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Stress-free two-way shape-memory (2W-SM) polymers are highly desired for soft actuators and flexible sensors. Semicrystalline networks with a broad melting transition can be imparted with stress-free 2W-SM effects by facile thermal-mechanical programming. However, the reversible elongation achieved is generally in the range of 5–20%. Further improvement of the reversible elongation requires deep insights into the stress-free 2W-SM mechanism. Herein, we reported a broad melting transition semicrystalline network that can be programmed with a reversible elongation above 10%, investigated structural origins of the reversible elongation by experiments, and theoretically analyzed thermodynamic and molecular mechanisms associated with the reversible elongation. The results show that a semicrystalline skeleton composed of oriented crystals and compressed amorphous chains is formed in the programmed network, which provides internal tensile stress required for the stress-free 2W-SM effect. In addition, it is found that the reversible elongation is primarily a direct result of variation in amorphous orientation of the network; crystalline orientation of the network varies only slightly during actuation. Furthermore, the theoretical analysis reveals that although the direct contribution of the crystalline orientation to the reversible elongation is small, the crystalline orientation induces an entropy increase in the amorphous section, which enhances the reversible elongation significantly. Hence, the stress-free 2W-SM mechanism of the network is clearly clarified in this study, which provides basic guidelines for the design and development of semicrystalline stress-free 2W-SM polymers and paves new avenues for improving the reversible elongation.

Background: Braking force is a gait marker associated with gait stability. This study aimed to determine the alteration of braking force and its correlation with gait stability in Alzheimer disease (AD). Methods: A total of 32 AD patients and 32 healthy controls (HCs) were enrolled in this study. Gait parameters (braking force, gait variability, and fall risk) in the walking tests of Free walk, Barrier, and Count backward were measured by JiBuEn gait analysis system. Gait variability was calculated by the coefficient of variation (COV) of stride time, stance time, and swing time. Results: The braking force of AD was significantly weaker than HCs in three walking tests (P < 0.001, P < 0.001, P = 0.007). Gait variability of AD showed significant elevation than HCs in the walking of Count backward (COV stride : P = 0.013; COV swing : P = 0.006). Fall risk of AD was significantly higher than HCs in three walking tests (P = 0.001, P = 0.001, P = 0.001). Braking force was negatively associated with fall risks in three walking tests (P < 0.001, P < 0.001, P < 0.001). There were significant negative correlations between braking force and gait variability in the walking of Free walk (COV stride : P = 0.018; COV swing : P = 0.013) and Barrier (COV stride : P = 0.002; COV swing : P = 0.001), but not Count backward (COV stride : P = 0.888; COV swing : P = 0.555). Conclusion: Braking force was weaker in AD compared to HCs, reflecting the worse gait stability of AD. Our study suggests that weakening of braking force may be a new gait marker to indicate cognitive and motor impairment and predict fall risk in AD.

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Terminalia chebula Retz. (TC) is a well-known Chinese herbal medicine and rich in chemical components with multiple pharmacological effects. In this study, an ultra-performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS) method was developed and used to determine the blood concentrations of nine active compounds (chebulic acid, gallic acid, protocatechuic acid, corilagin, chebulagic acid, chebulinic acid, 1,2,3,4,6-O-pentagalloylglucose, ellagic acid and ethyl gallate) after oral administration of TC extracts in rats. Pretreatment of plasma samples with protein precipitate with methanol was carried out, and caffeic acid was used as the internal standard (IS). Compounds precisions of intra- and inter-day were less than 14.6%, and the accuracy ranged from −11.7% to 13.5%. The extraction recoveries of compounds were between 84.9% and 108.4%, while matrix effects occurred between 86.4% and 115.9%. Stability tests showed that all nine analytes had been stable under four storage conditions, and statistically significant the relative standard deviations were under 13.7%. The validated UPLC-MS/MS method was applied with great success to plasma pharmacokinetics analysis of the TC extracts, and the pharmacokinetic results showed that among the nine components, the area under the concentration-time curve (AUC(0-tn), 231112.38 ± 64555.20 h ng/mL) and maximum concentration (Cmax, 4,983.57 ± 1721.53 ng/mL) of chebulagic acid were relatively large, which indicated that it had a higher level of plasma exposure. The half-life of elimination (T1/2) of chebulinic acid, corilagin and chebulagic acid were 43.30, 26.39 and 19.98 h, respectively, suggesting that these analytes showed prolonged retention and metabolize more slowly in vivo. This study would deliver a theoretical foundation for the further application of TC in clinical practice.