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Squeezable gel separates cells Researchers have developed a cryogel that can separate cells from a mixture without harming their viability.
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of Bath (U.K.). “But the problem is get- spaces of the crystal lattice. “When you issue engineering, stem-cell reting cells off [the] support matrix you’ve thaw the whole thing, the liquid comes search, and other areas need viable out and you have pores where the ice used to immobilize your binding recepcells isolated from complex mixtures. crystals were,” adds Mattiasson. The tor.” Shear stress resulting from fluid However, “If you look into the options flow has been used to generate forces to monoliths can be squeezed 4 –6-fold for cell separation, there aren’t very without being damaged, and good methods,” says Bo Mattiaswhen they are given more son of Lund University (Swebuffer, they swell up again and den). So, Mattiasson and colrevert to their original shape. leagues at Protista Biotechnology The investigators have demonAB (Sweden) and the Indian Instrated that the cryogel monoliths stitute of Technology Kanpur work for an assortment of affinideveloped a special type of gel ty-ligand–receptor pairs, such as made out of polymers that binds IgG–protein-A and metal-ion– cells and then deforms to release chelating agent. The yields of the cells without harming them bound particles or cells from the (Proc. Natl. Acad. Sci. U.S.A. monoliths are 80 – 90%, and the 2006, 103, 849– 854). viability of the released cells is Alois Jungbauer of the Unigenerally >80%. “We first develversity of Natural Resources and oped [the system] for microbial Applied Life Sciences (Austria) cells that are robust, but we have explains that failed attempts were also been looking at cancer cells made in the 1970s to use affinity and lymphocytes, which are more chromatography to purify cells tricky to deal with,” explains from a mixture. “The method Mattiasson. “They have the same worked in principle, but the Scanning electron micrograph of a deformable cryogel for percentage yield and viability.” shortcomings were low capacity, cell purification. Scale bar = 100 µm. (Adapted with permisMechanical compression of low reproducibility, and low resion. Copyright 2006 National Academy of Sciences, U.S.A.) the monoliths isn’t the only way covery of cells,” he says. Jungto recover cells. Mattiasson and his colpull cells off solid supports; however, the bauer adds that the purification procenecessary volumes of liquid end up dilut- leagues have also shown that the addidure described by Mattiasson and his tion of buffer solutions heated up to colleagues “is important because it opens ing the cells, or worse, damaging them. “I think the fundamental approach of 40 °C caused the gel to contract and up a new dimension for adsorptionrelease bound particles. this paper is far more elegant in that it based separation of cells.” The investigators have incorporated doesn’t require any reagents,” continues The new gel is a spongy monolith of their elastic cryogel monoliths into the Hubble. “Mattiasson’s group has used an acrylamide-based material modified 96 wells of a microplate without a bota mechanical change in the physical diwith affinity ligands. The material has tom. A mixture of cells or particles can large (10–100-µm) pores that allow cells mensions of the support to induce the be incubated with the monoliths. The stresses needed to detach the cells withto pass through. If the cells have the apincubation can be done for as long as out reagents.” propriate receptors on their surfaces, needed because capillary forces inside The gel monolith is created by a they bind to the affinity ligands; if they the wells retain the buffer and prevent freezing process. The acrylamide-based don’t, they are washed out of the gel. the monoliths from drying out. After monomers are dissolved and frozen, To recover the bound cells, Mattiasson the incubation, the monoliths can be causing ice crystals to form. Mattiasson and colleagues squeeze the gel. The deformed to release the bound cells or says, “These ice crystals grow until they gel’s physical deformation breaks the particles. Because the plate format can meet another ice crystal. It means you bonds between the cell receptors and be used for quantitative studies, Mattiaffinity ligands, gently releasing the cells. get an interpenetrating network of ice asson points out, “We have a rather crystal connecting to ice crystal.” While “There are a number of ways of putin the frozen state, the acrylamide mono- nice, small analytical system.” a ting a system together to recover cells,” — Rajendrani Mukhopadhyay mers polymerize within the interstitial explains John Hubble of the University © 2006 AMERICAN CHEMICAL SOCIETY
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