The zeta potential of the milled powders was measured with a Malvern Zetasizer (Nano-ZS). In order to simulate in vivo ionic environments, the samples (A1, A2, A3, A4, A5) were suspended in 0.154 M NaCl solution (physiological saline) at different pH 5, 7.4, and 11. The zeta potential was also examined six times (each time being the average of 100 runs) and the mean values and standard deviations were calculated. Electrophoretic mobility and zeta potential were calculated automatically based on Smoluchowski's equation [19].