High‐Strength Hydrogels with Integrated Functions of H‐bonding and Thermoresponsive Surface‐Mediated Reverse Transfection and Cell Detachment

Zhu

et al. 2015

Adv Funct Materials

555

376

1 wileyonlinelibrary.com recoverability and self-healing property, due to their intrinsic structural heterogeneity and/or lack of effi cient energydissipation mechanisms, [ 13 ] which greatly limit their uses for other applications requiring highly mechanical properties such as cartilage, tendon, muscle, and blood vessel.Many efforts have been made to develop tough hydrogels with new microstructures and toughening mechanisms, such as double network hydrogels, [ 14 ] nanocomposite hydrogels, [ 15 ] sliding-ring hydrogels, [ 16 ] macromolecular microsphere composite hydrogels, [ 17 ] tetrapolyethylene glycol hydrogels, [ 18 ] hydrophobically associated hydrogels, [ 19,20 ] and dipole-dipole or hydrogen bonding enhanced hydrogels. [ 21,22 ] Among them, double network (DN) hydrogels have demonstrated their excellent mechanical properties. The existing knowledge of DN gels from synthesis methods, network structures, to toughening mechanisms mainly comes from chemically cross-linked DN gels. [ 23 ] Both networks with contrasting structures in DN gels are separately crosslinked by covalent bonds, [ 24 ] and the interpenetration of two contrasting networks makes the chemically linked DN gels both tough and soft, as evidenced by stiffness (elastic modulus of 0.1-1.0 MPa), strength (failure tensile stress of 1-10 MPa, strain 1000%-2000%, failure compressive stress 20-60 MPa, strain 90%-95%), and toughness (tearing fracture energy of 10 2 -10 3 J m −2 ). [ 23 ] Chemically linked DN gels have comparable toughness to cartilage and rubber. The toughening mechanisms are largely based on "sacrifi cial bonds" that break from the fi rst network to effectively dissipate energy, protect the second network, sustain stress, and store elastic energy, thus to reinforce the gels. However, the fracture of the fi rst network also causes irreversible and permanent bond breaks, making the gels very diffi cult to be repaired and recovered from damages and fatigues. [ 25 ] Thus, the internal fracture process of the fi rst network is considered to be critical for toughness enhancement, because relatively large damage zones formed in the fi rst network allow for more accumulated damage before macroscopic crack propagation occurs throughout whole networks. [ 26,27 ] Double network (DN) hydrogels with two strong asymmetric networks being chemically linked have demonstrated their excellent mechanical properties as the toughest hydrogels, but chemically linked DN gels often exhibit negligible fatigue resistance and poor self-healing property due to the irreversible chain breaks in covalent-linked networks. Here, a new design strategy is proposed and demonstrated to improve both fatigue resistance and self-healing property of DN gels by introducing a ductile, nonsoft gel with strong hydrophobic interactions as the second network. Based on this design strategy, a new type of fully physically cross-linked Agar/hydrophobically associated polyacrylamide (HPAAm) DN gels are synthesized by a simple one-pot method. Agar/ HPAAm DN gels exhibit excellent mech...

mentioning

confidence: 99%

A Novel Design Strategy for Fully Physically Linked Double Network Hydrogels with Tough, Fatigue Resistant, and Self‐Healing Properties

Zhu

et al. 2015

Adv Funct Materials

555

376

“…Therefore, the dual physical crosslinking from DAT-DAT hydrogen bonding and Ca 2+ complexation can act synergistically to greatly increase the mechanical strength of hydrogels. 26,30 Shape memory performance It is known that the shielding effect is dependent on the concentration of the counter ions.…”

Section: Effect Of Calcium Ions On the Mechanical Properties Of Hydromentioning

confidence: 99%

Hydrogen bonded and ionically crosslinked high strength hydrogels exhibiting Ca²⁺-triggered shape memory properties and volume shrinkage for cell detachment

