https://hdl.handle.net/10481/24912 2026-04-11T17:33:52Z 2026-04-11T17:33:52Z Vázquez Pérez, Francisco Jesús Leon-Cecilla, Alberto Álvarez de Cienfuegos, Luis Martin, James E. López López, Modesto Torcuato https://hdl.handle.net/10481/105949 2025-09-01T11:50:12Z

Inducing Chirality and Chiral Instabilities in Ferrogels with Homogenous Magnetic Fields Vázquez Pérez, Francisco Jesús; Leon-Cecilla, Alberto; Álvarez de Cienfuegos, Luis; Martin, James E.; López López, Modesto Torcuato Soft magnetic actuators are materials that undergo bending, elongation, contraction or torsion in magnetic fields. In this paper, ferrogel-based cylindrical actuators that undergo deterministic chiral deformations and chiral instabilities in uniform applied magnetic fields are investigated. Such fields cannot induce body forces but can induce body torques. These actuators are in the form of hydrogel cylinders containing magnetic particles (MPs) that are field structured into particle chains in a direction normal to its cylindrical axis during gelation. When one end of the cylinder is fixed and a uniform magnetic field is applied normal to the cylindrical axis, but at an angle to the particle chains, the cylinder twists. A subsequent rotation of the cylinder base can lead to a metastable state, and further deformation can lead to a chiral instability wherein the sign of the chirality switches. This actuation is studied as a function of the type of polymer used in the hydrogel preparation (alginate or acrylamide), the type of MPs used (silica-coated iron particles or permalloy flakes particles) and the volume fraction of the magnetic phase. The torsional deformations, as well as certain hysteresis effects, are compared to a theoretical model developed herein.

Lirio Piñar, Juan Antonio Orozco Barrera, Sergio Delgado Mora, Ángel Vicente Ahualli Yapur, Silvia Alejandra https://hdl.handle.net/10481/91123 2024-04-24T10:35:53Z

Concentration polarization around polyelectrolyte-coated electrodes. Model and observations Lirio Piñar, Juan Antonio; Orozco Barrera, Sergio; Delgado Mora, Ángel Vicente; Ahualli Yapur, Silvia Alejandra An investigation on the phenomenon of concentration polarization (CP) in conducting porous particles is presented in this work, considering both bare and polyelectrolyte-coated particles. The conducting nature of the porous structure brings about the induction of a surface (and hence volume) charge distribution by the applied external field. The polymer charge (with its counterions from solution) is superimposed on this field-induced component. From the solution of Poisson’s equation, the concentration and potential profiles are evaluated, and from them, the concentration polarization can be calculated. The results are presented as concentration perturbation as a function of time after application of the field, both for bare and coated particles. Experiments are also performed aimed at measuring the CP using a solution of fluorescent dye (rhodamine B). From the increase or decrease of fluorescence, the concentration perturbations are observed around the particle. Importantly, depletion of concentration is observed on both sides of the particle when this is bare. In contrast, if the particles are coated, the classical pattern of a pole of increased concentration and an opposite one of decreased concentration is found. Dielectric dispersion experiments in suspensions of bare and brush-coated particles confirm this fact. Financial support of this investigation by FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades, Spain (Grant No. P20_00233) and Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía, Spain (Grant No. A-FQM492-UGR20) is gratefully acknowledged. Thanks are also due for the grant TED2021-131855BI00/AEI/10.13039/501100011033/Unión Europea Next Generation EU/PRTR.

Leon-Cecilla, Alberto Gila-Vilchez, Cristina Vázquez Pérez, Francisco Jesús Capitán Vallvey, Luis Fermín Fernández Ramos, María Dolores Martos Núñez, María Vanesa Álvarez de Cienfuegos Rodríguez, Luis Medina Castillo, Antonio Luis López López, Modesto Torcuato https://hdl.handle.net/10481/88287 2024-02-05T13:25:21Z

