Grain boundary plasticity initiated by excess volume.

Grain boundaries (GBs) serve not only as strong barriers to dislocation motion, but also as important carriers to accommodate plastic deformation in crystalline solids. During deformation, the inherent excess volume associated with loose atomic packing in GBs brings about a microscopic degree of freedom that can initiate GB plasticity, which is beyond the classic geometric description of GBs. However, identification of this atomistic process has long remained elusive due to its transient nature. Here, we use Au polycrystals to unveil a general and inherent route to initiating GB plasticity via a transient topological transition process triggered by the excess volume. This route underscores the general impact of a microscopic degree of freedom which is governed by a stress-triaxiality-based criterion. Our findings provide a missing perspective for developing a more comprehensive understanding of the role of GBs in plastic deformation.

Controllable Pseudoelasticity in Metallic Nanocrystals by Grain Boundary Engineering.

Materials with pseudoelasticity can recover from large strains exceeding their elastic limits during unloading, making them promising damage-tolerant building blocks for advanced nanodevices. Nevertheless, a practical approach to realize controllable pseudoelastic behavior at nanoscale remains challenging. Here, we proposed a grain boundary (GB) engineering approach to endow metallic nanocrystals with a controllable pseudoelasticity. Both in situ nanomechanical testing and atomistic simulations demonstrate that such controllable pseudoelasticity is governed by the extension and contraction of an inherent stacking fault array at the GB. By precisely tuning GB misorientation and inclination, our simulation results reveal that metallic nanocrystals can exhibit tailored pseudoelastic performance across a broad spectrum of GBs in different face-centered cubic metals. These findings enrich our understanding of the intrinsic pseudoelasticity of GBs and provide a GB engineering approach toward metallic materials with reversible deformability.

Penta-Twin Destruction by Coordinated Twin Boundary Deformation.

Penta-twinned nanomaterials often exhibit unique mechanical properties. However, the intrinsic deformation behavior of penta-twins remains largely unclear, especially under the condition of high shear stress. In this study, we show that the deformation of penta-twins often subject to a structural destruction via dislocation-mediated coordinated twin boundary (TB) deformation, resulting in a reconstructed pentagon-shaped core. This reconstructed core region is mainly induced by the coordinated TB migration along different directions (for the nucleation and growth) and accelerated by the TB sliding (for the growth). The destructed penta-twin core can effectively accommodate the intrinsic disclination of the penta-twin, which further collapses beyond a critical size, as predicted by an energy-based criterion. These intrinsic deformation behaviors of penta-twins would enable the possibility of controlling the morphology of penta-twinned nanomaterials with unique properties.

Baicalin augments the differentiation of osteoblasts via enhancement of microRNA-217.

Baicalin (BAI), a sort of flavonoid monomer, acquires from Scutellaria baicalensis Georgi, which was forcefully reported in diversified ailments due to the pleiotropic properties. But, the functions of BAI in osteoblast differentiation have not been addressed. The intentions of this study are to attest the influences of BAI in the differentiation of osteoblasts. MC3T3-E1 cells or rat primary osteoblasts were exposed to BAI, and then cell viability, ALP activity, mineralization process, and Runx2 and Ocn expression were appraised through implementing CCK-8, p-nitrophenyl phosphate (pNPP), Alizarin red staining, western blot, and RT-qPCR assays. The microRNA-217 (miR-217) expression was evaluated in MC3T3-E1 cells or rat primary osteoblasts after BAI disposition; meanwhile, the functions of miR-217 in BAI-administrated MC3T3-E1 cells were estimated after miR-217 inhibitor transfection. The impacts of BAI and miR-217 inhibition on Wnt/ß-catenin and MEK/ERK pathways were probed to verify the involvements in BAI-regulated the differentiation of osteoblasts. BAI accelerated cell viability, osteoblast activity, and Runx2 and Ocn expression in MC3T3-E1 cells or rat primary osteoblasts, and the phenomena were mediated via activations of Wnt/ß-catenin and MEK/ERK pathways. Elevation of miR-217 was observed in BAI-disposed MC3T3-E1 cells or rat primary osteoblasts, and miR-217 repression annulled the functions of BAI in MC3T3-E1 cell viability and differentiation. Additionally, the activations of Wnt/ß-catenin and MEK/ERK pathways evoked by BAI were both restrained by repression of miR-217. These explorations uncovered that BAI augmented the differentiation of osteoblasts via activations of Wnt/ß-catenin and MEK/ERK pathways by ascending miR-217 expression.

