Design And Application Of Photo-responsive ¹⁹F MRI Nanoprobe For Theranostics

Objective:This paper mainly focuses on the longitudinal and non-invasive visualization of biological processes at the subcellular level in tumors using multifunctional nanoprobes,as well as their organic combination with cancer treatment methods.Targeting,imaging,and loading drugs.The reversible addition-fragmentation chain transfer（RAFT）free radical polymerization method was employed to synthesize a stimuli-responsive amphiphilic block copolymer for Fluorine-19 Magnetic Resonance Imaging(¹⁹F MRI)nanoprobes.The effects of reaction conditions on the structure,molecular weight,and molecular weight distribution of the polymer were clarified,the photodecomposition process and mechanism of the polymer were explained,and the structure-imaging effect relationship of the molecule was explored.Secondly,photoresponsive multifunctional drug-loaded nanoparticles were further prepared using self-assembly technology.By studying their light-controlled decomposition,biological imaging,and drug release behaviors,the diagnostic and therapeutic effects of this multifunctional drug delivery system in biological environments were evaluated.A nanocarrier platform for diagnosing and integrating drugs,capable of both visual and dynamic tracking of their in vivo distribution,can be developed on the theoretical basis provided by this.Quantitatively regulate their liberation and action processes.Methods:1.A macromolecular chain transfer agent,photoresponsive in nature,was initially created.Using RAFT（reversible addition-fragmentation chain transfer）free radical polymerization,a series of photoresponsive amphiphilic block copolymers with varying hydrophilic-hydrophobic segment ratios were created.Light-responsive groups,ortho-nitrobenzyl benzyl ether（o NB）,were introduced between the hydrophilic and hydrophobic segments of the polymer,which can undergo photodecomposition reaction under 365 nm ultraviolet（UV）light irradiation.The polymer structure was comprehensively characterized by 1H nuclear magnetic resonance（¹H NMR）and Fourier transform infrared spectrometer（FTIR）,and the effects of polymerization reaction kinetics and reaction conditions on the structure,molecular weight,and molecular weight distribution of the polymer were explored by size exclusion chromatography（SEC）.The photodecomposition process and mechanism of the polymer were elucidated by ultraviolet-visible-near infrared spectrophotometer（UV-Vis-NIR）.Further optimization of the polymerization reaction conditions and adjustment of the hydrophilic-hydrophobic segment ratios resulted in a photoresponsive amphiphilic block copolymer material system suitable for nanoscale self-assembly.2.The amphiphilic block copolymers and drug molecules were co-assembled using dialysis to form morphologically controllable and uniformly sized nanoparticles.Pyrene was used as a fluorescence probe to determine the critical micelle concentration（CMC）of the amphiphilic block copolymer micelles using a fluorescence spectrophotometer（Flu）,and to evaluate the nanoscale assembly ability of the polymers.The average diameter,size distribution,and aggregation state of the nanoparticles before and after drug loading were determined using dynamic light scattering（DLS）to clarify their physical and chemical properties.Using transmission electron microscopy（TEM）in high-resolution conditions,the morphology,size,aggregation state,and distribution of the nanoparticles were evaluated.The nanoparticles laden with the drug were seen to disperse and encapsulate it.3.Construction and performance evaluation of an intelligent responsive nanomedical platform.The imaging capability of the nanoparticles was investigated using ¹⁹F NMR and¹⁹F MRI,including longitudinal relaxation time T₁,transverse relaxation time T₂,and signal-to-noise ratio（SNR）,to explore the effects of different ¹⁹F contents on imaging performance.Drug loading capacity（DLC）,drug loading efficiency（DLE）,nanoparticle stability,photon correlation spectrum（PCS）counting rate,and drug release behavior were evaluated using UV-Vis-NIR and DLS to assess the drug loading ability and photoresponsive drug release sensitivity of the nanomedical platform.The biocompatibility and safety of the nanomedical carrier and its photodegradation products were evaluated by analyzing cell viability（MTT assay）.Results:1.A photoresponsive o NB group was bridged between a RAFT agent（PABTC）and amino-terminated polyethylene glycol（m PEG-NH2-5K）.Results from ¹H NMR and FTIR showed successful preparation of the photoresponsive RAFT polymer chain transfer agent PEG₁₀₀-o NB-PABTC.UV-Vis absorption spectra results showed that with prolonged UV light exposure（0.196 W/cm²,365 nm）,the maximum absorbance of the o NB group in the PEG100-o NB-PABTC structure continued to decrease at 310 nm,indicating that the polymer chain transfer agent exhibited photoresponsiveness under 365 nm UV light irradiation.At the same time,the ¹H NMR results showed