Comparative study of retrograde intramedullary nailing versus locking extramedullary plating in complete articular fractures with metaphyseal comminution of the distal femur.

INTRODUCTION: Fractures of the distal femur with metaphyseal comminution and complete intra-articular involvement (AO/OTA classifications 33C2 and 33C3) present challenges for reduction and fixation. However, an optimal fixation method remains unknown. This study aimed to compare the clinical and radiographic outcomes of locking extramedullary plating (LEP) and retrograde intramedullary nailing (RIN) for complete distal femoral intra-articular fractures with metaphyseal comminution. MATERIALS AND METHODS: Between January 2016 and May 2022, 80 patients (45 men and 35 women; average age, 56.7 years) diagnosed with AO/OTA 33C2 and 33C3 were treated with either LEP or RIN and followed up for at least one year. Post-operative evaluations included radiographic assessments of bone union rate, timing, and alignment. Clinically, the knee joint range of motion (ROM), lower extremity functional scale (LEFS), and Kellgren and Lawrence (KL) grade were analyzed. The complications were also compared. RESULTS: 36 underwent LEP and 44 underwent RIN. Bone union was observed in 69.4% and 63.6% of the patients in the LEP and RIN groups, respectively (p = 0.64). The average union time was 6.9 months for the LEP group and 6.6 months for the RIN group (p = 0.51). A tendency toward varus deformity was observed in the RIN group, although the difference was not statistically significant. No significant differences were observed in knee ROM, LEFS, or KL grade. Complications included non-union (33.8%; RIN, 11; LEP, 16), varus deformity (5%; RIN, 4; LEP, 0), infection (1.3%; RIN, 0; LEP, 1), heterotrophic ossification (1.3%; RIN, 0; LEP, 1), and wound dehiscence (2.5%; RIN, 2; LEP, 0). CONCLUSIONS: The surgical fixation methods, RIN and LEP, for complete distal femoral intra-articular fractures with metaphyseal comminution showed similar clinical and radiological outcomes. However, regardless of the type of fixation device used, there was a reduced rate of bone union owing to high energy and a less favorable prognosis.

Biomechanical Comparison of Fixation Methods for Posterior Wall Fractures of the Acetabulum: Conventional Reconstruction Plate vs. Spring Plate vs. Variable Angle Locking Compression Plate.

Background and Objectives: Acetabular fractures, though infrequent, present considerable challenges in treatment due to their association with high-energy trauma and poor prognoses. Posterior wall fractures, the most common type among them, typically have a more favorable prognosis compared to other types. Anatomical reduction and stable fixation of the posterior wall are crucial for optimal treatment outcomes. This study aimed to biomechanically compare three commonly used fixation methods for posterior wall fractures of the acetabulum-a conventional reconstruction plate, a spring plate, and a 2.7 mm variable angle locking compression plate (VA-LCP). Materials and Methods: The study utilized 6 fresh-frozen cadavers, yielding 12 hemipelvises free from prior trauma or surgery. Three fixation methods were compared using a simple acetabulum posterior wall fracture model. Fixation was performed by an orthopedic specialist, with prebending of plates to minimize errors. Hemipelvises were subjected to quasi-static and cyclic loading tests, measuring fracture gap, stiffness, and displacement under load. Results: It showed no significant differences in fracture gap among the three fixation methods under cyclic loading conditions simulating walking. However, the conventional reconstruction plate exhibited a greater stiffness compared to the spring and variable angle plates. Fatigue analysis revealed no significant differences among the plates, indicating a similar stability throughout cyclic loading. Despite differences in stiffness, all three fixation methods demonstrated adequate stability under loading conditions. Conclusions: While the conventional reconstruction plate demonstrated a superior stiffness, all three fixation methods provided sufficient stability under cyclic loading conditions similar to walking. This suggests that postoperative limitations are unlikely with any of the three methods, provided excessive activities are avoided. Furthermore, the variable angle plate-like the spring plate-offers an appropriate stability for fragment-specific fixation, supporting its use in surgical applications. These findings contribute to understanding the biomechanical performance of different fixation methods for acetabular fractures, facilitating improved surgical outcomes in challenging cases.