Highly deformable and strongly magnetic semi-interpenetrating hydrogels based on alginate or cellulose Leon-Cecilla, Alberto; Gila-Vilchez, Cristina; Vázquez Pérez, Francisco Jesús; Capitán Vallvey, Luis Fermín; Fernández Ramos, María Dolores; Martos Núñez, María Vanesa; Álvarez de Cienfuegos Rodríguez, Luis; Medina Castillo, Antonio Luis; López López, Modesto Torcuato The effective implementation of many of the applications of magnetic hydrogels requires the development of innovative systems capable of withstanding a substantial load of magnetic particles to ensure exceptional responsiveness, without compromising their reliability and stability. To address this challenge, double-network hydrogels have emerged as a promising foundation, thanks to their extraordinary mechanical deformability and toughness. Here, we report a semi-interpenetrating polymer networks (SIPNs) approach to create diverse magnetic SIPNs hydrogels based on alginate or cellulose, exhibiting remarkable deformability under certain stresses. Achieving strong responsiveness to magnetic fields is a key objective, and this characteristic is realized by the incorporation of highly magnetic iron microparticles at moderately large concentrations into the polymer network. Remarkably, the SIPNs hydrogels developed in this research accommodate high loadings of magnetic particles without significantly compromising their physical properties. This feature is essential for their use in applications that demand robust responsiveness to applied magnetic fields and overall stability, such as a hydrogel luminescent oxygen sensor controlled by magnetic fields that we designed and tested as proof-of-concept. These findings underscore the potential and versatility of magnetic SIPNs hydrogels based on carbohydrate biopolymers as fundamental components in driving the progress of advanced hydrogels for diverse practical implementations.

Medina Castillo, Antonio Luis López López, Modesto Torcuato Fernández Ramos, María Dolores https://hdl.handle.net/10481/84479 2024-01-31T12:38:48Z

Theoretical Formulation of the Distribution Function of Critical Nuclei under Precipitation Polymerization Conditions Medina Castillo, Antonio Luis; López López, Modesto Torcuato; Fernández Ramos, María Dolores Precipitation Polymerization (Pre-Poly) can be considered a nucleation and growth process in which complex and high molecular weight branched polymers are involved. From an experimental point of view, it is well-known that under Pre-Poly conditions the phase transition (nucleation) occurs in the first minutes of polymerization, and then a long growth stage is observed in which the critical nuclei simultaneously grow until reaching a highly monodisperse distribution of microspheres (characteristic mechanism of binodal decomposition). The high rate at which nucleation and growth processes usually take place when radical polymerization (extremely high polymerization rate) under Pre-Poly conditions is used, makes it very difficult to study experimentally some aspects of these processes, such as the size and concentration of critical nuclei, among others. Based on the thermodynamic principles of Pre-Poly, this analytical paper covers for the first time, to the best of 2 our knowledge, the theoretical formulation of the distribution function of critical nuclei under PrePoly conditions. In addition, a simple empirical method to calculate the concentration of critical nuclei was also developed using only three global, physical experimental parameters, and good agreement was found between empirical and theoretical calculations.

Gila Vilchez, Cristina Mañas Torres, María del Carmen García García, Óscar Darío Escribano Huesca, Alfredo Rodríguez Arco, Laura Carriel Araya, Víctor Rodríguez Ismael, Ángel Alaminos Mingorance, Miguel López López, Modesto Torcuato Álvarez Cienfuegos Rodríguez, Luis https://hdl.handle.net/10481/80509 2023-03-10T09:10:45Z

Biocompatible Short-Peptides Fibrin Co-assembled Hydrogels Gila Vilchez, Cristina; Mañas Torres, María del Carmen; García García, Óscar Darío; Escribano Huesca, Alfredo; Rodríguez Arco, Laura; Carriel Araya, Víctor; Rodríguez Ismael, Ángel; Alaminos Mingorance, Miguel; López López, Modesto Torcuato; Álvarez Cienfuegos Rodríguez, Luis Fibrin hydrogels made by self-assembly of fibrinogen obtained from human plasma have shown excellent biocompatible and biodegradable properties and are widely used in regenerative medicine. The fibrinogen self-assembly process can be triggered under physiological conditions by the action of thrombin, allowing the injection of pregel mixtures that have been used as cell carriers, wound-healing systems, and bio-adhesives. However, access to fibrinogen from human plasma is expensive and fibrin gels have limited mechanical properties, which make them unsuitable for certain applications. One solution to these problems is to obtain composite gels made of fibrin and other polymeric compounds that improve their mechanical properties and usage. Herein, we prepared composite hydrogels made by the self-assembly of fibrinogen together with Fmoc-FF (Fmoc-diphenylalanine) and Fmoc-RGD (Fmoc-arginine-glycine-aspartic acid). We have shown that the mixture of these three peptides co-assembles and gives rise to a unique type of supramolecular fiber, whose morphology and mechanical properties can be modulated. We have carried out a complete characterization of these materials from chemical, physical, and biological points of view. Composite gels have improved mechanical properties compared to pure fibrin gels, as well as showing excellent biocompatibility ex vivo. In vivo experiments have shown that these gels do not cause any type of inflammatory response or tissue damage and are completely resorbed in short time, which would enable their use as vehicles for cell, drug, or growth factor release.