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Plastics Today, September 2015

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Materials 44 Global Plastics rePort 2015 Plasticstoday.coM Breathing new life into biomaterials Material scientists are learning to program biomaterials, giving them the ability to better interface with the body. Brian Buntz and Chris newmarker W e have smartphones. Why not smart biomaterials? In a way, traditional materials destined for use within the body are like the phones from yesteryear: Good for a single pur- pose and not much else (though they do last for decades). In the past, the best biomaterials were thought to be as inert and stable as possible; the best possible outcome for a biomaterial was to be ignored by the body. The reason for that aim was clear: Biomaterial degradation was often linked to medical device failure. Now, however, designer biomaterials are being devised that can either interface with the body or dissolve, leaving the body to remodel the tissue as it breaks down. "You have a lot of little levers to tweak, and those levers are all levers in organic chemistry," says Walter E. Voit, PhD, Assistant Professor of materials sci- ence and engineering at the University of Texas at Dallas. In addition to breakthroughs in mate- rial science, advances in implantable bio- electronics, 3-D printing and computer processing have also changed the game. Material scientists are not only tweak- ing how they make polymers and how those polymers are linked together, but also how they interface with electronics, according to Voit. "The tools of today allow us to do that with far greater precision than what could have been done 20 or 30 years ago," says Voit, whose group has received funding support from GlaxoSmithKline. One example of what Voit is describ- ing is the use of dissolvable thiolene/ acrylate-based substrates to house flex- ible biocompatible electronics (such as gold). Those electronics can be used to interact with nerve bundles only 60 microns in diameter, or even tinier nerve fibers. Such elec- tronics cannot be sealed off from the body in the same manner as, say, a pacemaker is with a metal can, Voit says. In fact, it helps to have them degrade in a con- trolled way so that cells from the body can grow in and create a better, safer interface. "You have these giant devices that we want to interact with very, very small nerves. It becomes a size-distance prob- lem. It would be great if we could design tiny components that are themselves well-encapsulated enough to prevent long-term disruption from the body but still interact with the body in controlled ways," Voit says. Over the years, material scientists have worked on a variety of synthetic materials that degrade in the body in a controlled manner. The first notable example of this was the debut of the first polyglycolide sutures in the 1960s, which gradually dissolved, eliminating the need for a physician to remove them later. Until recent years, though, Voit could only count a handful of degradable materials included in FDA master files. But that is gradually changing, and bio- degradable implants are in ever-greater demand. A new world of advanced biomaterials has arrived. Programming degradation A major focus of Voit's research has involved shape-shifting thiolene/acry- lates that could open the door for a whole new host of medical applications. The substance could enable self-coiling cochlear implants inside the ear and a host of cardiovascular implants. Voit is still engaged in preclinical tri- als with animals with the technology. He has financial backers including the Defense Advanced Research Projects Agency, GlaxoSmithKline and Texas Instruments. 3M Co. undertook research on thiol- type polymers in the late 1970s but did not commmercialize it, probably because computers at the time were not avail- able to handle the data rates that now make these devices useful, Voit says. In addition, poor shelf life of the materials restricted their commercial applications. Only in recent years have researchers begun to capitalize on the thiol-type polymers' ability to soften and change shape under human body temperatures for promising potential commercial applications. A polymer, for example, could be engineered to coil around a nerve inside the human body. Another aspect of the polymers that can be controlled is degradation, based on placement of ester-based substrates. Such controlled degradation could be useful in a number of ways. For example, the shape-shifting poly- mers could be used to place electronics Launched in the United States in 2010, the TIGR mesh is billed as the only long- term absorbable mesh.

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