Overcoming strength-ductility tradeoff with high pressure thermal treatment.

Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials.

[Discectomy and discectomy plus Coflex fixation for lumbar disc herniation, a clinical comparison study].

OBJECTIVE: To compare clinical efficacy between discectomy and discectomy plus Coflex fixation for lumbar disc herniation. METHODS: From December 2007 to August 2008, 50 patients (31 males and 19 females) were treated by surgery of discectomy and discectomy plus Coflex fixation. The average age was 52.5 years (range, 30 - 72 years). There were 24 cases in the group of discectomy plus Coflex fixation and 26 cases in the group of discectomy. Preoperative and postoperative visual analogue scales (VAS), Japanese Orthopadic Association (JOA) and Oswestry disability index (ODI) were recorded, as well as radiological index. And use a paired t-test and one-way analysis of variance (one-way ANOVA) statistical method to evaluate the Coflex dynamic stabilization system in value in the treatment of lumbar disc herniation. RESULTS: Both groups received significant improvement of JOA, ODI and VAS (t = -33.2 - 64.5, P < 0.01), but the group of discectomy was found with deterioration of ODI at last follow-up, 12 months after surgery 6.7 ± 1.5 to 10.2 ± 2.3 (t = -19.3, P < 0.05). The group of discectomy plus Coflex fixation was found with significant increase of height of dorsal intervertebral discs (HD), distance across the two adjacent spinous processes (DS), distance of intervertebral foramina (DIF) and spinal canal area(SA) (t = -34.4 - 4.5, P < 0.05). In contrast, the group of discectomy was found with significant decrease of HD, DS, DIF and SA (t = 3.4 - 52.8, P < 0.05). Coflex fixed group in HD, DIF, DS significant difference with simple discectomy group, with a statistically significant (F = 14.1 - 25.6, P < 0.05). CONCLUSIONS: Both discectomy and discectomy plus Coflex fixation are apparently effective when treating lumbar disc herniation. Coflex can significantly increase the HD and DIF when used for lumbar disc herniation, and it has positive influence for keeping height of lumbar vertebral space and treating the nerve root symptom of lumbar disc herniation. Discectomy plus Coflex is better than pure discectomy in preventing lumbar degeneration.

[Clinical evaluation of interspinous process device Coflex for degenerative disk diseases].

OBJECTIVE: To study indications and complications of interspinous process device Coflex for degenerative disk diseases. METHODS: One hundred and eight patients with degenerative lumbar disc diseases were underwent procedures of surgical decompression and additional fixation of Coflex between November 2007 and October 2010. Sixty-eight patients were male and the other fourty were female, and their average age was 53.5 years (range from 37 to 75 years). Fifty-nine patients were underwent surgery of excision of nucleus pulposus and Coflex fixation, 41 patients were underwent surgery of decompression by fenestration and Coflex fixation, 6 patients were underwent surgery of topping-off, and 2 patients were underwent surgery of Coflex fixation for two level. Preoperative and postoperative visual analogue scales (VAS) and Oswestry disability index (ODI) were recorded, as well as height of ventral intervertebral space (HV), height of dorsal intervertebral space (HD), height of intervertebral foramen (HIF) and segmental range of motion (ROM). One-way ANOVA was used for statistical analysis. Surgical complications were also recorded. RESULTS: The average follow-up time was 28.8 months. All groups had apparent improvement of VAS and ODI, and maintained well to last follow-up (F = 6.16-25.92, P = 0.00). Statistical analysis showed that HD and HIF increased significantly in group with excision of nucleus pulposus and Coflex fixation and group with decompression by fenestration and Coflex fixation (F = 7.37 - 11.68, P < 0.05). Although both HD and HIF decreased one-year after surgery, they were still higher than those preoperatively (F = 6.31 and 7.05, P = 0.00). Preoperative segmental ROM was respectively 6.3° ± 1.8° and 6.2° ± 1.7° in group with excision of nucleus pulposus and Coflex fixation and group with decompression by fenestration and Coflex fixation, and 3.1° ± 0.6° and 3.0° ± 0.8° at last follow-up. Three cases were found with device-related complications and five with non-device-related complications, and all five cased were cured after appropriate treatment. CONCLUSIONS: Surgical method assisted with Coflex has significant clinical efficacy for degenerative disc disease, it can maintain segmental stability, simultaneously, partly reserve movement. It's key to strictly master indications and precisely choose patients.

