The contact angles for Groups 1 to 4 were 33.8° ± 2.5°, 77.8° ± 5.6°, 43.8° ± 2.8°, and 56.7° ± 5.9°, respectively (p < 0.001; Figure 1). The multiple-comparison result is shown in Figure 1. The small contact angle of the hydroxyapatite disk treated with polydopamine and PEG indicated a strong hydrophilic property of the surface.