Xuexin Duan
Abstract
Efficient intracellular delivery of exogenous materials remains a critical issue in fundamental biological researches and clinical applications. Here, we developed a novel chemical-free method for intracellular delivery enhancement using a designed gigahertz ultrasonic electromechanical resonator. When excited by a sinusoidal electric signal, the propagation and attenuation of acoustic wave in liquid will generate high-speed acoustic streaming. The liquid above the device working area will be accelerated and strike the substrate surface, thus generates pressure on cells, induces deformation and membrane poration, and finally realizes delivery of exogenous materials. To verify the intracellular delivery ability, DOX was selected as an example, and an enhanced fluorescence of DOX in cells exposed to resonator stimulation can be seen. We also realized the delivery of fluorescent-labeled DNA strains and plasmids. Besides, different power applied to the resonator can induce different fluid velocity, thus generate different force intensity and control the deliver efficiency. Pores on membranes induced by acoustic streaming treatment were observed by SEM. Disrupted cell membranes and porous structures can be seen after treatment, and resealed after 10 min recovery, indicating a strong fluid force exerted on cells and the influence is temporary and reversible. When light, for example from a switched Q laser operating with nanosecond laser pulses, is concentrated on a single nanoparticle optically trapped, the laser-induced failure can occur, leading to plasma formation and the emission of shock waves by its expansion followed by the vaporization of the nanoparticle or liquid (surrounding water media). This volume of steam does form a cavitation bubble, which expands as the volume of the abbread nanoparticle or vaporized liquid increases. The expansion of the bubbles and its subsequent collapse may be accompanied by the emission of acoustic transients and microjets depending on the position of the cavitation bubble in relation to the substrate. These photomechanical properties can lead to the permeabilisation of the plasma membrane of cells. The formation and jet emission of acoustic transients on collapse depend on the sizeless stand-off parameter, Between the bubble and the wall, Z0/Rmax, where Z0 is the distance between the bubble center/nanoparticle and the wall, and Rmax is the maximum bubble radius (Hentschel, W. and Lauterborn, W., Appl Sci Res 38, 225-230 (1982)). When the bubble wall is in contact with the boundary, the formation of the jet is predominant in relation to the acoustic emission. On the other hand, when the bubble is free of distortion (i.e., the bubble is free of distortion), the bubble energy is more efficiently transformed into acoustic energy. Thus, the jet can cause localized membrane poration of several cells in a targeted area, while acoustic transients can produce large-scale poration of cells in a large area (hundreds of micrometers) because acoustic waves can propagate a long distance (usually hundreds of micrometers) in the middle of the sample. It is important to control the volume/size of the cavitation (determines the total bubble energy available for the jet and acoustic energies) as well as its axial position from the limit (determines the relative intensity between the jet and acoustic emissions). Optical clamps allow the containment and positioning of microparticles and nanoparticles at a desired location within the sample. With this approach, the threshold energy required for lib depends on the nanoparticle material and its size and is free of the surrounding environment. Thus, the technique can optimize bubble energy and stand-off parameter, which lead to membrane permeabilisation of mammalian cells with retention of cellular viability.