Mimicking Dynamic Adhesiveness and Strain-Stiffening Behavior of Biological Tissues in Tough and Self-Healable Cellulose Nanocomposite Hydrogels

Recent advances in tannic acid-based gels: Design, properties, and applications

With the flourishing of mussel-inspired chemistry, the fast-growing development for environmentally friendly materials, and the need for inexpensive and biocompatible analogues to PDA in gel design, TA has led to its gradual emergence as a research focus due to its remarkable biocompatible, renewable, sustainable and particular physicochemical properties. As a natural building block, TA can be used as a substrate or crosslinker, ensuring versatile functional polymeric networks for various applications. In this review, the design of TA-based gels is summarized in detail (i.e., different interactions such as: metal coordination, electrostatic, hydrophobic, host-guest, cation-π and π-π stacking interactions, hydrogen bonding and various reactions including: phenol-amine Michael and Schiff base, phenol-thiol Michael addition, phenol-epoxy ring opening reaction, etc.). Subsequently, TA-based gels with a variety of functionalities, including mechanical, adhesion, conductive, self-healing, UV-shielding, anti-swelling, anti-freezing, shape memory, antioxidant, antibacterial, anti-inflammatory and responsive properties are introduced in detail. Then, a summary of recent developments in the use of TA-based gels is provided, including bioelectronics, biomedicine, energy, packaging, water treatment and other fields. Finally, the difficulties that TA-based gels are currently facing are outlined, and an original yet realistic viewpoint is provided in an effort to spur future development.

Perspective of nanocellulose production, processing, and application in sustainable agriculture and soil fertility enhancement: A potential review

Nanocellulose, a promising green material derived from various bio-sources, has potentiality on and off-site in the agricultural sector. Due to its special qualities, which include high strength, hydrophilicity, and biocompatibility, it is a material that may be used in a variety of industries, especially agriculture. This review explores in this article production processes, post-processing procedures, and uses of nanocellulose in soil fertility increment and sustainable agriculture. A variety of plant materials, agricultural waste, and even microbes can be used to isolate nanocellulose. Nanocellulose is produced using both top-down and bottom-up methods, each of which has benefits and limitations of its own. It can be applied as nano-biofertilizer in agriculture to enhance beneficial microbial activity, increase nutrient availability, and improve soil health. Moreover, nanocellulose can be used in fertilizer and pesticide formulations with controlled releases to increase efficacy and lessen environmental effects. Innovative approaches to sustainable agriculture are provided by nanocellulose technologies, which also support the UN's Sustainable Development Goals (SDGs), especially those pertaining to eradicating hunger and encouraging responsible consumption. Nanocellulose promotes climate action and ecosystem preservation by increasing resource efficiency and decreasing dependency on hazardous chemicals, ultimately leading to the development of a circular bioeconomy. Nonetheless, there are still issues with the high cost of production and the energy-intensive isolation procedures. Despite its various potentialities, challenges such as high production costs, environmental concerns, and regulatory issues must be addressed for nanocellulose to be widely adopted and effectively integrated into farming practices.

Advancing the design of conductive composite cryogels based on hydroxypropyl cellulose derivatives for improving the compressibility and anti-freezing properties

Conductive hydrogels are an appealing class of "smart" materials with great application potential, as they combine the stimuli-responsiveness of hydrogels with the conductivity of magnetic fillers. However, fabricating multifunctional conductive hydrogels that simultaneously exhibit conductivity, self-healing, adhesiveness, and anti-freezing properties remains a significant challenge. To address this issue, we introduce here a freeze-thawing approach to develop versatile, multiresponsive composite cryogels able to preserve their features under low-temperature conditions. Thus, we engineered robust 3D polymer networks by combining oxidized hydroxypropyl cellulose (HPCox) and polyvinyl alcohol (PVA) in glycerol-water mixtures. The presence of glycerol reduces the water loss by evaporation and prevents elasticity decrease upon storage at -20 °C by forming hydrogen bonds with water, HPCox, and PVA. These interactions result in flexible, stable composite cryogels with an extremely fast shape recovery (few seconds) after 100 % mechanical compression, even after freezing. Additionally, the homogeneous dispersion of magnetite nanoparticles (FeNP) into cryogels imparts both magnetic responsiveness and electrical conductivity. Overall, our innovative strategy generates highly adaptable composite cryogels that retain their properties even after exposure to freezing conditions. This opens new avenues for the development of new functional materials for electronics, sensors, wearable devices, and energy storage systems operating at extremely low temperatures.

Wet adhesives for hard tissues

The development of wet adhesives capable of bonding in aqueous environments, particularly for hard tissues such as bone, tooth, and cartilage, remains a significant challenge in material chemistry and biomedical research. Currently available hard tissue adhesives in clinical practice lack well-defined wet adhesion properties. Nature offers valuable inspiration through the adhesive mechanisms of marine organisms, advancing the design of bioinspired wet adhesives. Beyond biomimetic approaches, alternative strategies have emerged for the design of wet adhesives. This review systematically summarizes the current design strategies for wet adhesives, focusing on their applications to hard tissues. Then, the unique chemical, physical, mechanical, and biological requirements for wet adhesives applied to hard tissues are also discussed. The importance of understanding natural adhesion mechanisms and the need for high-performance materials that can meet the complex demands of hard tissue adhesion in a complex and delicate physiological microenvironment are highlighted. Finally, this review clarifies the future research directions that can further facilitate the clinical application of wet adhesives for hard tissues. STATEMENT OF SIGNIFICANCE: The significance of this review lies in its comprehensive analysis of wet adhesives for hard tissues, a field that has been largely overlooked despite its critical importance in biomedical applications. The insights gained from studying natural adhesives and the translation of these mechanisms into synthetic materials have the potential to revolutionize medical procedures involving hard tissue repair and regeneration. This review meticulously addresses the distinct challenges and specific requirements of hard tissue adhesives, providing an exhaustive roadmap for researchers striving to develop wet adhesives that can endure the demanding physiological conditions inside the human body. In doing so, it aims to facilitate the transition from laboratory findings to practical clinical applications.

