Vinculin focal adhesion of osteoblast-like cells on PEEK coated with ultra-thin polymer nano films

PEEK is the polymer of choice to replace metal encapsulants and other parts in active medical implants fixated into bone. The current challenge is to improve its biocompatibility with bone tissue to ultimately achieve osseointegration. PEEK sheets surfaces coated with plasma deposited nano thin polymer films using CH₄, (CH₄ + O₂) and (CH₄ + N₂) gases. PEEK samples plasma treated with nonpolymerizing gases (O₂) were also used for comparison. The adhesion performance of osteoblast like cells on the plasma-treated PEEK surfaces and the presence of Vinculin in these cells were evaluated after long culturing period (12 days). X-ray photoelectron spectroscopy and Auger spectroscopy were used to provide surface molecular information, surface hardness and molecular density. All plasma-treated surfaces retained functionality after the sterilization process. PEEK surfaces with high number of oxygen functional groups and particularly oxygen rich thin polymer coating (plasma deposition using CH₄+O₂ gas mixture) resulted in strong cellular adhesion strength and large Vinculin amount. Further, osteoblast-like cells responded better to surfaces with lower molecular density acting like another signal for cell adhesion. The osteoblast-like cells response was weaker for surfaces with both thin films with nitrogen functional groups and nonfunctional (nonpolar) films. Furthermore, thin films rich in nitrogen functional groups repelled the cells, showed abnormal cells shape, smaller Vinculin amount and induced thicker cellular clusters with poor spread.