Magnetically Driven Pump for Solid-State Microfluidic Flow Control
Authors: Smith Aaron R. , Fologea Daniel , Mullner Peter 
Published: February 2020

Microfluidics is a rapidly developing field due to the many advantages that handling fluids in the microliter and nanoliter scale. This includes reduced volumes of samples and reagents used, quicker processing times and more precise and consistent results. A key requisite to exploit these advantages is fluid control at the nanoliter scale. Fluid handling systems that can accurately dose the volumes needed in microfluidics are underdeveloped, particularly options that are small and easy to manufacture. Some options include capillary flow, electroosmotic, piezoelectric and peristaltic technologies. The magnetic shape memory (MSM) pump is similar in principle to a peristaltic pump except that there are no mechanical parts such as gears or valves. The MSM material itself replaces the classical mechanical components found in traditional pumping mechanisms. The material is the machine.

The MSM material is an alloy of nickel, manganese and gallium (Ni-Mn-Ga). The MSM effect, which is the coupling of the material’s atomistic and magnetic structures, is responsible for the large shape change (up to 10%) that has been observed in the single crystalline material. Through a process known as twinning, the crystallographic structure of the material can be manipulated by converting energy from an applied magnetic field. This is advantageous in that the material’s shape can be precisely changed without contacting the device itself. The MSM pump is realized when this material is integrated into a microfluidic channel and controlled using a localized magnetic field. The material becomes a metal muscle.

The MSM pump is a solid-state microfluidic flow control device that operates similar to a peristaltic pump. The material’s shape changes to create a cavity at the inlet channel due to a locally applied, external magnetic field. The formation of this cavity creates a negative pressure which is then filled with a bolus of fluid from the outlet. This cavity is then translated across the material until it reaches the outlet channel, at which it is then ejected from the material and into the microfluidic system. There are no moving parts, such as gears or check valves, in the micropump itself.

The current peristaltic MSM micropump has a resolution of 40 – 150 nL per complete pumping cycle. New techniques have been developed to achieve a resolution nearing 1 – 2 nL. The MSM pump has repeatable, stable performance even at pumping pressures exceeding 100 kPa and can pump both gas and liquids (and is thus self-priming). Furthermore, the material acts simultaneously as both the pumping mechanism and a valve. This multi-functionality, and the simplicity of the overall MSM pump, make it a competitive technology for devices requiring flow rates from nearly zero to 1,500 µL/min, particularly devices where the pumping mechanism must be integrated directly into the microfluidic device such as a lab-on-a-chip, as shown in the figure.

Using the MSM pump, we created and manipulated a droplet lipid bilayer and delivered sub-microliter volumes of the electrically controlled nano-valve lysenin. We will present the performance of the MSM pump as well as the results from these recent experiments. This demonstrates the capabilities of this technology and illustrates its capacity for other applications within the field of microfluidics.

Figure 1