[Influence of intravertebral cleft for outcome of percutaneous kyphoplasty].

OBJECTIVES: To study incidence and radiological features of intravertebral cleft (IVC) in patients with chronic pain due to osteoporotic vertebral compression fractures (OVCFs), and analyze influence of IVC for surgery of percutaneous kyphoplasty (PKP). METHODS: Seventy-six patients with osteoporotic vertebral compression fractures and pain duration more than one month were underwent procedures of PKP between August 2005 and August 2010. The incidence and radiological features of IVC were analyzed. Sixty-one patients with single-level OVCFs were divided into two groups with and without IVC. Preoperative and postoperative kyphotic angle and relative anterior vertebral height were recorded, as well as visual analogue scales (VAS) and Oswestry disability index (ODI). Cement patterns of opacification and leakage were also recorded. RESULTS: Thirty two patients with 39 vertebrates were found with IVC sign. The diagnostic sensitivity of X ray, CT and MRI for IVC was respectively 33.3%, 85.7% and 84.6%. Two groups with IVC and without IVC both had apparent correction of kyphotic angle and reduction of anterior height at 3 days after surgery and last follow-up (F = 21.82 - 72.18, P < 0.01). There was no statistical significance between two groups (P > 0.05). In addition, both groups had significant improvement as regard to VAS and ODI (F = 131.06 - 364.12, P < 0.01). Solid pattern accounted for 72.0% of all cemented vertebrates in the group with IVC and 19.4% in the group without IVC. Four cement leakage were found in the group with IVC and another four in the group without IVC. CONCLUSIONS: There is a high incidence of IVC in patients with chronic pain due to osteoporotic vertebral compression fractures. CT and MRI are sensitive for detection of IVC. The procedure of PKP is effective for both groups with and without IVC. IVC produces an apparent influence on cement opacification and leakage location during the procedure of PKP.

Asiaticoside ameliorates osteoarthritis progression through activation of Nrf2/HO-1 and inhibition of the NF-κB pathway.

Osteoarthritis has become the fourth cause of disability in the world and its occurrence and development are caused by apoptosis and extracellular matrix (ECM) degradation of chondrocytes. Asiaticoside (ASI) is a triterpene saponin compound obtained from Centella Asiatica and has anti-inflammatory and anti-apoptotic effects in various diseases. However, its effects on OA are not clear. In this study, we reported that ASI has a protective effect on the occurrence and progression of OA in vivo and in vitro, and demonstrated its potential molecular mechanism. In vitro, ASI treatment inhibited the release of pro-apoptotic factors induced by TBHP and promoted the release of the anti-apoptotic proteins. In addition, ASI promotes the expression of Aggrecan and Collagen II, while inhibiting the expression of thrombospondin motifs 5 (ADAMTS5) and matrix metalloproteinase-13 (MMP-13), which causes extracellular matrix (ECM) degradation. Mechanistically, ASI exerts its anti-apoptotic effect by activating the Nrf2/HO-1 pathway and preventing p65 from binding to DNA. Similarly, in vivo, ASI has been shown to have a protective effect in a mouse OA model. The conclusion is that our research shows that ASI can be used as a potential drug for the treatment of OA.

