See-saw rocking: an in vitro model for mechanotransduction research.

In vitro mechanotransduction studies, uncovering the basic science of the response of cells to mechanical forces, are essential for progress in tissue engineering and its clinical application. Many varying investigations have described a multitude of cell responses; however, as the precise nature and magnitude of the stresses applied are infrequently reported and rarely validated, the experiments are often not comparable, limiting research progress. This paper provides physical and biological validation of a widely available fluid stimulation device, a see-saw rocker, as an in vitro model for cyclic fluid shear stress mechanotransduction. This allows linkage between precisely characterized stimuli and cell monolayer response in a convenient six-well plate format. Models of one well were discretized and analysed extensively using computational fluid dynamics to generate convergent, stable and consistent predictions of the cyclic fluid velocity vectors at a rocking frequency of 0.5 Hz, accounting for the free surface. Validation was provided by comparison with flow velocities measured experimentally using particle image velocimetry. Qualitative flow behaviour was matched and quantitative analysis showed agreement at representative locations and time points. Maximum shear stress of 0.22 Pa was estimated near the well edge, and time-average shear stress ranged between 0.029 and 0.068 Pa. Human tenocytes stimulated using the system showed significant increases in collagen and GAG secretion at 2 and 7 day time points. This in vitro model for mechanotransduction provides a versatile, flexible and inexpensive method for the fluid shear stress impact on biological cells to be studied.

Insects in flight: direct visualization and flow measurements.

The study of insect flight has been advanced in recent years by the advent and application of new quantitative flow diagnostic techniques, not least digital particle image velocimetry. More classical qualitative methods such as smoke flow visualization have also been applied with new goals for the rigorous description of flows around insects. The combination of techniques has led to the development of ideas which may be of some consequence to the designers of micro-air vehicles wishing to follow a biomimetic principle. Specifically, kinematic parameters such as wingbeat frequency and amplitude are discussed, along with some discussion of the investigation of morphological parameters such as wing design.