Memory effect of spider major ampullate silk in loading-unloading cycles and the structural connotations.

Spider silk is repeatedly stretched while performing biological functions. There is a close relationship between the shape change of the fibre materials and their mechanical properties. However, the effect of the deformation and interval time on the structure and tensile behaviour properties of spider silk after repeatedly stretching by given strain value has been rarely reported. Here we found that major ampullate silk (MAS) can revert its tensile behaviour independent of its previous loading history via intervals of approximately 8 s to 5 min with constant and increased elongation, respectively, after being subjected to yield and hardening regions. The true stress-true strain curve beyond a given value of true strain is independent from the previous loading history of the sample. Even after longer intervals (≥1 h), MAS can reproduce the last tensile behaviour via one stretched. Despite recognizing the development of irreversible deformations in the material when tested in air, the reversible change in tensile behaviour outside the spider silk's elastic region has rarely been observed before. MAS has at least one proper ground state that allows it to present good shape and mechanical behaviour memory in terms of longitudinal stretching, functioning as a new strategy to achieve certain tensile properties. The analysis of the true stress-true strain curves was performed from a series of loading‒unloading tests to evaluate the evolution of those mechanical parameters with the cycle number. The elastic modulus measured in the loading steps increases monotonously with increasing values of true strain reached in the cycles. In contrast, a marginal variation is found in the values of the yield stress measured in the different cycles. The memory and variation in the mechanical behaviour and performance of MAS can be accounted for through the irreversible and reversible deformation micromechanisms and its combination in which the viscoelasticity of the material plays a leading role. These findings may be helpful to guide the biomimetic design of novel fibre materials such as spider silk gut via artificially stretching spider silk glands.

Completed atrioventricular block induced by atrial septal defect occluder unfolding: A case report.

BACKGROUND: An atrial septal defect is a common condition and accounts for 25% of adult congenital heart diseases. Transcatheter occlusion is a widely used technique for the treatment of secondary aperture-type atrial septal defects (ASDs). CASE SUMMARY: A 30-year-old female patient was diagnosed with ASD by transthoracic echocardiography (TTE) 1 year ago. The electrocardiogram showed a heart rate of 88 beats per minute, normal sinus rhythm, and no change in the ST-T wave. After admission, TTE showed an atrial septal defect with a left-to-right shunt, aortic root short-axis section with an ASD diameter of 8 mm, a parasternal four-chamber section with an ASD diameter of 9 mm, and subxiphoid biatrial section with a diameter of 13 mm. Percutaneous occlusion was proposed. The intraoperative TTE scan showed that the atrial septal defect was oval in shape, was located near the root of the aorta, and had a maximum diameter of 13 mm. A 10-F sheath was placed in the right femoral vein, and a 0.035° hard guidewire was used to establish the transport track between the left pulmonary vein and the inferior vena cava. A shape-memory alloy atrial septal occluder with a waist diameter of 20 mm was placed successfully and located correctly. TTE showed that the double disk unfolded well and that the clamping of the atrial septum was smooth. Immediately after the disc was revealed, electrocardiograph monitoring showed that the ST interval of the inferior leads was prolonged, the P waves and QRS waves were separated, a junctional escape rhythm maintained the heart rate, and the blood pressure began to decrease. After removing the occluder, the elevation in the ST segment returned to normal immediately, and the sinus rhythm returned to average approximately 10 min later. After consulting the patient's family, we finally decided to withdraw from the operation. CONCLUSION: Compression of the small coronary artery, which provides an alternative blood supply to the atrioventricular nodule during the operation, leads to the emergence of a complete atrioventricular block.