The effects of monomer on the diffusion behavior of drug molecules in acrylic pressure-sensitive adhesive

Acrylic pressure-sensitive adhesive (PSA) is widely used in transdermal drug delivery systems (TDDS). In this study, PSAs with different monomer proportion were synthesized, the effects of soft monomer/hard monomer ratio on the diffusion of drug molecules were investigated by Fourier transform infrared attenuated total reflection (ATR-FTIR) measurement and molecular dynamics simulation. The accuracy of the diffusion coefficient was confirmed by the consistency of the results from the above two methods. Based on the characterization of diffusion behavior, the diffusion mechanism was revealed. Three dominant factors, which affect the diffusion behavior: the wriggling of the polymer chain, the free volume and the drug-PSA interaction, were discussed. The wriggling of the polymer chain and the free volume of PSA are positive to the diffusion process while drug-PSA interaction is negative. Through the synergy of the three factors, the diffusion rate of drug molecules in PSA can be controlled by adjusting the proportion of soft monomer and hard monomer.