Risk factors for pubic ramus fracture nonunion after conservative treatment of pelvic ring injuries: a retrospective cohort multicenter study.

PURPOSE: To determine the incidence of nonunion, clinical and radiological outcomes, and risk factors for nonunion in conservatively treated pubic ramus fractures among patients diagnosed with pelvic ring injury. METHODS: A total of 546 patients (192 men, 354 women) diagnosed with pubic ramus fracture, treated conservatively, and who had completed > 1 year follow-up at three level 1 trauma centers between January 2014 and December 2020, were enrolled. Clinical and radiological evaluations were compared between union and nonunion groups. Logistic regression and Kaplan-Meier analyses were used. RESULT: At the final follow-up, 527 (96.5%) and 19 (3.5%) patients had union and nonunion of fractures, respectively. The union and nonunion groups exhibited statistically significant differences in posterior injury (p = 0.040), bilateral ramus fracture (p < 0.001), initial displacement (p < 0.001), and clinical result (p < 0.001). In the multivariate logistic regression analysis, initial displacement (odds ratio, 4.727; p = 0.005) was analyzed as a risk factor for nonunion. According to the Kaplan-Meier analysis, the median initial displacement of nonunion occurrence was 17.9 mm (standard error, 1.211; 95% confidence interval 15.526-20.274), and nonunion patients were included if the displacement was > 15.9 mm (standard error, 1.305) on the 75th percentile. CONCLUSION: Conservative treatment is ineffective in some ramus fracture cases with pelvic ring injury. As ramus nonunion causes functional deterioration, active treatment is required if the displacement is ≥ 16 mm.

The Unknown Abnormal Condition Monitoring Method for Pumped-Storage Hydroelectricity.

Pumped-storage hydroelectricity (PSH) is a facility that stores energy in the form of the gravitational potential energy of water by pumping water from a lower to a higher elevation reservoir in a hydroelectric power plant. The operation of PSH can be divided into two states: the turbine state, during which electric energy is generated, and the pump state, during which this generated electric energy is stored as potential energy. Additionally, the condition monitoring of PSH is generally challenging because the hydropower turbine, which is one of the primary components of PSH, is immersed in water and continuously rotates. This study presents a method that automatically detects new abnormal conditions in target structures without the intervention of experts. The proposed method automatically updates and optimizes existing abnormal condition classification models to accommodate new abnormal conditions. The performance of the proposed method was evaluated with sensor data obtained from on-site PSH. The test results show that the proposed method detects new abnormal PSH conditions with an 85.89% accuracy using fewer than three datapoints and classifies each condition with a 99.73% accuracy on average.

Continuous Structural Displacement Monitoring Using Accelerometer, Vision, and Infrared (IR) Cameras.

With the rapid development of computer vision, vision cameras have been used as noncontact sensors for structural displacement measurements. However, vision-based techniques are limited to short-term displacement measurements because of their degraded performance under varying illumination and inability to operate at night. To overcome these limitations, this study developed a continuous structural displacement estimation technique by combining measurements from an accelerometer with vision and infrared (IR) cameras collocated at the displacement estimation point of a target structure. The proposed technique enables continuous displacement estimation for both day and night, automatic optimization of the temperature range of an infrared camera to ensure a region of interest (ROI) with good matching features, and adaptive updating of the reference frame to achieve robust illumination-displacement estimation from vision/IR measurements. The performance of the proposed method was verified through lab-scale tests on a single-story building model. The displacements were estimated with a root-mean-square error of less than 2 mm compared with the laser-based ground truth. In addition, the applicability of the IR camera for displacement estimation under field conditions was validated using a pedestrian bridge test. The proposed technique eliminates the need for a stationary sensor installation location by the on-site installation of sensors and is therefore attractive for long-term continuous monitoring. However, it only estimates displacement at the sensor installation location, and cannot simultaneously estimate multi-point displacements which can be achieved by installing cameras off-site.

Comparison between anterior and posterior plating systems in extra-articular distal-third diaphyseal humeral fractures.

