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Objective: The aim of this study was to develop radiopaque microspheres (RMs) for application in interventional therapy of embolization.With advantage of minimal invasion,transcatheter arterial embolization (TAE) has emerged as a widely used treatment in hypervascular diseases,such as hepatocellular carcinomas,renal angiomyolipomas,uterine fibroids,arterio-venous malformations (AVMs) and hemorrhages.Embolic agents,such as microparticles,microspheres or beads have successfully employed in the embolization therapy for several decades.However,most of these embolic agents are undetectable under X-ray fluoroscopy,the location of particles is only guided indirectly by mixing with iodinated contrasts and the endpoint of embolization cannot be accurately determined in the process of TAE.In addition,some possible migration of the embolic agents over time cannot be found to guide in cases in which a second injection of an embolic agent is necessary (e.g.repeated treatment).Methods: By entrapping lipiodol in biocompatible polyvinyl alcohol (PVA) with multiple emulsion chemical crosslinking method,RMs were developed and a series of tests was performed to evaluate the feasibility of RMs for embolization.The morphology and size distribution of RMs were determined with optical microscope and environmental scanning electron microscope (ESEM).Then the lipiodol content and lipiodol release were quantified by ultraviolet spectrophotometry method.The compressibility and catheter deliverability were investigated.Furthermore,the radiopaque capability of RMs was detected by an X-ray imaging system both in vials and in mice and the biocompatibility of RMs was investigated in vitro with mouse L929 fibroblasts cells and in mice after subcutaneous injection.Finally,RMs were embolized to renal artery of a rabbit and the embolism property of RMs was performed with CT imaging and micro-CT imaging.Results: Morphology of RMs revealed that the RMs were smooth,spherical and well dispersed (Figure 1).The particle size range of RMs was 100-1200 μm and the number-average diameter was 333.3 ± 27.4 μm.The average content of lipiodol in RMs was (0.366 ± 0.018) g/ml.Lipiodol in RMs was barely released and the cumulative release percentage was less than 0.14% for 72 h.The abilities of compression and deliveribility through catheter for RMs were both good.The visibility of RMs under X-ray was stronger than saline and weaker than pure lipiodol (Figure 2).The X-ray images of a same mouse at 0 day,1 week,1 month and 3 months after subcutaneous injection of RMs proved that RMs were radiopaque and the visibility did not decreased for 3 months (Figure 3).No toxicity of RMs was found to the survival of mouse L929 fibroblasts cells (Figure 4) and RMs caused just a moderate inflammatory reaction in surrounding tissue of mice after subcutaneous injection.RMs were successfully occluded the left renal of rabbits (Figure 5).With CT imaging and higher-resolution of micro-CT,RMs were found to fill all the arteries in renal parenchyma and extend toward renal coetex (Figure 6).Conclusion: The RMs were proved to be potential for embolization therapy with good physical and mechanical properties,radiopacity and biocompatibility.