Precision-injecting smart needle

03 March 2019


Gloved hand pushing plunger of filled syringe


Smart needles that automatically inject in the right place are now a reality...

Medical professionals train for years to perform delicate injections, often through many layers of tissue and into difficult locations in the body such as the spine or into the eye.

Sites like eyes pose additional challenges: each person's tissue feels different, and the clinician is often operating blind and relying purely on their sense of touch and the "feel" of the tissue to manoeuvre the point of the needle into the right place.

Sensing its location, and then automatically injecting at the right point, is what a new smart needle, created by Jeff Karp and his team at Harvard Medical School, can do. According to Karp, “as you push on the plunger of our needle, the needle will advance. It’s actually the needle that is moving in response to pushing on the plunger, which is very different from a standard needle.”

Like a standard needle, the operator would first introduce it to approximately the right region, but once the plunger is pressed the needle takes over to administer the injection.

And why doesn’t this fluid leak out as soon as the needle enters the body? Karp explains that often the initial location “is a very dense tissue where the tip of the needle will be clogged”. It is only “when that needle then enters the target cavity the fluid will actually come out the tip of the needle”. It is this that also causes the needle to stop its automatic advance in the right place.

This is vital for preventing complications. During an epidural, for isntance, where analgesic medication is injected around the spinal cord to block pain signals, “if you go too far, you get spinal fluid that can leak out and this causes a lot of complications, a massive headache, and requires a number of procedures” to deal with such overshoot injuries, says Karp.

Overshooting is easier to do than you might think, so Karp uses a simple balloon inside a balloon analogy to describe the layers of the eye that a healthcre worker might be looking to inject between.

Illustrating the point, he says they are “essentially touching but not attached...when you put the needle into the outermost tissue, imagine going through that outer balloon, our needle will automatically stop when it transitions in between those two layers”. This means the fluid can go precisely between those two tissues, despite them only being as thick as 5-10 human hairs! 

The work has just been published in Nature Biomedical Engineering, and Karp is confident that “once we demonstrate that this can be effective, then we will be able to move it to patients and we think that we could probably do that in clinical trials within 2-3 years.”


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