Preparation And Application Of Superhydrophilic ¹⁹F Magnetic Resonance Imaging Contrast Agents

Fluorine-19 magnetic resonance imaging(¹⁹F MRI)is a non-invasive and non-radioactive diagnostic technique with no endogenous background signals,and it has huge potential in the field of biomedicine.However,the nano-contrast agents prepared mainly from superhydrophobic perfluorinated nanoemulsion or amphiphilic fluorinated macromolecules have problems such as poor stability,low bioavailability,insufficient fluorine content,and signal attenuation caused by hydrophobic aggregation.All of these issues seriously restrict the in vivo imaging effect of quantitative study.Based on this,this study proposes ideas from the molecular design and preparation of super-hydrophilic zwitterionic contrast agents to the application of quantitative tracking in vivo.First,we introduce carboxylic acid betaine zwitterionic structure in each fluorination unit through the synthesis of monomer molecules to enhance the hydrophilicity,and at the same time,the fluorine content is controlled by a group with magnetically equivalent fluorine atoms.Then the polymers with controllable molecular weight and polymer dispersity index（PDI）are prepared through Reversible Addition-Fragmentation Chain Transfer（RAFT）reaction to obtain trifluoromethylated zwitterionic fluorinated polymer contrast agent（PCBF₃）with high magnetic equivalent fluorine content and superhydrophilicity.And the polymer has a fluorine content of19.1wt%.PCBF₃ contrast agent has excellent anti-protein adsorption ability and it can maintain stable magnetic resonance properties in biological samples such as plasma,tissue homogenate and complex biological environment in vivo.Then we establish quantitative calculation based on ¹⁹F magnetic resonance spectroscopy(¹⁹F MRS)because of its excellent properties.This computational quantification was applied to the evaluation of the metabolic kinetic behavior of the contrast agent which was used to quantitatively evaluate the bioavailability and tissue distribution of the contrast agent in vivo.Moreover,the PCBF₃contrast agent has good biocompatibility and low immunogenicity,which is beneficial to avoid rapid clearance by the reticuloendothelial system and prolong systemic circulation time.Second,the superhydrophilic zwitterionic PCBF₃ contrast agent was combined with the neovascular integrin ligandα_vβ₃（α_vβ₃-PCBF₃）for specific targeted diagnosis of liver cancer,and the uptake of contrast agent was quantitatively calculated.Studies have shown that the uptake ofα_vβ₃-PCBF₃ contrast agent by tumor tissues is about 9.04±1.86%which is not only conducive to targeted and precise diagnosis of tumors,but also laid the foundation for subsequent targeted tumor drug delivery research.Thirdly,in order to prove the feasibility of the application of super-hydrophilic polymer contrast agent in nanoscience,nanogels with controlled particle size and cross-linking degree were prepared by inverse microemulsion polymerization.It was found that the super-hydrophilic zwitterionic nanogel can still maintain stable magnetic resonance properties in complex biological samples,and it cannot be taken up by cells with strong cell uptake capacity such as macrophages and dendritic cells.More importantly,it has a significantly prolonged systemic circulation time.In addition,it was found that the superhydrophilic zwitterionic nanogel with a particle size of about80 nm and a cross-linking degree of 5%can be eliminated by the kidney metabolism.And this result still needs further investigation.Finally,superhydrophilic zwitterionic contrast agents are used for hydrogel labeling to assess the degradation rate of hydrogel quantitatively.We synthesis trifluoromethylated carboxylic acid betaine zwitterionic molecules（PA-CBF₃）containing an alkynyl group which can label a polyethylene glycol-polyvaline（PEV）hydrogel modified by an azide group matrix using a"click"reaction.The labeling of the PEV hydrogel by the PA-CBF₃contrast agent does not affect the properties of the hydrogel and the contrast agent can also maintain the original magnetic resonance properties in the hydrogel matrix.Furthermore,the use of ¹⁹F MRI not only can obtain the accurate positioning information of the 3D and 2D anatomy of CBF₃-PEV hydrogel in vivo,but also can quantitatively calculate the real-time degradation rate of the hydrogel in vivo.This proves feasibility of this approach to evaluating the degradation rate in vivo of hydrogel quantitatively.Next,the PA-CBF₃ contrast agent was successfully labeled with alginic acid,polyacrylamide and poloxamer hydrogel,etc.,proving the versatility of this method.In general,superhydrophilic trifluoromethylated carboxybetaine zwitterionic molecules have the advantages of high magnetic equivalent fluorine content,stable magnetic resonance properties and high bioavailability.Therefore,it can be defined as a new generation of high-performance ¹⁹F MRI contrast agents,and it is beneficial to promote the application of ¹⁹F MRI in the field of biomedicine.In addition,through this study,we obtain superhydrophilic materials that can be detected by ¹⁹F MRS/MRI quantitatively with no radioactive isotopes or fluorescent molecular labels.It plays an important role in the development of multi-modal imaging probes for visualization nano drugs,nano vaccines and implant materials.