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New ultra-soft, dry silicone rubber
This ultra-soft elastomer fabricated by crosslinking bottlebrush polymers contains only crosslinks (red chains) and no entanglements.
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Medical implants mimic the softness of human tissue by mixing liquids such as oil with long, silicone polymers to create a squishy, wet gel. While implants have improved dramatically over the years, there is still a chance of the liquid leaking, which can be painful and sometimes dangerous.
A research team led by David A. Weitz, the Mallinckrodt Professor of Physics and Applied Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and an associate faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard, has developed a way to create an ultra-soft, dry silicone rubber. The new rubber features tunable softness to match a variety of biological tissues, thereby opening new opportunities in biomedical research and engineering.
"Conventional elastomers are intrinsically stiff because of how they are made," says Li-Heng Cai, a postdoctoral fellow at SEAS. "The network strands are very long and are entangled, similar to a bunch of Christmas lights in which the cords are entangled and form knots. These fixed entanglements set up an intrinsic lower limit for the softness of conventional elastomers."
In addition to controlling the softness, the team also found a way to independently control the liquid-like behavior of the elastomer. The researchers can adjust the length of "hairy" polymers on the bottlebrush molecules to tune the liquid-like behavior of soft elastomers -- without swelling, thereby allowing them to make these elastomers exceptionally non-adhesive yet ultra-soft. These qualities make the material not only ideal for medical devices, such as implants, but also for commercial products such as cosmetics.
This research was supported in part by the National Science Foundation (grant DMR 13-10266) and the Harvard Materials Research Science and Engineering Center (grant DMR 14-20570), an NSF Materials Research Science and Engineering Center.
To learn more, see the Harvard news story Eliminating entanglements. (Date image taken: unknown; date originally posted to NSF Multimedia Gallery: Jan. 6, 2016)
Credit: Li-Heng Cai, Harvard University
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