Water droplet encased by polymer membrane
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Water droplet encased by polymer membrane
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ncapsulation of micro-objects with a polymeric membrane is desired in many applications such as pharmaceutics and microelectronics. This is currently achieved through three-dimensional (3D) printing, lithography, or microfluidics. These are demanding techniques. For example, microfluidics requires oil–water interfaces that may not be compatible with the chemistry of a drug. To address this issue, the research teams of Paolo Netti of the University of Naples Frederico II and Istituto Italiano di Tecnologia in Naples, Pietro Ferraro of the Institute of Applied Sciences and Intelligent Systems in Pozzuoli, Italy, and their colleagues are proposing an unusual and very efficient alternative, using polymer solutions. The “quick liquid packaging” method they developed was published in Science Advances (doi:10.1126/sciadv.aat5189). The approach stands out for its simplicity. It relies on surface tension and the need for two non-miscible solutions to minimize their interfacial energy. In the process, a polymer solution such as poly(lactic-co-glycolic acid) (PLGA) is dissolved at a given concentration in a solvent, for instance dimethyl carbonate (DMC). PLGA is a common biocompatible polymer, whereas DMC is an organic solvent widely used for biomedical applications. DMC also easily dissolves PLGA, and evaporates slowly. When a hydrophilic object, such as a droplet of water, is placed in the DMC-PLGA solution, a PLGA film forms around it, adopting its form. DMC then diffuses into the water, leaving behind a stiff and highly packed 3D PLGA membrane. Using the same method to produce self-standing PLGA films, the researchers recorded a thickness as small as 1.65 µm, hydrophilicity, transparency, and an
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(a–d) Sequence of the formation of the poly(lactic-co-glycolic acid) (PLGA) film around a hydrogel sphere of diameter ~200 µm with (a) deposition of the PLGA-dimethyl carbonate (DMC) solution (stained in pink), (b) its spreading, (c) the drying of the PLGA by DMC evaporation, forming a membrane, and (d) retrieving the membrane. (e) PLGA film formed around polystyrene spheres ~50 µm in diameter, submerged in water. Credit: Sara Coppola.
elastic modulus of 75 MPa. This is in the range of polyethylene used in most electrical or water pipes. The PLGA film is also permeable to oxygen and other liquid exchanges. These properties were demonstrated by encapsulating a microdroplet containing the worm Caenorhabditis elegans. When encapsulated, the worms decreased their activity, but remained alive for the duration of the experiment, demonstrating the biocompatibility of the process. Biocompatibility was further confirmed by the cultivation of human stem cells directly onto the PLGA membrane. Many other objects could also be packaged, such as polystyrene microparticles, pillar arrays, or even optical microfibers. “Packaging of optical fibers could provide an attractive solution for sensing applications revealed by a change in refractive index,” says Sara Coppola, the first
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