Viscoelastic Properties of the Aortic Valve Interstitial Cell

Abstract

There has been growing interest in the mechanobiological function of the aortic valve interstitial cell (AVIC), due to its role in valve tissue homeostasis and remodeling. In a recent study we determined the relation between diastolic loading of the AV leaflet and the resulting AVIC deformation, which was found to be substantial. However, due to the rapid loading time of the AV leaflets during closure (~0.05 s), time-dependent effects may play a role in AVIC deformation during physiological function. In the present study, we explored AVIC viscoelastic behavior using the micropipette aspiration technique. We then modeled the resulting time-length data over the 100 sec test period using a standard linear solid (SLS) model which included Boltzmann superposition. To quantify the degree of creep and stress relaxation during physiological timescales, simulations of micropipette aspiration were preformed with a valve loading time of 0.05 s and a full valve closure time of 0.3 s. The 0.05 s loading simulations suggest that, during valve closure, AVICs act elastically. During diastole, simulations revealed creep (4.65%) and stress relaxation (4.39%) over the 0.3 s physiological timescale. Simulations also indicated that if Boltzmann superposition was not used in parameter estimation, as in much of the micropipette literature, creep and stress relaxation predicted values were nearly doubled (7.92% and 7.35%, respectively). We conclude that while AVIC viscoelastic effects are negligible during valve closure, they likely contribute to the deformation time-history of AVIC deformation during diastole.

The elastic properties of valve interstitial cells undergoing pathological differentiation

“…However, the creep time constant for VICs is at least an order of magnitude greater than the $ 1 Hz cardiac cycle, suggesting that VICs respond primarily elastically under physiologically-relevant loading (Merryman et al, 2009). Thus, we characterized VIC mechanical behavior by the instantaneous Young's modulus (E 0 ), rather than the equilibrium Young's modulus or other viscoelastic parameters.…”

“…VICs are viscoelastic, exhibiting creep under constant pressure during MA (Merryman et al, 2009;Zhao et al, 2009). However, the creep time constant for VICs is at least an order of magnitude greater than the $ 1 Hz cardiac cycle, suggesting that VICs respond primarily elastically under physiologically-relevant loading (Merryman et al, 2009).…”

“…The viscoelastic properties of freshly isolated VICs and VICs expanded in growth medium in vitro (Merryman et al, 2009) have been reported previously. Remarkably, Merryman et al (2006) found that the elastic moduli of subcultured VICs correlated with the transvalvular pressure of the valve from which the VICs were isolated and a-SMA content;…”

Prediction of matrix-to-cell stress transfer in heart valve tissues

“…Several factors may contribute to the stress distribution that evolves within heart valve leaflet tissues, such as the orientation of collagen fibers, morphologies and/or sizes of the VICs and the local composition and degree of crosslinking of the ECM. Moreover, it is well recognized that valvular tissues [57] and VICs [58] are viscoelastic; the effects of viscoelasticity on stress distribution evolution within leaflet tissue and at the level of individual VICs remain to be ascertained.…”

An Undergraduate Lab (on-a-Chip): Probing Single Cell Mechanics on a Microfluidic Platform

“…12,18 MA simply uses suction pressure to partially aspirate a cell into a small-diameter glass tube. Geometric constraints and the resulting deformation as a function of applied pressure can then be used with relevant analytical 16,23 or computational 1,35,36 models to determine the mechanical properties of a single cell.…”