ES injection pipette manufacture
The following is an outline of the method that I use to manufacture injection needles for ES cell injection. I use high quality borosilicate glass obtained from World Precision Instruments (see vendor listing). This glass has an external diameter of 1.0 mm and an internal diameter of 0.8 mm. It is NON FILAMENTED.
Using a Kopf Model 750 vertical puller, I draw out glass such that it has a long shank of similar diameter. This will give me the advantage of several attempts to cut the glass before it becomes too wide. After pulling out a number of such needles on the puller (I always do these in batches as my proficiency escalates with higher numbers) I set up the dissecting microscope for glass cutting. I place a square of Parafilm TM on the glass stage (this can be secured with tape if necessary) and get a fresh one-sided razor for cutting. Placing a glass needle on the Parafilm TM and viewing through the dissecting microscope, I cant the needle to bring the shank onto the surface of the stage. Using a light, North-South stroke and tilting the top of the razor at 45 o away from my hand holding the needle, I lightly sweep across the shank of the glass close to the point. If this breaks correctly I will put it carefully in a needle holder to await further quality control testing. If not, I will be able to try to cut it 2-3 times more before the shank will be too wide to make a useful needle.
So what are the defining parameters? I try to avoid making needles whose tip apertures exceed 20 microns and are less than 15 microns. The preferred shape is concoid, that it to say that when viewed from the side it appears to be asymmetrically concave (as one half of a semicircle) where the tip on one side projects as far forward in excess of the other as the glass is wide. When viewed from above (plan view) the glass tip appears triangular.
The cut needles are QC'd on the microforge, where they are assessed for correct size and sharpness, excluding those which have ragged edges.
