title: Lifetime assessment of atomic-layer-deposited Al2O3-Parylene C bilayer coating for neural interfaces using accelerated age testing and electrochemical characterization.
abstract: The lifetime and stability of insulation are critical features for the reliable operation of an implantable neural interface device. A critical factor for an implanted insulation's performance is its barrier properties that limit access of biological fluids to the underlying device or metal electrode. Parylene C is a material that has been used in FDA-approved implantable devices. Considered a biocompatible polymer with barrier properties, it has been used as a substrate, insulation or an encapsulation for neural implant technology. Recently, it has been suggested that a bilayer coating of Parylene C on top of atomic-layer-deposited Al2O3 would provide enhanced barrier properties. Here we report a comprehensive study to examine the mean time to failure of Parylene C and Al2O3-Parylene C coated devices using accelerated lifetime testing. Samples were tested at 60°C for up to 3 months while performing electrochemical measurements to characterize the integrity of the insulation. The mean time to failure for Al2O3-Parylene C was 4.6 times longer than Parylene C coated samples. In addition, based on modeling of the data using electrical circuit equivalents, we show here that there are two main modes of failure. Our results suggest that failure of the insulating layer is due to pore formation or blistering as well as thinning of the coating over time. The enhanced barrier properties of the bilayer Al2O3-Parylene C over Parylene C makes it a promising candidate as an encapsulating neural interface.
authors.affiliation: Electrical and Computer Engineering Department, George Mason University, 4400 University Dr. MSN 1G5, Fairfax, VA 22030, USA. Electronic address: sminnika@masonlive.gmu.edu.
authors.forename: Saugandhika
authors.initials: S
authors.lastname: Minnikanti
authors.affiliation: Department of Statistics, George Mason University, 4400 University Dr., Fairfax, VA 22030, USA.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Diao
authors.affiliation: Electrical and Computer Engineering Department, George Mason University, 4400 University Dr. MSN 1G5, Fairfax, VA 22030, USA; Bioengineering Department, George Mason University, 4400 University Dr. MSN 1G5, Fairfax, VA 22030, USA.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Pancrazio
authors.affiliation: Electrical and Computer Engineering, University of Utah, 50 S. Central Campus Dr., Salt Lake City, UT 84112, USA.
authors.forename: Xianzong
authors.initials: X
authors.lastname: Xie
authors.affiliation: Electrical and Computer Engineering, University of Utah, 50 S. Central Campus Dr., Salt Lake City, UT 84112, USA.
authors.forename: Loren
authors.initials: L
authors.lastname: Rieth
authors.affiliation: Electrical and Computer Engineering, University of Utah, 50 S. Central Campus Dr., Salt Lake City, UT 84112, USA.
authors.forename: Florian
authors.initials: F
authors.lastname: Solzbacher
authors.affiliation: Electrical and Computer Engineering Department, George Mason University, 4400 University Dr. MSN 1G5, Fairfax, VA 22030, USA; Bioengineering Department, George Mason University, 4400 University Dr. MSN 1G5, Fairfax, VA 22030, USA. Electronic address: npeixoto@gmu.edu.
authors.forename: Nathalia
authors.initials: N
authors.lastname: Peixoto
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D055119:Elastic Modulus; D004560:Electricity; D055664:Electrochemical Techniques / Q000379:methods*; D004566:Electrodes; D058117:Neural Prostheses; D011108:Polymers / Q000737:chemistry*; D013997:Time Factors; D014992:Xylenes / Q000737:chemistry*
chemical_list: D020099:Coated Materials, Biocompatible; D011108:Polymers; D014992:Xylenes; C011055:parylene; D000537:Aluminum Oxide
keywords: Accelerated lifetime testing; Al(2)O(3); Electrochemical impedance spectroscopy; Interdigitated electrode arrays; Parylene C