Painless Injections

Blog post by Tianyou Xu.

Remember this scene from the 2006 film Casino Royale, when James Bond gets a GPS chip subdermally injected into his forearm so that M could track his whereabouts (Image 1)?

Well, it appears that Mr. Bond isn't the only one with out-of-this-world technologies anymore. Last month, a team of engineers at MIT developed a prototype device that, too, is able to inject stuff into the body without the passage of a needle. Stuff, however, in this case, refers to medicine (a more benevolent form of a tracking-chip). Indeed, the device, shown to the left (Image 2), will literally shoot the medication past the skin, depositing it into the underlying tissue.

Now the question: does it hurt? Remarkably, not at all! Because the nozzle size of the apparatus is extremely narrow - as wide as a mosquito's proboscis - the injection process is nearly undetectable to one's senses (in theory). No more dreaded visits to the doctor's office!

In designing this jet-injection mechanism, the engineers relied on what's known as a Lorentz force actuator (Image 3). The Lorentz force actuator in this case is a small permanent magnet surrounded by a coil of wires. The coil of wires, or solenoid, is part of a piston system that is separate from the permanent magnet which lies in the center. If we recall from high school physics, we know that when a current is passed through the wires of a solenoid, the solenoid becomes an electromagnet which, in turn, creates its own magnetic field. Now, if this new field is opposite that of the permanent magnet, meaning if their fields repel, then a repulsive force will be established. This force will accelerate the piston towards the nozzle, creating a sudden change in pressure which then ejects the medicine out of the nozzle.

The series of time-lapse images shown (Image 4) captures the injection of a tissue-marking dye into acrylamide gel at a constant jet speed (100 m/s). Acrylamide gels are a convenient model because of skin tissues because of "their transparency, and their skin-like stiffness and damping properties."

How fast? Well, that depends on the applied current. Since the amount of the current through the solenoid directly controls the strength of electromagnet, the current also determines the force applied and the velocity of the piston! The device, at maximum power, can eject particles from its nozzle at velocities close to the speed of sound in air (~ 300 m/s)
The relation between the coil voltage and jet speed is shown in the graph to the left (Image 5).

If your head isn't spinning thinking about all the possibilities that could become of this device, here are a few to consider.

(1) For healthcare professionals, working with needles poses a constant and unnecessary risk. The Centers for Disease Control and Prevention (CDC) estimates that "each year 385,000 needlesticks and other sharps-related injuries are sustained by hospital-based healthcare personnel.²" Imagine the relief if subdermal needles were rendered completely obsolete.

(2) While those working in healthcare can benefit from the non-needle jet injection technology, those not in healthcare can certainly reap the rewards as well. For diabetics who need daily injections of insulin or for those suffering from auto-immune diseases who depend on the autopen, the switch to a jet-injection system could eliminate the hassle of syringes and reduce the risks of compliance.

(3) Another cutting-edge advantage of this novel system is that it has the capacity to deliver drugs that are normally in a powdered form. Indeed, the engineering of a vibrating device mode makes it now possible to ‘liquidize' powdered medicine for injection. The principal investigator of this project, Dr. Hunter, believes that such a power-delivery system may help bring much relief to traditional problems faced by developing countries, wherein the lack or frequent breakdown of refrigerants spoils the efficacy of drugs that are in liquid form. Since drugs in powdered form usually do not require cooling, such problems could be easily avoided.

Over the years we've seen the birth of many new technologies, all with a common goal of bypassing the use of subdermal needles. The transdermal patch, for example, designed to release medication into the body through the skin, has seen tremendous success. The nicotine patch, used to release nicotine in controlled doses to help terminate tobacco smoking, and the contraceptive patch, used to release synthetic estrogen and progestin hormones to prevent pregnancy, are two popular examples. While there are also jet-injection systems on the market, their mechanisms are different; in these systems, the delivery is rather set - the same dose to the same depth, every time. The flexibility in dose administration and in the depth of deposition makes this system a truly remarkable improvement over its predecessors.

Perhaps after seeing James Bond receive a subdermal implant, children with phobias for needles will change their minds the next time they go to the doctor's office.

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References & Images:

Hunter et al. "Needle-free jet injection using real-time controlled linear Lorentz-force actuators." Medical Engineering & Physics. (2012)

Workbook for Designing, Implementing, and Evaluating a Sharps Injury Prevention Program. Centers for Disease Control and Prevention. (2004)

Images for educational purposes only. Attribution to original authors. RightsLink Image Permissions License number: 2944041342923.