Numerical Simulation of Transdermal Delivery of Drug Nanocarriers Using Solid Microneedles

Solid microneedles can successfully puncture the stratum corneum and thus enable the drugs to migrate from the adhesive patch to the viable skin tissues for therapy. The treatment in different skin layers can vary greatly. However, how to improve its effectiveness remains less understood. In this study, numerical simulation is employed to predict the transport and disposition of drugs in each skin layer and blood using a skin model rebuilt from the real skin anatomical structure. The therapeutic effect is assessed by exposure to drugs over time. Results reveal the dominance of diffusion in determining the transport of nanosized drug carriers and free drugs in viable skin tissues. Delivery outcomes are highly sensitive to drug delivery system properties. Increasing the nanocarrier partition coefficient or diffusion coefficient in the skin can successfully enhance the treatment in entire skin tissue and blood. The enhancement can also be obtained by reducing the microneedle spacing or patch thickness. However, several properties should be optimised individually with respect to the target sites location, including the microneedle length, diffusion coefficient of nanocarriers in the skin, drug release rate and nanocarrier vascular permeability. Drug concentrations in the blood can be effectively increased when administered to skin areas rich in capillaries; whereas, the treatment in the skin tissues slightly would reduce simultaneously. Furthermore, delivery results are insensitive to changes in lymphatic function and the properties of free drugs introduced by the medicated patch. These findings can be used to improve transdermal drug delivery for better treatment.