INNOVATION
TRANSDERMAL DRUG DELIVERY IS BIG BUSINESS - ESTIMATED TO BE WORTH $32BILLION WORLDWIDE EACH YEAR. NOW, QUEEN’S UNIVERSITY, BELFAST IS TAKING INNOVATION IN TRANSDERMAL DELIVERY FURTHER...
MICRONEEDLES : BIG THINGS FROM A SMALL PATCH
By Emma McAlister T
he transdermal drug market is currently thriving, accounting for over twelve per cent of the total global drug delivery market. In 2015, the transdermal delivery market was valued at $31.5 billion. Indeed, this area of ongoing innovation is a very attractive alternative to oral and parenteral routes of drug administration (most common routes of drug delivery) because of the advantages it offers. Delivering drugs across the skin straight into the systemic circulation means that a lower dose could be delivered and hence result in fewer and less severe side effects. Therefore, as a patient-friendly approach, this would ultimately increase patient compliance.
For successful delivery of drugs through the skin, drug candidates need to have particular properties. However, one of the biggest challenges of transdermal drug delivery is the limited number of drugs that have these ideal characteristics. Therefore, to tackle this challenge, research, conducted in the research group of Pharmacist Professor Ryan Donnelly at Queen’s University Belfast (QUB) has focused on enhancing the skin permeability to allow more drugs to be delivered in this way. It was from this problem that the concept of microneedles was born.
Microneedles consist of a number of tiny micro-projections, approximately half a millimetre in height, arranged
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on a small base that forms the patch for application to the skin. When applied, the microneedles can cross the outermost layer of the skin, the stratum corneum, creating temporary pathways which allow drug delivery to the deeper skin layers, followed by subsequent transport to the systemic circulation. Once removed, the tiny holes close rapidly and skin function returns to normal.
The ability to deliver a greater range of drugs transdermally is considered the principal benefit of microneedles. Because the needles are very small, when applied, there is no pain or bleeding. Better still, the fear of getting an injection which is experienced by many people with the ‘traditional’ needle is also eliminated. Moreover, as microneedles form only temporary micro-channels, the risk of getting an infection is minimised. Microneedles are in some ways similar to the conventional transdermal patches eg, a fentanyl patch. Unlike these patches, however, microneedles do not simply adhere to the skin surface, but rather pierce the upper layer of the skin. Microneedle patches have been described as feeling similar to the sensation of Velcro or a cat’s tongue when applied.
Microneedles have been manufactured worldwide from a variety of materials including silicon and metal. In our research group at QUB, microneedles are prepared from a polymer which is not toxic to the body. This polymer is the same material found in many toothpastes, mouth rinses and denture adhesives.
This unique, novel design which was developed in 2012 is called hydrogel- forming microneedles. The needles are hard in the dry state, so they can be easily applied to the skin. The drug is held on top, in a separate reservoir. When inserted into the skin, the microneedles take up the skin’s fluid and swell. This causes the reservoir containing the drug to dissolve, which then moves through the microneedles and into the skin. When removed, these microneedles do not leave any polymer behind and are too soft to be reinserted into another patient, reducing the risk of transmission of infection.
Microneedles have been investigated for delivery of a wide range of drugs, from those traditionally given as tablets or capsules such as metronidazole to injectables such as insulin and the influenza vaccine. Specifically, within Queen’s University Belfast, we have demonstrated the delivery of a number of clinically relevant drugs, including high-dose delivery of ibuprofen, cytotoxic drugs such as methotrexate, the antibody therapeutic Avastin®, donepezil for the treatment of Alzheimer’s Disease and the combined delivery of aspirin, lisinopril and atorvastatin for cardiovascular disease. However, the use of microneedles is not limited solely to drug delivery. Within our research team, it has been shown that microneedles can be used to take up fluid around tissues in the skin as a potential means of monitoring metabolites, such as blood sugar with, particular application for
diabetic patients. More recently, microneedles are also being used in the cosmetic industry to minimise skin imperfections such as acne scars, surgical scars, fine wrinkles, stretch marks and cellulite, in addition to improving skin texture and firmness.
Studies conducted within our research team have recently demonstrated the successful self application of microneedles in human volunteers, following counselling from a pharmacist. We also investigated the use of a film that changed colour when the microneedle patches were applied properly, as a means of providing a level of assurance to the patient of correct application.
To date, our research team and other groups worldwide have been successful in delivering a wide range of drugs using microneedles. As microneedles progress towards becoming a product on the market in the next three-five years, processes will be needed to be put in place to enable mass production of microneedles, as well as addressing any regulatory questions. Indeed, the future for the microneedle sector appears to be very bright as the microneedle field continues to evolve and improve for other drugs, cosmetic applications and, potentially monitoring/diagnostic systems.
Emma McAlister is a registered pharmacist and PhD student at Queen’s University Belfast. •
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