Nano-enabled dynamically responsive living acellular hydrogels

As a key building block of mammalian tissues, extracellular matrices (ECMs) stiffen under shear deformation and undergo cell-imparted healing after damage, features that regulate cell fate, communication, and survival. The shear-stiffening behavior is attributed to semi-flexible biopolymeric ECM networks. Inspired by the mechanical behavior of ECMs, we develop acellular nanocomposite living hydrogels (LivGels), comprising network-forming biopolymers and anisotropic hairy nanoparticle linkers that mimic the dynamic mechanical properties of living counterparts. We show that a bifunctional dynamic linker nanoparticle (nLinker), bearing semi-flexible aldehyde- and carboxylate-modified cellulose chains attached to rigid cellulose nanocrystals converts bulk hydrogels to ECM-like analogues via ionic and dynamic covalent hydrazone bonds. The nLinker not only enables the manipulation of nonlinear mechanics and stiffness within the biological window, but also imparts self-healing to the LivGels. This work is a step forward in designing living acellular soft materials with complex dynamic properties using bio-based nanotechnology.

Self-healing cellulose-based hydrogels: From molecular design to multifarious applications

Self-healing cellulose-based hydrogels (SHCHs) exhibit wide-ranging potential applications in the fields of biomedicine, environmental management, energy storage, and smart materials due to their unique physicochemical properties and biocompatibility. This review delves into the molecular design principles, performance characteristics, and diverse applications of SHCHs. Firstly, the molecular structure and physicochemical properties of cellulose are analyzed, along with strategies for achieving self-healing properties through molecular design, with particular emphasis on the importance of self-healing mechanisms. Subsequently, methods for optimizing the performance of SHCHs through chemical modification, composite reinforcement, stimulus responsiveness, and functional integration technologies are discussed in detail. Furthermore, applications of SHCHs in drug delivery, tissue engineering, wound healing, smart sensing, supercapacitors, electronic circuits, anti-counterfeiting systems, oil/water separation, and food packaging are explored. Finally, future research directions for SHCHs are outlined, including the innovative development of new SHCHs, in-depth elucidation of cooperative strengthening mechanisms, a further expansion of application scope, and the establishment of intelligent systems. This review provides researchers with a comprehensive overview of SHCHs and serves as a reference and guide for future research and development.

Design and Improvement of Bone Adhesive in response to Clinical Needs

Fracture represents one of the most common diagnoses in contemporary medical practice, with the majority of cases traditionally addressed through metallic device fixation. However, this approach is marred by several drawbacks, including prolonged operative durations, considerable expenses, suboptimal applicability to comminuted fractures, increased infection risks, and the inevitable requirement for secondary surgery. The inherent advantages of bone adhesives in these fields have garnered the attention of orthopedic surgeons, who have commenced utilizing biocompatible and biodegradable bone adhesives to bond and stabilize bone fragments. Regrettably, the current bone adhesives generally exhibit insufficient adhesive strength in vivo environments, and it is desirable for them to possess effective osteogenesis to facilitate fracture healing. Consequently, aligning bone adhesives with practical clinical demands remains a significant hurdle, which has catalyzed a surge in research endeavors. Within this review, the conceptual framework, characteristics, and design ideas of bone adhesives based on clinical needs are delineated. Recent advancements in this domain, specifically focusing on the enhancement of two pivotal characteristics-adhesive strength and osteogenic potential are also reviewed. Finally, a prospective analysis of the future advancements in bone adhesives, offering new insights into solutions for diverse clinical problems is presented.

Supramolecular Luminescent Copper-Nanocluster-Based Dough with Excellent Electrical Conductivity Sensing Properties

In recent years, the rapid advancement of flexible conductive materials has significantly increased the demand for dough materials that offer high flexibility and conductivity for diverse applications. Here, we developed a flexible, stretchable, and self-healing dough utilizing hydrogen-bonding interactions between glutathione-stabilized copper nanoclusters (GSH-Cu NCs) and poly(acrylic acid) (PAA). The dough materials can be kneaded, readily reshaped, and further processed to create bulk materials of arbitrary form factors. The incorporation of PAA not only preserved the vibrant blue emission of GSH-Cu NCs but also enhanced their electrical conductivity and stretchability. The dough can be stretched up to 25 times its initial length and achieves complete self-healing in a short time. Moreover, the dough can automatically repair physical damage and return to its initial conductivity levels after healing. Surprisingly, the electrical conductivity of the dough can reach as high as 2.97 S/m, which is relatively superior compared to that of conventional conductive materials. This study presents a dough that serves as a highly sensitive strain sensor, capable of effectively monitoring human movement across a broad range of strains.

A review of biopolymer-based hydrogels and IoT integration for enhanced diabetes diagnosis, management, and treatment

The prevalence of diabetes has been increasing globally, necessitating innovative approaches beyond conventional blood sugar monitoring and insulin control. Diabetes is associated with complex health complications, including cardiovascular diseases. Continuous Glucose Monitoring (CGM) devices, though automated, have limitations such as irreversibility and interference with bodily fluids. Hydrogel technologies provide non-invasive alternatives to traditional methods, addressing the limitations of current approaches. This review explores hydrogels as macromolecular biopolymeric materials capable of absorbing and retaining a substantial amount of water within their structure. Due to their high-water absorption properties, these macromolecules are utilized as coating materials for wound care and diabetes management. The study emphasizes the need for early diagnosis and monitoring, especially during the COVID-19 pandemic, where heightened attention to diabetic patients is crucial. Additionally, the article examines the role of the Internet of Things (IoT) and machine learning-based systems in enhancing diabetes management effectiveness. By leveraging these technologies, there is potential to revolutionize diabetes care, providing more personalized and proactive solutions. This review explores cutting-edge hydrogel-based systems as a promising avenue for diabetes diagnosis, management, and treatment, highlighting key biopolymers and technological integrations.

Trends in polysaccharide-based hydrogels and their role in enhancing the bioavailability and bioactivity of phytocompounds

Over the years, polysaccharides such as chitosan, alginate, hyaluronic acid, k-carrageenan, xanthan gum, carboxymethyl cellulose, pectin, and starch, alone or in combination with proteins and/or synthetic polymers, have been used to engineer an extensive portfolio of hydrogels with remarkable features. The application of polysaccharide-based hydrogels has the potential to alleviate challenges related to bioavailability, solubility, stability, and targeted delivery of phytocompounds, contributing to the development of innovative and efficient drug delivery systems and functional food formulations. This review highlights the current knowledge acquired on the preparation, features and applications of polysaccharide/phytocompounds hydrogel-based hybrid systems in wound management, drug delivery, functional foods, and food industry. The structural, functional, and biological requirements of polysaccharides and phytocompounds on the overall performance of such hybrid systems, and their impact on the application domains are also discussed.