PURPOSE: The ideal surgical treatment of extra-articular distal-third diaphyseal humeral fractures is controversial in terms of the surgical approach and plate position. The aim of this study was to compare the clinical and radiological outcomes between anterior and posterior plating methods for extra-articular distal-third diaphyseal humeral fractures. METHODS: Twenty-four patients were treated with anterior plating with modified placement of the proximal humeral internal locking system (PHILOS) plate, and 22 patients were treated with posterior plating of the extra-articular distal humerus plate (EADHP). Patient demographics, the fracture configuration, the number of screws in the distal fragment, the operation time, and the time to union were analyzed. The range of elbow motion, Mayo elbow performance score (MEPS), plate-related symptoms, and complications were evaluated at the final follow-up. RESULTS: There were no statistically significant differences in the demographic data between the two groups. The mean operation time for anterior plating (108.2 ± 24.5 min) was significantly shorter than that for posterior plating (144.2 ± 29.5 minutes, p < 0.001). The average number of screws used in the distal humeral fragment was significantly higher with anterior plating (5.7 ± 0.7) than with posterior plating (4.8 ± 0.5, p < 0.001). No patients in the anterior plating group had plate-related symptoms, while 17 patients in the posterior plating group (77%) had discomfort or cosmetic problems related to the plate (p < 0.001). Plate removal was performed upon patient request in nine patients of the posterior plating (52.9%) and four (17%) in anterior plating (p = 0.040). Nonunion occurred in one patient who underwent anterior plating, and one patient who underwent posterior plating had post-operative radial nerve palsy. There were no significant differences in the MEPS or elbow range of motion between the two surgical methods. CONCLUSION: Both anterior and posterior plating provide satisfactory clinical and radiologic outcomes for extra-articular distal-third diaphyseal humeral fractures. Despite the satisfactory outcomes, however, posterior plating is highly associated with plate-related complaints, which might be one of the considerations when the surgical method is selected for extra-articular distal-third diaphyseal humeral fractures.

Outcomes of embedded rafting k-wire technique for intermediate articular fragment fixation in comminuted olecranon fractures.

BACKGROUND: Severely comminuted olecranon fractures are challenging injuries. Commonly used tension band wiring exerts excessive compressive forces causing olecranon shortening and joint incongruity. This study aimed to introduce the embedded rafting k-wire technique with the bridging technique for intermediate articular fragment fixation in comminuted olecranon fractures and evaluate its clinical and radiological outcomes. MATERIALS AND METHODS: A total of 34 patients with comminuted olecranon fractures were treated with rafting k-wire fixation combined with a locking plate. Time to union, the number of rafting k-wires in the intermediate articular fragment, quality of joint reduction, and secondary reduction loss were analyzed. Elbow range of motion, Mayo Elbow Performance Score (MEPS), and complications were evaluated at the final follow-up. RESULTS: Fracture union was obtained in all patients. The mean number of intermediate articular fragments was 2.4 ± 0.7, and the average number of rafting k-wires was 3.0 ± 1.2. There were mild and moderate degree early posttraumatic osteoarthritis in 6 cases (17.6%) at the mean 20.8 months of follow-up. At the final follow-up, the mean range of elbow motion was 4.6° of flexion contracture and 133.5° of further flexion. The average MEPS was 97.1 (range, 75-100). Two patients had heterotrophic ossification without functional impairment. CONCLUSION: The embedded rafting k-wire technique with bridging plates in comminuted olecranon fractures exhibited satisfactory outcomes. This method might serve as an alternative when considering the ability to restore articular congruency and stability in severely comminuted olecranon fragments. LEVEL OF EVIDENCE: Level IV, therapeutic.

Dynamic Displacement Estimation for Long-Span Bridges Using Acceleration and Heuristically Enhanced Displacement Measurements of Real-Time Kinematic Global Navigation System.

