Robust hydrogel-integrated microsystems enabled by enhanced interfacial bonding strength

Noncovalent hydrogels, compared to covalent hydrogels, have distinctive advantages including biocompatibility and self-healing property but tend to have poor mechanical robustness, thus restricting their application spectrum. A clue to increase utility of such soft hydrogels without chemical bulk modification can be witnessed in biological organ walls where soft mucous epithelial layers are juxtaposed with tough connective tissues. Perhaps, similarly, bonding noncovalent hydrogels to stronger materials, such as tough hydrogels, might be a viable approach for increasing stability and scalability as well as creating novel functions for hydrogel-based systems. However when attempting to bond these two materials, each of the four existing hydrogel-hydrogel bonding method has practical shortcomings. In this work, we introduce a mucosa-inspired bonding method that realizes interfacial bonding of noncovalent hydrogels to tough, hybrid hydrogels without external glue or bulk modification of the noncovalent gel while preserving interfacial micropatterns. The procedure is simple and we confirmed broad applicability with various noncovalent hydrogels and tough hydrogels. We demonstrated the utility of our bonding method with novel applications regarding in vitro assay, soft robotics and biologically inspired systems.

Fabrication of Enzyme-Loaded Cartridges Using CO2-Assisted Polymer Compression

An enzyme-loaded disk-shaped cartridge was fabricated using CO2-assisted polymer compression (CAPC), which is a polymer-bonding method that does not use heat. In this process, after the enzyme was loaded onto mesoporous silica, it was placed in a container fabricated from laminated fibrous sheets using CAPC. Subsequently, the lid and container were bonded via CAPC. Verification using the reductive decomposition reaction of an azo dye (methyl red) showed that the enzyme was not deactivated and that a reaction cartridge was created successfully.

Three-dimensional numerical analysis of tubular adhesive joints under torsional loads

Bonding method using adhesives has gained a lot of presence in the design of mechanical structures in several industries, especially in the aeronautics and automobile industry. Bonded joints are widely used to join tubular components, in vehicle frames like aeroplanes and automobiles. For the design process of these joints, analytical or numerical predictive techniques can be used. This work performs a numerical study in order to evaluate the torsional performance of aluminium tubular adhesive joints (AW6082-T651), considering the variation of the main geometric parameters, such as overlap length (L O) and tubes’ thickness. In order to predict the strength, the Finite Element Method (FEM) was used with Cohesive Zone Models (CZM), whose analysis based itself on the internal stresses of the adhesive, namely the analysis of shear stress (τxy) and joint strength, measured by the maximum torsional moment (M m). Previously, validation with experimental data was carried out. The technique was positively validated, and a significant geometry on M m was found, except for L O.

Effect of various parameters on the shear strength of solid-state nanoporous Cu bonding in Cu–Cu disks for power device packaging

Nanoparticle sintering is considered a promising alternative bonding method to Pb- based soldering for the attachment of components in high-temperature electronic devices. However, the technology still poses certain challenges, such as difficulty controlling joint thickness and the generation of voids owing to solvent evaporation. In this study, a solid-state (solvent-free), nanoporous-Cu (NPC) bonding method was examined. The effect of bonding temperatures (200–400°C) and atmospheres (N2 or formic acid) on the shear strength of joints formed between NPC sheets and bare Cu disks were investigated by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. It was shown that the bondability of NPC under an N2 atmosphere is closely related to the oxide layer formed on its surface that impairs the diffusion of Cu atoms between the NPC and Cu substrate. Furthermore, the coarsening of the NPC microstructure under a formic acid atmosphere at ≥ 350°C owing to the rapid diffusion of Cu atoms and accompanying plastic deformation induced by surface stress enhances the shear strength of the resulting NPC/Cu joint. The shear strength of NPC/Cu joints formed under a formic acid atmosphere increased from 14.1 to 35.9 MPa with increasing bonding temperature. Based on the results of the investigation, a mechanism was proposed to explain the superiority of the Cu–Cu joints achieved using this method.

Microstructure and Mechanical Properties of Vacuum Diffusion Bonded Ti2AlNb/Ti/TC4 Joint

In this paper, the Ti2AlNb alloy was bonded to TC4 alloy using the vacuum diffusion bonding method with a Ti interlayer. The interfacial microstructure of the Ti2AlNb/Ti/TC4 joint was characterized. The relationship between the bonding parameters and the microstructure and mechanical property of the joints was explored. Results indicated that the interdiffusion of Nb and Al elements between the interlayer and substrates promoted the formation of the lamellar α + β dual-phase structure in the joint. The bonding parameters determined the diffusion distance of Nb and Al elements, thus controlling the characteristics of the lamellar α + β dual-phase structure. When the Ti2AlNb alloy and TC4 alloy were bonded at 950 °C for 30 min under a pressure of 10 MPa, the elemental diffusion in the bonding couple was sufficient and the joint possessed the maximum shear strength of 549 MPa.