Fear of needles is, for part of the population, the main reason for not having a Covid-19 vaccine. That fear is of all times, clearly demonstrated by the fact that needleless techniques have been developed for over 150 years. The current technology, developed by David Fernandez Rivas and his team, is safer than previous ones, it is better possible to steer the injection fluid and the depth it penetrates into the body. This is reason enough for researcher Jelle Schoppink to compare the different options, in a 'perspective paper' in Advanced Drug Delivery Reviews.
Needlel-free injection that uses a liquid jet that is heated and 'shot' by a laser, is a development that the University of Twente, as well as its spinoff company FlowBeams is working hard on. It takes away barriers for people that are afraid of needles and reduces the huge amount of waste in hospitals. An important property is that the jet can be controlled to a large extent: in this way, no more fluid is used than actually needed, and the dosage depth that is sent to the dermis and epidermis - close to the outer skin surface - is highly controllable.
This is entirely different from early mass vaccination techniques that were used in the fifties of the 20thcentury. Here, the fluid got its speed by the energy stored in a spring that was released. The penetration depth was 2 to 10 millimeter and it was not easy to control it.
Using this technique came to an end when part of the blood appeared to came back to the injector, with large-scale cross contamination as a result. World Health Organization (WHO) decided to end this type of vaccination.
For about ten years now, application of lasers seems to be most attractive, after experiments had been done using compressed gas or using piezoelectric devices to generate the necessary force to 'shoot' the liquid. Laser powered fluid jets were already developed by the Physics of Fluids group of Professor Detlef Lohse, using a so-called pulsed laser. This already came close to the technology David Fernandez Rivas and his team is currently developing, but he uses a continuous laser instead: this has some advantages like the size and cost. The fluid dynamics is highly controllable, with a typical depth of 0.1 millimeter to 1 millimeter. Compare that to the old spring-powered technique! You might expect that the function of the injection fluid might change by heating it, but there are no indications that it does, so far.
The danger of returning jets, can be prevented as well. Although the laser-induced injection technique is not tested on humans yet, tests on gels that look like human skin as well as on pig skin, look fine. Replacing a needle clearly is not necessary, but the question may be asked if there is not some plastic nozzle that has to be replaced for each patient. In the current situation, this is the case, but according to Schoppink, this even will not be necessary in future, actually reducing the amount of waste more.
Schoppink is also comparing the needleless technology to a technique that does use needles, but very tiny, microsized ones that you hardly feel - just like sandpaper. Although these are made using silicon technology and there is an issue with recyclability, these patches of microneedles could be used in combination with the fluidic solution, as a sort of signposts directing multiple jets in the right way.
The article of Jelle Schoppink, concluding, does not only illustrate the advantages of current technology, but it places it in perspective and also explores ways of combining techniques for the best patient-friendly solution.
Schoppink, J & Rivas, D.F., (2022) Jet injectors: Perspectives for small volume delivery with lasers. Advanced Drug Delivery Reviews. doi.org/10.1016/j.addr.2021.114109.