A review of cellulose-based catechol-containing functional materials for advanced applications

With the increment in global energy consumption and severe environmental pollution, it is urgently needed to explore green and sustainable materials. Inspired by nature, catechol groups in mussel adhesion proteins have been successively understood and utilized as novel biomimetic materials. In parallel, cellulose presents a wide class of functional materials rating from macro-scale to nano-scale components. The cross-over among both research fields alters the introduction of impressive materials with potential engineering properties, where catechol-containing materials supply a general stage for the functionalization of cellulose or cellulose derivatives. In this review, the role of catechol groups in the modification of cellulose and cellulose derivatives is discussed. A broad variety of advanced applications of cellulose-based catechol-containing materials, including adhesives, hydrogels, aerogels, membranes, textiles, pulp and papermaking, composites, are presented. Furthermore, some critical remaining challenges and opportunities are studied to mount the way toward the rational purpose and applications of cellulose-based catechol-containing materials.

Strong, Tough, and Biocompatible Poly(vinyl alcohol)-Poly(vinylpyrrolidone) Multiscale Network Hydrogels Reinforced by Aramid Nanofibers

Poly(vinyl alcohol) (PVA) hydrogels are water-rich, three-dimensional (3D) network materials that are similar to the tissue structure of living organisms. This feature gives hydrogels a wide range of potential applications, including drug delivery systems, articular cartilage regeneration, and tissue engineering. Due to the large amount of water contained in hydrogels, achieving hydrogels with comprehensive properties remains a major challenge, especially for isotropic hydrogels. This study innovatively prepares a multiscale-reinforced PVA hydrogel from molecular-level coupling to nanoscale enhancement by chemically cross-linking poly(vinylpyrrolidone) (PVP) and in situ assembled aromatic polyamide nanofibers (ANFs). The optimized ANFs-PVA-PVP (APP) hydrogels have a tensile strength of ≈9.7 MPa, an elongation at break of ≈585%, a toughness of ≈31.84 MJ/m3, a compressive strength of ≈10.6 MPa, and a high-water content of ≈80%. It is excellent among all reported PVA hydrogels and even comparable to some anisotropic hydrogels. System characterizations show that those performances are attributed to the particular multiscale load-bearing structure and multiple interactions between ANFs and PVA. Moreover, APP hydrogels exhibit excellent biocompatibility and a low friction coefficient (≈0.4). These valuable performances pave the way for broad potential in many advanced applications such as biological tissue replacement, flexible wearable devices, electronic skin, and in vivo sensors.

A co-type ductile film with high tensile strength and fast self-healing properties for shaped fruit preservation

Traditional petroleum-based plastics have high energy consumption, require professional equipment, are non-degradable after use, and lack antibacterial properties, making it impossible to achieve long-lasting freshness in fruits and vegetables. Herein, we report a novel co-type film-forming method with low energy consumption and without production equipment, which uses PVA-borax gel as a substrate and adds a certain proportion of CMC and TA to prepare multifunctional CMC/TA@PVA-borax composite hydrogels (CTPB). The dynamic borax ester bonding and hydrogen bonding in the CTPB hydrogel results in an ultra-high tensile strength of more than 5500% and rapid self-healing within 8 s. Interestingly, hydrogels can be arbitrarily shaped and stretched like play dough and thus can be stretched into ductile films by co-type film formation. The antimicrobial properties of the hydrogel film can be attributed to the synergistic effects of TA and borax. The mussel structure of TA allows the hydrogel film to adhere directly to different surfaces for more effective bacterial killing. In addition, the hydrogel film has a high level of biosafety and biodegradability and shows good performance in fruit storage. This study provides a convenient and low-energy method for the preparation of films, which in part reduces the increasing environmental pollution caused by petroleum-based plastics.

Tailoring the properties of poly(vinyl alcohol) "twin-chain" gels via sebacic acid decoration

HYPOTHESIS

The development of gels capable to adapt and act at the interface of rough surfaces is a central topic in modern science for Cultural Heritage preservation. To overcome the limitations of solvents or polymer solutions, commonly used in the restoration practice, poly(vinyl alcohol) (PVA) "twin-chain" polymer networks (TC-PNs) have been recently proposed. The properties of this new class of gels, that are the most performing gels available for Cultural Heritage preservation, are mostly unexplored. This paper investigates how chemical modifications affect gels' structure and their rheological behavior, producing new gelled systems with enhanced and tunable properties for challenging applications, not restricted to Cultural Heritage preservation.

EXPERIMENTS

In this study, the PVA-TC-PNs structural and functional properties were changed by functionalization with sebacic acid into a new class of TC-PNs. Functionalization affects the porosity and nanostructure of the network, changing its uptake/release of fluids and favoring the uptake of organic solvents with various polarity, a crucial feature to boost the versatility of TC-PNs in practical applications.

FINDINGS

The functionalized gels exhibited unprecedented performances during the cleaning of contemporary paintings from the Peggy Gugghenheim collection (Venice), whose restoration with traditional solvents and swabs would be difficult to avoid possible disfigurements to the painted layers. These results candidate the functionalized TC-PNs as a new, highly promising class of gels in art preservation.

Tough Hydrogels with Different Toughening Mechanisms and Applications

Load-bearing biological tissues, such as cartilage and muscles, exhibit several crucial properties, including high elasticity, strength, and recoverability. These characteristics enable these tissues to endure significant mechanical stresses and swiftly recover after deformation, contributing to their exceptional durability and functionality. In contrast, while hydrogels are highly biocompatible and hold promise as synthetic biomaterials, their inherent network structure often limits their ability to simultaneously possess a diverse range of superior mechanical properties. As a result, the applications of hydrogels are significantly constrained. This article delves into the design mechanisms and mechanical properties of various tough hydrogels and investigates their applications in tissue engineering, flexible electronics, and other fields. The objective is to provide insights into the fabrication and application of hydrogels with combined high strength, stretchability, toughness, and fast recovery as well as their future development directions and challenges.

