Detection of defects in cellular solids using highly nonlinear solitary waves: a numerical study of the proximal femur.

This study investigates the suitability of a relatively new non-destructive evaluation (NDE) technique for the detection of non-visible defects in cellular solids using highly nonlinear solitary waves (HNSWs) in a one-dimensional granular chain. Specifically, the HNSW-based NDE approach is employed to identify the existence of micro-fractures in trabecular bone within the femoral neck (FN) and the intertrochanteric (IT) region of the proximal femur which are fracture-prone sites due to their relatively low bone density, particularly in osteoporosis patients. The availability of a HNSW-based bone quality assessment tool could not only help in early diagnosis of osteoporosis but also affect surgical decisions and improve clinical outcomes in joint replacement surgeries which motivated this study. To obtain a realistic representation of the trabecular microstructure, high-resolution finite-element (FE) models of the FN and the IT region are first constructed using a topology optimization-based bone reconstruction scheme. Then, artificial defects in the form of fractured ligaments are generated in the FN and IT models by selectively disconnecting various struts within the trabecular network. Using the FE models as the inspection medium, hybrid discrete-element/finite-element (DE/FE) simulations are performed to examine the interaction of the HNSWs with the cellular bone samples through two different inspection modes, i.e., inspection via direct contact with the sample and indirect contact through an adequately chosen face sheet inserted between the cellular sample and the granular chain. The delays and amplitudes of the HNSWs are used to estimate the effective elastic moduli of the cellular samples and these estimates were found to be reasonably accurate only in case the face sheet was applied. For the latter case, it was shown that the HNSW-based modulus estimates can be used as indicators for defect detection, allowing to discern between pristine and damaged cellular solids. These results suggest that HNSW-based NDE is a reliable and cost-effective technique for the identification of defects in cellular solids, and is expected to find applications in various fields, such as non-invasive screening of bone diseases and fractures, or damage detection in additively manufactured cellular structures.

Strain Transfer Function of Distributed Optical Fiber Sensors and Back-Calculation of the Base Strain Field.

Distributed optical fiber sensors are a promising technology for monitoring the structural health of large-scale structures. The fiber sensors are usually coated with nonfragile materials to protect the sensor and are bonded onto the structure using adhesive materials. However, local deformation of the relatively soft coating and adhesive layers hinders strain transfer from the base structure to the optical fiber sensor, which reduces and distorts its strain distribution. In this study, we analytically derive a strain transfer function in terms of strain periods, which enables us to understand how the strain reduces and is distorted in the optical fiber depending on the variation of the strain field. We also propose a method for back-calculating the base structure's strain field using the reduced and distorted strain distribution in the optical fiber sensor. We numerically demonstrate the back-calculation of the base strain using a composite beam model with an open hole and an attached distributed optical fiber sensor. The new strain transfer function and the proposed back-calculation method can enhance the strain field estimation accuracy in using a distributed optical fiber sensor. This enables us to use a highly durable distributed optical fiber sensor with thick protective layers in precision measurement.

Predictions of the elastic modulus of trabecular bone in the femoral head and the intertrochanter: a solitary wave-based approach.

This paper deals with the numerical prediction of the elastic modulus of trabecular bone in the femoral head (FH) and the intertrochanteric (IT) region via site-specific bone quality assessment using solitary waves in a one-dimensional granular chain. For accurate evaluation of bone quality, high-resolution finite element models of bone microstructures in both FH and IT are generated using a topology optimization-based bone microstructure reconstruction scheme. A hybrid discrete element/finite element (DE/FE) model is then developed to study the interaction of highly nonlinear solitary waves in a granular chain with the generated bone microstructures. For more robust and reliable prediction of the bone's mechanical properties, a face sheet is placed at the interface between the last chain particle and the bone microstructure, allowing more bone volume to be engaged in the dynamic deformation during interaction with the solitary wave. The hybrid DE/FE model was used to predict the elastic modulus of the IT and FH by analysing the characteristic features of the two primary reflected solitary waves. It was found that the solitary wave interaction is highly sensitive to the elastic modulus of the bone microstructure and can be used to identify differences in bone density. Moreover, it was found that the use of a relatively stiff face sheet significantly reduces the sensitivity of the wave interaction to local stiffness variations across the test surface of the bone, thereby enhancing the robustness and reliability of the proposed method. We also studied the effect of the face sheet thickness on the characteristics of the reflected solitary waves and found that the optimal thickness that minimizes the error in the modulus predictions is 4 mm for the FH and 2 mm for the IT, if the primary reflected solitary wave is considered in the evaluation process. We envisage that the proposed diagnostic scheme, in conjunction with 3D-printed high-resolution bone models of an actual patient, could provide a viable solution to current limitations in site-specific bone quality assessment.

