| With the rapid development of nanomedicine,nanomaterials have shown unique advantages in tumor diagnosis and treatment,and have become one of the spotlight fields of precision and personalized medicine technologies and biomedical materials.The development trend of current research lies in multi-function integration and the integration of diagnosis and treatment,among which the key to achieving integration is using the nanomaterial probe to solve the efficient combination and coordination of functional components.The supramolecular assembly method is characterized by modular design and stimulus response,which provides an important approach for the convenient preparation of multi-component and multifunctional nanocomposites on demand.As for the selection of functional groups,polyoxometalate clusters have become an ideal detection probe and therapeutic agent in various imaging technologies and the treatment of diseases due to their abundant optical,electrical,magnetic,redox and biological properties.However,its further application in vivo is limited by its strong non-specific effects and stability requirements in the physiological environment.For these reasons,in this dissertation,we designed and synthesized biocompatible cationic polymers with different structural characteristics,then assembled them with functional inorganic polyoxometalate through electrostatic assembly to construct a series of polyoxometalates/polymer nanocomposites,which have biocompatibility,in vivo stability and multiple responsiveness.Moreover,we realized the functional integration of enhanced magnetic resonance imaging,photothermal therapy induced by local reactions,drug loading and controlled release.The research results mainly focus on the following three aspects:First,we synthesized a polyethyleneimine derivative modified with polyethylene glycol,which was moderately cross-linked with diethylene glycol dimethacrylate to obtain a light-crosslinking PEGylated polyethylenimine cationic polymer with a low cross-linking degree as a carrier.A gadolinium-containing polyoxometalates[K17[Gd（P2Mo17O61）2]with redox ability and the synthetic polymer were used for electrostatic assembly,and the redox-responsive polyoxometalates/polymer nanocomposite was obtained.The obtained complex assembled in an aqueous solution to form an irregular shape assembly with a hydrodynamic diameter of 37 nm and remained stable in PBS and DMEM solutions.The in vitro cytotoxicity test showed that the Hela cells treated with the nanocomposite had a high survival rate,indicating the good biological safety.The magnetic characterization of the prepared nanocomposite before and after reduction showed that the composite under the two conditions had close relaxivity(r1=23 m M?1 s?1,0.5 T),which was about 4 times higher than the commercial MRI contrast agent Gd-DTPA under the same magnetic field,indicating that its magnetic resonance imaging properties were not affected by the reduction state of polyoxometalates.Polyoxometalates in the complex were reduced to heteropoly blue by glutathione GSH,which was abundant in the tumor cell environment.It was found that the complex exhibited near-infrared absorption in the wavelength range of 600–1000nm and its photothermal conversion efficiency could reach up to 61%under irradiation of 808 nm laser.Here,the polyoxometalates were both an imaging agent and a photothermal treatment agent,indicating the feasibility of simultaneously realizing enhanced magnetic resonance imaging and photothermal treatment.This kind of near-infrared photothermal conversion effect generated by the complex reduction in tumor microenvironment can not only be used to kill tumor cells,achieve locally targeted therapy,but also reduce the damage to normal tissues caused by photothermal therapeutic agent.Second,while achieving the above-mentioned bifunctional properties,in order to introduce chemotherapeutic effects into the system,we combined two polyoxometalates[K7[Gd P2W17O61]and[K6[α-P2W18O62]at the reduction state with cationic polymer poly（diallyldimethylammonium chloride）and biocompatible block copolymer poly（polyethylene glycol methyl ether methacrylate）-b-polymethacrylic acid for quaternary co-assembly to prepare a p H-responsive polyoxometalate-polymer nanocomposite.The complex assembled in an aqueous solution to form an assembly with a hydrodynamic diameter of 67 nm and had good structural stability in PBS and DMEM solutions.Its longitudinal relaxivity before and after drug loading had been measured to be about 50 m M?1 s?1,which was 10 times higher than that of the commercial contrast agent Gd-DTPA under the same conditions.Utilizing the reduced polyoxometalates with higher