Electrochemically-assisted deposition of apatite coating on biomimetic TiO2 scaffolds

A requested goal for bioactive implants is the production of a bone filling biomaterial with the appropriate architectural/mechanical properties realizing osteoconduction and osteoproduction.1 Ti-6Al-4V has long been favored for biomedical applications, however, in the last decades alternative materials (polymers or metal oxides) has been deeply investigated. Among these, TiO2 could be a suitable material for its biological and chemical inertness. Otherwise, hydroxyapatite (HA), has been widely used in medical and dental applications due to its close similarity in chemical composition and high biocompatibility with natural bone tissue.2 In this work a novel synthesis of a TiO2 porous scaffolds and the electrochemical-assisted deposition of HA onto the TiO2 scaffold surface are presented. TiO2 scaffolds were prepared by soaking cellulose sponges3 in a solution composed by Ti(OC3H7)4 and 2-propanol in Milli-Q water.4 Once the sponges were soaked (2h), they were left to decant and dry in air for 24 h and then sintered at 1200 °C for 2 h in flowing air. To increase the mechanical properties of the TiO2 scaffolds two further sintering processes were made (1200°C, 900°C). In fig. 1 is reported the SEM micrograph of a obtained TiO2 scaffold (rutile phase) with biomimetic porosity similar to that present, for example, in the spongy bone. Electrochemically-assisted methods are well known as an effective way for the deposition of HA onto conductive supports,5,6 however, an effective method of deposition onto a porous, non conductive material is still missing. The deposition technique is based on inserting the TiO2 scaffold inside a Pt spiral which is polarised at H2 evolution reaction potentials under galvanostatic conditions in a solution containing Ca2NO3 and NH4H2PO4; pH is therefore locally increased (fig. 2), thus creating a favourable situation for the HA nucleation onto the TiO2 surface. Several experimental conditions are varied. The relative coating are analyzed by means of SEM, EDX, µ-XRD, Diffuse Reflectance Infrared Fourier Transform Spectroscopy and XPS. In fig. 3 the SEM images of the TiO2 scaffold surface (3a) and the TiO2 scaffold electrochemically coated with apatite (fig. 3b) are shown. The apatite coating obtained suggests a possible scaffolds application as a platform for osteoblasts growth.