Fig. 1.

Morphology and dissolution of copper nanoparticles (Cu NPs) and copper microparticles (Cu MPs). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of (a, b) Cu NPs and (c, d) Cu MPs show generally spherical shape. e The color changes of artificial gastric fluid (AGF; pH 1.5), vehicle (1 % hydroxypropyl methylcellulose, HPMC; pH 6.5), and deionized water (pH 7.8) solution before (top, t = 0) or after mixing with the Cu NPs and Cu MPs for 10 min (middle, t = 10 min) and 24 h (bottom, t = 24 h). f Dissolution ratios of Cu NPs and Cu MPs in AGF, vehicle (pH 6.5), and deionized water (pH 7.8) milieus, which simulated in vivo physiological conditions. Cu NPs and Cu MPs (5 mg/mL) were suspended in above solutions and percentage of dissolution was measured using inductively coupled plasma mass spectrometry after 24 h of incubation (t = 24 h)