Cell sorting is an essential technique in cell biology research and in many diagnostic and therapeutic applications. Especially sorting methods that refrain from the biochemical labeling of cells are in high demand. Several microfluidic techniques provide solutions to this by making use of the intrinsic characteristics of cells like size, shape, electrical polarisability or hydrodynamic properties. Further advantages: microfluidic technologies operate on the micrometer scale and require small sample volumes.
One of the microfluidic label-free sorting techniques is deterministic lateral displacement (DLD). In short, this is a way to separate particles in fluids by driving them through an array of regularly placed pillars. By positioning the pillars at determined angles, particles of different sizes are forced into different streamlines and are this way separated. The pattern of the array of pillars is determining the streamlines of the particles.
One of the projects Micronit was involved in over the past few years, was the Lapaso project, initiated by Professor Jonas Tegenfeldt of Lund University. In this project, DLD was used to detect a certain parasite in human blood that causes sleeping sickness. Sleeping sickness is a disease found in rural areas of sub-Saharan Africa. It is spread by the tsetse fly and infected patients suffer from painful symptoms. If not treated, the disease is fatal. Quick examination of the blood is therefore of the essence. The DLD sorting method, based on particle morphology, proved to be very useful.
To get a good impression of the DLD-process, take a look at this video, published on the Lapaso website, and made by Stefan Holm, one of the project’s participants.
For this project, a thermoplastic polymer chip was developed that contains an array of pillars as small as 20 µm in diameter. Developing the first version of this chip in polymer was a cost-driven choice. When the chips need to be replicated in larger volumes, the process can be easily switched into injection moulding at a reasonable cost and without losing much time.