A new class of smart structural hydrogels is prepared by introducing dual cross-linkers into a single-network system. The present hydrogel, on the one hand, exhibits excellent mechanical properties; on the other hand, it exhibits thermally induced plasticity and a shape memory effect without any overlap.

A new class of smart structural hydrogels is prepared by introducing dual cross-linkers into a single-network system. The present hydrogel, on the one hand, exhibits excellent mechanical properties; on the other hand, it exhibits thermally induced plasticity and a shape memory effect without any overlap.

CO2-responsive hydrogels, using CO2 as a “green” trigger, have recently been of considerable interest. Herein, a novel CO2-responsive self-healable hydrogel is fabricated by simply mixing hydrophobically modified polyacrylamide (HMPAM) with sodium dodecyl sulfate (SDS)–N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA) surfactant micelles. In the presence of CO2, the SDS–TMPDA spherical micelles transform into long wormlike micelles, serving as multivalent cross-linkages to bridge HMPAM chains based on hydrophobic interactions. The interpenetrating three-dimensional network induces a sol-to-gel transition, accompanied by a 360 and 400 times enhancement of the zero-shear viscosity and storage modulus, G′ (ω = 6.28 rad s−1), respectively. In additon, the sol–gel transition can be repeatedly and reversibly switched by cyclically bubbling and removing CO2 without any harm. Furthermore, the CO2-responsive hydrogel exhibits significant shear-thinning and self-healing properties, suggesting that the hydrogel is injectable and could be used as a potential plug to block CO2 gas breakthrough channels during CO2 flooding. Therefore, we believe that the presented work will enable the development of the design of CO2-responsive self-healable hydrogels and their practical applications.

It is highly desirable to develop hydrogels that possess excellent mechanical properties and self-healing ability. In this study, a highly stretchable, puncture resistant and self-healing hydrogel is prepared, via in situ copolymerization of a functional monomer, N-acryloyl-6-aminocaproic acid (AACA), and Pluronic F127 diacrylate (F127DA) as macro-cross-linkers in aqueous solution at 50 °C. Owing to the toughness-enhancement mechanism induced by F127DA micelles, the elongation ratio and tensile strength at break of the optimal hydrogel reach up to 2500% and 69 kPa, respectively. Meanwhile, a stab test shows that the hydrogels can be stabbed by a steel needle without any damage. What's more, the hydrogels exhibit excellent self-healing ability, due to multiple hydrogen bonding between protonated PAACA groups. And the hydrogels show pH-responsive cyclic swelling and de-swelling behaviors because of the pH sensitivity of AACA. Thus, the present hydrogels would provide new opportunities with regard to the design and practical application of hydrogel systems.

Injectable self-healing hydrogels have found broad applications in drug delivery, tissue engineering and controlled 3D cell culture. Recently, cyclic disulfides were found to be useful in cross-linking and stabilizing liposomes by disulfide exchange polymerization, benefiting from the enhanced reactivity of the disulfide bonds. Herein, we report an injectable self-healing hydrogel constructed from cross-linked F127 with thermo and pH dual responsivity. The rapid sol–gel transition ability at body temperature allows it to be used as an injectable hydrogel. And the increased reactivity of the disulfides of cyclic dithiolane due to the ring tension makes the hydrogel self-heal under not only alkaline conditions but also neutral or even mildly acidic conditions.

Injectable self-healing hydrogels have found broad applications in drug delivery, tissue engineering and controlled 3D cell culture. Recently, cyclic disulfides were found to be useful in cross-linking and stabilizing liposomes by disulfide exchange polymerization, benefiting from the enhanced reactivity of the disulfide bonds. Herein, we report an injectable self-healing hydrogel constructed from cross-linked F127 with thermo and pH dual responsivity. The rapid sol–gel transition ability at body temperature allows it to be used as an injectable hydrogel. And the increased reactivity of the disulfides of cyclic dithiolane due to the ring tension makes the hydrogel self-heal under not only alkaline conditions but also neutral or even mildly acidic conditions.

