Microinjection technique: routine system for characterization of microcapillaries by bubble pressure measurement.

Five tubing types with different outer and inner diameter dimensions were used to pull injection capillaries with different openings. The correlation between threshold bubble pressure and tip inner and outer diameter was established for each type of tubing. Statistical analysis revealed that the bubble pressure is an accurate measure for the tip inner diameter independent of the tubing used to pull the capillary. A graph directly relating the tip inner diameter to the threshold bubble pressure is presented. The tip outer diameter could not be related to the bubble pressure for tubings of different size. This diameter depends on the wall thickness of the tubing and the puller configuration. Data on the inner tip diameter were used to test the relationship between volume released from injection capillaries and their tip radius. It was found that the volume increases with the fourth power of the radius. Strategies for optimizing the injection capillary are discussed.