Numerical predictions of the interaction between highly nonlinear solitary waves and the microstructure of trabecular bone in the femoral head.

The unique properties of highly nonlinear solitary waves in granular chains have prompted extensive research in the area of non-destructive testing and led to the development of new diagnostic schemes with potential applications in the healthcare industry. Here, we study numerically the interaction between highly nonlinear solitary waves in a granular chain and the microstructure of trabecular bone in the femoral head. High-resolution finite element models of bone microstructures with varying bone volume fraction are generated using a topology optimization-based bone microstructure reconstruction scheme. The obtained FE models of the trabecular bone were then used to develop a hybrid discrete/finite element model able to simulate the propagation of highly nonlinear solitary waves in a vertical array of steel particles, and their interaction with the adjacent bone microstructure model was studied. Two test modes were considered, one where the granular chain was placed in direct contact with the bone microstructure model, while in the second test mode, a face sheet was included between the chain and the bone model. For both test modes, we found that the characteristic features of the reflected solitary waves are sensitive to the effective compressive modulus of the bone microstructure models and follow similar trends than those obtained for a homogeneous, non-porous solid. It was also found that the use of the face sheet substantially reduces the sensitivity of the predictions to small changes in the bone topology, making it a robust and reliable method for non-destructive evaluation of the effective elastic modulus of cellular materials with small structural dimensions, as it is required for the site-specific evaluation of the mechanical properties of trabecular bone.

A model for developing job rotation schedules that eliminate sequential high workloads and minimize between-worker variability in cumulative daily workloads: Application to automotive assembly lines.

The aim of study is to suggest a job rotation schedule by developing a mathematical model in order to reduce cumulative workload from the successive use of the same body region. Workload assessment using rapid entire body assessment (REBA) was performed for the model in three automotive assembly lines of chassis, trim, and finishing to identify which body part exposed to relatively high workloads at workstations. The workloads were incorporated to the model to develop a job rotation schedule. The proposed schedules prevent the exposure to high workloads successively on the same body region and minimized between-worker variance in cumulative daily workload. Whereas some of workers were successively assigned to high workload workstation under no job rotation and serial job rotation. This model would help to reduce the potential for work-related musculoskeletal disorders (WMSDs) without additional cost for engineering work, although it may need more computational time and relative complex job rotation sequences.

Improved enantioselectivity of thermostable esterase from Archaeoglobus fulgidus toward (S)-ketoprofen ethyl ester by directed evolution and characterization of mutant esterases.

Thermostable esterases have potential applications in various biotechnology industries because of their resistance to high temperature and organic solvents. In a previous study, we isolated an esterase from Archaeoglobus fulgidus DSM 4304 (Est-AF), which showed high thermostability but low enantioselectivity toward (S)-ketoprofen ethyl ester. (R)-ketoprofenor (S)-ketoprofenis produced by esterase hydrolysis of the ester bond of (R,S)-ketoprofen ethyl ester and (S)-ketoprofen has better pharmaceutical activity and lower side effects than (R)-ketoprofen. Therefore, we have generated mutants of Est-AF that retained high thermostability whilst improving enantioselectivity. A library of Est-AF mutants was created by error-prone polymerase chain reaction, and mutants with improved enantioselectivity were isolated by site-saturation mutagenesis. The regions of Est-AF containing amino acid mutations were analyzed by homology modeling of its three-dimensional structure, and structure-based explanations for the changes in enantioselectivity are proposed. Finally, we isolated two mutants showing improved enantioselectivity over Est-AF (ee% = -16.2 ± 0.2 and E = 0.7 ± 0.0): V138G (ee% = 35.9 ± 1.0 and E = 3.0 ± 0.1) and V138G/L200R (ee% = 89.2 ± 0.2 and E = 19.5 ± 0.5). We also investigated various characteristics of these mutants and found that the mutants showed similar thermostability and resistance to additives or organic solvents to Est-AF, without a significant trade-off between activity and stability.

Posttraumatic stress disorder associated with orthopaedic trauma: a study in patients with extremity fractures.