Cyclodextrin–polypseudorotaxane hydrogels have attracted extensive attention for their potential application in biomedical fields. Herein, we develop a facile strategy for the in situ formation of mechanically tough polypseudorotaxane hydrogels through photoinitiated copolymerization of poly(ethylene glycol) methyl ether methacrylate, acrylamide and sodium acrylate in α-CD solution at 60 °C. For the first time, we manage to screen the host–guest interaction between α-CD and PEG before copolymerization in the presence of a temporary hydrogen bonding weakening monomer (acrylamide) at a suitable temperature (60 °C). This shielding effect weakens gradually during polymerization, thus leading to the formation of polypseudorotaxane aggregations and a tough physical hydrogel. The hydrogel can bear a large compressive strain (80%) without rupture, and exhibits excellent antifatigue properties. Furthermore, this hydrogel could be endowed with thermal/ascorbic acid activated shape memory performance after being treated with FeCl3 solution. This simple method will contribute to the design and application of smart supramolecular hydrogels.

Stimuli-triggered degradable hydrogels have found broad applications in controlled release of drugs, fragrances, flavourings and fertilizers. Recently, multi-stimuli responsive micelle-based hydrogels have gained focus, since they could respond to a combination of external stimuli. Herein, a multi-stimuli responsive supramolecular hydrogel with great potential for biomedical application was prepared, which was composed of the micelle-forming diblock copolymer poly[(N-isopropylacrylamide-co-2-nitrobenzyl acrylate)-block-(N,N-dimethylacrylamide-co-acrylic acid)] (P(NIPAM-co-NBA)-b-P(DMA-co-AA)), and physically cross-linked by supramolecular complexation between AA groups and ferric ions (Fe3+), exhibiting gel–sol transition caused by UV irradiation, multidentate ligands (EDTA) and redox agents (Na2S2O4).

Shape memory hydrogels offer the ability to recover their permanent shape from temporarily trapped shapes without application of external forces. Here, we report a novel dual-responsive shape memory hydrogel with characteristic thermoplasticity. The water-insoluble hydrogel is prepared by simple ternary copolymerization of acrylamide (AM) and acrylic acid (AA) with low amounts of a cationic surfmer, in the absence of organic crosslinkers. Through either ionic/complex binding of carboxyl groups via trivalent cations or salt-dependent hydrophobic association, the hydrogel can memorize a temporary shape successfully, which recovers its permanent form in the presence of a reducing agent or deionized water. Besides, the unique thermoplasticity of the hydrophobic polyampholyte hydrogel allows the change of its permanent shape upon heating and the fixation after cooling, which is in strong contrast to the conventional chemically cross-linked shape memory hydrogels. This fascinating feature undoubtedly enriches the shape memory hydrogel systems. Thus, we believe that the facile strategy could provide new opportunities with regard to the design and practical application of stimulus-responsive hydrogel systems.

Light-induced shape memory polymers represent a class of stimuli-responsive materials that can recover their permanent shapes from temporarily trapped ones upon exposure to light illumination. Although much effort has been devoted to developing various light-responsive shape memory polymers, fabrication of such a light-responsive shape memory hydrogel still remains a challenge compared to neat polymers in their dry state. Herein, we developed a facile and general strategy to endow conventional hydrogel systems with ultraviolet (UV)-controlled shape memory performance simply using a photoacid generator (PAG) as a trigger. The process involves shape fixity through coordination interaction between imidazole groups and metal ions, and shape recovery by switching off the complexation via PAG photolysis reaction which leads to the protonation of imidazole groups. Furthermore, this convenient strategy is proved to be applicable to other pre-existing hydrogels such as a boronate ester cross-linked melamine–poly(vinyl alcohol) (PVA) hydrogel. We believe this method could provide a new opportunity with regard to the design and practical application of light-controlled shape memory hydrogels.

