Gre factors prevent thermal and mechanical stresses induced by terahertz irradiation during transcription.

During transcription in cells, the transcription complex consisting of RNA polymerase, DNA and nascent RNA is exposed to fluctuating temperature and pressure. However, little is known about the mechanism of transcriptional homeostasis under fluctuating physical parameters. In this study, we generated these fluctuating parameters using pulsed local heating and acoustic waves in the reaction system of transcription by Escherichia coli RNA polymerase, using a terahertz free-electron laser. We demonstrated that transcription processes, including abortive initiation and elongation pausing, and the fidelity of elongation are significantly affected by the laser-based local perturbations. We also found that all these functional alternations in the transcription process are almost completely mitigated by the presence of Gre proteins. It is well known that Gre proteins enhance RNA cleavage of polymerase by binding to the pore structure termed secondary channel. Recently, the chaperone activities have also been proposed for Gre proteins, yet the details directly associated with transcription are largely unknown. Our finding indicates that Gre proteins are necessary for maintaining transcriptional homeostasis under thermal and mechanical stresses.

Technical Proposal for Monitoring Thermal and Mechanical Stresses of a Runway Pavement.

Airport pavements should ensure regular and safe movements during their service life; the management body has to monitor the functional and structural characteristics, and schedule maintenance work, balancing the often conflicting goals of safety, economic and technical issues. This paper presents a remote monitoring system to evaluate the structural performance of a runway composed of concrete thresholds and a flexible central runway. Thermometers, strain gauges, and pressure cells will be embedded at different depths to continuously monitor the pavement's response to traffic and environmental loads. An innovative system allows data acquisition and processing with specific calculation models, in order to inform the infrastructure manager, in real time, about the actual conditions of the pavement. In this way, the authors aim to develop a system that provides useful information for the correct implementation of an airport pavement management system (APMS) based on real-life data. Indeed, it permits comprehensive monitoring functions to be performed, based on the embedded sensing network.

Functional principles of baobab fruit pedicels - anatomy and biomechanics.

BACKGROUND AND AIMS: Fruit pedicels have to deal with increasing loads after pollination due to continuous growth of the fruits. Thus, they represent interesting tissues from a mechanical as well as a developmental point of view. However, only a few studies exist on fruit pedicels. In this study, we unravel the anatomy and structural-mechanical relationships of the pedicel of Adansonia digitata, reaching up to 90 cm in length. METHODS: Morphological and anatomical analyses included examination of stained cross-sections from various positions along the stalk as well as X-ray microtomography and scanning electron microscopy. For mechanical testing, fibre bundles derived from the mature pedicels were examined via tension tests. For establishing the structural-mechanical relationships, the density of the fibre bundles as well as their cellulose microfibril distribution and chemical composition were analysed. KEY RESULTS: While in the peduncle the vascular tissue and the fibres are arranged in a concentric ring-like way, this organization shifts to the polystelic structure of separate fibre bundles in the pedicel. The polystelic pedicel possesses five vascular strands that consist of strong bast fibre bundles. The fibre bundles have a Young's modulus of up to 5 GPa, a tensile strength of up to 400 MPa, a high density (>1 g cm-3) and a high microfibril angle of around 20°. CONCLUSIONS: The structural arrangement as well as the combination of high density and high microfibril angle of the bast fibre bundles are probably optimized for bearing considerable strain in torsion and bending while at the same time allowing for carrying high-tension loads.

The influence of slope on Spartium junceum root system: morphological, anatomical and biomechanical adaptation.

