DOW-UAP-D136 — Biosensors and Biomedical Microsystem Survey

The report surveys biomedical microsystems and forecasts future applications; it is not evidence that every described device was clinically available or validated.

This paper examines some of the most recent advances in the field, as well as the technologies that are likely to appear in the next few years.

BioMEMS spans sensors, actuators, neuroprosthetics, drug delivery, retinal devices, and lab-on-chip systems made at micro- and increasingly nanoscale dimensions.

Their applications include neuroprosthetics, sensors and actuators, and microchemistry systems.

The report says implanted-device development must address biocompatibility, tissue degradation, clinical trials, safety, and FDA requirements.

Devices must be shown to be effective for their intended use, and above all devices must be proved safe.

Implanted micromachines face distinctive reliability problems because motion requires sliding surfaces and power while surgical devices cannot be easily serviced.

Motion within the human body by a device is difficult since it implies sliding surfaces, a need for electrical power, and long term reliability and stability.

Brain-electrode systems can detect motor intent before movement and potentially route those signals through computers to assist paralyzed users.

In a healthy person the in tent to move can be detected by measurement of microvolt signals from the brain cell s about 120 milliseconds before any muscle movement occurs.

The report says no self-contained implantable sensor had achieved successful long-term continuous monitoring despite decades of work.

So far, despite decades of work, no continuous monitoring sensor that is self contained and implantable has been successful for long term usage.

It attributes days-to-weeks implant failures chiefly to sensor chemistry wear and immune-system attack at the interface.

Even our most advanced biosensors fail over a period of days or weeks if continuously exposed to the body environment.

The thermopile glucose-sensor work measured very small temperature changes, requiring differential sensing to reject much larger ambient shifts.

the temperature r ise is very small, on the order of a hundredth of a degree (10 millidegrees).

An Arizona State glucose catheter recorded insulin-related blood-glucose changes in a short pig implant, while the report says implantation success remained limited.

The devi ce was implanted in a pig over a short duration and the decrease in blood glucose concentrations in response to administration of insulin were recorded

The report describes laboratory thought-control demonstrations as feasible but not yet practical because durable, high-channel brain interfaces were unavailable.

Crude forms of these thought-controlled devices have been shown in research laboratories to be feasible, even if they are at present not practical.

It says dense clinical brain-machine interfaces may need hundreds or thousands of simultaneous neurons while risking blood-flow disruption, tissue damage, and material reactions.

clinical applications of such BMis may require t he activities of hundreds or thousands of neurons to be simultaneously sampled.

Retinal prostheses were being designed to evoke patterned light sensations through electrical stimulation, with miniaturization, wireless power, bandwidth, and heat as system constraints.

Bidirectional communication is often needed to provide feedback on device function. Some communication links need a wide bandwidth for real-time data transmission and this is challenging

An ultrasound-powered microstimulator had been implanted in rats and shown effective under varied test conditions, but the report frames human therapeutic uses as potential applications.

This device has been implanted in rats and shown effective in neurostimulation under a wide variety of conditions.

Commercial lab-on-chip systems had become established research tools for automated analysis with smaller samples and lower reagent use.

Automated MEMS- based lab-on-a-chip platforms have become an established system for basic life science research and drug discovery.

NASA-supported microfluidic systems automated sub-milliliter cell culture and monitored fluorescent stress markers, glucose, oxygen, and pH for spaceflight studies.

The device contains thermopneumatic micropumps, microvalves, culture media reservoirs, cell culture chamber, and optical readout systems to detect fluorescent markers

The report describes microcantilevers detecting nanogram-to-picogram mass changes, with smaller beams increasing sensitivity.

small amounts (nanograms to picograms) of adsorbed material can be detected.

A cited microcantilever experiment detected one vaccinia virus particle, while multiplexed antibody sensors still faced shelf-life, specificity, and interference limits.

This cantilever beam was used as a mass detector, with sensitiv ity to a single vaccinia virus particle

The conclusion characterizes BioMEMS and NEMS as a rapidly expanding field with new fabrication methods still being developed.

Advanced fabrication processes are still being discovered to further miniaturize electromechanical systems and to bring us into the realm of nanomechanical systems (NEMS).