Bone Cells Grown on Micropatterned Surfaces are More Sensitive to Fluid Shear Stress

Abstract

Bone has the ability to adapt its structure to meet its mechanical environment. In spite of great efforts to understand the mechanisms underlying this phenomenon, little is known about bone mechanotransduction at the cellular level. In this work, we propose that there is an interaction between the architecture of the cell and mechanosensitivity. Specifically, we hypothesized that cell spreading plays an important role in bone cell mechanotransduction. To test our hypothesis, we utilized micropatterned surfaces that allowed us to control the degree of cell spreading. Focal adhesion area is also known to depend on cell spreading. Thus patterns were utilized that maintained a constant total adhesive contact area, but permitted differing degrees of spreading. MC3T3-E1 osteoblasts cultured on these patterned surfaces were exposed to dynamic fluid shear stress. The fluid flow-induced changes in intracellular calcium [Ca 2+ ] i were determined as a function of the degree of spreading. Cells grown on micropatterned surfaces were more responsive in general than those grown on traditional unpatterned surfaces. Interestingly, however, we found that cells with a higher degree of spreading were less responsive to mechanical loading. This work provides new insights into the interplay of cellular structure and mechanotransduction.

Boning up on Wolff's Law: Mechanical regulation of the cells that make and maintain bone

“…Steady fluid flow (SFF) accelerated actin stress fiber formation in osteoprogenitors (Malone et al, 2007b) compared with OFF (Ponik et al, 2007). The responsiveness of osteoprogenitors to flow may depend on cytoskeletal tension: using micropatterning to control cell spreading while maintaining constant total adhesive contact area, You et al (2008a) showed that more spread osteoprogenitors were less responsive to mechanical loading.…”

Fluid Dynamics Analysis of a Novel Micropatterned Cell Bioreactor

“…While the above numerical calculations are based on the orientation of inlet velocity vector being normal to entrance section, as used in a series of flow chambers, 4,11,16,31,40 different orientations of inlet velocity vector have also been applied in other flow chambers. 9,20,27 In this article, the impact of two alternative orientations of inlet velocity vector on flow field has been tested: one is 45°relative to height-direction in x-z plane (Fig.…”

“…Flow chamber is a well-defined in vitro model to mimic the physiological conditions for elucidating the effect of biofluid flow on cellular responses such as cell proliferation, 17,33 apoptosis, 24 differentiation 1,28 migration, 35 adhesion, 29 cell interaction in co-culture, 5 and intra/intercellular signalings. 16,31,40 Flow chamber also serves as a cell/tissue bioreactor in space cell biology to maintain cellular metabolism under microgravity, 32 since the refreshment of culture medium, a conventional procedure under ground-based conditions, becomes complicated and hard to perform in space and should be automatically done via continuous perfusion in a closedloop system. In the past decades, different types of flow chambers or flow-based bioreactors have been developed mainly with parallel-plate flow approach, where cells are seeded on the bottom plate and grown to a confluent monolayer while the medium is driven to flow over cells providing sufficient nutrient supply and mass transportation.…”

“…In previous studies, a few fluid mechanics models were proposed to predict the flow field at the vicinity of curved endothelial cell monolayer in blood vessel, 15,22 and the wall shear stress was found to vary more than 80% across the chamber because of the so-called end effects. 40 Moreover, growing cells are highly sensitive to the alterations of hydrodynamic parameters, for example, alkaline phosphatase activity increases dramatically with shear stress in engineered bone tissue, 3,13,14,16,19,31,40 and intracellular process and cell body respond differentially to various mechanical loadings. 21 Thus, fluid dynamics analysis is a prerequisite to monitor the hydrodynamic parameters, such as flow flux, velocity, and shear stress, and to understand the mechanism of cell mechanotransduction.…”

“…8,15,18,20 For example, intracellular calcium response to shear flow of isolated osteoblasts on micropatterned islands was found to be quite different from that of the osteoblasts in a confluent monolayer. 16,31,40 The shape and size of hydrophilic island designed to confine the spreading configuration and contact area of a cell resulted in distinct phenotypes in apoptosis, differentiation, and proliferation of mesenchymal stem cells. 7 Microfabricating technique with micropatterned cells is especially beneficial for a cell bioreactor used in space life science where the impact of shear flow from continuous perfusion is coupled with the effect of microgravity.…”