Root systems have a pivotal role in plant anchorage and their mechanical interactions with the soil may contribute to soil reinforcement and stabilization of slide-prone slopes. In order to understand the responses of root system to mechanical stress induced by slope, samples of Spartium junceum L., growing in slope and in plane natural conditions, were compared in their morphology, biomechanical properties and anatomical features. Soils sampled in slope and plane revealed similar characteristics, with the exception of organic matter content and penetrometer resistance, both higher in slope. Slope significantly influenced root morphology and in particular the distribution of lateral roots along the soil depth. Indeed, first-order lateral roots of plants growing on slope condition showed an asymmetric distribution between up- and down-slope. Contrarily, this asymmetric distribution was not observed in plants growing in plane. The tensile strength was higher in lateral roots growing up-slope and in plane conditions than in those growing down-slope. Anatomical investigations revealed that, while roots grown up-slope had higher area covered by xylem fibers, the ratio of xylem and phloem fibers to root diameter did not differ among the three conditions, as also, no differences were found for xylem fiber cell wall thickness. Roots growing up-slope were the main contributors to anchorage properties, which included higher strength and higher number of fibers in the xylematic tissues. Results suggested that a combination of root-specific morphological, anatomical and biomechanical traits, determines anchorage functions in slope conditions.

Characterization of pulmonary cysts in Birt-Hogg-Dubé syndrome: histopathological and morphometric analysis of 229 pulmonary cysts from 50 unrelated patients.

AIMS: To characterize the pathological features of pulmonary cysts, and to elucidate the possible mechanism of cyst formation in the lungs of patients with Birt-Hogg-Dubé syndrome (BHDS), a tumour suppressor gene syndrome, using histological and morphometric analyses. METHODS AND RESULTS: We evaluated 229 lung cysts from 50 patients with BHDS and 117 from 34 patients with primary spontaneous pneumothorax (PSP) for their number, size, location and absence or presence of inflammation. The BHDS cysts abutted on interlobular septa (88.2%) and had intracystic septa (13.6%) or protruding venules (39.5%) without cell proliferation or inflammation. The frequencies of these histological characteristics differed significantly from those seen in the lungs of patients with PSP (P < 0.05). Although the intrapulmonary BHDS cysts were smaller than the subpleural BHDS cysts (P < 0.001), there was no difference in size between them when there was no inflammation. The number of cysts diminished logarithmically and the proportion of cysts with inflammation increased as their individual sizes became greater (P < 0.05). CONCLUSIONS: These results imply that the BHDS cysts are likely to develop in the periacinar region, an anatomically weak site in a primary lobule, where alveoli attach to connective tissue septa. We hypothesize that the BHDS cysts possibly expand in size as the alveolar walls disappear at the alveolar-septal junction, and grow even larger when several cysts fuse.

SEM Analysis and Micro-CT Evaluation of Four Dental Implants after Three Different Mechanical Requests-In Vitro Study.

STATEMENT OF PROBLEM: Implant-supported rehabilitations are an increasingly frequent practice to replace lost teeth. Before clinical application, all implant components should demonstrate suitable durability in laboratory studies, through fatigue tests. OBJECTIVE: The purpose of this in vitro study was to evaluate the integrity and wear of implant components using SEM, and to assess the axial displacement of the implant-abutment assembly by Micro-CT, in different implant connections, after three distinct mechanical requests. MATERIALS AND METHODS: Four KLOCKNER implants (external connection SK2 and KL; and internal connection VEGA and ESSENTIAL) were submitted to three different mechanical requests: single tightening, multiple tightening, and multiple tightening and cyclic loading (500 N × 100 cycles). A total of 16 samples were evaluated by SEM, by the X-ray Bragg-Brentano method to obtain residual stresses, and scratch tests were realized for each surface and Micro-CT (4 control samples; 4 single tightening; 4 multiple tightening; 4 multiple tightening and cyclic loading). All dental implants were fabricated with commercially pure titanium (grade 3 titanium). Surface topography and axial displacement of abutment into the implant, from each group, were evaluated by SEM and Micro-CT. RESULTS: In the manufacturing state, implants and abutments revealed minor structural changes and minimal damage from the machining process. The application of the tightening torque and loading was decisive in the appearance and increase in contact marks on the faces of the hexagon of the abutment and the implant. Vega has the maximum compressive residual stress and, as a consequence, higher scratch force. The abutment-implant distances in SK2 and KL samples did not show statistically significant differences, for any of the mechanical demands analyzed. In contrast, statistically significant differences were observed in abutment-implant distance in the internal connection implants Vega and Essential. CONCLUSIONS: The application of mechanical compression loads caused deformation and contact marks in all models tested. Only internal connection implants revealed an axial displacement of the abutment into the implant, but at a general level, a clear intrusion of the abutment into the implant could only be confirmed in the Essential model, which obtained its maximal axial displacement with cyclic loading.