Integration of wood-based components - Cellulose nanofibrils and tannic acid - into a poly(vinyl alcohol) matrix to improve functional properties

Poly(vinyl alcohol) (PVA) biocomposite films reinforced with cellulose nanofibrils (CNF) and biologically active tannic acid (TA) were prepared. The influence of different concentrations of CNF and TA in the PVA polymer matrix was investigated in terms of mechanical properties, thermal properties and hydrophobicity improvement of the prepared films. The results showed that in all cases the addition of CNF and TA improved the values of tensile strength and elastic modulus. The PVA film with 10 % CNF exhibited a 30 % higher tensile strength, and the three-component PVA film with 2 % CNF and 10 % TA (P2C10T) exhibited a 40 % higher tensile strength compared to the neat PVA film. The thermal properties (Tg, Tonset) of the PVA biocomposite films were greatly improved, with a significant effect observed for the three-component PVA films. The Tg of the PVA film with 10 % CNF and 10 % TA was 87 °C, 12 °C higher than that of the neat PVA film. For three-component PVA biocomposites with 4 % and 6 % CNF and with all weight percentages of TA, the Tonset shifted to a higher temperature range by about 30 °C compared to the neat PVA film. The PVA film with 2 % CNF and 10 % TA exhibited about a 20° higher contact angle than the neat PVA film. Moreover, the addition of both fillers to the PVA matrix resulted in PVA biocomposites with lower water absorption. PVA film with 10 % TA absorbed about 90 % less water and PVA film with 10 % CNF and 10 % TA absorbed about 80 % less water than the neat PVA film after the films were soaked in water for one hour. The better properties of the composite films produced are due to hydrogen and ester bonds between the components of the composite, which was confirmed by FT-IR spectroscopy. Antioxidant effective films were also obtained due to the biologically active TA to the PVA and PVA/CNF systems.

Temporary Consolidation of Marine Artifact Based on Polyvinyl Alcohol/Tannic Acid Reversible Hydrogel

Underwater artefacts are vulnerable to damage and loss of archaeological information during the extraction process. To solve this problem, it is necessary to apply temporary consolidation materials to fix the position of marine artifacts. A cross-linked network hydrogel composed of polyvinyl alcohol (PVA), tannic acid (TA), borax, and calcium chloride has been created. Four hydrogels with varying concentrations of tannic acid were selected to evaluate the effect. The hydrogel exhibited exceptional strength, high adhesion, easy removal, and minimal residue. The PVA/TA hydrogel and epoxy resin were combined to extract waterlogged wooden artifacts and marine archaeological ceramics from a 0.4 m deep tank. This experiment demonstrates the feasibility of using hydrogel for the extraction of marine artifacts.

An overview to nanocellulose clinical application: Biocompatibility and opportunities in disease treatment

Recently, the demand for organ transplantation has promptly increased due to the enhanced incidence of body organ failure, the increasing efficiency of transplantation, and the improvement in post-transplant outcomes. However, due to a lack of suitable organs for transplantation to fulfill current demand, significant organ shortage problems have emerged. Developing efficient technologies in combination with tissue engineering (TE) has opened new ways of producing engineered tissue substitutes. The use of natural nanoparticles (NPs) such as nanocellulose (NC) and nano-lignin should be used as suitable candidates in TE due to their desirable properties. Many studies have used these components to form scaffolds and three-dimensional (3D) cultures of cells derived from different tissues for tissue repair. Interestingly, these natural NPs can afford scaffolds a degree of control over their characteristics, such as modifying their mechanical strength and distributing bioactive compounds in a controlled manner. These bionanomaterials are produced from various sources and are highly compatible with human-derived cells as they are derived from natural components. In this review, we discuss some new studies in this field. This review summarizes the scaffolds based on NC, counting nanocrystalline cellulose and nanofibrillated cellulose. Also, the efficient approaches that can extract cellulose with high purity and increased safety are discussed. We concentrate on the most recent research on the use of NC-based scaffolds for the restoration, enhancement, or replacement of injured organs and tissues, such as cartilage, skin, arteries, brain, and bone. Finally, we suggest the experiments and promises of NC-based TE scaffolds.

Establishing a Corrugated Carbon Network with a Crack Structure in a Hydrogel for Improving Sensing Performance

Electronic conductive hydrogels have prompted immense research interest as flexible sensing materials. However, establishing a continuous electronic conductive network within a hydrogel is still highly challenging. Herein, we develop a new strategy to establish a continuous corrugated carbon network within a hydrogel by embedding carbonized crepe paper into the hydrogel with its corrugations perpendicular to the stretching direction using a casting technique. The corrugated carbon network within the as-prepared composite hydrogel serves as a rigid conductive network to simultaneously improve the tensile strength and conductivity of the composite hydrogel. The composite hydrogel also generates a crack structure when it is stretched, enabling the composite hydrogel to show ultrahigh sensitivity (gauge factor = 59.7 and 114 at strain ranges of 0-60 and 60-100%, respectively). The composite hydrogel also shows an ultralow detection limit of 0.1%, an ultrafast response/recovery time of 75/95 ms, and good stability and durability (5000 cycles at 10% strain) when used as a resistive strain sensing material. Moreover, the good stretchability, adhesiveness, and self-healing ability of the hydrogel were also effectively retained after the corrugated carbon network was introduced into the hydrogel. Because of its outstanding sensing performance, the composite hydrogel has potential applications in sensing various human activities, including accurately recording subtle variations in wrist pulse waves and small-/large-scale complex human activities. Our work provides a new approach to develop economical, environmentally friendly, and reliable electronic conductive hydrogels with ultrahigh sensing performance for the future development of electronic skin and wearable devices.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