OBJECTIVE: The aims of this prospective study were to determine the prevalence of posttraumatic stress disorder (PTSD) in a population of young male military conscripts who experienced an extremity long-bone fracture, and to evaluate whether injury-related variables are associated with the development of PTSD. DESIGN: Prospective, nonrandomized comparative study. SETTING: Level 1 trauma center. PATIENTS AND METHODS: A total of 148 men (age older than 18 years) who had 1 or more acute long-bone extremity fractures within 12 months and were seen at the Seoul Regional Military Manpower Center for examination of military conscripts from March 2013 to March 2014, were enrolled. The Korean version of the posttraumatic disorder scale was used to identify aspects of PTSD. The injury-related variables assessed included injury mechanism, fracture location and multiplicity, fracture severity, and the occurrence of joint ankylosis and secondary osteoarthritis. RESULTS: Of the 148 participants, 40 (27.0%) met the criteria for the diagnosis of PTSD. Multivariate logistic linear analysis confirmed that lower extremity fracture, multiple fractures, and a higher pain visual analog scale score were significantly (P = 0.042, P = 0.043 and P < 0.001, respectively) related to the occurrence of PTSD. CONCLUSIONS: Lower extremity fracture, multiple extremity fractures, and higher pain visual analog scale scores were significantly related to the occurrence of PTSD. To achieve an optimal recovery after orthopaedic injury, clinicians must address both physical and psychologic needs of their patients. LEVEL OF EVIDENCE: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Chronic low back pain in young korean urban males: the life-time prevalence and its impact on health related quality of life.

OBJECTIVE: We assessed the life-time prevalence (LTP) of chronic low back pain (LBP) in young Korean males. We also evaluated the relationship between lumbar spinal lesions and their health related quality-of-life (HRQOL). METHODS: A cross-sectional, self-reported survey was conducted in Korean males (aged 19-year-old) who underwent physical examinations for the conscript. We examined 3331 examinees in November 2014. We included 2411 subjects, who accepted to participate this study without any comorbidities. We interviewed using simple binary questions for their LBP experience and chronicity. HRQOL was assessed by Short-Form Health-Survey-36 (SF-36) in chronic LBP and healthy control groups. Radiological assessment was performed in chronic LBP group to determine whether there were any pathological causes of their symptoms. RESULTS: The LTP of chronic LBP was 13.4%. Most (71.7%) of them didn't have any lumbar spinal lesions (i.e., non-specific chronic LBP). The SF-36 subscale and summary scores were significantly lower in subjects with chronic LBP. Between specific and non-specific chronic LBP group, all physical and mental subscale scores were significantly lower in specific chronic LBP group, except mental health (MH) subscale score. In MH subscale and mental component summary score, statistical significant differences didn't appear between two groups (p=0.154, 0.126). CONCLUSION: In Korean males 19 years of age, the LTP of chronic LBP was 13.4%, and more than two-thirds were non-specific chronic LBP. Chronic LBP had a significant impact on HRQOL. The presence of lumbar spinal pathoanatomical lesions affected mainly on the physical aspect of HRQOL. It influenced little on the mental health.

Isolation of microorganisms able to produce 1,3-propanediol and optimization of medium constituents for Klebsiella pneumoniae AJ4.

Microbial fermentation under anaerobic and microaerobic conditions has been used for the production of 1,3-propanediol (1,3-PD), a monomer used to produce polymers such as polytrimethylene terephthalate. In this study, we screened microorganisms using the high throughput screening method and isolated the Klebsiella pneumoniae AJ4 strain, which is able to produce 1,3-PD under aerobic conditions. To obtain the maximum 1,3-PD concentration from glycerol, the response surface methodology based on a central composite design was chosen to show the statistical significance of the effects of glycerol, peptone, and (NH(4))(2)SO(4) on 1,3-PD production by K. pneumoniae AJ4. The optimal culture medium factors for achieving maximum concentrations of 1,3-PD included glycerol, 108.5 g/L; peptone, 2.72 g/L; and (NH(4))(2)SO(4), 4.38 g/L. Under this optimum condition, the maximum concentration of 1,3-PD, 54.76 g/L, was predicted. A concentration of about 52.59 g/L 1,3-PD was obtained using the optimized medium during 26-h batch fermentation, a finding that agreed well with the predicted value.

Optimization of culture medium for enhanced production of exopolysaccharide from Aureobasidium pullulans.

