Development of novel skin-mimetic substrate with 3D printing to assess the adhesion properties of transdermal patches

Transdermal system (TDS) patches, a long-standing product in the market, still grapple with issues of secure skin adherence, efficacy, and safety. Hence, there is a pressing need to study factors affecting TDS patch adhesion on skin-mimetic substrates to enhance reliability and reduce reliance on extensive in vivo testing. The present study aims to develop novel skin-mimetic substrates with fused deposition modeling (FDM)-based three-dimensional (3D) printing using materials with similar surface energy as the skin and evaluating the adhesion property of pressure-sensitive adhesives (PSAs). Additionally, the study investigates the effect of various intrinsic factors, including coat weight, elastic properties of backing membranes, and viscosity of PSAs, on the adhesion properties of PSAs. We successfully fabricated our novel polypropylene (PP) probe using FDM printing and implemented an automated robotic arm setup for adhesion testing. Probe tack test results displayed no significant difference in peak adhesive force between the skin and PP probes. However, PP probes exhibited a 10.26-fold decrease (p < 0.0001) in the adhesive force compared to stainless steel (SS) probes. Probe tack and peel adhesion tests of the marketed Salonpas patch also displayed a significant decrease (p < 0.0001) in the adhesive force for PP probes/plates compared to SS probes/plates. In terms of coating, both amine-compatible (PSA-4302) and non-amine-compatible (PSA-4501) silicone-based PSAs displayed a significant increase in their adhesion properties at 10 mg/cm(2) compared to 5 mg/cm(2) coating (p < 0.05). Furthermore, the selection of backing membrane and the viscosity of silicone-based PSAs also demonstrated a significant (p < 0.0001) effect on the PSA's adhesion property. In conclusion, PP probes/plates could be a promising approach for in vitro adhesion testing of transdermal system (TDS) products. Furthermore, intrinsic properties, including coat weight and viscosity of silicone-based PSAs, could significantly affect the adhesion properties of TDS products.