Fabrication of an Electrically Conductive Adhesive for Skin Mounted Bioelectronic Devices

Background: Skin mounted bioelectronics are difficult to integrate with the skin since biocompatible adhesives are not conductive or unsuitable for long-term use. Skin conformability is essential but strong adhesives can damage soft tissue in younger and frail individuals as well as the device during removal. Developing a noninvasive long-lasting biocompatible conductive adhesive for skin that can be used with bioelectronics allows for better treatment options and the improvement of patient outcomes. Methods: This study creates a soft hydrogel using graphene oxide flakes (GO) and polyvinyl alcohol. Networked GO is reduced in a solution of sodium dithionite and sodium hydroxide to form a conductive network within the hydrogel. Adhesive properties are achieved by incorporating a polyacrylic acid polymer into the hydrogel with the addition of N-hydroxysulfosuccinimide (NHS) groups to the polymer. NHS reacts with amine groups found on tissue to form covalent bonds that can be released with a biocompatible trigger solution of sodium bicarbonate and glutathione. Results: Hydration of the hydrogel at 65°C demonstrated that the hydrogel swelled anistropically with swelling ratios of 1.05/1.06/5.5 (length/width/thickness). This showed that the hydrogel can integrate into various surfaces without deformation. The hydrogel demonstrated an impedance of 106.1~164.6 Ω⋅m (20~500 Hz), which is comparable to conventional devices. The hydrogel was chemically bound to amine functionalized polydimethylsiloxane (PDMS) and glass. Peel test showed peak adhesion forces of 100.5 N⋅m-1(Force⋅Width-1) when bound to PDMS or glass. Signal quality of the hydrogel showed that the hydrogels demonstrated ECG and EMG signals comparable to commercially available materials. Conclusions: The importance of this study is to create a soft material that bonds between electrodes and skin. The results demonstrate that the hydrogel has electrical characteristics comparable to conventional electrodes for use in ECG and EMG. In addition, it can create adhesion via chemical bonds that can be released on demand.

Influence of biobased polyol type on the properties of polyurethane hotmelt adhesives for footwear joints

Polyurethanes, one of the most used polymers worldwide, are strongly dependent of non-renewable fossil resources. Thus, boosting the production of new polyurethanes based on more sustainable raw materials is crucial to move towards the footwear industry decarbonisation. The aim of this study is to synthesise and characterise reactive hotmelt polyurethanes from biomass and CO2-based polyols as bioadhesives for the footwear industry. The influence of biobased polyols on the polyurethane structure, and therefore, on their final properties was analysed by different experimental techniques such us Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Melting viscosity, Softening temperature and T-peel strength test, in order to assess their viability for the upper to sole bonding process. The results obtained indicated that the incorporation of different amounts of the biobased polyols produces changes in the structure and final performance of the polyurethanes. Therefore, adhesion test carried out by the T-peel test 72 h after the upper -to- sole bonding of the sustainable adhesives show high final adhesion values. These sustainable raw materials provide polyurethane adhesives with additional beneficial non-toxicity and sustainable characteristics, without harming their properties during their useful life.

Influence of Alloying Elements on the Mechanical Properties of Anodized Aluminum and on the Adhesion of Copper Metallization

The active development of the power electronics market and a constant increase in the prices of components require new materials and approaches, including a power module packaging technology. The use of aluminum instead of copper in the power module baseplate is an interesting and promising solution. The insulated metal baseplate is one of the most extensively developed technologies nowadays. The object of this study is an insulated metal substrate based on anodized aluminum. The main goal of the article is the comparison of copper topology adhesion to an anodized aluminum oxide layer formed on different aluminum alloys with aluminum content of at least 99.3 wt %. Peel test and pull-off adhesions showed a twofold difference for both aluminum alloys. The high ordered defect-free anodized alumina formed on alloys with copper content of 0.06 wt % had a mean pull-off adhesion of 27 N/mm2 and hardness of 489 HV. In the case of the alloy with copper content of around 0.15 wt %, it had hardness of 295 HV and a mean pull-off adhesion of 12 N/mm2. The results of our microstructure investigation showed that anodized alumina based on alloys with copper content of around 0.15 wt % is fragile due to spherical holes. Summing up the results, it can be concluded that not all initial impurities are critical for anodized alumina, but some, specifically copper, dramatically decreased the mechanical properties of anodized alumina.

