Keratin is a protein in the intermediate filament family and the key component of hair, nail, and skin. Here we report a bottom-up atomistic model of the keratin dimer, using the complete human keratin type k35 and k85 amino acid sequence. A detailed analysis of geometric and mechanical properties through full-atomistic simulation with validation against experimental results is presented. We introduce disulfide cross-links in a keratin tetramer and compare the mechanical behavior of the disulfide bonded systems with a system without disulfide bonds. Disulfide bond results in a higher strength (20% increase) and toughness (49% increase), but the system loses α-helical structures under loading, suggesting that disulfide bonds play a significant role in achieving the characteristic mechanical properties of trichocyte α-keratin. Our study provides general insight into the effect of disulfide cross-link on mechanical properties. Moreover, the availability of an atomistic model of this protein opens the possibility to study the mechanical properties of hair fibrils and other fibers from a bottom-up perspective.

consists of two major tasks: (1) the development. of fracture mechanics models for assessing the piping reliability in light water reactor plants; and (2) the validation of the models developed in task (1) by comparing the results with real piping failure data observed. The results of task (2) impact the confidence level for the models developed in task (1). This report is only concerned with task (1). Task (2) results are reported in another NUREG report, 11 Piping Reliability Model Validation and Potential Use for Licensing Regulation Development ... The ultimate objective of this pnoject is to provide guidance for nuclear powe.r plant piping design so that high-reliability piping systems can result. The piping reliability model presented in this report covers two major failure modes, namely, fatigue failure ~nd stress corrosion cracking failure. Both have been observed in the piping systems of light water reactor plants~ Various failure mechanisms such as vibratory stresses, residual stresses, seismic stresses, assembly stresses, and operating stresses, attributed to these two failure modes are considered in the model. Initial interior surface flaws are assumed to exist along either the pipe circumferential direction or the longitudinal direction. In-service inspection is also included in the model. In summary_,. this piping reliability model has wide application to piping 5y5tems in nuclea~ powet• plants .

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Ionically conductive elastomers are necessary for realizing human−machine interfaces, bioelectronic applications, or durable wearable sensors. Current design strategies, however, often suffer from solvent leakage and evaporation, or from poor mechanical properties. Here, we report a strategy to fabricate ionic elastomers (IHPs) demonstrating high conductivity (0.04 S m −1 ), excellent electrochemical stability (>60,000 cycles), ultrastretchability (up to 1400%), high toughness (7.16 MJ m −3 ), and fast self-healing properties, enabling the restoration of ionic conductivity within seconds, as well as no solvent leakage. The ionic elastomer is composed of in situ formed physically crosslinked poly(2-hydroxyethyl methacrylate) networks and poly-(ethylene glycol) (PEG). The long molecular chains of PEG serve as a solvent for dissolving electrolytes, improve its long-term stability, reduce solvent leakage, and ensure the outstanding mechanical properties of the IHP. Surprisingly, the incorporation of ions into PEG simultaneously enhances the strength and toughness of the elastomer. The strengthening and toughening mechanisms were further revealed by molecular simulation. We demonstrate an application of the IHPs as (a) flexible sensors for strain or temperature sensing, (b) skin electrodes for recording electrocardiograms, and (c) a tough and sensing material for pneumatic artificial muscles. The proposed strategy is simple and easily scalable and can further inspire the design of novel ionic elastomers for ionotronics applications.

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