Anyone who’s ever had an injection would welcome the replacement of normal syringes with ‘microneedles’. These micron-sized needles only penetrate the outer layer of the skin. This means that they deliver their drug payload without contacting any nerve cells, ensuring that the process is entirely painless. Fiorenzo Omenetto and his team from Tufts University have improved the delivery system by making their microneedles out of silk.
Silk has several advantages over metal and the other materials that have been tried in microneedles. Unlike metal, silk is biodegradable. Because the silk protein can be molded into appropriate shapes at room temperature, drugs can be incorporated directly into the pre-formed silk matrix without loss of potency. This allows the embedded drug to be released slowly as the silk biodegrades, rather than being injected all at once.
The researchers successfully tested their silk microneedles both in vitro (observing the diffusion of enzymes into a gel pad and delivering antibiotics to a tissue culture) and in vivo (using the microneedles on mice). They were able to control the rate of drug delivery by manipulating the consistency of the silk matrix.
Of course, a slower release of drugs, while advantageous in many ways, would require a longer exposure to the apparatus. Rather than one quick injection, a patient might have to place a microneedle patch on his arm for as long as 30 minutes. On the other hand, perhaps people could apply the microneedles themselves at home.