Preparation And Dual-modal Imaging Study Of Four-arm Star-shaped Polylactic Acid-loaded PFP/SA Nanoparticles

Objective:In recent years,medical imaging techniques have been increasingly used in clinical practice.A variety of technologies such as magnetic resonance imaging(MRI),ultrasound imaging(US)and fluorescence imaging are applied to the observation of tissue and organ morphology,diagnosis of cardiovascular diseases and tumor diagnosis,which are non-invasive,free of ionizing radiation and easy to operate.Various imaging techniques have their own advantages and shortcomings that are difficult to change due to their different principles.For example,ultrasound imaging is inexpensive and can image in real time,but the resolution is not high;while magnetic resonance imaging has high spatial resolution and high penetration,but the cost is high and the imaging is slow.In order to achieve better imaging results,multimodal imaging technology has become a hot research topic.However,because the structure of certain tissues or tumor tissues in the human body is more complex,it is difficult to distinguish the difference between diseased and normal tissues simply by imaging techniques,and the imaging effect is not good;therefore,the intervention of contrast agents is needed to enhance the visualization of the tissue structure of the body and improve the accuracy and contrast of diagnosis.This study investigates the preparation of four-armed star-shaped polylactic acid-loaded PFP/SA nanoparticles and dual-modality imaging study.Ultrasound imaging is performed by scanning the body with an ultrasound beam and receiving and processing the reflected signals to obtain images of organs in the body.Chemical exchange saturation transfer(CEST)imaging is a more specific magnetic resonance molecular imaging technique that can indirectly detect signals with exchangeable protons with higher sensitivity than MRI.The combined use of ultrasound and CEST imaging can combine the advantages of both and can effectively improve the diagnosis.Ultrasound-chemical exchange saturation transfer(US/CEST)contrast agents are a mixture of ultrasound imaging enhancement components and CEST imaging enhancement components encapsulated within a carrier material.The US/CEST dual-modality contrast agent is constructed by using perfluoropentane as the ultrasound imaging enhancement component and salicylic acid as the CEST imaging enhancement component.Methods:In this study,four-armed star poly(lactic acid)polymers were prepared by ring-opening polymerization using hematoporphyrin dihydrochloride(HP)and L-propyleneglyceride as APIs and stannous octanoate[Sn(Oct)₂]as catalyst in an oil bath at 120°C for 2 h.The chemical structure and physical properties of the polymers were characterized by infrared spectroscopy(FT-IR),nuclear magnetic resonance hydrogen spectroscopy(H-NMR),X-ray diffraction spectroscopy(XRD),and thermogravimetric analysis(TGA).The appearance and morphology of the nanoparticles were observed by transmission electron microscopy(TEM),the particle size,potential and stability of the nanoparticles were detected by laser particle size measurement,and then the nanoparticles were evaluated by CCK8 test,cell scratch test,blood biochemical analysis and hemolysis test.The biocompatibility of the nanoparticles was evaluated by CCK8 test,cell scratch test,blood biochemical analysis and hemolysis test,and finally,the clinical ultrasound imaging system and 7.0T MRI scanner were used to study the ex vivo imaging effects of SA/PFP@HP-PLLA NPs.Results:The FT-IR and ~1H-NMR results showed that the HP-PLLA polymer was prepared successfully,the XRD results showed that the crystal structure changed,and the TGA results showed that the HP-PLLA polymer had better thermal stability.the SA/PFP@HP-PLLA NPs showed a spherical structure and homogeneous dispersion under TEM observation,and the average particle size and zeta potential were(The results of CCK8 test,cell scratch test and hemolysis test showed that different concentrations of HP-PLLA NPs solution did not affect the growth of cells and had good biocompatibility.The results of blood biochemical analysis experiments showed that there was no significant difference in various liver and kidney function indexes of rabbits before and after intravenous injection of SA/PFP@HP-PLLA NPs into the ear margins of rabbits(P>0.05),providing strong support for the in vivo study of SA/PFP@HP-PLLA NPs.Under the scanning conditions of clinical ultrasound imaging system and 7.0T MRI scanner,SA/PFP@HP-PLLA NPs could form a high contrast signal in vitro and in vivo,which could enhance the ultrasound imaging and CEST imaging of tumors.Conclusion:The four-armed star poly(lactic acid)polymer(HP-PLLA)prepared by ring-opening polymerization has good biocompatibility and stability.SA/PFP@HP-PLLA NPs prepared with HP-PLLA polymer as the carrier material showed signal enhancement in vivo and ex vivo for enhanced ultrasound imaging and CEST imaging.