In this paper, we propose a dynamic displacement estimation method for large-scale civil infrastructures based on a two-stage Kalman filter and modified heuristic drift reduction method. When measuring displacement at large-scale infrastructures, a non-contact displacement sensor is placed on a limited number of spots such as foundations of the structures, and the sensor must have a very long measurement distance (typically longer than 100 m). RTK-GNSS, therefore, has been widely used in displacement measurement on civil infrastructures. However, RTK-GNSS has a low sampling frequency of 10-20 Hz and often suffers from its low stability due to the number of satellites and the surrounding environment. The proposed method combines data from an RTK-GNSS receiver and an accelerometer to estimate the dynamic displacement of the structure with higher precision and accuracy than those of RTK-GNSS and 100 Hz sampling frequency. In the proposed method, a heuristic drift reduction method estimates displacement with better accuracy employing a low-pass-filtered acceleration measurement by an accelerometer and a displacement measurement by an RTK-GNSS receiver. Then, the displacement estimated by the heuristic drift reduction method, the velocity measured by a single GNSS receiver, and the acceleration measured by the accelerometer are combined in a two-stage Kalman filter to estimate the dynamic displacement. The effectiveness of the proposed dynamic displacement estimation method was validated through three field application tests at Yeongjong Grand Bridge in Korea, San Francisco-Oakland Bay Bridge in California, and Qingfeng Bridge in China. In the field tests, the root-mean-square error of RTK-GNSS displacement measurement reduces by 55-78 percent after applying the proposed method.

Multifunctional Smart Ball Sensor for Wireless Structural Health Monitoring in a Fire Situation.

A variety of sensor systems have been developed to monitor the structural health status of buildings and infrastructures. However, most sensor systems for structural health monitoring (SHM) are difficult to use in extreme conditions, such as a fire situation, because of their vulnerability to high temperature and physical shocks, as well as time-consuming installation process. Here, we present a smart ball sensor (SBS) that can be immediately installed on surfaces of structures, stably measure vital SHM data in real time and wirelessly transmit the data in a high-temperature fire situation. The smart ball sensor mainly consists of sensor and data transmission module, heat insulator and adhesive module. With the integrated device configuration, the SBS can be strongly attached to the target surface with maximum adhesion force of 233.7-N and stably detect acceleration and temperature of the structure without damaging the key modules of the systems even at high temperatures of up to 500 °C while ensuring wireless transmission of the data. Field tests for a model pre-engineered building (PEB) structure demonstrate the validity of the smart ball sensor as an instantly deployable, high-temperature SHM system. This SBS can be used for SHM of a wider variety of structures and buildings beyond PEB structures.

A Real-Time, Non-Contact Method for In-Line Inspection of Oil and Gas Pipelines Using Optical Sensor Array.

Corrosion is considered as one of the most predominant causes of pipeline failures in the oil and gas industry and normally cannot be easily detected at the inner surface of pipelines without service disruption. The real-time inspection of oil and gas pipelines is extremely vital to mitigate accidents and maintenance cost as well as to improve the oil and gas transport efficiency. In this paper, a new, non-contact optical sensor array method for real-time inspection and non-destructive evaluation (NDE) of pipelines is presented. The proposed optical method consists of light emitting diodes (LEDs) and light dependent resistors (LDRs) to send light and receive reflected light from the inner surface of pipelines. The uniqueness of the proposed method lies in its accurate detection as well as its localization of corrosion defects, based on the utilization of optical sensor array in the pipeline, and also the flexibility with which this system can be adopted for pipelines with different services, sizes, and materials, as well as the method's economic viability. Experimental studies are conducted considering corrosion defects with different features and dimensions to confirm the robustness and accuracy of the method. The obtained data are processed with discrete wavelet transform (DWT) for noise cancelation and feature extraction. The estimated sizes of the corrosion defects for different physical parameters, such as inspection speed and lift-off distance, are investigated and, finally, some preliminary tests are conducted based on the implementation of the proposed method on an in-line developed smart pipeline inspection gauge (PIG) for in-line inspection (ILI) application, with resulting success.

An Overview of Non-Destructive Testing Methods for Integrated Circuit Packaging Inspection.

