Optimising diamond surface for a better neural interface
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1
University of Melbourne, School of Physics, Australia
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2
RMIT University, School of Aerospace, Mechanical and Manufacturing Engineering, Australia
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3
The Bionic Institute, Australia
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4
University of Melbourne, Department of Anatomy and Neuroscience, Australia
Introduction: Recent years have seen an upsurge in research on developing electronic implantable prostheses for alleviating clinical conditions such as hearing loss and vision impairment, in cases where function of the nervous system is damaged or lost due to diseases or injuries. The selection of implantable electronics materials in these applications is critical, particularly for the electrodes operating at the interface between devices and neural tissue. In addition to the requirements of biocompatibility and biostability, it is necessary for the interfacing materials to withstand procedures such as sterilization, exhibit robust mechanical stability and maintain electronic functionality in the harsh biological environment over a long term. Diamond is such a candidate.
Another property of great significance to the long-term efficacy of implantable electrodes is the electrochemical performances of the stimulating electrodes. To deliver sufficient charge densities and evoke action potentials within safe voltage limits without damaging the surrounding tissues, the electrode surface must exhibit a high charge injection capacity. Nevertheless, existing diamond surfaces have low charge injection capacities. Therefore, prior to its application as a stimulating electrode material for neural interfaces, it is critical that new forms of diamond surface be produced and optimized.
In this work, we present a strategy of optimizing diamond surface by exposing the nitrogen included ultrananocrystalline diamond (N-UNCD) to oxygen plasma. The modified diamond surfaces exhibited giant charge injection capacities as well as excellent biocompatibility.
Materials and Methods: N-UNCD films were deposited on silicon by microwave plasma enhanced chemical vapor deposition and subsequently modified using a 50w oxygen plasma for various periods of time. The charge injection capacities were calculated by cyclic voltammetry in PBS, using Ag/AgCl reference electrode and a platinum counter electrode. To test the biocompatibility, primary rat cortical neurons were cultivated on them, then fixed and immunostained.
Results and Discussion: The charge injection capacities were enhanced 50 times after exposure to oxygen plasma (Fig 1). A charge injection capacity of over 1mC/cm2 was found, which to our knowledge is the highest-ever reported from N-UNCD. The incorporation of oxygen functional groups and the selective etching of sp2 bonded grain boundaries were verified by XPS and NEXAFS. The wettability was seen to increase accordingly, leading to an increase of the affinity between diamond surface and ions in the electrolyte, thus a thinner double layer at the interface. High-resolution SEM images showed the formation of pillar nanostructures, which enlarged the surface area and may be responsible for the huge increase of charge injection capacity. Rat cortical neurons survived after a week, extended neurites and formed dense neurite network on the long oxygen plasma treated diamond films, indicating its excellent biocompatibility for neural interfacing (Fig 2).
Conclusion: Diamond films were optimized by oxygen plasma treatment. The resulted charge injection capacities were enhanced 50 times due to higher wettability and real surface area. The biocompatibility of the optimized surface was also verified. The optimization strategy is simple, efficient and promising for building a better diamond/neural interface.
This research was supported by the Australian Research Council (ARC) through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA).
Keywords:
in vitro,
Biocompatibility,
Surface modification,
bioinerface
Conference:
10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016.
Presentation Type:
Poster
Topic:
Surface and interfacial characterization
Citation:
Tong
W,
Fox
K,
Stacey
A,
Garrett
D,
Turnley
A and
Prawer
S
(2016). Optimising diamond surface for a better neural interface.
Front. Bioeng. Biotechnol.
Conference Abstract:
10th World Biomaterials Congress.
doi: 10.3389/conf.FBIOE.2016.01.01423
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Received:
27 Mar 2016;
Published Online:
30 Mar 2016.
*
Correspondence:
Dr. Kate Fox, University of Melbourne, School of Physics, Parkville, Australia, kate.fox@rmit.edu.au
Dr. Alastair Stacey, University of Melbourne, School of Physics, Parkville, Australia, alastair.stacey@unimelb.edu.au
Dr. David Garrett, University of Melbourne, School of Physics, Parkville, Australia, dgarrett@unimelb.edu.au
Dr. Ann Turnley, University of Melbourne, Department of Anatomy and Neuroscience, Parkville, Australia, turnley@unimelb.edu.au
Dr. Steven Prawer, University of Melbourne, School of Physics, Parkville, Australia, s.prawer@unimelb.edu.au