Biofunctionalisation of Ti Surfaces by Means of Self-assembled Polypeptide Films

Objectives: Physico-chemical modifications of a potential implant material, commercially pure titanium with self-assembled polypeptide films (SPF) were investigated by atomic force microscopy (AFM). Important aspects of industrial applicability were clarified related to their morphology, time stability, pH-dependence, and rehydration capability. Furthermore, fibronectin, deposited on these films, was visualized by AFM. Methods: Titanium discs were covered with SPF's formed by alternating layering of cationic poly-L-lysine (PLL) and anionic poly-L-glutamic acid (PGA) in aqueous solution. Surface roughness (Ra), root mean square (RMS) values of the film and diameter of grains (D) were determined. Results: The frequently used ex situ and the rarely used in situ build-up methods were compared. The SPF's revealed granular pattern up to 10 bilayers with grain diameters of 303 ± 89 nm, independent of the build-up procedure and a very good time stability could be seen. Upon rehydration of dry samples roughness values almost reached those measured in situ. A significant pH effect has been also observed in the morphology of the SPF's. The high roughness values found at extreme pH were related to the degree of ionization of PGA and PLL. Human plasma fibronectin molecules (at a concentration close to the physiologic ones) was successfully deposited on the SPF coating and visualized with AFM. Conclusions: The alternating adsorption technique of the polypeptides PLL and PGA proved to be a successful method to coat the Ti implant material and presented numerous advantages. It can be automated, uses aqueous solution of biodegradable polypeptides and can provide films with well controlled surface charge and finely tuneable thickness and roughness. The demonstrated stability and rehydration capability of PLL/PGA multilayer coatings built on titanium by immersion is of prime importance concerning their biomedical applications. Acknowledgment: This work was supported by the SIMI-NAS Project of the 5th FWP of the European Commission (GRD3-2001-61801).