Application Of Compressive Force Research Articles

Effects of nano-micelles curcumin-based photodynamic therapy on expression of RUNX2 as an indicator of bone regeneration in orthodontic tooth movement

ObjectivesThe aim was to evaluate the impact of nano-micelles curcumin (NMCur) based photodynamic therapy (PDT) during compressive force application on human PDL-derived fibroblasts (HPDFs) in vitro for up to 6 days on the expression of RUNX2 as an indicator of bone development and remodeling. Materials and methodsHPDFs viability during 2 g/cm2 compressive force application was investigated using membrane-impermeable DNA-binding stain propidium iodide (PI) in flow cytometry. Gene and protein expressions of RUNX2 were assessed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and flow cytometry, respectively, following NMCur-PDT at different concentrations of NMCur (25, 50, and 75 µM plus irradiation of 180 mW/cm2 diode laser at the wavelength of 450 ± 10 nm for 5 min) during the static compressive force of 2 g/cm2 on HPDFs via weight approach-based in-vitro loading model up to 6 days. One-way ANOVA and Tukey post hoc tests at a p-value equal to/or less than 0.05 were used to analyze the obtained data. ResultsAfter 6 days of application of compressive force, 99.21 ± 6.12% of HPDFs were PI negative and therefore considered alive, while only 0.89 ± 0.06% of the population were PI positive and considered dead. In comparison with controls (loaded HPDFs), expression of RUNX2 gene was dose-dependent and the highest expression (14.38-fold; P < 0.01) was observed at a concentration of 75 µM NMCur following 5 min of diode laser irradiation (i.e., 75 µM NMCur-PDT) during compressive force application on day 5. The greatest and lowest upregulations of RUNX2 protein were observed in 75 µM NMCur-PDT during compressive force application on HPDFs, on day 5 (3.19-fold; P < 0.01) and day 6 (2.09-fold; P < 0.05), respectively. ConclusionNMCur-PDT during weight approach-based in-vitro loading model can promote orthodontic tooth movement by upregulating RUNX2 signaling pathway in HPDFs.

Pre-applied underfill Technique for Fine-pitch Cu Pillar 3D Die Stacking to Enable 2.5/3D Advanced Packaging

Increased performance and smaller form factor have driven demand for next generation architectures for integrated circuit 3D (IC) chip packaging. Advanced chip packaging technologies, such as 2.5D and 3D, offer greater chip compatibility and lower power consumption. Given these advantages, the adoption of advanced packaging is inevitable. One key driver is the copper pillar interconnect technology which offers several benefits such as improved electromigration resistance, improved electrical and thermal conductivity, simplified under bump metallization (UBM), and higher input/output (I/O) density. The fine pitches that copper pillars are capable of helps the technology to supersede solder bump technology, which reaches its lowest pitch around 40 microns. Finer pitches allow for a higher I/O count, which enhances performance. One of the major innovations has been 2.5/3D integration, a technique of vertically stacking multiple dies. However, traditional encapsulation techniques become challenging because traditional capillary underfill methods become restrictive as enlarged surface area is required in order to provide underfill protection on multiple surfaces. Here, we discuss a novel approach of vertically stacking dies with an integrated underfill process that minimizes the required area for underfilling in fine-pitch IC chip packages by creating a technique to apply underfill during thermo-compression bonding. This process offers a reliable method for vertical stacking of multiple chips and eliminates post-processing need for underfill application. Additionally, the process provides precise temperature control to both the substrate and die by using a mechanism of dual heat application. This is used in combination with a controlled variable application of compressive force on the package. Through fine-tuning of the force and temperature applied to the IC components, the bonding process can be tailored to simultaneously provide the ideal underfill curing conditions while forming solder joints. In this work, we used dies with 80µm pitch Cu pillar flip chip copper pillars with tin/silver caps bonded to Electroless Nickel and Immersion Gold (ENIG) pads in conjunction with commercially available pre-applied underfill material. The interconnect strength was determined though destructive shear testing and cross-sectional analysis to evaluate for the bonding quality and strength. A scanning electron microscope was used to visually examine joint properties, and X-ray analysis was conducted to review for underfill voiding. Finally, completed assemblies were thermal-cycled to evaluate for the degradation of joint strength and voiding of underfill under induced stress.

