Temperature-responsive polymer

Abstract: Poly(N-isopropyl acrylamide) (PIPAAm) demonstrated a fully expanded chain conformation below 32 degrees C and a collapsed, compact conformation at high temperatures. This unique temperature responsive polymer was grafted onto surfaces of commercial polystyrene dishes and used as temperature switches for creating hydrophilic surfaces below 32 degrees C and hydrophobic surfaces above 32 degrees C. Cell attachment and the growth of bovine endothelial cells and rat hepatocytes on PIPAAm-grafted surfaces at 37 degrees C demonstrated similar behavior to the commercialized culture dishes. Both cell types were observed to detach from the PIPAAm-grafted surface simply by reducing the temperature below the polymer transition temperature (collapse). Cells recovered by this method maintained substrate adhesivity, growth, and secretion activities nearly identical to those found in primary cultured cells in contrast to the compromised function found in cultured cells damaged by trypsinization. These results provide strong evidence that PIPAAm-grafted surfaces, as thermal switches are very effective for reversing cell attachment and detachment without cell damage. Properties of cell culture surfaces can be readily transformed by this technique reversibly into hydrophilic and hydrophobic coatings of PIPAAm-grafted polymers.

Abstract: A new concept in chromatography is proposed that utilizes a temperature-responsive surface with a constant aqueous mobile phase. The surface of the silica stationary phase in high-performance liquid chromatography (HPLC) has been modified with temperature-responsive polymers to exhibit temperature-controlled hydrophilic/hydrophobic changes. Poly(N-isopropylacrylamide) (PIPAAm) was grafted onto (aminopropyl)silica using an activated ester-amine coupling method. These grafted silica surfaces show hydrophilic properties at lower temperatures which, as temperature increases, transform to hydrophobic surface properties. The elution profile of five mixed steroids on an HPLC column packed with this material depends largely on the temperature of the aqueous mobile phase. Retention times increase with increasing temperature without any change in the eluent. Changes in the retention times of hydrophobic steroids were larger than those for hydrophilic steroids. The temperature-responsive interaction between PIPAAm-modified silica and these steroids is proposed to result from changes in the surface properties of the HPLC stationary phase by the transition of hydrophilic/hydrophobic surface-grafted IPAAm polymers. We demonstrate a novel and useful new chromatography system in which surface properties and the resulting function of the HPLC stationary phase are controlled by external temperature changes. This method should be effective in biological and biomedical separations of peptides and proteins using only aqueous mobile phases.

Abstract: A very straightforward approach was developed to synthesize pegylated thermoresponsive core-shell nanoparticles in a minimum of steps, directly in water. It is based on RAFT-controlled radical crosslinking copolymerization of N,N-diethylacrylamide (DEAAm) and N,N′-methylene bisacrylamide (MBA) in aqueous dispersion polymerization. Because DEAAm is water-soluble and poly(N,N-diethylacrylamide) (PDEAAm) exhibits a lower critical solution temperature at 32 °C, the initial medium was homogeneous, whereas the polymer formed a separate phase at the reaction temperature. The first macroRAFT agent was a surface-active trithiocarbonate based on a hydrophilic poly(ethylene oxide) block and a hydrophobic dodecyl chain. It was further extented with N,N-dimethylacrylamide (DMAAm) to target macroRAFT agents with increasing chain length. All macroRAFT agents provided excellent control over the aqueous dispersion homopolymerization of DEAAm. When they were used in the radical crosslinking copolymerization of DEAAm and MBA, the stability and size of the resulting gel particles were found to depend strongly on the chain length of the macroRAFT agent, on the concentrations of both the monomer and the crosslinker, and on the process (one step or two steps). The best-suited experimental conditions to reach thermosensitive hydrogels with nanometric size and well-defined surface properties were determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2373–2390, 2009

Abstract: Materials exhibiting antibacterial properties at room temperature and turning biocompatible and non-adhesive for in vivo conditions, are extremely attractive for devices that have to be ultimately introduced in living beings. Indeed, infections related to the use of invasive biomedical and medical items are still one of the main medical complications that cause high rates of mortality. [ 1 ] Despite sanitation protocols, a well-identifi ed route for patient bacterial infection is transmission through contaminated instruments such as intubation tubes, catheters, surgical drains or endoscopes that bypass the natural protective barriers of the body. [ 1 ]