An introductory review on advanced multifunctional materials

This review summarizes the applications of some of the advanced materials. It included the synthesis of several nanoparticles such as metal oxide nanoparticles (e.g., Fe₃O₄, ZnO, ZrOSO₄, MoO_3-x, CuO, AgFeO₂, Co₃O₄, CeO₂, SiO₂, and CuFeO₂); metal hydroxide nanosheets (e.g., Zn₅(OH)₈(NO₃)₂·2H₂O, Zn(OH)(NO₃)·H₂O, and Zn₅(OH)₈(NO₃)₂); metallic nanoparticles (Ag, Au, Pd, and Pt); carbon-based nanomaterials (graphene, graphene oxide (GO), graphitic carbon nitride (g-C₃N₄), and carbon dots (CDs)); biopolymers (cellulose, nanocellulose, TEMPO-oxidized cellulose nanofibers (TOCNFs), and chitosan); organic polymers (e.g. covalent-organic frameworks (COFs)); and hybrid materials (e.g. metal-organic frameworks (MOFs)). Most of these materials were applied in several fields such as environmental-based technologies (e.g., water remediation, air purification, gas storage), energy (production of hydrogen, dimethyl ether, solar cells, and supercapacitors), and biomedical sectors (sensing, biosensing, cancer therapy, and drug delivery). They can be used as efficient adsorbents and catalysts to remove emerging contaminants e.g., inorganic (i.e., heavy metals) and organic (e.g., dyes, antibiotics, pesticides, and oils in water via adsorption. They can be also used as catalysts for catalytic degradation reactions such as redox reactions of pollutants. They can be used as filters for air purification by capturing carbon dioxide (CO₂) and volatile organic compounds (VOCs). They can be used for hydrogen production via water splitting, alcohol oxidation, and hydrolysis of NaBH₄. Nanomedicine for some of these materials was also included being an effective agent as an antibacterial, nanocarrier for drug delivery, and probe for biosensing.

Strong, conductive, and freezing-tolerant polyacrylamide/PEDOT:PSS/cellulose nanofibrils hydrogels for wearable strain sensors

Hydrogels with prominent flexibility, versatility, and high sensitivity play an important role in the design and fabrication of wearable sensors. In particular, these flexible conductive hydrogels exhibit elastic modulus that is highly compatible with human skin, demonstrating the great potential for flexible sensing. However, the preparation of high-performance hydrogel-based sensors that can restrain extreme cold conditions is still challenging. Herein, a novel anti-freezing composite hydrogel with superior conductivity based on polyacrylamide (PAM), LiCl, and PEDOT:PSS coated cellulose nanofibrils (PAM/PEDOT:PSS/CNF) is constructed. The addition of CNF increased the hydrogen bonding sites of the molecular chains in the micro, thus improving the mechanical strength and the conductivity of the hydrogel in the macro. The hydrogels achieve a high tensile strength of 0.19 MPa, compressive strength of 0.92 MPa, and dissipation energy of 41.9 kJ/m³. Otherwise, LiCl increases the interactions between the colloidal phase and water molecules, endowing the hydrogels with excellent freezing tolerance. Specifically, the optimized hydrogel of 45 % LiCl exhibited stable mechanical properties at -40 °C. Finally, the composite hydrogel was used to assemble flexible sensors with high sensitivity of 10.3 MPa^-1, which can detect a wide range of human movements and physiological activities.

Functional Enhancement of Guar Gum−Based Hydrogel by Polydopamine and Nanocellulose

The development of green, biomedical hydrogels using natural polymers is of great significance. From this viewpoint, guar gum (GG) has been widely used for hydrogel preparation; however, its mechanical strength and adhesion often cannot satisfy the biomedical application. Therefore, in the present study, gelatin and a cellulose nanocrystal (CNC) were first applied to overcome the defects of guar gum hydrogel. Dopamine was self−polymerized into polydopamine (PDA) on the gelatin chain at alkaline condition, and gelatin−polydopamine (Gel−PDA) further cross−linked with guar gum and CNC via the borate−didiol bond, intramolecular Schiff base reaction, and Michael addition. CNC not only interacted with guar gum using borate chemistry but also acted as a mechanical reinforcer. The obtained Gel−PDA+GG+CNC hydrogel had an excellent self−healing capacity, injectability, and adhesion due to the catechol groups of PDA. Moreover, dopamine introduction caused a significant increase in the anti−oxidant activity. This hydrogel was cyto− and hemo−compatible, which implies a potential usage in the medical field.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

3D Printable Self-Adhesive and Self-Healing Ionotronic Hydrogels for Wearable Healthcare Devices

Ionotronic hydrogels have attracted significant attention in emerging fields such as wearable devices, flexible electronics, and energy devices. To date, the design of multifunctional ionotronic hydrogels with strong interfacial adhesion, rapid self-healing, three-dimensional (3D) printing processability, and high conductivity are key requirements for future wearable devices. Herein, we report the rational design and facile synthesis of 3D printable, self-adhesive, self-healing, and conductive ionotronic hydrogels based on the synergistic dual reversible interactions of poly(vinyl alcohol), borax, pectin, and tannic acid. Multifunctional ionotronic hydrogels exhibit strong adhesion to various substrates with different roughness and chemical components, including porcine skin, glass, nitrile gloves, and plastics (normal adhesion strength of 55 kPa on the skin). In addition, the ionotronic hydrogels exhibit intrinsic ionic conductivity imparting strain-sensing properties with a gauge factor of 2.5 up to a wide detection range of approximately 2000%, as well as improved self-healing behavior. Based on these multifunctional properties, we further demonstrate the use of ionotronic hydrogels in the 3D printing process for implementing complex patterns as wearable strain sensors for human motion detection. This study is expected to provide a new avenue for the design of multifunctional ionotronic hydrogels, enabling their potential applications in wearable healthcare devices.

Wearable Hydrogel-Based Epidermal Sensor with Thermal Compatibility and Long Term Stability for Smart Colorimetric Multi-Signals Monitoring

Hydrogel-based wearable epidermal sensors (HWESs) have attracted widespread attention in health monitoring, especially considering their colorimetric readout capability. However, it remains challenging for HWESs to work at extreme temperatures with long term stability due to the existence of water. Herein, a wearable transparent epidermal sensor with thermal compatibility and long term stability for smart colorimetric multi-signals monitoring is developed, based on an anti-freezing and anti-drying hydrogel with high transparency (over 90% transmittance), high stretchability (up to 1500%) and desirable adhesiveness to various kinds of substrates. The hydrogel consists of polyacrylic acid, polyacrylamide, and tannic acid-coated cellulose nanocrystals in glycerin/water binary solvents. When glycerin readily forms strong hydrogen bonds with water, the hydrogel exhibits outstanding thermal compatibility. Furthermore, the hydrogel maintains excellent adhesion, stretchability, and transparency after long term storage (45 days) or at subzero temperatures (-20 °C). For smart colorimetric multi-signals monitoring, the freestanding smart colorimetric HWESs are utilized for simultaneously monitoring the pH, T and light, where colorimetric signals can be read and stored by artificial intelligence strategies in a real time manner. In summary, the developed wearable transparent epidermal sensor holds great potential for monitoring multi-signals with visible readouts in long term health monitoring.

