If you squirm at the thought of an injection, there's no need to look away now. Researchers at the Tyndall National Institute in Cork are developing "microneedles" that can deliver drugs painlessly through the skin, writes Dr Claire O'Connell
The barely visible silicon needles have a range of potential medical applications, including cancer therapy and vaccination
"Microneedles penetrate the skin and so increase its permeability," explains Nicolle Wilke, a final year PhD student at the institue. "The outer layer of the skin has a high resistance to drugs, and the idea of needles is to make tiny channels into the skin to allow drugs to enter."
The beauty from a patient perspective is that the application of the needles is painless. Wilke explains that because microneedles are so small - less than 0.5mm high - they do not touch nerves, which lie deep in the skin layers, so there's no sensation of pain.
Microneedles can also aid drug delivery through a technique called electroporation, where an electric field temporarily opens channels in cell membranes, making them more permeable to drugs.
Tyndall researchers are collaborating with the Cork Cancer Research Centre at the Mercy Hospital across the road to look at electroporation in cancer therapy. "The skin has very high resistance from an electrical point of view, and for cancer therapy you want a really high field with very short pulses," says Wilke. "But the skin reduces the efficiency of the electric field."
Frank Stam, who leads the Tyndall's biomedical microsystems team, says they initially found that flat electrodes were not effective at delivering the required electric fields to promote drug uptake into tumours. Then the idea of needles came up. The microneedles penetrate the skin and can increase the efficiency of the electric field, meaning less voltage would have to be applied - again good news for the patient.
At the Tyndall - which brings together research activities from the National Microelectronics Research Centre, University College Cork and Cork Institute of Technology - researchers fabricate microneedles on a chip using processes called dry- or wet-etching. They start with a silicon wafer, then remove material selectively from the surface to create arrays of upstanding needles.
According to Wilke, 100 needles fit well on one 8x8mm chip, and the researchers can vary their number, density, thickness and height. It was this flexibility that attracted Dr James Birchall from the Welsh School of Pharmacy to approach Wilke's PhD supervisor, Dr Anthony Morrissey, about working together.
Dr Birchall's gene delivery research group at Cardiff University looks at drug delivery into samples of isolated human skin donated by patients undergoing surgery. "We wanted to collaborate with someone with microneedles to see if that's a new way of putting DNA into skin," says Dr Birchall. His group aims to use DNA to treat skin diseases or for genetic vaccination, where a piece of DNA injected into the body produces a protein that triggers an immune response.
"The external skin barrier - the stratum corneum - is the rate-limiting barrier. But the moment you make holes in it, it does open up possibilities for delivering a wider range of drugs," he says. The Welsh researchers use microneedles to target immune-processing cells within the skin layers. They coat DNA directly onto the microneedles, or else they use uncoated needles to create channels into the skin so that a solution or gel containing DNA can fall in from the skin's surface.
Dr Birchall notes the microneedles approach has many possible advantages over conventional needles, including cost-effectiveness, easy disposal and lower infection risk. He says they could also reduce the need for clinicians to administer vaccines in the developing world. "Potentially with microneedles they are self-administrable, so you could basically give a microneedle patch to someone and they would put it on for 24 hours and then throw it away," he says. Dr Birchall expects it will be several years before microneedles are in general use.