Abstract

The ability to deliver sequences of DNA and other molecular loads across the membrane of a cell and into its nucleus is an area of interest in the medical community. One of its many applications is that of gene therapy. In contrast to other forms of treatment, gene therapy seeks to treat diseases at the cellular level. The success of these treatments depends on the technologies for cell transfection that are available. Physical methods are sometimes able to overcome poor efficiencies of chemical methods and the safety concerns of viral methods, but are usually impractical due to the limited number of cells that are able to be transfected at a time, isolation, and immobilization of the cells. Nanoinjection is capable of using millions of small lances in an array to inject hundreds of thousands of cells simultaneously with relatively high efficiencies and viabilities. The solid nature of the lances also allows them to be smaller than their hollow-needle counterparts, which results in higher cell viability. Propidium Iodide (PI), a dye whose fluorescence increases greatly when bound to nucleic acids, was used as an injection molecule for testing the efficacy of the nanoinjection process on HeLa 229 cancer cells in a portion of the experiments, with a GFP plasmid of DNA being used in the rest. After injection, flow cytometry was used to detect the concentration of PI or the expression of the GFP in the injected cells. Since PI cannot normally penetrate the membrane of living cells, those found with high concentrations of PI were either successfully injected or dead, which can be determined by the flow cytometry. Investigation of the parameters that affect the efficiency of the nanoinjection process will help improve it for further research. Some of these parameters that were investigated include the force of injection, the material used for the lances (silicon versus carbon nanotubes), and the injection speed of the lance arrays. An injection device capable of small changes in deflection was designed to ensure accurate increments in force for testing, as well as a pulsed current control injection system. Results for injections of varying forces indicate a slow rise in PI uptake from 0 to 1.8 Newtons where it reaches a maximum uptake of 4.11 when normalized to the PI uptake of the positive controls. The PI uptake then remains relatively level as the force continues to increase, averaging an uptake of approximately 3.1. The slow rise is likely due to more of the cells being punctured as the force increases until most have been punctured and the PI uptake levels off. The viability of the injected cells was close to that of the controls with no clear trend. A comparison of lance arrays made from silicon and carbon nanotubes using DNA as the molecular load shows little difference between materials. Different injection speeds tested show that only 1-5% of the cells in the injection process are lost for speeds in the range of 0.08-0.16 mm/sec, whereas 49-69% of the cells are lost using speeds between 0.6-3 mm/sec.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

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