Wireless High-Bandwidth Trans-cutaneous Signal Transmission
Lead Research Organisation:
Newcastle University
Department Name: Institute of Neuroscience
Abstract
Many experiments on animals record a signal from inside the body: examples might be blood pressure and heart rate, or the electrical activity of muscles or the brain. In order to analyse these signals, they must be transferred to a system outside the body. This is often done using a connector implanted surgically on the skin. The experimenter plugs a recording device in to this connector to make measurements. Unfortunately, this approach can be problematic.
The skin is a natural barrier to infection. Normally, if we sustain a minor injury, the wound heals rapidly. The body mounts an immediate immune response, and counteracts any infection which might have entered during the short time that the wound remained open. However, if a wire and connector is permanently implanted onto an animal?s skin, it creates a breach of this natural barrier. It is very difficult to prevent infections in such a case. These infections can pose a significant welfare problem to the animal. An infected animal may give reduced data, or even in extreme cases invalid data, so infections also impair the conduct of the experiment. Finally, sometimes very severe infections may require the animal to be humanely killed, terminating an otherwise productive experiment, and requiring another animal to be used to obtain the results.
In a previous project funded by NC3Rs, we designed a novel radio-based system to transmit signals wirelessly through the skin; it was also wirelessly powered. Although telemetry systems have been developed previously, our system took such technology to new limits. It has 16 channels; current systems have only 2-3. It faithfully transmits rapidly changing signals: existing telemeters work only with slowly varying waveforms. Finally, wireless powering avoids the need for frequent battery changes, allowing a long implant life without further surgery. The system was successfully implanted in a monkey, and remained infection free. It powered up on demand, and transmitted data. However, a problem with the initial signal amplifier stage prevented it from being practically useful.
In this proposal, we will develop the system further to solve the problem with the amplifier. We will then test it in a monkey, as part of experiments carried out in the principal applicant?s laboratory. This will be an immediate refinement of technique for the principal applicant. We will then commercialise the system so that it can be used by other laboratories, in a wide range of applications and species.
The skin is a natural barrier to infection. Normally, if we sustain a minor injury, the wound heals rapidly. The body mounts an immediate immune response, and counteracts any infection which might have entered during the short time that the wound remained open. However, if a wire and connector is permanently implanted onto an animal?s skin, it creates a breach of this natural barrier. It is very difficult to prevent infections in such a case. These infections can pose a significant welfare problem to the animal. An infected animal may give reduced data, or even in extreme cases invalid data, so infections also impair the conduct of the experiment. Finally, sometimes very severe infections may require the animal to be humanely killed, terminating an otherwise productive experiment, and requiring another animal to be used to obtain the results.
In a previous project funded by NC3Rs, we designed a novel radio-based system to transmit signals wirelessly through the skin; it was also wirelessly powered. Although telemetry systems have been developed previously, our system took such technology to new limits. It has 16 channels; current systems have only 2-3. It faithfully transmits rapidly changing signals: existing telemeters work only with slowly varying waveforms. Finally, wireless powering avoids the need for frequent battery changes, allowing a long implant life without further surgery. The system was successfully implanted in a monkey, and remained infection free. It powered up on demand, and transmitted data. However, a problem with the initial signal amplifier stage prevented it from being practically useful.
In this proposal, we will develop the system further to solve the problem with the amplifier. We will then test it in a monkey, as part of experiments carried out in the principal applicant?s laboratory. This will be an immediate refinement of technique for the principal applicant. We will then commercialise the system so that it can be used by other laboratories, in a wide range of applications and species.
Technical Summary
Our current neurophysiological experiments in behaving monkeys implant electrodes to record electromyogram (EMG) from the arm and hand. Wires from these electrodes pass sub-cutaneously to a connector on the head. The electrodes yield stable, high quality recordings. However, the permanently open wound around the connector often becomes infected, impairing the welfare of the animal and reducing data quality.
In work carried out under a previous award from NC3Rs, we developed a novel implantable electronic device. This amplifies and digitises 16 channels of EMG recording (5 kSamples/s/channel), and transmits the data through the skin by radio. Power is supplied by inductive coupling to an implanted coil antenna, obviating the need for an implanted battery. The system is wholly internal - the skin is closed over the device after implant, which avoids breaching the skin?s natural barrier to infection. We tested this system in a macaque monkey. The device integrated well with the tissue, and after 3 months there was no sign of infection or tissue rejection. It powered up, and successfully transmitted data. However, a problem with the function of the front-end amplifier prevented the signals from being of practical use. Thus although we had solved major engineering challenges of high bandwidth radio transmission, inductive powering, and biocompatible and stable encapsulation and insulation of a complex circuit, the device had to be explanted.
In this award, we seek to capitalise on the achievements of the previous award to produce a fully functional telemeter. The circuit will be redesigned using a newly developed amplifier, better suited to EMG. We will implant the device into a macaque monkey as part of our ongoing experiments in movement control, providing in vivo performance data.
We consider that repeated infections associated with the transcutaneous connector currently represent the major welfare cost to monkeys both in our experiments and those of similar groups around the world. Eliminating these infections would be a considerable refinement of technique. In addition, such infections can reduce the quality of behavioural data which is obtained, due to the clinical malaise suffered by the animal. This limits the science which can be achieved (i.e. new knowledge discovered) per animal used. Finally, severe infections may cause an experiment to be terminated prematurely, before sufficient data has been gathered. This would require the use of a further animal to complete the project. The proposed solution can therefore also achieve a reduction in animal numbers.
In work carried out under a previous award from NC3Rs, we developed a novel implantable electronic device. This amplifies and digitises 16 channels of EMG recording (5 kSamples/s/channel), and transmits the data through the skin by radio. Power is supplied by inductive coupling to an implanted coil antenna, obviating the need for an implanted battery. The system is wholly internal - the skin is closed over the device after implant, which avoids breaching the skin?s natural barrier to infection. We tested this system in a macaque monkey. The device integrated well with the tissue, and after 3 months there was no sign of infection or tissue rejection. It powered up, and successfully transmitted data. However, a problem with the function of the front-end amplifier prevented the signals from being of practical use. Thus although we had solved major engineering challenges of high bandwidth radio transmission, inductive powering, and biocompatible and stable encapsulation and insulation of a complex circuit, the device had to be explanted.
In this award, we seek to capitalise on the achievements of the previous award to produce a fully functional telemeter. The circuit will be redesigned using a newly developed amplifier, better suited to EMG. We will implant the device into a macaque monkey as part of our ongoing experiments in movement control, providing in vivo performance data.
We consider that repeated infections associated with the transcutaneous connector currently represent the major welfare cost to monkeys both in our experiments and those of similar groups around the world. Eliminating these infections would be a considerable refinement of technique. In addition, such infections can reduce the quality of behavioural data which is obtained, due to the clinical malaise suffered by the animal. This limits the science which can be achieved (i.e. new knowledge discovered) per animal used. Finally, severe infections may cause an experiment to be terminated prematurely, before sufficient data has been gathered. This would require the use of a further animal to complete the project. The proposed solution can therefore also achieve a reduction in animal numbers.