James Edward Carroll IV - Middlesex Community College
Co-Author(s): Carol Livermore and Majid Bigdeli Karimi, Northeastern University, MA
Techniques for three dimensional tissue creation have been slow to develop due in part to the difficulty in creating biomimetic tissue that functions like native tissue. One potential approach is to use directed assembly to locate different types of cells into their proper places on a tissue scaffold, which may then be assembled into a three dimensional structure by origami folding techniques. At the microscale cells are simply too small for macroscale assembly techniques and too large for chemically-based nanoscale assembly techniques. Templated assembly by selective removal (TASR) is a process for assembly of objects from fluid onto a surface at the micro level that has been shown to have potential for cell assembly, but assembly yields are not always high. The goal of my research was to improve the TASR process so that higher templating yields could be achieved. In TASR, objects (e.g. cells) assemble in holes; the objects stay in the holes if they are of similar size, and they are removed from the holes by acoustic waves if they are different in size. For these experiments the objects (particles) used were polystyrene microbeads, a model for biological cells. Particles ranging in diameter from 5 to 20 microns were assembled onto hydrophobic microchips in which holes of matching diameters had been machined at the micro level. The microchip, particles, and an ethanol/water solution were suspended in a small beaker inside a larger container that housed an acoustic transducer that was tunable between drive voltages of 20 V and 80 V. The largest challenge in improving the yield was the settlement of dense particles in the solution, resulting in maximum yields of between 50% and 85% with the highest outlier showing a yield of 91%. It was hypothesized that improving mixing could be key to improving yields. Density matching of the solution to the particles slowed particle settlement, but the main improvement came with utilizing a magnetic stirrer along with the transducer’s excitation. A 3D printed housing for the chip allowed for the addition of the magnetic stirrer without disrupting the microchip. This new design showed significant improvement to the yield, which rose to typical values of between 80% and 90%, with the highest outlier showing a yield of 97%. The improved yield seems to be a direct effect of keeping the particles and solution suspended in the liquid. Further research is still required on how magnetic stirring will affect live cells.
Funder Acknowledgement(s): Funding for this research was provided by the NSF through the EFRI-REM program under award #1332249.
Faculty Advisor: Majid Bigdeli Karimi,