Recent Advancements in Microneedle Technology for Multifaceted Biomedical Applications

Oral delivery is the most accepted route of administration for the treatment of disease, diagnosis, treatment, and the most widely studied topic by formulation scientists during the first and second generations of drug delivery. Oral drug delivery has the disadvantages of systemic metabolism, poor absorption, and a lack of tissue selectivity, leading to decreased therapeutic effects. This necessitates the development of other dosage forms such as parenteral, transdermal, intravesical and other novel drug delivery systems. Ancient medicines for therapeutic effect applied on skin surface area, for various types of skin disease, wound healing activity, and cosmetic dermatological applications. However, the skin has an impermeable barrier for efficient and targeted delivery. Scientists developed syringes and needles for local drug delivery applications to overcome this limitation. Although, these developed systems also have some disadvantages, such as poor patient compliance due to the pain in administration and the invasive nature that requires trained medical practitioners. Furthermore, with the advent of polymer science, nanotechnology, and applied engineering, the concept of MNs was introduced in the literature report.

MNs are micro projections ranging 25–2500 μm in height available in different shapes with the attachment of a base for support. MNs are used to sample fluid from the body and deliver therapeutic agents to cells. MNs are tiny, unique, novel, and promising devices made using microelectromechanical systems to detect, diagnose, and treat several diseases. Vaccines, nanoparticles, high or low molecular weight drugs of various categories, high molecular weight protein, and antibodies are easily loaded into MNs to deliver it into different layers of skin and deep within the skin to neutrophil Langerhans, dendritic cells for immunological effect. MNs are classified into various classes depending upon their fabrication methods, such as solid, hollow, dissolving coated and hydrogel-forming MNs. The associated advantages and limitations vary with the type of MNs desired for the targeted site of action. MNs fabrication depends on the material used and the intended application. For the design of MNs, various materials have been used, such as silicon, zeolite, glass, metals, polymers and sugars. MNs array density was developed using instant microfabrication techniques (prototyping), including hot embossing, micro-molding, lithography, deep reactive ion etching, thin film deposition, etc.. One of the most important applications of MNs in vaccine delivery to the skin is patient compliance, high immunogenic nature of skin, vaccine targeting at desired skin site, and reliable vaccine delivery methods [8]. Numerous drugs, growth hormones, insulin, vaccines, DNA, and oligonucleotides are in the preclinical and clinical stages designed as MNs.

In this present article, we review various types of MNs, different materials used for fabrication, properties of the MNs, characterization of MNs for biological and mechanical properties, toxicity assessment of MNs with various in vivo and in vitro methods, application of MNs in several diseases, as well as the regulatory aspect, marketed product, and patent of the MNs.