| Transcatheter arterial chemoembolization（TACE）is the first-line clinical treatment for unresectable advanced liver cancer,and blood-vessel embolic agents play an important role in TACE.However,there is a‘Fluidity-Embolism Dilemma’in current embolic agents.For example,the classic chemoembolization based on Lipiodol?（C-TACE）is the‘gold standard’to evaluate the therapeutic effect of embolization.Although Lipiodol has good fluidity and can diffuse to the peripheral vascular network of liver cancer,its embolic intensity is relatively low,and easy to metabolize quickly,which leads to the recanalization of blood vessels.To solve this problem,we further designed h PNA nanogels with core-shell brush structure for the stabilization of Lipiodol emulsion based on the previous work of thermosensitive nanogels.The thermosensitive Pickering gel emulsion of Lipiodol（TPGEL）has excellent stability both in vitro and in vivo（room temperature and body temperature）.Unlike the usual thermosensitive Pickering emulsion,TPGEL has good temperature sensitive sol-gel transformation behavior.It does not demulsification at the body temperature,but forms a homogeneous emulsion gel.The Lipiodol is locked in the droplet structure,not only preserving the X-ray imaging ability of Lipiodol but also effectively solving the‘Fluidity-Embolism Dilemma’of the embolic agent.The results showd that the TPGEL can achieve long-term casting embolization and improve the hypoxic microenvironment of tumor vessels after embolization,enhance the curative effect of vascular embolization for liver cancers.The main results are as follows:（1）Effects of molecular size on phase transition behavior of thermosensitive nanogels and its phase transition mechanism were studied:Firstly,three kinds of poly（N-isopropylacrylamide-co-methyl methacrylate）（PIB）nanogels with different particle sizes（80 nm,200 nm and 300 nm）and linear PIB were prepared by emulsion polymerization.The microstructure of PIB nanogels was studied by transmission electron microscopy（TEM）and atomic force microscopy（AFM）.At different temperature,by observing the binding of phosphotungstic acid and nanogels,the hydrophobicity of nanogels at different temperature was observed.As the temperature rises from 25 to 37℃,the PIB nanogels change from hydrophilic to hydrophobic,due to the change of hydrophobicity,they change from swelling state to shrinkage state,form a gel by hydrophobic interaction and transform from liquid to solid.The rheological study showed that the viscosity of PIB-200 at room temperature was only 33.1 m Pa·s,while the viscosity of linear polymer PIB-L was 71.9 m Pa·s.Besides,the flow embolism index（FE Index）of PIB-200 and PIB-80 was 132 and 302 respectively,which were significantly higher than that of PIB-L of 114.Through the above research,we can conclude that the thermosensitive nanogels have good fluidity and embolic properties,which can effectively solve the‘Fluidity-Embolism Dilemma’of commercial embolic agents.（2）We have developed an in vitro vascular embolization model based on microfluidic chip technology.The pipeline diameter ranges from 20 to 1000μm,and the monitoring system can respond to the pressure changes in the embolization system.The results showed that under the same conditions,the system pressure dropped to the pre embolization level within 1 min after the end of Lipiodol injection,indicating that the embolization strength of Lipiodol was insufficient.PIBI-6150 and PIBI-2240 maintained relatively high system pressure.In addition,PIBI-2240 with the viscosity of 25 m Pa·s could embolize all the branches of 20-1000μm pipeline while retaining enough embolization capacity.While PIBI-6150 with the viscosity of 328 m Pa·s can also achieve permanent embolism,but due to its poor fluidity,it can not flow into the pipeline less than 200μm.The above results show that PIBI-2240 has better peripheral embolization effect than PIBI-6150 while retaining the permanent embolization performance.（3）Preparation and characterization of thermosensitive Pickering gel emulsion of Lipiodol（TPGEL）:three kinds of poly（N-isopropylacrylamide-co-acrylic acid）nanogels（h PNA-1/2/3）with core-shell structure were prepared by two-step seed emulsion polymerization,random copolymerization nanogels u PNA were also prepared.Through TEM observation,h PNA-1/2/3 showed obvious core-shell structure,and the shell became thicker with the increase of AA content.In the concentration range of 6～10 wt.%,all kinds of thermosensitive nanogels can form stable TPGEL at room temperature（oil/water ratio from 1:9 to 3:7）.However,the TPGEL stabilized by u PNA nanogels was demulsified at37℃.The TPGEL stabilized by three h PNA nanogels did not demulsification at 37℃,but turned into a non flowing gel state.In addition,the rheological test of TPGEL showed the viscosity of the solution is 90 m Pa·s(300 s-1 shear rate),and the modulus is 320 Pa,the yield stress is 70 Pa at gel state,and the zero shear viscosity can reach 5500 Pa s,this indicates that TPGEL has good fluidity and embolic property,which can solve the‘Fluidity-Embolism Dilemma’of clinical vascular embolic agents.（4）Embolization of rabbits with TPGEL and evaluation of long-term peripheral embolization effect.Through the rabbit’s kidney embolization experiment,we found that compared with the traditional Lipiodol emulsion,TPGEL can not only achieve more persistent embolism,but also play a role of long-term X-ray imaging.Through the VX2tumor rabbits embolization,we proved that TPGEL can achieve long term embolization of tumor vessels.In the fluorescence sections of postoperative tumor tissues,we can clearly find that TPGEL exists in tumor vessels in the form of emulsion,indicating that after TPGEL embolization,Lipiodol can be locked in the original droplet structure and will not be scoured by blood flow.In order to further study the effects of long-term peripheral embolization on the establishment of tumor collateral circulation,immunohistochemistry of VEGF and CD31 was studied.It is found that the expression of VEGC and CD31 in VX2tumor rabbits treated with TPGEL is significantly lower than that in the traditional Lipiodol emulsion+gelatin sponge control group,which means that long-term peripheral embolization can effectively inhibit the formation of neovascularization and enhance the anti-tumor effects.In this study,the effect of molecular size on the phase transition behavior of PIB thermosensitive nanogels were studied.The embolization effects of PIBI-2240 is demonstrated by in vitro vascular embolization model and animal experiments.On this basis,the thermosensitive Pickering gel emulsion of Lipiodol（TPGEL）was designed,which can achieve long-term peripheral embolization and X-ray imaging. |
