Jose Gabriel Martinez

Advances in combining soft electromechanically active polymers with textiles at the fibre and yarn levels of the textile hierarchy contribute to the development of textile actuators or, by borrowing terms from physiology, of textile muscles. Textile muscle fibres, made by continuous electropolymerisation of pyrrole (Py) onto polyamide 6/6 multifilaments coated with poly(3-4-ethylenedioxythiophene) (PEDOT), are able to perform shortening, isometric, and lengthening contractions in liquid electrolytes and withstand the fabric manufacturing processes. To date, the contractile performance in liquid electrolytes of these textile muscle fibres, dependent on electrochemically driven volume change, has yet to be translated to in air as part of a fabric. Therefore, textile muscle fibres are explored as a fundamental unit of textile muscles together with ionofibres for their innervation. Ionofibres, continuously produced by UV polymerisation of ionogel precursors onto the surface of polyamide 6/6 multifilaments, are used to interlace closely with the textile muscle fibres and act as ion source/sink during the electrochemical processes. Their close contacts in a fabric enable the textile muscle fibres to contract in air under electrical stimuli. Regarding the ionofibres, two ionogels based on either 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm⁺OTf⁻) entrapped in a polythioether network or choline acetate (Chol⁺OAc⁻) entrapped in a poly(2-hydroxyethyl methacrylate) network are explored. All the different produced fibres are evaluated individually in terms of electrical conductivity, tensile properties, and, for the textile muscle fibres, contractile properties. The investigation of the contractile properties includes repeated stimuli of yarn samples in individual warp rib structures with multiple signal frequencies and shapes. This contribution evaluates textile muscle fibres during contractions in air within a weave, representing for such fibres the first demonstration of actuation in ambient air. Beyond this milestone, the study seeks to identify critical manufacturing bottlenecks that limit realistic applications, establishing a foundation for developing practical textile muscles through standardised characterisation.

Cellular mechanotransduction signals play a crucial role in physiological and pathological conditions, including skeletal disorders. Although various systems exist to mechanically stimulate cultured cells, most are constrained by incubator incompatibility, limited physiological relevance, nonuniform stimulation, or complexity. The objective of this article is to develop and validate a compact, incubator‐compatible tool capable of delivering localized and physiologically relevant mechanical stimulation to small cell populations. Here, we introduce a polypyrrole‐based wire‐shaped microactuator designed to induce localized mechanical stress to adjacent cells. These wire‐shaped microactuators are biocompatible, easy‐to‐use, and compact for use within standard in vitro cell culture systems. Using a noncontact optical method, we characterize the actuation of polypyrrole‐coated wires in an aqueous NaDBS electrolyte, showing radial expansion of 1.5–8 µm depending on the deposited polypyrrole film thickness, comparable to cellular dimensions. Next, the actuation is confirmed to be robust and stable to use in cell culture media at physiological temperature. To evaluate biological relevance, osteoblastic KUSA‐A1 cells are mechanically stimulated inside the incubator and transcriptomic changes are assessed. Mechanical stimulation resulted in upregulation of genes previously associated with mechanotransduction, including Fos and Fosb. Additionally, several uncharacterized long noncoding RNAs are differentially expressed, suggesting potential novel players in the mechanotransduction pathway.

Mechanotransduction, i.e., the conversion of mechanical cues into biochemical signals, is essential for bone development, remodeling, and adaptation. Although mechanical loading is known to regulate osteoblast function and bone homeostasis, dissecting the early and sustained mechanotransductive responses at the microscale remains challenging due to limitations of existing in vitro models. Here, we report the development and application of a mechanostimulation system comprising a polypyrrole (PPy)-based wire actuator that expands and contracts (4 μm in radius) upon electrical actuation and enables precise, localized micromechanical stimulation of a small number of cells within standard culture formats. Using this system, we applied short-term (30 min) cyclic (C30) or static (S30), as well as prolonged (120 min) cyclic (C120) stimulations to two osteoblast-like cells (MC3T3-E1 or KUSA-A1). Subsequent transcriptomic profiling and computational network analyses revealed that C30 was not capable of inducing significant changes in mRNA expression, suggesting cellular adaptation to short-term cyclic loading. In contrast, S30 induced the upregulation of Fos, Btg2, Egr1, and Fosl1, all known genes associated with mechanotransduction, supporting the validity and reproducibility of our experimental mechanostimulation system. Notably, two long non-coding RNAs (B930036N10Rik and 5430431A17Rik) were identified for the first time as being upregulated in response to S30 stimuli. Among the differentially expressed genes (DEGs) upregulated by C120 stimuli, Hmox1, a stress-inducible enzyme known for its roles in maintaining cellular homeostasis and promoting survival, was the only DEG repeatedly observed across the C30/C120 and S30/C120 comparisons in both cell types, potentially emerging as a key stress-response gene under prolonged mechanical loading. Collectively, these results establish the PPy-based microactuator as a powerful tool for microscale mechanobiology, and provide molecular insight into immediate-early responsive transcriptional programs underlying osteoblastic mechanoadaptation conserved across different cell types.

