N EWS OF THE WE E K
MEDICINE: Coating could prevent implant rejection
T
HE HUMAN BODY almost immediately recog-
nizes surgically implanted objects as foreign and rushes to surround them with a dense layer of collagen. That so-called foreign-body response is part of an immune-system reaction to a strange object. However, it interferes with medical implants such as drug pumps. Coating implants with some novel hydrogels may help. The hydrogels are zwitterionic—carrying both positive and negative charges—and are based on carboxybetaine. When Shaoyi Jiang, Buddy D. Ratner, and coworkers at the University of Washington, Seattle, put these hydrogels in mice, the implants resisted the foreign-body reaction for at least three months (Nat. Biotechnol. 2013, DOI: 10.1038/nbt.2580). The researchers made poly(carboxybetaine methacrylate), or PCBMA, hydrogels from a CBMA monomer mixed with 5% CBMA cross-linker. They found that the new hydrogels adsorbed fewer proteins and cells than
MICROFLOWERS FROM MINERALS MATERIALS: Tweaking pH deposits
B
EACHCOMBERS WHO GATHER seashells and
corals know just how good nature is at building intricate structures. Chemists have rarely achieved similar prowess. But by mimicking how the environment shapes biological materials, a team at Harvard University has sculpted tiny, beautiful flowerlike structures (Science 2013, DOI: 10.1126/science.1234621). In the future, the work might be adapted to craft patterned surfaces for catalysis and other applications. In nature, developing shells can change patterns abruptly—from dots to wavy lines, for instance. Changes in temperature, pH, or other factors affect patterns while the shell grows, says postdoc Wim L. Noorduin, first author of the new study. So Noorduin, Alison Grinthal,
“The first time we looked at our slides with a good microscope, I coincidentally focused on a roselike structure,” Noorduin says. This is a digitally colored SEM image; “flower” is about 100 μm tall.
COU RTESY OF WI M NO OR DU I N
remarkable structures onto glass
Lakshminarayanan Mahadevan, and Joanna Aizenberg set out to apply this concept in the lab. Their setup was deceptively simple: a glass microscope slide, a solution of barium chloride and sodium silicate in water, and a beaker covered with a petri dish. The two compounds aren’t used by living things, but others have shown they can generate lifelike shapes. Two different minerals—SiO2 and BaCO3—precipitate from that solution onto the slide. By moving slides from one pH or temperature condition to another as the minerals grew on them, the team sculpted the substances into flowers. Some conditions led to stemlike spirals, others to flowerlike bulbs. Pupa Gilbert, who studies biominerals at the University of Wisconsin, Madison, marvels at their results. “They just open and close the beaker,” adding pulses of CO2 from air, she says. “Yet the structures produced are stupendously complex.” The method doesn’t make structures uniform enough to use as catalytic materials, Noorduin says. The team is exploring microfluidics to attain that reproducibility. For now, Noorduin enjoys gazing at his handiwork under an electron microscope. “It’s amazing—like diving in the ocean,” he says. “You can really get lost.”—CARMEN DRAHL
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MAY 20, 2013
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did a widely used hydrogel, poly(2-hydroxyethyl methacrylate), or PHEMA. Both four weeks and three months after the researchers implanted the hydrogels under the skin of mice, the PHEMA implants were surrounded by a dense layer of collagen, a sign of immune rejection. But the collagen structure around the PCBMA implants was similar to that found in normal tissue, suggesting that the CH3 O immune system was tolerating them. “The O– N+ zwitterionic hydrogel gives a reaction much O more like normal tissue,” Ratner says. Reduced CH3 O interaction with proteins and cells, the researchCBMA monomer ers suspect, is behind the improved tolerance. Although the results are promising, zwitterionCH3 ic hydrogels have yet to be tested in humans O O and as a coating on actual implantable mediN+ O O cal devices, cautions Ulrike W. Klueh, a professor of surgery and an expert on implanted devices at the University of Connecticut Health Center, O in Farmington. In addition, the work doesn’t take into O– account biomechanical properties such as the size, CBMA cross-linker shape, and elasticity of the hydrogel, which can also affect biocompatibility, says Natalie A. Wisniewski, a San Francisco-based medical device expert. Still, the researchers are confident. “Given the excellent results in mice and the inert quality of this hydrogel, we believe the translation to clinical implants will be rapid,” Ratner says.—CELIA ARNAUD
HYDROGELS DEFEAT BODY’S DEFENSES
Digitally colored confocal microscopy image of “flowers” (top), made by layering precipitates grown under iterative conditions, and fluorescent image (bottom).
