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The effect of compression on the chemical degradation of Nafion is investigated. Results indicate a nonlinear dependence of chemical degradation on compression level, with a slight decrease at 1 MPa and then increase up to 10 MPa. The results confirm the synergistic nature of mechanical effects on chemical fuel-cell membrane degradation, which are expected to occur in operando. The impact of compression is also shown to change the nano-domain structure, consistent with the increase in chemical decomposition. Thus, deformation energy accumulated in the membrane due to mechanical loads seemingly accelerates the chemical reactions driving the decomposition of the polymer membrane. © 2014 The Electrochemical Society. [DOI: 10.1149/2.008405eel] All rights reserved. Perfluorinated sulfonic-acid (PFSA) membranes are the most widely studied class of ionomer membrane for polymer-electrolyte fuel-cell (PEFC) applications, with Nafion being the prototypical PFSA. Membrane degradation in PEFCs due to chemical and mechanical stressors represents a barrier to realizing the necessary fuelcell lifetimes for commercialization.1 During cell operation, chemical decomposition of the membrane can occur due to attack of polymer moieties by radicals produced during operation.1-3 These radicals are produced under chemical stressors, such as high potentials (i.e., open-circuit voltage (OCV) conditions). In addition to chemical degradation, membranes can fail due to loss of mechanical integrity caused by mechanical stressors. These latter stressors originate from the deformation of the membrane due to cell assembly (constraint) and subsequent operational stresses driven by the hydration/dehydration of the constrained membrane. [1][2][3][4][5][6][7] To understand the impact of various stressors, accelerated stress tests (ASTs) are typically conducted with the aim of enhancing a single failure mode, 1,2,8 with Fenton's tests accelerating chemical degradation 7,9-14 and relative-humidity (RH) cycling used for mechanical degradation. [1][2][3]6,8,15 However, failure mechanisms in operando are controlled by combination of chemical and mechanical stressors, which makes understanding any synergistic chemical/mechanical interactions of great importance.Chemical degradation is believed to occur when the polymer is attacked by radicals. 1,[9][10][11][12][13][14]16 Fenton's Test is commonly employed to study the chemical-decomposition behavior of a membrane by monitoring the release of fluoride ions from the PFSA membrane's fluorocarbon chains. 1,7,[9][10][11][12][13][14] While it is known that chemical degradation changes the membrane's mechanical and other properties, 7,17,18 it is unknown as to whether concurrent mechanical and chemical stressors act independently or in concert to alter membrane degradation rates. Such combined stresses are expected to occur under actual operation due to simultaneous load and humidity changes. Thus, it is worthwhile to explore chemical degradation in the presence of mechanical loads to gain an increased understa...

Developing biomimetic cartilaginous tissues that support locomotion while maintaining chondrogenic behavior is a major challenge in the tissue engineering field. Specifically, while locomotive forces demand tissues with strong mechanical properties, chondrogenesis requires a soft microenvironment. To address this challenge, 3D cartilage-like tissue is fabricated using two biomaterials with different mechanical properties: a hard biomaterial to reflect the macromechanical properties of native cartilage, and a soft biomaterial to create a chondrogenic microenvironment. To this end, a bath composed of an interpenetrating polymer network (IPN) of polyethylene glycol (PEG) and alginate hydrogel (MPa order compressive modulus) is developed as an extracellular matrix (ECM) with self-healing properties. Within this bath supplemented with thrombin, human mesenchymal stem cell (hMSC) spheroids embedded in fibrinogen are 3D bioprinted, creating a soft microenvironment composed of fibrin (kPa order compressive modulus) that simulate cartilage's pericellular matrix and allow a fast diffusion of nutrients. The bioprinted hMSC spheroids present high viability and chondrogenic-like behavior without adversely affecting the macromechanical properties of the tissue. Therefore, the ability to locally bioprint a soft and cell stimulating biomaterial inside of a mechanically robust hydrogel is demonstrated, thereby uncoupling the micro-and macromechanical properties of the 3D printed tissues such as cartilage.

Limited studies measure extensional rheology in protein solutions due to volume constraints and measurement challenges. We developed a small-volume, Dripping-onto-Substrate (DoS) extensional rheology device to measure the capillary thinning of...

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