Exploring the use of diamond in medical implants
AuthorSikder, Md Kabir Uddin
Document TypePhD thesis
Access StatusOpen Access
© 2019 Dr Md Kabir Uddin Sikder
Over recent decades, there is increasing interest in implantable devices that interact with neural tissue in the human body. Applications are broad, ranging from cardiac pacemakers to cochlear implants and beyond. The emergence of microelectronics and microfabrication has led to the miniaturization of these neural implants. Small devices are safer to implant but a number of challenges need to be addressed before very small devices are routinely deployed. For instance, it is difficult to transfer sufficient power to small implants wirelessly, and difficult to fabricate small neurostimulation microelectrodes with high enough charge injection capacity to operate safely. Compounding this, the immune system of the body can react to the implant. Unfavourable interactions of the electrode with tissue/neurons leads to a sharp drop in performance caused by scar tissue surrounding them. These challenges, among others, must be overcome in order to reduce the size of implants into the low millimeter dimensions. Devices at this scale will be insertable with minimal trauma and will hence be deployable in a greater range of circumstances. Here we investigate the use of diamond as a biomaterial with the potential to mitigate or ameliorate some of these challenges. In this work, a novel technique for microcoil fabrication is introduced. Trenches were milled into a diamond substrate and filled with silver active braze alloy, enabling the manufacture of small, high cross-section, low impedance microcoils capable of wireless power transmission of 10 mW over 6 mm. The coils were encapsulated in a second layer of diamond, characterized, and accelerated ageing was performed to verify the longevity of the construct. Building on previous work, a method was developed to grow conducting diamond films on platinum foil. A laser roughening method was used to increase adhesion of the diamond to the platinum. This approach enables the superior properties of diamond to be integrated into devices constructed using traditional fabrication methods such as wire bonding or laser welding. Laser roughened platinum was coated with nitrogen induced ultra-nanocrystalline diamond (N-UNCD) films and the electrochemical performance of these films was measured relative to platinum. Stronger attachment of N-UNCD to platinum substrates of higher roughness was observed. Diamond on platinum electrodes were found to be more capacitive and stable compared to platinum controls, a favorable characteristic for neural stimulation. Finally, an extracellular matrix protein (laminin) known to be involved in inter-neuron adhesion and recognition, was covalently coupled to diamond electrodes. Biologically, active interlayers have the potential to increase neural adhesion to electrodes and/or reduce the immune response, thus increasing longevity. Electrochemical analysis found that covalently coupled films were robust and resulted in minimal change to electrochemical properties of the electrodes. Neurons cultured on laminin coated surfaces exhibited improved adhesion. This thesis demonstrates that diamond is a versatile material for use in medical implants. It can be used as a construction material and as an encapsulant containing electrically active elements. It can be made electrically conductive and possesses suitable electrochemical properties for neural stimulation. Finally, it can be employed as a chemically active substrate for attachment of additional chemistries, including biomolecules.
Keywordsmicrocoil embedded in diamond; nitrogen introduced ultra nanocrystalline diamond (N-UNCD) electrode; charge injection capacity; laminin coating on N-UNCD electrode; cell adhesion
- Click on "Export Reference in RIS Format" and choose "open with... Endnote".
- Click on "Export Reference in RIS Format". Login to Refworks, go to References => Import References