Self‐propelled micromotors using bubble propulsion show great promise for miniaturized devices with multiuse purposes such as cargo delivery and sensing. However, there is currently no method to electrically switch the micromotors on or off. Here, we demonstrate a novel way to control the movement of a micromotor, turning it on or off by using the electroactive polymer polypyrrole on platinum. By applying reducing or oxidizing potentials to polypyrrole we can electronically control the diffusion of H₂O₂ toward the catalytic platinum and thus control catalyzation of H₂O₂ into oxygen bubbles and water turning the propulsion mechanism on or off. Employing these switchable motors in multiengine designs, we created miniature vehicles that can be electrically controlled in speed and direction of movement. This method offers efficient and versatile control for micromotors and microvehicles.

The fabrication of mechanically robust and reconfigurable hydrogel filaments remains a major challenge in biofabrication of perfusable architectures, dynamic tissue models, and complex 3D cell‐laden constructs. Conventional extrusion‐based bioprinting techniques generate filaments that are soft and fragile, limiting post‐processing, scalability, and functional adaptability. Rerouting of Free‐Floating Suspended Hydrogel Filaments (REFRESH) is introduced as a biofabrication strategy that integrates an aqueous two‐phase system (ATPS)‐compatible elastic extracellular matrix mimicking bioink material with a flexible printing and post‐processing approach to overcome these constraints. This method enables the formation of highly elastic hydrogel filaments cross‐linked via strain‐promoted azide‐alkyne cycloaddition (SPAAC) of bicyclo[6.1.0]non‐4‐yne‐functionalized hyaluronan, exhibiting a strain at break exceeding 100%. The printed filaments maintain mechanical integrity during manual handling and post‐processing using textile‐inspired techniques, such as knotting and braiding, into reconfigurable 3D architectures. A distinct shape memory function enables programmed mechanical actuation and recovery of deformed structures. The hydrogel system supports high cell viability across multiple cell types and enables the fabrication of multicellular constructs with spatially defined organization. By incorporating protease‐degradable cross‐linkers, REFRESH‐generated filaments function as sacrificial templates for perfusable tubular structures. This approach significantly expands the biofabrication design space, offering new possibilities for engineering vascularized tissues and complex hydrogel‐based architectures.

Electropolymerized polypyrrole (PPy) is considered as one of the promising polymers for use in ionic-electroactive or conducting polymer (CP) actuators. Its electromechanical properties surpass those of other prominent CPs such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) or polyaniline. However, freestanding and linear contracting actuator fibers made solely of electropolymerized PPy are not available yet. This work therefore targets the development of all-CP-based actuator fibers: electromechanically active PPy is electropolymerized on the surface of wet-spun, also electromechanically active PEDOT/PSS fibers. The thickness of the PPy fiber sheath is varied by using different electropolymerization durations. Mechanical and actuation properties of the different PEDOT/PPy core-sheath actuator fibers are investigated via tensile tests and isotonic actuation strain and isometric actuation force measurements, respectively. The fiber actuators show high tensile stability in both dry and aqueous conditions, rendering them highly suitable for actuation in aqueous electrolyte media. Regarding linear, untwisted, and uncoiled CP fiber actuators, the presented actuation measurements demonstrate to the best of our knowledge the highest reported linear contractile actuation strains of up to 2.2% in electrolytes and remarkable tensile actuation stresses of 1.64 MPa, as well as a high long-term cyclic actuation stability using varying actuation durations. This renders the fibers as a highly promising material, particularly with regard to their further structural textile processing for use in actuating wearables or soft robots.

Bovine serum albumin (BSA) was covalently bound to different carboxyl-modified polypyrroles and electrochemically switched. It was found that the immobilized BSA could change its presentation depending on carboxyl modification and the redox state.

