Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Eliminating entanglements

10.08.2015

A new strategy towards ultra-soft yet dry rubber

Medical implants mimic the softness of human tissue by mixing liquids such 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.


This is an ultra-soft elastomer fabricated by crosslinking bottlebrush polymers contains only crosslinks (red chains) and no entanglements.

(Image courtesy of Li-Heng Cai, Harvard SEAS.)

Now, led by David A. Weitz, Mallinckrodt Professor of Physics and Applied Physics at Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and associate faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard, a team of polymer physicists and chemists has developed a way to create an ultra-soft dry silicone rubber. This new rubber features tunable softness to match a variety of biological tissues, opening new opportunities in biomedical research and engineering.

The material is featured on the cover of the journal Advanced Materials.

"Conventional elastomers are intrinsically stiff because of how they are made," said lead author 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 order to fabricate a soft elastomer, the team needed to eliminate the entanglements from the beginning by developing a new type of polymer that was fatter and less prone to entanglement than linear polymers. The polymers, nicknamed bottlebrushes, are easily synthesized by mixing three types of commercially available linear silicone polymers.

"Typically the fabrication of such bottlebrush molecules requires complex chemical synthesis," said co-first author Thomas E. Kodger, Ph.D.' 2015, now a postdoctoral fellow at University of Amsterdam. "But we found a very simple strategy by carefully designing the chemistry. This system creates soft elastomers as easily as silicone kits sold commercially."

The softness of the elastomers can be precisely controlled by adjusting the amount of cross-linked polymers to mimic everything from soft brain tissue and relatively stiff cells.

"If there are no crosslinks, all the bottlebrush molecules are mobile and the material will flow like a viscous liquid such as honey," said Cai. "Adding crosslinks connects the bottlebrush molecules and solidifies the liquid, increasing the material stiffness."

In addition to controlling the softness, the team also found a way to independently control the liquid-like behavior of the elastomer.

"To make the conventional elastomer softer, one needs to swell it in a liquid," said coauthor Michael Rubinstein, John P. Barker Distinguished Professor in Chemistry at the University of North Carolina at Chapel Hill. "But now we can adjust the length of 'hairy' polymers on the bottlebrush molecules to tune the liquid-like behavior of soft elastomers -- without swelling -- allowing us 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.

"The independent control over both softness and liquid-like behavior of the soft elastomers will also enable us to answer fundamental questions in biomedical research," said Weitz. "For example, stem cell differentiation not only depends on the softness of materials with which they are in contact, but recent findings suggest that it is also affected by how liquid-like the materials are. This discovery will provide entirely new materials to study the cell behavior on soft substrates."

"The exceptional combination of softness and negligible adhesiveness will greatly broaden the application of silicon-based elastomers in both industry and research," said Weitz.

###

In addition to his role on the faculty at SEAS, Weitz is the director of Harvard's Materials Research Science and Engineering Center, co-director of the BASF Advanced Research Initiative, a member of the Kavli Institute for Bionano Science and Technology, and an Associate Faculty Member at the Wyss Institute for Biologically Inspired Engineering.

In addition to Cai, Kodger, Weitz, and Rubinstein, coauthors included Rodrigo E. Guerra, Ph.D.' 2015, now a postdoctoral fellow at New York University; and Adrian F. Pegoraro, a postdoctoral fellow at SEAS.

This research was supported in part by the National Science Foundation (DMR-1310266) and the Harvard Materials Research Science and Engineering Center (DMR-1420570).

Leah Burrows | EurekAlert!

More articles from Materials Sciences:

nachricht New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University

nachricht Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>