Y-shaped microfluidic channels have been built with Computer Numerical Control (CNC) and laser cutting manufacturing techniques. Fluid is delivered to each port via external syringe pumps. Each Y-shaped channel contains thermal inkjet (TIJ) resistors built using conventional microfabrication techniques. The resistors vaporize water and generate drive bubbles. This work focuses on utilizing TIJ technology as an active mixing technique in microfluidics. By varying the electrical firing frequency of the resistors, fluid was successfully mixed with an effective mixing length equal to the length of the TIJ resistor. As such, we demonstrate the use of TIJ resistors as a scalable, active mixing approach in microfluidics. A metric to characterize the extent of mixing using TIJ resistors was proposed and utilized. In addition, the fundamental framework of TIJ bubble dynamics with respects to mixing was assessed.

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IntroductionBlood contacting medical devices, including rotary blood pumps, can cause shear-induced blood damage that may lead to adverse effects in patients. Due in part to an inadequate understanding of how cell-scale fluid mechanics impact red blood cell membrane deformation and damage, there is currently not a uniformly accepted engineering model for predicting blood damage caused by complex flow fields within ventricular assist devices (VADs).MethodsWe empirically investigated hemolysis in an axial Couette flow device typical of a rotary VAD to expand our current understanding of shear-induced blood damage in two ways. First, we used a magnetically levitated device to accurately control the shear rate and exposure time experienced by blood and to minimize the effects of other uncharacterized stresses. Second, we explored the effects of both hematocrit and plasma viscosity on shear-induced hemolysis to characterize blood damage based on the viscosity-independent shear rate, rather than on shear stress.ResultsOver a shear rate range of 20,000-80,000 1/s, the Index of Hemolysis was found to be largely independent of hematocrit, bulk viscosity, or the suspension media viscosity.ConclusionIt is recommended that future investigations of shear-induced blood damage report findings with respect to the viscosity-neutral term of shear rate, in addition to the bulk whole blood viscosity measured at an appropriate shear rate relevant to the flow conditions of the device.

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