Oct 12, 2016 | By Alec

While it may still take a few years before we can 3D print and implant completely new blood vessels, a team of engineers from Northwestern University are using 3D printing to help maintain and support the blood vessels we already have. That is, they have pioneered flexible 3D printed biodegradable stents, which can easily be customized for individual patients and provide life-saving support in the case of weak or clogged up arteries.

This important breakthrough has been realized by a team of researchers from Northwestern University’s Engineering Department, led by Guillermo Ameer and Cheng Sun. Through support from the American Heart Association, they have just published their research in a paper in the Advanced Materials Technologies journal, with postdoc Robert van Lith and graduate student Evan Baker serving as co-first authors.

Guillermo Ameer and Cheng Sun

As they explain in the paper, their 3D printing breakthrough has the potential to fundamentally change the way patients are treated. Currently, artery stents almost completely rely on a one-size-fits-all approach that can cause significant complications. Made from metal and only available in a few sizes, there’s always a danger that stents move into the artery and fail – necessitating an expensive opening surgery or even a bypass with vascular grafts. “Right now, the vast majority of stents are made from a metal and have off-the-shelf availability in various sizes,” said Ameer, who is professor of biomedical engineering at Northwestern and professor of surgery in the Feinberg School of Medicine. “The physician has to guess which stent size is a good fit to keep the blood vessel open. But we’re all different and results are highly dependent on physician experience, so that’s not an optimal solution.”

In fact, there are many reasons why a stent would not fit, and those reasons can be directly related to the patient’s current health. “There might be geometric constraints in the patient’s vessel, such as a significant curvature that can disturb blood flow, causing traditional stents to fail. This is especially a problem for patients who have conditions that prevent the use of blood thinners, which are commonly given to patients who have stents,” Ameer explains.

Together with Cheng Sun, associate professor of mechanical engineering, Ameer therefore turned to 3D printing and its numerous benefits. “By printing a stent that has the exact geometric and biologic requirements of the patient’s blood vessel, we expect to minimize the probability of these complications,” Ameer said.

In order to develop the custom stents, however, the team had to first adapt existing 3D printing techniques. Their custom version of projection micro-stereo-lithography, which relies on an especially-developed polymer, actually resembles CLIP 3D printing technology though on a miniscule scale. The stents themselves can be smaller than 3mm in diameter, and Sun’s 3D microCLIP printing solution actually 3D prints up to a hundred simultaneously. With features as small as 7 microns in size, they are highly detailed, and an entire batch can be manufactured in a matter of minutes.

Notably, Ameer’s material breakthrough plays a crucial role as well. Whereas conventional stents are made from metal, Ameer uses a citric-acid based polymer that is flexible, biodegradable and inherently antioxidant. It can even act as a drug carrier, with the drugs being loaded onto the polymer and slowly released after implantation – speeding up the healing process. The same polymer was previously used to inhibit clot formation on vascular grafts.

Most importantly, the material is strong enough to ensure that the stent supports a vessel’s dilation and will slowly dissolve after the artery recovers – unlike those other plastic stents that are sometimes used. “In theory, it’s safer because the patient doesn’t have permanent foreign metal devices in the body,” Ameer said. “If, for any reason in the future, the surgeon needs to go back in to that location in the vessel, they can. There’s not a metal stent in the way.”

With their customizable 3D printed stents, Ameer and Sun are envisioning a future in which doctors obtain the dimensions of a patient’s blood vessel through standard imaging techniques (already available at hospitals) and 3D print exactly fitting stents, ready for use during surgery. “Not only can we customize the stent for a patient’s blood vessels,” Ameer said. “But we can create all new types of patient-specific medical devices that could make the outcomes of surgical procedures better than what they are today.”

Before that becomes a reality, however, Ameer and Sun will be extensively testing the stent’s biodegradation process – as it is crucial to establish exactly how long it takes for a 3D printed stent to be absorbed into the body. They are also looking into new stent designs that could improve long term performance.

Posted in 3D Printing Application

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