Engineering a smart intrauterine device based on pH-controlled copper release

Contraceptive methods based on intrauterine devices (IUD) typically result in women being constantly exposed to either hormones or copper ions. Although it is well known that the pH in vaginal fluids increases from around 3.5 to 7 during intercourse, pH-responsive materials have yet to be explored for controlling the local release of contraceptive agents. Here, we describe the design of an open-source smart IUD able to modulate copper ion release on demand thanks to the integration of pH-sensitive biopolymer-based hydrogels. Both anionic and cationic hydrogels with different release strategies were investigated. In anionic gels, an increase in pH promotes an increase in the diffusion coefficient; while in cationic gels, an alkaline environment results in shrinking, exposing part of the copper wire. Computational simulations were used to verify that gel thickness was appropriate for minimal copper ion leaching at low pH and effective dose release at higher pH. A thin gel coating was integrated into a commercial IUD using a custom 3D printed mold. Copper ion release was investigated at different time points in acid and basic solutions. The results show that both anionic and cationic gels can be used to engineer smart and safer IUDs.