Academic literature on the topic 'Electroactive hydrogels'

This paper reports a nontoxic, soft and electroactive hydrogel made with polyvinyl alcohol (PVA) and cellulose nanocrystal (CNC). The CNC incorporating PVA-CNC hydrogels were prepared using a freeze–thaw technique with different CNC concentrations. Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy results proved the good miscibility of CNCs with PVA. The optical transparency, water uptake capacity and mechanical properties of the prepared hydrogels were investigated in this study. The CNC incorporating PVA-CNC hydrogels showed improved displacement output in the presence of an electric field and the displacement increased with an increase in the CNC concentration. The possible actuation mechanism was an electrostatic effect and the displacement improvement of the hydrogel associated with its enhanced dielectric properties and softness. Since the prepared PVA-CNC hydrogel is nontoxic and electroactive, it can be used for biomimetic soft robots, actively reconfigurable lenses and active drug-release applications.

Tissue engineering scaffolds provide biological and physiochemical cures to guide tissue recovery, and electrical signals through the electroactive materials possess tremendous potential to modulate the cell fate. In this study, a novel electroactive hydrogel scaffold was fabricated by assembling poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles on a carboxymethyl chitosan/gelatin (CMCS/Gel) composite hydrogel surface via in situ chemical polymerization. The chemical structure, morphology, conductivity, porosity, swelling rate, in vitro biodegradation, and mechanical properties of the prepared hydrogel samples were characterized. The adhesion, proliferation, and differentiation of neural stem cells (NSCs) on conductive hydrogels were investigated. The CMCS/Gel-PEDOT hydrogels exhibited high porosity, excellent water absorption, improved thermal stability, and adequate biodegradability. Importantly, the mechanical properties of the prepared hydrogels were similar to those of brain tissue, with electrical conductivity up to (1.52 ± 0.15) × 10−3 S/cm. Compared to the CMCS/Gel hydrogel, the incorporation of PEDOT nanoparticles significantly improved the adhesion of NSCs, and supported long-term cell growth and proliferation in a three-dimensional (3D) microenvironment. In addition, under the differentiation condition, the conductive hydrogel also significantly enhanced neuronal differentiation with the up-regulation of β-tubulin III expression. These results suggest that CMCS/Gel-PEDOT hydrogels may be an attractive conductive substrate for further studies on neural tissue repair and regeneration.

The intrinsic regeneration potential of hyaline cartilage is highly limited due to the absence of blood vessels, lymphatics, and nerves, as well as a low cell turnover within the tissue. Despite various advancements in the field of regenerative medicine, it remains a challenge to remedy articular cartilage defects resulting from trauma, aging, or osteoarthritis. Among various approaches, tissue engineering using tailored electroactive scaffolds has evolved as a promising strategy to repair damaged cartilage tissue. In this approach, hydrogel scaffolds are used as artificial extracellular matrices, and electric stimulation is applied to facilitate proliferation, differentiation, and cell growth at the defect site. In this regard, we present a simulation model of electroactive hydrogels to be used for cartilage–tissue engineering employing open-source finite-element software FEniCS together with a Python interface. The proposed mathematical formulation was first validated with an example from the literature. Then, we computed the effect of electric stimulation on a circular hydrogel sample that served as a model for a cartilage-repair implant.

Electroconductive hydrogels (EHs) are promising composite biomaterials of hydrogels and conductive electroactive polymers, incorporating bionic physicochemical properties of hydrogels and conductivity, electrochemistry, and electrical stimulation (ES) responsiveness of conductive electroactive polymers. The biomedical domain has increasingly seen EHs’ application to imitating the biological and electrical properties of human tissues, acclaimed as one of the most effective biomaterials. Bone’s complex bioelectrochemical properties and the corresponding stem cell differentiation affected by electrical signal elevate EHs’ application value in repairing and treating bone, cartilage, and skeletal muscle. Noteworthily, the latest orthopedic biological applications require broader information of EHs. Except for presenting the classification and synthesis of EHs, this review recapitulates the advance of EHs application to orthopedics in the past five years and discusses the pertinent development tendency and challenge, aiming to provide a reference for EHs application direction and prospect in orthopedic therapy.