Mechanical impact of epiretinal membranes on the retina utilizing finite element analysis.

BACKGROUND AND OBJECTIVE: Epiretinal membrane (ERM) is a transparent membrane that forms on the surface of the neurosensory retina, causing tangential traction on the retinal surface, which may contribute to cell proliferation and contraction. Epiretinal membranes (ERMs) may be asymptomatic in some patients, while in others the membranes can progress, resulting in macular thickening and macular traction, thus distorting and inducing loss of central visual function and metamorphopsia. Currently, treatment options include follow-up or pars plana vitrectomy with an ERM peel, aiming to relieve the macular traction and improve vision and metamorphopsia. No specific criteria exist for predicting which patients might progress and need early surgery to improve and maintain good vision. The decision for surgery is based on the individual's symptoms and the physician's judgment. This study aimed to evaluate the mechanical impact in terms of stress and deformations of the ERM and to qualitatively compare them with the clinical progression of fovea thickening observed through optical coherence tomography (OCT) images. METHODS: Numerical simulation on a three-dimensional geometrical retina and ERM model was applied to isolate factors that can be used to predict its progression and prognosis. OCT images of 14 patients with ERM were used to derive the fovea thickness progression before and after vitrectomy surgery with ERM peeling. RESULTS: The results clearly show that the increase in ERM contractility level increases the developed stress at the fovea, which spreads and advances toward its base. The highest stress level (2.1 kPa) was developed at the highest and asymmetric contractility, producing non-uniform distributed deformations that distort the fovea structure. CONCLUSIONS: These findings imply that high and asymmetric ERM contractility should be evaluated clinically as a factor that might signal the need for early vitrectomy surgery to avoid irreversible visual loss. Moreover, the OCT images revealed that in some cases, the thickness of the fovea indeed remains high, even after ∼12 months postoperatively, which also indicates that the deformation of the fovea in these cases is irreversible.

Impact of baculoviral transduction of fluorescent actin on cellular forces.

Live staining of actin brings valuable information in the field of mechanobiology. Gene transfer of GFP-actin has been reported to disturb cell rheological properties while gene transfer of fluorescent actin binding proteins was not. However the influence of gene transfer on cellular forces in adhered cells has never been investigated. This would provide a more complete picture of mechanical disorders induced by actin live staining for mechanobiology studies. Indeed, most of these techniques were shown to alter cell morphology. Change in cell morphology may in itself be sufficient to perturb cellular forces. Here we focus on quantifying the alterations of cellular stresses that result from baculoviral transduction of GFP-actin in MDCK cell line. We report that GFP-actin transduction increases the proportion of cells with large intracellular or surface stresses, especially in epithelia with low cell density. We show that the enhancement of the mechanical stresses is accompanied by small perturbations of cell shape, but not by a significant change in cell size. We thus conclude that this live staining method enhances the cellular forces but only brings subtle shape alterations.

Reverse Torque Value of Angulated Screw Channel Abutment before and after Cyclic Loading: An In Vitro Study.

