Bright prospects for pain-free vaccination using microneedles
Administering vaccines with microneedles could become a pain-free alternative to conventional thick injection needles. Koen van der Maaden devised a new strategy for using microneedles. Dissertation defence on 10 December.
For about ten years now it has been possible to introduce vaccines into the skin using microneedles, but the methods for doing that are not yet efficient enough. Koen van der Maaden developed a new strategy. He made needles that a vaccine bonds to well in a slightly acidic solution, but that easily release it in a neutral environment, such as in the skin. This approach is new and could in principle be used for a whole range of vaccines and medicines.
Van der Maaden has received a patent for this approach: microneedles with an acidity-dependent electrical charge. Although there’s a long way to go before it can be used on humans, the method has good prospects. The most important advantage is that the vaccine or medicine is in a dry form. That means it can be kept for longer periods than a vaccine or medicine in a liquid solution, even without refrigeration. Another advantage is that microneedles only pierce the top layer of skin, the dead epidermis. They don’t touch any nerve bundles, so the injection is pain-free and causes no discomfort. Microneedles do not need to be more expensive than conventional injection needles.
In his research, Van der Maaden took microneedles with a vaccine on their surface as his starting point. He explains: ‘The disadvantage is that the coating forms a thick layer. The vaccine sticks to the needles with a layer of “glue”. That makes the needles dull, and if they are pierced into the skin, a lot of the vaccine slides off on the outside.’ He found a solution for that: apply a layer of chemical substances that have an electrical charge in an acidic environment, but not in a neutral environment. ‘Vaccines are protein molecules that also have an electrical charge. If an opposite charge is applied, the proteins will be attracted from an acidic solution to the needles and bond electrically. But they’ll come off again in the skin. This coating is ultrathin, so the needles stay sharp. And it can be applied during the process of manufacturing the needles.
The idea proved feasible in practical terms. To give the needles an acidity-dependent electrical charge, Van der Maaden first dips them in an aggressive ‘piranha mixture’ of sulphuric acid and hydrogen peroxide. With a few more intermediary steps he then binds pyridine clusters to that which are positive in an acidic environment. And finally he loads a negative protein onto this foundation. He tested this method using a protein called ovalbumine (a model vaccine, that bonded well to the needles. In human skin tissue the pyridine groups lose their charge, and the ovalbumine was released properly. In mice, the protein administered in this way triggered an immune reaction just as a vaccine is supposed to do.
(4 December 2014)