Shear and tensile delamination of ice from surfaces : The Ice Adhesion Peel Test (IAPT)

For decades, researchers have sought to understand the adhesion of ice to surfaces so that low-cost ice mitigation strategies can be developed. Presently, the field of ice adhesion is still without formal standards for performing ice adhesion tests. The U.S. Army Corps Engineers’ Research and Development Center’s Cold Regions Research and Engineering Laboratory (ERDC-CRREL) has a longstanding history as an independent third party for ice adhesion testing services. Most notably, CRREL’s Zero-Degree Cone Test (ZDCT) has been an industry favorite for more than 30 years. Despite its wide acceptance, the ZDCT contains some shortcomings, namely that freshwater ice is formed on the surface of interest within the confines of an annular gap. To address this limitation, CRREL developed and uses the Ice Adhesion Peel Test (IAPT) for testing ice adhesion. This test employs an open planar substrate from which the ice can be removed under either tensile or shear loading, thereby allowing ice to be grown directly on the target substrate without the use of molds. The IAPT configuration is therefore amenable to different ice types and geometries and will provide utility to research studies that aim to develop surface treatments to mitigate ice in a wide range of environments. This report describes the IAPT and its use for characterizing the ice adhesion properties of materials.

Influence of the Type of Adhesive on the Properties of the GFRP Composite Adhesive Joint, Determined on the Basis of the Static T-Peel Test

The article presents the results of experimental studies determining the influence of the type of adhesive on the static strength properties of the Glass Fiber Reinforced Polymer (GFRP) composite joint determined on the basis of the T-peel test. As part of the static tests on peeling joints, a comparison of peak load and stiffness for individual joints was made. The fracture surfaces were also analyzed, showing various failure mechanisms. It was shown that the variant of joints made with the Enguard BP72A polyester adhesive was characterized by the highest strength properties with a mean peak load of 836.73 N.

PDMS Bonding Technologies for Microfluidic Applications: A Review

This review summarizes and compares the available surface treatment and bonding techniques (e.g., corona triggered surface activation, oxygen plasma surface activation, chemical gluing, and mixed techniques) and quality/bond-strength testing methods (e.g., pulling test, shear test, peel test, leakage test) for bonding PDMS (polydimethylsiloxane) with other materials, such as PDMS, glass, silicon, PET (polyethylene terephthalate), PI (polyimide), PMMA (poly(methyl methacrylate)), PVC (polyvinyl chloride), PC (polycarbonate), COC (cyclic olefin copolymer), PS (polystyrene) and PEN (polyethylene naphthalate). The optimized process parameters for the best achievable bond strengths are collected for each substrate, and the advantages and disadvantages of each method are discussed in detail.

Energizing ASTM lap joint fracture standards

Several ASTM standards on the fracture of glued and welded joints need attention because they do not consider the Griffith energy criterion of cracking which was proposed a century ago. It is almost as if Griffith never existed because the ASTM definition of failure is the stress criterion postulated by Galileo in 1638 in which stress at failure (i.e. strength = force/area) is defined as the determinant of fracture. Irene Martinez Villegas (Villegas, Rans 2021 Phil. Trans. R. Soc. A 376, 20200296. ( doi:10.1098/rsta.2020.0296 )) shows in this volume that attempts to use ASTM D5868 to standardize welded composite (carbon fibre reinforced polymer, CFRP) lap joints reveal major problems. First, the test is a low angle bend–peel test; not shear. Second, the energy required to break the joint is not emphasized so that joints may have high strength properties but also low toughness; third, the fracture force is not proportional to the lap joint area so the concept of strength independent of sample size is false; fourth, as the CFRP panels are made thicker, the strength rises at constant overlap area so the strength can be any value you want; fifth, the strength of larger joints goes down; this is the size effect noted in many bend-cracking tests, much as Galileo suggested for bent beam fracture in his famous book ‘the larger the machine, the greater its weakness'. The purpose of this paper is to demonstrate that poor ASTM ‘shear strength’ standards should be replaced by a definition of welded lap joint performance based on Griffith's energy conservation argument in which fracture surface energy is the main parameter resisting failure. The foundation of this Griffith-style lap joint analysis for long cracks goes back to 1975 but has been largely ignored until now because it does not fit the Griffith equation for cracked sheets, has no ‘stress intensity factor’, and travels at constant speed, not accelerating like the standard Griffith tension crack. This study of tensile delamination shows that a long lap crack is not driven by stress near the crack but by changes in stored elastic energy in the stretched strips remote from the crack tip, while strain energy release rate is negative. It would be more appropriate to call this lap failure a tensile delamination crack. This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’.

Characterisation of the opening behavior of multilayer films with cohesive failure mechanism by in situ peel tests in the ESEM

In this work, peel tests inside the chamber of an ESEM ( in situ peel tests) are described with heat-sealed test specimens of packaging systems made of multilayer films that simulate different flexible packaging types, according to the packaging line used. The in situ peel tests provided evidence to describe the influence of three different main aspects of the packaging process in relation to the opening behavior of the sealing packages. The investigated aspects are the peel angle, the alignment angle between the orientation of the multilayer films and the seal, and the bulge formation as a consequence of inadequate sealing parameters. In situ peel tests enabled the differentiation between peel angle and local (micro) peel angle, which results from the overall stiffness of the multilayer structure film. Alignment angles of 90° and 45° were found to produce similar opening forces. Images showing the formation of various new local micro fissures on new planes during the in situ peel test explained how the opening force can be dramatically increased during the tearing of two sealed multilayer films.