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The development of soft hydrogel actuators with outstanding mechanical properties, fast actuation speed, and available quantification of self-sensing actuation remains a challenging ...endeavor. In this work, dopamine-decorated polypyrrole nanofibers (DAPPy) were introduced into the polyethylene glycol diacrylate (PEGDA)-crosslinked poly(N-isopropyl acrylamide) network to generate a stretchable, NIR-responsive, and strain sensitive DAPPy/PNIPAM hydrogel layer. Besides, this active layer was combined with the passive ligninsulfonate sodium/polyacrylamide (LS/PAAM) to give DAPPy/PNIPAM//LS/PAAM bilayer hydrogel actuator, which exhibits ultrafast thermo-responsive actuation (19°/s) and underwater grasping and lifting performance. Moreover, the DAPPy/PNIPAM layer has excellent electrical conductivity (0.29 S/m) and thermal conversion ability (10.8 °C/min), which enable such a conductive hydrogel to act as a highly sensitive strain and temperature sensor with real-time resistance change in response to tensile strain (gauge factor up to 3.4), applied pressure, temperature, and remote NIR light irradiation. More importantly, the bilayer hydrogel actuator can integrate both actuation and self-sensing functions through the bending angle-surface temperature-relative resistance change relationship of the photothermal process. With excellent mechanical actuation and self-sensing ability, the resulting bilayer hydrogel showed a promising application potential as soft biomimetic actuating materials and soft intelligent actuators.
Modular sensor platforms are a fashion approach that allows the use of advanced materials to promote the evolution of portable electrochemical sensors. A modular platform building by the combination ...of carbonized poly(acrylonitrile) electrospun mat (C‐PAN; fiber diameter ca. 300 nm) and a poly(N‐isopropylacrylamide; PNIPAm) hydrogel was assayed. The individual components of the platform were physicochemically characterized before assembling. The swelling behavior and the capacity of sorption of a redox complex tris(1,10‐phenanthroline)iron(II) of the polymeric hydrogel were evaluated. Moreover, the morphological aspects of the electrospun fibers before and after carbonization were analyzed. Finally, cyclic voltammetry and chronocoulometry experiments were performed to analyze the electrochemical performance of the modular platform. In this work, we demonstrated that the platform takes advantage of the3D structure of the electrospun mat and the selective sorption of the hydrogel for the electrochemical sensing target analyte. The iron sensing using its complexation into the tris(1,10‐phenanthroline)iron(II) redox complex was assessed by differential pulse voltammetry (DPV). The anodic peak current showed a linear relation versus iron complex concentration in the range of 10–80 μmol L−1 with a detection limit of 0.103 μmol L−1. All the results herein presented suggest that a synergistic combination of large surface area carbon fiber electrodes and ion retaining hydrogel has been achieved.
In vitro construction of cell-laden nerve grafts has huge promising for promoting nerve regeneration after peripheral nerve injury (PNI). Herein, a photothermal responsive cell-laden self-rolling ...poly-N-isopropylacrylamide (PNIPAM) hydrogel containing dopamine hydrochloride (DOPA) modified multi-walled carbon nanotubes (MWCNTs) is fabricated by surface modification technology and in-situ free radical polymerization. The MWCNTs modified with 2 mg/mL dopamine (2 DM) has the most obvious photothermal responsiveness with good dispersibility and stability. The PNIPAM photothermal responsive hydrogel containing 2 DM displays a porous structure, good hydrophilicity, and reversible photothermal responsiveness. MTT detection shows that the hydrogel is non-toxic while near infrared radiation does not affect Schwann cell's viability. Compared with the Schwann cells grown on the 2D plane, the Schwann cells in the 3D hydrogel possess better growth behavior, release more nerve growth factors, and significantly upregulate the gene expression related to myelin sheath and cytoskeleton. Thus, the prepared hydrogel here possesses a promoting effect on nerve cells growth, and is expected to further improve the capability of nerve grafts on repairing PNI. The study is expected to provide experimental and theoretical basis for the design and preparation of cell-laden tissue-engineered nerve grafts with excellent performance.
Here it is demonstrated that mesoporous silicas (MPSs) can be used as effective “topological crosslinkers” for poly(N‐isopropylacrylamide) (PNIPA) hydrogels to improve the mechanical property. ...Three‐dimensional bicontinuous mesporous silica is found to effectively reinforce the PNIPA hydrogels, as compared to nonporous silica and two‐dimensional hexagonally ordered mesoporous silica.
Firm to the touch: It is demonstrated that mesoporous silicas (MPSs) can be used as effective “topological crosslinkers” for poly(N‐isopropylacrylamide) (PNIPA) hydrogels to improve the mechanical properties. The three‐dimensional bicontinuous mesporous silica is found to effectively reinforce the PNIPA hydrogels, as compared to nonporous silica and two‐dimensional hexagonally ordered mesoporous silica.
