Tech Briefs Magazine - February 2022 - 25

The surfaces of a barnacle - a small
crustacean that attaches itself to rocks,
ship hulls, and even other animals such
as whales - are wet and often dirty.
These conditions make adhesion difficult.
The researchers' analysis of barnacle
glue revealed that it has a unique
composition. The sticky protein molecules
that help barnacles attach to surfaces
are suspended in an oil that repels
water and any contaminants found on
the surface, allowing the adhesive proteins
to attach firmly to the surface.
The team mimicked this glue by
adapting an adhesive they had previously
developed. This sticky material consists
of a polymer called poly(acrylic
acid) embedded with an organic compound
called an NHS ester, which provides
adhesion, and chitosan, a sugar
that strengthens the material. The
researchers froze sheets of this material,
ground it into microparticles, and then
suspended those particles in medical
grade silicone oil.
When the resulting paste is applied to
a wet surface such as blood-covered tissue,
the oil repels the blood and other
substances that may be present, allowing
the adhesive microparticles to crosslink
and form a tight seal over the wound.
Within 15 to 30 seconds of applying the
glue, with gentle pressure applied, the
glue sets and bleeding stops.
The seal remains intact for several
weeks, giving the tissue below time to
heal itself. The glue induces little inflammation,
similar to that produced by currently
used hemostatic agents. The glue
is slowly resorbed within the body over
months and it can also be removed earlier
by applying a solution that dissolves
it if surgeons need to go in after the initial
application to repair the wound.
The researchers plan to test the glue
on larger wounds, which they hope will
demonstrate that the glue would be useful
to treat traumatic injuries. They also
envision that it could be useful during
surgical procedures, which often require
surgeons to spend a great deal of time
controlling bleeding.
For more information, contact Anne
Trafton at trafton@mit.edu; 617-253-7147.
Load-Bearing Material Mimics Human Cartilage
The synthetic material is soft but can withstand heavy loading with minimum wear and tear
for engineering applications.
University of Leeds, United Kingdom
E
ngineers have developed a material
that mimics human cartilage - the
body's shock absorbing and lubrication
system - and it could herald the development
of a new generation of lightweight
bearings.
Cartilage is a soft, fibrous tissue found
around joints that provides protection
from the compressive loading generated
by walking, running, or lifting. It also
provides a protective, lubricating layer,
allowing bones to pass over one another
in a frictionless way. Cartilage is a bi-phasic
porous material, meaning it exists in
solid and fluid phases. It switches to its
fluid phase by absorbing a viscous substance
produced in the joints called synovial
fluid. This fluid not only lubricates
the joints, but also when held in the
porous matrix of the cartilage, it provides
a hydro elastic cushion against
compressive forces.
Because the cartilage is porous, the
synovial fluid eventually drains away and
as it does, it helps dissipate the energy
forces traveling through the body, protecting
joints from wear and tear and
impact injuries. At this point, the cartilage
returns to its sold phase, ready for
the cycle to be repeated.
Earlier attempts at developing a synthetic
cartilage system focused on the use
of hydrogels - materials that absorb
water. Hydrogels are good at reducing
friction but perform poorly when under
Tech Briefs, February 2022
Cov
The interface between the hydrogel (left) and the PDMS. The image was taken at 100,000 times
magnification. (Photo: University of Leeds)
compressive force. One of the problems
is that it takes time for the hydrogel to
return to its normal shape after it has
been compressed.
The researchers overcame this problem
by creating a synthetic porous material
made of a hydrogel held in a matrix of
polydimethylsiloxane - a silicone-based
polymer. The matrix keeps the shape of
the hydrogel. The hydrogel also provides
a lubricating layer. The load-bearing
behavior of the hydrogel held in the
matrix was 14 to 19 times greater than the
hydrogel on its own. The equilibrium elastic
modulus of the composite was 452 kPa
at a strain range of 10 percent to 30 perwww.techbriefs.com
ToC
cent,
close to the values reported for the
modulus of cartilage tested.
The researchers believe future applications
of a new material based on the
function of cartilage could challenge
many traditional oil-lubricated engineering
systems. The ability to use water as
an effective lubricant has many applications
from energy generation to medical
devices; however, this often requires a
different approach when compared to
traditional engineering systems that
often use oil-based lubricants and hardsurface
coatings.
For more information, contact David
Lewis at d.lewis@leeds.ac.uk.
25
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Tech Briefs Magazine - February 2022

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