SIMPLE analytical model for smart microfluidic chip design

The flow control of pumping systems is an important aspect of microfluidic devices. Technically, it allows the integration of bioassays on-chip by accurately controlling the flow dynamics. Self-powered micropumps are available in different sizes to permit portability and use in different applications. In addition, surface tension-based platforms, in which the pumping process is supported by liquid wicking through capillary action, is widely preferred owing to its robustness, affordability, and portability.

Despite the advantages, self-powered channel-based systems are prone to low sensitivity and specificity of the analysis attributed to the interferences due to unsteady capillary effects. This requires hydrophilization of the channels to obtain the desired capillary effects, which is time-consuming and expensive. To this end, researchers have been looking for alternative solutions and have identified hybrid microfluidic devices, which is a combination of both channel-based and paper-based microfluidics, as a promising candidate.

Even though hybrid microfluidic devices have exhibited significant improvements, a few challenges including the need for hydrophilic channels and the difficulty to work with little volumes are yet to be resolved. However, the recent development of self-powered imbibing microfluidic pump by liquid encapsulation (SIMPLE) have addressed most of the aforementioned challenges. The system does permit any contact between the sample and the porous materials thus eliminating any possibility of interference. Alternatively, studies have also shown that the performances and flexibility of the microfluidics can be enhanced by effective chip design to allow adjustment of the flow control of pumping systems. This will ensure precise control of the flow dynamics, which are an important consideration in the development of point-of-care bioassays. Furthermore, several analytical models have been presented to describe the pumping dynamics in both paper- and channel-based microfluidics with little done for hybrid systems like SIMPLE. This includes taking into account the design parameters to optimize the chip design and obtain the desired flow rate.

Recently, researchers: Dr. Francesco Dal Dosso, Yura Bondarenko, Dr. Tadej Kokalj and led by Professor Jeroen Lammertyn at MeBioS-Biosensors Group of KU Leuven, investigated the pumping behavior of the hybrid SIMPLE systems. Fundamentally, a tool for designing the SIMPLE-based chips was developed which provides the design parameters to be used to achieve the targeted flow rate. This consists in an analytical model that was derived and used to validate the assumption that the flow rate is dependent on the porous material geometry and not channel geometry and porous volume. Eventually, they compared the experimental results with the model results. The model results obtained were in good agreement with the experimental results. Their work is currently published in the journal, Sensors and Actuators A: Physical. For instance, the authors confirmed that the sample liquid flow rate was dependent on the porous material shape and independent on the porous material volume and channel geometry. The model distributions enabled prediction of the pumping behaviors for the design of several chips. Additionally, the model provided precise design parameters for achieving the targeted flow rate thus avoiding the initially used trial and error method. This reduced tremendously the design and optimization time to achieve the final chip configuration.

The University of Leuven scientists presented an analytical approach and showed its feasibility for designing microfluidic chips based on the SIMPLE concept. It also gives more insight into the pumping process by predicting the channel flow rate. Altogether, the study will advance the implementation of the concept in more complex microfluidic devices for various applications.