% at 24 h, and show proliferation and protein secretion over one week, suggesting that Gel-UPy-Tyr-based constructs under physiological temperature not only can keep high fidelity, but also can support the growth and functions of the loaded cells.

Chameleon Luminophore for Erasable Encrypted and Decrypted Devices: From Dual-Channel, Programmable, Smart Sensory Lanthanide Hydrogel to Logic Devices

With the rapid development of the data security technology, increasing attention has been paid to programmable memory materials with desirable security. However, most conventional memory devices only have a single switchable color state. In this research, a kind of pH-responsive Chameleon luminescent sensor (Lap@Eu-OFX, Lap = laponite, OFX = ofloxacin) based on lanthanide doping has been fabricated, which can realize highly contrast, dynamically controlled full-color display by changing the pH value of the solution. The advanced programmable security inks, including the green and red luminescent inks, have been prepared and used to protect confidential information. More interestingly, triethylamine and hydrochloric acid are selected as encryption and decryption reagents, which can repeatedly switch the emission color of important data. Hence, the high-tech security inks show great potential in data coding, multiencryption, and decryption under UV light. Furthermore, the designed dual-channel memory device, Lap@Eu-OFX@CS (CS = Chitosan), enables reversible synchronous switching of sol-gel and emission color when converting from acid to base conditions. This can be dynamically monitored by a subsequent logic gate system and can be converted and stored into binary values. This work provides an effective approach for the design and promising application of information encryptor, smart monitor, and circuit controllers.

Hierarchical patterning via dynamic sacrificial printing of stimuli-responsive hydrogels

Inspired by stimuli-tailored dynamic processes that spatiotemporally create structural and functional diversity in biology, a new hierarchical patterning strategy is proposed to induce the emergence of complex multidimensional structures via dynamic sacrificial printing of stimuli-responsive hydrogels. Using thermally responsive gelatin (Gel) and pH-responsive chitosan (Chit) as proof-of-concept materials, we demonstrate that the initially printed sacrificial material (Gel/Chit-H⁺ hydrogel with a single gelatin network) can be converted dynamically into non-sacrificial material (Gel/Chit-H⁺-Citr hydrogel with gelatin and an electrostatic citrate-chitosan dual network) under stimulus cues (citrate ions). Complex hierarchical structures and functions can be created by controlling either the printing patterns of citrate ink or the diffusion time of citrate ions into the Gel/Chit-H⁺ hydrogel. Specifically, mechanically anisotropic hydrogel film and cell patterning can be achieved via two-dimensional (2D) patterning; complex external and internal 3D structures can be fabricated in stimuli-responsive hydrogel and other hydrogels that are not stimuli-responsive under experimental conditions (also owing to the erasable properties of Gel/Chit-H⁺-Citr hydrogel) via 3D patterning; and an interconnected or segregated fluidic network can be constructed from the same initial 3D grid structure via 4D patterning. Our method is very simple, safe and generally reagentless, and the products/structures are often erasable, compatible and digestible, enabling advanced fabrication technologies (e.g. additive manufacturing) to be applied to a sustainable materials platform.