Polysaccharides produced by microorganisms are utilized for a variety of purposes, including the use in cosmetics and as food additives. More recently, polysaccharides have been exploited by the medical and pharmaceutical industries, and those originated from many species of mushrooms have been especially useful in industrial applications; however, the production and synthesis of these compounds is costly and time consuming. In this study, we developed a method for low-cost production of exopolysaccharide (EPS) that effectively screens components and optimizes medium composition using statistical methods (Plackett-Burman and Box-Behnken design). As a result, we obtained the following optimized medium: sucrose 165.73 g/L, sodium nitrate 3.08 g/L, dipotassium phosphate 1.00 g/L, potassium chloride 0.50 g/L, magnesium sulfate 0.50 g/L, ferrous sulfate 0.01 g/L, and 0.71 g/L of Ashbya gossypii extract. The maximum production of about 29 g/L EPS was achieved in the optimized medium during 84 h batch fermentation.

Structural and functional characterization of S-adenosylmethionine (SAM) synthetase from Pichia ciferrii.

S-adenosylmethionine synthetase (SAM-s) catalyzes the synthesis of S-adenosylmethionine (SAM), which is essential for methylation, transcription, proliferation, and production of secondary metabolites. Here SAM-s from Pichia ciferrii were selectively cloned using RNA CapFishing and rapid amplification of cDNA ends (RACE). The putative full-length cDNA of SAM-s encoded a 383 amino acid protein (42.6 kDa), which has highly conserved metal binding sites, a phosphate-binding site, and functionally important motifs. The corresponding enzyme was over-expressed in a heterologous host of Pichia pastoris, and then purified to a homogenous form. Enzyme kinetics, immunoblotting, circular dichroism (CD), high performance liquid chromatography (HPLC), and molecular modeling were conducted to characterize the SAM-s from P. ciferrii. Structural and functional studies of SAM-s will provide important insights for industrial applications.

Characterization of a novel oligomeric SGNH-arylesterase from Sinorhizobium meliloti 1021.

A novel oligomeric SGNH-arylesterase (Sm23) from Sinorhizobium meliloti 1021 was characterized using biochemical and biophysical methods. A sequence comparison of Sm23 with other SGNH members confirmed the presence of catalytic triad (Ser(10), Asp(187), and His(190)) and oxyanion holes (Ser(10)-Gly(50)-Asn(90)). The wild type enzyme was able to hydrolyze p-nitrophenyl acetate, alpha- and beta-naphthyl acetate, while S10A mutant completely lost its activity. Structural properties of Sm23 were investigated using circular dichroism (CD), fluorescence, dynamic light scattering (DLS), chemical cross-linking, electron microscopy (EM), and time of flight (TOF) mass spectrometry. Furthermore, spherical or globular aggregates were observed with 1-butyl-3-methylimidazolium tetrafluoroborate, while amorphous aggregates were formed with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Identification and characterization of a novel oligomeric decaprenyl diphosphate synthase.

A novel oligomeric decaprenyl pyrophosphate synthase was identified. Circular dichroism measurements indicated that it is alpha-helical, and stable against pH changes and denaturants. Three peptides corresponding to the conserved regions were synthesized and metal affinities were investigated. Crystallographic analyses of this oligomeric DDS are currently in progress.

Purification, crystallization and preliminary crystallographic analysis of Est-Y29: a novel oligomeric beta-lactamase.

beta-Lactam antibiotics such as penicillins and cephalosporins have a four-atom ring as a common element in their structure. The beta-lactamases, which catalyze the inactivation of these antibiotics, are of great interest because of their high incidence in pathogenic bacteria. A novel oligomeric class C beta-lactamase (Est-Y29) from a metagenomic library was expressed, purified and crystallized. The recombinant protein was expressed in Escherichia coli with an N-terminal 6xHis tag and purified to homogeneity. EstY-29 was crystallized and X-ray intensity data were collected to 1.49 A resolution using synchrotron radiation.

Identification and characterization of a novel (S)-ketoprofen-specific esterase.

A new (S)-ketoprofen specific esterase (EST-Y29) was identified from a metagenome library from environmental samples, which showed homologies with class C-beta lactamase, penicillin binding protein, and other lipases/esterases. In order to investigate the biochemical and biophysical properties, the recombinant protein was overexpressed, purified to homogeneity, and characterized. This EST-Y29 has high catalytic activity against p-nitrophenyl esters of short fatty acids (C(2) and C(4)) and alpha-naphthyl acetate with activation energy of 30.4 kJ/mol. We have further characterized EST-Y29 using high performance liquid chromatography (HPLC), circular dichroism (CD), dynamic light scattering (DLS) and size exclusion chromatography (SEC).