11/18/15 Thinking back to the late 1960s when scientific researchers were envisioning using a tube made out of metal (stent) to open up an artery, they would never have imagined we are on the verge of stents that dissolve in the body over time!
For decades metal has been the main source used in stents. But recently dissolvable versions reached an important milestone, with the release of clinical trial data in The New England Journal of Medicine showing a degradable device that performed as well as its traditional counterpart. In theory, dissolvable implants reduce the risk of inflammation, blood clots and other side effects. The report not only represents the likely future of stents but also a highly visible advance from the emerging field of biodegradable technologies. Todays researchers in the field envision the day when most medical hardware implanted into the body will last only as long as it is needed.
This concept has been rolling around in research institutes since the 1970s, when synthetic dissolvable stitches were beginning to be used. But recent progress has been plodding, partly because the materials in degradable devices have to satisfy a long list of criteria, including strength, durability, safety and even the ability to show up on an x-ray.
Today, researchers have been increasingly able to manipulate degradable substances to perform specific functions, such as delivering drugs, aiding organ function and performing other tasks. Like a sugar cube, these materials gradually disintegrate in liquid, usually into components that the body can break down and excrete.
The problem with most current medical implants is that “there is no material that can be placed in the body without an immunological response over time, with very few exceptions,” says Joachim Kohn of Rutgers University, with complications like inflammation and pain. Given enough time all joint replacements eventually fail, according to doctors writing in the May 2014 issue of Mediators of Inflammation. Or consider the track record of a surgical mesh used after incontinence surgery in women, in which the U.S. Food and Drug Administration recently warned that complications and failures are “not rare.” With approximately half a million people receiving implants each year in the U.S., stents have long been attractive for developers of degradable technology. The device’s purpose is to support a vessel as it recovers from angioplasty, which uses a small balloon at the end of a catheter to widen a narrowed artery. Modern stents are coated with drugs that help prevent scar tissue from forming and plaque from reestablishing itself. Within a year the vessel is fully restored but the implants are not removed. That means the artery can never return to its original flexibility. Long-term risks, like the return of blockage, are small but real.
More than a dozen companies have degradable stents in development. Manufacturers tend to stick to materials that are already used in medicine or known to be metabolized by the body. Approval of an entirely new polymer would add to the time and expense of development. Companies are developing stents using iron and manganese, common nutrients that the body can easily break down. And other companies are working with stents made from poly(L-lactic acid), or PLLA, a lactic acid chain that is commonly used in medicine. Once the entire drug is delivered, and the vessel has healed, the degradable stent gradually vanishes over the first few years.
In practice, it sounds like a win, but some in the field remain cautious. In an editorial published with the NEJM study, Robert Byrne, a physician at the German Heart Center in Munich, was particularly uncomfortable with a short-term higher rate of clot formation among those with the dissolvable stent. The study’s authors say the difference (1.5 versus 0.7 percent) was not statistically significant but Bryne wrote that a doubling of risk would give many doctors pause. “Although the concept of self-degrading stents is intuitively attractive, promise alone is not enough to make us unconditionally embrace this technology,” he wrote in the journal.
A host of other researchers are using biodegradable substances for other types of innovative drug delivery—as a means to get drugs to exactly where they are needed, just at the time they are needed. A research lab has developed a drug-coated mesh that is used after hernia operations. Traditionally, surgeons insert a lattice to support the abdomen during healing, it contains an antibiotic that seeps into the incision as it heals. A similar product that encases pacemakers and other small cardiac devices has dramatically reduced infection rates in clinical trials.
The researchers envision other uses for degradable meshes. The number of knee replacement operations have soared, often because the cartilage has become worn or damaged beyond repair. Doctors are experimenting with ways to grow new cartilage cells in the laboratory and insert them into the joint using a degradable scaffold. This scaffold would help the body repair itself, lessening the need for knee replacement.
The future of dissolvable medical devices is here and we are proud to be an integral part of it!