Soft Modulus Research Articles

Tough, recyclable and biocompatible carrageenan-modified polyvinyl alcohol ionic hydrogel with physical cross-linked for multimodal sensing

Biocompatibility hydrogel conductors are considered as sustainable bio-electronic materials for the application of wearable sensors and implantable devices. However, they mostly face the limitations of mismatched mechanical properties with skin tissue and the difficulty of recycling. In this regard, here, a biocompatible, tough, reusable sensor based on physical crosslinked polyvinyl alcohol (PVA) ionic hydrogel modified with ι-carrageenan (ι-CG) helical network was reported. Through simulating the ion transport and network structure of biological systems, the ionic hydrogels with skin-like mechanical features exhibit large tensile strain of 640 %, robust fracture strength of 800 kPa, soft modulus and high fatigue resistance. Meanwhile, the ionic hydrogel-based sensors possess a high response to strain/pressure over a wide range and could be utilized for multimodal sensing of human activity signals. Benefit from biosafety and temperature reversibility of ι-CG and PVA endow hydrogels with not only biocompatibility, but also meaningfully recyclability. The as-prepared hydrogels could be freely reconstructed into new flexible electronics and safely integrated with the human skin. It could be anticipated that the physically cross-linked ionic hydrogel conductor could expand the options for next-generation bio-based sensors.

THE STUDIES OF STRESS-INDUCED I/C TRANSITION AND INTERFACE DYNAMICS IN NiTi ALLOY

The internal friction (IF) Q-1, modulus f2, electrical resistance R and stress s of superelastic Ni51Ti49 alloy in the process of stress induced incommensurate/commensurate (I/C) transition was measured as a function of strain e by a middle torsion pendulum on a tensile testing machihe modified with a four-terminal potential equipment.The effects of number of stress cycles and strain rate e (in the range of 7×10-7/s to 1×10-4/s) were studied. An IF peak and a minimum of modulus were observed respectively in the Q-1-εand f2-εcurves. The IF peak height Qp-1 and modulus defect △M/M increase with an increasing of ε/ω, where ω is angular frequency of measuring. By utilizing an expression obtained from phase interface dynamics and experimental data of Qp-1 (as a function of ε/ω and amount of phase transition F), an explicit functional relationship of average I/C phase interface velocity V and effective phase transition driving force △G′= △G - △GR (where △GR is resistance) was derived as V =V*(△G - △CR)m, where V* and m are dynamic parameters an △GR is a resistance force exerting on the moving interface, which has the order of 1 cal/mol for stress-induced I/C transition of superelastisity NiTi alloy. The relationship between Q-1 and modulus defect △M/M and soft modulus effect are disussed.