Despite the significant advancements in intervertebral disc prostheses in recent years ^[1], they remain, to this day, the least favored medical solution among surgeons and the least appreciated by patients for treating damaged discs ^[2]. The current prostheses are still unable to accurately replicate several fundamental mechanical properties of the natural disc, such as auxeticity, energy absorption, and nonlinear stiffness ^[3]. This inability prevents them from mimicking correctly the natural mechanical behavior of the disc, adversely affecting the post-operative health and well-being of patients. To address these challenges, the current study explores novel bioinspired lattice-based polymeric architected structures, designed to mimic the complex mechanical behavior of the human annulus fibrosus. New cellular structures are developed to introduce complex mechanical functionalities into the lattices, whose performance is investigated using different polymers (hydrogels such as poly(ethylene glycol) diacrylate, alginate and gelatin methacrylate, and soft thermoplastics such as thermoplastic polyurethane and polylactide) to assess the coupled influence of cellular architecture and material microstructure. By tailoring cellular geometry, thickness, and material, these structures can reproduce nonlinear stiffness and axial-circumferential behaviors, including regional variations observed in natural discs. This precise control leads to sophisticated behaviors that conventional prostheses cannot achieve. The first derived replacement systems succeeded in replicating key mechanical characteristics of the natural annulus fibrosus, including auxeticity, nonlinear stiffness and region-dependent responses. These biomimetic lattices provide a promising pathway for the development of personalized, high-performance disc prostheses.

References:
1. Song, Guangsheng, et al. "Total disc replacement devices: Structure, material, fabrication, and properties." Prog. Mater. Sci. (2023): 101189.
2. Zechmeister, Ingrid, et al. "Artificial total disc replacement versus fusion for the cervical spine: a systematic review." Eur. Spine J. 20 (2011): 177-184.
3. Kandil, Karim, et al. "A novel bio-inspired hydrogel-based lattice structure to mechanically mimic human annulus fibrosus: A finite element study." Int. J. Mech. Sci. 211 (2021): 106775.

This work advances the modeling of complex polymer systems by developing physically based constitutive frameworks capable of predicting the nonlinear, anisotropic, and history-dependent mechanical behavior of multi-network materials such as double-network hydrogels and filled elastomers [1-2]. These soft materials exhibit remarkable toughness and resilience due to intricate energy dissipation mechanisms involving chain scission, interfacial sliding, filler debonding, and viscoelastic relaxation. A multiscale modeling approach is proposed, combining molecular-level statistical mechanics with homogenization techniques to link microscale deformation mechanisms to macroscopic responses. The resulting models account for anisotropic softening, directional damage, and the influence of deformation history, achieving excellent agreement with multiaxial experimental observations. For filled elastomers, the framework incorporates visco-hyperelastic effects by representing the material as coupled elastic-viscous networks subjected to strain amplification from the filler phase. This description captures key phenomena such as the Mullins effect, hysteresis, and the evolution of anisotropy under cyclic loading. A comprehensive formulation is also proposed to explicitly represent the interaction between polymer and filler subnetworks, integrating mechanisms like chain-cluster debonding and interfacial viscous sliding. The finite element implementation of the hydrogel model demonstrates its robustness for simulating heterogeneous deformation fields. Altogether, this research establishes a unified and predictive basis for the design of architectured polymer materials, opening pathways toward multiphysics extensions coupling mechanical, electrical, or thermal effects for advanced functional applications.

References:

1. Ogouari, L., Guo, Q., Zaïri, F., Mai, T.-T., Gong, J.P., Urayama, K., 2024. A multiscale model for the multiaxial anisotropic damage of double-network gels. Mechanics of Materials 105058.
2. Ogouari, L., Guo, Q., Zaïri, F., Mai, T.-T., Urayama, K., 2024. An anisotropic damage visco-hyperelastic model for multiaxial stress-strain response and energy dissipation in filled rubber. International Journal of Plasticity 182, 104111.

The aggregation behavior of π-conjugated molecules critically influences their excited-state dynamics and thus their performance in optoelectronic applications. In this work, we deal with the title substance (hereafter referred to as Tt), used as a unimer for metallo-supramolecular polymers, and study the dynamics of its photophysical properties in various solvents using femtosecond transient absorption spectroscopy (fs-TA), steady-state absorption and emission spectroscopy, and dynamic light scattering (DLS). Experimental studies are completed with DFT and time-dependent DFT calculations, providing more detailed insight into the electronic structure of Tt and excited-state processes in it.