The article provides a review of the state-of-art non-destructive testing (NDT) methods used for evaluation of integrated circuit (IC) packaging. The review identifies various types of the defects and the capabilities of most common NDT methods employed for defect detection. The main aim of this paper is to provide a detailed review on the common NDT methods for IC packaging addressing their principles of operation, advantages, limitations and suggestions for improvement. The current methods such as, X-ray, scanning acoustic microscopy (SAM), infrared thermography (IRT), magnetic current imaging (MCI) and surface acoustic waves (SAW) are explicitly reviewed. The uniqueness of the paper lies in comprehensive comparison of the current NDT methods, recommendations for the improvements, and introduction of new candidate NDT technologies, which can be adopted for IC packaging.

Development of a High Precision Displacement Measurement System by Fusing a Low Cost RTK-GPS Sensor and a Force Feedback Accelerometer for Infrastructure Monitoring.

A displacement measurement system fusing a low cost real-time kinematic global positioning system (RTK-GPS) receiver and a force feedback accelerometer is proposed for infrastructure monitoring. The proposed system is composed of a sensor module, a base module and a computation module. The sensor module consists of a RTK-GPS rover and a force feedback accelerometer, and is installed on a target structure like conventional RTK-GPS sensors. The base module is placed on a rigid ground away from the target structure similar to conventional RTK-GPS bases, and transmits observation messages to the sensor module. Then, the initial acceleration, velocity and displacement responses measured by the sensor module are transmitted to the computation module located at a central monitoring facility. Finally, high precision and high sampling rate displacement, velocity, and acceleration are estimated by fusing the acceleration from the accelerometer, the velocity from the GPS rover, and the displacement from RTK-GPS. Note that the proposed displacement measurement system can measure 3-axis acceleration, velocity as well as displacement in real time. In terms of displacement, the proposed measurement system can estimate dynamic and pseudo-static displacement with a root-mean-square error of 2 mm and a sampling rate of up to 100 Hz. The performance of the proposed system is validated under sinusoidal, random and steady-state vibrations. Field tests were performed on the Yeongjong Grand Bridge and Yi Sun-sin Bridge in Korea, and the Xihoumen Bridge in China to compare the performance of the proposed system with a commercial RTK-GPS sensor and other data fusion techniques.

Fatigue crack localization using noncontact laser ultrasonics and state space attractors.

A fatigue crack and its precursor often serves as a source of nonlinear mechanism for ultrasonic waves, and the resulting nonlinear features are often much more sensitive to the fatigue crack than their linear counterparts. Among various nonlinear ultrasonic techniques, the proposed laser nonlinear wave modulation spectroscopy (LNWMS) is unique in that (1) it utilizes a pulse laser to exert a single broadband input instead of conventional two distinctive sinusoidal waves, and (2) a complete noncontact measurement can be realized based on LNWMS. Under a broadband excitation, a nonlinear source exhibits modulations due to interactions among various input frequency components. These modulations are often weak and can be hardly directly detected. In this paper, a damage feature called Bhattacharyya distance is extracted from the ultrasonic time signal corresponding to a pulse laser input and used to quantify the degree of damage-induced nonlinearity and localize the crack. This feature is a measure of a statistical distance used to detect the geometrical changes between state space attractors reconstructed before and after damage formation. It has been successfully used for localizing fatigue cracks in metallic plates.

Mechanical impedance measurement and damage detection using noncontact laser ultrasound.

This Letter proposes a mechanical impedance (MI) measurement technique using noncontact laser ultrasound. The ultrasound is generated by shooting a pulse laser beam onto a target structure, and its response is measured using a laser vibrometer. Once ultrasound propagation converges to structural vibration, MI is formed over the entire structure. Because noncontact lasers are utilized, this technique is applicable in harsh environments, free of electromagnetic interference, and able to perform wide-range scanning. The formation of MI and its feasibility for damage detection are verified through thermo-mechanical finite element analysis and lab-scale experiments.

Minimally invasive plate osteosynthesis for proximal humeral fractures: clinical and radiologic outcomes according to fracture type.

