Samples of the rough, absorbent patches are being tested in the laboratories at Queen’s by award-winning researcher, Dr Ryan Donnelly.
The experiments are showing that the forest of tiny polymer needles on the underside of the patch, when pressed into the skin, can absorb the fluid in the surface tissue, taking up at the same time the salts, fatty acids and other biological molecules found there as well.
“The important thing is that we typically find the same compounds in this interstitial fluid as you would find in the blood,” Dr Donnelly explains. “But, compared with drawing blood, our patches can get their samples in a minimally invasive way. And it’s far safer than using a conventional needle. These microneedles, once they have been used, become softened, so that there’s no danger of dirty needles transferring infection to another patient, or one of the healthcare workers. Two million healthcare workers are infected by needlestick injuries every year.”
The microneedle sampling technique is a development of earlier and ongoing experiments using similar patches to deliver drugs and vaccines painlessly – the sensation when they are pressed onto the skin is a bit like the roughness of Velcro, Dr Donnelly reports.
The microneedles are made of polymer gel – similar to the material used in superabsorbent nappies. For their original, injecting function, they are pre-loaded with vaccine or drug compounds that will be released into the skin on contact with the interstitial fluid.
But the flow can go both ways. So that for the sampling variants, the backing material can be made chemically attractive to target compounds, encouraging them to diffuse into the gel with interstitial fluid drawn out of the skin and locking them in place for later analysis. Real-time monitoring could be a realistic option in the future and might involve combining the microneedle technology with simple laser-based detection (“SERS”) of drug compounds inside the gel. The group already has proof-of-concept for this idea and are now looking to extend the range of drug concentrations that can be detected in this manner. Electrochemical detection is another attractive possibility that might allow patients to use the technology in their own homes. If connected wirelessly to their healthcare provider, they could then have their medicines or doses changed based on the microneedle readings, both enhancing patient care and saving NHS resources.
Children’s charity Action Medical Research, through a generous donation from The Henry Smith Charity, is now funding Dr Donnelly to develop the minimally-invasive microneedle sampling technology for monitoring therapeutic drug levels in babies.
“Premature babies have very limited blood volumes and are prone to bruising and scarring when blood samples are taken,” Dr Caroline Johnston, Research Evaluation Manager at Action Medical Research for children explains. “There is a real need for a safe, reliable and painless way to monitor these babies’ drug levels, and these microneedles are so far proving to have all the right characteristics.”
The group is currently in discussions with a major medical manufacturer with a view to producing prototype commercial devices, the first stage ahead of full clinical trials.