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Delivering Drugs with MEMS

An MIT spinoff is finally ready to begin testing smart implants for drug delivery and sensing.

After nearly a decade of working on microelectromechanical systems (MEMS) for medical implants, a startup based in Bedford, MA, called MicroChips has prototypes for its first commercial products. By the beginning of January, the company plans to start animal trials of a device for healing bones damaged by osteoporosis. In a year and a half, it hopes to begin human trials on an implant for monitoring glucose levels in diabetics.

Healing holes: These millimeter-sized reservoirs, carved from silicon, can be used to store drugs in new implantable devices for smart drug delivery. Tiny channels sealed by microscale caps (not shown) allow the drugs to escape.

The first product, a device for delivering an anti-osteoporosis drug automatically, could allow patients to replace 500 daily injections with a single outpatient implant procedure. The glucose sensor, by continuously monitoring glucose levels, could reveal spikes in blood-sugar levels that go undetected using conventional sensors. Such spikes, if not treated, can contribute to organ damage, including blindness.

While a graduate student at MIT in the mid 1990s, John Santini, now MicroChips’ CEO, began to build devices that could release chemicals from any of dozens of reservoirs carved out of silicon and glass using conventional lithography techniques. (See “TR 35, John Santini” and “Implantable Medication.”) But transforming this technology into a commercially viable product has proved to be a long process.

Santini and his team at MicroChips faced a number of hurdles. For example, to protect the drugs and sensors until they were released or exposed, it was necessary to hermetically seal all of the electronics, including radios for controlling the device, along with the MEMS reservoirs and caps. The trick was that conventional welding required temperatures that would damage the enzymes and peptides that were to be stored in the wells. So the company developed a cold-compression technique that forms an unbreakable bond.

The remaining challenges had to do with finding particular applications that needed the MEMS array technologies. The company discovered that its technology could provide an answer to a “vexing problem” that had stymied researchers at Medtronic, a multibillion-dollar implant manufacturer, for years, says Stephen Oesterle, Medtronic’s senior vice president for technology and a MicroChips board member. A sensor that monitored glucose continuously hadn’t been possible, he says, because sensors degrade over time, lasting for at most a month. With the MEMS technology, however, it became possible to implant an array of sensors, activating just one at a time. The sensor is read by onboard electronics, with the data transmitted via radio to an external monitor.

In the case of osteoporosis treatment, the technology offered a way to deliver a medicine that normally requires daily injections. Parathyroid hormone is the only osteoporosis drug approved that can help the body to repair damage caused by osteoporosis, rather than just stop the damage, Santini says. The problem is that the drug cannot be delivered gradually, in a conventional control-release delivery system. That’s because if it remains in the body continuously, it will promote the degradation of bone, making things worse rather than better. As a result, the drug had to be administered via daily injections. MicroChips technology offered a way to deliver quick bursts of the drug automatically. The chip can be programmed to release the drug at regular intervals. It can also be controlled via radio signals.

These two applications are only the beginning of potential uses for the technology. It could be used with a number of different sensors, providing early warning of heart attacks and strokes. It could also be used to deliver multiple drugs in response to signals from integrated sensors. For diabetes, the glucose sensor could be paired with insulin pumps. Such a system, Oesterle says, would more closely mimic the body’s mechanisms for regulating blood sugar.

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