Brillouin Spectroscopy as an Innovative Tool to Investigate Biomechanical Properties of Native Human Aortic Valve and Bioprostheses Tissue

Abstract

Objective: Proper aortic valve (AV) function is enabled by a complex multi-layered extracellular matrix structure and embedded valvular interstitial and endothelial cells (VICs/VECs). In a highly dynamic environment, VICs and VECs respond to biomechanical stimuli thereby influencing valvular matrix remodelling and pathological changes. Thus, it is of cardinal importance to understand the mechanobiology of AV tissue. It is hypothesized that biomechanical properties of native human AV as well as biological AV prostheses tissue can be determined using Brillouin spectroscopy. Methods: Native AV tissue (n=4) and explanted AV prosthesis (n=1) were obtained from operating theatre after AV replacement, 1mm-thick vibratome cuts were prepared (cross section in radial direction) and directly analysed by means of a confocal Brillouin microscope (10x/0.25NA). Here, the inelastically back-scattered laser light (780nm) is analysed by a custom-build Brillouin spectrometer based on a two-stage virtually imaged phased array (VIPA) set-up. Brillouin maps have been acquired pixel-by-pixel (acquisition time 1s/pixel). Tissue slides adjacent to the vibratome sections were fixed and examined histologically. Results: In stenotic AV tissue mineralized regions in the fibrosa exhibit higher Brillouin shift values compared to non-mineralized spongiosa (Figure 1A). The matrix of the examined explanted AV bioprosthesis (glutaraldehyde-fixed porcine AV) showed higher Brillouin shift values than the massive endocarditic vegetation covering both surfaces of the cusp. Calcified regions at the coaptation area were correlated with higher Brillouin shift values (Figure 1B). Conclusions: Brillouin spectroscopy enables detection of differentiated degrees of tissue stiffness within native stenotic and fibrotic human AV. It represents a promising tool to analyze biomechanical properties of human AV. Figure 1. Procedure of Brillouin spectroscopy on (a) stenotic human aortic valve and (b) aortic valve prothesis (from porcine AV cusps) with florid endocarditis and subsequent histological analysis, high Brillouin shift values indicate enhanced stiffness