In this paper, we report a CO2/N2-switchable sol to gel transition system based on a triblock copolymer of dimethylaminoethyl methacrylate (DMAEMA) and ethylene oxide (EO), with a measured composition DMAEMA6–EO109–DMAEMA6, in aqueous nanoclay dispersions. LAPONITE® is exfoliated and stabilized by Pluronic F127. The aqueous mixture exhibits a strong response to CO2, changing from a low viscous sol to a self-healable gel. In the presence of CO2, the PDMAEMA blocks are protonated and the positive charged triblock copolymer bridge the negative charged nanoclays, formation of a physical network. As a consequence, a sol to gel transition is observed at the macro level. Upon removal of CO2 through bubbling with N2, a corresponding gel to sol transition occurs due to the deconstruction of the physical network, which is a result of the departure of the deprotonated PDMAEMA blocks from the nanoclays. This sol to gel transition is fully reversible. Furthermore, the formed gel possesses excellent self-healing ability, meaning that this hydrogel is capable of autonomous healing upon damage. Thus, we believe the fundamentals of the present CO2-responsive smart hydrogel may hold promise for a wide range of areas, such as intelligent delivery systems and smart biomaterial fields, or a potential CO2 plugging agent for enhanced oil recovery (EOR) performed by CO2 flooding.

Self-healing systems that can spontaneously repair their damage would significantly improve the safety and prolong the lifetime of man-made materials. As external energy or healing agents are required in most of the self-healing approaches, non-covalently cross-linked polymeric hydrogels with intrinsic healing nature have attracted much attention recently. We present here a P(AM-co-DMAPS) zwitterionic copolymer based self-healing hydrogel, where AM and DMAPS are acrylamide and 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, respectively. The electrostatic interactions within DMAPS and hydrogen bonding between AM moieties contribute to the physical cross-linking of the polymer chains and self-healing ability of the hydrogel. The reported strategy represents a general and facile route to construct zwitterionic copolymer based self-healable functional hydrogels for potential applications in the field of enhanced oil recovery (EOR).

A novel ferric-phosphate induced shape memory (SM) hydrogel is prepared by the one-step copolymerization of isopropenyl phosphonic acid (IPPA) and acrylamide (AM) in the presence of a cross-linker polyethylene glycol diacrylate (PEGDA). Different from the traditional SM hydrogels, our SM hydrogel can be processed into various shapes as needed and recovers to its original form in ‘multi-conditions’ such as in the presence of a reducing agent or in the presence of a competitive complexing agent. This unique feature is attributed to the fact that the oxidized ferric ions show a high complexation ability with phosphate groups of IPPA, which acts as a physical crosslinker to form the secondary networks within the hydrogels to induce the shape memory effect. The memory behavior was totally reversible, owing to Fe3+ that can be reduced to Fe2+ and extracted by the complexing agent. Particularly, the SM hydrogels exhibit controllable and good mechanical characteristics by introduction of the ferric ions, i.e., the elastic modulus can increase from 2 kPa to 70 kPa dramatically. Learning from biological systems, phosphate-metal ion based hydrogels could become an attractive candidate for various biomedical and environmental applications.

A new C22 tailed sarcosinate anionic surfactant, 2-(N-erucacyl-N-methyl amido) acetate (EMAA), has been synthesized by use of the erucic acid and a hydrotrope—sarcosine. In contrast to the common method, which blends the hydrotrope with a surfactant, the sarcosine has been introduced into the anionic surfactant through chemical modification. Interestingly, the resultant C22 tailed anionic surfactant shows excellent water solubility despite the ultra-long alkyl chain. Besides, the EMAA also exhibits high surface activity, and pH controllable micelles to vesicles transition (MVT). Rheology studies have revealed that the rheological properties of EMAA solutions are influenced by the concentration, temperature, salt, and pH dramatically. Aside from the excellent water solubility, the original feature highlighted in this work is that such a new C22 tailed sarcosinate anionic surfactant exhibits good temperature resistance. Compared to the potassium oleate (KOA), the zero-shear viscosity of the EMAA solution is nearly 3 orders of magnitude higher under the same conditions.

