Synthetic molecules mimic bone growth

With an eye toward new bone-repair treatments, researchers have designed molecules that assemble into tiny fibers that serve as templates for growing hydroxyapatite, the mineral in bone. What’s more, hydroxyapatite crystals align along the synthetic fibers much as they do along collagen fibers in natural bone.

Molecules with thin hydrophobic tails (left) assemble themselves in water to form a tiny fiber (right). Science

“This [alignment] is one of the fundamental elements of the nanostructure of bone,” Samuel I. Stupp said in Boston at a meeting of the Materials Research Society on Nov. 26. Stupp and his coworkers, all at Northwestern University in Evanston, Ill., also reported their results in the Nov. 23 Science.

In their work, the researchers designed conical molecules with hydrophobic tails and hydrophilic heads–a combination that made them assemble loosely in water to form fibers just 8 nanometers wide. The use of sulfur-containing amino acids in each molecule led to strong sulfur-sulfur bonds that helped lock the structures into their cylindrical shape.

Other portions of the conical molecules encouraged hydroxyapatite crystal formation on the fibers, while yet other parts were designed to attract various cells in the body. The hydroxyapatite crystals’ alignment along the fibers came as a pleasant surprise, notes Stupp.

“It’s really a wonderful example of molecular engineering,” comments Ulrich B. Wiesner of Cornell University, an organizer of the symposium in which Stupp spoke. The Northwestern team exploited what’s known about biology and applied it to materials science, he says.

Doctors might one day repair bone injuries with injections of nanofiber solutions, Stupp suggests. He notes that the technique might also be used for making nanostructures that organize nerve cells, pancreatic cells, and other types of cells into new tissues and organs. Beyond medicine, such a method might prove useful for building highly aligned inorganic crystals for electronics and photonics applications.

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