Adaptive backstepping-based NTSM control for unmatched uncertain nonlinear systems

An adaptive backstepping-based non-singular termi- nal sliding mode （NTSM） control method is proposed for a class of uncertain nonlinear systems in the parameteric-strict feedback form. The adaptive control law is combined with the first n - 1 steps of the backstepping method to estimate the unknown pa- rameters of the system. In the nth step, an NTSM control strategy is utilized to drive the last state of the system to converge in a finite time. Furthermore, the derivate estimator is used to obtain the derivates of the states of the error system; the higher-order non-singular terminal sliding mode control （HONTSMC） law is de- signed to eliminate the chattering and make the system robust to both matched and unmatched uncertainties. Compared to the adaptive backstepping-based linear sliding mode control method （LSMC）, the proposed method improves the convergence rate and the steady-state tracking accuracy of the system, and makes the control signal smoother. Finally, the compared simulation results are presented to validate the method.

Tumor microenvironment-responsive self-assembly of barium titanate nanoparticles with enhanced piezoelectric catalysis capabilities for efficient tumor therapy

Catalytic therapy based on piezoelectric nanoparticles has become one of the effective strategies to eliminate tumors.However,it is still a challenge to improve the tumor delivery efficiency of piezoelectric nanoparticles,so that they can penetrate normal tissues while specifically aggregating at tumor sites and subsequently generating large amounts of reactive oxygen species(ROS)to achieve precise and efficient tumor clearance.In the present study,we successfully fabricated tumor microenvironment-responsive assembled barium titanate nanoparticles(tma-BTO NPs):in the neutral pH environment of normal tissues,tma-BTO NPs were monodisperse and possessed the ability to cross the intercellular space;whereas,the acidic environment of the tumor triggered the self-assembly of tma-BTO NPs to form submicron-scale aggregates,and deposited in the tumor microenvironment.The self-assembled tma-BTO NPs not only caused mechanical damage to tumor cells;more interestingly,they also exhibited enhanced piezoelectric catalytic efficiency and produced more ROS than monodisperse nanoparticles under ultrasonic excitation,attributed to the mutual extrusion of neighboring particles within the confined space of the assembly.tma-BTO NPs exhibited differential cytotoxicity against tumor cells and normal cells,and the stronger piezoelectric catalysis and mechanical damage induced by the assemblies resulted in significant apoptosis of mouse breast cancer cells(4T1);while there was little damage to mouse embryo osteoblast precursor cells(MC3T3-E1)under the same treatment conditions.Animal experiments confirmed that peritumoral injection of tma-BTO NPs combined with ultrasound therapy can effectively inhibit tumor progression non-invasively.The tumor microenvironment-responsive self-assembly strategy opens up new perspectives for future precise piezoelectric-catalyzed tumor therapy.