An in vivo Biocompatibility Assessment of MEMS Materials for Spinal Fusion Monitoring

The site-specific biocompatibility of silicon chips and commercially available silicon pressure sensor die were evaluated after implantation in caprine (goat) spine. Surgical procedures were developed to insert silicon chips into the nucleus pulposus regions of the lumbar discs and pressure sensors into autologous bone grafts for cervical spine fusion. After a six-month implantation period, the animal was sacrificed and the spinal segments were meticulously harvested and analyzed for local tissue response via gross examination and histological techniques. Gross examination of cervical and lumbar spinal segments after harvest and dissection did not reveal any visible signs of adverse reactions to the MEMS materials. Furthermore, the surrounding tissues and musculature for both spinal regions were devoid of necrosis. Histological analysis of compromised spinal segments did not reveal evidence of any adverse foreign body response by the caprine spinal tissue to the implanted MEMS materials. These preliminary results support the further development of a spinal fusion monitoring system based on implantable MEMS sensors.