that during the photolysis process,the para-nitrobenzyl chromophore was excited and extracted a hydrogen from theγ-methylene group,forming a carboxynitro isomerization,then underwent molecular rearrangement,and finally underwent photoinduced cleavage,with the main products being carboxylic acid and para-nitrobenzaldehyde.The chemical shift of the original structure changed significantly,with a new peak of aldehyde（-CHO）appearing at 9.45 ppm,indicating the formation of cleavage products.2.A series of photoresponsive block copolymers PEG₁₀₀-o NB-b-PTFEA_m（P1-P6）with different hydrophobic chain lengths were synthesized by optimizing the polymerization conditions using PEG₁₀₀-o NB-PABTC as the RAFT macro-chain transfer agent,AIBN as the initiator,and TFEA as the monomer.The polymer structure was confirmed by ¹H NMR,and SEC results showed that the average molecular weight of P1-P6 was in the range of4700-11500 g/mol with a low dispersity index（PDI<1.3）.Moreover,SEC was used to characterize the molecular weight of the polymers before and after UV irradiation（0.196W/cm²,365 nm）,and the results showed that the polymer molecular weight distribution exhibited a bimodal distribution and shifted towards the low molecular weight region due to the cleavage of the bridging structure upon UV irradiation.The photodegradation rate was found to increase with the increase in the length of the hydrophobic chain segments,as characterized by UV-Vis absorption spectroscopy.3.During the self-assembly process of the polymer PEG₁₀₀-o NB-b-PTFEA_m（P1-P6）nanoparticles,the CMC gradually decreases（from 0.583-0.477 mg/m L）,indicating an increase in the self-assembly ability of the polymer molecules as the length of the hydrophobic chain segment increases.DLS results show that the particle size of all nanoparticles is below 150 nm,with a monodisperse distribution（PDI<0.2）;compared with blank nanoparticles,drug-loaded nanoparticles have slightly increased particle size,while the particle size distribution andζpotential remain basically unchanged,indicating successful drug loading.UV-Vis spectroscopy results show that the DLC and DLE gradually increase,indicating an improvement in the drug-loading ability of the nanoparticles as the length of the hydrophobic chain segment increases.TEM shows that the blank nanoparticles have a uniform spherical structure,and point-like drug distribution is visible in the drug-loaded nanoparticles,further demonstrating successful drug loading.The photo-decomposition experiment results of the nanoparticles show that the drug-loaded nanoparticles CLX@P2（1 mg/m L）under UV light（0.196 W/cm²,365 nm,15 min）decrease the PCS count rate by about 50%.The results of the in vitro drug release experiment show that the cumulative release of the drug-loaded nanoparticles CLX@P2（1 mg/m L）after 30minutes of UV light exposure（0.196 W/cm²,365 nm）is about 49%within 24 hours.The results of ¹⁹F NMR and ¹⁹F MRI show that the low-fluorine content nanoparticles P1B(T₂^Short=2.6 ms,T₂^Long=7.9 ms,SNR=7.0)and P2B(T₂^Short=1.7 ms,T₂^Long=5.9 ms,SNR=5.5)exhibit good imaging ability in the PBS buffer system（p H=7.4）.The cell compatibility results show that after co-culturing with human umbilical vein endothelial cells（HUVEC）for 48 hours,even at a concentration of 100μM,nanoparticles（P1B-P6B）and their degradation products still maintain a survival rate of over 80%,indicating good biocompatibility of the nanoparticles.Conclusion:A series of photoresponsive amphiphilic block copolymers PEG₁₀₀-o NB-b-PTFEA_mwith different hydrophobic chain lengths were synthesized via RAFT polymerization technique.Nanoparticles,self-assembling from these copolymers in aqueous solution,can be utilized as"smart"drug delivery carriers with ¹⁹F MRI capability,playing a critical part in biomedical applications.With the extension of the hydrophobic chain length,the self-assembly ability of the nanoparticles is enhanced,and both DLC and DLE are improved.However,the activity of ¹⁹F nucleus decreases with the increase of hydrophobic chain length,leading to severe MR signal attenuation or even quenching.Among them,the nanoparticle P2B with low fluorine content exhibits good ¹⁹F MRI capability,ideal photodegradation time（720 seconds）,higher DLE（10.22%）,and better stability.In addition,the comprehensive results of particle size,nanoparticle morphology,drug release,and biocompatibility of P2B indicate that it can be an ideal"smart"¹⁹F MRI diagnostic and therapeutic probe candidate material.A solid theoretical foundation for optimizing polymer structure is revealed by these results,unveiling the intricate connection between molecular structure and diagnostic and therapeutic effectiveness.The construction of diagnostic and therapeutic integrated nanoplatforms,as well as the enhancement of clinical efficacy,can be advantageous in constructing more efficient drug delivery systems,as well as creating more precise disease diagnosis techniques and treatment approaches.Ultimately,clinical results are enhanced.