Hierarchical twinning governed by defective twin boundary in metallic materials.

Dense networks of deformation twins endow metals and alloys with unprecedented mechanical properties. However, the formation mechanism of these hierarchical twin structures remains under debate, especially their relations with the imperfect nature of twin boundaries (TBs). Here, we investigate the intrinsic deformability of defective TBs in face-centered cubic metallic materials, where the inherent kinks on a set of primary TBs are demonstrated to facilitate the formation of secondary and hierarchical nanotwins. This defect-driven hierarchical twinning propensity is critically dependent on the kink height, which proves to be generally applicable in a variety of metals and alloys with low stacking fault energies. As a geometric extreme, a fivefold twin can be constructed via this self-activated hierarchical twinning mechanism. These findings differ from the conventional twinning mechanisms, enriching our understanding of twinning-mediated plasticity in metallic materials.

Pedicle screw insertion accuracy with different assisted methods: a systematic review and meta-analysis of comparative studies.

Studies revealed that navigation systems that provided intraoperative assistance might improve pedicle screw insertion accuracy, and also implied that different systems provided different pedicle screw insertion accuracy. A systematic review and meta-analysis was conducted to focus on the pedicle screw insertion accuracy with or without the assistance of image-guided system, and the variance among the different navigation systems. Comparative studies were searched on pedicle screw insertion accuracy between conventional and navigated method, and among different navigation systems. A total of 43 papers, including 28 clinical, 14 cadaveric and 1 model studies, were included in the current study. For clinical articles, there were 3 randomized clinical trials, 4 prospective comparative studies and 21 retrospective comparative studies. The incidence of pedicle violation among computer tomography-based navigation method group was statistically significantly less than that observed among the conventional group (OR 95% CI, in vivo: 0.32-0.60; in vitro: 0.24-0.75 P < 0.01). Two-dimensional fluoroscopy-based navigation system (OR 95% CI, in vivo: 0.27-0.48; in vitro: 0.43-0.88 P < 0.01) and three-dimension fluoroscopy-based navigation system (OR 95% CI, in vivo: 0.09-0.38; in vitro: 0.09-0.36 P < 0.01) also obtained significant reduced screw deviation rate over traditional methods. Between navigated approaches, statistically insignificant individual and pooled RR values were observed for all in vivo subgroups. Pooled estimate of in vitro studies show that computer tomography-based and three-dimension fluoroscopy-based navigation system provided more accurate pedicle screw insertion over two-dimension fluoroscopy-based navigation system. Our review showed that navigation provided a higher accuracy in the placement of pedicle screws compared with conventional methods. The superiority of navigation systems was obvious when they were applied to abnormal spinal structure. Although no strong in vivo evidence has detected significantly different pedicle screw placement accuracy among the three major navigation systems, meta-analysis revealed the variance in pedicle screw insertion accuracy with different navigation methods.

[Prediction of spinal cord decompression after cervical laminoplasty: the SC-line].

OBJECTIVES: To report a new index (the SC-line) and a new classification for predicting of postoperative spinal cord decompression after cervical laminoplasty. METHODS: From March 2008 to August 2009, MRI images of 25 patients treated with cervical laminoplasty were retrospectively studied. Using T2-weighted images of the cervical spine, point A was anterior point of the spinal cord at inferior endplate level of cranial compressed vertebra. Point B was anterior point of the spinal cord at superior endplate level of caudal compressed vertebra. The SC-line was defined as a line that connects A and B. Posterior surface of compressor at compression level did not exceed the line in Type I, connected the line in Type II, and exceeded it in Type III. Twenty-five patients who underwent cervical laminoplasty were classified into 3 groups according to the SC-line classification. The posterior shift of the spinal cord after the posterior decompression procedure was evaluated by using a modified gradation of degree of anterior spinal cord compression by MRI finding. The relationship between the degree of anterior spinal cord compression after surgery and the SC-line types were analyzed. RESULTS: Preoperative cervical SC-line classification showed high correlations to the degree of spinal cord decompression. There were 3.82 ± 0.39 points in Type I before surgery, 3.90 ± 0.32 points in Type II, and 4.00 ± 0.00 points in Type III, respectively. After surgery, there were 1.15 ± 0.50 points in Type I, 2.70 ± 0.48 points in Type II, and 3.50 ± 0.55 points in Type III, respectively. Significant differences were found between each Type (F = 42.49, P < 0.01; Type I vs. Type II: P < 0.01; Type I vs. Type III: P < 0.01; Type II vs. Type III: P = 0.038). CONCLUSION: SC-line can be used to predict the degree of postoperative spinal cord decompression following cervical laminoplasty.