Electroactive hydrogels based on derivatives of polyethyleneglycol (PEG), chitosan and polypyrrole were prepared via a combination of photopolymerization and oxidative chemical polymerization, and optionally doped with anions (e.g., lignin, drugs, etc.). The products were analyzed with a variety of techniques, including: FT-IR, UV-Vis, 1H NMR (solution state), 13C NMR (solid state), XRD, TGA, SEM, swelling ratios and rheology. The conductive gels swell ca. 8 times less than the non-conductive gels due to the presence of the interpenetrating network (IPN) of polypyrrole and lignin. A rheological study showed that the non-conductive gels are soft (G′ 0.35 kPa, G″ 0.02 kPa) with properties analogous to brain tissue, whereas the conductive gels are significantly stronger (G′ 30 kPa, G″ 19 kPa) analogous to breast tissue due to the presence of the IPN of polypyrrole and lignin. The potential of these biomaterials to be used for biomedical applications was validated in vitro by cell culture studies (assessing adhesion and proliferation of fibroblasts) and drug delivery studies (electrochemically loading the FDA-approved chemotherapeutic pemetrexed and measuring passive and stimulated release); indeed, the application of electrical stimulus enhanced the release of PEM from gels by ca. 10–15% relative to the passive release control experiment for each application of electrical stimulation over a short period analogous to the duration of stimulation applied for electrochemotherapy. It is foreseeable that such materials could be integrated in electrochemotherapeutic medical devices, e.g., electrode arrays or plates currently used in the clinic.

Graphene–nanometal enzymatic biosensors were prepared using hydrogels composed of chitosan, poly-N-isopropylacrylamide, silk fibroin, or cellulose nanocrystals. The comparative study investigated electroactive surface area, charge transfer, response time, limit of detection, and sensitivity toward alcohols.

Les hydrogels de Polyacrylamide (PAAM) hydrolysés sont des matériaux électroactifs biocompatibles non biodégradables. Ils possèdent des propriétés très proches de celles du muscle naturel et leur mode opérationnel basé sur la diffusion d’ions est similaire à celui existant dans les tissus musculaires naturels. Compte tenu de ces caractéristiques, ces hydrogels sont de bons candidats pour la conception de nouveaux muscles artificiels. Le problème qui limite leur utilisation réside dans leur temps de réponse qui reste encore inférieur à celui du système de fibres musculaires naturelles. Leur fonction actuatrice est limitée par le phénomène de diffusion en raison de leur structure massique qui est à l’origine de cycles de fonctionnement relativement lents. Dans le but de développer un nouveau système artificiel mimant le comportement du muscle squelettique naturel cette étude se divise en deux grandes étapes. La première étape vise le développement d’une étude de la synthèse de l’hydrogel de PAAM et de son mode de fonctionnement. Dans cette étude les effets des paramètres gouvernant la polymérisation sur les propriétés des hydrogels sont évalués. Les propriétés électrochimiques et le mécanisme d’activation des actuateurs soumis à une excitation électrique sont étudiés et le mode de fonctionnement des actuateurs est caractérisé et expliqué. La seconde étape est la proposition et le développement d’une nouvelle architecture de muscle artificiel à base de PAAM. Cette architecture consiste en une structure fibreuse du gel encapsulée par une couche en gel conducteur jouant le rôle d’électrodes. La structure fibreuse permet au système d’exhiber une réponse rapide et la couche en gel améliore ses propriétés mécaniques. Comme un premier pas dans la réalisation du modèle nous avons mis en place un nouveau procédé basé sur la technique d’électrofilage qui permet la génération de fibres linéairement disposées. En utilisant ce processus nous avons réussi à fabriquer des microfibres de PAAM réticulées, électroactives montrant des réponses rapides
Hydrolyzed Polyacrylamide (PAAM) hydrogels are electroactive, biocompatible and non-biodegradable materials. Their main attractive characteristic is their operative similarity with biological muscles and particularly their life-like movement. They suit better the artificial muscle fabrication despite their response time which stays low compared to natural human muscle due to their bulky structure and due to the kinetics of the size dependence of their volume change. In order to copy the natural skeletal muscle design into a new artificial muscle system this study is divided into two steps. The first step is the development of a comprehensive study of the hydrogel itself in order to obtain the elementary background needed for the design of actuating devices based on this material. The effect of polymerization parameter on the hydrogel properties is investigated. The electrochemical properties and actuation mechanisms of the hydrogel is studied, the bending of PAAM actuators induced by electric field is discussed and a mechanism for the bending phenomenon is proposed. The second step is the proposition of a new artificial muscle architecture based on PAAM hydrogel. The model consists on a fiber like elements of hydrolyzed PAAM, working in parallel, embedded in a thin conducting gel layer which plays the role of electrodes. The fiber-like elements enable the system to exhibit relatively rapid response and the gel layers enhance their mechanical properties. Aiming to realize the model we have put in place a new electrospinning setup which is a modified process for the production of micro to nanofibers via electrostatic fiber spinning of polymer solutions. The main advantage of this technology is to produce aligned electrospun fibers over large areas by simple and a low cost process making it possible to produce fiberbased devices efficiently and economically. Using this setup, we succeeded in the fabrication of electroactive crosslinked hydrogel microfibers that can achieve fast electroactive response

