(314h) Measurement of Muscle Force in C. Elegans Worm Using Microfluidics

We have designed, fabricated, and tested a microfluidic device which allows biologists to better understand the contraction of muscles used in locomotion of the worm Caenorhabditis elegans (C. elegans). Biologists who have genetically altered worms in ways thought to affect the muscle contraction force need a means for comparing mutant worms to wild type worms. Due to the worms' size, traditional methods for measuring muscle force are not feasible. The worm C. elegans has been studied extensively due to its relative simplicity and straightforward use as a model for genetic manipulation. Results from the study of the C. elegans worm have resulted in two Nobel prizes, and show potential for breakthroughs in diseases such as muscular dystrophy. However, due to the worms' small physical size, 1 mm in length and ~80 µm in diameter, manipulation of the worm can be difficult. Microfluidics, which deals with controlling and transporting fluids through channels of micro meter dimensions, has been utilized in studying and controlling the worm because of its ability to confine the worm within small channels and allow for manipulation. Microfluidic devices are often made from polymers, the most common being Polydimethylsiloxane (PDMS). PDMS devices offer the advantage of maintaining the worms in a nontoxic, oxygenated environment. Microfluidic devices have been constructed to trap the C. elegans worm allowing for imaging and surgery, however these devices have not been used in a sensing application. We have developed a device which immobilizes the worm and is capable of distinguishing differences in muscle contraction force between wild and mutant type worms. Our device consists of three layers: a fluid layer, air layer, and a flexible membrane which separates the fluid and air layers. The flexible membrane is used in measuring the force generated by the muscles of the C. elegans worm which are responsible for locomotion. A thin 30 µm flexible membrane is used to immobilize the worm. Using sensitive air regulators the air pressure on the membrane face opposite that of the worm can be finely increased extending the membrane into a fluid channel which contains a worm. As the membrane extends into the channel it contacts the worm and applies a force on the worm. As the air pressure is increased, the force the membrane exerts on the worm increases until the worm becomes immobilized, at which point the air pressure is recorded. Three strains of C. elegans worms were tested in our device, a wild type strain and two strains with genetic knockouts, UNC-29 and ACR-16, which removed ligand gated ion channels on the muscle responsible for contraction. Immobilization pressures for the mutant worms showed statistical differences when compared to the wild type worm allowing us to rank the worm strains according to muscle contraction force (fig. 1). Utilizing microfluidic techniques we have created a device which uses a flexible membrane and sensitive air regulator to establish a relationship between air pressure and the muscle contraction force of the C elegans worm.