Nannan Zhu,Bolin Yang,Shengnan Li,Hailong Yang,Yueyue Miao,Yang Cong,Rui Zhang,Jun Fu
A combination of multiple non-covalent interactions has been used to fabricate strong and tough hydrogels. However, mechanisms behind toughening remain unclear. In this study, a series of single-network (SN), double-network (DN), and triple-network (TN) hydrogels sequentially crosslinked by chemical bonds, freeze-thawed polyvinyl alcohol (PVA) crystallites, and ion coordination of alginate chains are systematically prepared. The contributions of hydrogen bonding, entanglements, crystallite crosslinking, and ion coordination to the dynamics of the hydrogels are comparatively studied. Dynamic mechanical analysis (DMA) reveals the apparent activation energy of hydrogen bonding from 41.1 kJ/mol to 50.6, 56.8, and 65.5 kJ/mol for SN gels with increasing PVA concentration (from 0 to 2, 6, 10 wt/vol%, respectively), whereas the corresponding apparent activation energy of chain entanglements increases from 148.3 to 160.2, 163.5, and 167.0 kJ/mol. PVA crystallites formed upon freeze-thawing act as physical crosslinks to further improve the strength and toughness of gels, as well as the activation energy (251.7 kJ/mol). Subsequent ion coordination with alginate further enhances the activation energy to 304.7 kJ/mol (Cu 2+ ), 309.3 kJ/mol (Fe 3+ ). Structural evolution studies on pre-cracked hydrogels reveal that PVA crystallites render crack blunting upon stretching. Polarized optical microscopy and scanning electron microscopy reveal the rearrangement and reconstruction of internal structures during crack propagation, including orientation and alignment of PVA crystallites. This study provides first insights to synergetic energy dissipation by non-covalent interactions of multi-network hydrogels.
There are limited fluid hemostatic agents capable of reliably controlling bleeding in wet and high-pressure environments. This study presented a barnacle-derived adhesion hemostatic paste (BAH-paste) exhibiting rapid adhesion to biological tissues and operating independently of the coagulation pathway. Upon contacting with the wound, the lipidic phase would repel blood from the interface while the adhesive phase filled with calcium–aluminum layered double hydroxide (Ca–Al LDH) nanosheets absorb blood to form a tough gel that can adhere to wet tissues, seal blood vessels, and achieve hemostasis. Benefiting from the hindering effect of dislocation movement and crack propagation of Ca–Al LDH nanosheets, the BAH-paste could withstand high burst pressures, and exhibit robust adhesion characterized by interfacial toughness ranging from 150 to 200 J·m −2 , alongside shear and tensile strengths of 40–60 kPa, respectively. The BAH-paste offered considerable fluidity, lower swelling, and efficient hemostatic properties. It demonstrated superior performance over commercial hemostatic agents in facilitating in vivo liver hemostasis in SD rats and New Zealand rabbits. Furthermore, this adhesive hemostatic paste can serve as a drug delivery platform for wound repair, significantly enhancing antimicrobial efficacy. Thus, the adhesive hemostatic paste developed here is anticipated to be effective for controlling deep and irregular bleeding.
This paper initially examines the feasibility and effectiveness on interfacial adhesion of composites when grafting nanoparticle-structured polydopamine (PDA) and chitosan around carbon fiber periphery. The resulting interfacial shear strength was maximized as 92.3 MPa, delivering 50.1 % and 15.7–16.2 % gains over those of control fiber and only polydopamine nanospheres (PDA NPs ) or only chitosan modified fiber composites. Measuring surface morphology and thermal stability of fibers found that abundant PDA NPs well adhered with the help of chitosan, highlighting nanoscale size effects and intrinsic adhesiveness of PDA. Under good wettability , rich and dense interfacial interactions (covalent and hydrogen bond , electrostatic interaction , and π conjugation) caused by PDA NPs /chitosan coating provides impetus for effective stress transfer. Additionally, the stable “soft-rigid” combination of chitosan and PDA NPs adds the efficiency of crack passivation. As such, it is hoped that this work could fully explore the possibility of PDA geometry in interphase engineering of fiber composites.
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