This in vitro experiment aimed to understand the difference in preload acting on an abutment screw under different angles of angulated screw-retained crown and the performance after cyclic loading. In total, thirty implants with angulated screw channel (ASC) abutments were divided into two parts. The first part consisted of three groups: a 0° access channel with a zirconia crown (ASC-0) (n = 5), a 15° access channel with a specially designed zirconia crown (sASC-15) (n = 5), and a 25° access channel with a specially designed zirconia crown (sASC-25) (n = 5). The reverse torque value (RTV) was measured at 0° for each specimen. The second part consisted of three groups: a 0° access channel with a zirconia crown (ASC-0) (n = 5); a 15° access channel with a zirconia crown (ASC-15) (n = 5), and a 25° access channel with a zirconia crown (ASC-25) (n = 5). The manufacturer's recommended torque was applied to each specimen, and baseline RTV was measured before cyclic loading. Each ASC implant assembly was cyclically loaded at 0 to 40 N with 1 million cycles at 10 Hz. RTV was measured after cyclic loading. Kruskal-Wallis test and Jonckheere-Terpstra test were used for statistical analysis. All specimens were examined under a digital microscope and scanning electron microscope (SEM) to observe the wear of the screw head before and after the whole experiment. A significant difference in the different percentages of straight RTV (sRTV) between the three groups was found (p = 0.027). The angle of ASC to the different percentages of sRTV showed a significant linear trend (p = 0.003). No significant differences were found in RTV difference after cyclic loading among the ASC-0, ASC-15, and ASC-25 groups (p = 0.212). The ASC-25 group had the most serious degree of wear based on a digital microscope and SEM examination. The ASC angle will affect the actual preload acting on a screw: the larger the ASC angle, the smaller the preload. The performance of the angled ASC groups in RTV difference was comparable to that of 0° ASC after cyclic loading.

ß2-Adrenergic receptor expression in subchondral bone of patients with varus knee osteoarthritis.

An important causative factor in osteoarthritis (OA) is the abnormal mechanical stress-induced bone remodeling of the subchondral bone. ß2-adrenergic receptor (Adrb2) plays a major role in mechanical stresses that induce bone remodeling. The medial tibial plateau (MTP) and lateral tibial plateau (LTP) of patients with varus Knee osteoarthritis (KO) bear different mechanical stresses. The present study aimed to investigate the expression of Adrb2 in medial tibial plateau subchondral bone (MTPSB) and lateral tibial plateau subchondral bone (LTPSB) in patients with varus KO. A total of 30 tibial plateau samples from patients undergoing total knee arthroplasty for varus KO and MTPSB and LTPSB were studied. Statistical analysis was performed using paired sample t-tests. Safranin O-Fast Green staining and Micro-computed tomography showed significant differences in the bone structure between MTPSB and LTPSB. Tartrate-resistant acid phosphatase (TRAP)-positive cell density in MTPSB was higher than that in LTPSB. Immunohistochemistry, reverse transcription-quantitative polymerase chain reaction, and Western blot analysis revealed that compared to LTPSB, the levels of Adrb2, tyrosine hydroxylase (TH), and osteocalcin increased significantly in MTPSB. Double-labeling immunofluorescence showed Adrb2 was present in the majority of TRAP-positive multinuclear cells of the MTPSB. The expression of Adrb2 and TH was significantly higher in MTPSB than in LTPSB, confirming the involvement of these molecules in the development of OA.

Axial and para-axial loading response evaluation on human cadaver-harvested lumbar vertebral blocks: In vitro experiment with possible clinical implications for clinical practice.

The aim of the present study conducted on the lumbar spine was to confirm that the pronounced decrease in resistance in the system is a phenomenon that can be eminently affected by the adaptive changes that occur at the level of the intervertebral disc at axial mechanical stresses. The biomechanical trial was carried out on 11 lumbar segments L1-L5, gathered from adult human cadavers. The dissection considered the complete keeping of all bone, disc, articulated and ligamentous components in their anatomical position. All 11 samples were frozen 24 h prior to the performance of the biomechanical measurement. The specimens were placed in the testing device, their placement being conditioned by the estimated dimensional values. Thus, to calculate the load and axial resistance, the models were placed vertically, central between the test machine ferries. The testing was carried out by applying variable forces and displacement supervision. The displacement interval was represented by a segment of 0-10 mm with surveillance every 2 mm. Mobility in the sagittal plane (flexion earlier in our case) was much higher than that in the frontal plane, obviously limiting mobility via the intervertebral disc and articular complex through the presence of arches. Statistical analysis demonstrated the lack of any correlation values between the two types of movements (R2=0.005507), underlining the absence of any prediction elements. A noteworthy aspect is that the correlations appeared low, statistically insignificant, even within the same movement in the sagittal plane between the two levels, L1-L3 and L3-L5 (R2=0.610427), which may lead to the possibility of the emergence of significant differences in mobility between respective levels. The behavior type of the monitored specimens and the results obtained allowed the mapping of objective parallelism between the values obtained and the behavior in vivo of the lumbar vertebral segment.

