Density-dependent scanning electron microscopy was performed at University College London as previously described (8 (link)). Briefly, human carotid artery or aortic valve sections on glass slides were secured to aluminum sample holders with carbon tape, and silver paint was applied to the area immediately surrounding each sample. Samples were then coated with 5-nm carbon (Quorum Technologies Turbo-Pumped Thermal Evaporators model K975X, Lewes, UK). Following coating, samples were imaged on a scanning electron microscope (SEM; Zeiss VP), operated at 10 kV, and equipped with both an inlens detector that recorded secondary electrons and a backscatter electron detector. Images were obtained by imaging a region in inlens mode and subsequently imaging the same region in backscatter mode. Adobe Photoshop CC 2018 was used on stacked images, and the inlens image was assigned to the green channel whereas the backscatter image was assigned to the red channel.