In the presented work, immunosensors for detection of Aflatoxin B1 based on different immobilization platforms were studied. Synthesis of an electroactive hydrogel was also carried out. Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. Electrochemical immunosensor for the determination of Aflatoxin B1 (AFB1) was developed with anti-aflatoxin B1 antibody immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of Pt/PANi-PSSA electrode, Pt/PANi-PSSA/AFB1-Ab immunosensor and Pt/PANi-PSSA/AFB1-Ab incubated in BSA were 0.458, 720 and 1066 k&Omega
, respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron-transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 k&Omega
for Pt/PANi-PSSA electrode to 1066 k&Omega
for Pt/PANi-PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 k &Omega
L/mg.

碩士
中原大學
化學研究所
105
In this dissertation, two main subjects associated with the self-healing hydrogels were involved. In the first part, the best rheological parameters were studied for the synthesis of non-electroactive self-healing hydrogels (non-ESHs). Subsequently, the electroactive self-healing hydrogels (ESH) were prepared by incorporating as-synthesis conjugated diamine with/without sulfonated group. In the first part, non-ESH were synthesized by reacting primary amine group of chitosan (Mw = 50,000 ~ 190,000 (LC) and Mw = 310,000 ~ 375,000 (HC)) and aldehyde group of double-sided aldehyde-based polyethylene glycol (DF-PEG) (Mw = 2,000 (DP-2000), 4,000 (DP-4000) and 6,000 (DP-6000)). FTIR spectra of all six non-ESH samples were used to identify the imine bonding formation between amine group of chitosan and aldehyde of DF-PEG. Rheology studies of non-ESH were found to reveal best self-healing behavior in LC-DP-6000 (shortest healing time and best recovery). For the second part, the ESHs were prepared by incorporating the conjugated diamine with/without sulfonated group. First of all, the amine-capped aniline trimer (ACAT) and sulfonated ACAT (SACAT) was synthesized by oxidative coupling reaction, followed by characterized by 1H-NMR, FTIR and Mass spectroscopy. Subsequently, the ESHs were prepared by reacting 0.9 ml of 0.07 M ACAT aqueous solution or 0.9 ml of 0.07 M or 0.14 M SACAT aqueous solution with 0.1 g of DP-6000, followed by introducing 2.5 g of 2 wt-% of LC aqueous solution. The as-prepared mixture was under magnetic stirring for ~ 10 minutes to give the desired ESHs. Redox capability of as-prepared ESHs was identified by electrochemical cyclic voltammetry (CV) studies. It should be noted that the incorporation of ACAT into non-ESH may introduce the redox capability into ESH. Secondly, the incorporation of SACAT into ESHs was found to reveal higher redox capability as compared to that of ACAT. Moreover, higher loading of SACAT in ESHs was found to exhibit higher redox capability as compared to that of lower loading of SACAT in ESHs. For the studies of self-healing behavior of ESHs, a series of experiments were performed by rheometer. First of all, ESH containing ACAT was found to reveal an enhancement in original storage modulus, slightly decrease in G and G from strain amplitude sweep, slightly enhancement in self-healing process after damage and constant in recovery percentage as compared to that of non-ESH. Moreover, the incorporation of SACAT in ESH was found to exhibit slightly decrease in original storage modulus, slightly increase in G and G from strain amplitude sweep, slightly increase the self-healing process after damage and significantly decrease in recovery percentage as compared to that of ESH containing ACAT at same feeding concentration. Moreover, the increase of SACAT in ESH was found to reveal significantly decrease in original storage modulus, significantly decrease in G and G from strain amplitude sweep, slightly decrease in self-healing process after damage and slightly decrease in recovery percentage. To sum up, incorporating of conjugated diamine into self-healing hydrogels may introduce electroactivity into gels and significantly affect the self-healing behavior of original hydrogels.

