MicroNanophysics Research Laboratory, Monash University, Clayton, VIC 3800, Australia.
Biomicrofluidics. 2009 Jan 2;3(1):12002. doi: 10.1063/1.3056040.
We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and microbioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1-10 cms velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micronanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1-2 cm in length or atomization of the entire drop to produce 1-10 mum monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymerprotein solutions can also be used for the rapid synthesis of 150-200 nm polymerprotein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physicalchemical templating.
我们证明，表面声波（SAWs），即在兆赫兹频率下驱动的纳米振幅瑞利波，在压电衬底表面传播，为驱动一系列极快的微流控致动和微生物颗粒操纵方案提供了一种强大的方法。我们表明，液滴可以在平面衬底上快速平移，或者可以以 1-10 cms 的速度通过微通道泵送流体，这通常比当前微流控技术提供的速度快一到两个数量级。通过打破对称，可以在液滴内诱导角向再循环，以驱动强烈的惯性微离心作用进行微混合和颗粒浓缩或分离。通过改变 SAW 频率，通过利用来自微通道侧壁的辐照声波的叠加，可以在相同的微通道中诱导类似的微混合策略，从而将均匀的直通流快速切换为混沌振荡流。如果流动足够静止，横跨微通道产生的横向驻波节点也允许颗粒聚集，因此，可以在节点线上进行分类。此外，SAW 还促进了其他微流控功能。例如，通过在其下方的 SAW 在液滴的自由表面上激发的毛细波可以用于在节点或线处收集和分类微米纳米颗粒。在更高的功率下，当 SAW 在基板表面上传播时，由于基板表面上的大加速度，液滴的自由表面会迅速失稳，从而产生持续 1-2 cm 长的惯性液体射流，或者整个液滴雾化以产生 1-10 微米的单分散气溶胶液滴，可用于喷墨打印、质谱接口或肺部药物输送。聚合物-蛋白质溶液的雾化也可用于快速合成 150-200nm 的聚合物-蛋白质颗粒或可生物降解的聚合物壳，其中蛋白质、肽和其他治疗分子被包封在其中以进行控制释放药物输送。含有聚合物溶液的平移液滴后面的薄膜雾化也会导致规则聚合物斑点的远程空间有序，其大小和间距取决于 SAW 频率，因此提供了一种简单而强大的聚合物图案化方法，而无需表面处理或物理化学模板。
