Micro/Nanomotor Motion And Tissue Penetration Mechanisms And Antitumor Efficacy

Drug delivery systems（DDS）for tumor treatment are confronted with a series of barriers in blood circulation,tumor accumulation,intratumoral penetration,and cell internalization,resulting in poor therapeutic effect.Micro/nanomotors can convert the surrounding energy into mechanical motion,complete the transition from traditional passive diffusion to active infiltration,and have significant advantages in improving drug delivery efficacy.In this thesis,a series of Janus micro/nanomotors are designed to improve tumor accumulation,deep penetration and cellular uptake through active transportation.Cell targeting,non-chemotherapeutic treatment and selective tumor cellular uptake are integrated into micro/nanomotors to enhance antitumor effect and reduce toxicity to normal tissues.Urease and targeting ligands are grafted on the respective sides of fiber rods with distinct Janus structure,and micromotors with cell targeting capabilities are prepared based on the urease-catalyzed decomposition of urea that can provide the driven force.Doxorubicin（DOX）-loaded Janus fiber rods with different groups on both sides were prepared by a combination of“side-by-side”electrospinning and cryocutting,followed by grafting folic acid and urease on the respective sides of rods.The grafting density of urease determines the trajectory and motion velocity of micromotors,and the high motion velocity and large mean-square displacement are detected in both phosphate-buffered saline and simulated extracellular matrices of tumor tissues.Micromotors with a grafting density of 0.24nmol/cm² show the largest phagocytosis,cytotoxicity and apoptosis rate,and there is no interference with the phagocytosis mechanism mediated by folate receptors.The self-propelled properties of micromotors increase drug accumulation in tumor tissues by around 2.6 folds,effectively improve the therapeutic effect of drugs.To further improve the permeability and diffusivity in tumor tissues,urease and hyaluronidase are grafted on the respective sides of Janus nanorods to drive the motion of nanomotors and degrade the extracellular matrix.Janus nanorods containing different groups were constructed via seed-mediated growth of silica nanoparticles（NPs）on DOX-loaded hydroxyapatite nanorods.The hyaluronidase degradation and self-propulsion ability show no effect on the phagocytic mechanism of nanomotors,but lead to over 3-fold higher cellular uptake than those of pristine nanorods.The rod-like properties of nanomotors prolong blood circulation,and the self-propulsion force and instantaneous degradation of hyaluronidase along the moving paths promote vascular extravasation and tumor penetration,leading to2-fold higher drug levels in tumors after nanomotor administration than those with unmodified nanorods.The digestion of hyaluronidase in the diffusion paths is more effective to improve drug retention and diffusion in tumors compared with enzyme-mediated motion,enhance antitumor effects,and inhibit lung metastasis to tumor.To alleviate the effect of the substrate concentration and enzyme activity on the urease-driven motors,light-activated Zn Ga₂O₄:Cr³⁺（ZGC）nanodots are used as an internal light source to prepare thermophoresis-driven nanomotors with persistent motion.ZGC nanodots were in situ deposited on mesoporous silica NPs（MSN）,followed by conjugation of silicon phthalocyanine and capping with polydopamine（PDA）to fabricate Janus m PL-Pc@PDA NPs.The light-activated ZGC can emit near-infrared（NIR）to excite the phthalocyanine and PDA for persistent productions of reactive oxygen species（ROS）and heat,and the heat gradients around the Janus NPs create thermophoretic force to persistently drive their motions.In addition,the persistent luminescence of ZGC can be repeatedly activated by external illumination.The persistent motions increase the chance of contact with cells,and enhance their cellular uptake,the productions of heat and ROS endow NPs with persistent and combined antitumor capabilities of photothermal（PTT）and photodynamic（PDT）.In vivo experiments show that the light activation of m PL-Pc@PDA obviously produces heat and persistently generates ROS,leading to the significant synergistic antitumor effect of PTT and PDT.In order to overcome the limitation of light penetration in biological tissues and improve the motion profiles of NPs,nanomotors are driven by ultrasonication activation with assisted gas propulsion.Ultrasonication activates mechanoluminescent nanodots to excite ZGC nanodots and NIR emission generates thermophoresis to drive NP motion and NO release.The mechanoluminescent Sr Al₂O₄:Eu²⁺（SAOE）and ZGC nanodots were deposited on MSNs to prepare m SZ NPs,followed by partially coating with PDA caps and loading NO donors to prepare Janus m SZ@PDA-NO NPs.The mechanoluminescent emission bands of SAOE are overlapped with the excitation band of ZGC,and the persistent NIR emission can be repeatedly generated by ultrasonication activation.The emissions of ZGC act as an internal NIR source to produce thermophoretic force and NO gas propellers to drive the motion of Janus NPs.Compared with the commonly used intermittent NIR illumination,the persistent motion of ultrasound-activated NPs enhances cellular uptake and promotes intratumoral accumulation and tumor distribution of therapeutics.The long-lasting PTT and intracellular NO levels to combat tumor cells without using any chemotheray drugs and improve tumor growth inhibition.In order to effectively reduce cytotoxicities to normal cells during cancer chemotherapy,ultrasound-driven Janus nanomotors with hollow structure and in-situ electric field are fabricated to improve the selective uptake into tumor cells.SAOE and ZGC nanodtos are deposited in situ on the surface of carbon NPs,and then calcined at high temperature to obtain h SZ NPs with hollow structure,followed by physical vapor deposition of Au layer and loading DOX to construct drug-loaded Janus h SZ-Au@DOX NPs.The carbon templates are burned away at high temperature to produce the atmosphere for reducing Eu³⁺and obtain the hollow structure,which is beneficial to increase the drug loading and ultrasonic cavitation effect.The introduction of Au layer further improves the cavitation effect to enhance the ultrasound-driven motion,leading to over 80%deeper penetration in agarose matrix than those of pristine NPs.Au layers also trap the stored electrons of ZGC after activation to form persistent electric outputs,which increase the fluidity of tumor cell membrane and enhance the intracellular uptake.The persistent electric outputs cause over20-fold higher cellular uptake by tumor cells after coculture with normal cells due to their different membrane potentials,and finally increase chemotherapeutic efficacy and reduce the toxicity to normal cells.In summary,Janus micro/nanomotors driven by urease catalysis,thermophoretic force and ultrasonication can prolong blood circulation,promote tumor accumulation and penetration,enhance cell phagocytosis,and finally achieve synergistic antitumor efficacy with minimal side effect to normal tissues.These designs offer a novel and feasible strategy for nanomotor construction to overcome the biological barriers of DDS.