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 due to the lack of techniques that can quantify the stiffness of tissue in-situ with 3D high-resolution and in a non-contact manner. In this work, we used two all-optical technique, optical coherence tomography (OCT) and Brillouin microscopy, to map the longitudinal modulus of the neural tube tissue of mouse embryo in-situ. We found the tissue stiffens significantly after the closure of the neural tube at cranial regions by comparing embryos at E 8.5 and E 9.5. In addition, we observed that the region of fusion following neural tube closure is softer than the adjacent neural folds, and the neural folds show a modulus gradient along dorsal-ventral direction. Furthermore, we found the overlaying ectoderm is much softer and more pliable than the closed neural tube, and thus can be distinguished based on its mechanical properties. In conclusion, we demonstrated the capability of OCT and Brillouin microscopy to quantify tissue modulus of mouse embryos in-situ, and observed a distinct change of tissue modulus during the closure of cranial neural tube, suggesting this method could be helpful in investigating the role of tissue biomechanics in the regulation of embryo development.
A leading cause of death and decrease in the quality of life in the USA is myocardial infarction (MI). Molecular and genetic analyses have revealed a plethora of information about critical processes involved with MI. However, there is a lack of accompanying information about cardiac tissue biomechanical properties, which may provide additional critical information to understand the tissue remodeling process after MI. In this work, we utilize two complementary noncontact optical coherence elastography (OCE) techniques to assess the changes in mouse cardiac tissue biomechanical properties 6 weeks after the MI was induced. A focused micro air-pulse induced localized displacements, which were detected by a phase-sensitive OCE (PhS-OCE) system. The localized tissue displacement was modeled by a spring-mass damper model to quantify the tissue stiffness. Additionally, the propagation of an air-pulse induced elastic wave was measured at various meridional angles as a complementary measurement of tissue stiffness and anisotropy. The damping results show that the MI caused a decrease in the stiffness of the cardiac tissue. Similarly, the analysis of elastic wave propagation showed that the cardiac tissue became softer and more isotropic after MI. These results show that OCE can detect the changes in cardiac tissue biomechanical properties after MI. OCE may also be useful for developing targeted therapies by identifying regions of cardiac tissue affected by MI.
Myocardial infarction (MI) is a leading cause of death and decrease of quality of life in the USA. An immense amount of research and development has been focused on the molecular mechanisms associated with MI, which have led to numerous therapies for treating and repairing cardiac tissue after MI. However, there is a relative lack of information about the changes in cardiac tissue biomechanical properties due to MI. Therefore, there is a direct need for techniques that can measure cardiac tissue biomechanical properties, which would help further develop our understanding of tissue biomechanical dynamics associated with MI as well as aid in the development of therapies that consider biomechanical properties. In this work we utilize noncontact dynamic optical coherence elastography (OCE) to evaluate the changes in cardiac biomechanical properties 6 weeks after MI in a mouse model. We performed complementary analysis based on elastic wave propagation and damping analyses. Our results show that the left ventricle cardiac tissue became more isotropic and softer after 6 weeks in the MI-affected mice as compared to the sham mice based on the elastic wave propagation measurements. The damping measurements also showed that the MI-affected mice had softer left ventricles as compared to the sham mice. Moreover, the damping analysis was able to localize the boundary of the MI-damaged region. These results show that OCE can be a powerful tool for understanding the dynamics in biomechanical changes in murine cardiac tissue and could potentially reveal diseased areas for targeted therapies.
Embryogenesis is regulated by numerous changes in mechanical properties of the cellular microenvironment. Thus, studying embryonic mechanophysiology can provide a more thorough perspective of embryonic development, potentially improving early detection of congenital abnormalities as well as evaluating and developing therapeutic interventions. A number of methods and techniques have been used to study cellular biomechanical properties during embryogenesis. While some of these techniques are invasive or involve the use of external agents, others are compromised in terms of spatial and temporal resolutions. We propose the use of Brillouin microscopy in combination with optical coherence tomography (OCT) to measure stiffness as well as structural changes in a developing embryo. While Brillouin microscopy assesses the changes in stiffness among different organs of the embryo, OCT provides the necessary structural guidance.
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