Exploring factors for uniformly distributing liquid droplets in a bifurcation tree microfluidic chip

Abstract

Our objective was to develop an accurate bifurcation tree microfluidic chip and to identify factors influencing the uniform distribution of liquid plugs. Factors such as flow rate, microchannel length between bifurcation features, and geometry of daughter microchannels were examined on polymeric microfluidic platform. Three types of microfluidic chips (1-to-2 chip, 1-to-4 chip, and 1-to-8 chip) were micromachined on PMMA substrates, and the microchannels were sealed using thermal bonding. Twenty experiments were repeated on each chip and numerical simulations were used to explain the observed phenomena. From the experiments and simulations, we draw the following conclusions: (1) The average deviation among daughter plugs increased with the number of bifurcations, as follows: 1-to-2 chip (1.43%), 1-to-4 chip (5.76%), and 1-to-8 chip (12.97%). (2) The mother plug flow rate was shown to be crucial to distribution uniformity, as demonstrated in experiments on 1-to-2 microfluidic chips. (3) Longer daughter channels between consecutive bifurcations tend to mediate flow resulting in more uniform distribution, as demonstrated in experiments on 1-to-4 microfluidic chips. (4) The geometry of daughter microchannels could be adjusted to minimize the bouncing of the daughter liquid plugs after splitting in order to enhance the uniformity of distribution and reduce reagent loss.