can potentially allow the transdermal delivery of many medicaments including large macromolecules that typically cannot diffuse through the skin. This paper addresses the use of microneedles coated with a drug solution film. In particular, we identify how the geometries of various microneedles affect the drug permeability in skin. Effective skin permeability is calculated for a range of microneedle shapes and dimensions in order to identify the most 20 efficient geometry. To calculate effective permeability (P eff ), the effective skin thickness (H eff ) is calculated. These are then plotted for insulin as a model drug to see how various microneedle parameters affect the profiles of both H eff and P eff . It is found that the depth of penetration from the microneedle array is the most important factor in determining P eff , followed by the microneedle spacings. Other parameters such as microneedle diameter and 25 coating depth are less significant.

In the past few years, a number of microneedle designs have been proposed for transdermal drug delivery of high molecular weight drugs. However, most of them do not increase the drug permeability in skin significantly. In other cases, designs developed based on certain criteria (e.g. strength of the microneedles) have failed to meet other criteria (e.g. drug permeability in skin, throughputs of the drugs, etc.). It is obvious therefore that in order to determine the 'optimum' design of these microneedles, the effect of different factors (e.g. length of the microneedle, surface area of the patch, etc.) along with various transport properties of drug transport behaviour using microneedles should be determined accurately. Appropriate mathematical models for drug transport from these systems into skin have the potential to resolve some of these issues. To address this, a parametric analysis for transdermal delivery of a high molecular weight drug from a microneedle is presented in this paper. The simulations have allowed us to identify the significance of various factors that influence the drug delivery while designing microneedle arrays. A scaling analysis is also done which shows the functional dependence of drug concentration on other variables of skin and microneedle arrays.

Improving drug permeability in the skin is one of the most important issues for designing new methods of transdermal drug delivery. Consequently, many techniques have been proposed to effectively deliver drugs across the stratum corneum. The microneedle is a new technology to enhance transdermal delivery of high-molecular-weight drugs. This technique combines the concepts of transdermal drug delivery across the skin with patches and hypodermic injections. The microneedles have been shown experimentally to increase the skin permeability by orders of magnitude in vitro for a range of drugs that differ in molecular size and weight. Recently, other questions appeared while using these microneedles, such as how to reduce needle diameters by which the hole is produced to be as small as possible to exclude bacteria and other foreign particles. Another issue is how to correlate the skin thickness and microneedle length with the skin permeability. In this work, we have developed an optimization framework for improving skin permeability to drugs by using microneedle arrays, which considers different classifications of skin thickness arising from different races, sex groups, ages, and anatomical regions. To know the optimum design of these microneedles, the effect of the microneedle geometry (e.g., number of microneedles, microneedle radius) on skin should be determined. In this work, the optimization algorithm is presented. The outcome of this work will be used to suggest optimum microneedle designs based on the parameters of interest.