Conducting polymers (CP) have shown great features in building textile actuators. To date, most of the yarn-based or CP-yarn actuators have been operated in liquid electrolytes in a three-electrode-cell configuration, comprising an external counter and a reference electrode. For integration in textiles, a two-electrode system is needed, where both electrodes are in a yarn format. This can be achieved by having two CP-yarns, where one acts as the anode and the other as the cathode. For these two CP-yarns to operate synchronically, they both need to expand (or contract) during opposite reactions. This can be achieved by doping one CP-yarn with mobile anions that will expand during oxidation, while the other CP-yarn should be doped with immobile anions expanding during reduction. As a result, the same movement is created upon opposite redox reactions, both collaborating with the actuation in the same direction without the need for an external passive electrode to close the electrical circuit, which could oppose or hinder the movement. Most of the studies on textile actuators are based on cation-driven CP-yarn actuators, while little is known about anion-driven systems in CP-yarn actuators. Here, we first present a study of the effect of the dopants, solvents, and polymer layer combinations on the mechanism and strain of CP-yarns. The CP-yarns are coated with two layers: an inner poly(3,4-ethylenedioxythiophene) (PEDOT) layer and the outer and active polypyrrole (PPy) layer. According to our results, the dopant of the inner PEDOT layer seems to affect the actuation mechanism of the outer PPy layer and, thereby, of the whole CP-yarn actuator, influencing the direction of the movement and enhancing or hindering the total strain of the actuator. We show that a CP-yarn coated with PEDOT(Tos)/PPy(ClO4) and actuated in LiClO4 aqueous solution showed a pure anion-driven actuation. Next, based on the latter results, we demonstrate for the first time the dual actuation of two CP-yarns, doped with two different dopants, ClO4- and DBS-, actuating simultaneously driven by opposite redox reactions and exhibiting an average of 0.5% of strain, an important step toward in-air actuating yarns.

Like skeletal muscles having a fibrous structure, conducting polymers can actuate upon electrical stimulation and can be shaped into fibers. Through textile assembly strategies of such fibers, complex actuating architectures are possible. However, state‐of‐the‐art strategies using short pieces of yarn, which compel manual integration, are not fully taking advantage of textiles. To manufacture actuating textiles that best exploit textile properties like softness and pliability, and to enable production upscaling, a production of continuous, actuating fibers is presented here. These fibers are produced from commercial polyamide 6/6 filaments by first continuously dip‐coating in a modified commercial poly(3,4−ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) dispersion before the electropolymerization of polypyrrole (PPy), where the fibers are withdrawn continuously through an electrolyte solution containing the pyrrole monomer. By employing a cyclic dip‐coating with individual viscosity, drying temperature, and withdrawal speed for each layer, and by adjusting the tension, speed, and applied potential of the electropolymerization, their isotonic strain is enhanced threefold. Their specific tension, at 400 µN tex⁻¹, reaches slightly higher than human skeletal muscle fibers. Furthermore, these continuous actuating fibers produced on the meter are processable in an industrial knitting machine. This study anchors the development of textile muscle fibers for future textile muscles.

Poly(3,4‐ethylenedioxythiophene) (PEDOT), an inherently electrically conductive or conjugated polymer (CP), exhibits the potential to play a significant role in the development of innovative fiber materials for use in smart textiles, such as wearables. Furthermore, these fibers can function as artificial muscles in the emerging field of interactive fiber rubber composites. This study introduces a straightforward and efficient method for creating PEDOT‐based, biomimetic, fiber‐shaped, linearly contracting ionic electroactive polymer actuators. To achieve this, a wet‐spinning technique is presented, which enables a continuous production of PEDOT:polystyrene sulfate (PSS) fibers at high production rates of 34 m h⁻¹, an additional fiber washing step and a sulfuric acid posttreatment step to increase the fibers conductivity. The fibers provide a high conductivity of 1028 S cm⁻¹, maximum tensile strength reaching 182 MPa, and a maximum elongation of 24%. When utilized as CP actuators in an aqueous sodium dodecylbenzenesulfonate electrolyte medium, the fibers demonstrate a repeatable maximum isometric contractile force of 1.64 mN and repeatable linear contractile strain up to 0.56%. Furthermore, a high level of cyclic long‐term actuation stability can be demonstrated. Notably, these contractile strains are, to the best of knowledge, the highest reported values for pristine PEDOT:PSS fibers.