Current Issues and Future Possibilities for Biomedical Sensors

Abstract

Sensors and instrumentation were one of the original areas of biomedical engineering when it started to emerge as a new field back in the 1960’s, and this area is still an important aspect of the discipline today. Many facets of this subarea of our field have not changed much over the last half-century while others have evolved considerably due to technological advances. Although many of the problems limiting the application of sensors and instruments to biomedical measurements have been addressed, others remain as challenging today as they were years ago. These include: (1) developing stable, reproducible instrumentation; (2) minimizing biological interaction with the sensor; (3) packaging the sensor and instrumentation to withstand the hostile biological environment; (4) powering implantable devices; (5) creating and producing devices that are practical for developing countries; (6) economic production of single-use instrumentation for ambulatory or at home use; (6) communicating effectively between devices and other devices, medical records, medical institutions and clinical staff, and finally (7) creating instrumentation that impacts health care. These issues have been and are being addressed by many industry, university and government researchers around the world, and our department at Michigan Technological University is no exception. Some of our past and on-going work to address these issues and that of others will be described.

The development of stable, reproducible sensors to interface with biologic tissue, especially when implanted, remains a major challenge. Biologic tissue is designed to search and destroy foreign material in its midst, and this foreign body response can greatly affect the behavior of implanted sensors. As the body fights off the foreign invader, it creates a local environment that can be quite different from what the sensor set out to measure. Thus approaches to minimize this interaction are needed. One such approach is to counter the biologic response processes by using packaging materials for implants that release or produce substances that minimize inflammation. Another approach is to make devices so small as to not be recognized by tissue and, therefore, not elicit the foreign body response. Drug-releasing polymers and microneedles for percutaneous drug delivery are examples.

Energy for powering implants remains a problem. Although there have been great strides in battery development in recent years, they still discharge and fail requiring the replacement of internally-powered implants. Alternate energy sources such as harvesting mechanical energy from the body and using super capacitors for storage is an example of how batteries can be eliminated in the future. The use of so-called passive implantable sensors is another example of what can be done by taking energy from external sources. In addition to eliminating the batteries, these techniques allow implantable devices to be small enough to be injectable.

Sensors not only have to gather information, but they must communicate it to appropriate processing or actuator sites. In the past this had to be done with wires or by biotelemetry, but today various wireless protocols and integrated circuit chips are available to do this. Wireless sensor networks can be used on and within the body. An example is a system for detecting falls in elderly subjects. Accelerometers integrated into clothing and communicating with an external controller can be used to alert care-givers or first-responders when serious falls occur.

As one can see, biomedical sensors and their associated instrumentation are still quite active fields in biomedical engineering. New technologic approaches will help to make them more pervasive in health care and society in general. It is important, however, that their applications address important problems in clinical medicine and basic medical science. It is likely that this will remain an active aspect of biomedical engineering and medical physics for years to come.