On the use of ultrasounds to quantify the longitudinal threshold force to detach osteoblastic cells from a conditioned glass substrate

Development, Optimization, Biological Assays, and In Situ Field Immersion of a Transparent Piezoelectric Vibrating System for Antifouling Applications

This paper presents the development and experimentations of transparent vibrating piezoelectric micromembranes dedicated to protecting immersed measurement instruments from marine biofouling. As any surface immersed is subject to the adhesion and settlement of organisms, especially in seawater, transparent materials quickly become opaque, resulting in deteriorated accuracy for optical sensors. According to this, we developed a transparent vibrating membrane to promote biofouling detachment in order to reduce the data quality drift and the frequency of maintenance operations on deployed optical sensors. In the first part, the design, the materials, and the steps to manufacture demonstrators are described. Then, the electromechanical characterizations of the demonstrators are carried out and interpreted with the support of FEM simulations. The last part describes the laboratory bioassays and the field immersion tests. Laboratory bioassays assess the antifouling potential of the vibrating piezoelectric membranes by exposing their surface to a suspended bacterial solution. In situ assays allow the membrane to perform in the Mediterranean Sea to assess their effectiveness in real conditions. Laboratory bioassays showed a great potential against the adhesion and settlement of a bacterial solution, while in situ tests confirmed the antifouling effect of piezoelectric vibrating micromembrane. Nevertheless, in situ experimentations revealed troubles with the piezo driver actuating the vibrating membranes, and tests should be carried out again with an improved piezo driver to reveal the full potential of the vibrating membranes. These are the first steps to set up an efficient antifouling vibrating system for immersed optical sensors.

Probing single-cell mechanics with picosecond ultrasonics

The mechanical properties of cells play a key role in several fundamental biological processes, such as migration, proliferation, differentiation and tissue morphogenesis. The complexity of the inner cell composition and the intricate meshwork formed by transmembrane cell-substrate interactions demands a non-invasive technique to probe cell mechanics and cell adhesion at a subcell scale. In this paper we review the use of laser-generated GHz acoustic waves--a technique called picosecond ultrasonics (PU)--to probe the mechanical properties of single cells. We first describe applications to vegetal cells and biomimetic systems. We show how these systems can be used as simple models to understand more complex animal cells. We then present an opto-acoustic bio-transducer designed for in vivo measurements in physiological conditions. We illustrate the use of this transducer through the simultaneous probing of the density and compressibility of Allium cepa cells. Finally, we demonstrate that this technique can quantify animal-cell adhesion on metallic surfaces by analyzing the acoustic pulses reflected off the cell-metal interface. This innovative approach allows investigating quantitatively cell mechanics without fluorescent labels or mechanical contact to the cell.

Ultrasound-induced release of micropallets with cells

Separation of selected adherent live cells attached on an array of microelements, termed micropallets, from a mixed population is an important process in biomedical research. We demonstrated that adherent cells can be safely, selectively, and rapidly released from the glass substrate together with micropallets using an ultrasound wave. A 3.3-MHz ultrasound transducer was used to release micropallets (500 μm × 500 μm × 300 μm) with attached HeLa cells, and a cell viability of 92% was obtained after ultrasound release. The ultrasound-induced release process was recorded by a high-speed camera, revealing a proximate velocity of ∼0.5 m/s.

Picosecond acoustics in vegetal cells: non-invasive in vitro measurements at a sub-cell scale

A 100 fs laser pulse passes through a single transparent cell and is absorbed at the surface of a metallic substrate. Picosecond acoustic waves are generated and propagate through the cell in contact with the metal. Interaction of the high frequency acoustic pulse with a probe laser light gives rise to Brillouin oscillations. The measurements are thus made with lasers for both the opto-acoustic generation and the acousto-optic detection, and acoustic frequencies as high as 11 GHz can be detected, as reported in this paper. The technique offers perspectives for single cell imaging. The in-plane resolution is limited by the pump and probe spot sizes, i.e. approximately 1 microm, and the in-depth resolution is provided by the acoustic frequencies, typically in the GHz range. The effect of the technique on cell safety is discussed. Experiments achieved in vegetal cells illustrate the reproducibility and sensitivity of the measurements. The acoustic responses of cell organelles are significantly different. The results support the potentialities of the hypersonic non-invasive technique in the fields of bio-engineering and medicine.