Its hydrophilic property and poor water resistance prevent the application of starch in electrospun nanofibers for biomedical applications. In this paper, we apply a periodate oxidation–adipic acid dihydrazide crosslinking strategy to electrospun starch nanofibers and develop a new nanofiber material with excellent mechanical strength, superior water resistance, and excellent cytocompatibility. The crosslinked starch nanofiber membranes exhibit a Young’s modulus up to 2.65 MPa in the wet state, can maintain 91.0% of their initial mass after four weeks’ incubation in simulated body fluid, and do not cause toxicity to L929 fibroblast cells. The control nanofibers prepared with a conventional glutaraldehyde crosslinking strategy show only a 60 kPa Young’s modulus, retain only 31.9% of their initial mass after four weeks in simulated body fluid, and cause toxicity to cells. The crosslinked starch nanofibers with high mechanical strength, excellent water resistance and good biocompatibility are promising for biomedical applications.
It is difficult to detect and evaluate the structural damage in a shield tunnel during operation because many traditional techniques based on the observation of vibrations are limited in daily monitoring in tunnels. Thus, the curvature radius of a static longitudinal settlement curve is used to identify the residual health and safety of an in-service shield tunnel. However, there are still two problems. The curvature radius is suitable for a qualitative judgment rather than a quantitative evaluation for longitudinal damage detection. Moreover, the curvature radius, which is calculated from the measured settlements of three neighboring points, gives an average damage degree in a wide scope only and is difficult to use to identify the damage’s precise location. By means of the analysis of three kinds of longitudinal failure modes in a shield tunnel, this paper proposes: (1) a damage detection method based on the monitored increment of the neutral axis depth; and (2) an index to evaluate longitudinal damage. The index is composed of the residual ratios of the equivalent flexural stiffness (HFM1) and the equivalent shear stiffness (HFM3). The neutral axis position and the proposed damage index can be determined using long-gauge Fiber Bragg Grating sensors. Results from numerical simulations show that the deviation between the HFM1 and the true value residual ratio of the equivalent flexural stiffness is no more than 1.7%. The HFM3 is equal to its true value in the entire damage process. A loading experiment for a scaled-down model of a shield tunnel using long-gauge Fiber Bragg Grating sensors indicated that the errors in the HFM1 were no more than 5.0% in the case of early damage development (HFM1 ≥ 0.5). The maximum error did not exceed 9.0% even under severe damage conditions in the model. Meanwhile, the HFM3 also coincided with its true value in the entire testing process.
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