Preparation And Application For Robust And Self-healable Nanocellulose Composite Hydrogels

Cellulose is the most abundant natural polymer polysaccharide on the earth,featured with green environmental protection,wide range of sources and sustainable circulation,which is an ideal raw material for the preparation of hydrogel.However,cellulose-based hydrogels are usually limited by their poor mechanical properties.Profitted by the natural crystalline structure,high modulus of elasticity,good modification and biocompatibility,nanocellulose can be introduced into composite hydrogel networks to enhance the mechanical properties.In addition,the gel material will inevitably produce cracks in the practical applications,thus it is necessary to afford the gel with self-healing properties to repair damage,maintaining the integrity of structure and function and prolonging the service life of the material.Unfortunately,there is still a trade-off between self-healing capability and mechanical property because reversible healing benefits from weak and dynamic interactions but strong and stable interactions favor the mechanical properties.Therefore,it is of substantial need,but often challenging,to design an integrated cellulose-based hydrogel with a unique combination of remarkable mechanical properties and autonomous self-healing property.Dynamic non-covalent interactions with reversible nature are critical for the integral synthesis of self-healing biological materials,thus we develop a simple one-pot strategy to prepare a fully physically cross-linked nanocomposite hydrogel through the formation of the hydrogen bonds and dual metal-carboxylate coordination bonds within supramolecular networks,in which iron ions(Fe³⁺)and TEMPO oxidized cellulose nanofibrils(CNFs)acted as cross-linkers and led to the integration of excellent mechanical strength and self-healing property.The hydrogen bonds tend to preferentially break prior to the coordination bonds associated complexes that act as skeleton to maintain primary structure integrity,and the survived coordination bonds with dynamic feature also serve as sacrificial bonds to dissipate another amount of energy after the rupture of hydrogen bonds,which collectively maximizing the contribution of sacrificial bonds to energy dissipation while affording elasticity.Additionally,the multiple non-covalent interactions in diverse types synergistically serve as dynamic but highly stable associations,leading to the effective self-healing efficiency.We expect that this facile strategy of incorporating the biocompatible and biodegradable CNFs as building blocks may enrich the avenue in exploration of dynamic and tunable cellulosic hydrogels to expand their potential applications in the biomedical field.Inspired by mussel-inspired adhesive mechanism,we design a tough,self-healing and self-adhesive ionic gel by constructing synergistic multiple coordination bonds among tannic acid-coated cellulose nanocrystals(TA@CNCs),poly(acrylic acid)chains and metal ions in a covalent polymer network.The incorporated TA@CNC acts as a dynamic connected bridge in the hierarchically porous network mediated by multiple coordination bonds,endowing the ionic gels the superior mechanical performance.Reversible nature of dynamic coordination interactions leads to excellent recovery property as well as reliable mechanical and electrical self-healing property.Intriguingly,the ionic gels display durable and repeatable adhesiveness ascribed to the presence of catechol groups from the incorporated tannic acid,which can be adhered directly on human skin without inflammatory response and residual.Additionally,the ionic gels with a great strain sensitivity can be employed as flexible strain sensors to monitor and distinguish both large motion and subtle motions.This work provides a new prospect for the design of the biocompatible cellulose-based hydrogels with stretchable,self-adhesive,self-healing and strain sensitive properties for potential applications in wearable electronic sensors and healthcare monitoring.Mimicking the mechanical and sensory properties of human skin to develop a highly conformable electronic skin that integrated with robust,self-healable,and ultra-sensitive properties is promising but still a great challenge.In this work,we report a novel dynamic self-adhesive and self-healable conductive hydrogel material that is applicable to highly conformal and ultrasensitive electronic skin devices.In the obtained gel system,the incorporated tannic acid coated cellulose nanocrystals(TA@CNCs)acts as dynamic reinforcing bridges in the dual cross-linked gel network that mediated by reversible hydrogen bonds and electrostatic interactions,allowing an unique combination of superior mechanical performance and reliable autonomous self-healing capability(HE>90%).The formation of conductive polyaniline(PANI)network in the obtained TC-Gel leads to both high conductivity and high sensitivity,which are advantageous for the real-time detection of large human motions,tiny muscle movements,and physiological signals.Notably,the TC-Gel exhibits the dynamic self-adhesive performance that integrates with both strong adhesion and easy detachment in water for 3 min.As a proof of concept,we demonstrate that this unique self-adhesive strategy is able to increase interface interlocking and conformal contact between TC-Gel based sensor and dynamic biological surface,contributing to the high sensory performance with a low noise level and negligible baseline fluctuation.We envisage that this work broads a new avenue for designing the multifunctional cellulosic-based hydrogels to promote the application of integrated electronic skin with high sensory properties and comfortable user experiences.Despite self-healing gels with structural resemblance to biological tissues attract great attention in biomedical field,it remains a dilemma for combination between fast self-healing properties and high mechanical toughness.Based on the design of dynamic reversible cross-links,we incorporate rigid tannic acid-coated cellulose nanocrystal(TA@CNC)motifs into the poly(vinyl alcohol)(PVA)-borax dynamic networks for the fabrication of a high toughness and rapidly self-healing nanocomposite(NC)hydrogel,together with dynamically adhesive and strain stiffening properties that are particularly indispensable for practical application in soft tissues substitutes.The results demonstrate that the obtained NC gels present a highly interconnected network,where flexible PVA chains wrap onto the rigid TA@CNC motifs and form the dynamic TA@CNC-PVA clusters associated by hydrogen bonds,affording the critical mechanical toughness.Moreover,the obtained NC hydrogels not only mimic the main feature of biological tissue with the unique strain stiffening behavior,but also display unique dynamic adhesiveness to nonporous and porous substrates.It is expected that this versatile approach opens up a new prospect for the rational design of multifunctional cellulosic hydrogels with remarkable performance to expand their applications.