Nanoscale chemical and structural investigation of solid solution polyelemental transition metal oxide nanoparticles

Although it has been shown that configurational entropy can improve the structural stability in transition metal oxides (TMOs), little is known about the oxidation state of transition metals under random mixing of alloys. Such information is essential in understanding the chemical reactivity and properties of TMOs stabilized by configurational entropy. Herein, utilizing electron energy loss spectroscopy (EELS) technique in an aberration-corrected scanning transmission electron microscope (STEM), we systematically studied the oxidation state of binary (Mn,Fe)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 solid solution polyelemental transition metal oxides (SSP-TMOs) nanoparticles. Our findings show that the random mixing of multiple elements in the form of solid solution phase not only promotes the entropy stabilization but also results in stable oxidation state in transition metals spanning from binary to quinary transition metal oxide nanoparticles.

Optimal Design of Hydraulic Disc Brake for Magnetorheological (MR) Application

This paper aims to provide a new design considering compressive force application in the MR fluid andimprove its braking torque by optimizing it. According to the current study, compressing the MR region will increase braking torque compared to no compression. The area covered by an existing model of the conventional disc brake is taken into consideration for the unique design of the MR brake to operate in shear and compression mode, and the required compression given by the hydraulic pressure similar to a conventional disc brake. The suggested MR brake’s structural layout is presented. The Herschel-Bulkley shear thinning model’s mathematical expression for the torque equation for the compression and shear modes is provided. An analytical magnetic circuit is done for the proposed design for determining the relationship between applied current and magnetic field strength as a function of the geometrical and material attributes of the MR brake. Simulation is done on COMSOL software with the help of an AC/DC module, considering the non-linear relationship between the magnetic field and magnetic flux. Simulation results of braking torque achieved with the varying current are determined. The graph displays the braking torque for current in the compression plus shear mode as well as shear mode. After that, optimization is done on the proposed model for optimal design parameters. For optimization, we adopt the most popular Genetic Algorithm (GA) method. Optimization aims to increase the braking torque capacity of the MR brake for the given volume.

Design and development of lever operated maize cob sheller for marginal and small farmers

In the present study, a low cost lever operated maize cob sheller was designed, developed and evaluated for its performance and techno-economic feasibility in comparison to two existing maize shelling methods (tubular maize shelling and beating method). It consists of different components viz. frame, handle, handle support, depressor and push rod assembly, shelling unit. The main working principle of developed prototype is based on the application of compressive force on the maize cob along its length. The maize cobs are fed manually to the shelling unit between the depressor plate and the top end of shelling unit. By pressing the lever, the depressor and push rod comes down vertically and due to the downward stroke, a compressive force applies on the maize cob and grains are detached from the cob. The developed prototype was evaluated under two levels of cob moisture content (16–20% and 12–16%) and three levels of cob diameter size (< 30 mm, 30–40 mm, and > 40 mm). The effect of different performance parameters like labour requirement, energy requirement and cost of shelling were discussed. Both moisture content and cob size significantly affected labour requirement and energy requirement. The labour requirement and energy involved for maize shelling increased directly with increase in cob moisture content and decrease in cob size. The mean shelling capacity for developed prototype (30.50 kg/h) was 2.92 and 1.73 times higher than tubular maize sheller (10.43 kg/h) and beating method (17.56 kg/h), respectively. The average grain damage was 5.33% for the developed prototype which was slightly higher (1.28%) than tubular maize sheller (4.05). The shelling efficiency for the developed prototype was observed 1.46% and 18.37% higher than tubular maize sheller and beating method, respectively. The cost of operation of lever operated maize shelling was Rs1398/t which were about two times less than beating method and three times less than tubular maize shelling. So, the lever operated maize cob sheller is very useful and innovative shelling equipment for marginal and small farmers of the hilly regions.

Association between intra-operative hemodynamic changes and corrective procedures during posterior spinal fusion in adolescent patients with scoliosis: A case-control study.

Previous reports indicated that a decrease in intra-operative cardiac output and mean arterial pressure occurs due to thoracic cage deformities when patients with scoliosis are placed in the prone position. The aims of this study were to investigate the occurrence of hypotension during posterior spinal fusion in adolescent patients with scoliosis, and the association between hypotension, surgical procedures, changes of thoracic cage morphology.This retrospective, single-center, case-control study included 106 patients who underwent surgeries for spinal deformity at our institute between June 2014 and March 2020. The inclusion criteria were: age ≤19 years at the time of surgery, lowest instrumented vertebra over L5, posterior spinal fusion as the first surgery for scoliosis, and no severe cardiac or pulmonary disease pre-operatively. Finally, 49 patients met the criteria, and were divided to 3 groups as follows: thoracic constructive curve using a 6.0-mm cobalt-chromium alloy circular rod (T-C group; n = 28); thoracolumbar/lumbar constructive curve using a 6.0-mm cobalt-chromium alloy circular rod (L-C group; n = 8); and thoracic constructive curve using a 5.5-mm cobalt-chromium alloy beam-like rod (T-B group; n = 13). The beam-like rod is characteristic as the rod is mounted to screw heads without cantilever force. Intra-operative changes in circulation associated with corrective procedures, perioperative data, and sagittal depth and sternum deviation of thoracic cage were compared between the 3 groups.The T-C group had a higher rate of hypotension alarm than did the other groups (7 vs 0 vs 0; P = .047). Corrective procedures included rodding 4 times, rod rotation maneuver once, and direct vertebral rotation twice. Blood pressure was increased by pausing the correction procedures, increasing infusion, and administering vasopressors. The T-C and T-B groups had greater sternum deviation parameters than the L-C group, both before and after surgery. All parameters associated with sagittal depth and sternum deviation decreased significantly after surgery in the T-C and the T-B groups.In corrective surgery for constructive thoracic scoliosis, the corrective procedures requiring the application of compression force in the forward direction should be closely monitored in view of their possible influence on circulatory conditions.

