Development of new colloidal and electrochemical processing techniques for orthopaedic implant coatings and biosensors

Abstract

Development of a new generation of nanocomposite biomedical implant coatings that contain bioactive ceramics and polymers and tailored surface features, both of which promote cell adhesion, proliferation, and interlocking at the bone tissue/implant interface, is crucial to extending the lifespan of orthopaedic implants. Use of combined colloidal and electrochemical processing techniques, in particular electrophoretic deposition (EPD), have the ability to fabricate these new multi-component materials with relative ease. They also can be used to fabricate nanostructures and surface topography, that mimic the structure of human skeletal tissue at the nanoscale. Furthermore, colloidal-electrochemical processing techniques may also be easily upscaled, towards clinical product development and mass manufacturing, unlike many processing techniques commonly used in nanotechnology. Since the success of EPD depends on the use of a stable colloidal precursor, barriers to widespread use of colloidal-electrochemical methods for fabrication of these novel biomaterials, is the lack of efficient and biocompatible dispersants and extractors. One approach to developing suitable dispersing and extracting agents lies in deriving inspiration from the natural world, also known as biomimetics. Based on this approach, new extracting agents inspired by the chemical structure of mussel adhesive proteins (MAPs) were discovered for the efficient particle extraction and formation of organic-inorganic composite films, containing hydroxyapatite (HA) nanorods. Building upon this approach, we utilized catechol (CAT), the functional group in MAPs that allows for their ultra-strong adhesion, and functionalized amine-containing biopolymers. We used chitosan (CHIT) and poly-L-lysine (PLL) as model biopolymers and found that CAT functionalization imparted remarkable properties such as robust adhesion, stability across a wider pH range, and redox-capacitance. Future applications of these films were explored, including not only orthopaedic implant applications, but also electrochemical and photoelectrochemical sensing applications. Finally, biomimetic inspiration was derived from the human digestive system, to use bile acid salts (BAS) as powerful solubilizing, charging, dispersing and film-forming agents for the fabrication of composite coatings, containing water insoluble drugs. These coatings can be used for local drug delivery of anti-biotics, to prevent surgical infection post-implantation, and use of BAS surfactants paves the way for solubilization and dispersion of other hydrophobic functional drugs and molecules, as well as fabrication of functional composite films using EPD.