Multifunctional Protein-Immobilized Plasma Polymer Films for Orthopedic Applications

Osseointegration is essential for ensuring optimal functioning and longevity of orthopedic implants. In a significant number of patients, the body does not fully integrate with the orthopedic implant, which opens the potential for the formation of bacterial biofilms and adverse foreign body reactions. Protein-functionalization of the implant surfaces can reduce this potential by stimulating rapid cell attachment or bone formation. Ideally, a multifunctional protein surface should simultaneously stimulate cell attachment and bone formation for optimal osseointegration. In this study, we utilized primary mouse osteoblasts to examine the osteogenic potential of a multifunctional fusion protein, combining the fibronectin (FN) attachment and osteocalcin (OCN) bone signaling sequences, compared against that of the individual proteins. These three biomolecules were immobilized on radical-functionalized plasma polymer films (rPPFs) that covalently bond proteins through interactions with embedded radicals that migrate to the surface. The fusion protein was also compared to a coimmobilized ratio of FN:OCN prepared through a two-step sequential exposure to OCN solution followed by FN solution. The preparation and characterization overhead for the two protein surfaces was substantial when compared to the fusion protein functionalization process. Significantly greater osteoblast attachment and spreading were observed for the FN, FN:OCN, and fusion protein surfaces compared to titanium (p < 0.05), while the calcium deposition after 17 days showed a significant increase (p < 0.01) on the fusion protein surface alone. The greater osseointegration potential of the fusion protein surface compared to the single and coimmobilized protein surfaces is attributed to the homogeneous distribution of the attachment and signaling sequences. Overall, the fusion protein-coated rPPFs produced easily functionalizable and highly osteogenic surfaces with the potential to greatly improve the tissue integration of orthopedic implants.