Probing the Structural Dynamics of the Coil–Globule Transition of Thermosensitive Nanocomposite Hydrogels

Abstract

Nanocomposite hydrogels have emerged to exhibit multipurpose properties, boosting especially the biomaterial field. However, the development and characterization of these materials can be a challenge, especially stimuli-sensitive materials with dynamic properties in response to external stimuli. By employing UV–vis spectroscopy and NMR relaxation techniques, we could outline the formation and behavior of thermosensitive nanocomposites obtained by in situ polymerization of poly­(N-vinylcaprolactam) (PNVCL) and mesoporous silica nanofibers under temperature stimuli. For instance, inorganic nanoparticles covalently linked to PNVCL changed the pattern of temperature-induced phase transition despite showing similar critical temperatures to neat PNVCL. Thermodynamic parameters indicated the formation of an interconnected system of silica and polymer chains with reduced enthalpic contribution and mobility. The investigation of water molecule and polymer segment motions also revealed that the absorption and release of water happened in a wider temperature range for the nanocomposites, and the polymer segments respond in different ways during the phase transition in the presence of silica. This set of techniques was essential to reveal the polymer motions and structural features in nanocomposite hydrogels under temperature stimuli, demonstrating its potential use as experimental guideline to study multicomponent nanocomposites with diverse functionalities and dynamic properties.

Analyzing the Effects of Silica Nanospheres on the Sol–Gel Transition Profile of Thermosensitive Hydrogels

“…Sala et al 21 also reported a decrease in the transition enthalpy with the insertion of 1% and 5% of silica nanofibers. However, it is possible to see in Table 2 that there is no statistical difference between nanocomposites synthesized with 1% and 5% of silica nanospheres with 80 and 330 nm.…”

“…This behavior can be correlated to changes in the solvation of the polymer−silica system and thereby the hydrophilic/hydrophobic interactions during the coil−globule transition, as previously demonstrated. 21 The entropy of a mixture of the PNVCL solution is decreased with an increase in temperature, causing the polymer chains to start to agglomerate, leading to phase separation. The presence of nanoparticles in the polymeric matrix may disrupt the interaction between the water molecules and the polymer chains, facilitating the agglomeration of globules at temperatures below the T cp , decreasing the transmittance.…”

“…properties of nanocomposites as well as drug delivery vehicles. 18−20 In a previous work by our group, 21 PNVCL nanocomposites with 1 and 5% w/w of mesoporous silica nanofibers were studied. The presence of silica altered the sol−gel transition pattern, which occurred in a diffuse manner due to the formation of intermediate coil−globule states between the silica and the PNVCL systems.…”

“…These materials showed a volume phase transition over a wide temperature range, similar to the nanocomposites of PNVCL and silica nanofibers. 21 As the temperature increased, the segments of NIPAM began to expel water molecules from the polymeric network due to the increase in hydrophobicity, initiating microscopic transitions. Then, the macroscopic transition occurred with the formation of intra-and intermolecular hydrogen bonds between the polymer chains, resulting in major particle agglomeration and hydrogel formation.…”

Multifunctional Arabinoxylan-functionalized-Graphene Oxide Based Composite Hydrogel for Skin Tissue Engineering

“…The wetting behavior changed from hydrophilic to hydrophobic as the cross-linker quantity was increased, owing to increased and close packing that changed surface characteristics. Because of the dense packing and higher cross-linking, there is less hydrogen bonding available to create functional groups ( Sala et al, 2021 ). As a result, the hydrogel sample (AGP-1) was found to have the highest hydrophilicity (64.50°) with minimal cross-linking and the highest hydrophobicity (AGP-4) with maximal cross-linking (110.80°) as presented in Figure 3 .…”