BIOLOGY BEAT
HUMPTY-DUMPTY MEDICINE
ORTHOMIMETICS
When quarterback Tom Brady tore
a knee ligament last year, the New
England Patriots got a rude lesson in
the limits of modern medicine: Repairing injured ligaments, tendons, and
cartilage is dif;cult, much trickier than
mending a broken bone. When tendons—essential connectors between
muscle and bone—are severed, surgical attempts to anchor the tendon to
bone often fail because the materials
are so different. The problem is akin to
joining a rope to a cement wall.
Now researchers are building
synthetic interfaces that re-create
the architecture of natural connective
tissue in hopes of tricking the body to
regrow the broken connection. Stavros Thomopoulos and Younan Xia,
biomedical engineers at Washington
University in St. Louis, are working
with a scaffold made of microscopic
nano;bers. It is pliable and tendon-like at one end but denser and more
bonelike toward the other. “There’s
lots of mineral in bone and none in
tendon. At the interface, there’s a
gradation,” Thomopoulos says. The
scaffold simulates that gradient. In
recent experiments, precursors of
bone and connective tissue cells
regenerated on the scaffold, yielding
the desired properties for tendon
reattachment. Thomopoulos is testing the system in rats.
Synthetic mimics of cartilage, the
body’s shock absorber, are even farther along. In February, U.K.–based
Orthomimetics began a human trial
of one such implant, built from the
protein collagen (a building block of
many body tissues) and the mineral
calcium phosphate (found in bone).
Monica Heger
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