* Corresponding author. Tel.: # 34-93-402-1134; fax: # 34-93-402- 1138. E-mail address: lcleries@fao.ub.es (L. Cle`ries) Biomaterials 21 (2000) 967}971 Technical Note Mechanical properties of calcium phosphate coatings deposited by laser ablation L. Cle`ries*, E. Martm H nez, J.M. Ferna H ndez-Pradas, G. Sardin, J. Esteve, J.L. Morenza Departament de Fn & sica Aplicada i O " ptica, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona, Spain Received 18 June 1999; accepted 1 November 1999 Abstract Amorphous calcium phosphate and crystalline hydroxyapatite coatings with di!erent morphologies were deposited onto Ti}6Al}4V substrates by means of the laser ablation technique. The strength of adhesion of the coatings to the substrate and their mode of fracture were evaluated through the scratch test technique and scanning electron microscopy. The e!ect of wet immersion on the adhesion was also assessed. The mechanisms of failure and the critical load of delamination di!er signi"cantly depending on the phase and structure of the coatings. The HA coatings with granular morphology have higher resistance to delamination as compared to HA coatings with columnar morphology. This fact has been related to the absence of stresses for the granular morpho- logy.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Hydroxyapatite; Calcium phosphate coatings; Laser ablation; Adhesion 1. Introduction The combination of the good mechanical properties of titanium with the bioactive properties of the calcium phosphates has fostered the application of calcium phos- phate coatings on titanium as implants for bone substitu- tion. Laser ablation is being developed as a valuable technique for the deposition of the coatings [1,2]. The variation of the deposition parameters (wavelength and #uence of the laser beam, water vapor pressure in the chamber and substrate temperature) can directly give rise, in a reproducible and controlled manner, to coatings with di!erent crystalline and non-crystalline phases [3]. In order to predict the feasibility of these coatings as implants, their dissolution behavior has been previously evaluated [4], and their osteoconductive properties have also been assessed [5]. Another concern dictating the success of the potential implant is the adhesion of the coating to the substrate, but the mechanical properties of the coatings have not been su$ciently studied [1,6]. Therefore, we present in this work a study of the mechanical properties of three selected types of calcium phosphate coatings deposited by laser ablation varying in crystallinity and morphology. The scratch test method combined with scanning electron microscopy has been used for this purpose. 2. Experimental Commercially available titanium alloy (Ti}6Al}4V) foils 11 cm, polished up to a roughness around 0.03 m and degreased with trichlorethylene, acetone and ethanol washes are used as substrates. A pulsed laser beam is focused onto a rotating hydroxyapatite (HA) target inside a vacuum chamber, where a controlled water vapor atmosphere can be introduced. The species that are ejected in each laser pulse conform the coating as they reach the substrate, which can also be heated to a "xed temperature. A KrF excimer laser of 248 nm wavelength and pulse duration 23 ns was used to obtain an amorphous calcium phosphate coating (ACP) and a crystalline HA coating (HA-ex). Through the 355 nm wavelength of a Nd:YAG laser with a pulse duration of 10 ns, a crystalline HA coating (HA-Nd) was also ob- tained. The deposition parameters for each type of coat- ing are presented in Table 1. The thickness of excimer laser-deposited coatings was around 1.7 m and near 4.0 m for the Nd:YAG- deposited one. The density was around 3 g/cm for the 0142-9612/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 6 1 2 ( 9 9 ) 0 0 2 4 0 - 9