Without Scar Tissue, Medicine Flows Freely

Our immune system has an arsenal of tools to fight off illness-causing foreign bodies. But sometimes those biological tools don’t work in our favor, particularly when it comes to implantable drug devices that keep medication flowing on a strict schedule.

Scar tissue soon builds up around the small instrument because our body recognizes it as an invader that must be protected against. The problem is, the layer of scar tissue traps the medication and keeps it from flowing to where it’s needed. This is particularly a problem when the medication needs to be continually adjusted, as with insulin.

Now, engineers at the Massachusetts Institute of Technology and Washington University in Saint Louis said they’ve created a device that solves that problem. The device, based on the principle of soft robotics, could help many patients, particularly those with Type 1 diabetes who would no longer need to either inject themselves with insulin or receive it through an intravenous (IV) tube.

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The device, which they call STAR, or soft transport augmenting reservoir, can circulate medicine for two months, much longer than for other implantable devices, they said.

The soft robotic device consists of two chambers. The first chamber carries the drug, while the second is an inflatable reservoir controlled from outside the body. In studies, the researchers steadily inflated and deflated the second chamber for five minutes every 12 hours, which kept scar tissue from the device while preserving long-term, rapid drug delivery, said Ellen Roche, an MIT associate professor of mechanical engineering who worked on the project.

The STAR worked for about two months with no buildup of scar tissue, she added.

The actuation-mediated rapid release allows patients to fine-tune the amount of insulin they receive, Roche said.

“We’re using this type of motion to extend the lifetime and the efficacy of implanted reservoirs that can deliver drugs like insulin,” Roche said. “We think this platform can be extended beyond this application.”

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Most patients with Type 1 diabetes inject themselves with insulin daily, often two times a day. Some patients need four daily shots. They often have difficulty timing the insulin shots to the required dose. And the repeated injections cause to sore spots in the body, Roche said.

To address these issues, researchers have long tried to develop an implantable device that could automatically secrete insulin into the blood when the body needs it. But most insulin-releasing implants quit working within weeks or months due to the scar tissue that eventually encapsulates the device, she added.

Conventional strategies had focused on changing the attributes of the device itself, including its size and shape or on transmitting steroids along with the medication in order to keep scar tissue from forming. But they haven’t succeeded in keeping scar tissue at bay and steroids can cause toxicity of the liver, kidney, heart, and other organs, she added.

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While STAR was able to resist scar formation, it wasn’t able to prevent it completely. Still, the researchers found that scars around STAR were different. Instead of a messy tangle, collagen fibers were more neatly aligned—a feature that the team hypothesized would help drugs seep through better.

The researchers will now study other medications that can be used with STAR, focusing first on the ones that need to be adjusted daily, or “tunable,” in physician speak.

Among other possible applications, the researchers now plan to see if they can use the device to deliver pancreatic islet cells that could act as a “bio-artificial pancreas” to help treat diabetes, Roche said.

Jean Thilmany is a science and technology writer in Saint Paul, Minn.