An injectable and self-healing cellulose nanofiber-reinforced alginate hydrogel for bone repair

Biomedical materials are in high demand for transplantation in cases of diseased or damaged bone tissue. Hydrogels are potential candidates for bone defect repair; however, traditional hydrogels lack the necessary strength and multiple functions. Herein, we effectively synthesized a cellulose nanofiber (CNF)-reinforced oxidized alginate (OSA)/gelatin (Gel) semi-interpenetrating network hydrogel through a facile one-step approach without a cross-linker by using the synergistic effects of dynamic imine bonds and hydrogen bonds. The OSA/Gel/CNF sample showed a notable compressive modulus (up to 361.3 KPa). The gelation time (~150 s) ensured excellent injectability. Self-healing exhibited a high efficiency of up to 92 %, which would enable minimally invasive, dynamic adjustments and personalized therapies. Furthermore, the OSA/Gel/CNF hydrogel showed excellent biomineralization (Ca/P ratio ~ 1.69) and enhanced preosteoblast cell (MC3T3-E1) viability (over 96 %), proliferation, and osteogenic differentiation. Thus, this multifunctional hydrogel has promising potential for using in the bone tissue repairs.

Robust hydrogel adhesives for emergency rescue and gastric perforation repair

Development of biocompatible hydrogel adhesives with robust tissue adhesion to realize instant hemorrhage control and injury sealing, especially for emergency rescue and tissue repair, is still challenging. Herein, we report a potent hydrogel adhesive by free radical polymerization of N-acryloyl aspartic acid (AASP) in a facile and straightforward way. Through delicate adjustment of steric hindrance, the synergistic effect between interface interactions and cohesion energy can be achieved in PAASP hydrogel verified by X-ray photoelectron spectroscopy (XPS) analysis and simulation calculation compared to poly (N-acryloyl glutamic acid) (PAGLU) and poly (N-acryloyl amidomalonic acid) (PAAMI) hydrogels. The adhesion strength of the PAASP hydrogel could reach 120 kPa to firmly seal the broken organs to withstand the external force with persistent stability under physiological conditions, and rapid hemostasis in different hemorrhage models on mice is achieved using PAASP hydrogel as physical barrier. Furthermore, the paper-based Fe³⁺ transfer printing method is applied to construct PAASP-based Janus hydrogel patch with both adhesive and non-adhesive surfaces, by which simultaneous wound healing and postoperative anti-adhesion can be realized in gastric perforation model on mice. This advanced hydrogel may show vast potential as bio-adhesives for emergency rescue and tissue/organ repair.

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The hydrogel with good mechanical properties and adhesiveness is designed.

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The hydrogel adhesive can act as physical barrier for emergency rescue.

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The Janus hydrogel can realize efficient gastric perforation repair on mice.

Self-Healing Hydrogels: Development, Biomedical Applications, and Challenges

Polymeric hydrogels have drawn considerable attention as a biomedical material for their unique mechanical and chemical properties, which are very similar to natural tissues. Among the conventional hydrogel materials, self-healing hydrogels (SHH) are showing their promise in biomedical applications in tissue engineering, wound healing, and drug delivery. Additionally, their responses can be controlled via external stimuli (e.g., pH, temperature, pressure, or radiation). Identifying a suitable combination of viscous and elastic materials, lipophilicity and biocompatibility are crucial challenges in the development of SHH. Furthermore, the trade-off relation between the healing performance and the mechanical toughness also limits their real-time applications. Additionally, short-term and long-term effects of many SHH in the in vivo model are yet to be reported. This review will discuss the mechanism of various SHH, their recent advancements, and their challenges in tissue engineering, wound healing, and drug delivery.

Anti-Fouling, Adhesive Polyzwitterionic Hydrogel Electrodes Toughened Using a Tannic Acid Nanoflower

Conductive polyzwitterionic hydrogels with good adhesion properties show potential prospect in implantable electrodes and electronic devices. Adhesive property of polyzwitterionic hydrogels in humid environments can be improved by the introduction of catechol groups. However, common catechol modifiers can usually quench free radicals, resulting in a contradiction between long-term tissue adhesion and hydrogel toughness. By adding tannic acid (TA) to the dispersion of clay nanosheets and nanofibers, we designed TA-coated nanoflowers and nanofibers as the reinforcing phase to prepare polyzwitterionic hydrogels with adhesion properties. The hydrogel combines the mussel-like and zwitterionic co-adhesive mechanism to maintain long-term adhesion in underwater environments. In particular, the noncovalent cross-linking provided by the nanoflower structure effectively compensates for the defects caused by free-radical quenching so that the hydrogel obtained a high stretchability of over 2900% and a toughness of 1.16 J/m³. The hydrogel also has excellent anti-biofouling property and shows resistance to bacteria and cells. In addition, the hydrogel possesses a low modulus (<10 kPa) and ionic conductivity (0.25 S/m), making it an ideal material for the preparation of implantable electrodes.

Combination wound healing using polymer entangled porous nanoadhesive hybrids with robust ROS scavenging and angiogenesis properties

