NEWS OF THE WEEK BIOMATERIALS
SAVING JOINTS Polymer coat reduces wear and bone loss around artificial joint implants
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ONE LOSS AROUND THE SITE
of an implant caused by an inflammatory response to wear-particles is the most important factor limiting the lifetime of artificial joints. Japanese researchers now show that grafting a biocompatible polymer layer onto artificial joints reduces wear and bone loss. M PC The team, led by Hiroshi Kawaguchi from the de(CH3 partment of orthopedic surgery at the University of Tokyo, covalently attaches a biocompatible phospholipid polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC), to the liner surface of an artificial hip made of polyethylene [Nat. Mater., published online Oct.
24, http://dx.doi.org/10.1038/ nmatl233}. In mechanical tests ofthe coated joint in a hip-joint simulator, the MPC layer decreases friction and the production of wear-particles compared to uncoated joints. "The reduction of wear is
likely to arise from the hydrated lubricating layer formed by the MPC grafting," Kawaguchi says. In addition, the MPC coating appears to prevent bone loss: MPC-coated polystyrene particles injected into mice do not in-
NEUROMEDICINE CURIOUS Anormal mouse explores a maze; mice treated with an SSRI in early life were less likely to explore new environments as adults.
PARADOX OF ANTIDEPRESSANTS Effect of fluoxetine on young mice highlights serotonin's growth role
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Prozac (fluoxetine
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NFANT MICE GIVEN FLUOXETINE
(Prozac) for a short period grow into adult mice that exhibit abnormal behavior resembling anxiety and depression [Science, 306, 879 (2004)}. The finding is unsuspected because adrninistering fluoxetine to anxious and depressed adults—whether mouse or human—makes them less anxious, less depressed, and more emotionally even-keeled. The work, by Mark Ansorge, Jay A. Ginhydrochloride) grich, and coworkers
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at Columbia University, indicates that serotonin could play a crucial role in brain development. Those with depression often suffer from low levels of serotonin, a neurotransmitter that influences mood. Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, increase the availability of serotonin by inhibiting its removal from the nerve synapse by the serotonin transporter. 'Yet serotonin is also a growth factor, Gingrich says. It helps with nerve differentiation and migration of cells in the developing central nervous system.
duce bone resorption. The researchers use polystyrene because trying to isolate the wear-particles from the hip-joint simulator damages the MPC layer. "Since the structure ofMPC polymer is similar to that ofbiomembranes, it prevents macrophages from recognizing the particles as foreign bodies," Kawaguchi says. The usual inflammatory response that triggers bone loss around artificial joints does not ensue. "These are promising results," says Tirnmie Topoleski, a biomaterials scientist at the University of Maryland, Baltimore County, who also studies joint implants. "The ultimate test will be going through the hurdles to apply the new material to orthopedic devices and then study results in patients." Kawaguchi and his colleagues plan to start clinical trials of MPC-grafted implants by June 2005 and expect results by the end of 2007—CELIA HENRY
The effect of SSRIs on immature mice is far different from that on mature mice, Gingrich notes. If the same pattern applies to humans, these age-dependent effects could help explain why SSRIs are sometimes not effective or even countereffective in children and adolescents. In the study, Gingrich administered fluoxetine for 18 days to infant mice, beginning when they were four days old, and then observed the behavior of the mice nine weeks later. The mice, by then adults, displayed indicators of what would be called anxiety and depression in humans. Mouse brain development during the time of dosing corresponds to that of humans from the third trimester into early childhood. Further studies in humans will establish the human response and maybe able to determine the window of time when serotonin plays a role in brain development.-LOU ISA DALT0N HTTP://WWW.CEN-ONLINE.ORG
