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Research Papers

An Instrument for Controlled, Automated Production of Micrometer Scale Fused Silica Pipettes

[+] Author and Article Information
Nikita Pak

George W. Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332nikpak@gatech.edu

Michael J. Dergance

George W. Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332Mike.Dergance@gmail.com

Matthew T. Emerick

George W. Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332matt@mattemerick.com

Eric B. Gagnon

George W. Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332egagnon3@gatech.edu

Craig R. Forest

George W. Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332cforest@gatech.edu

J. Mech. Des 133(6), 061006 (Jun 15, 2011) (5 pages) doi:10.1115/1.4004194 History: Received August 24, 2010; Revised April 22, 2011; Published June 15, 2011; Online June 15, 2011

Micropipettes are hollow glass needles with tip openings ranging from less than 1 μm up to 75 μm. Based on the size of the inner diameter of the micropipettes, they can be used for applications such as patch clamping, microinjection, and cell transfer. In the state-of-the-art fabrication of micropipettes, a skilled individual is able to produce about 2 − 4 micropipettes per minute. Many labs, which utilize hundreds of pipettes on a weekly basis, would benefit from the increased speed, accuracy, and repeatability of an automated fabrication apparatus. We have designed, built, and tested a working prototype of a fully automated fused silica micropipette puller. Our device pulls pipettes from a continuous spool of capillary glass, which leads to minimized setup time for the operator and the ability to produce 6 micropipettes per minute. Micropipettes were pulled with average lengths ranging from 6–20 mm and average tip diameters ranging from 18–175 μm. Standard deviations for length and diameter were calculated to range from 0.24-2.9 mm and 3.5–12 μm, respectively. Through measurements of the pulled pipettes, a trend has been determined which shows higher pulling velocity increases tip length and decreases tip diameter. A new model for heat transfer and geometrical analysis for the heating and cooling of the pipettes has been developed and matches closely to this experimental data. This can be used to predict pipette geometry.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

A conceptual heating and cooling model for pulling a micropipette. The amount of time it takes to cool the pipette back to the glass transition temperature determines the geometry.

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Figure 2

The basic operation of a fully automated micropipette puller. The inset shows a microscope image of a pulled micropipette manufactured using our machine.

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Figure 3

Photograph of the main mechanical and thermal components of a fully automated micropipette puller

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Figure 4

Diagram of pneumatic clamp and vee-groove used to secure both ends of the capillary for pulling

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Figure 5

Photograph of an instrument for controlled, automated, continuous production of fused silica micropipettes

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Figure 6

The sequence of events that the pipette pulling program runs. The user inputs the number of pipettes, N, length, heat time, tH , slow pull speed, vs, slow pull distance, Ps , fast pull speed, vf , fast pull distance, Pf , and delay, td .

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Figure 7

Relationship between pull speed and micropipette tip length, with standard deviation. N = 10, tH  = 14 s, vs  = 0.27 m/s, Ps  = 2.54 mm, Pf  = 22.9 mm, td  = 70 ms, and a varied vf as indicated. The solid lines indicate the upper and lower bounds achieved using our thermal model and Eq. 4.

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Figure 8

Relationship between pull speed and tip diameter, with standard deviation. N = 10, tH  = 14 s, vs  = 0.27 m/s, Ps  = 2.54 mm, Pf  = 22.9 mm, td  = 70 ms, and a varied vf as indicated. Electron microscope images of three micropipettes verify the tip diameter and also show the results of velocity on micropipette geometry. The solid lines indicate the upper and lower bounds achieved using our model and Eq. 6. Deviation between the models and experimental results may be attributed to the complex nature of cooling, and the simplifications used in our conservation of volume analysis, but the model fits well.

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