The degree of wetting (wettability) of the hydroxyapatite disks with coating was evaluated by measuring the contact angle using a drop-shape analyzer (DSA100. Krüss GmbH, Hamburg, Germany) equipped with a pendant drop module. It quantifies the wettability of the hydroxyapatite samples by water via the Young equation. Three replicates were measured for each group, and three samples per group were assessed. Each water drop (5 µL) was deposited onto the disk surface and kept for 15 s. Then, an image of the drop was taken by a built-in camera and analyzed using the software (Image J 1.51a, National Institutes of Health, Bethesda, MD, USA) supplied by the manufacturer. All measurements were conducted at room temperature.