Tissue biomechanics during cranial neural tube closure measured by Brillouin microscopy and optical coherence tomography

Abstract

Background Embryonic development involves the interplay of driving forces that shape the tissue and the mechanical resistance that the tissue offers in response. While increasing evidence has suggested the crucial role of physical mechanisms underlying embryo development, tissue biomechanics is not well understood because of the lack of techniques that can quantify the stiffness of tissue in situ with 3D high‐resolution and in a noncontact manner. Methods We used two all‐optical techniques, optical coherence tomography (OCT) and Brillouin microscopy, to map the longitudinal modulus of the tissue from mouse embryos in situ. Results We acquired 2D mechanical maps of the neural tube region of embryos at embryonic day (E) 8.5 (n = 2) and E9.5 (n = 2) with submicron spatial resolution. We found the modulus of tissue varied distinctly within the neural tube region of the same embryo and between embryos at different development stages, suggesting our technique has enough sensitivity and spatial resolution to monitor the tissue mechanics during embryonic development in a noncontact and noninvasive manner. Conclusions We demonstrated the capability of OCT‐guided Brillouin microscopy to quantify tissue longitudinal modulus of mouse embryos in situ, and observed distinct change in the modulus during the closure of cranial neural tube. Although this preliminary work cannot provide definitive conclusions on biomechanics of neural tube closure yet as a result of the limited number of samples, it provides an approach of quantifying the tissue mechanics during embryo development in situ, thus could be helpful in investigating the role of tissue biomechanics in the regulation of embryonic development. Our next study involving more embryo samples will investigate systematic changes in tissue mechanics during embryonic development.

Nuclear Mechanics within Intact Cells Is Regulated by Cytoskeletal Network and Internal Nanostructures

“…For embryonic tissue, Brillouin microscope has been shown to reach the depth of about 200 µm. [ 61 ]…”

Long-term Brillouin imaging of live cells with reduced absorption-mediated damage at 660nm wavelength

“…The recent expansion of Brillouin microscopy into other biomedical fields has brought forward detailed studies of live non-labelled mammalian cells [7], plant cells and their environment [8], medically important tissue sections [9,10], and protein concentrations in body fluids [11]. Most recently, Brillouin microscopy has been used to image whole mouse [12] and zebrafish embryos [13] as part of animal development studies.…”

Understanding the Mechanobiology of Early Mammalian Development through Bioengineered Models

“…Of these, we here highlight some that appear particularly suited to application for in vitro embryonic models and are generally responsive to criteria of high spatial resolution, scalability, and minimal invasiveness. One such technique is Brillouin microscopy (Scarcelli and Yun, 2007), already used to measure changes in local stiffness in late post-implantation mouse embryos (Raghunathan et al, 2017;Zhang et al, 2018a) as well as in simpler embryonic systems (Pukhlyakova et al, 2018). This type of microscopy exploits the so-called Brillouin scattering effect, originating from the interactions between light waves-illuminating the sample-and acoustic waves-originating from random thermal fluctuations of molecules within the sample and which can be related to the local viscoelastic properties of the tissue (see Prevedel et al, 2019).…”