Tese no âmbito do doutoramento em Engenharia Química, apresentada ao Departamento de Engenharia Química da Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
The main objective of the present thesis was the development and characterization of novel electroactive ionic liquid-based polycationic hydrogels. These materials were obtained by the functionalization of natural-origin and/or synthetic polymers with an ionic liquid-based vinyl monomer (functionalized at the cation) by two different approaches, namely by the formation of semi-interpenetrating polymer networks (s-IPNs) and by copolymerization with a non-charged comonomer. Through this doctoral work, three different multi-responsive systems were developed targeting a broad range of applications, such as, drug delivery devices, bioseparators, soft actuators, tissue engineering scaffolds, iontophoretic patches and wound dressings. The first approach was employed to obtain multi-responsive s-IPNs hybrid structures based on natural polymers (starch and chitosan) and homopolymers/copolymers of poly(1-butyl-3-vinylimidazolium chloride) (poly(BVImCl) and poly(2-hydroxyethyl methacrylate-co-1-butyl-3-vinylimidazolium chloride) (poly(HEMA-co-BVImCl)). In the case of the starch-based s-IPNs, results demonstrated that the sorption/release capacity of these hydrogels towards L-tryptophan (used as a model biomolecule) could be adjusted depending on the intensity of the applied DC voltage and/or sorption/release medium. It was also confirmed that the process employed to dry the hydrogels (oven and freeze-drying) has a major influence on the conductivity of the materials and that freeze-drying induced higher conductivity values. Furthermore, biological tests demonstrated that the prepared s-IPNs were able to guarantee fibroblasts viability. These newly obtained hybrid materials demonstrated to have potential to be employed for bio-separation processes and for the sustained delivery of specific charged-biomolecules. In the case of the chitosan-based s-IPNs it was demonstrated that the prepared hybrid hydrogels presented enhanced mechanical properties, water swelling capacities (at different pH and ionic strengths) and sorption capacities towards charged molecules when compared to pristine chitosan. Obtained s-IPN hydrogels also demonstrated to have modulated lidocaine hydrochloride permeation/delivery profiles at low current densities (0.56 mA/cm2) and as a function of their charge density. Moreover, biological tests showed that the prepared s-IPN hydrogels were non-hemolytic and presented potential hemostatic capability. These “smart” s-IPNs presented advantageous properties for the design of topical iontophoretic patches and/or hemostatic agents. The second approach was employed to obtain multi-responsive electro-actuating hydrogels based on poly(HEMA-co-BVImCl) copolymers. Studies were performed to evaluate the influence of surface properties on the actuating behavior of the hydrogels in different aqueous media, with different pH and ionic strength values. The different surface properties were obtained by simply employing different mold subtracts, with different hydrophobicities (namely Teflon® and glass) during the copolymer free radical polymerization in aqueous media. Obtained results demonstrated that hydrogels synthesized on Teflon® molds presented the highest electro-actuation capacity in aqueous media, with equivalent bending motion on both directions according to the polarization applied. Moreover, it was also noticed that hydrogels surface charge density and water swelling capacity could be modulated depending on the type of mold utilized during polymerization. Resulting soft stimuli-responsive materials can be regarded as “smart” platforms for the design of soft actuators and cell culture scaffolds for biomedical applications. Overall, this PhD thesis allows concluding that the functionalization of natural and/or synthetic polymers with ILs represents a viable and efficient strategy for the development of multi-responsive electroactive materials for applications in biomedicine, (bio)separation and electrochemistry.
O objetivo principal desta tese foi o desenvolvimento e caracterização de novos hidrogéis eletroativos policatiónicos à base de líquidos iónicos. Esses materiais foram obtidos pela funcionalização de polímeros de origem natural e/ou sintéticos com um monómero vinílico à base de líquidos iónico (funcionalizados no catião) por meio de duas diferentes abordagens, nomeadamente redes poliméricas semi-interpenetradas (s-IPNs) e copolimerização com um comonómero não carregado. Durante a realização do trabalho, foram desenvolvidos três sistemas multi-responsívos diferentes visando uma vasta gama de aplicações, por exemplo, dispositivos para a entrega de fármacos, bioseparadores, atuadores soft, scaffolds para engenharia de tecidos, pensos para iontoforese e para tratamento de feridas. A primeira abordagem consistiu na obtenção de s-IPNs híbridos multi-responsívos à base de polímeros naturais (amido e quitosano) e homopolímeros/copolímeros de poli(cloreto de 1-butil-3-vinilimidazólio) (poli(BVImCl) e poli(metacrilato de 2-hidroxietila-co-cloreto de 1-butil-3-vinilimidazólio) (poli(HEMA-co-BVImCl)). No caso dos hidrogéis s-IPNs à base de amido, os resultados demonstraram que a capacidade de sorção/entrega de L-triptofano, usado como biomolécula modelo, poderia ser otimizada consoante a diferença de potencial aplicada e/ou o tipo de meio utilizado na sorção/libertação. O processo de secagem utilizado nos hidrogéis (secagem em estufa e liofilização), provou ter uma influência significativa na condutividade dos materiais estudados, sendo que os foram sujeitos ao processo de liofilização apresentaram valores superiores de condutividade. Concomitantemente, a viabilidade de fibroblastos na presença dos s-IPNs foi comprovada com recurso a testes biológicos. Desta forma, os materiais híbridos e inovadores desenvolvidos nesta abordagem demonstraram potencial para serem utlizados em processos de biosseparação e para entrega contínua de biomoléculas carregadas específicas. No caso dos s-IPNs à base de quitosano, foi demonstrado que os hidrogéis híbridos desenvolvidos apresentaram melhores propriedades mecânicas, capacidades de entumecimento em água (em diferentes condições de pH e força iónica) e capacidades de sorção para moléculas carregadas, quando comparados com o quitosano puro. Os s-IPNs exibiram perfis modulares de permeação/entrega de lidocaína, a baixas intensidades de corrente (0.56 mA/cm2), em função da respetiva densidade de cargas. Além disso, após testes biológicos, os hidrogéis s-IPN provaram ser não-hemolíticos e hemostáticos. Estes s-IPNs “inteligentes” apresentaram propriedades vantajosas para a preparação de pensos tópicos para iontoforese e/ou pensos hemostáticos. A segunda abordagem estudada foi baseada na obtenção de copolímeros electroactuators híbridos multi-responsívos à base de hidrogéis de poli(HEMA-co-BVImCl). A influência das propriedades de superfícies no comportamento de atuação dos hidrogéis em diferentes meios aquosos (com diferentes valores de pH e força iónica), foi avaliada. Diferentes propriedades de superfície foram obtidas pela simples utilização de diferentes moldes com hidrofobicidade distintas, nomeadamente Teflon® e vidro, durante a copolimerização por polimerização radicalar livre, em meio aquoso. Os resultados demonstraram que os hidrogéis preparados em moldes de Teflon® apresentaram superior capacidade de eletroatuação em meio aquoso, com atuação mecânica equivalente em ambas direções, de acordo com a polaridade aplicada. Para além disso, foi também verificado que a densidade de carga na superfície dos hidrogéis e a capacidade de entumecimento em água pode ser modulada de acordo com o tipo de molde utilizado durante a polimerização. Os materiais responsivos a estímulos podem ser equiparados a plataformas “inteligentes” para a produção de atuadores soft e scaffolds para cultura celular em aplicações biomédicas. Em suma, a presente tese de doutoramento permitiu concluir que a funcionalização de polímeros naturais e/ou sintéticos, com ILs, representa uma estratégia viável e eficiente para o desenvolvimento de materiais eletroativos multi-responsívos para aplicações na biomedicina, biosseparação e eletroquímica.