near-infrared absorption capability,the temperature of the composite solution increased rapidly under the irradiation of 808 nm laser,and the photothermal conversion efficiency was still up to 47.8%.At the same time,owing to the synergistic loading effect of polyoxometalates ionic crosslinking and the coating shell,the drug loading efficiency of the composite could reach to 90%.According to the electrostaitic repulsion and exchange effect caused by the increase of positive charge,the drug loaded in the composite exhibited significant p H responsive release behavior.The experimental results showed that the cumulative drug release amount under the condition of p H=5.0 reached 3 times that of p H=7.4 after 47 h.Cytotoxicity and flow cytometric apoptosis experiments showed that the drug-loaded composite can effectively inhibit tumor cell growth and achieve a photothermal-chemical synergistic therapeutic effect under laser irradiation,which provided a new strategy for the further development of polyoxometalate-based multifunctional nanocomposite for the integration of tumor diagnosis and treatment.Third,we further synthesized a water-soluble ionic polymer poly（polyethylene glycol methyl ether methacrylate）-b-poly（methacrylic acid-co-trimethyl ammonium bromide propyl methacrylate）by reversible addition-fragmentation chain transfer（RAFT）polymerization,using which as a carrier to electrostatically assemble with gadolinium-containing polyoxometalates K13[Gd（β2-Si W11O39）2],an integrated multifunctional diagnosis and treatment nanocomposite for enhanced MRI imaging was prepared.The obtained nanocomposite had strong hydrophilicity,high molecular weight,and good water exchange capacity of the paramagnetic polyoxometalates,thus exhibiting high relaxivity(50 m M?1 s?1,0.5 T).Based on this characteristic of the material,after intravenous injection into the tail vein of tumor-bearing mice,the passive targeted enrichment of nanocomposites at the tumor site could be observed through the magnetic resonance imaging instrument.Continuous imaging tests showed that the in vivo circulation time of the composite could exceed 5 h,making the composite one of the imaging materials with the highest circulation time.Since the negative charge of the polyoxometalates and the carboxyl group in the polymer chain could simultaneously enable loading of doxorubicin,the complex exhibited a high drug loading efficiency of96.7%.The doxorubicin-loaded composite exhibited good stability under multiple p H conditions and only produced high drug release under p H conditions similar to the tumor microenvironment.Compared with other similar research work based on the polyoxometalates,in vivo experiments in mice showed that the drug-loaded composite had a significantly enhanced tumor therapeutic effect.This in vivo experimental result further demonstrated that the polymer-encapsulated polyoxometalates nanocomposite could enhance the MRI performance more effectively,and provided a new direction for the realization of passive targeted MRI-enhanced imaging and synchronous chemotherapy for tumor diagnosis and treatment in vivo.The above research results show that the co-assembly of the polyoxometalates with ionic polymer not only effectively enhances the structural stability,but also maintains its magnetic resonance imaging and photothermal conversion properties.At the same time,in the supramolecular composite,the biocompatible cationic polymers both encapsulate the polyoxometalates and perform ionic cross-linking to obtain a uniform nano-scale particle composite.In such a composite system,imaging and near-infrared photothermal conversion properties can be completely compatible,and both the diagnosis and treatment occur at the tumor site through passive targeting and in-situ reduction,which is expected to realize imaging-guided treatment.Importantly,through molecular structure design,polymer nanoparticle composites can efficiently achieve drug loading and in-situ responsive release,which strengthens the control of drug release and reduces damage to normal biological tissues.In conclusion,such a supramolecular composite nanoparticle platform experimentally verifies and demonstrates our idea of integrating multiple functions into one material,and it also contributes to the further development of the polyoxometalates/polymer composite system in the integration of disease diagnosis and treatment.It is believed that new advances in active targeting and controlled drug release will greatly promote the versatility of this system,and new explorations in the utilization of polyoxometalates will facilitate the expansion of the current system into the fields of CT imaging and PET imaging. |
