A transparent low intensity pulsed ultrasound (LIPUS) chip for high-throughput cell stimulation.

We report an on-chip platform for low-intensity pulsed ultrasound (LIPUS) stimulation of cells directly cultured on a biocompatible surface of a transparent ultrasound transducer (TUT) fabricated using lithium niobate. The high light transmittance (>80%) and compact size (3 mm × 3 mm × 2 mm) of TUTs allowed easy integration with powerful optical microscopy techniques with no additional acoustic coupling and risk for contamination. TUTs were excited with varying acoustic excitation parameters (voltage amplitude and duty cycle) and resulting live cell calcium signaling was simultaneously imaged using time-lapse confocal microscopy, while the temperature change was measured by a thermocouple. Quantitative single-cell fluorescence analysis revealed the dynamic calcium signaling responses and together with the temperature measurements elucidated the optimal stimulation parameters for non-thermal and thermal effects. The fluorescence change profile was distinct from the recorded temperature change (<1 degree Celsius) profile under LIPUS treatment conditions. Cell dead assay results confirmed cells remain viable after the LIPUS treatment. These results confirmed that the TUT platform enables controllable, safe, high-throughput, and uniform mechanical stimulation of all plated cells. The on-chip LIPUS stimulation using TUTs has the potential to attract several in vitro and in vivo biomedical applications such as controlling stem cell differentiation and proliferation, studying biomechanical properties of cancer cells, and gaining fundamental insights into mechanotransduction pathways when integrated with state-of-the-art high-speed and high-resolution microscopy techniques.

A High Sensitivity Transparent Ultrasound Transducer based on PMN-PT for Ultrasound and Photoacoustic Imaging.

We recently introduced piezoelectric lithium niobate (LN) based transparent ultrasound transducers (TUT) as a new platform for developing multimodal optical, ultrasound and photoacoustic imaging systems. However, LN based TUT is limited in its signal-to-noise ratio due to material's low piezoelectricity (d 33). In this paper, we report, for the first time, a 0.2 mm thick transparent lead magnesium niobate-lead titanate (PMN-PT) based TUT (PMN-PT-TUT) for ultrasound and photoacoustic applications and compared its performance with a 0.25 mm thick transparent LN based TUT (LN-TUT). To improve the ultrasound energy transmission efficiency, TUTs were fabricated with a two-matching-layer design. This resulted in a dual frequency response with center frequencies of 7.8 MHz/13.2 MHz and corresponding bandwidths of 28.2%/66.67% for PMN-PT-TUT, and center frequencies of 7.2 MHz/11.8 MHz and bandwidths of 36.1%/62.7% for LN-TUT. The optical transmission rate of PMN-PT-TUTs and LN-TUTs are measured as ~73% and ~91% respectively at 532 nm optical wavelength. The PMN-PT-TUT exhibited higher sensitivity compared to LN-TUT with a nearly three-fold higher pulse echo amplitude and more than two-fold higher photoacoustic amplitude. Furthermore, optical resolution photoacoustic microscopy (ORPAM) experiments on phantom targets demonstrated lateral resolutions of 7 µm and 5.1 µm, and axial resolutions of 285.6 µm and 375.9 µm for PMN-PT-TUT and LN-TUT respectively. These results indicated that PMN-PT is a viable alternative to LN for developing TUT based multimodal ultrasound and photoacoustic imaging systems.