From Droplets to Cells: Physics, Devices and Applications

Abstract

The ability to introduce drugs, genes, nucleic acids, and/or imaging agents into living cells is critical to drug design and delivery, as well as to many cell biology and genetic modification protocols. However, intracellular delivery and transfection remain difficult tasks. Through synergetic use of focused physical fields (e.g., fluidic, acoustic, electric, thermal and solutal), micro-fabricated devices can enable localized control of the extracellular environment leading to desired bioeffects. Conception, analysis and demonstration of one such device are presented. The Electrosonic Actuation Microarray is a novel microelectromechanical systems (MEMS)-enabled device that ejects sample containing biological cells through microscopic (of order size of a single cell) nozzles with incorporated electroporation electrodes. Focused mechanical (pressure and shear) and electrical forces are generated on a microsecond time scale-dictated by nozzle geometry, ejection frequency and velocity, and electroporation voltage. This yields identical "active" microenvironments for each ejected cell. Technical details of device operation and the physics describing droplet formation and ejection are included. The ejection process enables a number of cellular bioeffects, from uptake of small molecules to gene delivery and transfection. Specifically, we demonstrate calcein uptake and transfection of DNA plasmid encoding green fluorescent protein (GFP) into human malignant glioma and human embryonic kidney cells using microarrays with 30 to 55 μm diameter nozzle orifices and operating at ultrasound frequencies between 0.90 and 1.4 MHz. Typical electroporation field strengths are 0.4-1.7 kV/cm.