Comparative study of variations in mechanical stress and strain of human blood vessels: mechanical reference for vascular cell mechano-biology

Ultrafast Axial Freezing in a Liquid-Filled Capillary Tube

Liquid-filled capillary tubes are a kind of standard component in life science (e.g., blood vessels, interstitial pores, and plant vessels) and engineering (e.g., MEMS microchannel resonators, heat pipe wicks, and water-saturated soils). Under sufficiently low temperatures, the liquid in a capillary tube undergoes phase transition, forming an ice nucleus randomly on its inner wall. However, how an ice layer forms from the nucleus and then expands, either axially or radially to the tube inner wall, remains obscure. We demonstrated, both experimentally and theoretically, that axial freezing along the inner wall of a water-filled capillary tube occurs way ahead of radial freezing, at a nearly constant velocity 3 orders in magnitude faster than the latter. Rapid release of latent heat during axial freezing was identified as the determining factor for the short duration of recalescence, resulting in an exponential rise of the supercooling temperature from ice nucleation via axial freezing to radial freezing. The profile of the ice-water interface is strongly dependent upon the length-to-radius ratio of the capillary tube and the supercooling degree at ice nucleation. The results obtained in this study bridge the knowledge gap between the classical nucleation theory and the Stefan solution of phase transition.

Compromised homeostasis in aged carotid arteries revealed by microstructural studies of elastic lamellae

Healthy arteries are continuously subjected to diverse mechanical stimuli and adapt in order to maintain a mechanical homeostasis which is characterized by a uniform distribution of wall stresses. However, aging may compromise the homeostatic microenvironment within arteries. Structural heterogeneity has been suggested as a potential microstructural mechanism that could lead to homogeneous stress distribution across the arterial wall. Our previous study on the unfolding and stretching of the elastic lamellae revealed the underlying microstructural mechanism for equalizing the circumferential stresses through wall; inner elastic layers are wavier and unfold more than the outer layers which helps to evenly distribute lamellar stretching (Yu et al., 2018). In this study, we investigated the effect of aging on lamellar deformation and its implications for tissue homeostasis. Common carotid arteries from aged mice were imaged under a multi-photon microscope while subjected to biaxial extension and inflation at five different pressures ranging from 0 up to 120 mmHg. Lamellar unfolding during pressurization was then determined from the reconstructed cross-sectional images of elastic lamellae. Tissue-level circumferential stretch was combined with the lamellar unfolding to calculate lamellar stretching. Our results revealed that the straightness gradient of aged elastic lamellae is similar to the young ones. However, during pressurization, the inner elastic lamella of the aged mice unfolded significantly more than the inner layer in young arteries. An important finding of our study is the uneven increase in inter-lamellar space which contributed to a nonuniform stretching of the elastic lamellae of aged mice arteries, elevated stress gradient, and a shifting of the load-bearing component to adventitia. Our results shed light into the complex microstructural mechanisms that take place in aging and adversely affect arterial mechanical behavior and homeostasis.

A novel method for calculating CTFFR based on the flow ratio between stenotic coronary and healthy coronary

BACKGROUND

Epicardial coronary stenosis may lead to myocardial ischaemia, and the resulting obstructive coronary artery disease is one of the leading causes of death. CT-derived fractional flow reserve (CT-FFR) has been clinically shown to be an effective method for the noninvasive assessment of coronary artery stenosis. However, this method has the problem that the measurement result is affected by the selected measurement position.

OBJECTIVES

This study was to obtain a novel flow-based approach to coronary CTFFR (CTQFFR), which was not affected by the measurement location.

METHODS

This study established healthy-assumed coronary arteries based on narrowed coronary arteries. Based on the assumption that the microvascular resistance remains unchanged in the short term after coronary stenosis treatment, the blood flow in the stenotic coronary artery and the healthy-assumed coronary artery was obtained by numerical simulation, and the CTQFFR based on the blood flow ratio was calculated. The functional relationship between CTQFFR and FFR was fitted by the results of 20 cases.

RESULTS

In this study, the functional relationship between CTQFFR and FFR was fitted by a quadratic curve, and the variance was 0.8744; the functional relationship between CTQFFR and pressure-based approach to coronary CTFFR (CTPFFR) was fitted by a primary curve, and the variance was 0.9971. There was coronary artery growth in all 20 cases. Preliminary validation results using 10 cases showed 100% accuracy in determining whether coronary artery stenosis required for clinical intervention. The relative error of the coefficient with the results proposed in a previous study was 0.316%.

CONCLUSION

This study proposes a new method for calculating coronary CTFFR, namely, coronary CTQFFR, which is the flow ratio between stenotic coronary and healthy-assumed coronary. This method solves the problem that the downstream CTFFR of coronary stenosis is related to the selected location, which effectively improves the CTFFR at the critical value (CTFFR= 0.8) near reliability. Preliminary research results show that the method obtained in this study has a high accuracy for determining whether there is significant coronary stenosis. However, large multi-centre validation for the feasibility of this method was necessary in our future work.

Involvement of the FAK Network in Pathologies Related to Altered Mechanotransduction

Mechanotransduction is a physiological process in which external mechanical stimulations are perceived, interpreted, and translated by cells into biochemical signals. Mechanical stimulations exerted by extracellular matrix stiffness and cell–cell contacts are continuously applied to living cells, thus representing a key pivotal trigger for cell homeostasis, survival, and function, as well as an essential factor for proper organ development and metabolism. Indeed, a deregulation of the mechanotransduction process consequent to gene mutations or altered functions of proteins involved in perceiving cellular and extracellular mechanics can lead to a broad range of diseases, from muscular dystrophies and cardiomyopathies to cancer development and metastatization. Here, we recapitulate the involvement of focal adhesion kinase (FAK) in the cellular conditions deriving from altered mechanotransduction processes.