Hot Deformation Behavior and Microstructure Evolution Mechanisms of Ti6Al4V Alloy under Hot Stamping Conditions.

Through the study of the thermal rheological behavior of Ti6Al4V alloy at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C) and different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1, and 0.005 s-1), a constitutive model was developed for Ti6Al4V alloy across a wide temperature range in the hot stamping process. The model's correlation coefficient reached 0.9847, indicating its high predictive accuracy. Hot processing maps suitable for the hot stamping process of Ti6Al4V alloy were developed, demonstrating the significant impact of the strain rate on the hot formability of Ti6Al4V alloy. At higher strain rates (>0.05 s-1), the hot processing of Ti6Al4V alloy is less prone to instability. Combining hot processing maps with hot stamping experiments, it was found that the forming quality and thickness uniformity of parts improved significantly with the increase in stamping speed. The phase composition and microstructures of the forming parts under different heating temperature conditions have been investigated using SEM, EBSD, XRD, and TEM, and the maximum heating temperature of hot stamping forming was determined to be 875 °C. The recrystallization mechanism in hot stamping of Ti6Al4V alloys was proposed based on EBSD tests on different sections of a hot stamping formed box-shaped component. With increasing deformation, the effect of dynamic recrystallization (DRX) was enhanced. When the thinning rate reached 15%, DRX surpassed dynamic recovery (DRV) as the dominant softening mechanism. DRX grains at different thinning rates were formed through both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), with CDRX always being the dominant mechanism.

Finite Element Simulation and Microstructural Evolution Investigation in Hot Stamping Process of Ti6Al4V Alloy Sheets.

Titanium alloy hot stamping technology has a wide range of application prospects in the field of titanium alloy part processing due to its high production efficiency and low manufacturing cost. However, the challenges of forming titanium alloy parts with large depths and deformations have restricted its development. In this study, the hot stamping process of a Ti6Al4V alloy box-shaped part was investigated using ABAQUS 2020 software. The thermodynamic properties of a Ti6Al4V alloy sheet were explored at different temperatures (400 °C, 500 °C, 600 °C, 700 °C, 800 °C) and different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1). In addition, the influence law of hot stamping process parameters on the minimum thickness of the formed part was revealed through the analysis of response surface methodology (RSM), ultimately obtaining the optimal combination of process parameters for Ti6Al4V alloy hot stamping. The experimental results of the hot stamping process exhibited a favorable correlation with the simulated outcomes, confirming the accuracy of the numerical simulation. The study on the microstructure evolution of the formed parts showed that grain refinement strengthening occurred in the part with large deformation, and the formed box-shaped parts exhibited a uniform and fine microstructure overall, demonstrating high forming quality. The achievements of the work provide important guidance for the fabrication of titanium alloy parts with large depths and deformations used in heavy industrial production.

SiRNA in MSC-derived exosomes silences CTGF gene for locomotor recovery in spinal cord injury rats.

BACKGROUND: How to obtain a small interfering RNA (siRNA) vector has become a moot point in recent years. Exosomes (Exo) show advantages of long survival time in vivo, high transmission efficiency, and easy penetration across the blood-spinal cord barrier, renowned as excellent carriers of bioactive substances. METHODS: We applied mesenchymal stem cell (MSC)-derived exosomes as the delivery of synthesized siRNA, which were extracted from rat bone marrow. We constructed exosomes-siRNA (Exo-siRNA) that could specifically silence CTGF gene in the injury sites by electroporation. During the administration, we injected Exo-siRNA into the tail vein of SCI rats, RESULTS: In vivo and in vitro experiments showed that Exo-siRNA not only effectively inhibited the expressions of CTGF gene, but quenched inflammation, and thwarted neuronal apoptosis and reactive astrocytes and glial scar formation. Besides, it significantly upregulated several neurotrophic factors and anti-inflammatory factors, acting as a facilitator of locomotor recovery of rats with spinal cord injury (SCI). CONCLUSIONS: In conclusion, this study has combined the thoroughness of gene therapy and the excellent drug-loading characteristics of Exo for the precise treatment of SCI, which will shed new light on the drug-loading field of Exo.

Clinical Benefit of Rehabilitation Training in Spinal Cord Injury: A Systematic Review and Meta-Analysis.

