Comprehensive Computational and Experimental Analysis of Biomaterial toward the Behavior of Imidazolium-Based Ionic Liquids: An Interplay between Hydrophilic and Hydrophobic Interactions

Abstract

To provide insights into the aggregation behavior, hydration tendency and variation in phase transition temperature produced by the addition of ionic liquids (ILs) to poly(N-isopropylacrylamide) (PNIPAM) aqueous solution, systematic physicochemical studies, and molecular dynamic simulations were carried out. The influence of ILs possessing the same [Cl] anion and a set of cations [Cmim] with increasing alkyl chain length such as 1-ethyl-3-methylimidazolium ([Emim]), 1-allyl-3-methylimidazolium ([Amim]), 1-butyl-3-methylimidazolium ([Bmim]), 1-hexyl-3-methylimidazolium ([Hmim]), 1-benzyl-3-methylimidazolium ([Bzmim]), and 1-decyl-3-methylimidazolium ([Dmim]) on the phase transition of PNIPAM was monitored by the aid of UV-visible absorption spectra, fluorescence intensity spectra, viscosity (η), dynamic light scattering (DLS), and Fourier transform infrared (FTIR) spectroscopy. Furthermore, to interpret the direct images and surface morphologies of the PNIPAM-IL aggregates, we performed field emission scanning electron microscopy (FESEM). The overall specific ranking of ILs in preserving the hydration layer around the PNIPAM aqueous solution was [Emim][Cl] > [Amim][Cl] > [Bmim][Cl] > [Hmim][Cl] > [Bzmim][Cl] > [Dmim][Cl]. Moreover, to investigate the molecular mechanism behind the change in the lower critical solution temperature (LCST) of the polymer in the presence of the ILs, a molecular dynamics (MD) study was performed. The MD simulation has clearly shown the reduction in hydration shell of the polymer after interacting with the ILs at their respective LCST. MD study revealed significant changes in polymer conformation because of IL interactions and strongly supports the experimental observation of polymer phase transition at a temperature lower than typical LCST for all the studied ILs. The driving force for concomitant sharp configurational transition has been attributed to the displacement of water molecules on the polymer surface by the ILs because of their hydrophobic interaction with the polymer.

Regulation and Directing Stem Cell Fate by Tissue Engineering Functional Microenvironments: Scaffold Physical and Chemical Cues

“…Hydrophilic biomaterial is more conducive to protein adsorption, promoting the transport and excretion of nutrients. Therefore, it is more conducive to tissue regeneration [121,122]. The chemical composition of the material is similar to that of the host tissue, which is more conducive to the integration of the tissue.…”

Influence of additives on thermoresponsive polymers in aqueous media: a case study of poly(N-isopropylacrylamide)

“…Very recently, Umapathi et al 440 carried out a comprehensive computational and experimental analysis of the behavior of PNI-PAM in response to imidazolium-based ILs such as…”

“…PNIPAM with self-associated hydrogen bonds forms mesoglobules with a ''cotton ball-like'' structure without a clear distribution gradient of water molecules, which does not vary much upon an increase in temperature. 440 For the sake of clarity and distinction between the effects of ILs on the LCST of PNIPAM and PVCL in aqueous solution, 59,440 these structures are represented in Fig. 8.…”

“…The extent of the response of PNIPAM to an IL solute is consistent with the Hofmeister series, [Emim][Cl] being the weakest inducer of the hydrophobic collapse of PNIPAM and [Dmim][Cl] being the strongest inducer of the hydrophobic collapse of PNIPAM in water. 440 It has already been noted that the increase in the LCST of PVCL follows the order of the ILs as follows: 59 The extent to which the LCST increases is observed to be significantly greater for [Dmim][Cl] and less for [Emim][Cl]. 59 As a result, the ILs in an aqueous solution of PNIPAM obey the Hofmeister series; in contrast, the same ILs in an aqueous solution of PVCL do not obey the Hofmeister series.…”

“…As was reported by Cremer et al, 388,470 PNIPAM exhibits a two-step phase transition in the presence of a sufficient concentration of ionic salts. However, Venkatesu et al 438,440 observed a single phase transition of PNIPAM in the presence of a series of ILs.…”