Particle Enrichment In 3D-printed Microfluidics With River Meander-inspired Cross-section And Its Applications

In recent years,microfluidic techniques have attracted great attention in terms of tumor cell enrichment.In related works,Traditional microfluidic cross-sections are limited to several common geometries,which seriously imposes restrictions on the studies of flow fields and particle manipulations in microchannels.Inspired by the bed topography in river meanders,here,we report a novel 3D-printed river meander-like cross-section in helical microchannels for size-based inertial focusing and enrichment.Microfluidic cross-sections with different parameters were designed.By numerical simulations,1000 ?m was selected as the optimal vertex length,which could locate the cores of vortices near the outer channel wall,resulting in enough space for the balance between forces acting on particles.River meander-inspired channels with different vertex lengths were 3D-printed and used for the experiment of 26 ?m particle focusing,in which the simulation results were proved reasonable.The pattern of particle focusing in channels with different loop numbers were explored.To quantify the performance of particle focusing,the distribution of the fluorescent particles across the channel was measured and Gaussian fitted.Full width at half maximum(FWHM)of the fitting curve was used.Compared to the circular,rectangular and trapezoidal channels,the river meander-like microfluidic channel can successfully realize 26 ?m particle focusing with a thinner focusing band in a shorter channel length.The mixture of 12 ?m particle and 26 ?m particle were used for the enrichment of larger particles.Also,in a single test,the river meander-inspired channel can achieve 85.4% recovery and the enrichment ratio of 1.86(theoretical maximum is 2)of spiked MDA-MB-231 cells in the whole blood.While the inertial focusing was successful achieved,viscoelastic fluid was introduced to the microfluidic system.Under the influence of the elastic force resulted from polyoxyethylene(PEO),the focusable particle size was lowered from 26 ?m to 18 ?m.Using viscoelastic with different concentration and molecular weight of PEO,the pattern of 18 ?m particle focusing was studied.By mixing with 6 ?m particles,the enrichment of 18 ?m particles was achieved.Using blood samples with dilution times varying from 500 to 50,the enrichment of MDA-MB-231 cells was achieved.Meanwhile recovery rate and enrichment ratio has increased to 96.25% and 1.97,respectively.By increasing channel width from 1000 ?m to 2000 ?m and decreasing channel height from 500 ?m to 300 ?m,position of the focusing band of 18 ?m particles migrated from channel center to the outer wall.Experiments using channels with different height were conducted and the difference of focusing condition was found in channel with height of 352 ?m.Moreover,MDA-MB-231 cells were successfully focused close to the channel outer wall at the flowrate of 600 ?L/min.This work has systematically studied the size-based particle focusing behavior with the 3Dprinted river meander-inspired microchannel in both inertial fluid and viscoelastic fluid.The results showed the superiority of the river meander-inspired cross-section in terms of particle focusing,which has overcome the restriction imposed on channel cross-section and inspired further studies on 3D-printed uncommon microfluidic cross-sections.In addition to particle focusing,this work achieved the enrichment of tumor cells spiked in whole blood,which has proved its potential in sized-based cell/particle sorting and enrichment for clinical application.