Thermo-responsive polymers interactions

Moreover, ellipsometric studies allow to unravel peculiarities in the switching kinetics of thermo-responsive copolymers. For example, the variety of interaction mechanisms in a thermo-responsive polymer may lead to the coexistence of different contributions to the swelling process acting on different time scales (Schmaljohann et al., 2004). 

Beyond the elastic modulus, SFM-based colloidal probe measuronents were successfully applied to study interaction forces between thermo-responsive polymers and protein-coated surfaces. This was shown by Cole, Voelcker, Thissen, Horn, and Griesser (2010) with bovine serum albumin-coated probes on PNiPAAm surfaces. Furthermore, time-dependent colloidal probe measuronents on thermo-responsive polymer coatings... 

Physically dependent stimuli include a wide range of variables such as temperature and mechanical deformation, amongst others. However, thermo-responsive polymers are the most relevant class of smart polymers studied because of their enormous variety and their great potential for different biomedical applications. Usually these polymers have both hydrophilic and hydrophobic phases, and undergo abrupt changes in their electrostatic and hydrophobic interactions in an aqueous medium at a critical solution temperature. 

On the other hand, cells and proteins exhibit space- and time-dependent dynamic changes in their conformations and functionalities in the human body. Since the 1990s, dynamic switchable surfaces have been comprehensively studied in order to control the biomolecular dynamics by modification with smart polymers [6], which show changes in their conformations and properties in response to external stimuli. Among them, thermo-responsive poly(AT-isopropylacrylamide) (PNlPA/ m) is one of the most successful models to control the interaction between biomolecules and the grafted substrates by temperature... 

The di-block copolymers of hydrophobic-hydrophiUc PLGA-PEG also showed thermo-responsive behavior with sol-to-gel transition on increase in temperature (Choi et al., 1999). These polymers formed micelles, with a core of hydrophobic PLGA and an outer shell composed of hydrophilic PEG blocks. There is formation of bridged micelles due to interactions between PEG chains of adjacent micelles. The bridge density increases with increase in temperature, leading to aggregation and gelation. 

The di-block system of PLLA-PEG/PDLA-PEG enantiomers also showed thermo-responsive sol-gel transition. However, the solution of individual polymers does not show any gelation with temperature variation. In an aqueous solution, individual copolymers of PLLA-PEG or PDL A-PEG form micelles with a core of PLLA/PDLA and a shell of PEG chains on mixing with each other, these lead to hexagonal crystal formation of polymer chains and gelation at room temperature. With a rise in temperature, hydrophobic interactions increase, which enhances micellar aggregation. These polymers exhibit irreversible gel-to-sol conversion at 75 °C. At higher temperatures... 

Hydrogels have been synthesized based on both chemical (covalent bonds between polymer chains) and physical crosslinking (e.g., polymer chain entanglements, ionic interactions, and hydrogen bonds) methods (Hoffman, 2002) (Figure 1.5). Covalently crosslinked thermo-responsive hydrogels exhibit reversible swelling of the crosslinked... 

Chemomechanical gels that function with phase transition caused by temperature changes Various pol)maers exhibit reversible phase transition in aqueous solution due to temperature variations. Representative examples include poly(vinyl methyl ether) (PVME) and poly(N-isopropylacrylamide) (PNIPAAm) [16, 17]. Common features of thermoresponsive polymers are the coexistence of hydrophilic and hydro-phobic portions in the same polymer chain. Increased hydrophobic interaction at an elevated temperature causes phase separation to take place. Gels obtained by crosslinking these polymers also show thermo-responsivity. The PNIPAAm gel shows the phase transition at 33°C in pure water. It swells at a temperature below the transition and vice versa (see Fig. 5) [18]. 

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