[The application of minimally invasive surgery for different type of thoracolumbar fractures].

OBJECTIVE: To study the therapeutic method and effect of minimally invasive surgery for the thoracolumbar fractures. METHODS: A retrospective review of the minimally invasive surgically treatment thoracolumbar fractures from February 2005 to June 2010 was performed. There were 183 cases, 126 males and 57 females, aged 18 to 68 years, average 38.9 years. The involved levels of fractures were T(11) in 22, T(12) in 61, L(1) in 71, L(2) in 29. According to Gertzbein classification, 145 cases were type A fractures, 34 cases were type B fractures, 4 cases were type C fractures; According to Load-sharing score, 51 cases were 4 scores, 56 cases were 5 scores, 17 cases were 6 scores, 12 cases were 7 scores, 24 cases were 8 scores, 23 cases were 9 scores. Different surgical methods were selected according to the minimally invasive surgical strategy, 22 patients were treated with the minimally invasive percutaneous pedicle screws osteosynthesis (MIPPSO group), 102 patients were treated with the small-incision pedicle screws osteosynthesis (SISPSO group), 31 patients were treated with the small incision anterior thoracolumbar surgery (SIATS group) assisted by thoracoscope or headlight, and 28 patients were treated with the 270° decompression and reconstruction surgery (270° DRS group) via a posterior small incision. Preoperative and postoperative neurological status, the correction and loss of Cobb's angle, the decompression scope of spinal canal, the location and union of bone graft were followed up and reviewed. RESULTS: All of 183 cases had successful surgery and were followed up. In the MIPPSO group, operative time was 52 - 100 min, blood loss was 35 - 55 ml. In the the SISPSO group, operative time was 48-68 min, the blood loss was 45 - 65 ml the correction of Cobb's angle in the two groups was 8° - 19°. In the SIATS group, operative time was 140 - 220 min, the blood loss was 160 - 1500 ml the correction of Cobb's angle was 15° - 25°, 1 case had pleural effusion, 1 had lateral femoral cutaneous nerve damage, the complications disappeared after treatment. In the 270° DRS group the operative time was 160-280 min, the blood loss was 700 - 4700 ml, the correction of Cobb's angle was 15° - 28°. The spinal canal mass was removed, the spinal canal was enlarged and completely decompressed. Neurological status improved in all of the preoperative incomplete paraplegia patients except 1 case whose neurological symptoms aggravated. CONCLUSION: It is satisfactory that the minimally invasive surgical strategy was rational used in the treatment of thoracolumbar fractures.

[Therapeutic effects and complications of percutaneous pedicle screw fixation for thoracolumbar fractures].

