Study On Functional Nano-polysaccharide Microfiber Composite Hydrogel

Hydrogels are a class of three-dimensional networks formed by hydrophilic polymer chains embedded in a water-rich environment with widely tunable physical and chemical properties.The water-rich nature of hydrogels makes them widely used in tissue engineering,drug delivery,soft electronics,and other fields.Conventional hydrogels have limited mechanical properties and are prone to permanent breakage,limiting the functionalization of hydrogels.Cellulose is an abundant,green,renewable,and biodegradable polymer.Cellulose is important in the synthesis of bio-based hydrogels or soft materials for various applications.Microfibrillated cellulose（MFC）is an ideal material for hydrogel reinforcement due to its extremely large aspect ratio,intertransferred network structure,and high mechanical properties.In this paper,microcrystalline cellulose was used as raw material.MFC was prepared by alkali treatment followed by high pressure homogenization.Then dialdehyde microfibrillated cellulose（DAMFC）was prepared by sodium periodate oxidation.Using DAMFC as the backbone and crosslinking agent,functional nanopolysaccharide fiber composite hydrogels were prepared through a series of physical and chemical methods.（1）High mechanical strength DAMFC/PVA composite hydrogelDAMFC was compounded with polyvinyl alcohol（PVA）to produce DAMFC/PVA composite hydrogel.With a chemical-physical combination method,DAMFC/PVA hydrogel showed high compressive strength.In this composite hydrogel,DAMFC acts as a cross-linking agent.An acetal reaction takes place between the aldehyde groups on the surface of DAMFC and the hydroxyl groups on PVA macromolecular chains.Due to the covalent bonds between the reinforcing agent and the matrix polymer,DAMFC can bear the stress efficiently and improve the mechanical properties of the hydrogel.DAMFC/PVA hydrogel was soaked in various salt solution to improve the mechanical properties further.The results showed that SO₄^2-ion soaking can significantly enhance the mechanical properties of DAMFC/PVA hydrogels.When the mass ratio of PVA to DAMFC was 15%,DAMFC exhibited the best enhancing effect,showing a compressive strength of 5.819 MPa,35 times of that of the unsoaked hydrogel.The SEM results show that the interior of the composite hydrogel presents a three-dimensional network-like dendritic structure and a honeycomb structure.The shape and size of the pores vary with the immersion ions,and the size of the pores shows the law of H₂O>Cl^->CO₃^2->SO₄^2-.With excellent mechanical strength and three-dimensional network structure,the investigated DAMFC/PVA composite hydrogel shows a promising application prospect in wound dressings.（2）Multi-functional DAMFC/ChN/gel hybrid composite hydrogelChitin nanofibers（ChNs）were prepared by TEMPO oxidation-high pressure homogenization method.The DAMFC/ChN/gel hybrid composite hydrogel was prepared by compounding dialdehyde microfibrillated cellulose（DAMFC）,gelatin（gel）and chitin（ChN）.Due to the large difference in diameter and aspect ratio of ChN and DAMFC,a synergistic reinforcing effect was observed in DAMFC/ChN/gel hybrid composite hydrogel.A giant network structure was formed as the result of the Schiff-base reaction between the aldehyde groups of DAMFC fibrils and the amino groups of gelatin chains.DAMFC formed the backbone in the hydrogel and play the role of bearing the main load.ChN dispersed in the network.Chitin has excellent mechanical strength and ChN whiskers also may block the spreading of the micro cracks in the system ChN whiskers,contributing to the mechanical properties.The mechanical strength of the composite hydrogel was greatly improved by the synergistic enhancement of the hybrid effect.The dynamic Schiff-base bonds endows the hydrogel good self-healing property.The DAMFC/ChN/gel hydrogels were soaked in ions.The Hofmeister effect results in a greater mechanical strength.The introduction of ions endows the hydrogel good ion conductivity and freeze tolerance.The investigated multi-functional all natural polymer-based hydrogel has potential in flexible electronics and biomedical fields.（3）PA/DAMFC/gel composite hydrogel with adhesive,antibacterial and antioxidant propertiesUsing the method of physical blending,procyanidin（PA）was added to DAMFC/gelatin system to prepare high-strength composite hydrogels with adhesion,antibacterial and antioxidant properties.Proanthocyanidins can form hydrogen bonds with gelatin and DAMFC and play the role of physical cross-linking,thereby enhancing the mechanical strength of the composite hydrogel.Compression and tensile experiments showed that both the compressive stress and tensile fracture stress of the composite hydrogels increased with the increase of PA content.The compressive stress of the composite hydrogel under 85%strain reaches 3.681 MPa,and the tensile fracture stress reaches 76.900 k Pa.SEM results show that the introduction of PA gives the composite hydrogel a denser pore structure,thereby improving its mechanical properties.The ortho-diphenol hydroxyl structure of PA endows the composite hydrogel with excellent adhesion properties and antioxidant properties.The presence of PA enables the composite hydrogel effectively inhibit the growth of Staphylococcus aureus and Escherichia coli.