Do microneedles represent the future in the field of drug delivery? Rachel Sully argues for the benefits they offer in terms of ease of administration, effective sterilisation and avoidance of waste.
In 1979, the first transdermal system for systemic drug delivery for the treatment of motion sickness was approved, and since then, several generations of transdermal drug delivery products have been explored. In the mid-1990s, advances in microfabrication enabled large-scale research exploration into microneedles.
Microneedles, sometimes referred to as microneedle arrays, are three-dimensional micromechanical, canula-like structures which have a length ranging from 50μm to 3mm. Depending on the length of the microneedle, penetration into the dermis can be achieved, bypassing the stratum corneum barrier of the skin.
There are many different types of microneedles – solid microneedles, coated microneedles, hollow microneedles, biodegradable/ dissolvable microneedles and hydrogel forming microneedles – making them incredibly versatile, with a wide range of applications, including cosmetics, vaccine delivery, drug delivery, blood sampling and diagnostics, cancer therapies and insulin administration.
Due to their relative novelty, the desired penetration depth and insertion force of microneedles are still being determined, with different applications requiring different characteristics of the microneedles.
One of the main challenges with drug delivery in general is patient compliance. Although microneedles are visibly a lot smaller than hypodermic needles, there may still be a concern from patients about pain and side effects of microneedle insertion. One of the many exciting advantages of using microneedles for drug-delivery is their potential at-home application, without the need for healthcare professionals.
For example, in developing countries where trained healthcare professionals are few; or in cases where consistent injection would hinder more than benefit your way of life. The use of microneedles in these cases would be highly beneficial, especially as they only require a single-step administration. In developing countries, vaccines and other medicines that are administered by hypodermic needles can lead to dose wastage and to missed treatments. Incorporating vaccines into microneedles overcomes this challenge as patches are single use and single dose, meaning that no vaccines are wasted.
The use of microneedles in these cases would be highly beneficial, especially as they only require a single-step administration
There can often be reusing of medical equipment in developing countries, leading to transmission of diseases due to incomplete sterilisation. Microneedles can also overcome this risk, as they are single use, preventing transmission of diseases via medical equipment. For this, microneedles need to be biocompatible and non-toxic for the body, but also safely disposable and not environmentally detrimental.
Although microneedles have gained significant interest over the past decade, there are still many challenges that need to be overcome for their translation to the clinic. I believe a universal acceptance criterion needs to be created to enable good manufacturing practice when commercialising microneedles fabrication. I feel that the following are extremely important factors that need to be considered: scalability, regulatory standards, stability and cytotoxicity.
- Dr Rachel Sully is a senior formulation chemist
