Micro-indentation and optical coherence tomography for the mechanical characterization of embryos: Experimental setup and measurements on chicken embryos

Marica Marrese,Nelda Antonovaite,Ben K.A Nelemans,Theodoor H Smit,Davide Iannuzzi

doi:10.1016/j.actbio.2019.07.056

Abstract

The investigation of the mechanical properties of embryos is expected to provide valuable information on the phenomenology of morphogenesis. It is thus believed that, by mapping the viscoelastic features of an embryo at different stages of growth, it may be possible to shed light on the role of mechanics in embryonic development. To contribute to this field, we present a new instrument that can determine spatiotemporal distributions of mechanical properties of embryos over a wide area and with unprecedented accuracy. The method relies on combining ferrule-top micro-indentation, which provides local measurements of viscoelasticity, with Optical Coherence Tomography, which can reveal changes in tissue morphology and help the user identify the indentation point. To prove the working principle, we have collected viscoelasticity maps of fixed and live HH11-HH12 chicken embryos. Our study shows that the instrument can reveal correlations between tissue morphology and mechanical behavior. Statement of SignificanceLocal mechanical properties of soft biological tissue play a crucial role in several biological processes, including cell differentiation, cell migration, and body formation; therefore, measuring tissue properties at high resolution is of great interest in biology and tissue engineering. To provide an efficient method for the biomechanical characterization of soft biological tissues, we introduce a new tool in which the combination of non-invasive Optical Coherence Tomography imaging and depth-controlled indentation measurements allows one to map the viscoelastic properties of biological tissue and investigate correlations between local mechanical features and tissue morphology with unprecedented resolution.

Highlights

During embryogenesis, embryos experience a sequence of morphogenetic processes that, under the influence of a complex signaling network, shape the organism and form the organs (Miller and Davidson, 2013a; Wozniak and Chen, 2009)
While this study shows that the Atomic Force Microscopy (AFM) can provide local and direct mechanical measurements of native embryonic tissue, it seems that this approach, as all the ones previously discussed, is not capable to investigate possible correlations between mechanics, morphology, and tissue structure at the micro- and mesoscopic scale
One can distinguish the separation between individual somites – a result that confirms that the indentation method is able to sense structures underneath the endoderm

Summary

Introduction

Embryos experience a sequence of morphogenetic processes that, under the influence of a complex signaling network, shape the organism and form the organs (Miller and Davidson, 2013a; Wozniak and Chen, 2009). It can be concluded that, despite the numerous studies in the field, there is at present no tool to systematically analyze the local mechanical properties of embryonic tissue, more particular: an adequate instrumental techniques that accurately maps the local viscoelastic response of the embryo at both the micro- and mesoscopic scales To solve this impasse, we developed a tool that combines a cantilever-based micro-indentation setup with a non-invasive OCT imaging system to infer the local viscoelastic properties of embryos while simultaneously monitoring its morphological features. To further validate the potential of the approach proposed, we demonstrate the non-linear behavior of chicken embryos by evaluating its mechanical properties as a function of indentation strain (Antonovaite et al, 2018; Lin et al, 2009a)

Methods

Results

Conclusion