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Thoughts on Instrumental Insemination Tip Shape

Having looked at some "normal" tips under the microscope they seem somewhat like the top of a milk bottle. Even after flame polishing they still seem somewhat blunt. The outside diameter at the tip needs to be 0.25 mm or 0.27 mm with a maximum of 0.3 mm. The Inside diameter at the tip needs to be 0.15 mm to 0.17 mm 0.15 mm is most common and 0.17 mm or more will give problems with mucous.

All diagrams indicate cross sections through the tips.

normal shape of glass II tip

The tip illustrated is about 35 mm long and made from 2 mm diameter "green band" capillary tubing, the straight portion is not shown to give greater clarity to the drawn down section. Providing that the heating of the glass is even then the tube will stay in ratio, wall thickness to diameter, as it reduces in diameter. However there is a temperature gradient that causes less draw to occur at the thickest portion of the melted glass. Most tips are about 35 mm long, but those for use in the Schley syringe need to be 85 mm - 90 mm long.

Many different styles of tip shape are possible and no doubt some have particular favourites. A trend that I have noticed recently is to use tips that have a much shorter and more blunt drawn section, this gives a more severe taper to the insertion portion and so gives a tapered plugging action that helps with sealing.

Short drawn tips

The very short version at left is probably taking this technique too far, but the centre and right hand draws are achievable and feasible.

magnified tip mouth of glass tip The magnified section
Maximum flame polished II tip mouth
at right shows, a fairly short drawn, standard tip that has been flame polished to the minimum rounding of corners. The left inset shows maximum flame polishing.

Scale = each small square is 0.01 mm.

Cutting or grinding the mouth of the tip at various angles is being tried by some.

If you consider the cross section:- you will notice that the insertion resistance rises abruptly at the tip... I propose that the shape be modified to one that is similar to the tip of a hypodermic needle, although much more blunt. A hypodermic needle shape is relieved at the sides for easy penetration of a tough membrane (skin), but the principles behind the shape can be applied to insemination tip design.

The proposed shapes are derived from the diagram at right. The normal shape being 90 ° The shallower the angle selected the easier insertion will be, but at the shallowest angles the risk of leakage is increased and also as the angle increases the orifice gets larger and may give problems with mucous pick up. Tips with angles of between 70 ° and 80 ° are currently being distributed (although the samples that I have seen are somewhat sharp on the edges and could do with a minor amount of dressing then re-polishing). These new shapes give improvements in the penetration resistance graphs. The versions previously shown on this page were too crude and too shallow in the cutting.

The proposed shapes are derived from the diagram at right. The normal shape being 90 ° The shallower the angle selected the easier insertion will be, but at the shallowest angles the risk of leakage is increased and also as the angle increases the orifice gets larger and may give problems with mucous pick up.

Tips with angles of between 70 ° and 80 ° are currently being distributed (although the samples that I have seen are somewhat sharp on the edges and could do with a minor amount of dressing then re-polishing).

These new shapes give improvements in the penetration resistance graphs. The versions previously shown on this page were too crude and too shallow in the cutting.

Possible cutting angles for II tip mouths

Reduced penetration resistance due to angled trimming of tips.

The improvements give easier entry of the tip with a much reduced risk of damage to the queen. The tapered portion immediately behind the tip may need to have a slightly steeper taper to effect a seal without penetrating too far.

NOTE... The taper starts at the inner wall of the tube, reducing the "sharpness".

The shape can be produced by grinding. The tip should be supported in a beeswax bed in a "U" shaped channel (something like an umbrella rib) and the grind done with a "Dremel" type tool running at about 30,000 RPM. A smooth finish is achieved using flame polishing. If you examine an insulin syringe needle you will see that the sides of the chamfered end are also relieved. If this was done to our glass tips, but in a very minor and more blunt fashion, before the flame polishing, then the penetration resistance is reduced still further. (John Harbo reports that he uses similar chamfered tips.)

Angled Insemination Tip Apart from tip shape all the commercially produced items I have seen, have been straight. I propose an angled end to the tip to enable better vision. This requires an extra angled joint on the advancing mechanism, but the extra complexity and cost would (should) be outweighed by the ease and speed that may result. The Scale of the above diagram is 1 mm per square, note that the melt for the bend can be made using the same heating coil as for tip drawing. A slight stretching will occur on the outside of the bend and the corresponding inner radius will thicken. Care should be taken that the outer surface does not collapse onto the inner one and spoil your work.

Cranked Instrumental Insemination Tip Another possibility for improved vision without the extra joint would be a cranked tip. The original drawing that was on this page in this position was too abrupt and used two right angles that were not practical to make, this joggled version is quite strong.

Right Angle II Tip

If A use can be imagined for a right angled tip it should be made in the fashion indicated at right, with two smaller bends. A single right angle bend is too fragile and the risk of collapse in the bending is very high.

If a truly right angled tip is required, for any reason, the method indicated on the illuminated tips page should be used.

Bulbous flame polishing on II Tip Bulbous tips... a rather exaggerated description for an incredibly small swelling. The idea here is that the mouth of the tip is heated until a "rim" is formed. This rim is of very slightly greater diameter than the bulk of the glass that ends up inserted into the queen. The axial length of the rim is only of the order of a few hundredths of a millimetre long and performs two functions, the first of these is an extension of flame polishing with extreme smoothness of surface finish, the second benefit is that the rim will cause a smoothing out and minor stretching of the vaginal tissue as it flows over the "ridge", allowing easier passage past the valvefold. The rim also makes the tip more robust and the method could be applied just as simply to obliquely cut tips. The diagrams show a progression of possibilities.

None of the items on this page are 'set in stone', comments and discussion are welcomed... By either direct Email or via the Instrumental Insemination Discussion List.

Written... Autumn 2000, Revised... 30 October 2001, Upgraded... 24 December 2005,