A new computational method of modeling and evaluation of dissolving microneedle for drug delivery applications: Extension to theoretical modeling of a novel design of microneedle (array in array) for efficient drug delivery.

Today, dissolving microneedles have grabbed much attention due to their fascinating features. As the first step, recognition of their behavior under different circumstances is needed. By gathering such information, modifications with the aim of eliminating the defects of the last models would be possible. Accordingly, a numerical simulation of dissolution process of dissolving microneedle in porous medium has been performed. This framework is validated with the experimental study of dissolving microneedle application for drug delivery to corneal. The effects of initial amount of drug loaded in microneedle and pitch size on dissolution rate and drug concentration in tissue have been discussed. The obtained results reveal that, faster microneedle dissolution and higher drug concentration can be achieved by increasing the initial drug concentration in microneedle. Although decreasing the pitch size can provide higher drug concentration, it has no significant effect on dissolution time. To extend the current study, as the next part, a new approach called array in array theory, a cone with an array of hemispherical convexities localized in the second half of the microneedle, has been proposed. This new proposed structure has the capability of diminishing the risk of delivery of insufficient amount of drug when partial insertion occurs, reducing the drug waste, providing rapid drug delivery process, and increasing the drug flux through drug delivery procedure. According to the numerical simulation of this new design, the drug concentration left in tissue is 4.85 × 10 kg/m, which is higher than the last case as 2.43 × 10 kg/m, while it only takes 8 s longer to be fully dissolved; hence, it does not impair the convenience of drug administration process. This design offers an economical and effective way for drug delivery process. Such studies allow the user to visually monitor microneedle performance to reach the appropriate design before fabrication.