In aprotic solvents such as toluene and DMSO, Tt predominantly exists as free solvated molecules, exhibiting long-lived excited states with lifetimes extending up to hundreds of picoseconds. In contrast, different types of aggregation behavior have been observed in proton-donating solvents. In pure and aqueous hexafluoropropan-2-ol, HFIP and HFIP (aq), the formation of nanoaggregates ranging from 12 to over 1000 nm in size has been observed by DLS. These aggregates exhibit blue-shifted absorption bands characteristic of H-type aggregation and show significantly accelerated excited-state decay due to enhanced nonradiative relaxation pathways. Interestingly, in the more acidic solvent mixture of pH 1 (HFIP/0.01 M HClO₄ in H₂O (4:1)), a red-shifted absorption band characteristic of J-type aggregation has been observed.

Solvent polarity and hydrogen bonding strongly modulate excited-state lifetimes, with the fastest internal conversion observed in acidic HFIP/water mixtures. Solvation dynamics in HFIP/0.01 M HClO₄-H₂O mixtures completed within 1.2 ps, further influencing relaxation processes. In the most acidic environment tested (HFIP/0.01 M HClO₄ in H₂O (4:1); pH=1), relaxation is considerably faster than in other solvent systems due to hydrogen bonding.

The combination of experimental and theoretical analyses reveals how hydrogen bonding and aggregation govern the photodynamics of Tt, providing valuable insights for designing polymeric materials with tailored optoelectronic properties.

This study presents a comparative investigation of ultrafast photophysical processes in thin-film of eosin Y (EY) and palladium (II) octaethylporphyrin (PdOEP) as triplet sensitizers, combined with bis(terpyridine-4'-yl) terthiophene (T) as an annihilator. Thin films were fabricated by spin-coating on quartz substrates using chloroform (CHCl₃) and hexafluoroisopropanol (HFIP) solvents. Excitation wavelengths were chosen based on the absorption maxima of the individual and mixed components.

Steady-state spectroscopy revealed distinct fluorescence and absorption features, with emission maxima ranging from 600 to 750 nm. Transient absorption spectroscopy (TAS) further confirmed efficient triplet energy transfer from both sensitizers to T, as evidenced by the characteristic ground-state bleaching (GSB) and excited-state absorption (ESA) signals spanning the 400-700 nm range. Global analysis of TAS data revealed multiexponential decay dynamics, with EY+T and PdOEP+T mixtures showing significantly extended triplet lifetimes compared to isolated components. Specifically, the EY+T system (1:4 ratio in HFIP, spin-coated) exhibited a rapid initial decay followed by a long-lived state exceeding 6 ns, while PdOEP+T (1:4 ratio in HFIP, spin-coated) displayed broader ESA bands related to triplet–triplet transitions.

These results demonstrate the effectiveness of EY and PdOEP as sensitizers for triplet state generation and energy transfer to T. The insights gained provide valuable guidance for optimizing triplet–triplet annihilation mechanisms in next-generation optoelectronic and photonic devices.

In the tire industry, tackifying resins are essential ingredients because they modulate green tack and green strength of the uncured rubbers, facilitating their manipulation and preventing creep and tear of the final products. From a molecular perspective, the presence of the resin alters the dynamics of the polymer chain, resulting in the modification of the rheological and viscoelastic behaviour of the rubber compounds. Since the mechanical response of the final compounds varies depending on the type of resin added, it is important to dissect the molecular origins of such differences. In this research, we compared the effect of a natural- and a petroleum-origin resins on the dynamics of Styrene-Butadiene Rubber (SBR) in compounds of interest for the tyre industry. To this end, we employed a variety of Solid-State Nuclear Magnetic Resonance experiments (SS-NMR) at variable temperature. These include 1H Field Cycling NMR, DIPolar chemical SHIFT correlation and Centerband Only Detection of Exchange experiments. These techniques enabled the study of polymer dynamics on a wide range of motion time scales, form the fast segmental motions related to glass transition to the slower and collective motions of the polymer chains. In addition, measurements of ¹H T₁ and T_1ρ relaxation times provided information on the polymer-resin miscibility on the nanometer scale, which is essential for achieving compounds with the desired mechanical properties. Dipolar-Filtered Magic Sandwich Echo experiments were also carried out to obtain information on the presence of domains with different degree of mobility, as well as on the onset of their motions with temperature. The SS-NMR results were compared with those from dynamic-mechanical, rheometric, calorimetric and chemical characterization. This approach provided valuable information to elucidate the complex relationship between molecular and macroscopic properties in rubber compounds, aiding the design of formulations with improved performances.

