Optical coherence tomography guided Brillouin microscopy to study early embryonic development

The mechanisms involved in neural tube formation are complex and can be easily disrupted. Neurulation is one such process, governed by mechanical forces where tissues physically fold and fuse. When neural tube folding and closure fail to complete during neurulation, it results in structural and functional abnormalities of the brain and spinal cord. Thus, it is important to understand the interplay between forces and tissue stiffness during neurulation. Brillouin microscopy is an all-optical, noninvasive, high-resolution imaging technique capable of mapping tissue stiffness, but it cannot provide structural information, resulting in "blind" imaging. To overcome this limitation, we have combined a Brillouin microscopy system with optical coherence tomography (OCT) in one synchronized and co-aligned instrument to provide structural guidance whenmapping the biomechanical properties of neural tube formation in mouse embryos. We developed custom instrumentation control software that utilizes the OCT structural image to guide Brillouin imaging. We acquired first 3D OCT images and then 2D structural and mechanical maps of mouse embryos at embryonic day (E) 8.5, 9.5, and 10.5. Brillouin microscopy showed the cell-dense layer of neural plate derived from the ectoderm at E 8.5, which was unable to be distinguished with OCT. At E 9.5 and 10.5, the neuroepithelium could be clearly seen by Brillouin microscopy with a greater stiffness than the surrounding tissue. Our results show the capability of the co-aligned and synchronized Brillouin-OCT system to map tissue stiffness of murine embryos using OCT-guided Brillouin microscopy.