Poly(
N-isopropylacrylamide)/poly(ethylene glycol) diacrylate (PNIPAAm/PEG-DA) microgels were used as an additive during the polymerization and/or crosslinking of PNIPAAm hydrogels to improve their ...thermosensitive properties. The influence of this additive on the property of resulting PNIPAAm hydrogels was investigated and characterized. The interior morphology by scanning electron microscopy (SEM) revealed that microgel impregnated PNIPAAm hydrogels have tighter and constrained porous network structures, although large cavities of 30–40
μm in diameter, occupied by the microgels were sporadically distributed in this constrained network. Differential scanning calorimetry (DSC) studies did not show apparent difference in lower critical solution temperature (LCST) between normal and microgel-impregnated PNIPAAm hydrogels. The incorporating of PNIPAAm/PEG-DA microgels, however, significantly improved mechanical properties of modified hydrogels when comparing with a normal PNIPAAm hydrogel, although the tendency was not strictly proportional to the microgel amount. Based on the temperature-induced swelling ratio data as well as response kinetics, microgel-impregnated hydrogels exhibited improved thermosensitive characteristics in terms of higher equilibrium swelling ratio as well as faster response rates and the level of improvement depended on the amount of microgel impregnated.
Abstract A family of injectable and thermosensitive hydrogels suitable for myocardial injection was developed to deliver cardiosphere-derived cells (CDCs), an emerging and promising cell type for ...cardiac cell therapy. The hydrogels were based on polycaprolactone, N-isopropylacrylamide, 2-hydroxyethyl methacrylate and dimethyl-γ-butyrolactone acrylate. Atom transfer radical polymerization was used to synthesize hydrogels with a well-defined structure and well-controlled properties. The hydrogel solutions possessed thermal transition temperatures around room temperature and exhibited injectability suitable for myocardial injection. At 37 °C, the hydrogel solutions were capable of forming solid gels within 5s. This would allow the hydrogels to largely retain in the heart during injection. The hydrogels were highly flexible at body temperature with moduli matching those of the rat and human myocardium, and breaking strains higher than those of the myocardium, enabling them to respond synchronically with heart motion. The well-controlled polymer structure allowed for precisely controlling and decoupling water content and stiffness that affect cell differentiation. DNA assay demonstrated that CDCs proliferated in the 3D hydrogels during a 2-week culture period. CDCs maintained their colony formation capability in the hydrogel. Interestingly, hydrogels directed CDCs differentiation into mature cardiac lineage. At mRNA level, the mature cardiac specific transcript factors cardiac troponin T (cTnT) and cardiac myosin heavy chain (MYH6) were up-regulated, while the pre-mature cardiac marker GATA4 was down-regulated even after 1 day of encapsulation. CDC differentiation was interplayed by hydrogel stiffness and collagen in the hydrogel. Hydrogel with modulus ∼31 kPa was found to more significantly up-regulate cardiac expression than that with modulus ∼5 or ∼63 kPa. cTnT expression was largely regulated by both stiffness and collagen while MYH6 was mainly regulated by stiffness. Immunohistochemistry study showed that CDCs expressed cardiac troponin I and MYH6 proteins after 2 weeks of culture. These results demonstrate that the thermosensitive hydrogels not only possess physical properties suitable for myocardial injection, but also promote CDC proliferation and cardiac differentiation. These hydrogels represent potential candidates for delivery of CDCs into infarcted hearts.
Cell sheet engineering technique has been applied to treat various tissues without the use of a traditional scaffold. To date, methods for the cell sheet harvesting depend mostly on grafted ...poly(N-isopropylacrylamide) (pNIPAAm) thin layers, while the native pNIPAAm hydrogel, which possibly presents the easiest way to prepare thermo-responsive materials, is not suitable for the cell sheet harvesting due to its low cell attachment. In this study, the graphene oxide (GO) nanosheet was utilized as an additive to enhance the bio-compatibility of the pNIPAAm hydrogel. Different concentrations of GO nanosheets were added to prepare GO/pNIPAAm composite hydrogels through the in-situ free radical polymerization with polyethylene glycol dimethacrylate (PEGDA) as a cross-linker. The results indicated that the physical properties of the composite hydrogels had little difference with that of the native pNIPAAm hydrogel. However, the cell attachment, proliferation and detachment behaviors on the composite hydrogel surface were greatly enhanced. Monkey fibroblast COS7 cells attached and proliferated better on the GO/pNIPAAm composite hydrogel, while intact COS7 cell sheets could be harvested from the composite hydrogels by simply lowering the temperature. In contrast, the cells appeared as clusters on the native pNIPAAm hydrogel. Furthermore, when HeLa and COS7 cells were seeded successively onto the micropatterned GO/pNIPAAm hydrogel, there could be the formation of a patterned HeLa/COS7 cell layer. The geometrically patterned GO/pNIPAAm hydrogel may provide an easy-to-prepare material for releasing patterned cell sheets compared to the specific cell-adhesive proteins reported to make patterned cell layers.
