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Development of a High Density Percutaneous Connector System

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Principal Investigator Affiliation Contract Number Link
Lou Rucker, Ph.D. Bioelectric Corp. N01-DC7-2301

Project Title: The Development of a High Density Percutaneous Connector System, May 1996

STATEMENT OF WORK

1. Background

A need exists for a reliable and effective high-contact-density percutaneous connector system for transferring multichannel signals and power through the skin. This system will initially be used in animal experiments related to the development of auditory prostheses, but the ultimate goal is to develop a new percutaneous connector system that can be utilized in auditory prostheses which are implanted in the human cochlea and in the human cochlear nucleus. Such a percutaneous connector system should permit direct connections between signal processors located outside the body and electrode arrays implanted in close proximity to sensory neurons.

The percutaneous connector system will consist of a pedestal firmly attached to the skull (preferably by osseointegration) and a replaceable electrical connector with at least 70 separate contacts. The system must be of low physical profile and made of durable materials to reduce the possibility of it being mechanically damaged during activities of everyday living. It must utilize biocompatible materials in the parts that directly contact tissue and must be designed to minimize the likelihood of infection and chronic drainage due to invasion of microorganisms and/or a poor seal between the device and the skin. Non-human animal experiments will be required to demonstrate the above mentioned properties as well as mechanical stability of the system and electrical isolation of the connector contacts for a period of at least six months. However,the design must be such that the system should retain these properties for the lifetime of the recipient.

Research on auditory prostheses for deaf individuals is supported by the National Institute on Deafness and Other Communication Disorders (NIDCD). This request for proposals represents a competitive renewal of an ongoing research and development project and will be administered by the Neural Prosthesis Program (NPP).

A high density percutaneous connector allows the flexibility of direct connections to implanted electrodes in auditory prostheses without the bandwidth and signal parameter limitations of a transcutaneous transmission system.

A number of percutaneous connectors have been developed in the past but none meets the needs of present auditory prosthesis investigators. This need is for a low profile connector system that features high density contacts with essentially zero disconnect force in a biocompatible package that osseointegrates with the bone of the skull.

Progress in the first two years of the ongoing three year contract has included the design and fabrication of a prototype percutaneous connector and initial animal testing. The use of Bioglass as an interface between the titanium shell of the connector and the bone has been abandoned because of poor osseointegration. A more promising method of achieving osseointegration appears to be the use of miniature titanium beads sintered to the bottom of the titanium connector shell. New bone has been demonstrated growing into the interstices of the beads and attaching directly to the titanium.

It will be permissible for an offeror to subcontract portions of this research such as the animal implantation and histopathological examination of tissue.

Copies of progress reports from the first two years of the ongoing contract and a copy of a bibliography of publications from NPP studies are available on the internet at:

www.ninds.nih.gov/npp

2. Objectives

This competitive renewal will permit the completion of the in-vitro and animal testing of the prototype connector system. It will also include the redesign and fabrication of a high density percutaneous connector system suitable for human implantation.

3. Work to be Performed

Independently and not as an agent of the Government, the contractor shall furnish all the necessary services, qualified personnel, material, equipment and facilities, not otherwise provided by the Government as needed to perform the statement of work. The contractor shall design, develop, fabricate and evaluate in animals a percutaneous connector system suitable for humans for transferring electrical signals directly through the skin. Specifically the Contractor shall:

A. Design and fabricate a pedestal to attach to the skull in a mechanically stable manner preferably by osseointegration.

1. The pedestal shall be designed to accept a replaceable connector assembly.

2. All materials in the pedestal that contact tissues must be biocompatible.

3. The pedestal must have a low profile to minimize the likelihood of physical trauma to the pedestal and its mating connector assembly during activities of everyday living.

B. Design and fabricate or procure a connector assembly consisting of an implantable component with attached flexible leads and a mating detachable component.

1. The high-contact-density miniature connector will have at least 70 contacts.

2. The electrical isolation between the contacts shall be designed to withstand at least 18 volts without electrical breakdown between the contacts themselves or between the contacts and the body tissues.

3. The connector contacts when mated with the contacts in the plug assembly shall be capable of passing up to 20 ma. with less than a 1.0 v. drop across the connection.

4. The implantable part of the connector assembly must be capable of being easily attached to the pedestal and of being replaced without replacing the pedestal.

5. Select materials for the leads and assemble them into a flattened, flexible cable segment to accommodate subcutaneous implantation. Materials that will be in direct contact with tissue must be biocompatible.

6. The attached leads should exit from only one side of the pedestal.

7. The length of the leads and the method of terminating them (e.g., on electrodes furnished by the Project Officer) will be determined after the start of the contract in consultation with the Project Officer.

8. The mating detachable component will also be furnished with flexible leads and appropriate stain relief. The length and termination of these leads will also be determined after the start of the contract in consultation with the Project Officer.

9. A positive latch coupling mechanism must be included to allow easy mating between the detachable and implanted components. Consideration should be given to designing this coupling mechanism with a "break away" feature to allow release of the components without damage if the external leads become snagged or the connector is bumped.

C. In the design of the percutaneous connector system consideration must be given to:

1. Using materials that are durable and can withstand the physical abuse that might be expected from activities of daily living.

2. Providing for an interface between the skin and the device that prevents the passage of microorganisms into the body and prevents fluid drainage out of the body.

3. Encouraging epithelial attachment to the connector and discouraging epithelial downgrowth around the implant. 4. Keeping the total height above the skin of the assembled pedestal and connectors as low as possible and in no case greater than 10 mm.

D. Before the end of the first year of the contract, supply the Project Officer with 10 pedestals and connector assemblies suitable for animal testing. A mating 70 contact plug and lead assembly must be furnished with each percutaneous connector system.

E. Select an animal model for testing the percutaneous connector system.

1. The bone of the skull of the animal on which the pedestal is to be mounted should have physical characteristics similar to the diploic portions of the human skull bone.

2. The skin of the animal model must have healing characteristics after being incised similar to human scalp so as to produce attachments to the connector assembly and/or pedestal and adjacent tissue which simulates human implantation.

F. Implant 8 pedestal and the connector assemblies (from the 10 supplied to the Project Officer) on the skulls of 8 of the selected animals, for a period of six months.

1. At least 5 pairs of the connector assembly contacts should have insulated wires connected between them as 5 separate loops of at least 2 inches in length. These loops should be implanted in the subcutaneous space of the scalp.

2. Maintain an 18 volt bias on each of the loops relative to a platinum wire implanted in the subcutaneous space of the scalp and connected to one of the unused contacts.

a. Periodically disconnect the bias and monitor the leakage current between separate loops and the leakage current between the loops and the bare platinum conductor.

b. Periodically check the continuity of the 5 lead wires through the connector contacts.

3. If more than 10 nanoamperes of current is detected in any of the above leakage tests, determine the source of leakage, correct it, and reimplant the connector assembly, if necessary.

G. Following six months of implantation, remove the implants and conduct gross and microscopic examinations of:

1. The attachment of the pedestal to the skull.

2. The attachment of the skin and other soft tissues at the edge of the percutaneous connector.

3. The reaction of the adjacent tissue to the implanted device.

4. The connector contacts for evidence of corrosion.

H. Following the examinations of the retrieved implants, redesign the connector system, if necessary, to be suitable for human implantation. Supply the Project Officer with 5 of the redesigned pedestals and connector assemblies, or of the previous design if redesign is unnecessary, for use in human implants.

Last updated November 24, 2008