Small Model Biology Research

Model organisms are non-human systems widely studied in biological research, ranging from simple single cells to animals. Small model organisms such as Caenorhabditis elegans provide a high level of biological complexity, which are cost-effective, experimentally easy to handle, and compatible with microscope-based techniques. Moreover, they also have a complete genetic technology toolbox, sequenced genomes, and different numbers of genes homologous to humans.

Because they are of the right size and can be immersed in liquid during part or all of their life stages, these multicellular model organisms can benefit from the development of microfluidic technology. This technology can classify, capture, immobilize, and other operations on organisms in a single chip. It also can better control the size and repeatability of mechanical stimuli.

Typical Small Model Organisms

Caenorhabditis Elegans

C. elegans is a small roundworm. Almost all individuals are hermaphrodite, so it is easier to maintain a homozygous genotype. Worms can be frozen in liquid nitrogen for decades to recover, which can minimize the genetic variability of the population. Approximately 38% of worm genes are human orthologs.

Figure.1 Microfluidics for Mechanobiology of Model Organisms. (Kim A. A, et al. 2018)

Drosophila

The generation time of fruit flies is very short and easy to reproduce, so it is conducive to genetic hybridization. About 40% of Drosophila genes are human orthologs. Drosophila is widely used to study aging and neurobiology.

Danio Rerio

Zebrafish is an emerging model for studying human diseases because of its genetic similarity to humans and relatively easy genetic manipulation. Like humans, zebrafish are vertebrates. Approximately 55%-70% of zebrafish genes are human orthologs.

Microfluidic Design for Model Biology Research

Alfa Chemistry is capable of designing and manufacturing microfluidic devices for the study of small model organisms in high-resolution imaging processes. The following content highlights our considerations for microfluidic device design:

Actuator

When designing a pneumatic actuator in a microfluidic device, the key performance index we choose is the deflection distance of the actuator membrane, because this is usually sufficient to quantify the magnitude of the mechanical stimulus.

• Minimizing the thickness of the diaphragm can produce better performance. Using a chrome-plated mask and a collimated UV light source, we are able to produce a 10 μm thick film.
• The width and height of the actuator will also affect the maximum deflection distance. We design an actuator with equal width and height (50 x 50 μm), because the deflection of the membrane is mainly affected by the smallest size.

Immobilization

Active fixation strategies require additional external components to implement. We choose to use a passive method, which can avoid the complexity of other moving parts. We tested two passive fixation strategies for our service.

Figure.2 Passive trap designs for immobilization. (A) Continuous taper channel and (B) form-fitting channel. (Kim A. A, et al. 2018)

Design A can adapt to changes in animal size for studying target organisms at different life stages in the same microfluidic device. The disadvantages are blockage and low experimental throughput due to cone function. Design B allows animals to be preloaded into a larger entry chamber, which significantly reduces the preparation time. The minimum contraction of the trap is about half the width of the worm, which facilitates the removal of animals and minimizes the possibility of blockage.

Flow Rate

The flow rate through the device may be important to the animal's sensitivity to shear stress and the design of the fluid network, depending on the model animal. Besides, in a microfluidic platform with an extended fluid network, laminar flow profiles and flow rates need to be considered, for example for the delivery of drugs or nutrients.

Fabrication

We use polydimethylsiloxane (PDMS) to manufacture microfluidic devices. The process includes the photolithography of the master mold and the copy molding and bonding of the PDMS equipment.

Microfluidics for Model Organisms

Many of the above design considerations apply to the design of new microfluidic devices for studying model organisms. Many microfluidic devices have been used to study model organisms, such as worms. Read on for more information.

• Caenorhabditis Elegans Research
• Microfluidic Methods for Fixing and Positioning C. Elegans
• Microfluidic Chips for Classification and Synchronization of C. Elegans

Reference

• Kim A. A, et al. (2018). "Microfluidics for Mechanobiology of Model Organisms." Methods Cell Biol. 146: 217-259.

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