Injectable hydrogels based on alginates grafted with LCST side-chains of different chemistry

A homologous series of thermoassociating copolymers was prepared by grafting onto alginates different amounts of three different temperature responsive polymers: poly(N-isopropylacrylamide), poly(di(ethylene glycol)methacrylate) and poly(ethylene oxide-co-propylene oxide). From a large set of analytical techniques combining rheology, calorimetry, NMR and SAXS, the relevant parameters controlling the sol/gel transition and the gel properties, mainly the degree of entanglement of macromolecules and the fraction of responsive stickers, were highlighted and interpreted objectively by considering the particularities of the phase diagrams of LCST polymers. Complementary analyses were implemented to investigate adhesiveness, injectabilty, gel swelling and molecular release in physiological environment of thermogelling formulations. In particular, it is shown that steady shear experiments allow to predict the injection forces by taking into account the characteristics of the system (syringe and needle), and that the rapid gelation of the formulations when they are heated at 37 °C delays the release of small molecules into the environment. The overall set of data is discussed in the framework of scaling relations in order to draw quantitative guidelines for the design of injectable thermoresponsive hydrogels.

100th Anniversary of Macromolecular Science Viewpoint: Modeling and Simulation of Macromolecules with Hydrogen Bonds: Challenges, Successes, and Opportunities

Macromolecular materials with directional interactions such as hydrogen bonds exhibit numerous attractive features in terms of structure, thermodynamics, and dynamics. Besides enabling precise tuning of desirable geometries in the assembled state (e.g., programmable coordination numbers depending on the valency of the directional interaction), mixing in a blend/composite through stabilization via hydrogen bonds between the various components, hydrogen bonds can also impart responsiveness to external stimuli (e.g., temperature, pH). In biomacromolecules (e.g., proteins, DNA, polysaccharides), hydrogen bonds play a key role in stabilizing secondary and tertiary structures, which in turn define the function of these macromolecules. In this Viewpoint, I present the challenges, successes, and opportunities for molecular modeling and simulations to conduct fundamental and application-focused research on macromolecular materials with hydrogen bonding interactions. The past successes and limitations of atomistic simulations are discussed first, followed by highlights from recent developments in coarse-grained modeling and their use in studies of (synthetic and biologically relevant) macromolecular materials. Model development focused on polynucleotides (e.g., DNA, RNA, etc.), polypeptides, polysaccharides, and synthetic polymers at experimentally relevant conditions are highlighted. This viewpoint ends with potential future directions for macromolecular modeling and simulations with other types of directional interactions beyond hydrogen bonding.

Inclusion Complexation between α-Cyclodextrin and Oligo(ethylene glycol) Methyl Ether Methacrylate

The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.

The role of hydrophobic hydration in the LCST behaviour of POEGMA300 by all-atom molecular dynamics simulations

The role of hydrophobic hydration in the LCST phase transition of POEGMA₃₀₀ by means of the breakage of cage-like water formations around the side chains.