Nanoadhesives can achieve tight wound closure by connecting biomacromolecules from both sides. However, previously developed adhesive systems suffered from suboptimal wound healing efficiency due to the lack of interparticle cohesion, sufficient reactive oxygen species (ROS)-scavenging sites, and angiogenesis consideration. Herein, we developed a polymer entangled porous nanoadhesive system to address the above challenge by synergy of three functional components. Firstly, hybrid mesoporous silica nanoparticles with highly integrated polydopamine (MS-PDA) were prepared by templated synthesis. The entangling between PVA polymer and MS-PDA contributed to much stronger cohesion between nanoparticles, which led to 75% larger adhesion strength. As confirmed by in vitro and in vivo evaluations, the highly exposed catechol groups boosted the scavenging activity of ROS (1.8-4.1 fold enhancement as compared with nonporous counterpart). Consequently, more macrophages exhibited anti-inflammatory phenotype, leading to 2-2.6 fold lower pro-inflammatory cytokine levels. Moreover, the sustained release of bioactive SiO₄^4- by the disintegration of nanoparticles contributed to ∼3-fold higher expression of VEGF and enhanced new blood vessel formation, as well as better wound repair. This platform can provide a new paradigm for developing multifunctional nanoadhesive systems in treating skin wounds. STATEMENT OF SIGNIFICANCE: PVA polymer entangled mesoporous nanoadhesives of polydopamine (PDA)/silica hybrids with the combination of excellent wound closure effect, boosted ROS-scavenging activity, and significant angiogenesis ability were developed for improving the suboptimal skin wound healing efficiency. This strategy not only greatly advances our ability to rationally integrate repairing elements in nanoadhesives for manipulating combined processes of interfacial events during wound healing, but also offers general implications toward application of polymers to reinforce the adhesion strength in nanoadhesive systems. In addition, our findings on the impacts of pore effects mediated ROS species conversion and polymer entanglement may also trigger great interests and facilitate the development/broad application of therapeutic adhesives.

Tannic acid: a versatile polyphenol for design of biomedical hydrogels

Tannic acid (TA), a natural polyphenol, is a hydrolysable amphiphilic tannin derivative of gallic acid with several galloyl groups in its structure. Tannic acid interacts with various organic, inorganic, hydrophilic, and hydrophobic materials such as proteins and polysaccharides via hydrogen bonding, electrostatic, coordinative bonding, and hydrophobic interactions. Tannic acid has been studied for various biomedical applications as a natural crosslinker with anti-inflammatory, antibacterial, and anticancer activities. In this review, we focus on TA-based hydrogels for biomaterials engineering to help biomaterials scientists and engineers better realize TA's potential in the design and fabrication of novel hydrogel biomaterials. The interactions of TA with various natural or synthetic compounds are deliberated, discussing parameters that affect TA-material interactions thus providing a fundamental set of criteria for utilizing TA in hydrogels for tissue healing and regeneration. The review also discusses the merits and demerits of using TA in developing hydrogels either through direct incorporation in the hydrogel formulation or indirectly via immersing the final product in a TA solution. In general, TA is a natural bioactive molecule with diverse potential for engineering biomedical hydrogels.

A Review of Properties of Nanocellulose, Its Synthesis, and Potential in Biomedical Applications

Cellulose is the most venerable and essential natural polymer on the planet and is drawing greater attention in the form of nanocellulose, considered an innovative and influential material in the biomedical field. Because of its exceptional physicochemical characteristics, biodegradability, biocompatibility, and high mechanical strength, nanocellulose attracts considerable scientific attention. Plants, algae, and microorganisms are some of the familiar sources of nanocellulose and are usually grouped as cellulose nanocrystal (CNC), cellulose nanofibril (CNF), and bacterial nanocellulose (BNC). The current review briefly highlights nanocellulose classification and its attractive properties. Further functionalization or chemical modifications enhance the effectiveness and biodegradability of nanocellulose. Nanocellulose-based composites, printing methods, and their potential applications in the biomedical field have also been introduced herein. Finally, the study is summarized with future prospects and challenges associated with the nanocellulose-based materials to promote studies resolving the current issues related to nanocellulose for tissue engineering applications.

Materials with Tunable Optical Properties for Wearable Epidermal Sensing in Health Monitoring

Advances in wearable epidermal sensors have revolutionized the way that physiological signals are captured and measured for health monitoring. One major challenge is to convert physiological signals to easily readable signals in a convenient way. One possibility for wearable epidermal sensors is based on visible readouts. There are a range of materials whose optical properties can be tuned by parameters such as temperature, pH, light, and electric fields. Herein, this review covers and highlights a set of materials with tunable optical properties and their integration into wearable epidermal sensors for health monitoring. Specifically, the recent progress, fabrication, and applications of these materials for wearable epidermal sensors are summarized and discussed. Finally, the challenges and perspectives for the next generation wearable devices are proposed.

Stretchable solvent-free ionic conductor with self-wrinkling microstructures for ultrasensitive strain sensor

Stretchable solvent-free ionic conductors with outstanding physicochemical stability are attractive in emerging sensing devices. However, existing ionic conductors struggle to keep high strain sensitivity with a gauge factor (GF) smaller than 4 at a strain range of up to 100%, which seriously affects the reliability of the signal output. Herein, we prepared a novel solvent-free ionic conductor, consisting of a hybrid cross-linked polymer network and mobile ions. Exquisite reticular wrinkling microstructures with ion channels were formed spontaneously by utilizing modulus mismatch in shrinkage during polymerization. The ion channels promote the ionic transport in the polymer, and the reticular wrinkling microstructures dramatically reinforce the mechanical stability and enhance energy dissipation. After being carefully optimized, the as-prepared ionic conductor demonstrated many unique advantages including perfect physicochemical stability, wide operating temperature range, the high ionic conductivity of 1.17 mS cm^-1 at 15 °C and excellent sensitivity with GF as high as 7.03 at 100% strain. Moreover, benefiting from the abundant hydrogen bonds and ionic interactions in the polymer network, the ionic conductor also possesses self-healable and adhesion ability. The resulting devices can be used for quantitative evaluation of human joint motion and exhibit great potential in soft electronics or iontronics.

Superabsorbent cellulose-based hydrogels cross-liked with borax

Cellulose, the most abundant biopolymer on Earth, has been widely attracted owing to availability, intoxicity, and biodegradability. Environmentally friendly hydrogels were successfully prepared from water hyacinth-extracted cellulose using a dissolution approach with sodium hydroxide and urea, and sodium tetraborate decahydrate (borax) was used to generate cross-linking between hydroxyl groups of cellulose chains. The incorporation of borax could provide the superabsorbent feature into the cellulose hydrogels. The uncross-linked cellulose hydrogels had a swelling ratio of 325%, while the swelling ratio of the cross-linked hydrogels could achieve ~ 900%. With increasing borax concentrations, gel fraction of the cross-linked hydrogels increased considerably. Borax also formed char on cellulose surfaces and generated water with direct contact with flame, resulting in flame ignition and propagation delay. Moreover, the cross-linked cellulose-based hydrogels showed antibacterial activity for gram-positive bacteria (S. aureus). The superabsorbent cross-linked cellulose-based hydrogels prepared in this work could possibly be used for wound dressing, agricultural, and flame retardant coating applications.