STUDY DESIGN: A systematic review and meta-analysis. OBJECTIVE: This study was performed to evaluate the effects of different rehabilitation interventions in spinal cord injury. SUMMARY OF BACKGROUND DATA: Several activity-based interventions have been widely applied in spinal cord injury in the past, but the effects of these rehabilitation exercises are controversial. METHODS: Publications were searched from databases (PubMed, Embase, Cochrane, the database of the U.S. National Institutes of Health and World Health Organization International Clinical Trials Registry Platform) using the searching terms like spinal cord injury, transcranial magnetic stimulation, functional electrical stimulation, activity-based therapy, and robotic-assisted locomotor training. Randomized controlled trials and controlled trials were included. The primary outcomes included functional upper/lower extremity independence, walking capacity, spasticity, and life quality of individuals with spinal cord injury. Meta-analysis was performed using Revman 5.0 software. RESULTS: Thirty-one articles were included. Meta-analysis showed that transcranial magnetic stimulation improved walking speed (95% confidence interval [CI] 0.01, 0.16) and lower extremity function (95% CI 1.55, 7.27); functional electrical stimulation significantly increased upper extremity independence (95% CI 0.37, 5.48). Robotic-assisted treadmill training improved lower extremity function (95% CI 3.44, 6.56) compared with related controls. CONCLUSION: Activity-based intervention like transcranial magnetic stimulation, functional electrical stimulation, and robotic-assisted treadmill training are effective in improving function in individuals with spinal cord injury.Level of Evidence: 1.

Clinical effectiveness of percutaneous vertebroplasty in conjunction with postoperative radiotherapy in the treatment of spinal metastases.

PURPOSE: This study aimed to evaluate the clinical effects of percutaneous vertebroplasty (PVP) combined with postoperative radiotherapy (RT) in the treatment of spinal metastases. METHODS: Nine patients (4 males and 5 females, mean age 59.56 years) with painful pathologic compression vertebral fractures caused by metastatic cancers of the spine (5 thoracic levels, 8 lumbar levels) were admitted to our hospital between July 17, 2016 and September 25, 2018. All patients were treated with PVP via bilateral pedicle approach combined with postoperative RT to treat metastatic lesions of the centrum. The clinical records of the patients were retrospectively analyzed. Patients' demographic features and medical conditions including the Visual Analogue Scale (VAS), Oswestry Disability Index (ODI) and Imageology data were observed. RESULTS: Patients' mean VAS scores decreased from 8.67 ± 0.50 preoperatively to 1.78 ± 0.83 at 6 months after PVP. Moreover, the mean ODI score decreased from 74.07 ± 13.15 preoperatively to 31.87 ± 10.00 at 6 months after PVP. Significant improvement in the degree of pain and dysfunction among the enrolled patients were observed. Furthermore, the metastatic carcinoma lesion within the vertebral body was well controlled according to imaging. CONCLUSION: PVP in conjunction with postoperative RT is a good treatment strategy for vertebral compression fractures caused by metastases.

Primary multiple angiosarcoma of vertebra: A case report.

RATIONALE: Angiosarcoma is a rare malignant tumors. The objective of this study is to report a patient who suffered from a progressive low back pain and left lower extremities radiation pain for about 8 months, After diagnoses, this was identified as an extremely rare case of primary multiple angiosarcoma of vertebra. PATIENT CONCERNS: A 54-year-old man with a history of 2-year hypertension and 8-year diabetes, both of which were well controlled by drug management. Lately, he suffered from a progressive low back pain and left lower extremities radiation pain for about 8 months. DIAGNOSES: Magnetic resonance imaging of lumbar showed a clear pathological fracture and primary multiple angiosarcoma of all vertebra. Postoperative pathology and High-throughput sequencing confirmed the diagnosis of primary multiple angiosarcoma of vertebra. INTERVENTIONS: The patient underwent minimally invasive pedicle screw fixation combined with bone cement augmentation for the purpose of stabilizing the damaged vertebrae. Following operation, he received both radiotherapy and chemotherapy for a period of time. OUTCOMES: The operation has achieved positive results in relieving pain and stabilizing the spine. No wound problem or operative complications occurred after operation. The patient reported an obvious remission of low back pain and was only capable to perform restricted physiological activities. A long-term palliative radiotherapy and chemotherapy were performed after operation. Unfortunately, the patient died 18 months later. CONCLUSION: This article emphasizes primary multiple angiosarcoma of vertebra. Despite being rare, it should be part of the differential when the patient manifested back pain and radiculopathy. We recommended the minimally invasive pedicle screw fixation for angiosarcoma of vertebra. Osteoplasty by bone cement augmentation was also an ideal choice for surgical treatment. It also advocates the use of specific targeted radiotherapy drugs based on gene analysis of tumors.

Treatment of Thoracolumbar Fractures Through Different Short Segment Pedicle Screw Fixation Techniques: A Finite Element Analysis.

