New gel coatings may lead to better catheters and condoms
Adapted Media Release
Bonded layers of rubber and
hydrogel yield tough, slippery, and impermeable coatings.
Catheters, intravenous lines,
and other types of surgical tubing are a medical necessity for managing a wide
range of diseases. But a patient's experience with such devices is rarely a
comfortable one.
Now MIT engineers have
designed a gel-like material that can be coated onto standard plastic or rubber
devices, providing a softer, more slippery exterior that can significantly ease
a patient's discomfort. The coating can even be tailored to monitor and treat
signs of infection.
In a paper published in the
journal Advanced Healthcare Materials, the team describes their method for strongly
bonding a layer of hydrogel - a squishy, slippery polymer material that
consists mostly of water - to common elastomers such as latex, rubber, and
silicone. The results are "hydrogel laminates" that are at once soft,
stretchable, and slippery, and impermeable to viruses and other small
molecules.
The hydrogel coating can be
embedded with compounds to sense, for example, inflammatory molecules. Drugs
can also be incorporated into and slowly released from the hydrogel coating, to
treat inflammation in the body.
The team, led by Xuanhe Zhao,
the Robert N. Noyce Career Development Associate Professor in the Department of
Mechanical Engineering at MIT, bonded layers of hydrogel onto various
elastomer-based medical devices, including catheters and intravenous tubing.
They found that the coatings were extremely durable, withstanding bending and
twisting, without cracking. The coatings were also extremely slippery,
exhibiting much less friction than standard uncoated catheters - a quality that
could reduce patients' discomfort.
The group also coated hydrogel
onto another widely used elastomer product: condoms. In addition to enhancing
the comfort of existing latex condoms by reducing friction, a coating of
hydrogel could help improve their safety, since the hydrogel could be embedded
with drugs to counter a latex allergy, the researchers say.
"We've demonstrated
hydrogel really has the potential to replace common elastomers," Zhao
says. "Now we have a method to integrate gels with other materials. We
think this has the potential to be applied to a diverse range of medical
devices interfacing with the body."
Zhao's co-authors are lead
author and graduate student German Parada, graduate students Hyunwoo Yuk and
Xinyue Liu, and visiting scientist Alex Hsieh.
A tailored gel
Zhao's group previously
developed recipes to make tough, stretchable hydrogels from mixtures composed
mostly of water and a bit of polymer. They developed a technique to bond
hydrogels to elastomers by first treating surfaces such as rubber and silicone
with benzophenone, a molecular solution that, when exposed to ultraviolet
light, creates strong chemical bonds between the elastomer and the hydrogel.
The researchers applied these
techniques to fabricate a hydrogel laminate: a layer of elastomer sandwiched
between two layers of hydrogel. They then put the laminate structure through a
battery of mechanical tests and found the structure remained strongly bonded,
without tearing or cracking, even when stretched to multiple times its original
length.
The team also placed the
laminate structure in a two-chamber tank, filled on one side with deionized
water and the other with molecular dye. After several hours, the laminate
prevented any dye from migrating from one side of the chamber to the other,
whereas a layer of hydrogel alone let the dye through. The laminate's elastomer
layer, they concluded, made the structure as a whole strongly impermeable - a
feature they reasoned could also prevent viruses and other small molecules from
passing through.
In other tests, the team
chemically mixed pH-sensing molecules into the layer of hydrogel lining one
side of the elastomer layer, and green food dye into the opposite hydrogel
layer. They once again placed the entire structure into the two-chamber tank and
filled both sides with dioinized water.
As the researchers changed the
acidity of the tank's water, they observed that the parts of the hydrogel
containing pH indicators lit up. Meanwhile, the green dye seeped slowly from
the opposite hydrogel layer into the second tank, mimicking the action of drug
molecules.
"We can put pH-sensing
molecules in hydrogels, or drugs that are gradually released," Parada
says. "For different applications, we can modify the gel to accommodate
that application."
Tying knots
As a first foray into possible
applications for hydrogel laminates, the researchers used their previously
developed techniques to coat hydrogel onto various elastomer devices, including
silicone tubing, a Foley catheter, and a condom. "Our first major focus
was catheters, because they are rigid and not very comfortable, and infection
of catheters can cause around 50 percent of readmissions to hospitals,"
Parada says. "We also thought we could apply this to condoms, because
existing latex condoms cause lots of sensitivities and allergies, and if you
can put drugs in the gel, you could have better protection."
Even after sharply bending and
folding the coated tubing into a knot, the researchers found the hydrogel
coating remained strongly bonded to the tubing without causing any tears. The
same was true when the researchers inflated both the coated catheter and the
coated condom.
Parada says the dimensions of
a hydrogel laminate may be tuned to accommodate different devices. For
instance, scientists can choose a thicker elastomer to increase a laminate's
rigidity, or use a thicker coating of hydrogel to incorporate more drug
molecules or sensors. Hydrogels can also be designed to be more or less
slippery, depending on the amount of friction desired.
"We have the capability
to fabricate large-scale hydrogel structures that can coat medical devices, and
the hydrogel won't agitate the body," Zhao says. "This is a
technological platform onto which you can imagine many applications."
This research was funded, in part,
by the Office of Naval Research, the MIT Institute for Soldier
Nanotechnologies, and the National Science Foundation (NSF).
Article: Impermeable Robust
Hydrogels via Hybrid Lamination, German A. Parada, Hyunwoo Yuk, Xinyue Liu,
Alex J. Hsieh, Xuanhe Zhao, Advanced Healthcare Materials, doi:
10.1002/adhm.201700520, published online 17 July 2017.
SOURCE:
MEDICAL NEWS TODAY
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