Scanning acoustic microscopy

The scanning acoustic microscope (SAM) allows one to measure mechanical parameters of living cells with high lateral resolution. By analyzing single acoustic images’ sound attenuation and sound velocity, the latter corresponding to stiffness (elasticity) of the cortical cytoplasm can be determined. In this study, measurements of stiffness distribution in XTH-2 cells were compared with the organization of F-actin and microtubules. Single XTH-2 cells exhibit relatively high stiffness at the free margins; toward the cell center this value decreases and reaches a sudden minimum where the slope of the surface topography enlargens at the margin of the dome-shaped cell center. The steepness of the increase in slope is linearly related to the decrease in sound velocity at this site. Thus, a significant determinant of cell shape is paralleled by an alteration of stiffness. In the most central parts, no interferences could be distinguished, therefore, this region had to be excluded from the calculations. Stiffness distribution roughly coincided with the distribution of F-actin, but no correlation to microtubule arrangement was found.

Acoustic microscopy of cultured cells. Distribution of forces and cytoskeletal elements.

SUMMARY

The reactions of XTH-2 cells (line derived from Xenopus laevis tadpole hearts) to cytochalasin D (CD) were followed using scanning acoustic microscopy (SAM) at 0.9 GHz, fluorescence and electron microscopy. The first reaction to CD which can be detected by SAM is a loss of image contrast, indicating a decrease in acoustic impedance of about 30%. Based on structural changes revealed by staining of actin with TRITC-phalloidin, and taking theoretical considerations into account, a relationship between impedance decrease and tension in the actin fibrillar system is deduced.

Scanning acoustic microscopy visualizes cytomechanical responses to cytochalasin D.

The disclosed scanning acoustic microscope comprises a solid lens body consisting of two sections of materials having different sound propagation characteristics but matching acoustic impedances. A lens is formed by the interface of said two sections and has a focal point coinciding with the apex of a sharply pointed tip formed at the free surface of one of said sections. The tip and the specimen to be investigated are immersed in a coupling medium having a relatively high acoustic absorption coefficient. The lens body carries an acoustic transducer on its surface remote from the tip for sending plane sound waves through the lens and tip onto the specimen. Acoustic waves reflected from the specimen are also received by this transducer. Acoustic waves transmitted through the specimen optionally may be received by a transducer arranged on the opposite side of the specimen. By appropriate processing of the received signals, high-resolution (10 nm) images of the specimen can be obtained.

Scanning acoustic microscope

Shape and locomotion of tissue cells depend on the interaction of elements of the cytoskeleton, adhesion to the substrate and an intracellular hydrostatic pressure. The existence of this pressure becomes obvious from increase in cell volume on cessation of contractile forces and from observations with ultrasound acoustic microscopy. Wherever such an internal pressure is established, it is involved in generation of shape and driving force of cell locomotion. Therefore each hypothesis on cell shape and locomotion must consider this property of a living cell. Apparently different types of locomotion depend on differences in substrate adhesion and/or cytoskeleton organization.

Architecture of tissue cells the structural basis which determines shape and locomotion of cells

Although the technique of scanning acoustic microscopy was introduced more than a decade ago, there still is a general lack of wide-spread applications research due to the limited number of instru- ments worldwide To enlarge the spectrum of applications, this contri- bution presents selected results of work in materials science (ceramics, single crystals, polymers, thin ams, and integrated circuits) and biol- ogy (living cells, mucous coats, and cuticle structures) and an opening angle of 100" are used The broadband design of the matching network and transducer and anti- reflection coating enables the frequency range to be cov- ered by two acoustic objectives, operating from 08 to 13 and 13 to 20 GHz, respectively The x- and y-scanning is performed by electromagnetic coil systems driving the objective in a raster mode (x-scanning frequency locked

Applications of Scanning Acoustic Microscopy - Survey and New Aspects

Maintaining the fidelity during mass production of nanostructures over large surface areas poses several challenges. Thin polymer optic components are susceptible to warping, birefringence, and errors in nanostructure form and periodicity. These issues can vary across the entirety of the surface, much more than in smaller injection molded parts. We discuss some of these challenges, their effects on the performance of the nanostructures, and some methods for mitigation.

M. Hoppe

Papers

Applications of Scanning Acoustic Microscopy - Survey and New Aspects

Injection molding of subwavelength structures over a large surface area