Helical rosette nanotubes: A biomimetic coating for orthopedics?

Helical rosette nanotubes (HRN) are obtained through an entropically driven self-assembly process of low-molecular-weight synthetic modules under physiological conditions. Counter-intuitively, these materials undergo extensive self-assembly under the effect of temperature, resulting in networks of very long nanotubes. We have previously shown, using an in vitro model, that titanium (Ti) coated with HRN containing a lysine side chain (HRN-K1) displayed enhanced osteoblast (OB) adhesion when compared to uncoated Ti (p < 0.01). Because it has been widely known that proteins play a critical role in OB adhesion on nanophase materials, here we examine OB adhesion on heated (+T) and unheated (-T) HRN-K1-coated Ti under serum (+S, presence of proteins) and serum-free (-S, absence of proteins) conditions. The results demonstrated that (a) while proteins enhanced OB adhesion on +T HRN-K1-coated Ti, they had no effect on -T HRN-K1-coated Ti, suggesting an active role played by the rosette nanotubes in promoting OB adhesion, and (b) under -S conditions, +T HRN-K1 induced the same level of OB adhesion as uncoated Ti under +S conditions, suggesting that +T HRN-K1 acts as a protein substitute. Finally, transmission electron microscopy and atomic force microscopy studies of +T and -T HRN-K1-coated Ti revealed a significant change in surface coverage, density and hierarchical organization of the nanotubes upon heating, which was correlated with their ability to promote cell adhesion. (c) 2005 Elsevier Ltd. All rights reserved.