Electrospraying of a nano-hydroxyapatite suspension

Over the past two decades it has been established that bone repair in the presence of implant materials can be optimized by control of their surface chemistry. Certain calcium phosphate materials are similar in composition to bone mineral and have been found to be osteoconductive [1–3]. These ceramic materials have therefore been developed as biomaterials for a range of different applications. However, although they promote direct bone apposition, their mechanical properties are relatively poor compared with other monolithic ceramics. Therefore, classes of applications have been developed to exploit the excellent biological properties of the materials while maintaining mechanically viable implants [4, 5]. There is now increasing evidence that surface topography both on the micro and nano-scale are important in determining the cell response to biomaterials [6– 11]. A number of studies have indicated that cell activity can be up-regulated through optimization of the surface properties of the substrate. Investigations originally concentrated on surface features of several tens of micrometers in scale, but more recently, evidence suggests that surface topography at a much finer scale may influence the cell response. Hydroxyapatite (HA) has been used in a number of different forms and several powder processing routes have been investigated in conjunction with HA [12– 18]. The application of jet-based suspension processing methods, such as ink-jet printing (IJP) [19, 20] and electrostatic atomization printing (EAP) [21, 22] allows solid freeforming of fine structures of advanced materials. In particular, EAP in the cone-jet mode enables the formation of