simple method makes cell skeleton mimics

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Page 1: Simple method makes cell skeleton mimics

page 6). But then the $4.2 billion global settlement to compensate implant re­cipients for alleged damages began to unravel. The settlement included im­plant and material makers Bristol-Myers Squibb, Baxter Health Care, 3M, and Dow Corning. It did not in­clude Dow Chemical, which never made implants.

The federal judge overseeing the set­tlement said in June that the fund was not large enough to compensate eligible women among the 248,500 U.S. women who had applied for compensation. Ef­forts to salvage a settlement including Bristol-Myers Squibb and Baxter Health Care, but not Dow Coming, are still un­der way. In April, the same federal judge also decided breast implant suits against Dow Chemical could go to trial under the laws of some states.

Marc Rcisch

Simple method makes cell skeleton mimics No sooner was Halloween over last week than a team of materials chemists at the University of Toronto announced discovery of a quick and simple method for making "skeletons in the beaker/' The "skeletons" are self-assembling inorgan­ic materials whose elaborate shapes and patterns mimic those in the exoskeletons of single-cell marine organisms like dia­toms and radiolaria.

Besides aiding understanding of how nature builds skeletal structures, the work could lead to materials with novel electronic, optical, or other prop­erties, says Toronto materials chemistry professor Geoffrev A. Ozin. Such mate­rials might have an important impact on computer chips, bone replacement materials, industrial catalysts, separa­tion technology, and "smart" materials that respond to changes in their envi­ronment. One chemist familiar with the work calls it "extremely exciting."

Nature uses simple, abundant miner­als such as silica, calcium carbonate, and calcium phosphate to construct "an ex­traordinary array of exquisite architec­tures," Ozin notes. These architectures are seen in bones, teeth, seashells, sea ur­chins, corals, opals, and the microskele-tons of single-cell organisms. The multi­level complexities of these structures have both delighted and puzzled scientists.

But despite much effort, chemists

Colonzed scanning electron microscope images of the surfaces of synthetic aluminophosphate spheroids reveal a pattern of micrometer bowls (left) and of "meshed" bowls that resemble the silica microskeletons of radiolanan, a single-cell organism (right). The tivo patterns are produced using slightly different chemical systems.

haven't come close to matching na­ture's architectural feats. One of the biggest challenges is how to control the complexity and shape of such so-called hierarchical materials.

Now, the tide is beginning to turn, says Ozin, thanks to a "new materials synthesis paradigm" that he, graduate student Scott Oliver, and other cowork­ers have developed over the past three years. The method can "mimic nature's dexterity for sculpting biominerals" with intricate structural features that span three size realms—the nanoscopic (less than 10 A), mesoscopic (10 to 1,000 A), and macroscopic (more than 1,000 A).

Overall, Ozin says, many of the arti­ficial skeletons his group has generated bear a striking resemblance to natural­ly occurring structures, such as the del­icate "lacelike" microskeletons of dia­toms and radiolaria, the exquisitely sculpted spicules of marine sponges, the quiltlike patterns seen in sea ur­chins, and the star-dodecahedral pat­terns of certain rushes.

Ozin's new approach to materials synthesis is detailed in several pa­pers—the first of which was published last week [Nature, 378, 47 (1995)]. Co-authored with Oliver, Alex Kuperman, Neil Coombs, and Alan Lough, the pa­per describes synthesis of well-ordered, stacked aluminophosphate structures using self-assembled organic vesicles (hollow sacs) as templates.

The recipe, notes Nature chemistry ed­itor Philip Ball in the same issue, "sounds alarmingly simple: throw to­gether phosphoric acid and pseudo-boehmite (a hydrated aluminum oxide) in tetraethylene glycol in the presence of an alkylamine; heat, dry, and [crystal­

lize]." The millimeter-sized alumino­phosphate spheroids produced show in­tricate surface features like disks, ridges, pores, platelets, and honeycomb arrays.

Ozin believes that the alkylammoni-um dihydrogen phosphate bilayers, which initially form, interact with the tetraethylene glycol to produce contig­uous arrays of vesicles around which the aluminophosphate is deposited. The bowl-shaped craters on these spher­oids, he thinks, are the imprints of ves­icles packed together like soap bubbles. And the finer scale patterns may arise from precipitation of aluminophos­phate into specific domains in the vesi­cle walls. But this explanation is still speculative.

Although heating is a necessary step in the chemistry detailed in the Nature paper, Ozin tells C&EN that subse­quent papers will describe room-temperature reactions with a number of other chemical systems.

Ron Dagani

Praxair makes hostile bid for CBI Industries Praxair has made a hostile $2.1 billion bid for Oakbrook, Ill-based CBI Indus­tries, parent to carbon dioxide maker Liquid Carbonic. The cash tender offer to CBI stockholders comes after failure of six months of merger negotiations between the two and of a bid to CBTs board of directors.

Liquid Carbonic is the largest carbon dioxide business worldwide. Praxair is a power in the air separation business but lacks carbon dioxide capabilities. Its only major stake in carbon dioxide

NOVEMBER 6, 1995 C&EN 7