Micromanipulation of biological cells using a microelectromagnet matrix
Original entry by Sagar Bhandari, APPHY 225 Fall 2010
H. Lee, A.M. Purdon, R.M. Westervelt, "Manipulation of Biological Cells using a Microelectromagnet Matrix", Applied Physics Letters 85, 1063 (2004).
cells, microelectromagnet, manipulation
In this paper, the authors demonstrate the noninvasive manipulation of biological cells by microelectromagnetic matrix created using optical lithography. An array of straight wires aligned perpendicular to each other are created on a Si/SiO2 substrate. As shown in Fig. 1, the array of conducting wires is covered with an insulating layer (made of bisbenzocyclobutene (BCB)), to prevent electrical shorting between wires. To control the flow of solution containing cells, a microfluidic channel was separately fabricated with poly(dimethylsiloxane) (PDMS) using soft lithography13 and sealed over the surface of the microelectromagnet matrix.
Yeast cells were attached to magnetic beads by having the surface of the magnetic bead functionalized with Concanavalin–A, a lectin that specifically binds to sugar molecules15 (a-D-mannose) on the yeast cell’s surface with a binding force of approximately 100 pN.Strong and localized magnetic field can be created by applying current to the wires. A large force F,40 pN can be exerted on the bead as shown in Fig. 2. Cells attached to magnetic beads, therefore, can be stably trapped and moved by the matrix at room temperature.
Figure 4(b) demonstrates how In this experiment, the authors also demonstrated that multiple biological cells could be controlled independently and sorted according to their characteristics. A group of yeast cells, one viable cell and two nonviable cells, were initially trapped by a single magnetic field peak. As show in Fig. 3, viable cell and the non viable cells were separated by controlling them separately using two peaks. Also, the authors demonstrate the rotation of cells using time varying currents. Various applications of this device would include assembling of magnetically tagged cells to grow artificial tissues on micrometer length scales, sorting of cells according to their characteristics.
Soft matter connection
This experiment described by the paper involves various aspects of soft matter such as PDMS, microfuildics and control of cells in fluid. PDMS is silicon based organic polymer which is widely used to make microfuildic devices. It shows soft matter properties such as viscoelasticity. Also, it is well known fact that microfluidics involve precise control and manipulation of fluids that are constrained to millimeter scale space. This would involve understanding soft matter traits such the surface tension, energy dissipation, and fluidic resistance.