Cellulose-Based Nanomaterials Advance Biomedicine: A Review

There are various biomaterials, but none fulfills all requirements. Cellulose biopolymers have advanced biomedicine to satisfy high market demand and circumvent many ecological concerns. This review aims to present an overview of cellulose knowledge and technical biomedical applications such as antibacterial agents, antifouling, wound healing, drug delivery, tissue engineering, and bone regeneration. It includes an extensive bibliography of recent research findings from fundamental and applied investigations. Cellulose-based materials are tailorable to obtain suitable chemical, mechanical, and physical properties required for biomedical applications. The chemical structure of cellulose allows modifications and simple conjugation with several materials, including nanoparticles, without tedious efforts. They render the applications cheap, biocompatible, biodegradable, and easy to shape and process.

Highly Conformal Polymers for Ambulatory Electrophysiological Sensing

Stable ambulatory electrophysiological sensing is widely utilized for smart e-healthcare monitoring, clinical diagnosis of cardiovascular diseases, treatment of neurological diseases, and intelligent human-machine interaction. As the favorable signal interaction platform of electrophysiological sensing, the conformal property of on-skin electrodes is an extremely crucial factor that can affect the stability of long-term ambulatory electrophysiological sensing. From the perspective of materials, to realize conformal contact between electrodes and skin for stable sensing, highly conformal polymers are strongly demanding and attracting ever-growing attention. In this review, we focused on the recent progress of highly conformal polymers for ambulatory electrophysiological sensing, including their synthetic methods, conformal property, and potential applications. Specifically, three main types of highly conformal polymers for stable long-term electrophysiological signals monitoring were proposed, including nature silk fibroin based conformal polymers, marine mussels bio-inspired conformal polymers, and other conformal polymers such as zwitterionic polymers and polyacrylamide. Furthermore, the future challenges and opportunities of preparing highly conformal polymers for on-skin electrodes were also highlighted. This article is protected by copyright. All rights reserved.

Biomimetic Strain-Stiffening in Chitosan Self-Healing Hydrogels

The strain-stiffening and self-healing capabilities of biological tissues enable them to preserve the structures and functions from deformation and damage. However, biodegradable hydrogel materials with both of these biomimetic characteristics have not been explored. Here, a series of strain-stiffened, self-healing hydrogels are developed through dynamic imine crosslinking of semiflexible O-carboxymethyl chitosan (main chain) and flexible dibenzaldehyde-terminated telechelic poly(ethylene glycol) (crosslinker). The biomimetic hydrogels can be reversibly stiffened to resist the deformation and can even recover to their original state after repeated damages. The mechanical properties and stiffening responses of the hydrogels are tailored by varying the component contents (1-3%) and the crosslinker length (4 or 8 kDa). A combinatorial system of in situ coherent small-angle X-ray scattering with rheological testing is developed to investigate the network structures (in sizes 1.5-160 nm) of hydrogels under shear strains and reveals that the strain-stiffening originates from the fibrous chitosan network with poly(ethylene glycol) crosslinking fixation. The biomimetic hydrogels with biocompatibility and biodegradability promote wound healing. The study provides an insight into the nanoscale design of biomimetic strain-stiffening self-healing hydrogels for biomedical applications.

Polyphenol-based hydrogels: Pyramid evolution from crosslinked structures to biomedical applications and the reverse design

As a kind of nature-derived bioactive materials, polyphenol-based hydrogels possess many unique and outstanding properties such as adhesion, toughness, and self-healing due to their specific crosslinking structures, which have been widely used in biomedical fields including wound healing, antitumor, treatment of motor system injury, digestive system disease, oculopathy, and bioelectronics. In this review, starting with the classification of common polyphenol-based hydrogels, the pyramid evolution process of polyphenol-based hydrogels from crosslinking structures to derived properties and then to biomedical applications is elaborated, as well as the efficient reverse design considerations of polyphenol-based hydrogel systems are proposed. Finally, the existing problems and development prospects of these hydrogel materials are discussed. It is hoped that the unique perspective of the review can promote further innovation and breakthroughs of polyphenol-based hydrogels in the future.

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Polyphenol-based hydrogels combine advantages of polyphenols with common hydrogels.

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Cognition of such hydrogels underwent from structures to properties to applications.

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Various crosslinked structures of such hydrogels can derive outstanding properties.

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Such hydrogels can be widely used in biomedicine due to the outstanding properties.

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Reverse design thought from applications to properties to structures is promising.

Bio-based and bio-inspired adhesives from animals and plants for biomedical applications

With the "many-headed" slime mold Physarum polycelphalum having been voted the unicellular organism of the year 2021 by the German Society of Protozoology, we are reminded that a large part of nature's huge variety of life forms is easily overlooked - both by the general public and researchers alike. Indeed, whereas several animals such as mussels or spiders have already inspired many scientists to create novel materials with glue-like properties, there is much more to discover in the flora and fauna. Here, we provide an overview of naturally occurring slimy substances with adhesive properties and categorize them in terms of the main chemical motifs that convey their stickiness, i.e., carbohydrate-, protein-, and glycoprotein-based biological glues. Furthermore, we highlight selected recent developments in the area of material design and functionalization that aim at making use of such biological compounds for novel applications in medicine - either by conjugating adhesive motifs found in nature to biological or synthetic macromolecules or by synthetically creating (multi-)functional materials, which combine adhesive properties with additional, problem-specific (and sometimes tunable) features.

Research progress of smart response composite hydrogels based on nanocellulose

In recent years, smart-responsive nanocellulose composite hydrogels have attracted extensive attention due to their unique porous substrate, hydrophilic properties, biocompatibility and stimulus responsiveness. At present, the research on smart response nanocellulose composite hydrogel mainly focuses on the selection of composite materials and the construction of internal chemical bonds. The common composite materials and connection methods used for preparation of smart response nanocellulose composite hydrogels are compared according to the different types of response sources such as temperature, pH and so on. The response mechanisms and the application prospects of different response types of nanocellulose composite hydrogels are summarized, and the transformation of internal ions, functional groups and chemical bonds, as well as the changes in mechanical properties such as modulus and strength are discussed. Finally, the shortcomings and application prospects of nanocellulose smart response composite hydrogels are summarized and prospected.