Esters of dicarboxylic acids and oxyethylated alcohols are an important class of plasticizers. Plasticizers based on them are considered environmentally friendly. Plasticization remains the key method of PVC modification. Studying the process of processing PVC into materials by melting requires knowledge of the relationship between the process parameters and the properties of the flow. For this purpose, measurement of rheological properties using the melt fluidity index is widely used. Two esters butylbutoxyethyladipate and decylbutoxyethyladipate were synthesized and their properties were investigated. Evaluation of the effect of the ether structure on intermolecular interactions and the magnitude of the energy barrier of the transition state revealed a clear dependence of the properties on the length of the alkyl radical. Thus, the introduction of BBEA reduces the viscosity of the PVC melt by 30-50% compared to DOF, for example, at 190 °C and 50 wt. The MFI of a PVC composition with a BBEA content is 7.0 g/10 min versus 1.4 g/10 min for a composition with DOP. There is a pronounced temperature dependence of viscosity for compositions with BBEA, as a result of the high mobility of PVC chains in its presence and the thermodynamic stability of the mixture, and a less pronounced dependence using DBEA due to limited conformational mobility. Compositions with BBEA retain their white color up to 195°C (at 50-70 wt.h.), which is associated with better homogenization and screening of labile chlorine-containing PVC groups. When using plasticizers, an enthalpy-entropy compensation effect was revealed: high ΔH values of the viscous flow of PVC melts are accompanied by less negative ΔS. The Gibbs energy (ΔG) remains stable (1.85–2.15 kJ/g), confirming the universality of the flow mechanism. The concentration dependence of the thermodynamic parameters is to reduce Ea by 20-40% with an increase in the plasticizer content to 70 wt.h.

In this study, the electronic and optical properties of polyaniline were systematically investigated using density functional theory (DFT) within the Vienna Ab Initio Simulation Package (VASP). Structural optimization was performed to ensure the stability of the polymer configuration prior to electronic and optical analyses. The calculations revealed a characteristic density of states and an electronic band gap of approximately 3.77 eV, indicating semiconducting behavior with potential for optoelectronic applications. From an optical standpoint, several key parameters were extracted, including the absorption coefficient and dielectric function, both showing a pronounced absorption peak in the ultraviolet (UV) region, suggesting strong photon–matter interaction in this energy range.

The strong UV absorption, combined with the wide band gap, positions polyaniline as an excellent candidate for a range of optoelectronic devices. These properties make it particularly attractive for organic solar cells, UV photodetectors, optical sensors, and light-emitting devices, where materials with high optical stability and strong absorption are critical for efficient performance. Additionally, the intrinsic structural tunability, high environmental stability, and chemical versatility of polyaniline enable easy processing, doping, and functionalization, broadening its applicability in flexible electronics, wearable technologies, and advanced photonic systems.

Overall, the results highlight polyaniline as a promising and versatile material for next-generation optoelectronic and photonic technologies, offering a desirable balance between performance, scalability, and cost-effectiveness. Future research directions could involve experimental validation, exploration of doped or composite forms of polyaniline, and investigation of device-level integration to fully harness its potential for commercial applications.

Mixtures of oppositely charged polyelectrolytes and surfactants play a crucial role in various industrial applications,. The interactions between these components influence key physicochemical properties, making it essential to develop a thorough understanding of the mechanisms governing their association. In particular, their bulk interactions and adsorption at fluid/fluid interfaces are of great interest due to their impact on emulsification, foaming, and other stabilization processes. However, the study of these systems remains challenging, as their complexation is often influenced by nonequilibrium phenomena, leading to kinetically trapped aggregates that exhibit distinct physicochemical properties compared to their equilibrium counterparts.

