Enthalpy-driven micellization of oligocarbonate-fluorene end-functionalized Poly(ethylene glycol)

Orthogonally crosslinked alginate conjugate thermogels with potential for cell encapsulation

Hydrogels with more than one mode of crosslinking have gained interest due to improved control over hydrogel properties such as mechanical strength using multiple stimuli. In this work, sodium alginate was covalently conjugated onto thermoresponsive polyurethanes to prepare hybrid polymers (EPC-Alg) that are responsive to both temperature and Ca²⁺, forming orthogonally crosslinked hydrogels which are non-toxic to cells. Notably, the crosslinks are fully reversible, allowing for gel strength to be modulated via selective removal of either stimulus, or complete deconstruction of the hydrogel network by removing both stimuli. Higher alginate fractions increased the hydrophilicity and Ca²⁺ response of the EPC-Alg hydrogel, enabling tunable modulation of the thermal stability, stiffness and gelation temperatures. The EPC-Alg hydrogel could sustain protein release for a month and encapsulate neural spheroids with high cell viability after 7-day culture, demonstrating feasibility towards 3D cell encapsulation in cell-based biomedical applications such as cell encapsulation and cell therapy.

Molecular mechanism underlying the effects of temperature and pH on the size and surface charge of octenylsuccinated oat β-glucan aggregates

Environmental temperature and pH induced significant changes in the size and surface charge (ζ) of octenylsuccinated oat β-glucan aggregates. The underlying mechanisms were explored by using ¹H-NMR, fluorescence spectra, thermodynamic analysis, and SAXS. At pH 6.5, the size decreased with temperature while ζ continuously increased. With increasing pH at 293 K, parabolic and U-shaped trends were observed in the size and ζ, peaking at pH 8.5 and 6.5, respectively. At any tested pH, the size decreased with temperature. Overall, ζ significantly increased with temperature at each pH. As temperature increased, the compactness of hydrophobic-domains increased while the compactness of hydrophilic-domains decreased. In an acidic environment, both the compactness increased with decreasing pH, but in an alkaline environment, they decreased with pH. The compactness changes were co-driven by enthalpy and entropy and corresponded to changes in the hydrophobic interactions in hydrophobic-domains, hydrogen bonds in hydrophilic-domains and electrostatic repulsions among octenylsuccinate molecules.

Lattice theory of competitive binding: Influence of van der Waals interactions on molecular binding and adsorption to a solid substrate from binary liquid mixtures

The reversible binding of molecules to surfaces is one of the most fundamental processes in condensed fluids, with obvious applications in the molecular separation of materials, chromatographic characterization, and material processing. Motivated in particular by the ubiquitous occurrence of binding processes in molecular biology and self-assembly, we have developed a lattice type theory of competitive molecular binding to solid substrates from binary mixtures of two small molecule liquids that interact between themselves by van der Waals forces in addition to exhibiting binding interactions with the solid surface. The derived theory, in contrast to previously existing theoretical frameworks, enables us to investigate the influence of van der Waals interactions on interfacial binding and selective molecular adsorption. For reference, the classic Langmuir theory of adsorption is recovered when all van der Waals interaction energies between the molecules in the bulk liquid phase and those on the surface are formally set to zero. Illustrative calculations are performed for the binding of molecules to a solid surface from pure liquids and from their binary mixtures. The properties analyzed include the surface coverage θ, the binding transition temperature T_bind, the individual surface coverages, θ_A and θ_C, and the relative surface coverages, σ_AC≡θ_A/θ_C or σ_CA≡θ_C/θ_A. The latter two quantities coincide with the degrees of adsorption directly determined from experimental adsorption measurements. The Langmuir theory is shown to apply formally under a wide range of conditions where the original enthalpies (Δh or Δh_A and Δh_C) and entropies (Δs or Δs_A and Δs_C) of the binding reactions are simply replaced by their respective "effective" counterparts (Δh_eff or Δh_A^eff and Δh_C^eff and Δs_eff or Δs_A^eff and Δs_C^eff), whose values depend on the strength of der Waals interactions and of the "bare" free energy parameters (Δh or Δh_A and Δh_C, and Δs or Δs_A and Δs_C). Numerous instances of entropy-enthalpy compensation between these effective free energy parameters follow from our calculations, confirming previous reports on this phenomenon obtained from experimental studies of molecular binding processes in solution.