A single NIH 3T3 fibroblast on a teardrop island, surrounded by a cell‐resistant background, extends lamellipodia from both sharp and blunt ends. However, the staggered arrangement of the islands and preferential extension of lamellipodia parallel to the cell body only permit attachment of lamellipodia extended from the blunt end, resulting in exclusive counterclockwise migration (the figure is ca. 200 μm wide).
We investigate the polymerization kinetics of microemulsions prepared with the cationic surfactant dodecyltrimethylammonium bromide and the hydrophobic monomers n-butyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, and styrene. Our previous model for microemulsion polymerization kinetics cannot account for the kinetics of these systems. Using the results of smallangle neutron scattering monomer partitioning studies and an extended kinetic model to analyze the data, the failure of the original kinetic model is shown to be due to a combination of nonlinear monomer partitioning, nonnegligible bimolecular termination, and, in some cases, diffusion limitations to propagation.
Liquid-core capsules have wide-ranging applications in the high-efficiency encapsulation and controlled release of drugs, dyes, enzymes, and other substrates. Their great utility has driven the rapid development of various preparation techniques. However, there remains no convenient technique for the preparation of submicrometer liquid-core capsules with shell thicknesses less than 100 nm. Here, we demonstrate a new interfacial free-radical polymerization approach for the straightforward preparation of liquid-core polymer capsules. Conceptually, this interfacial free-radical polymerization is analogous to the classical "nylon rope trick" wherein hydrophobic and hydrophilic monomers alternately copolymerize to constrain the polymerization at interfaces, but its free-radical mechanism allows precise control of initiation, which makes it possible to finely disperse the immiscible phases prior to polymerization.
Controlling the spatial organization of cells is a critical step toward engineering tissues with distributed networks of blood vessels or nerve cells. Here we report a new soft-lithography-based approach for micropatterning proteins and cells on the surface of biodegradable chitosan substrates that are more applicable to engineering tissues than the gold, silver, glass, or silicone substrates currently used in cell micropatterning studies. In this approach, we use random copolymers of oligo(ethylene glycol) methacrylate (OEGMA), which resists protein and cell adsorption, and methacrylic acid (MA), which adheres strongly onto the chitosan substrate via acid-base interactions, to form stable protein and cell resistant micropatterns on chitosan surfaces. At optimal ratios of OEGMA to MA, copolymers are formed that exhibit superior long-term resistance to protein adsorption and cell adhesion even under cell culture conditions. Spatial control of cell organization and alignment using OEGMA/MA micropatterned chitosan is demonstrated using human microvascular endothelial cells.
Polymerization of n-hexyl methacrylate
(C6MA) in aqueous microemulsions made with
mixed
dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium
bromide (DDAB) surfactants yields very small (∼30 nm) latex particles of high molecular
weight polymer. The results of an
online small-angle neutron scattering (SANS) experiment have verified
some of the assumptions of a
simple but accurate kinetic model that has been recently proposed for
aqueous microemulsion polymerization. The SANS results also support the predictions of an
analytical model that describes the evolution
of the chain length and particle size distribution throughout the
polymerization. During the microemulsion
polymerization of C6MA, the monomer does not
significantly swell the polymer particles. A model of
the
reacting particle as a polymer core surrounded by a monomer-rich shell
is consistent with both the kinetic
and SANS data if the monomer concentration in the shell is equal to
that in the core of the swollen
micelles
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