Preparation Of Charge-conversion Nano-drug Carriers For Tumor Imaging Based On Flash Nanoprecipitation

In the past decades,nanoparticles(NPs)used for carriers have been widely applied in the biomedical field including tumor therapy,bioimaging and nano-pesticide field due to their long circulation,targeting ability and various surface modifications that can introduce multifunctional groups.The ideal nano-drug carriers are expected not only to obtain long circulation time during the blood circulation but also to facilitate the cellular uptake by tumor cells.The nano-drug carriers with negative surface charge can circumvent the adsorption of serum proteins and endowed with long circulation time,but it is positive surface charge that is needed to promote the cellular uptake efficacy.To address this contradiction,the charge-conversion nano-drug carriers taking advantage of the acidic microenvironment of the tumor has drawn more and more attention.In this paper,a facile engineering strategy of preparing the NPs-Flash nanoprecipitation(FNP),was used to simply and fast construct charge conversion NPs that respond to pH quickly.The size,surface charge and fluorescence intensity of NPs can be systematically tuned by changing the solvent ratios,stream velocities and the mass ratio of two copolymers.Besides,the effects of FNP on the morphology of NPs are studied.In addition,the biological tumor imaging application of NPs was studied.The research contents of this paper include the following aspects:(1)The biocompatible and pH-responsive copolymers,dextran-b-poly(lactic-co-glycolic acid)(Dex-b-PLGA)and poly(2-(dimethylamino)ethylmethylacrylate)-b-poly(s-caprolactone)(PDMAEMA-b-PCL),were successfully synthesized.The chemical structure,molecular weight,and molecular weight distribution were characterized by 1H NMR and GPC.Besides,the critical micelle concentration(CMC)of copolymers was determined by pyrene fluorescent probe method.(2)The charge-conversion nanoparticles,Dextran/PDMAEMA/β-Carotene NPs,encapsulating the model hydrophobic drug β-Carotene,was prepared by FNP.The results show that with the increasing of the stream velocity ratio(the stream velocity of the aqueous phase:the stream velocity of the organic phase),the size of NPs decreased and the NPs had a higher surface charge density.Moreover,charge-conversion of NPs could be further tuned by adjusting the ratio of these two polymers.(3)Then,the AIE fluorescent dye ED,was successfully encapsulated into the Dextran/PDMAEMA/ED NPs by FNP.The experimental results demonstrate that the fluorescence intensity can be tuned by changing the the stream velocity ratio.The novel rod-like NPs with length 200 nm were prepared by FNP,and the effect of FNP on morphology of NPs was discussed.The fluorescent NPs exhibited excellent size and fluorescence stability.(4)MTT method was applied to examine the cytotoxicity of Dextran/PDMAEMA/ED NPs,and the results revealed that the ED encapsulated NPs had almost no cytotoxicity in a wide dose range(0-300 μg mL-1).Both laser confocal imaging and flow cytometry indicated that the charge-reversion Dextran/PDMAEMA/ED NPs can enhance the cellular uptake of cells in the acidic environment.Meanwhile,the laser confocal imaging demonstrated that the rod-like Dextran/PDMAEMA/ED NPs could enter into the nucleus.Finally,ex vivo imaging of mice showed that the NPs was almost exclusively concentrated in the tumor site.