Ren

Zhang

et al. 2015

J. Mater. Chem. B

Self Cite

A hydrogen-bonded and calcium ion crosslinked hydrogel, termed as PVDT-PAA, was synthesized by one-step photo-polymerization of 2-vinyl-4,6-diamino-1,3,5-triazine (VDT), acrylic acid (AA), and polyethylene glycol diacrylate (PEGDA, Mn=4,000). Combined physical crosslinkings from inter-diaminotriazine and coordination of Ca 2+ with carboxyls contributed to a significant enhancement in the mechanical properties of PVDT-PAA hydrogels. Furthermore, reversible Ca 2+ crosslinking imparted shape memory function to the hydrogel which were able to firmly memorize multiform shapes and return to the initial state in response to Ca 2+ . Interestingly, the PVDT-PAA hydrogels with weaker H-bonding interaction demonstrated a sharp volume change phenomenon induced by Ca 2+ . This volume change could be utilized to trigger unharmful cell detachment from hydrogel surface supposedly due to Ca 2+ -induced marked variation of 2 mechanotransduction between cells and substrate interface. This H-bonding and ion-crosslinking strategy opens a new opportunity for designing and constructing multifunctional high strength hydrogels for the biomedical applications. Graphic AbstractDiaminotriazine hydrogen bonding reinforced and Ca 2+ -crosslinked high strength shape memory hydrogels are fabricated. Ca 2+_ induced dramatic volume shrinkage is utilized to trigger the unharmful cell detachment.

Macromol. Rapid Commun.

“…[ 21,22,25 ] Also, by copolymerizing N-isopropylacrylamide (NIPAAm) or spiropyran monomer, these PVDT-based hydrogels were capable of responding to the thermal stimulus or light stimulus, respectively, without worsening their high strengths. [ 18,26,27 ] Nonetheless, these hydrogels were poor in dissipating external energy, and in particular sensitive to the notches preformed. Lately, we reported high strength and tough thermoresponsive shape memory hydrogels with the combination of DDR and hydrogen bonding interaction in one single network.…”

Section: Introductionmentioning

confidence: 99%

“…[ 13 ] The reported work suggests that introducing sacrifi cial network or reversible weak physical crosslinking into the hydrogel network can contribute to the enhancement of toughness. [14][15][16] Recently, we designed and constructed high strength stimuli-responsive hydrogels based on strong intermolecular hydrogen bonding of diaminotriazine (DAT) residues in poly(vinyl diaminotriazine) (PVDT) [ 8,[17][18][19][20] and CN-CN dipole-dipole reinforcement (DDR) in polyacrylonitrile. [21][22][23] These hydrogels turned out to exhibit high A double hydrogen bonding (DHB) hydrogel is constructed by copolymerization of 2-vinyl-4,6-diamino-1,3,5-triazine (hydrophobic hydrogen bonding monomer) and N , N -dimethylacrylamide (hydrophilic hydrogen bonding monomer) with polyethylene glycol diacrylates.…”

mentioning

confidence: 99%

Hydrogen-Bonding Toughened Hydrogels and Emerging CO₂ -Responsive Shape Memory Effect

Zhang

Liu

2015

Self Cite

A double hydrogen bonding (DHB) hydrogel is constructed by copolymerization of 2-vinyl-4,6-diamino-1,3,5-triazine (hydrophobic hydrogen bonding monomer) and N,N-dimethylacrylamide (hydrophilic hydrogen bonding monomer) with polyethylene glycol diacrylates. The DHB hydrogels demonstrate tunable robust mechanical properties by varying the ratio of hydrogen bonding monomer or crosslinker. Importantly, because of synergistic energy dissipating mechanism of strong diaminotriazine (DAT) hydrogen bonding and weak amide hydrogen bonding, the DHB hydrogels exhibit high toughness (up to 2.32 kJ m(-2)), meanwhile maintaining 0.7 MPa tensile strength, 130% elongation at break, and 8.3 MPa compressive strength. Moreover, rehydration can help to recover the mechanical properties of the cyclic loaded-unloaded gels. Attractively, the DHB hydrogels are responsive to CO2 in water, and demonstrate unprecedented CO2-triggered shape memory behavior owing to the reversible destruction and reconstruction of DAT hydrogen bonding upon passing and degassing CO2 without introducing external acid. The CO2 triggering mechanism may point out a new approach to fabricate shape memory hydrogels.