Materials Science

Clicking Bones

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Science  25 Jan 2013:
Vol. 339, Issue 6118, pp. 374
DOI: 10.1126/science.339.6118.374-d

A challenge in developing drug delivery vehicles or other tissue-specific biomaterials is to find ways to target them to the organs or tissues of interest. Heller et al. focused their study on modified dextran polymers, which can form porous nanoscale hydrogel particles. The dextran was initially modified with either alkyne or azide groups, which could then be clicked together within an inverse emulsion. The ratio of the two starting materials was biased to produce gels that had an excess of either alkyne or azide groups to allow for further functionalization of the gels. When injected into mice, unmodified dextran gels primarily accumulated in the liver as well as the lymph nodes, spine, and femur. Further, gels that entered the bone marrow were engulfed by F4/80÷ cells. Bisphosphonates have been used to treat osteoporosis and have been coupled to polymers that have shown bone-tissue localization; thus, this group was added via a second click reaction to gels showing excess alkyne groups. Once modified via a second click reaction to show bisphosphonates groups, the nanogel particles showed significantly less uptake by the liver and reduced uptake by the F4/80÷ cells. The particles also showed binding to both cortical and trabecular bone lining the marrow cavities. Perhaps more interesting was the overall reduction in F4/80÷ cells within the bone marrow, suggesting that they might also provide an anti-osteoporotic effect.

Adv. Mater. 10.1002/adma201202881 (2012).

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