title: Hermetic diamond capsules for biomedical implants enabled by gold active braze alloys.
abstract: As the field of biomedical implants matures the functionality of implants is rapidly increasing. In the field of neural prostheses this is particularly apparent as researchers strive to build devices that interact with highly complex neural systems such as vision, hearing, touch and movement. A retinal implant, for example, is a highly complex device and the surgery, training and rehabilitation requirements involved in deploying such devices are extensive. Ideally, such devices will be implanted only once and will continue to function effectively for the lifetime of the patient. The first and most pivotal factor that determines device longevity is the encapsulation that separates the sensitive electronics of the device from the biological environment. This paper describes the realisation of a free standing device encapsulation made from diamond, the most impervious, long lasting and biochemically inert material known. A process of laser micro-machining and brazing is described detailing the fabrication of hermetic electrical feedthroughs and laser weldable seams using a 96.4% gold active braze alloy, another material renowned for biochemical longevity. Accelerated ageing of the braze alloy, feedthroughs and hermetic capsules yielded no evidence of corrosion and no loss of hermeticity. Samples of the gold braze implanted for 15 weeks, in vivo, caused minimal histopathological reaction and results were comparable to those obtained from medical grade silicone controls. The work described represents a first account of a free standing, fully functional hermetic diamond encapsulation for biomedical implants, enabled by gold active alloy brazing and laser micro-machining.
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Samantha G
authors.initials: SG
authors.lastname: Lichter
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Mathilde C
authors.initials: MC
authors.lastname: Escudié
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Alastair D
authors.initials: AD
authors.lastname: Stacey
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Kumaravelu
authors.initials: K
authors.lastname: Ganesan
authors.affiliation: School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Victoria 3001, Australia.
authors.forename: Kate
authors.initials: K
authors.lastname: Fox
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Arman
authors.initials: A
authors.lastname: Ahnood
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Nicholas V
authors.initials: NV
authors.lastname: Apollo
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia; Department of Materials Engineering, Faculty of Engineering, Monash University, Victoria 3800, Australia.
authors.forename: Dunstan C
authors.initials: DC
authors.lastname: Kua
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia; Department of Materials Engineering, Faculty of Engineering, Monash University, Victoria 3800, Australia.
authors.forename: Aaron Z
authors.initials: AZ
authors.lastname: Lee
authors.affiliation: The Bionics Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia.
authors.forename: Ceara
authors.initials: C
authors.lastname: McGowan
authors.affiliation: The Bionics Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia.
authors.forename: Alexia L
authors.initials: AL
authors.lastname: Saunders
authors.affiliation: The Bionics Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia.
authors.forename: Owen
authors.initials: O
authors.lastname: Burns
authors.affiliation: The Bionics Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia; Department of Pathology, The University of Melbourne, Victoria 3010, Australia.
authors.forename: David A X
authors.initials: DA
authors.lastname: Nayagam
authors.affiliation: National Vision Research Institute, Department of Optometry and Vision Sciences, University of Melbourne, Victoria 3010, Australia; Department of Anatomical Pathology, St Vincent's Hospital, Fitzroy, Victoria 3065, Australia.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Williams
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia; The Bionics Institute, 384-388 Albert Street, East Melbourne, Victoria 3002, Australia. Electronic address: dgarrett@unimelb.edu.au.
authors.forename: David J
authors.initials: DJ
authors.lastname: Garrett
authors.affiliation: National Vision Research Institute, Department of Optometry and Vision Sciences, University of Melbourne, Victoria 3010, Australia.
authors.forename: Hamish
authors.initials: H
authors.lastname: Meffin
authors.affiliation: School of Physics, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Steven
authors.initials: S
authors.lastname: Prawer
mesh_terms: D000497:Alloys; D000818:Animals; D001672:Biocompatible Materials; D018130:Diamond; D006046:Gold; D006168:Guinea Pigs; D058117:Neural Prostheses; D015035:Zinc Oxide-Eugenol Cement
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; C510255:Hermetic; D015035:Zinc Oxide-Eugenol Cement; D006046:Gold; D018130:Diamond
keywords: Biocompatibility; Diamond; Gold; Hermetic encapsulation; Neuroprosthesis; Retinal prosthesis