BACKGROUND: This study evaluated the clinical and radiologic outcomes, according to fracture type, of proximal humeral fractures treated by the minimally invasive plate osteosynthesis (MIPO) technique. MATERIALS AND METHODS: Of 85 patients with proximal humeral fractures who were treated by the MIPO technique, 62 were evaluated: 27 with 2-part fractures, 24 with 3-part fractures, and 11 with 4-part fractures. An additional inferomedial screw or fibular allograft was used when severe medial cortical comminution was found in the proximal humerus. Clinical and radiographic outcomes were evaluated during the follow-up of 37 months. RESULTS: There was a significant difference in the Constant scores of patients with 4-part fractures compared with those with 3-part fractures (P = .039). The neck-shaft angle in 4-part fractures (121° ± 3°) at final follow-up was significantly lower compared with other fracture types (2-part: 129° ± 9°, P = .036; 3-part: 129° ± 2°, P = .031). Complication rates (72.7%) of 4-part fractures were significantly higher than with other fracture types (2-part, 7.4%; 3-part, 20.8%; P = .001). Sixteen fractures were fixed with an additional inferomedial screw, and 3 patients had insertion of a fibular allograft. CONCLUSION: Satisfactory clinical and radiologic outcomes were obtained by the MIPO technique in proximal humeral fractures. In addition, medial cortical support can be performed with an inferomedial screw or fibular allograft in the MIPO technique. However, the MIPO technique for 4-part fractures showed relatively inferior outcomes compared with 2- and 3-part fractures. Conversion to open plating is also considered if adequate reduction, that is, a neck-shaft angle >120°, is not able to be obtained in the MIPO technique for 4-part fractures of the proximal humerus.

Mortality Rate and Outcomes of Omicron Variant Positive Patients with Osteoporotic Fractures: A Retrospective Study.

BACKGROUND: During the lockdown period associated with the coronavirus disease 2019 (COVID-19) pandemic, increased mortality rates among patients with COVID-19 have been reported. This study aimed to analyze the mortality rate of osteoporotic hip fractures in patients who were COVID-19-positive after the lockdown during the Omicron period. METHODS: A retrospective study was performed with 194 patients who were aged 70 years or more and diagnosed with osteoporotic hip fracture. The patients were divided into two groups according to their COVID-19 diagnoses. Surgery was performed within 10 days of diagnosis. Age, sex, past medical history, time until surgery, postoperative complications, and the primary outcome of mortality rate at 30 and 90 days were analyzed. RESULTS: Among the 194 patients, 13 and 181 were in the COVID-19-positive and negative group, respectively. The total, 30-day, and 90-day mortality rates in the control and COVID-positive group were 11% and 0% (P=0.368), 1.7% and 0% (P=1.000), and 5.0% and 0% (P=1.000), respectively. No significant differences were observed in age, sex, history, time to surgery, postoperative complications, or postoperative mortality. In 1:1 propensity score matching, the time to surgery was 5.34 days in patients who were COVID-19-positive, and 3.00 days in patients who were COVID-19 negative, with no statistical significance (P=0.09). Age, sex, medical history, postoperative complications, and postoperative mortality were not significantly different between the groups. CONCLUSIONS: Regardless of the COVID-19 diagnosis, surgical treatment without delay is believed to result in positive outcomes in older patients with osteoporotic hip fractures, as no significant differences in mortality rate and respiratory complications were observed between patients who were COVID-19-positive and those who were COVID-19 negative.

Radiographic outcomes and non-union factor analysis in fragmentary segmental femoral shaft fractures (AO/OTA 32C3) treated with reamed antegrade nailing.

