The refractive index of PDMS () is in the near infrared (800 to 1300 nm), close to . PDMS (Sylgard 182, Dow Corning, Midland, MI) was mixed with three different particulates to prepare stock PDMS-particulate mixtures; one each with barium sulfate powder (, B-3758, Sigma-Aldrich, St. Louis, MO), titanium dioxide nanopowder (, 718467, Sigma-Aldrich, St. Louis, MO), and silica microspheres (, 24327, Polysciences, Inc., Warrington, PA). Particles were dispersed throughout PDMS using a probe tip sonicator for 10 h. To allow for heat dissipation, samples were sonicated with a 30-s on and 60-s off periodic cycle. Afterwards, the sample was placed in a vacuum chamber to remove air pockets. Each stock sample was further diluted with additional PDMS base to create samples with a particle concentration ranging from 1% to 10% by mass. To characterize the relationship between particle concentration and OCT signal intensity, small droplets of each sample were imaged with a similar PSI SDOCT instrument in our laboratory. Care was taken to fix the reference arm length and beam focus depth in the sample during each recording session. Each sample’s signal intensity was extracted near the surface just beneath the air-PDMS specular reflection signal. Using the linear relationship between PDMS-particle concentration and OCT signal intensity, the target concentration of each phantom layer was established.