Parallel-plate fluid flow systems for bone cell stimulation

Bone responds to changes in its mechanical environment, but the mechanisms by which it does so are poorly understood. One hypothesis of mechanosensing in bone states that osteocytes can sense the flow of fluid through the canalicular system. To study this in vitro a number of fluid flow devices have been designed in which cells are placed between parallel plates in sealed chambers. Fluid flows through the chambers at controlled rates, most commonly driven by a peristaltic pump. In addition to fluid flow, high pressures have been observed in these chambers, but the effect of this on the cellular responses has generally been ignored or considered irrelevant, something challenged by recent cellular experiments using pressure only. We have, therefore, devised a system in which we can considerably reduce the pressure while maintaining the flow rate to enable study of their effects individually and in combination. As reducing pressure also reduces the risk of leaks in flow chambers, our system is suitable for real-time microscopical experiments. We present details of the new systems and of experiments with osteoblasts to illustrate the effects of fluid flow with and without additional pressure on the translocation of β-catenin to the nucleus.