The successful construction of a thermogelling system for the hydrophobically modified polyacrylamide (HMPAM)/α-CD mixture is reported featuring an application to the host–guest approach. It has been shown that the thermogelling property, masked by the strong intermolecular hydrophobic interaction, can be engineered to display by means of the host–guest approach, requiring no special synthesis, no third competitive guest and no harsh conditions. The findings of this work provide the basis for understanding and controlling the properties of hydrophobically modified polymers, fostering their use in a wide range of applications, including microfluidics, controlled release, tertiary oil recovery and smart materials.

Stimuli-responsive materials are being developed at a rapid pace because of their many potential applications. Here, we report that the conventional responseless hydrophobically modified p(AM/C12) hydrogel can be engineered to show fascinating pH-responsive and self-healing abilities simply in combination with a responser, sodium oleate (NaOA). The use of vesicle-to-micelle transition (VMT) of a surfactant by altering the pH in a narrow range endows the reversible sol–gel transition property to the conventional responseless hydrogel. As a result, we can modulate the rheological properties of the networks from highly elastic to viscous repeatedly, as well as vary the dynamic modulus over four orders of magnitude by simply adjusting the pH. Another particular interest is that such a vesicle-loaded hydrogel displays self-healing features through the autonomic reconstruction without the use of a healing agent. This type of pH-responsive self-healing hydrogel holds promise for the invention of new “smart” polymer materials.

Combining the Langevin Dynamics method and the Computational Fluid Dynamics method, under the conditions of Knudsen number Kn ≤ 10−1, we investigated the dynamics of a linear polymer transported into a channel of width D = 4σ embedded in two dimensions, driven by force-mimicked steady convergent microfluidics. We have proven that a critical volume-flow rate Jc ∼ kBT/η ∼ 1/η exists in polymer transport, independent of chain length. Once the polymer has found the pore entrance in advance, we find that linear transport time, τ, is proportional to chain length N, but inversely proportional to volume-flow rate J; otherwise, if the polymer does not find the pore entrance in advance, we find that with regard to the linear transport probability, P, the law of P ∼ N0.25Jcexp(−k′/J) exists, where k′ is a positive constant dependent only on channel geometry, friction coefficient and the position fixing polymer head outside the channel before the transport process starts, indicating that polymer initial conformations can affect the polymer transport probability.

The sol-gel transition of methylcellulose (MC) solutions in the presence of ortho-methoxycinnamic acid (OMCA) or cetyltrimethylammonium bromide (CTAB) and in the coexistence of OMCA and CTAB was determined by the rheological measurement. It has been found that the sol-gel transition temperature of MC solutions increases linearly with the concentration of either OMCA or CTAB in solution, respectively. However, in the coexistence of OMCA and CTAB, the sol-gel transition temperature of MC solutions remains invariable, independent of the concentration of CTAB in solution. The experimental results show that OMCA has priority to adsorb on the methyl group of MC chains to form polymer-bound aggregates. In particular, these aggregates inhibit the hydrophobic interaction between CTAB and the methyl group of MC chains completely. Taking into account the fact that OMCA is almost insoluble in MC-free solutions but dissolves very well in aqueous MC solutions, we propose the formation of the core-shell architecture prompted by OMCA and the methyl group of MC chains, with the methyl group of MC chains serving as the core and the self-assembly of OMCA molecules serving as the shell. Obviously, the formation of the core-shell structure increases the solubility of OMCA, improves the stability of methyl groups of MC chains at high temperatures and inhibits the hydrophobic interaction between CTAB and the methyl group of MC chains in solution. The abnormal behavior relating to the sol-gel transition of MC solutions in the presence of OMCA or in the coexistence of OMCA and CTAB is therefore explained. Upon UV irradiation, the sol-gel transition temperature of MC solutions in the presence of OMCA, or in the coexistence of OMCA and CTAB, decreases notably. However, the dependence of the sol-gel transition temperature of MC solutions as a function of OMCA concentration, or CTAB concentration in the presence of OMCA, does not change after UV irradiation.

