Surface functionalization of an implantable device with bioactive molecules can overcome adverse biological responses by promoting specific local tissue integration. Bioactive peptides have advantages over larger protein molecules due to their robustness and sterilizability. Their relatively small size presents opportunities to control the peptide orientation on approach to a surface to achieve favourable presentation of bioactive motifs. Here we demonstrate control of the orientation of surface-bound peptides by tuning electric fields at the surface during immobilization. Guided by computational simulations, a peptide with a linear conformation in solution is designed. Electric fields are used to control the peptide approach towards a radical-functionalized surface. Spontaneous, irreversible immobilization is achieved when the peptide makes contact with the surface. Our findings show that control of both peptide orientation and surface concentration is achieved simply by varying the solution pH or by applying an electric field as delivered by a small battery.

Surface biofunctionalization aims to create cell-instructive surfaces that control the behavior of cells and modulate cellular interactions by incorporating cell signaling moieties at the materials–biosystem interface. Despite advances in developing bioinert and biocompatible materials, blood clotting, inflammation, and cell death continue to be observed upon the contact of foreign materials with living tissues leading to the materials' rejection. Specific examples include the application of foreign materials in implantable devices (e.g., bone implants, antimicrobial surfaces, and cardiovascular stents), biosensors, drug delivery, and 3D-bioprinting. Biofunctionalization of materials to date has been predominantly realized using wet chemical approaches. However, the complexity of wet chemistry, toxicity of reactants, waste disposal issues, reaction time, poor reproducibility, and scalability drive a need for a paradigm shift from wet chemical approaches to dry methods of surface biofunctionalization. Plasma-based technologies that enable covalent surface immobilization of biomolecules have emerged as dry, reagent-free, and single-step alternatives for surface biofunctionalization. This review commences by highlighting the need for bioinstructive surfaces and coatings for various biomedical applications such as bone implants, antimicrobial surfaces, biosensors, and 3D-bioprinted structures, followed by a brief review of wet chemical approaches for developing biofunctionalized surfaces and biomimetic devices. We then provide a comprehensive review of the development of plasma-based technologies for biofunctionalization, highlighting the plasma–surface interactions and underpinning mechanisms of biomolecule immobilization.

Titanium (Ti) has been widely used for manufacturing of bone implants because of its mechanical properties, biological compatibility, and favorable corrosion resistance in biological environments. However, Ti implants are prone to infection (peri-implantitis) by bacteria which in extreme cases necessitate painful and costly revision surgeries. An emerging, viable solution for this problem is to use copper (Cu) as an antibacterial agent in the alloying system of Ti. The addition of copper provides excellent antibacterial activities, but the underpinning mechanisms are still obscure. This review sheds light on such mechanisms and reviews how incorporation of Cu can render Ti–Cu implants with antibacterial activity. The review first discusses the fundamentals of interactions between bacteria and implanted surfaces followed by an overview of the most common engineering strategies utilized to endow an implant with antibacterial activity. The underlying mechanisms for antibacterial activity of Ti–Cu implants are then discussed in detail. Special attention is paid to contact killing mechanisms because the misinterpretation of this mechanism is the root of discrepancies in the literature.