Spira mirabilis enhanced whole blood processing in a lab-on-a-disk

• A new spira mirabilis inspired geometry for blood processing using density gradient media.
• Comparison of Boycott effect in new spiral geometry chambers to inclined linear chambers.
• Rate of blood processing can be faster in spiraled chambers but this is dependent on chamber geometry.

The centrifugal microfluidic “lab-on-a-disk” paradigm is particularly suited to white blood cell (WBC) separation from whole blood, a key step for sample preparation in point-of-care diagnostics. In this work, we define the curvature of sedimentation chambers using the spira mirabilis (equiangular spiral) and so, under identified geometric conditions, enhance the Boycott effect. Processing blood with density gradient medium (DGM), we report that, under certain geometric conditions, a significant increase in speed of blood stratification in spiraled chambers of up to 39% compared to non-inclined linear chambers, and up to 22% compared with equivalently inclined linear chambers. Surprisingly, we also identify that for certain channel cross sections – particularly for shallow sedimentation chambers – the spira mirabilis chambers underperform. We provide evidence suggesting that this effect is governed by the relative impact of two primarily geometrically determined mechanisms: (a) the speed at which erythrocytes sediment out of the DGM to the inclined walls and (b) the speed at which erythrocytes sediment along the inclined walls.