Gemini surfactants 22:1-s-22:1, where s = 2 and 6 methylene groups and 22:1 refer to erucyl dimethylammonium bromide chains, together with the monomeric surfactant erucyl bis-(hydroxyethyl) methylammonium bromide (EHAB) which has the same long unsaturated tails with gemini surfactants, were synthesized and characterized and solution properties of these surfactants were investigated using surface tension, conductivity and viscosity measurement. It has been found that the critical micelle concentration (cmc) values of 22:1-2-22:1 and 22:1-6-22:1 are 15.4 and 8.3 μM, respectively, less than the cmc value of EHAB (38 μM). On the other hand, the surface tension of 22:1-2-22:1 and 22:1-6-22:1 at cmc are 40.9 and 42.4, respectively, greater than the surface tension of EHAB (30.9 at cmc). Both 22:1-2-22:1 and 22:1-6-22:1 have nearly the same value of a0 (the minimum head group areas per surfactant molecule at the aqueous solution/air interface), which is almost the half value of a0 corresponding to EHAB. On the other hand, the ionization degree α of micelles of both 22:1-2-22:1 and 22:1-6-22:1 is approximately twice the value of α corresponding to micelles of EHAB. Though 22:1-2-22:1 has more similarity with 22:1-6-22:1 rather than EHAB as presented above, 22:1-2-22:1 in water cannot enhance the viscosity of the solution significantly in the presence of salt. In contrast, both 22:1-6-22:1 and EHAB in water can give rise to highly viscoelastic or gel-like solutions even at the high temperature in the presence of salt. In particular, 22:1-6-22:1 has proved to be a more efficient candidate for high temperature rheology-control applications than EHAB. The effect of salt upon the viscosity of 22:1-6-22:1 in aqueous solution is significant. The most proper ratio of 22:1-6-22:1/NaSal for enhancing the viscosity of solution has been proved to be 0.7.

The relative viscosity ηr and, thus, the reduced viscosity ηsp/C of polymer solution could be obtained by recording the flow times of the polymer solution and the pure solvent in a capillary viscometer. Our experimental results indicated that the measurement of the flow time of the pure solvent was unnecessary. In particular, if the recorded flow time of the pure solvent was used to determine the viscosity of polymer solution, the reduced viscosity ηsp/C exhibited either a drastic increase or a significant decrease in an extremely dilute solution, depending upon the properties of the polymer solution investigated. In this research work, a new method for determining the viscosity of polymer solutions is reported. In the proposed method, the flow time of polymer solution at zero concentration, , instead of the measured flow time of the pure solvent, was used to determine the viscosity of polymer solution. The reduced viscosity ηsp/C determined by the new method is proportional to concentration C even in an extremely dilute solution. The relative viscosity ηr vs. C plot also indicated clearly that , instead of the measured flow time of the pure solvent, should be used for determining the viscosity of polymer solution. At low concentrations, the flow time of the polymer solution was proportional to C. As a result, could be determined by extrapolating the flow time of the polymer solution to C=0.

Viscometric behavior of polyvinyl alcohol (PVA) in NaCl/water solution ranged from dilute to extremely dilute concentrations was thoroughly investigated. Due to the influence of the adsorbed polymer on the walls of Ubbelohde viscometer capillary, an upswing of the reduced viscosity (ηsp/C) vs. concentration (C) curve was observed in extremely dilute concentration. If using improved viscosity measurement procedure to delete the influence of the adsorbed polymer upon the viscosity of polymer solution, the linear relationship between ηsp/C and C of PVA in NaCl/water solution was observed to exist, even in extremely dilute solution. Furthermore, the experimental results show that the improved viscosity measurement procedure presented in this article is not only a more reasonable but also a more convenient technique to determine the viscosity of polymer solution. The adsorption of polymer on the walls of viscometer capillary has been found to be greatly associated with the solvent in which the polymer was dissolved.

