Needles, one of the tools of our trade.
We use them every day. But have you ever wondered how they are made?
How exactly do they get that teeny tiny hole in a 25G needle?
Well hang on to your sharps bin, ’cause I am about to get straight to the point and tell you everything you have never wanted to know about hypodermic needles.
Interestingly, in order to manufacture the those tiny tubes of steel needed for most medical needles, the process begins with a big thick tube.
To begin with, a large piece of sheet metal is fed into a series of rollers that bend it over and around into a tube. The tube then passes through a welder to seal the seam.
Alternatively, ‘seamless’ tubing is produced by taking a chunk of metal known as a ‘billet’, heating it and boring a hole through the center. In some instances this is done with a with a laser.
You would think that laser technology would be quicker and more accurate, but apparently the gold standard for producing these incredibly high tolerances and precise measurements remains the welding method.
Old school rules.
Where were we? Oh yes, the tube. This large tube is then heated to soften it (a process known as annealing), after which it is drawn by significant forces through a tool (or die) that has a much smaller diameter hole in it.
Think of those Play-Doh toys that squeeze out spaghetti worms of various shapes and diameters.
It wasn’t until I was 5 or 6 that I realised Play-Doh wasn’t one of the 5 food groups.
The tube is then extruded through smaller and smaller dies right down to the final diameter. Sometimes a rigid length of wire known as a mandrel is placed inside the tube to maintain its integrity during the process.
The final die pass is often done without any heat. This cold working of the tube increases its strength and rigidity.
The metal of choice used for needles, of course, is surgical steel, which is a type of stainless steel.
During the manufacturing of surgical steel, alloying elements of chromium, nickel and molybdenum are added to the mix. It is the molybdenum that gives the finished needle greater strength and a sharper cutting edge.
Molybdenum. Anyone about to have a baby girl and looking for a unique name?
Move over Shaniqwa and Shumonte there is a new girl in the class….
OK. I’m sure you have all seen BD syringes and needles, but did you know what the BD sands for?
Becton Dickinson is one of the largest manufacturers of medical devices and instrument systems in the world. But it all began back in 1897 developing syringes and needles (in fact it was BD that patented the luer lock connection).
BD use a 3/4 inch stainless steel tubing that is rolled and welded, heated, and drawn down to the required size with a final cold-draw.
This tubing is cut into the correct lengths and then the bevel is sliced across the end.
The very tip of the needle is known as the lancet and various shapes are used depending on the application.
From the lancet, the cutting edge sweeps elegantly back across the bevel to form the shoulder.
The actual shape of the bevel is also a highly specialized bit of kit. Check out the A-bevel, B-bevel, C-bevel, Bias, Chiba, Crawford, Deflected Tip, Francine, Hustead, Huber, Trocar, and Tuohey. Collect the whole set.
Finally, the hub is attached. These can be made from metal or plastic and are bonded to the needle by a crimping process or using an epoxy.
The final product is sometimes coated with a low-friction lubricant to create a smoother penetration that is less painful.
The diameter of the needle is referred to as its Gauge and is based on the ‘Stubs Needle Gauge’.
Smaller gauge numbers indicate a larger outer diameter. The Stubs Iron Wire Gauge system (also known as the Birmingham Wire Gauge or BWG) was adopted in Britain in 1884 to specify the thickness of metal wires. Although it was not used much anywhere else in the world, an Act of Congress in the US made it the only wire gauge system used there (and so here).
The other scale used to measure gauge is the French scale often written as FR or Fg.This is usually used to measure the external diameter of catheters.
- 1 French = diameter of 1/3mm. Therefore you can impress your colleagues by quoting the diameter of any catheter in millimeters by dividing the Fr guage by 3.
So now you are a bit of an expert on the old hypodermic.
Perhaps you can meducate your patients all about them to help pass the time as you are digging around looking for that recalcitrant vein.