We’ve been trying to replace hypodermic needles with jet injectors since the 60s, with variable success. Even though they were developed in an effort to replace needles and curtail disease transmission between patients, the jet injector is vulnerable to becoming a disease vector, just like anything else that breaks the skin. But in a new and very literal application of the phrase “magic bullet,” nanoengineers and analytical chemists from the University of San Diego have built an “acoustic microcannon” — an ultrasound-powered, needle-free drug delivery method that’s meant to get medication straight to deep tissue, where we need it to do its work.
Currently the WHO doesn’t recommend the use of jet injectors, because of their risk of disease transmission between patients. The hepatitis B virus, for example, is small enough that it can be transmitted by cross-contamination on the imperceptible order of nanoliters, and jet injectors were identified as the vector of a 57-patient hep B outbreak associated with a weight-loss clinic. Jet injectors can also inoculate the patient with environmental pathogens and skin flora during the vaccination. A podiatry clinic using jet injectors to apply lidocaine also inoculated a bunch of its patients with the charmingly named Mycobacterium chelonae sp. abscessus. The bacteria had been growing in the distilled water used to make the manufacturer-recommended solution used to store the instrument.
Obviously we need a better solution. Durable goods can be cost-effective but make great disease vectors, and disposables like syringes and needles can be a problem in the poorest places, where there’s desperate need of vaccines for diseases like polio. That’s where the UCSD scientists come in.
The microcannon starts with a membranous polymer film. Like poking a finger through plastic wrap, nanoengineers poked carefully sized holes in an elastic membrane, and spray-coated the membrane with layers of graphene and gold to make the cannon barrels rigid on the nanoscale. Then they backed the membrane with a gel matrix containing a perfluorocarbon (PFC) propellant and fluorescent “nanobullets” about a micron wide, and hit it with ultrasound. PFC vaporizes when hit with an ultrasound pulse, producing rapidly expanding gas bubbles that “fire” the nanobullets out of the microcannons at speeds on the order of meters per second — and the fluorescent microbullets light up to show exactly where they landed in the tissue target.
The authors of the study note that “This acoustic-microcannon approach could be translated into advanced microscale ballistic tools, capable of efficient loading and firing of multiple cargoes, and offer improved accessibility to target locations and enhanced tissue penetration properties.” Ultrasound is a little nimbler than gas tanks, in terms of the propellant for such a drug-delivery approach. And such a directly targeted administration of medication to tissue could be much more efficient than digestion, which forces drugs through the hepatic portal — part of the body’s sophisticated filter system.
An ultrasound device can even be handheld, as with a hypospray, although sadly that specific form factor already has a design patent — awarded to none other than Rick Sternbach, the “prop guy” from ST:TNG and Voyager. No word yet on whether we’ll be able to deliver vaccines by the time we need them to stave off the Melvaran mud flea contagion.
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