Early adhesion of cells to ferromagnetic shape memory alloys functionalized with plasma assembled biomolecules – a single cell force spectroscopy study

Biomaterial performance and integration of prostheses in vivo strongly depend on the ability of cells to adhere. Plasma-assisted functionalization of smart metals with biopolymers, including plasma polymerized l-lysine (PPLL), constitutes a recently-developed promising approach to synthesize highly flexible, yet robust and strongly adherent protein coatings that support cell-biomaterial interaction. In the present study we employ single cell force spectroscopy to demonstrate that PPLL coatings promote early adhesion of fibroblast cells on the ferromagnetic shape memory alloy FePd – a promising magnetically switchable biomaterial. By varying the contact time of a cell with the substrate surface, we show that the forces and work needed to fully detach a cell increase with time and quantify bioactivity of the material. In contrast to glass and PPLL-coated glass, cell detachment from FePd requires much larger work, while a PPLL biofunctionalization further improves cell adhesion and binding affinity by an increased detachment work on short time scales. Together with a time-dependent bond model we postulate a transition from unspecific to specific cell adhesion on FePd and PPLL-coated FePd, while on glass detachment forces are lower and level off to a saturation regime on short times prior to the expected time necessary for specific integrin-based bond formation.