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

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.