OBJECTIVE: To investigate the therapeutic effects and complications of percutaneous pedicle screw fixation for thoracolumbar fractures. METHODS: From January 2002 to December 2008, 103 patients with thoracolumbar fractures were treated with percutaneous pedicle screw fixation, including 75 males and 28 females, the average age was 45.6 years (range, 18 - 72 years). All of them were of no neurological deficits. There were 65 cases of traffic injury, 23 cases of fall injury and 15 cases of smashed injury. According to the Denis classification, 64 patients were of compression fractures, and 39 patients of burst fractures. There were 5 cases had fractures in T(11), 30 in T(12), 42 in L(1), 15 in L(2), 4 in L(3), 3 in L(4), 2 in T(11-12), 1 in L(1-2), and 1 in L(2-3). Radiological examinations, including X-ray and CT examinations, and clinical examinations were carried out to evaluate the therapeutic effects. RESULTS: Twenty one patients were lost to follow up, the remaining were followed up from 10 to 48 months with an average of 27.4 months. Before the operation, the vertebral height, the kyphosis angle and the occupation of spinal canal were (54.5 ± 8.7)%, 16.4° ± 2.9° and 1.2 ± 1.0, and were improved to (88.6 ± 6.4)%, 11.6° ± 2.7° and 0.5 ± 0.6 respectively after the operation. Preoperatively the visual analogue scale and the Oswestry disability index were 8.0 ± 1.2 and 41.2 ± 9.3, and were improved to 1.7 ± 1.8 and 6.7 ± 5.6 postoperatively, respectively. All of these values between pre- and post-operatively were significantly different (P < 0.01). Screw misplacement was found in 7 patients, superficial wound infection in 1, screw breakage in 3, screw dislodgment in 2, cement leakage in 5, transient neurological symptoms in 4, and 8 patients with low back pain remained, of which 2 patients required occasional oral analgesics. Bone fusion achieved in all cases. CONCLUSIONS: The clinical efficacy of percutaneous pedicle screw fixation is similar with conventional open surgery. With the advantages of convenient procedure, less invasive, and rapid recovery, percutaneous pedicle screw fixation is an alternative method for thoracolumbar fractures without neurological deficits.

Image measurements of os odontoideum in children.

BACKGROUND: Conservative therapy is used for children with odontoid fracture; however, when the odontoid fracture is complicated by significant displacement and unstable, surgery is required. Anterior cervical hollow lag screw fixation has been successfully used in adult patients, but until now, there has not been any relevant image measurement research in children with os odontoideum. The aim of the present study was to identify the morphometric changes of normal os odontoideum in children of different ages and to discuss parameters for screw fixation. METHODS: Computed tomography (CT) scanning data of normal os odontoideum in 120 children of different ages were measured. The parameters were as follows: transverse and vertical diameters of cancellous bone and cortical bone in os odontoideum basilar part, angle and distance from simulation screw insertion point (anterior mid-point of C2 vertebral body) to os odontoideum anterior angle as well as posterior angle, the optimal insertion angle, and the optimal screw length. RESULTS: The basilar part of normal os odontoideum was roughly round, and vertical diameter was slightly larger than transverse diameter. All parameters measured in the present study increased with age. The safety screw insertion angle range was 16-36°, and the optimal insertion angle ranged from 19° to 22°. The safety screw path length ranges in the 3-5-, 6-9-, and 10-14-year groups were 8-14, 10-16, and 12-21 mm, respectively, and the optimal screw length ranges were 13-14, 15-16, and 19-20 mm, respectively. The height of the axis showed a growing dimension followed by the advancing age in all groups. In each group, the height of the axis of the male is greater than the female. CONCLUSIONS: For children undergoing odontoid screw fixation for the treatment of type II odontoid fracture, it is important to select the appropriate screw diameter, length, and direction according to parameter changes of os odontoideum based on their age.

Feasibility analysis of the use of anterior screw fixation in the treatment of pediatric odontoid fracture.

BACKGROUND: This study aimed to determine the feasibility of using anterior percutaneous screw fixation to treat odontoid fractures in children of different ages based on computed tomography (CT) measurements. METHODS: A total of 176 children were enrolled and divided into 3 groups: group A (<6 years of age; 18 males and 22 females), group B (6 to 12 years old; 40 males and 35 females), and group C (12 to 18 years old; 34 males and 27 females). Using 2-dimensional CT reconstruction technology, we measured the children's odontoid parameters, including the coronal external diameter of the base of the odontoid process, the sagittal external diameter of the base of the odontoid process, the length of the odontoid process, the height of the axis vertebral body, and the angle between the axial line of the odontoid process and the vertical line of the anterosuperior border of the C3 vertebral body. RESULTS: The mean coronal external diameter of the odontoid process base in children under 6 years old was 4.21±1.62 mm, which was not sufficient to accommodate a single screw. Among children aged 6 to 12 years old, this parameter varied widely, and the mean diameter was 5.50±2.80 mm. In the 12- to 18-year-old group, the diameter was 8.64±1.68 mm, which is similar to that of adults. The values of the total height of the axis, and the angle between the axial line of the and the vertical line of the anterosuperior C3 vertebral body border were lower than those for adults. CONCLUSIONS: The percutaneous odontoid screw fixation technique is not recommended for children under 6 years old. For children aged 6 to 18 years old, this technique is feasible, but individual differences must be considered preoperatively. Selecting the appropriate screw diameter, length, and angle according to the actual CT measurement result is critical.