This study retrospectively assessed radiographic outcomes and risk factors associated with non-union in femoral shaft fragmentary segmental fractures (AO/OTA 32C3) treated with reamed antegrade intra-medullary nailing. Radiological outcomes, including union and alignment, were evaluated. The risk factors for non-union were investigated, including demographics and treatment-related characteristics, such as the number of interlocking screws, segmentation length, main third fragment length, distance of the main third fragment, width ratio and exposed nail length in one cortex from immediate post-operative radiographs. Multivariate logistic regression was used for statistical analysis. Among 2295 femoral shaft fracture patients from three level-1 trauma centers, 51 met the inclusion criteria. The radiological union was achieved in 37 patients (73%) with a mean union time of 10.7 ± 4.8 months. The acceptable axial alignment was observed in 30 patients (59%). Multiple logistic regression analysis identified only exposed nail length as a significant risk factor for non-union (odds ratio: 1.599, p = 0.003) and the cut-off value was 19.1 mm (sensitivity, 0.786; specificity, 0.811). The study revealed high rates of non-union (27%) and malalignment (41%). Therefore, patients who underwent intramedullary nailing with an exposed nail length greater than 19.1 mm or about twice the nail diameter should be cautioned of the potential non-union.

Duration of in vitro storage affects the key stem cell features of human bone marrow-derived mesenchymal stromal cells for clinical transplantation.

BACKGROUND AIMS: Mesenchymal stromal cells (MSCs) have the ability to self-renew and differentiate into various cell types. Their plasticity and easy availability make them promising candidates for regenerative medicine. However, for successful clinical application, MSCs need to be expanded under a Good Manufacturing Practices-compliant system to obtain a large quantity of these cells. Although the viability and potency of these in vitro-expanded MSCs need to be maintained during preparation and transportation before transplantation, these characteristics have not thoroughly been examined. Our goal in this study was to standardize MSC preparation and storage before their clinical application to ensure reproducible quality and potency for their clinically intended purpose. METHODS: We examined the viability, self-renewal capacity and differentiation capability of MSCs on short-term in vitro storage in saline or dextrose solution at 4°C and room temperature. RESULTS: MSCs harvested and suspended in saline for 1-2 h showed >90% viability regardless of storage temperature. However, when cells were stored for >2 h in saline, their viability decreased gradually over time. The viability of cells in dextrose deteriorated rapidly. MSCs lost colony-forming unit and differentiation capacities rapidly as storage time increased. Collectively, we found that a storage period >2 h resulted in a significant decrease in cell viability, cell proliferation capacity and differentiation potency. CONCLUSIONS: Storage of culture-harvested MSCs for >2 h is likely to result in suboptimal MSC-mediated tissue regeneration because of decreased cell viability and differentiation capacity.

Reference-free damage detection, localization, and quantification in composites.

In this study, a reference-free damage characterization technique is developed not only to identify but also to locate and quantify damage in composite structures subject to varying temperature conditions. First, damage is characterized in terms of a damage index (m-value) defined as the ratio of damage size to the wavelength of the A0 mode within the damage. Then, a feasible solution space defining all possible combinations of the damage location and size are estimated without using any prior baseline data obtained from the pristine condition of a structure or different paths. When additional information such as the A0 mode group velocity within the pristine region of the structure becomes available, the estimates for the damage location and size are updated with better accuracy. The uniqueness of this study lies in that damage localization and quantification as well as identification are all performed without comparing current Lamb wave signals with the ones obtained from the pristine condition of the target structure, making the proposed technique more attractive for online monitoring. Numerical and experimental tests are presented to demonstrate the effectiveness of the proposed damage detection technique under varying temperature.

Spectral noise and data reduction using a long short-term memory network for nonlinear ultrasonic modulation-based fatigue crack detection.

This paper presents a spectral noise and data reduction technique based on long short-term memory (LSTM) network for nonlinear ultrasonic modulation-based fatigue crack detection. The amplitudes of the nonlinear modulation components created by a micro fatigue crack are often very small and masked by noise. In addition, the collection of large amounts of data is often undesirable owing to the limited power, data storage, and data transmission bandwidth of monitoring systems. To tackle the issues, an LSTM network was applied to ultrasonic signals to reduce the noise level and the amount of data. The proposed technique offers the following benefits: (1) spectral noise reduction using the LSTM network for ultrasonic signals and (2) data reduction without compromising the spectral density amplitude of the existing nonlinear modulation components. Finally, the performance evaluation was conducted using the data obtained from complex geometry and real structure under external noises, indicating that the proposed method can be applied to various structures.