Injectable Liquid Metal Nanoflake Hydrogel As A Local Therapeutic For Enhanced Postsurgical Suppression Of Tumor Recurrence

Purpose: Despite the great progress achieved in nanomedicine,liquid metal(LM)nanodroplets have been mostly implemented as photo-agents for tumor phototherapy.However,in the rational design and construction of LM-based nanoplatforms for chemotherapy,limitations such as low drug-loading efficiency(LE),poor water stability,sterile and sensitive surface chemistry against ligand modification,and difficult morphology control remain to be addressed.This study attempts to develop a ligand-mediated liquid metal nanoflakes(LMNF)and investigate its morphology formation mechanism,drug loading capacity,and its potential in postsurgical cancer treatment.Method: LMNF is prepared by using hyperbranched poly(amido amine)(HPAA)as ligand under ultrasound conditions.Morphology of the LMNF was examined on Transmission electron microscopy(TEM)and atomic force microscopy(AFM).The Size,Zeta potentials,and in vitro stability of LMNF in water were detected by dynamic light scattering(DLS).The internal and surface elemental composition of LMNF were detected EDS(energy-dispersive X-ray spectroscopy)elemental mapping and X-ray photoelectron spectroscopy(XPS).The ratio of each crystalline phase of LMNF was detected X-ray diffraction(XRD).The loading efficiency(LE)and encapsulation efficiency(EE)of LMNF were detected by fluorescence spectrum analysis.Annexin V-FITC cell apoptosis detection kits were used to detect apoptosis in tumor cells.Mouse breast cancer 4T1 cells,human cervical cancer He La cells,and human breast cancer Bcap-37 cells were cultured for detecting cell uptake assay and cytotoxicity test.The hemolysis test was used to detect the biocompatibility of LMNF in the blood and provides a basis for subsequent in vivo experiments.The tumor resection model was constructed,and the tumor suppression experiment in vivo was performed.Results: With hyperbranched poly(amido amine)(HPAA)as the ligand,the obtained LM nanodroplets presented excellent aqueous stability and a unique flaky nanomorphology.The average size of LMNF detected by DLS is 132.4 nm,the Zeta potential is 39.2 ± 2.2 m V,and the stability in vitro is excellent.Chemotherapeutic drugs can also be conjugated to the surface of LMNF through Schiff base reaction,which is compared with liquid metal nanospheres(LMNS,EE 50.4%,LE 23.5%)or nanorods(LMNR,EE 61.8%,LE 31.4%),the loading efficiency and encapsulation efficiency reach 69.9% and 63.5% respectively,showing higher DOX loading capacity.The release of DOX reached equilibrium after 48 h,and the release rate was as high as 75% at p H 5.0,compared with p H 7.4,the release rate of LMNF-DOX increased nearly 4 times.In vitro cell experiments,with the extension of incubation time,the uptake of LMNF-DOX in the He La cell nucleus gradually increased,and the average fluorescence intensity(MFI)in the nucleus at 2.0 h was about 1.35 times that at 0.5 h.LMNF-DOX shows more significant cytotoxicity than free DOX in 4T1 cells and LMNF-DOX exhibited comparable anticancer activities to Bcap-37 cells and He La cells compared with free DOX,which had an inhibition ratio of 76% and 70%,respectively.In terms of the ability to induce tumor cell apoptosis,LMNF-DOX and free DOX both showed efficient apoptosis in He La cells,and LMNF-DOX exhibited a much higher total cell apoptotic ratio(83.6%)compared with free DOX(59.3%),live/dead cell assay also further proved this conclusion.Further encapsulation of LMNF-DOX within Pluronic F127(LMNF-DOX@Gel)was used to diminish burst drug release,achieve a long-term antitumor effect,and minimize systemic toxicity.Conclusions: This study has successfully developed an LM-based local drug delivery strategy for postsurgical cancer treatment.The strategy not only provides LM nanodroplets with excellent aqueous stability,along with the access to construct multivalent p H-responsive linker and enhance DOX loading capacity,but also generates a unique flaky nanomorphology.Further combined with F127 hydrogel,the formulation achieved enhanced tumor recurrence inhibition efficiency and decreased systemic toxicity compared with free DOX.This work extends the category of polymeric ligands to synthesize stable aqueous LM nanodroplets with tunable morphologies and provides a new strategy for postsurgical cancer treatment.