Hydroxyapatite (HA) coatings with different surface roughnesses were deposited on a Ti substrate via aerosol deposition (AD). The effect of the surface roughness on the cellular response to the coating was investigated. The surface roughness was controlled by manipulating the particle size distribution of the raw powder used for deposition and by varying the coating thickness. The coatings obtained from the 1100 degrees C-heated powder exhibited relatively smooth surfaces, whereas those fabricated using the 1050 degrees C-heated powder had network-structured rough surfaces with large surface areas and were superior in terms of their adhesion strengths and in vitro cell responses. The surface roughness (R-a) values of the coatings fabricated using the 1050 degrees C-heated powder increased from approximately 0.65 to 1.03 mu m as the coating thickness increased to 10 mu m. The coatings with a rough surface had good adhesion to the Ti substrate, exhibiting high adhesion strengths ranging from 37.6 to 29.5 MPa, depending on the coating thickness. The optimum biological performance was observed for the 5 mu m-thick HA coating with an intermediate surface roughness value of 0.82 mu m. (C) 2011 Elsevier B. V. All rights reserved.