This paper is interesting about anisotropic cell behaviours:

Crouch AS, Miller D, Luebke KJ, Hu W. (2009) Correlation of anisotropic cell behaviors with topographic aspect ratio. Biomaterials 30, 1560-7

Bin, you bring in a challenging topic. Previously we demonstrated that, both theoretically and experimentally, when immersed in a corrosive liquid and subjected to a non equi-biaxial in-plane stress loading, a metal surface with an initial isotropic roughness will automatically develop anisotropicity.

K.-S. Kim, J. A. Hurtado, and H. Tan (1999) Evolution of a Surface-Roughness Spectrum Caused by Stress in Nanometer-Scale Chemical Etching, Phys. Rev. Lett. 83, 3872 – 3875.

Many material surface properties, such as surface mobility and wettability, depend on the roughness tensor. We have to clarify, both experimentally and theoretically, this dependence in order to fix numerous contradicting data in literature as mentioned by Sara.

I totally agree that the conventional surfce roughness parameters do not seem to be enough to describe the morphology of the surfaces anymore. This is actually a problem that is resulting in numerous contradicting data on interaction of cell/bacteria with rough substrates in the literature. I believe new approaches have to be developed to characterize the spatial distribution of nano and micro features.

Henry，

Thanks for sharing this interesting topic. Regarding the description of roughness, are the spatial frequency and amplitude enough to characterize the interaction? I think isotropic and anisotropic roughness patterns will play a different role.

Bin

Yes, we are interested in this cushioning effect of the interactions between the nano-features of bacteria and implant materials. Understanding the adhesion mechanisms of gram-positive and gram-negative bacteria is important for the medical treatment of different type of implant-associated infections.

Interesting subject indeed. We postulated that different responses from gram negative bacteria could be due to the extra outer membrane surrounding their peptidoglycan layer that could cause a cushioning effect in the interaction with the nanofeatures of the substrate material. It would be great to model this interaction and if you are interested in the subject, we would be happy to provide you with any additional data you might need.

Best, Sara

Thank you Sara, this is a very interesting piece of experimental work. Could you explain why surface roughness effect to the adhesion is not that strong for gram-negative bacteria? Maybe mechanicians here can do some modelling for this?

Regards, Henry.

Thanks for highlighting our paper. This is a purely mechanical treatment that induces hierachical surface roughness without compromising the biocompatiblity of the treated material. This surface roughness turns out to particularly reduce the adhesion of gram positive bacteria to the surface.

the treatment itself enhances also the mechanical properties of the treated metallic material, thus I would say it is efficient in improving different aspects of the materials' functionality.

News from MaterialsToday:

A simple process that roughens the surface and alters the grain size of metallic biomedical implants could deter the bacteria that cause infections and complications after surgery, according to researchers from Politecnico di Milano, Massachusetts Institute of Technology, Northeastern University, University of Cambridge, and King Abdulaziz University.

Sara Bagherifard, Daniel J. Hickey, Alba C. de Luca, Vera N. Malheiro, Athina E. Markaki, Mario Guagliano, Thomas J. Webster (2015) The influence of nanostructured features on bacterial adhesion and bone cell functions on severely shot peened 316L stainless steel. Biomaterials 73, 185–197.