Daniele Parisi

Interpreting the rheological response of thermo-responsive hydrogels is challenging because heating alters both network elasticity and viscoelastic relaxation. Here, we establish a rheology-guided methodology to quantify these effects using a gelatin (Gel)/oxidized sodium alginate (OSA)/phenylboronic acid hydrogel. Two complementary normalized descriptors were introduced: the plateau-modulus loss ratio, quantifying retention of the elastically effective network during heating, and the normalized complex-viscosity ratio, capturing temperature-induced changes in viscoelastic response after accounting for solvent viscosity. Gelatin concentration governed network rigidity and deformability, while the Gel/OSA ratio controlled the balance between thermally labile physical junctions and Gel−OSA interactions. Within the investigated formulation space, a 2:1 Gel/OSA ratio provided the most favorable thermo-mechanical response, combining minimal elastic-network loss with a nearly frequency-independent normalized viscosity response. Self-healing, reprocessability, adhesion, and swelling tests further demonstrated multifunctional performance. These descriptors provide a quantitative framework for comparing thermo-responsive polymer networks and guiding formulation selection.

Chitosan-based ionogels are promising materials for extrusion-based processing, yet the influence of degree of deacetylation (DDA) on gelation and printability remains poorly understood. Here, chitosans with different DDA and molecular weight were dissolved in 1-ethyl-3-methylimidazolium acetate (EMImAc) to establish structure–network–processing relationships through rheology and 3D printing. Oscillatory rheology revealed distinct DDA-dependent pathways toward network formation. Chitosan with 76% DDA developed elastic domains at lower concentrations, consistent with associations involving residual acetylated units, hydrogen bonding, hydrophobic interactions, and residual ordered regions. These domains remained weakly interconnected until increasing chain overlap established long-range connectivity. In contrast, 90% DDA chitosan exhibited delayed but highly cooperative network development. Despite comparable complex viscosities, only the 90% DDA ionogels exhibited homogeneous extrusion and high printing fidelity. Nonlinear rheology revealed that lower-DDA ionogels generated larger first normal stress differences and greater structural recovery, indicating a resilient network that accumulated recoverable elastic stresses and hindered stable extrusion. The best printing performance was achieved with 4.5 wt.% 890 kDa chitosan (90% DDA). Overall, DDA governs network formation and the resulting nonlinear rheological response, ultimately determining extrusion stability and printability.

Polyelectrolyte complexes (PECs), formed by electrostatic association of oppositely charged polyelectrolytes, are promising low-environmental-impact materials. However, their extreme brittleness in the absence of water and a general lack of stimuli-responsive functionality severely limit practical applications. Here, we introduce a strategy to overcome both limitations by designing liquid crystalline polyelectrolyte complexes (LCPECs). Main-chain liquid crystalline (LC) polyanions with systematically varied charge densities and neutral flexible domains are first synthesized via a facile one-pot two-step polymerization combining Michael addition and thiol–ene chemistry. The LC polyanions are then complexed with poly(diallyldimethylammonium chloride) (PDADMAC) to form LCPECs with tunable properties. X-ray scattering reveals a fractal-like network with nanoscale phase separation between electrostatically associated and neutral flexible domains, alongside nematic ordering of the mesogens. Increasing the neutral monomer content lowers the glass transition temperature from 58 °C to −10 °C and transforms the mechanical response from stiff and brittle to soft and highly stretchable, achieving an elongation of 1160%, far exceeding the stretchability of any previously reported water- and salt-free PEC. Rheological analysis shows that higher charge density raises both moduli and delays chain relaxation, confirming that electrostatic interactions function as tunable physical cross-links. Uniaxial stretching induces macroscopic mesogen alignment, enabling reversible thermal actuation with 20% dimensional change upon cycling across the LC–isotropic transition. Furthermore, well-defined mesh structures are successfully prepared by melt electrowriting, demonstrating the processability of these materials through advanced additive manufacturing. This work establishes tuning of ionic cross-link density and backbone flexibility as a general strategy for transforming inherently brittle PECs into mechanically robust, stimuli-responsive, and processable materials.

Spider silk spinning begins with coacervation into a dense protein phase that organizes into liquid crystalline domains. Changes in salt concentration, together with shear forces, then direct the alignment needed to form highly ordered fibers. Inspired by this process, we developed a fully synthetic system of liquid crystalline complex coacervates designed to replicate the hierarchical organization and alignment mechanisms of spider silk, focusing on processing pathways. We show that salt concentration (tetrabutylammonium bromide, TBAB) governs the balance between isotropic and liquid crystalline states, with coacervation suppressed above 0.5 M, smectic order stabilized at ≤0.2 M, and isotropic chain networks prevailing at intermediate concentrations. Crucially, the degree of shear alignment depends strongly on salt: higher salt concentrations accelerate molecular relaxation and raise the threshold shear rate required to induce ordering, echoing the cooperative role of the ion composition and shear in natural silk spinning. Rheological and X-ray scattering measurements confirm that this salt-shear interplay dictates both the viscoelastic response and the molecular anisotropy. Finally, we demonstrate directional alignment through stretching and extrusion-based 3D printing and show that the unique tunability of salt concentration provides direct control over both processability and shear-induced alignment, offering a powerful biomimetic route to anisotropic material design.

Healthcare relies heavily on single-use plastics, creating major waste, as shown in the figure by Maria Koijck (copyright). Biobased biodegradable plastics could reduce this impact, but only if recycling and waste management are redesigned.

The mechanics of complex coacervates are governed not only by electrostatic interactions but also by polymer molecular weight ( M _w ) and chain stiffness, yet their combined role remains insufficiently resolved for biopolyelectrolytes.

Long-range electrostatic interactions provide unique opportunities to tune the conformation and phase behavior of polymeric micelles and soft colloids in solution, but their effects remain understudied due to the higher synthesis, characterization, and simulation complexity. We recently showed that micelles with long, charged polymer arms exhibit unique softness and glassy behavior at varying concentrations due to long-range electrostatic interactions, and developed a molecular dynamics model to validate the experimental results. Here we further explore our new system, and we investigate mixtures of highly charged star polyelectrolytes (SPEs, mimicking spherical micelles) and oppositely charged linear polyelectrolytes (LPEs) using molecular dynamics simulations and rheological validation. SPE size and conformation are strongly affected by LPE addition, which introduces charge neutralization within the SPEs’ bounding spheres, leading to shrinkage or expansion depending on the LPE length and concentration. Long LPEs form bridges between multiple SPEs, inducing clustering and promoting liquid–liquid phase separation at high charge ratios, triggering a glass-to-coacervate transition. Experimental rheology confirms that increasing the LPE initially decreases, then drastically increases viscosity, together with visual phase separation of the system, validating the simulation results. These findings highlight the interplay between electrostatic interactions, chain entropy, and packing effects, offering insights into how polyelectrolyte mixtures can be tuned for controlled complexation and phase behavior in soft materials design.