Construction Methods And Biological Applications Of Cellulose Nanocrystals Materials Loaded With High-load Metal Ion

Cellulose nanocrystals（CNC）,which are one-dimensional rod-shaped rigid nanomaterials with high aspect ratio and high crystallinity,have attracted extensive attention in biomedicine,plant protection and other fields due to their high biocompatibility,biodegradability,low toxicity and easy modification.Metal elements and their nanoparticles have unique application value in the above-mentioned fields such as integration of tumor diagnosis and treatment and plant antibacterial,antiviral and growth promotion,but there are trade-offs between efficacy,dosage and toxicity.The"dimension/shape/template"effect of CNC can realize the functional enhancement of the coupled functional elements during application.However,The technology of CNC coupling with metal elements is not mature enough,and the theory of application of enhanced functions in the above-mentioned fields is not perfect.In this paper,we used the advantages of"dimension/morphology/template"effect,high chemical activity and biocompatibility of CNC to couple functional Mn²⁺or Fe²⁺or Cu⁺on its surface and regulate the ion loading density.On the one hand,we built the CNC based functional carriers and developed chemical modification methods of CNC materials to clarify the synergistic effect of CNC and different functional substances.On the other hand,we explored the"dimension/morphology/template"effect of CNC and the relationship between the dispersion and distribution of functional substances on the constructed surface and functional efficiency,revealing the synergistic mechanism of functional substances on magnetic resonance imaging and photothermal conversion,as well as plant anti-bacterial,anti-virus and growth promotion.The specific research contents and results are as follows:（1）Taking advantage of the"dimension/morphology/template"effect,high chemical activity and biocompatibility of CNC,a series of high metal ion loaded cellulose nanocrystalline materials with controllable loading were constructed.Firstly,the modified method of anhydride esterification and ion complexation was used to construct Mn²⁺loaded CNC nanoparticles with adjustable density(Mn²⁺@DCNC).The loading amount of Mn²⁺in dcnc nanoparticles can be controlled between 0.213%and 0.325%,and the modified dcnc nanoparticles still maintain rod-shaped structure and have a high aspect ratio（17～19）.Then,using polydopamine（PDA）with complexing ability and photothermal conversion function as a bridge,using CNC as a template to construct rod-shaped manganese-based nano-formulations(Mn²⁺@PCNC)with integrated and synergistically enhanced MRI imaging and photothermal conversion functions.The loading of Mn²⁺in Mn²⁺@PCNC could be controlled between 0.179%and 3.324%and the Mn²⁺@PCNC nanoparticle still maintains the rod shape.Finally,by using the redox reaction between DA and Fe³⁺or Cu²⁺,DA was oxidized to form the coating process of PDA on CNC,and the reduced Fe²⁺or Cu⁺was complexed at the same time to construct the low valence nanoparticles.After 14 days of exposure to oxygen,the Fe²⁺/Fe³⁺or Cu²⁺/Cu⁺ratios of nanoparticles were 0.94 or 1.32,respectively,which still contained high content of low valent metal ions.（2）The two kinds of Mn based nano materials constructed in（1）were explored in the field of magnetic resonance and photothermal conversion.The theoretical analysis results show that the longitudinal relaxation（r₁）produced by Mn²⁺-H⁺interaction can be improved by the rod morphology,and the improvement depends on the degree of Mn²⁺complexation on the rod particles.The experimental data show that r₁ increases linearly with the amount of Mn²⁺loaded on Mn²⁺@DCNC nanoparticles,up to 57.71m M^-1·s^-1.The cytotoxicity of Mn²⁺@DCNC nanoparticles to raw 264.7 and HUVEC was low,and the survival rate of both cells was higher than 80%.At the same time,the in vitro MRI relaxation rate of the Mn²⁺@PCNC nanoparticles constructed by extending the modification method showed that with the increase of Mn²⁺content,r₁ first increased and then decreased,and the highest reached 36.45 m M^-1·s^-1.The Mn²⁺@PCNC nanoparticles also have a significant photothermal conversion efficiency,the highest photothermal conversion efficiency can reach 44.4%,which has a potential effect of photothermal treatment of tumor.（3）The antibacterial,antiviral and growth promoting properties of cellulose nanocrystals with high metal loading were studied.The results showed that the Mn²⁺@DCNC nanoparticles had significant anti TMV effect and could act on the replication and transfer of TMV.The Fe²⁺@DCNC nanoparticles could promote the growth of tobacco plants,especially the growth of leaves and roots.And the Cu⁺@PCNC had a certain effect on inhibiting the growth and reproduction of Phytophthora capsici and Alternaria alternata,and affecting the hypha morphology and reproduction of Pseudomonas syringae pv.tabac.Therefore,the nano materials that we constructed have certain anti TMV,promoting plant growth and antibacterial effect,and also have good biocompatibility,environmental protection and biodegradability,which has application value in different plant protection fields.In conclusion,the study achieved the regulation of functional materials and load on CNC surface by coupling functional Mn²⁺or Fe²⁺or Cu⁺,which maked the nano materials of CNC had synergistic effect.This study enriched the surface chemical modification methods and enhanced the controllable preparation technology of CNC,developed its application prospects in the fields of tumor diagnosis and co-treatment,plant virus prevention and growth promotion,and gave the potential of application of CNC based functional materials in biomedical plant protection.