UC San Diego bioengineers have developed smart, self-healing hydrogels with far-reaching applications including medial sutures, targeted drug delivery, industrial sealents and self-healing plastics. Photo Credit: Joshua Knoff, UC San Diego Jacobs School of Engineering. |
University
of California, San Diego bioengineers have developed a self-healing
hydrogel that binds in seconds, as easily as Velcro, and forms a bond
strong enough to withstand repeated stretching. The material has
numerous potential applications, including medical sutures, targeted
drug delivery, industrial sealants and self-healing plastics, a team of
UC San Diego Jacobs School of Engineering researchers reported March 5
in the online Early Edition of the Proceedings of the National Academy of Sciences.
Hydrogels
are made of linked chains of polymer molecules that form a flexible,
jello-like material similar to soft-tissues. Until now, researchers have
been unable to develop hydrogels that can rapidly repair themselves
when a cut was introduced, limiting their potential applications. The
team, led by Shyni Varghese, overcame this challenge with the use of
“dangling side chain” molecules that extend like fingers on a hand from
the primary structure of the hydrogel network and enable them to grasp
one another.
“Self-healing
is one of the most fundamental properties of living tissues that allows
them to sustain repeated damage,” says Varghese. “Being bioengineers,
one question that repeatedly appeared before us was if one could mimic
self-healing in synthetic, tissue-like materials such as hydrogels. The
benefits of creating such an aqueous self-healing material would be
far-reaching in medicine and engineering.”
To
design the side chain molecules of the hydrogel that would enable rapid
self-healing, Varghese and her collaborators performed computer
simulations of the hydrogel network. The simulations revealed that the
ability of the hydrogel to self-heal depended critically on the length
of the side chain molecules, or fingers, and that hydrogels having an
optimal length of side chain molecules exhibited the strongest
self-healing. When two cylindrical pieces of gels featuring these
optimized fingers were placed together in an acidic solution, they stuck
together instantly. Varghese’s lab further found that by simply
adjusting the solution’s pH levels up or down, the pieces weld (low pH)
and separate (high pH) very easily. The process was successfully
repeated numerous times without any reduction in the weld strength.
Bioengineering PhD student Ameya Phadke holds three bonded hydrogels. Photo Credit: Joshua Knoff, UC San Diego Jacobs School of Engineering. |
Ameya
Phadke, a fourth year PhD student in Varghese’s lab said the hydrogel’s
strength and flexibility in an acidic environment—similar to that of
the stomach—makes it ideal as an adhesive to heal stomach perforations
or for controlled drug delivery to ulcers.
Such
healing material could also be useful in the field of energy
conservation and recycling where self-healing materials could help
reduce industrial and consumer waste, according to Varghese.
Additionally, the rapidity of self-healing in response to acids makes
the material a promising candidate to seal leakages from containers
containing corrosive acids. To test this theory, her lab cut a hole in
the bottom of a plastic container, “healed” it by sealing the hole with
the hydrogel and demonstrated that it prevented any leakage of acid
through the hole.
Moving
forward, Varghese and her lab hope to test the material in its
envisioned applications on a larger scale. The team also hopes to
engineer other varieties of hydrogels that self-heal at different pH
values, thereby extending the applications of such hydrogels beyond
acidic conditions.