Philosophiae Doctor - PhD
In the presented work, immunosensors for detection of Aflatoxin B1 based on different immobilization platforms were studied. Synthesis of an electroactive hydrogel was also carried out. Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. Electrochemical immunosensor for the determination of Aflatoxin B1 (AFB1) was developed with anti-aflatoxin B1 antibody immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of Pt/PANi-PSSA electrode, Pt/PANi-PSSA/AFB1-Ab immunosensor and Pt/PANi- PSSA/AFB1-Ab incubated in BSA were 0.458, 720 and 1066 kΩ, respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron-transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 kΩ for Pt/PANi-PSSA electrode to 1066 kΩ for Pt/PANi- PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 k ΩL/mg. In the second platform an immunosensor based on gold nanoparticles (AuNP) and polythionine-modified glassy carbon electrode (GCE) for the determination of aflatoxin B1 (AFB1) was developed. Aflatoxin B1-BSA conjugate was immobilised on the modified GCE. Horseradish peroxidase (HRP) or Bovine serum albumin (BSA) were used to block sites against non-specific binding of the AFB1- conjugate with other compounds such as the salts used in preparing the buffer when the antibody interacts with the AFB1 conjugate and free AFB1. Competition reaction was allowed to take place between the free AFB1 and AFB1-conjugate for the binding sites of the anti-aflatoxin B1 antibody. Cyclic voltammetry (CV) was employed to characterize the electrochemical properties of the modified process. The peak separation of the immunosensor (ΔEp) was 62 mV indicating a quasi reversible process. Differential pulse voltammetry (DPV) was used to monitor the analytical signal. The response decreased with an increase in AFB1 concentration in the range of 0.6-2.4 ng/mL with a limit of detection of 0.07 and 0.16 ng/mL for HRP and BSA blocked immunosensors respectively. Significantly the low detection limit of 0.07 ng/mL is within the limits set by worl health organization (WHO) for AFB1 and its derivatives which is 2 ng/mL The proposed method eliminates the use of secondary antibody enzymatic labels. Synthesis and characterization of (p-(HEMA)-polyaniline hydrogels were investigated. The hydrogels were synthesized using: 2-Hydroxyeththyl methacrylate (HEMA), N-Tris (hydroxymethyl) methyl] acrylamide, 3- Sulfopropyl methacrylate potassium salt, Tetraethylene glycol diacrylate, Poly-(2- hydroxyethyl methacrylate), 2, 2-Dimethoxy-2-phenylacetophenone and aniline by UV irradiation. Two sets of the hydrogels were prepared using water / 1, 3, 3, 3-(tetramethyl butyl phenyl polyethylene glycol [Triton X-100] and water / ethylene glycol as the solvent. Scanning electron microscopy (SEM) revealed a more uniform pore size when Triton X 100 (TX-100 HG) was used as compared to ethylene glycol (EG-HG). Thermogravimetric analysis (TGA) showed that both hydrogels were stable up to 270 oC. Fourier transform-Infra red (FTIR) spectrum confirmed the incorporation of polyaniline (PANi) and HEMA in the composite. Electrochemical properties of the hydrogels evaluated using Cyclic Voltammetry and Electrochemical Impedance Spectroscopy (EIS) demonstrated the electroactivity and conductivity.

