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Bacteria make films blush
RESEARCH NEWS
Hydrogels help stem cells differentiate BIOMATERIALS
Better control of the differentiation of human embryonic stem cells (hESCs) could lead to advances in regenerative medicine and tissue engineering. In this process, three-dimensional scaffolds made from cellfriendly biomacromolecules provide some advantages over two-dimensional systems. Now researchers based in the US and Portugal have developed a bioactive hydrogel scaffold that enhances hESC differentiation into the vascular lineage, the cells which make up the embryonic circulatory system [Ferreira et al., Biomaterials (2007) 28, 2706]. The researchers, led by Robert Langer of Massachusetts Institute of Technology, used a cell-compatible photoinitiator to induce a dextran-acrylate monomer to polymerize when exposed to ultraviolet light. They suspended undifferentiated hESCs in the polymerization mixture, and the resulting polysaccharide hydrogel forms a three-dimensional scaffold in which the cells are embedded. After 10 days in the hydrogel, the researchers used fluorescence-
activated cell sorting (FACS) and immunostaining techniques to distinguish the percentage of cells that expressed vascular factors such as KDR/Flk-1 and PECAM1. Compared with spontaneously differentiated embryoid bodies (EBs), a cell culture used to assess the differentiation potential of stem cells, the cells in the hydrogels express markedly higher levels of the vascular endothelial growth factor (VEGF) receptor KDR/Flk-1. When biodegradable microparticles containing VEGF are added to the hydrogel mixture, PECAM1 is also heavily expressed. The researchers also removed hESCs from the hydrogel after 10 days of growth and cultured them for an additional six days in a Petri dish containing VEGF and endothelial differentiation media. They found a much larger percentage of vascular cells in these cultures than in similar controls using EBs. Mark E. Greene
Gram-positive bacteria, such as Bacillus cereus, generally show less pronounced blue-red transitions. The team was also able to distinguish the four types of bacteria apart using film composed of different lipids, calling this technique colorimetric bacterial fingerprinting. In all the tests, however, the bacteria had to be at concentrations approaching saturation (106/ml to 107/ml) to induce sufficient color change, Jelinek notes, but he is optimistic that this can be improved. “We believe that the simplest application would be a ‘yes/no’ test for bacterial presence,” he says.
Mark E. Greene
Mark E. Greene
BIOMATERIALS Fast, cheap, and easy detection of bacteria in trace amounts would be extremely useful in the healthcare, food service, and water treatment industries where bacteria is a daily concern. Now researchers at Ben Gurion University in Israel have developed thin films made of lipids and polydiacetylene (PDA) that change color from blue to red when exposed to bacterial solutions [Scindia et al., Langmuir (2007), doi: 10.1021/la0636208]. The researchers fabricated various heterogeneous LangmuirSchaeffer films colored blue by the PDA. When aliquots changes to red because of conformational changes in the PDA. “Bacteria secrete various substances into their environments through their metabolic processes, communication, and infectivity,” said Raz Jelinek, who led the research. The color change induced in the films results from an assortment of molecules produced and secreted by bacteria, he explains. These molecules can be amphiphilic, membrane active, lipophilic, or highly charged. “We simply observe their cumulative effects when they bind to the film surface and cause the color change.” Jelinek and coworkers looked at common strains of bacteria: Salmonella typhimurium, Bacillus cereus, and two strains of Escherichia coli. They found that both Gram-positive and Gram-negative bacteria induce color changes, but that
18
MAY 2007 | VOLUME 10 | NUMBER 5
BIOMATERIALS When a bone is damaged or diseased, a bone graft can mend the problem. Generally grafts are most effective when the tissue comes from the patient, but bone takes a long time to grow. Synthetic bone implants that can foster tissue regrowth without grafting real bone would be a benefit to regenerative medicine. Canadian and German researchers have used three-dimensional inkjet printing technology to fabricate bioceramic structures in complicated shapes for use as bone implants [Gbureck et al., Adv. Mater. (2007), 19, 795]. Using a two-step process, structures are made out of either brushite or hydroxyapatite with calcium phosphate powders using computer tomography (CT) data or computeraided design (CAD) files. The structures are then loaded with growth factors to promote blood vessel growth prior to surgical implantation in mice. After 15 days, the implants are removed and the extent of blood vessel proliferation in the bioceramics examined. The researchers, led by Jake E. Barralet at McGill University, Canada and Uwe Gbureck at the University of Würzburg, Germany, found that implants loaded with CuSO4, an inorganic growth factor, exhibit tissue growth throughout the structure, while implants loaded with vascular endothelial growth factor (VEGF) show significant tissue penetration, although not as much as with CuSO4. Both promote the growth of microvessels lined with endothelial cells testing positive for CD31, indicating that the tissue is capillary tissue. Vascular proliferation is much more efficient in brushite ceramics than hydroxyapatite ones, owing perhaps to the different microstructure.
Bacteria make films blush
of bacterial solutions are pipetted onto the film, the color
Inkjet printing for bones
Lipid/PDA film before (left) and after (right) exposure to E. coli XL1 cultured for the indicated number of hours. LB: Luria-Bertani growth medium. (© 2007 American Chemical Society.)
