The effects of microchannel deformability on the dynamic response of inertial microfluidic systems to pressure pulsations

The behaviour of pressure-driven microfluidic systems used in practical applications often deviates from that under ideal steady-flow conditions due to factors such as pump instability, tubing compliance, and pressure fluctuations. However, the effects of pressure pulsation on the dynamic response of microfluidic systems remain largely underexplored. Specifically, systematic investigation on the influence of device material elasticity on the dynamic behaviour of particle inertial focusing is limited. This paper investigates the effects of microchannel elasticity on inertial focusing of microparticles under pressure pulsations. Microfluidic devices were fabricated with four polydimethylsiloxane (PDMS) base-to-curing agent ratios (5:1, 10:1, 15:1, 20:1), corresponding to Young’s modulus values ranging from 2.22 to 0.45 MPa. The fluidic resistance ( R H ), device capacitance ( C device ), and the total capacitance of the system ( C H ) were quantified theoretically and experimentally. Softer PDMS increased dynamic compliance, leading to higher effective time constants ( τ ) and lower critical frequencies ( f c ), where the input pressure pulsation frequency below the effective f c disrupted stable focusing, and the pulsation frequency higher than the effective f c had a negligible influence. Experimental testing on microparticle focusing further validated these findings by demonstrating frequency-dependent sensitivity of focusing quality consistent with the dynamic response of the system. This work deciphers the relation between PDMS elasticity and the effective dynamic response of inertial microfluidic systems under pressure pulsation, offering a materials-based strategy for designing microfluidic platforms with tailored frequency-dependent behaviour.