Browsing by Author "Seligman, Peter"

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    Electrically conducting diamond films grown on platinum foil for neural stimulation
    (IOP Publishing, 2019-07) Sikder, Kabir; Shivdasani, Mohit; Fallon, James; Seligman, Peter; Ganesan, Kumaravelu; Villalobos, Joel; Prawer, Steven; Garrett, David
    Objective With the strong drive towards miniaturization of active implantable medical devices and the need to improve the resolution of neural stimulation arrays, there is keen interest in the manufacture of small electrodes capable of safe, continuous stimulation. Traditional materials such as platinum do not possess the necessary electrochemical properties to stimulate neurons safely when electrodes are very small (i.e. typically less than about 300 um (78400 microm2)). While there are several commercially viable alternative electrode materials such as titanium nitride and iridium oxide, an attractive approach is modification of existing Pt arrays via a high electrochemical capacitance material coating. Such a composite electrode could still take advantage of the wide range of fabrication techniques used to make platinum-based devices. The coating, however, must be biocompatible, exhibit good adhesion and ideally be long lasting when implanted in the body. Approach Platinum foils were roughened to various degrees with regular arrays of laser milled pits. Conducting diamond films were grown on the foils by microwave plasma chemical vapor deposition. The adhesion strength of the films to the platinum was assessed by prolonged sonication and accelerated aging. Electrochemical properties were evaluated and compared to previous work. Main results In line with previous results, diamond coatings increased the charge injection capacity of the platinum foil by more than 300% after functionalization within an oxygen plasma. Roughening of the underlying platinum substrate by laser milling was required to generate strong adhesion between the diamond and the Pt foil. Electrical stress testing, near the limits of safe operation, showed that the diamond films were more electrochemically stable than platinum controls. Significance The article describes a new method to protect platinum electrodes from degradation in vivo. A 300% increase in charge injection means that device designers can safely employ diamond coated platinum stimulation electrodes at much smaller sizes and greater density than is possible for platinum. .
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    Impedance changes in chronically implanted and stimulated cochlear implant electrodes.
    (WS Maney & Son, 2014) Newbold, Carrie; Mergen, Silvana; Richardson, Rachael; Seligman, Peter; Millard, Rodney; Cowan, Robert; Shepherd, Robert
    OBJECTIVES: Electrode impedance increases following implantation and undergoes transitory reduction with onset of electrical stimulation. The studies in this paper measured the changes in access resistance and polarization impedance in vivo before and following electrical stimulation, and recorded the time course of these changes. DESIGN: Impedance measures recorded in (a) four cats following 6 months of cochlear implant use, and (b) three cochlear implant recipients with 1.5-5 years cochlear implant experience. RESULTS: Both the experimental and clinical data exhibited a reduction in electrode impedance, 20 and 5% respectively, within 15-30 minutes of stimulation onset. The majority of these changes occurred through reduction in polarization impedance. Cessation of stimulation was followed by an equivalent rise in impedance measures within 6-12 hours. CONCLUSIONS: Stimulus-induced reductions in impedance exhibit a rapid onset and are evident in both chronic in vivo models tested, even several years after implantation. Given the impedance changes were dominated by the polarization component, these findings suggest that the electrical stimulation altered the electrode surface rather than the bulk tissue and fluid in the cochlea.
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    Laminin coated diamond electrodes for neural stimulation
    (Elsevier B.V., 2020-09) Sikder, Md..Kabir Uddin; Tong, Wei; Pingle, Hitesh; Kingshott, Peter; Needham, Karina; Shivdasani, Mohit; Fallon, James; Seligman, Peter; Ibbotson, Michael; Prawer, Steven; Garrett, David
    The performance of many implantable neural stimulation devices is degraded due to the loss of neurons around the electrodes by the body's natural biological responses to a foreign material. Coating of electrodes with biomolecules such as extracellular matrix proteins is one potential route to suppress the adverse responses that lead to loss of implant functionality. Concurrently, however, the electrochemical performance of the stimulating electrode must remain optimal to continue to safely provide sufficient charge for neural stimulation. We have previously found that oxygen plasma treated nitrogen included ultrananocrystalline diamond coated platinum electrodes exhibit superior charge injection capacity and electrochemical stability for neural stimulation (Sikder et al., 2019). To fabricate bioactive diamond electrodes, in this work, laminin, an extracellular matrix protein known to be involved in inter-neuron adhesion and recognition, was used as an example biomolecule. Here, laminin was covalently coupled to diamond electrodes. Electrochemical analysis found that the covalently coupled films were robust and resulted in minimal change to the charge injection capacity of diamond electrodes. The successful binding of laminin and its biological activity was further confirmed using primary rat cortical neuron cultures, and the coated electrodes showed enhanced cell attachment densities and neurite outgrowth. The method proposed in this work is versatile and adaptable to many other biomolecules for producing bioactive diamond electrodes, which are expected to show reduced the inflammatory responses in vivo.
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    Wireless induction coils embedded in diamond for power transfer in medical implants
    (Springer, 2017-08) Sikder, Kabir; Fallon, James; Shivdasani, Mohit; Ganesan, Kumaravelu; Seligman, Peter; Garrett, David
    Wireless power and data transfer to medical implants is a research area where improvements in current state-of-the-art technologies are needed owing to the continuing efforts for miniaturization. At present, lithographical patterning of evaporated metals is widely used for miniature coil fabrication. This method produces coils that are limited to low micron or nanometer thicknesses leading to high impedance values and thus limiting their potential quality. In the present work we describe a novel technique, whereby 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 transferring up to 10 mW of power up to a distance of 6 mm. As a substitute for a metallic braze line used for hermetic sealing, a continuous metal loop when placed parallel and close to the coil surface reduced power transfer efficiency by 43%, but not significantly, when placed perpendicular to the microcoil surface. Encapsulation of the coil by growth of a further layer of diamond reduced the quality factor by an average of 38%, which can be largely avoided by prior oxygen plasma treatment. Furthermore, an accelerated ageing test after encapsulation showed that these coils are long lasting. Our results thus collectively highlight the feasibility of fabricating a high-cross section, biocompatible and long lasting miniaturized microcoil that could be used in either a neural recording or neuromuscular stimulation device.