PDMS absorbs and releases estrogen. PDMS exhibits capacitance for small, hydrophobic molecules. (a) Pieces of PDMS of mass 10, 20, or 30 mg were incubated individually for 24 hours in 100 μl of serum-free media containing 10−7 M E2. When thoroughly rinsed and transferred to wells containing cells in stripped serum, estrogen was released from the PDMS in a manner independent of the mass, indicating that the PDMS was not saturated with estrogen (p < 0.005 each, n = 3 experiments). (b) MCF-7 MVLN cells stably expressing luciferase were cultured in 10% stripped serum or serum-free media in the presence of no PDMS (No PDMS), non-extracted PDMS (PDMS), or extracted PDMS (xPDMS) pieces. Left, Cells cultured in stripped serum exhibited no difference in luciferase induction between PDMS treatments, though both conditions caused a statistically significant drop in induction from no-PDMS controls. Right, Cells cultured in the absence of serum showed a clearer distinction between non-extracted and extracted PDMS in response to estrogen. Both PDMS conditions effected a statistically significant inhibition of estrogen signaling, and at 10−8 M estrogen were significantly different from each other (p < 0.05, n = 3 experiments).