Thermoresponsive polymer coating

Several thermoresponsive polymer coatings have been applied in the chromatographic separation of biomolecules. The group of Okano has been active in the field for some time. In recent work, silica beads modified with PNIPAM brushes prepared... 

Fig. 15 Specific protein separation by a smart thermoresponsive polymer coating. Left PNIPAM with immobilized lactose and RCA 120 is below the LCST. The moieties are separated and, therefore, proteins from the mobile phase can bind to RCA120. Right PNIPAM below LCST. Polymer-bound lactose and RCA120 come into close contact and lactose displaces the protein. Reprinted, with permission, from [194]. Copyright (2003) American Chemical Society...

Due to the relative ease of control, temperature is one of the most widely used external stimuli for the synthesis of stimulus-responsive bmshes. In this case, thermoresponsive polymer bmshes from poly(N-isopropylacrylamide) (PNIPAM) are the most intensively studied responsive bmshes that display a lower critical solution temperature (LOST) in a suitable solvent. Below the critical point, the polymer chains interact preferentially with the solvent and adopt a swollen, extended conformation. Above the critical point, the polymer chains collapse as they become more solvophobic. Jayachandran et reported the synthesis of PNIPAM homopolymer and block copolymer brushes on the surface of latex particles by aqueous ATRP. Urey demonstrated that PNIPAM brushes were sensitive to temperature and salt concentration. Zhu et synthesized Au-NPs stabilized with thiol-terminated PNIPAM via the grafting to approach. These thermosensitive Au-NPs exhibit a sharp, reversible, dear opaque transition in solution between 25 and 30 °C. Shan et al. prepared PNIPAM-coated Au-NPs using both grafting to and graft from approaches. Lv et al. prepared dual-sensitive polymer by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from trithiocarbonate groups linked to dextran and sucdnoylation of dextran after polymerization. Such dextran-based dual-sensitive polymer is employed to endow Au-NPs with stability and pH and temperature sensitivity. 

Figure 4 (a) Structure of thermoresponsive diblock copolymer poly(NIPAM-/ /oc/r-NVP) and (b) schematic illustration of the micellization of the block copolymer as a function of temperature and the formation of a polymer-coated gold nanoparticle. Reprinted with permission from Yusa, S. Yamago, S. Sugahara, M. etal. Macromolecules 20Q7, 40, 5907. Copyright 2007 American Chemical Society. 

PNIPAM shows a LCST very close to the body temperature, being therefore one of the most studied thermoresponsive polymers for biomedical applications. Various methods have been used to develop PNIPAM-coated substrates. Some of these surfaces were successfully used to generate cell sheets. However, some PNIPAM-coated surfaces are not suitable for the formation of tissue monolayers as they inhibit cell attachment at temperatures above LCST. Chitosan-based hydrogels have been also... 

Our work employs electrochemically initiated polymerization (EIP) which is an easy and flexible method to produce surface coatings of various kinds. The technique makes use of the decomposition of an electro-active initiator at an electrode to start a free-radical polymerization. The polymer is formed directly at the electrode surface. As a consequence, the films adhere tightly to the surface. Adhesion is based on physisorption of the hydrogel to the metal. Note in this context that EIP is different from electrografting of conductive polymers. In EIP, the initiator is the electro-active species, rather than the monomer. Recently, we reported on the formation of thermoresponsive poly-A -isopropylacrylamide (pNIPAm) hydrogel coatings on gold surfaces based on this approach. ... 

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