Injectable self-healing hydrogels have found broad applications in drug delivery, tissue engineering and controlled 3D cell culture. Recently, cyclic disulfides were found to be useful in cross-linking and stabilizing liposomes by disulfide exchange polymerization, benefiting from the enhanced reactivity of the disulfide bonds. Herein, we report an injectable self-healing hydrogel constructed from cross-linked F127 with thermo and pH dual responsivity. The rapid sol–gel transition ability at body temperature allows it to be used as an injectable hydrogel. And the increased reactivity of the disulfides of cyclic dithiolane due to the ring tension makes the hydrogel self-heal under not only alkaline conditions but also neutral or even mildly acidic conditions.

Injectable self-healing hydrogels have found broad applications in drug delivery, tissue engineering and controlled 3D cell culture. Recently, cyclic disulfides were found to be useful in cross-linking and stabilizing liposomes by disulfide exchange polymerization, benefiting from the enhanced reactivity of the disulfide bonds. Herein, we report an injectable self-healing hydrogel constructed from cross-linked F127 with thermo and pH dual responsivity. The rapid sol–gel transition ability at body temperature allows it to be used as an injectable hydrogel. And the increased reactivity of the disulfides of cyclic dithiolane due to the ring tension makes the hydrogel self-heal under not only alkaline conditions but also neutral or even mildly acidic conditions.

Stimuli-responsive materials are being developed at a rapid pace because of their many potential applications. Here, we report that the conventional responseless hydrophobically modified p(AM/C12) hydrogel can be engineered to show fascinating pH-responsive and self-healing abilities simply in combination with a responser, sodium oleate (NaOA). The use of vesicle-to-micelle transition (VMT) of a surfactant by altering the pH in a narrow range endows the reversible sol–gel transition property to the conventional responseless hydrogel. As a result, we can modulate the rheological properties of the networks from highly elastic to viscous repeatedly, as well as vary the dynamic modulus over four orders of magnitude by simply adjusting the pH. Another particular interest is that such a vesicle-loaded hydrogel displays self-healing features through the autonomic reconstruction without the use of a healing agent. This type of pH-responsive self-healing hydrogel holds promise for the invention of new “smart” polymer materials.

Cyclodextrin–polypseudorotaxane hydrogels have attracted extensive attention for their potential application in biomedical fields. Herein, we develop a facile strategy for the in situ formation of mechanically tough polypseudorotaxane hydrogels through photoinitiated copolymerization of poly(ethylene glycol) methyl ether methacrylate, acrylamide and sodium acrylate in α-CD solution at 60 °C. For the first time, we manage to screen the host–guest interaction between α-CD and PEG before copolymerization in the presence of a temporary hydrogen bonding weakening monomer (acrylamide) at a suitable temperature (60 °C). This shielding effect weakens gradually during polymerization, thus leading to the formation of polypseudorotaxane aggregations and a tough physical hydrogel. The hydrogel can bear a large compressive strain (80%) without rupture, and exhibits excellent antifatigue properties. Furthermore, this hydrogel could be endowed with thermal/ascorbic acid activated shape memory performance after being treated with FeCl3 solution. This simple method will contribute to the design and application of smart supramolecular hydrogels.

The successful construction of a thermogelling system for the hydrophobically modified polyacrylamide (HMPAM)/α-CD mixture is reported featuring an application to the host–guest approach. It has been shown that the thermogelling property, masked by the strong intermolecular hydrophobic interaction, can be engineered to display by means of the host–guest approach, requiring no special synthesis, no third competitive guest and no harsh conditions. The findings of this work provide the basis for understanding and controlling the properties of hydrophobically modified polymers, fostering their use in a wide range of applications, including microfluidics, controlled release, tertiary oil recovery and smart materials.