Twinning-assisted dynamic adjustment of grain boundary mobility.

Grain boundary (GB) plasticity dominates the mechanical behaviours of nanocrystalline materials. Under mechanical loading, GB configuration and its local deformation geometry change dynamically with the deformation; the dynamic variation of GB deformability, however, remains largely elusive, especially regarding its relation with the frequently-observed GB-associated deformation twins in nanocrystalline materials. Attention here is focused on the GB dynamics in metallic nanocrystals, by means of well-designed in situ nanomechanical testing integrated with molecular dynamics simulations. GBs with low mobility are found to dynamically adjust their configurations and local deformation geometries via crystallographic twinning, which instantly changes the GB dynamics and enhances the GB mobility. This self-adjust twin-assisted GB dynamics is found common in a wide range of face-centred cubic nanocrystalline metals under different deformation conditions. These findings enrich our understanding of GB-mediated plasticity, especially the dynamic behaviour of GBs, and bear practical implication for developing high performance nanocrystalline materials through interface engineering.

Revealing extreme twin-boundary shear deformability in metallic nanocrystals.

Metals containing abundant coherent twin boundaries (TBs) are able to sustain substantial plastic deformation without fracture due to shear-induced TB migration and sliding. Retaining ductility in these metals, however, has proven difficult because detwinning rapidly exhausts TB migration mechanisms at large deformation, whereas TB sliding was only evidenced for loading on very specific crystallographic orientations. Here, we reveal the intrinsic shear deformability of twins in nanocrystals using in situ nanomechanical testing and multiscale simulations and report extreme shear deformability through TB sliding up to 364%. Sliding-induced plasticity is manifested for orientations that are generally predicted to favor detwinning and shown to depend critically on geometric inhomogeneities. Normal and shear coupling are further examined to delineate a TB orientation-dependent transition from TB sliding to TB cracking. These dynamic observations reveal unprecedented mechanical properties in nanocrystals, which hold implications for improving metal processing by severe plastic deformation.

Apigenin Alleviates Intervertebral Disc Degeneration via Restoring Autophagy Flux in Nucleus Pulposus Cells.

Oxidative stress-induced apoptosis and senescence of nucleus pulposus (NP) cells play a crucial role in the progression of intervertebral disc degeneration (IVDD). Accumulation of studies has shown that activated autophagy and enhanced autophagic flux can alleviate IVDD. In this study, we explored the effects of apigenin on IVDD in vitro and in vivo. Apigenin was found to inhibit tert-butyl hydroperoxide (TBHP)-induced apoptosis, senescence, and ECM degradation in NP cells. In addition, apigenin treatment can restore the autophagic flux blockage caused by TBHP. Mechanistically, we found that TBHP may induce autophagosome and lysosome fusion interruption and lysosomal dysfunction, while apigenin alleviates these phenomena by promoting the nuclear translocation of TFEB via the AMPK/mTOR signaling pathway. Furthermore, apigenin also exerts a protective effect against the progression of IVDD in the puncture-induced rat model. Taken together, these findings indicate that apigenin protects NP cells against TBHP-induced apoptosis, senescence, and ECM degradation via restoration of autophagic flux in vitro, and it also ameliorates IVDD progression in rats in vivo, demonstrating its potential for serving as an effective therapeutic agent for IVDD.