Hydrogels help stem cells differentiate BIOMATERIALS
Better control of the differentiation of human embryonic stem cells (hESCs) could lead to advances in regenerative medicine and tissue engineering. In this process, three-dimensional scaffolds made from cellfriendly biomacromolecules provide some advantages over two-dimensional systems. Now researchers based in the US and Portugal have developed a bioactive hydrogel scaffold that enhances hESC differentiation into the vascular lineage, the cells which make up the embryonic circulatory system [Ferreira et al., Biomaterials (2007) 28, 2706]. The researchers, led by Robert Langer of Massachusetts Institute of Technology, used a cell-compatible photoinitiator to induce a dextran-acrylate monomer to polymerize when exposed to ultraviolet light. They suspended undifferentiated hESCs in the polymerization mixture, and the resulting polysaccharide hydrogel forms a three-dimensional scaffold in which the cells are embedded. After 10 days in the hydrogel, the researchers used fluorescence-
activated cell sorting (FACS) and immunostaining techniques to distinguish the percentage of cells that expressed vascular factors such as KDR/Flk-1 and PECAM1. Compared with spontaneously differentiated embryoid bodies (EBs), a cell culture used to assess the differentiation potential of stem cells, the cells in the hydrogels express markedly higher levels of the vascular endothelial growth factor (VEGF) receptor KDR/Flk-1. When biodegradable microparticles containing VEGF are added to the hydrogel mixture, PECAM1 is also heavily expressed. The researchers also removed hESCs from the hydrogel after 10 days of growth and cultured them for an additional six days in a Petri dish containing VEGF and endothelial differentiation media. They found a much larger percentage of vascular cells in these cultures than in similar controls using EBs. Mark E. Greene
Gram-positive bacteria, such as Bacillus cereus, generally show less pronounced blue-red transitions. The team was also able to distinguish the four types of bacteria apart using film composed of different lipids, calling this technique colorimetric bacterial fingerprinting. In all the tests, however, the bacteria had to be at concentrations approaching saturation (106/ml to 107/ml) to induce sufficient color change, Jelinek notes, but he is optimistic that this can be improved. “We believe that the simplest application would be a ‘yes/no’ test for bacterial presence,” he says.
Mark E. Greene
Mark E. Greene
BIOMATERIALS Fast, cheap, and easy detection of bacteria in trace amounts would be extremely useful in the healthcare, food service, and water treatment industries where bacteria is a daily concern. Now researchers at Ben Gurion University in Israel have developed thin films made of lipids and polydiacetylene (PDA) that change color from blue to red when exposed to bacterial solutions [Scindia et al., Langmuir (2007), doi: 10.1021/la0636208]. The researchers fabricated various heterogeneous LangmuirSchaeffer films colored blue by the PDA. When aliquots changes to red because of conformational changes in the PDA. “Bacteria secrete various substances into their environments through their metabolic processes, communication, and infectivity,” said Raz Jelinek, who led the research. The color change induced in the films results from an assortment of molecules produced and secreted by bacteria, he explains. These molecules can be amphiphilic, membrane active, lipophilic, or highly charged. “We simply observe their cumulative effects when they bind to the film surface and cause the color change.” Jelinek and coworkers looked at common strains of bacteria: Salmonella typhimurium, Bacillus cereus, and two strains of Escherichia coli. They found that both Gram-positive and Gram-negative bacteria induce color changes, but that
18
MAY 2007 | VOLUME 10 | NUMBER 5
BIOMATERIALS When a bone is damaged or diseased, a bone graft can mend the problem. Generally grafts are most effective when the tissue comes from the patient, but bone takes a long time to grow. Synthetic bone implants that can foster tissue regrowth without grafting real bone would be a benefit to regenerative medicine. Canadian and German researchers have used three-dimensional inkjet printing technology to fabricate bioceramic structures in complicated shapes for use as bone implants [Gbureck et al., Adv. Mater. (2007), 19, 795]. Using a two-step process, structures are made out of either brushite or hydroxyapatite with calcium phosphate powders using computer tomography (CT) data or computeraided design (CAD) files. The structures are then loaded with growth factors to promote blood vessel growth prior to surgical implantation in mice. After 15 days, the implants are removed and the extent of blood vessel proliferation in the bioceramics examined. The researchers, led by Jake E. Barralet at McGill University, Canada and Uwe Gbureck at the University of Würzburg, Germany, found that implants loaded with CuSO4, an inorganic growth factor, exhibit tissue growth throughout the structure, while implants loaded with vascular endothelial growth factor (VEGF) show significant tissue penetration, although not as much as with CuSO4. Both promote the growth of microvessels lined with endothelial cells testing positive for CD31, indicating that the tissue is capillary tissue. Vascular proliferation is much more efficient in brushite ceramics than hydroxyapatite ones, owing perhaps to the different microstructure.
Bacteria make films blush
of bacterial solutions are pipetted onto the film, the color
Inkjet printing for bones
Lipid/PDA film before (left) and after (right) exposure to E. coli XL1 cultured for the indicated number of hours. LB: Luria-Bertani growth medium. (© 2007 American Chemical Society.)