Mapping the Micromechanical Properties of Cryo-sectioned Aortic Tissue with Scanning Acoustic Microscopy

Abstract

Although the gross mechanical properties of ageing tissues have been extensively documented, biological tissues are highly heterogeneous and little is known concerning the variation of micro-mechanical properties within tissues. Here, we use Scanning Acoustic Microscopy (SAM) to map the acoustic wave speed (a measure of stiffness) as a function of distance from the outer adventitial layer of cryo-sectioned ferret aorta. With a 400 MHz lens, the images of the aorta samples matched those obtained following chemical fixation and staining of sections which were viewed with fluorescence microscopy. Quantitative analysis was conducted with a frequency scanning or V(f) technique by imaging the tissue from 960 MHz to 1.1 GHz. Undulating acoustic wave speed (stiffness) distributions corresponded with elastic fibre locations in the tissue; there was a decrease in wave speed of around 40 ms(-1) from the adventitia (outer layer) to the intima (innermost).

Figure 1

Ferret aorta section imaged first by with (a) 400 MHz SAM and (b) subsequently by fluorescence microscopy following paraformaldehyde-fixation and H&E staining. Scale bar represents 100 μm.

Figure 2

a) 1 GHz fluorescence image with plot of undulating acoustic wavespeed (stiffness) distribution which corresponds with the elastic fibre locations as demonstrated by b) Grayscale fluorescence image with plot showing similar undulation of grey values. The distance ‘0 μm’ in both plots represents the outermost (adventitial) edge of the tissue (leftmost in the figures).

Figure 3

Plot showing mean wave speed versus distance from the outer adventitial layer. Error bars represent standard error of the mean.