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The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young’s moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated iomaterials.

Polyampholyte hydrogels (PA gels) are drawing great attention for their excellent mechanical properties including self-healing, high toughness, and fatigue resistance. These mechanical performances are found to be attributed to the hierarchical structure of the PA gels, consisting of reversible ionic bonds at the 1 nm scale, permanent polymer network at the 10 nm scale, and icontinuous phase network at the 100 nm scale. In this work, we systematically studied the phase network formation of these gels aiming to answer the following three questions: (1) how the phase separation occurs? (2) what determines the phase structure? and (3) is this structure in thermodynamic equilibrium or not? Our results show that the phase separation occurs during dialysis of counterions from the gels and it is driven by the Coulombic and hydrophobic interactions. The phase size d0 and the number of aggregated chains in a unit cell of the phase structure n scale with the molecular weight of the partial chain between permanent effective cross-linking Meff as d0 ∼ Meff and n ∼ Meff 2, respectively. A chemical cross-linker and topological entanglement suppress phase separation, while hydrophobic interaction favors phase separation. An intrinsic correlation between the polymer density difference (Δρ) between two phases and d0 is observed (Δρ ∼ d02) as a result of the competition between the driving force to induce phase separation and the resistance to suppress the phase separation. The phase-separated structure is metastable, which is locally trapped by strong intermolecular interactions.

Polyelectrolyte complexation between oppositely charged polyelectrolytes forms coacervates in dilute solutions and thin films in concentrated solutions. It is difficult to obtain macroscopically uniform bulk polyelectrolyte complex (PEC) materials, since the two polymers form insoluble complexes quickly at the contact interface during mixing, resulting in heterogeneous aggregates. Here, we succedded in preparing bulk PEC materials based on desalting-induced polyelectrolyte complexation via viscolestic phase seperation. With a high ionic strength aquetious medium, a homogeneous and concentrated solution containing oppositely charged polyelectrolytes is prepared. Desalting of the counter-ions and co-ions of the solution through semi-permeable membranes induces viscoelastic phase separation of the solution to form a physical hydrogel with open pore structrue. Regulating the charge ratio of the two oppositely charged polymers results in significant changes in the porous morphology and mechanical properties. The charge-balanced PEC hydrogels show unique properties including high toughness and self-recovery due to the reversible ionic associations. The porous yet tough properties of bulk PEC hydrogels makes them potential candidates for applications such as cell scaffolds.

Tough triblock copolymer hydrogels with microstructures of sphere, cylinder, and laminae were constructed using a newly developed “drying and swelling” method without changing the chemical structures of their monomeric units. These tough triblock copolymer hydrogels commonly showed high fracture stress of ∼10 MPa but exhibited varied elastic moduli depending on their microstructures. Furthermore, the constructed laminar gel formed pH-sensitive photonic gel at the base conditions, providing the gel application with potential as a sensor. Given their high toughness, biocompatibility, and tunable modulus, this study helps expand the potential application of amphiphilic block copolymer hydrogels for medical and industrial use.

In this work, we develop a series of novel elastomers from acrylate monomers by one-step free radical copolymerization without using organic solvents. The dynamics of the elastomers, characterized by the Kuhn segment relaxation time τ0, is tuned over six orders of magnitude by varying the structure and composition of the acrylate monomers. Comprehensive studies on linear rheology at small deformation and tensile/fracture behaviors at large deformation of the materials are performed. A universal ductile–brittle transition of the elastomers with the criterion of [small epsi, Greek, dot above]τ0 ≂ 0.1 is observed for the diverse monomer pairs and stretch–strain rate [small epsi, Greek, dot above] and the elastomers exhibit maximum energy dissipation around the ductile–brittle transition reaching a work of extension at fracture of ∼25 MJ m−3 and a fracture energy of 20 kJ m−2. Such toughness is comparable to that of natural rubbers and is among the highest ever reported. In addition, these elastomers possess 100% self-recovery, and a relatively high self-healing efficiency (37–70%) of the cut samples at room temperature even for relatively rigid samples and strong adhesive strength on glass and polymethylmethacrylate (PMMA) substrates. The universal ductile–brittle transition of the materials means that we can use the linear rheology dynamics as fingerprints for predicting the dynamic spectra of toughness of the materials. The wide range of tunable dynamics substantially enriches the choice of elastomers for various applications, and the facile and solvent-free synthesis of these elastomers is eco-friendly, cost-effective and scalable, which greatly lowers the barrier for practical applications.

The numerical simulation results of 12 typical fire scenarios prove that the boundary conditions of tunnel entrance exert a significant influence on the accuracy and reliability of the fire numerical simulation results in metro station. In the fire scenarios with four 400-metre-long tunnels at both ends of the platform, the fire numerical simulation result is the most accurate, but the total numerical calculation time is twice more than the other fire scenarios, due to the additional volume of the computational meshes of the 4 tunnels. In order to guarantee the accuracy and reliability of the fire numerical simulation results on the condition that the computational mesh volume and numerical calculation time have not to be increased, 18 new fire scenarios with the different width of the tunnel entrance have been designed to simulate fire smoke movement in metro station, and the results are inserted into Lagrange's Interpolation Equation, then the equivalent width coefficient ε of tunnel entrance is found to be in the range of 0.34～0.55. In consideration of the mesh cell size and evacuation safety, ε is suggested to be 0.375.

この博士論文全文の閲覧方法については、以下のサイトをご参照ください。, https://www.lib.hokudai.ac.jp/dissertations/copy-guides/, (主査) 教授 龔 剣萍, 教授 佐々木 直樹, 准教授 黒川 孝幸（生命科学院）, 理学院（生命理学専攻）

(主査) 教授 龔 剣萍, 教授 佐々木 直樹, 准教授 黒川 孝幸（生命科学院）, 理学院（生命理学専攻）