|Cancer cells that break free from a tumor and circulate through the bloodstream spread cancer to other parts of the body. But this process, called metastasis, is extremely difficult to monitor because the circulating tumor cells (CTCs) can account for as few as one in every billion blood cells. Research led by scientists at the RIKEN Advanced Science Institute in Wako, in collaboration with colleagues at the University of California, Los Angeles, and the Institute of Chemistry at the Chinese Academy of Sciences, Beijing, has produced a polymer film that can capture specific CTCs. With further development, the system could help doctors to diagnose an advancing cancer and assess the effectiveness of treatments. The researchers used a small electrical voltage to help deposit a conducting polymer film of poly(3,4-ethylenedioxythiophene) (PEDOT) bearing carboxylic acid groups on to a 2 cm sq glass base. The polymer formed nanodots, tiny bumps that measure 100 to 300 nanometers across, depending on the voltage used (1-1.4 V). Adding a chemical linker to the film allowed it to bind a protein called streptavidin; this protein then joined to an antibody. In turn, the antibody could latch on to an antigen called epithelial cell adhesion molecule (EpCAM), which is produced by most tumor cells. In this way, the film could grab tumor cells from just a few milliliters of a blood sample. The film�s efficiency depends on the size and spacing of the nanodots, and the presence of the capturing antibody. Since these can be easily modified, the same method could be used to make films that sense other types of cells. The next step is to �further optimize the nanostructures of the conducting polymers and understand in more detail the cell-capturing mechanism,� says RIKEN unit leader Hsiao-hua Yu. �We are also currently working on a direct electrical readout of the captured cells, without needing to use a microscope.�
A new rainbow-colored polymer could lead to handheld applications for color identification. Used as a filter for light, this material could form the basis of handheld multispectral imaging devices that identify the �true color� of objects examined. �Such portable technology could have applications in a wide range of fields, from home improvement like matching paint colors, to biomedical imaging, including analyzing colors in medical images to detect disease,� says Alexander N. Cartwright, professor of electrical engineering at the University at Buffalo and one of the researchers who led the study. Because the engineers have developed a one-step, low-cost method to fabricate the polymer, it may be feasible to develop small devices that connect with cell phones to conduct multi-spectral imaging. Because the colors of the rainbow filter are produced as a result of the filter�s surface geometry, and not by some kind of pigment, the colors won�t fade over time. The same principle applies to the color of butterflies� wings and to peacock feathers. To create the rainbow material, students Ke Liu and Huina Xu, co-authors of the study, sandwiched photosensitive pre-polymer syrup between two glass slides. A photosensitive substance is one whose physical properties change upon exposure to light. Next, they directed a laser beam through a curved lens placed above the pre-polymer solution. The lens divided and bent the laser beam into light of continuously varying wavelengths. As this light hit the solution, monomers in the solution began joining into polymers, forming a continuous pattern of ridge-like polymer structures. Larger ridges rose where the light struck with more intensity. The resulting structure is a thin filter that is rainbow-colored when viewed under white light. This is because the periodic polymer layers reflect a continuous spectrum of colors, from red on one end to indigo on the other. The single-step fabrication method-shining a laser light through a curved lens-is affordable and relatively simple. The filter the researchers created was about 25 millimeters long, but the technique they used is scalable: It�s possible to create filters of different sizes by shining the laser through lenses of different sizes.
University of California, San Diego bioengineers have developed a self-healing hydrogel that binds in seconds, as easily as Velcro, and forms a bond strong enough to withstand repeated stretching. The material has numerous potential applications, including medical sutures, targeted drug delivery, industrial sealants and self-healing plastics. Hydrogels are made of linked chains of polymer molecules that form a flexible, jello-like material similar to soft-tissues. Until now, researchers have been unable to develop hydrogels that can rapidly repair themselves when a cut was introduced, limiting their potential applications. The team, led by Varghese, overcame this challenge with the use of "dangling side chain" molecules that extend like fingers on a hand from the primary structure of the hydrogel network and enable them to grasp one another. "Self-healing is one of the most fundamental properties of living tissues that allows them to sustain repeated damage. The benefits of creating such an aqueous self-healing material would be far-reaching in medicine and engineering." To design the side chain molecules of the hydrogel that would enable rapid self-healing, the team performed computer simulations of the hydrogel network. The simulations revealed that the ability of the hydrogel to self-heal depended critically on the length of the side chain molecules, or fingers, and that hydrogels having an optimal length of side chain molecules exhibited the strongest self-healing. When two cylindrical pieces of gels featuring these optimized fingers were placed together in an acidic solution, they stuck together instantly. Varghese's lab further found that by simply adjusting the solution's pH levels up or down, the pieces weld (low pH) and separate (high pH) very easily. The process was successfully repeated numerous times without any reduction in the weld strength. The hydrogel's strength and flexibility in an acidic environment -- similar to that of the stomach -- makes it ideal as an adhesive to heal stomach perforations or for controlled drug delivery to ulcers. Such healing material could also be useful in the field of energy conservation and recycling where self-healing materials could help reduce industrial and consumer waste. Additionally, the rapidity of self-healing in response to acids makes the material a promising candidate to seal leakages from containers containing corrosive acids. To test this theory, her lab cut a hole in the bottom of a plastic container, "healed" it by sealing the hole with the hydrogel and demonstrated that it prevented any leakage of acid through the hole. The team also hopes to engineer other varieties of hydrogels that self-heal at different pH values, thereby extending the applications of such hydrogels beyond acidic conditions. The self-healing hydrogel has several applications, including plastics, industrial sealants, targeted drug delivery and medical sutures.