Waterlogged wooden archaeological relics are prone to lose their dimensional and mechanical stability during dehydration, thus developing a green/effective strategy for consolidating a waterlogged wood upon its drying has drawn tremendous attention. Inspired by the specific topological structure and superior mechanical properties of human bone, we reported an environmentally friendly biomimetic consolidation method for restoring the waterlogged wood in this work. Briefly, branched PEI (poly(ethylenimine)) molecules were first incorporated into the waterlogged wood matrix by submerging to formulate a spongy interior, mimicking the structure of cancellous bone; then, GA (glutaraldehyde) solution or BDDE (1,4-butanediol diglycidyl ether) solution was sprayed onto the surface of a PEI-treated sample to form a dense exterior, mimicking the structure of cortical bone. Through two systematic orthogonal experiments, we identified the feasibility of this strategy and screened out the optimum feeding composition of the three reagents (10 wt % PEI, 6 wt % GA, and 3 wt % BDDE). As to targeted samples (10 wt % PEI + 6 wt % GA and 10 wt % PEI + 3 wt % BDDE), their dimension shrinkage rates along the X-, Y-, and Z-axis were all below or close to 3%. To figure out whether the rationale behind this strategy fitted well with our theoretical assumption, we first investigated the composition and structure of the BDDE/PEI-and GA/PEI-treated waterlogged wood samples through scanning electron microscopy (SEM), Fourier transform infrared spectrum (FT-IR), thermogravimetric−differential thermal (TGA−DTA) coupling tests, etc. and proved their biomimetic structure. Next, we explained the consolidation mechanism of this method by analyzing the crystalline phase and mechanical properties of the BDDE/PEI-or GA/PEI-treated samples. We thought that PEI induced the noncovalent cross-linking and BDDE-or GA-induced covalent cross-linking-mediated ordered arrangement of cellulose along different planes at the edge and middle of the waterlogged wood, respectively, therefore constructing a strong/stiff exterior and an elastic interior. Because of this specific biomimetic structure, the BDDE/PEI-or GA/PEI-treated waterlogged wood demonstrated simultaneously high strength, stiffness, and mechanical buffer capability and therefore could resist shrinkage stress and maintain high dimensional stability upon drying.
Currently, polymer‐based hydrogels have found applications in many fields but are faced with a challenge how to reach an optimum trade‐off between strength and toughness. In this regard, two prototypes (i.e., poly(AAm‐co‐AA)/CS‐Fe3+ and poly(AAm‐co‐AA)/PVA‐Fe3+ double‐network (DN) hydrogels), following the fundamental principles, are developed for the first time through constructing covalent/ionic dual cross‐links in the first networks while inducing polymer entanglement/crystallite‐based hidden chains in the second networks. Through systematic investigation of their comprehensive mechanical properties, the rationality of the proof‐of‐concept strategy is verified but some modifications are needed for further improvement. In summary, the synergy of DN structure and integrated irreversible/reversible dual cross‐links in a sacrificing network can formulate an effective energy‐dissipation system for high toughness, high toughness/strain recoverability, and high antifatigue capability. High‐functionality cross‐links based on polymer crystallites in the second network enhance the strength and elasticity of the as‐prepared hydrogels but destroy the flexibility and softness of the matrix phase, therefore sacrificing their stretchability. For optimal hydrogel design, introducing high‐functionality cross‐links in the matrix network while maintaining its flexibility or constructing hidden chains in the sacrificing network may be an ideal strategy to solve the afore‐mentioned problem.
Currently, hydrogels simultaneously featuring high strength, high toughness, superior recoverability, and benign anti-fatigue properties have demonstrated great application potential in broad fields; thus, great efforts have been made by researchers to develop satisfactory hydrogels. Inspired by the double network (DN)-like theory, we previously reported a novel high-strength/high-toughness hydrogel which had two consecutive energy-dissipation systems, namely, the unzipping of coordinate bonds and the dissociation of the crystalline network. However, this structural design greatly damaged its stretchability, toughness recoverability, shape recoverability, and anti-fatigue capability. Thus, we realized that a soft/ductile matrix is indispensable for an advanced strong tough hydrogel. On basis of our previous work, we herein reported a modified energy-dissipation model, namely, a “binary DN-like structure” for strong tough hydrogel design for the first time. This structural model comprises three interpenetrated polymer networks: a covalent/ionic dually crosslinked tightened polymer network (stiff, first order network), a constrictive crystalline polymer network (sub-stiff, second order network), and a ductile/flexible polymer network (soft, third order network). We hypothesized that under low tension, the first order network served as the sacrificing phase through decoordination of ionic crosslinks, while the second order and third order networks together functioned as the elastic matrix phase; under high tension, the second order network worked as the energy dissipation phase (ionic crosslinks have been destroyed at the time), while the third order network played the role of the elastic matrix phase. Owing to the “binary DN-like” structure, the as-prepared hydrogel, in principle, should demonstrate enhanced energy dissipation capability, toughness/shape recoverability, and anti-fatigue/anti-tearing capability. Finally, through a series of characterizations, the unique “binary DN-like” structure was proved to fit well with our initial theoretical assumption. Moreover, compared to other energy-dissipation models, this structural design showed a significant advantage regarding comprehensive properties. Therefore, we think this design philosophy would inspire the development of advanced strong tough hydrogel in the future.
Biological fixation of a Ti implant demonstrates significant advantages over conventional physical fixation. Modifying the surface of Ti implants with hydroxyapatite (HAp) coating has proven to be a promising strategy to enhance their bone integration capability in vivo. The currently reported strategies are confronted with the following problems: (i) low interfacial bonding strength and poor structural stability under mechanical force; (ii) being incapable of encapsulating Ti implants with complex 3D geometry; (iii) complicated processing procedures and high processing costs. Here, we fabricated a bone‐like polyacrylamide/poly(vinyl alcohol)/HAp (PAAm/PVA/HAp) coating on the surface of Ti implants with complex 3D geometry through thermal induced in situ radical polymerization of pre‐adhered vicious acrylamide/PVA/HAp (AAm/PVA/HAp) emulsion. Covalent interaction between the Ti matrix and the coating was constructed through incorporating vinyl groups on the surface of Ti matrix using 3‐(trimethoxysilyl)propyl methacrylate (TMSPMA). The as‐prepared coating demonstrated a record high shear bonding strength of 144.5 MPa and 75.50 MPa in dry and moist states, respectively. In addition, its interfacial toughness reached to 1.27 kJ/m2, while its maximum motion under shear mechanical force was only 0.64 mm (moist state). Anti‐fatigue tests (approximate 100% toughness retention rate at displacement of 0.1 mm) and degradation experiment exhibited the long‐term mechanical/structural stability of the coating in a in vivo environment. BMSCs co‐culture assay demonstrated the superior cytocompatibility and osteogenic property of the coating. In sum, this work provided a simple and cost‐effective strategy to construct homogeneous and tightly anchored HAp coating on the surface of Ti implants with complex 3D geometry.Highlights Homogeneous coating on Ti surface with bone‐like composition and structure. Being capable of encapsulating Ti implants with complex 3D geometry. Record high interfacial bonding strength/toughness. long‐term structural/mechanical stability in a moist environment. Superior biocompatibility and osteogenic property.
Developing customizable pH-responsiveness for supramolecular hydrogels is of great significance and has drawn tremendous attention. Through systematic simulation analysis, we formulated a simple supramolecular hydrogel (i.e., poly(AAm-co-NaSS)/BSA on basis of...
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