Micropipette puller design: form of the heating filament and effects of filament width on tip length and diameter

Though the ultrafine short tips provided by our micropipette puller are helpful for many preparations, longer tips are still needed for some cases where target cells for intracellular work are deeply embedded in tissue. Because the original 'loop' type of heating filament proved unsuitable for widening to provide the longer tips, we studied simpler forms of heating filaments. By comparison with the common loop design, a rectangular trough filament proved to have many advantages without any significant disadvantage. In particular, this type of filament may be used at varying widths to provide long tips as well as short ones. Thus our micropipette puller can now provide tip lengths that extend upward by continuous gradations from about 6 to 27 mm, while maintaining tip diameter in the ultrafine range of 0.1 micrometer or less. These long tips have proved more reliable and free from bending than long tips traditionally provided by the Livingston puller. By using narrow filaments in conjunction with other parameters that influence tip size, tips have also formed with diameters up to 1.5 micrometers and lengths of only 2-3 mm.