Mechano-chemistry of human femoral diaphysis revealed by correlative Brillouin\u2013Raman microspectroscopy

M A Cardinali,D Dallari,A Morresi,D Fioretto,M Govoni,S Caponi

doi:10.1038/s41598-020-74330-3

Abstract

Brillouin–Raman microspectroscopy is presented as an innovative label-free all-optical investigation approachable to characterize the chemical composition and the mechanical properties of human tissues at micrometric resolution. Brillouin maps unveil mechanical heterogeneities in a human femoral diaphysis, showing a ubiquitous co-existence of hard and soft components, even in the most compact sections. The novel correlative analysis of Brillouin and Raman maps shows that the relative intensity of Brillouin peaks is a good proxy for the fraction of mineralized fibers and that the stiffness (longitudinal elastic modulus) of the hard component is linearly dependent on the hydroxyapatite concentration. For the soft component, a gradient of composition is found, ranging from an abundance of proteins in the more compact, external, bone to abundance of lipids, carotenoids, and heme groups approaching the trabecular, inner, part of the diaphysis. This work unveils the strong potential of correlative mechano-chemical characterization of human tissues at a micrometric resolution for both fundamental and translational research.

Highlights

Brillouin–Raman microspectroscopy is presented as an innovative label-free all-optical investigation approachable to characterize the chemical composition and the mechanical properties of human tissues at micrometric resolution
A new method has been proposed to measure the mechanical properties of biological tissues, based on Brillouin micro-spectroscopy[2,3,4,5,6,7] The technique is based on the inelastic scattering of light from thermally activated acoustic waves propagating through the sample at GHz frequencies
Our results show the potential of the integrated use of Brillouin and Raman microscospectroscopy (BRaMS), paving the way for its use in translational research, such as in the early diagnosis of bone diseases as well as in developing innovative scaffolds

Summary

Introduction

Brillouin–Raman microspectroscopy is presented as an innovative label-free all-optical investigation approachable to characterize the chemical composition and the mechanical properties of human tissues at micrometric resolution. Mechanical properties of bones are usually studied in vivo by means of quantitative ultrasound This technique gives global information on bone elasticity but does not allow one to investigate the microscale level because of the limited spatial resolution. Identification of asymptomatic bone degeneration could be fundamental both for the management of the disease and for the containment of the relative health costs To this respect, the sensitivity of Brillouin spectra to micro-mechanical properties of the bone reported in the present work suggests Brillouin spectroscopy to be implemented in vivo, e.g. during surgery or in endoscopic applications, together with the already experienced Raman s pectroscopy[24] to discriminate tissue types, as well as diseases, directly in the region of interest within the human body

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