An Updated Telemetry System for Reliable Powering In Vivo Coupled to a Tablet Computer

Abstract

Accurate and reliable in vivo measurement systems for orthopedic applications will allow a better understanding of native joint loading, gait patterns, and changes during healing and tissue regeneration. Robust and reliable telemetry units with an implantable transmitter and data acquisition software are necessary to insure long-term measurements. It was the goal of this study to update the current implantable telemetry system. Updates included using a new tablet computer for increased rates of data acquisition and encasing transmitters in a new waterproof casing. Software was developed using Labview on a Windows based Acer Iconia Tab. The Labview program allowed the user to save data to a measurement file and view the data in real time. The increased processing power of the tablet resulted in an increase in data collection rates from 29Hz to 87Hz. Interfacing the tablet computer with the telemetry system required the use of a RS-232 protocol to USB adapter. The newly developed tablet computer system was also used for load measurement collection during the most recent in vivo study. In order to insure transmitter function in vivo it was necessary to characterize the factors affecting transmission in vivo and develop transmitter and power coil designs that operated reliably. In the past implantable transmitters were noted to operate properly during bench top testing, but often failed after being placed in vivo. The two factors studied that limited power transfer to the transmitters were immersion in an aqueous environment and exposure to elevated temperatures. An aqueous environment significantly decreased power transfer by 11.9% (p-value = 0.014) relative to testing on the bench top. Additionally, a temperature increase to 40°C decreased power transfer by 6.2% (p-value = 0.017) when compared to power transfer in room temperature air. A solution that restored transmitter function required encasing transmitters in a new waterproof casing. Different casing designs made of silicone and semi-solid triglycerides were developed and tested on the bench top. Two different casing designs were used during in vivo testing and implanted into test animals. One casing design insured transmission while the other separated in vivo and did not facilitate transmission.