Dynamic hemodialysis: a potential solution for middle molecule removal.

Better clearance of middle molecular weight solutes has been associated with improved patient outcomes. However, blood-membrane interaction during dialysis results in the development of secondary protein layers on the dialysis membrane surface, leading to impairments in middle molecular weight solute removal. The shear rate at the surface of the dialysis membrane is one of the important factors that influence blood-membrane surface interaction. In this paper, we discuss the concept of 'dynamic hemodialysis', i.e. using mechanical vibration to increase shear rate at the surface of dialysis membrane. For longitudinal and transverse vibratory motions, hemodynamic changes inside the membrane and their consequent effects on membrane morphology and dialysis efficiency are discussed. Longitudinal vibration generates a reverse flow by relative membrane motion, and transverse vibration generates a symmetric swirling flow inside the hollow fiber, which increases shear rate and enhances flow mixing. Additionally, the impulse induced by the vibration could sustain the absorption capacity of the membrane to specific uremic toxins. In conclusion, dynamic hemodialysis could enhance solute removal by minimizing the morphological changes in the dialysis membrane during hemodialysis. However, the operating conditions of dynamic hemodialysis (i.e. the amplitude and frequency of mechanical vibration) need to be optimized in terms of hemolysis and noise from the mechanical vibration.