Among the many polyelectrolyte–surfactant systems, the interaction between sodium alginate (SA) and hexadecyltrimethylammonium bromide (CTAB) serves as a model for investigating these phenomena. Sodium alginate, a natural anionic polysaccharide, interacts strongly with the cationic surfactant CTAB, forming aggregates with diverse morphologies depending on factors such as concentration, ionic strength, and mixing protocol. The resulting structures exhibit a wide range of sizes and interfacial behaviors, significantly affecting their adsorption at fluid/fluid interfaces. Understanding these processes is critical for optimizing their use in industrial applications, where controlling interfacial properties is key to achieving desired functionalities.

This study aims to provide, by combining bulk characterization techniques (electrophoretic mobility, fluorescence spectroscopy, conductimetry and UV/visible spectrosctopy) with surface tension measurements, new insights into the complexation mechanisms of SA-CTAB mixtures, with a special focus on the formation of nonequilibrium states and their impact on interfacial properties. Our results highlight the importance of kinetic effects in determining the final properties of polyelectrolyte–surfactant complexes. In fact, the presence of Marangoni stresses during the preparation of the solution results in a very different association process compared to that appearing when Marangoni stresses are absent. This presents strong implications in the nature of the systems, which can influence the final application.

Using Langevin Dynamic simulations we show two examples of how the competition between entropic forces and interactions arising from the mismatch between the non-polar and dipolar moieties present in a media (Kelvin Forces) can be used to tune the interaction between colloids and polymers via an external field. Results are important for both electric and magnetic systems. In a first example [Polymers 17, 366, (2025)], we show that it is possible to create dipolar polymer brushes whose interaction with colloidal particles can be switch from a repulsive to an attractive nature by just adjusting the strength of the external field. This effect can be used to favour applications of polymer brushes in which the entrapping and retention of colloidal particles for a later release is required. In a second example [Polymers 16, 820 (2024) ], we show that the depletion interaction of colloidal particles immersed in a bath of dipolar polymers can be also modulated using an external field. In many cases it is possible to switch from typical depletion force profiles between two colloidal particles to force profiles that contain one or several stationary points depending on the strength of the external field. Furthermore, the inter-particle distance at which these stationary points occur can be also controlled to a certain extend by adjusting the strength of the external field. These findings can be useful in the development of magnetic colloidal tweezers, and colloidal ratchets. We thank the funding support of the Spanish Ministry of Economy and Competitiveness (MINECO/AEI/FEDER,UE) via grant number DPI2017-86610-P, and MCIN/AEI/10.13039/501100011033 through grants number PID2020-118317GB-I00, and , PID2021-123723OB-C22.

In this study, the electronic and optical properties of polyaniline were systematically investigated using density functional theory (DFT) within the Vienna Ab Initio Simulation Package (VASP). Structural optimization was performed to ensure the stability of the polymer configuration prior to electronic and optical analyses. The calculations revealed a characteristic density of states and an electronic band gap of approximately 3.77 eV, indicating semiconducting behavior with the potential for optoelectronic applications. From an optical standpoint, several key parameters were extracted, including the absorption coefficient and dielectric function, both showing a pronounced absorption peak in the ultraviolet (UV) region, suggesting strong photon–matter interactions in this energy range.

The strong UV absorption, combined with the wide band gap, positions polyaniline as an excellent candidate for a range of optoelectronic devices. These properties make it particularly attractive for organic solar cells, UV photodetectors, optical sensors, and light-emitting devices, where materials with high optical stability and strong absorption are critical for efficient performance. Additionally, the intrinsic structural tunability, high environmental stability, and chemical versatility of polyaniline enable easy processing, doping, and functionalization, broadening its applicability in flexible electronics, wearable technologies, and advanced photonic systems.

Overall, the results highlight polyaniline as a promising and versatile material for next-generation optoelectronic and photonic technologies, offering a desirable balance between performance, scalability, and cost-effectiveness. Future research directions could involve experimental validation, exploration of doped or composite forms of polyaniline, and the investigation of device-level integration to fully harness its potential for commercial applications.