Effect of artificial saliva on the mechanical properties of a polymer material reinforced with fiber, used in esthetic tooth restorations.

BACKGROUND: The oral environment can negatively affect the physical properties of fiber-reinforced composite (FRC) materials, which can lead to the deterioration of mechanical stability and reduce the span of their clinical usefulness. OBJECTIVES: The aim of this study was to determine the influence of artificial saliva on the selected mechanical properties of FRC. MATERIAL AND METHODS: The core of the polymer material selected for the study was a bundle of ultrahighmolecular-weight polyethylene (UHMWPE) fibers. Fourteen samples were stored in an incubator at 37°C, in 20 mL of artificial saliva solution, and weighed on days 1 and 28. At the same time, mechanical tests were performed, including the measurements of Young's modulus, tensile stress, maximum tensile force, and tensile deformation. RESULTS: The analysis of basic statistics together with the results of the Shapiro-Wilk test and the distribution of Spearman's rho coefficient showed a strong negative relationship between the pair of variables - tensile deformation and the sorption of synthetic saliva. The results related to Young's modulus of elasticity and tensile stress were not statistically significant. CONCLUSIONS: Water penetration into the space between the fibers does not adversely affect the mechanical properties of the material tested. In the static tensile test, high and desired mechanical strength was observed, which may justify the effective use of this type of material in clinical practice and may be a good alternative to prosthetic restorations, whose retention is obtained only through a mechanical connection with the abutment tooth.

Compression and tension variably alter Osteoprotegerin expression via miR-3198 in periodontal ligament cells.

BACKGROUND: Osteoclasts play a critical role in bone resorption due to orthodontic tooth movement (OTM). In OTM, a force is exerted on the tooth, creating compression of the periodontal ligament (PDL) on one side of the tooth, and tension on the other side. In response to these mechanical stresses, the balance of receptor activator of nuclear-factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) shifts to stimulate osteoclastogenesis. However, the mechanism of OPG expression in PDL cells under different mechanical stresses remains unclear. We hypothesized that compression and tension induce different microRNA (miRNA) expression profiles, which account for the difference in OPG expression in PDL cells. To study miRNA expression profiles resulting from OTM, compression force (2 g/cm2) or tension force (15% elongation) was applied to immortalized human PDL (HPL) cells for 24 h, and miRNA extracted. The miRNA expression in each sample was analyzed using a human miRNA microarray, and the changes of miRNA expression were confirmed by real-time RT-PCR. In addition, miR-3198 mimic and inhibitor were transfected into HPL cells, and OPG expression and production assessed. RESULTS: We found that certain miRNAs were expressed differentially under compression and tension. For instance, we observed that miR-572, - 663, - 575, - 3679-5p, UL70-3p, and - 3198 were upregulated only by compression. Real-time RT-PCR confirmed that compression induced miR-3198 expression, but tension reduced it, in HPL cells. Consistent with previous reports, OPG expression was reduced by compression and induced by tension, though RANKL was induced by both compression and tension. OPG expression was upregulated by miR-3198 inhibitor, and was reduced by miR-3198 mimic, in HPL cells. We observed that miR-3198 inhibitor rescued the compression-mediated downregulation of OPG. On the other hand, miR-3198 mimic reduced OPG expression under tension. However, RANKL expression was not affected by miR-3198 inhibitor or mimic. CONCLUSIONS: We conclude that miR-3198 is upregulated by compression and is downregulated by tension, suggesting that miR-3198 downregulates OPG expression in response to mechanical stress.

Morphomechanical rules of embryonic development.

We start by comparing two explicatory approaches, which we call law-centered and "instructivistic". Although the latter dominates in modern biology, we find it inappropriate for treating developmental problems, especially those related to morphogenesis. As an example of a law-centered approach we suggest a simple morphomechanical rule based upon the idea of the hyper-restoration of mechanical stresses. We show that this rule not only provides a general framework for morphogenesis, but can also reproduce, via parametric modulations, quite specific developmental events.