OBJECTIVE: To compare the von Mises stresses of the pedicle screw system and the displacement of injured vertebrae using 3-D finite element analysis, and to evaluate the curative effect of the pedicle screw system. METHODS: Finite element methods were used for biomechanical comparison of four posterior short segment pedicle screw fixation techniques. The different pedicle screw models are traditional trajectory (TT), Universal Spine System (USS), cortical bone trajectory (CBT), and CBT at the cranial level and pedicle screw (PS) at the caudal level (UP-CBT). The stress distribution of the screws and connecting rods under different working conditions and the displacement of the injured vertebrae were compared and analyzed. RESULTS: After the pedicle screw system was fixed, the stress under vertical compression was mainly concentrated at the proximal end of the screw, while the stress was mainly concentrated on the connecting rod during flexion, extension, lateral flexion, and rotation. The TT group had the greatest stress during the flexion, extension, and left and right rotation. The UP-CBT group was most stressed when the left and right sides were flexed; the stress of the USS screw system was less than that of the other three models during flexion, lateral flexion, and rotation. The maximum von Mises stress values of pedicle screws in all exercise states were 556.2, 340.7, 458.1, and 533.4 MPa, respectively. In the USS group, the displacement of the injured vertebra was small in the flexion, and the left and right lateral flexion and the right rotation were higher than in the TT group and the CBT group. The maximum displacements of the injured vertebrae in all motion states were 1.679, 1.604, 1.752, and 1.777 mm, respectively. CONCLUSION: Universal Spine System pedicle screws are relatively less stressed under different working conditions, the risk of breakage is small, and the model is relatively stable; CBT screws do not exhibit better mechanical properties than conventional pedicle screws and USS pedicle screws.

Gene expression profiles and bioinformatics analysis of insulin-like growth factor-1 promotion of osteogenic differentiation.

BACKGROUND: Insulin-like growth factor-1 (IGF-1) promotes osteoblast differentiation and mineralization. The objective of this study was to investigate the effects of IGF-1 on proliferation, mineralization, alkaline phosphatase (ALP) synthesis, and gene expression of osteoblast differentiation in MC3T3-E1 osteoblasts cells, and to explore gene expression profiling differential genes. METHODS: MC3T3-E1 osteoblasts cells were cultured in medium with or without IGF-1. The ALP assay was employed to determine the osteoblast mineralization, and Alizarin red S to stain for calcium deposits, which were the indicators of mature osteocytes. The living cell number was assessed by the Cell Counting Kit-8 method. RNA-seq analysis was applied to identify genes that were differentially expressed in with or without IGF-1 as well as genes that varied between these two groups. The expression of osteogenic marker genes was determined by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis. RESULT: The cell number of osteoblasts exposed to IGF-1 at 200 µg/L significantly increased compared with the control group. The ALP activity in IGF-1-treated cells was higher than that in the control group. IGF-1 can increase ALP synthesis in osteoblasts in vitro. RNA-seq analysis showed that 677 triggered differentially expressed genes by IGF, of which 383 genes were downregulated and 294 genes were upregulated. Gene ontology (GO) analysis showed that IGF-1 caused a significant change in gene expression patterns. CONCLUSIONS: This result suggested that IGF-1 could probably promote the synthesis of organic matrix and mineralize action of bone. Osteogenic-related genes (DMP1, PHEX, SOST, BMP2, RUNX2, OPN, and OCN) were significantly upregulated both in GO analysis and in pathway analysis to perform qRT-PCR. Western blot analysis demonstrated that the Notch pathway was highly upregulated in MC3T3-E1 cells.

Study of engineered low-modulus Mg/PLLA composites as potential orthopaedic implants: An in vitro and in vivo study.

Low molecular weight poly-lactic acid (PLLA) is a polymer matrix of orthopaedic implants. The PLLA matrix incorporating bioactive magnesium ion (Mg2+) enhances bone regeneration. But the optimal ratio of Mg2+ to PLLA matrix has not been well reported and is worthy of study. We synthesized silane-coated Mg/PLLA composites containing 1%, 2%, 3%, 4% and 5% Mg micro-particles. The mechanical properties, in vitro cytocompatibility, cell viability and osteogenesis differentiation and in vivo performance of silane-coated Mg/PLLA composites were evaluated. These results showed that the bending and tensile strength of PLLA matrix was reduced by incorporation of Mg micro-particles. Mg/PLLA composites with higher Mg micro-particles ratio showed higher Mg2+ leaching rate and pH value in immersion solutions. MC3T3-E1 pre-osteoblasts incubated with Mg/PLLA composites containing higher ratio of Mg micro-particles showed higher cytocompatibility, cell viability, osteogenesis differentiation and migration. In vitro cellular responses showed that MC3T3-E1 pre-osteoblasts had the highest cell viability at 50 ppm Mg2+. In vivo animal studies showed there was no change in serum Mg2+ concentration after implanting Mg/PLLA composites comparing with control and the implants of silane-coated Mg/PLLA composites accelerated bone formation. In summary, our study revealed the feasibility of silane-coated Mg/PLLA composites as orthopaedic implants. Silane-coated Mg/PLLA composites with Mg micro-particles ratio of 3% ∼ 5% were optimal substitutes for bone regeneration.