Smart actuators can sense external stimuli and produce controllable mechanical responses, and convert these energies into mechanical energy. They have great applications in the aerospace, electronic circuits, medical and other fields. As a new manufacturing method, the combination of 3D printing and smart actuators had developed rapidly in recent years. In this paper, we summarize the research progress of 3D printing smart actuators and its materials. The smart driver includes water responsive driver, pH responsive driver, temperature responsive driver, light responsive driver and magnetic field responsive driver. The smart driver materials can be divided into shape memory materials, piezoelectric materials, responsive smart hydrogels and electroactive polymers. In addition, their stimulative effect and driving mechanism have been studied emphatically.

Electroactive polymers (EAP) have shown promise in producing significant and controllable linear displacement in slim and lightweight packages. EAPs allow for seamless integration and multi-functionality since they are actuated by a driving voltage that could be controlled by a microprocessor. Polyacrylamide (PAAM)/Polyacrylic acid (PAA) hydrogel EAPs are commonly chosen due to their low driving voltage, significant amount of displacement, and rapid manufacturing capabilities, as these gels can be 3D printed. To effectively extrude these gels in 3D printers, their viscosity, gelation time, shear thinning, and self-wettability must be characterized. In this research, ungelled solutions of PAAM are prepared and then strain-tested at temperatures from 60C to 80C and with 1–2 drops of TEMED catalyst to determine the gelation time that is optimal for 3D printing. Strain testing of ungelled PAAM solutions is also used to determine the shear thinning propertie of the gel. All strain testing is conducted using a rheometer with 25 mm diameter plates and an oven enclosure. A prototype extrusion system is designed and fabricated to be used for self-wettability testing of the gel. The process data will then be used in the design of a modified 3D printer to manufacture and test different configurations of these hydrogel actuators.