Comminution of Dry Lignocellulosic Biomass, a Review: Part I. From Fundamental Mechanisms to Milling Behaviour.

The comminution of lignocellulosic biomass is a key operation for many applications as bio-based materials, bio-energy or green chemistry. The grinder used can have a significant impact on the properties of the ground powders, of those of the end-products and on the energy consumption. Since several years, the milling of lignocellulosic biomass has been the subject of numerous studies most often focused on specific materials and/or applications but there is still a lack of generic knowledge about the relation between the histological structure of the raw materials, the milling technologies and the physical and chemical properties of the powders. This review aims to point out the main process parameters and plant raw material properties that influence the milling operation and their consequences on the properties of ground powders and on the energy consumption during the comminution.

Stress-generating tissue deformations in Xenopus embryos: Long-range gradients and local cell displacements.

BACKGROUND: Although the role of endogenous mechanical stresses in regulating morphogenetic movements and cell differentiation is now well established, many aspects of mechanical stress generation and transmission in developing embryos remain unclear and require quantitative studies. RESULTS: By measuring stress-bearing linear deformations (caused by differences in cell movement rates) in the outer cell layer of blastula - early tail-bud Xenopus embryos, we revealed a set of long-term tension-generating gradients of cell movement rates, modulated by short-term cell-cell displacements much increasing the rates of local deformations. Experimental relaxation of tensions distorted the gradients but preserved and even enhanced local cell-cell displacements. During development, an incoherent mode of cell behavior, characterized by extensive cell-cell displacements and poorly correlated cell trajectories, was exchanged for a more coherent regime with the opposite characteristics. In particular, cell shifts became more synchronous and acquired a periodicity of several dozen minutes. CONCLUSIONS: Morphogenetic movements in Xenopus embryos are mediated by mechanically stressed dynamic structures of two different levels: extended gradients and short-term cell-cell displacements. As development proceeds, the latter component decreases and cell trajectories become more correlated. In particular, they acquire common periodicities, making morphogenesis more coherent.

Feeling Stress: The Mechanics of Cancer Progression and Aggression.

The tumor microenvironment is a dynamic landscape in which the physical and mechanical properties evolve dramatically throughout cancer progression. These changes are driven by enhanced tumor cell contractility and expansion of the growing tumor mass, as well as through alterations to the material properties of the surrounding extracellular matrix (ECM). Consequently, tumor cells are exposed to a number of different mechanical inputs including cell-cell and cell-ECM tension, compression stress, interstitial fluid pressure and shear stress. Oncogenes engage signaling pathways that are activated in response to mechanical stress, thereby reworking the cell's intrinsic response to exogenous mechanical stimuli, enhancing intracellular tension via elevated actomyosin contraction, and influencing ECM stiffness and tissue morphology. In addition to altering their intracellular tension and remodeling the microenvironment, cells actively respond to these mechanical perturbations phenotypically through modification of gene expression. Herein, we present a description of the physical changes that promote tumor progression and aggression, discuss their interrelationship and highlight emerging therapeutic strategies to alleviate the mechanical stresses driving cancer to malignancy.

Effect of Mechanical Stresses in Rapidly Heated Fe73Cu1Nb3Si16B7 Ribbon Arising During the Ring Core Formation on Their Magnetic Properties.

The influence of winding-induced mechanical stresses on the magnetic anisotropy and core loss in toroidal cores made of Fe73Cu1Nb3Si16B7 ribbon is studied. The ribbon for the cores was rapidly pre-heated under tensile stress up to 120 MPa. It was found that magnetic characteristics of the material (magnetic anisotropy energy and the core loss) can be controlled by varying the tensile stress during the preliminary rapid heating of the ribbon. It was shown that with reducing core diameter, the magnetic anisotropy energy and core loss significantly increase. However, relatively high winding-induced core loss in small cores can be significantly reduced by increasing tensile stresses applied to the ribbon during pre-heating.