Researchers at the University
of California, Santa Barbara have developed a new and highly
efficient way to characterize the structure of polymers at the nanoscale—effectively
designing a routine analytical tool that could be used by industries that rely
on polymer science to innovate new products, from drug delivery gels to
Professor Omar Saleh and graduate student Andrew
Dittmore of the UCSB Materials department have successfully measured the
structure and other critical parameters of a long, string-like polymer molecule—polyethylene
glycol, or PEG—by stretching it with an instrument called magnetic tweezers.
“We attach one end of the PEG molecule to a
surface, and the other to a tiny magnetic bead, then pull on the bead by
applying a magnetic field,” explains Saleh. “The significance is that
we’re able to perform the elastic measurements—force vs. length measurement—to
see aspects of polymer structure that are hard to see in any other way, and we
can do it within minutes on a benchtop apparatus.”
Their research to characterize this particular
polymer will lay the groundwork for developing a screening tool that could be
used by a number of industries, according to Saleh’s research team.
“Our measurements of PEG can be used as a
baseline for comparison to other polymers, including biomolecules such as DNA,
RNA, and proteins, which display more complex physics,” says Dittmore.
“We chose to study PEG because it is an inert polymer that is
biocompatible, soluble in water, and used for many technological purposes. The
protocols we developed will be useful for future work with a variety of
polymers, greatly expanding the versatility of the magnetic tweezers
PEG is one of the most frequently used polymers in
creams, cosmetics, adhesives, and medicines, but its application goes beyond
everyday household products. As a coating, PEG can shield against an unwanted
immune response to give a medicine a stealth-like quality. To this end, it is
used to enhance the effectiveness of anticancer drugs by increasing the
circulation time in the body. PEG repels other molecules and is often used as a
nonfouling coating for biomedical implants and biosensors that detect the
presence of drugs or antibodies in blood.
In 1974, Paul Flory won the Nobel Prize in
Chemistry for his theories regarding polymer structure in a solvent. Inspired
by the work of Flory, and theories put forth decades earlier by UCSB materials
and physics professor Philip Pincus, Saleh, and Dittmore set out to develop an
experiment that would validate their theories.
“Flory and de Gennes taught us that the
structure of a polymer in solution depends on both the quality of solvent and
also the length of the chain. Pincus extended upon this theory, and brought
force into the picture as an important experimental variable,” says
Dittmore. “Now we have a method to directly test these ideas at the
single-molecule level, using a powerful and quantitative technique.”
“Until now, the most general method to obtain
comparable data is to use neutron or X-ray diffraction which involves expensive
national facilities such as nuclear reactors or particle accelerators. Thus,
this research opens up a broad area of research that can be carried out at
academic and industrial laboratories with modest resources,” comments
Professor Philip Pincus, Chair of Biomolecular Science and Engineering at UCSB.
The findings of Dittmore et al. were published in
the journal Physical Review Letters. The paper establishes a framework
for comparing biomolecules and synthetic polymers based on chain structure that
could be further refined and translated into a laboratory tool for industry.
“Many companies are looking to replace the
petroleum-based polymers they use in consumer products with polymers made from
biomass, such as sugar cane or cellulose,” says Professor Glenn
Fredrickson, Chair of Functional Materials and Founding Director of the Mitsubishi Chemical Center
for Advanced Materials at UCSB. “If their methods could be made into a
compact and inexpensive screening tool for polymer properties in an industrial
setting, it could be important in affecting industry transformation to
producing polymers from renewable resources.
Their research was made possible by support from
the National Science Foundation and was carried out at the Materials Research
Laboratory: an NSF MRSEC facility at UC Santa Barbara.
“This is an excellent example of high-risk, transformative research
that breaks down conventional wisdom,” says Craig Hawker, Director of the
Materials Research Laboratory at UCSB. “The MRL is proud to have
contributed to the success of this project through a Seed program designed to
fund research that will revolutionize existing fields. By establishing this
technique as a powerful, new strategy for characterizing synthetic polymers,
countless future studies are now possible.”