The pronucleus injection pipettes type PI-0.4 differ from the other types by the shape of the tip. The tip of the type PI-0.4 has a conical shape, whereas the tips of the other types are cylindrically shaped. The opening diameter of the pipette type PI-0.4 is approximately 0.2 µm - 0.4 µm. This is below the resolution of light microscopes. The opening diameters of the pipette types PI-1.2 and PI-1.6 are 1.2 µm and 1.6 µm, respectively. The openings are still clearly visible under 200- to 400-fold magnifications.

The different shapes of the tips and their different inner diameters have different impacts on the pronucleus injection. Due to the extremely small inner diameter of the PI-0.4 pipette one normally cannot observe an outflow of the solution at maintenance or injection pressures. Therefore it is necessary to break a tiny part of the tip before injecting. One can do this by striving the pipette laterally against the front site of the holding pipette. This procedure requires some training and is inherently non reproducible.

The tip of the pipette PI-0.4 can be broken several times. This is an advantage for injection of large constructs like BAC and YAG. The tip can be broken until an outflow of the solution appears. A limiting factor, however, is the higher lyses rates of the oocytes due to the larger pipette openings.

Because the breaking of the PI-0.4 pipette tip is inherently non reproducible and needs some training, different customers have asked for the development of a type of pipette, whose tip is already open in terms of observing an outflow at applied maintenance and injection pressures whitout breaking the tip.

We have found that pipettes with a cyndrical shape of the tip meet this requirement. A good compromise between easy filling and penetration capability is the PI-1.2 pipette.

Most microinjectionists use this type for injections of small and medium sized constructs. It is assumed that the due to the rather small inner diameter the shearing forces during the outflow are high what can lead to breaks of the chains of molecules.

For larger constructs we recommend therefore the PI-1.6 needles.

However, some of the microinjectionists report positive results using PI-1.2 needles also for large constructs. On the other hand, some researchers have no difficulties to penetrate the cells using the broader PI-1.6 needles.