6.7.Three-Point Bending Test

Test Description

Glass capsules of the same material and dimensions used in the BION™ encapsulation were prepared by the Bio-Medical Engineering Unit (BMEU) at Queen’s University. These capsules, 11,12 and 15mm in length, were subjected to a three-point bending test, with corresponding support lengths of 7.5, 9 and 12.5 mm.

Test Results

The glass capsules were found to sustain at least 2kg of lateral force in a three-point bending configuration along their long axis. The breaking point increased linearly with decreasing capsule length.

6.8.Impact Testing

Test Description

Test devices were instrumented with strain gauges and subjected to impacts from projectiles of various shapes, weights, and velocities while padded by a typical thickness of muscle (1 cm above, 2 cm below or the reverse) and artificial skin. The impact testing apparatus was built around an Instron Model 1122 Universal Tester. A straight vertical was used as a barrel to guide the impactor or missile in free-falls due to gravity over a target. The target tissue was mounted on a calibrated loadcell. BION™ capsules were positioned within this muscle at two depths and two horizontal locations. Missiles with different weights and impactor sizes were dropped from various heights onto the target tissue. Bending forces from the strain gauges on the capsules were recorded and compared to calibrated bending forces applied in the three-point bending test.

Test Results

Test results suggested that microstimulator failure would be unlikely to occur during any impact in vivo. Although glass is a brittle material, the symmetrical capsule geometry and the soft tissue padding afforded by its intramuscular location make fracture of a BION™ in situ highly unlikely. The recorded forces have been consistently below 20% of the breaking limit even for impacts likely to cause substantial injury (e.g. 25 mm diameter bullet weighing 1 kg dropped from 1.4 m). The highest recorded strain was about 25% of the 2 kg breaking point in the Instron test, with most values well below 10%. The bending forces actually decreased for devices directly under the highest energy impacts, apparently because the muscle tissues surrounding the capsule lost mechanical integrity before they could apply much force to the capsule. It was observed that a great deal of tissue damage occurred in the region of impact that was not associated with the presence of a BION™ capsule. This suggests that tissue damage to the muscle is likely to be of much greater concern than potential damage to the microstimulators.

2.4. Safety and Efficacy in Humans

2.4.1. Electrical Stimulation Using bioNs™ to Treat Shoulder Subluxation Soon After Stroke

6.9.Background

Investigational testing of the BION™ in stroke survivors suffering acute shoulder subluxation began at Queen’s University, Kingston, Ontario, Canada, where the principal investigators, Dr. Loeb and Dr. Richmond, were faculty members until 1999 when they moved to academic appointments at the University of Southern California. Stephen Bagg, M.D. is the physician conducting this trial. Dr. Bagg is an Assistant Professor in the Department of Rehabilitation Medicine and Director of the Stroke Rehabilitation Program at Queen’s University.

Strokes are considered to be the most important cause of adult disability in North America, with 500,000 new cases per year in the U.S. (National Stroke Association) and 45,000 in Canada (Langton Hewer, 1990; Shuaib and Hachinski, 1991). Three-quarters of these patients survive and half of the survivors have substantial muscle weakness after 6 months (Gresham et al., 1979) with little chance of rehabilitation (Anderson, 1990; Bonita and Beaglehole, 1988). The most commonly affected region is the shoulder; 80% of hemiplegic stroke patients suffer from shoulder subluxation and associated chronic pain (Smith et al., 1980).

The mechanical integrity of the human shoulder depends largely on tension in its soft tissue supports including the “rotator cuff” muscles and associated tendons and ligaments. If the muscles are paralyzed, the continuous traction from the weight of the arm stretches these soft tissues resulting in chronic subluxation and pain (Caillet, 1991; Griffin and Reddin, 1981) with progressive loss of the normal range of motion (Andrews and Bohannon, 1989; Joynt, 1992). The key muscles appear to be the deltoid and supraspinatus which are normally tonically active when walking with the arm hanging freely (Rowe, 1988). Exercises to rehabilitate the arm may actually increase shoulder pain if these muscles remain inactive (Kumar et al., 1990). Slings interfere with rehabilitation, provide little relief from pain and may accelerate contracture formation (Hurd et al., 1974).

Transcutaneous electrical stimulation of the supraspinatus and posterior deltoid muscle has been shown to be an effective, if labor intensive, treatment that reduces subluxation and pain and improves range of motion and overall arm function (Faghri et al., 1994). This approach is unlikely to gain widespread use because a therapist is required to position the skin electrodes and adjust the stimulation parameters for each treatment session. As described below, we are implanting two BIONs™ to provide stable and selective stimulation of these muscles, enabling the study participant to self-administer at home one or more exercise programs devised by their therapist.