Recent advances of surface acoustic wave-based sensors for noninvasive cell analysis.

In the past years, the application of surface acoustic waves (SAWs) as sensors for biological applications has reached high relevance in the field of biotechnology. From rapid advances in designs and materials, new opportunities have emerged, especially for sensing of living cells. Additionally, the combination of SAW sensors with microfluidics and optical microscopy has expanded the market of possible applications. Differentiation of infected and healthy red blood cells or aggressive and nonaggressive tumor cells, and monitoring of wound healing, bacteria, or viral antigen concentrations via SAW-based sensors are only a few examples of recent achievements in cell biology. The rapid growth of this field requires frequent reviewing of the recent progress to maintain high research standards and promote future developments.

One-dimensional acoustic potential landscapes guide the neurite outgrowth and affect the viability of B35 neuroblastoma cells.

On the way towards neuronal stimulation and signalling, standing surface acoustic waves (SSAWs) have become a widely used technique to create well-defined networks of living cellsin vitroduring the past years. An overall challenge in this research area is to maintain cell viability in long-term treatments long enough to observe changes in cellular functions. To close this gap, we here investigate SSAW-directed neurite outgrowth of B35 (neuroblastoma) cells in microchannels on LiNbO3chips, employing one-dimensional pulsed and continuous MHz-order SSAW signals at different intensities for up to 40 h. To increase the efficiency of future investigations, we explore the limits of applicable SSAW parameters by quantifying their viability and proliferation behaviour in this long-term setup. While cell viability is impaired for power levels above 15 dBm (32 mW), our investigations on SSAW-directed neurite outgrowth reveal a significant increase of neurites growing in preferential directions by up to 31.3% after 30 h of SSAW treatment.

Acetylcholinesterase Activity Influenced by Lipid Membrane Area and Surface Acoustic Waves.

According to the current model of nerve propagation, the function of acetylcholinesterase (AChE) is to terminate synaptic transmission of nerve signals by hydrolyzing the neurotransmitter acetylcholine (ACh) in the synaptic cleft to acetic acid (acetate) and choline. However, extra-synaptic roles, which are known as 'non-classical' roles, have not been fully elucidated. Here, we measured AChE activity with the enzyme bound to lipid membranes of varying area per enzyme in vitro using the Ellman assay. We found that the activity was not affected by density fluctuations in a supported lipid bilayer (SLB) induced by standing surface acoustic waves. Nevertheless, we found twice as high activity in the presence of small unilamellar vesicles (SUV) compared to lipid-free samples. We also showed that the increase in activity scaled with the available membrane area per enzyme.

Vibration enhanced cell growth induced by surface acoustic waves as in vitro wound-healing model.

We report on in vitro wound-healing and cell-growth studies under the influence of radio-frequency (rf) cell stimuli. These stimuli are supplied either by piezoactive surface acoustic waves (SAWs) or by microelectrode-generated electric fields, both at frequencies around 100 MHz. Employing live-cell imaging, we studied the time- and power-dependent healing of artificial wounds on a piezoelectric chip for different cell lines. If the cell stimulation is mediated by piezomechanical SAWs, we observe a pronounced, significant maximum of the cell-growth rate at a specific SAW amplitude, resulting in an increase of the wound-healing speed of up to 135 ± 85% as compared to an internal reference. In contrast, cells being stimulated only by electrical fields of the same magnitude as the ones exposed to SAWs exhibit no significant effect. In this study, we investigate this effect for different wavelengths, amplitude modulation of the applied electrical rf signal, and different wave modes. Furthermore, to obtain insight into the biological response to the stimulus, we also determined both the cell-proliferation rate and the cellular stress levels. While the proliferation rate is significantly increased for a wide power range, cell stress remains low and within the normal range. Our findings demonstrate that SAW-based vibrational cell stimulation bears the potential for an alternative method to conventional ultrasound treatment, overcoming some of its limitations.