Compressive force regulates cementoblast migration via downregulation of autophagy.

Migration of cementoblasts to resorption lacunae is the foundation for repairing root resorption during orthodontic tooth movement. Previous studies reported that autophagy was activated by compression in periodontal ligament cells. The aim of this study was to investigate the migration of cementoblasts and determine whether autophagy is involved in the regulation of cementoblast migration under compressive force. Flow cytometry was employed to examine the apoptosis of murine cementoblasts (OCCM-30) at different compression times (0, 6, 12, and 24 hours) and magnitudes (0, 1.0, 1.5, and 2.0g/cm2 ). Cell proliferation was examined using the CCK-8 method. Wound healing migration assays and transwell migration assays were performed to compare the migration of cementoblasts. Chloroquine (CQ) and rapamycin were used to inhibit and activate autophagy, respectively. The level of autophagy was determined using western blotting and immunofluorescence staining. The expression of matrix metalloproteinases (MMPs) was assessed using quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot analysis, and enzyme-linked immunosorbent assay (ELISA). Cell apoptosis and proliferation did not significantly change in OCCM-30 cells under mechanical compression at magnitude of 1.5g/cm2 for 12 hours. However, the migration of cementoblasts was significantly inhibited after the application of compressive force. MMP2, MMP9, and MMP13 mRNA expression was decreased, and MMP9 and MMP13 protein expression and secretion level were also decreased. Further, autophagic activity was inhibited in cementoblasts under compressive force. Treatment with chloroquine reduced the cellular migration, and rapamycin partially relieved the inhibition of cementoblast migration induced by the compressive force. MMP9 and MMP13 mRNA expression, protein expression, and secretion levels showed a similar trend. Migration of OCCM-30 cells was inhibited under compressive force partially dependent on the inhibition of MMPs, which was mediated by downregulation of autophagy. The findings provide new insights into the role of autophagy in biological behaviors of cementoblasts under compressive force and a potential therapeutic strategy for reducing external root resorption.

Carbon scaffold with controllable small pore structure based on mask projection stereolithography

Mask Projection Stereolithography (MPSL), due to its high printing resolution, is suitable for fabricating porous polymer architectures that are used as carbon scaffold precursors. In the present work, a carbon scaffold with a controllable small porous structure was fabricated by MPSL. A polymer lattice structure used as the carbon scaffold precursor was first fabricated by MPSL. Sodium chloride was selected as the granular support, and nano-silica particles were introduced into the granular support so that sodium chloride could easily fill the lattice structure. A carbon scaffold with controllable low shrinkage (41.3%) and a small porous structure (skeleton thickness=~40 µm and pore size=~300 µm) was obtained by pyrolyzing the polymer lattice structure in the granular support, and subsequently, it was processed by hydrofluoric acid (HF). The unprocessed and HF-processed scaffolds were both composed of simple substance carbon, and silicon oxide particles embedded on the unprocessed scaffold were cleaned by HF. Finally, the compressive properties of the scaffold were examined. The fracture appearances of the scaffold under the application of compressive forces parallelly and vertically to the stacking direction were different, and compressive properties in vertical to the stacking direction were superior to those in parallel to the stacking direction. Therefore, it can be inferred that the proposed method is effective in fabricating multi-scale carbon scaffolds with small controllable porous structures based on stress analysis to obtain optimum mechanical properties, which makes it a promising material for many applications.

A Flexible Microdevice for Mechanical Cell Stimulation and Compression in Microfluidic Settings

Evidence continues to emerge that cancer is a disease not only of genetic mutations, but also of altered mechanobiological profiles of the cells and microenvironment. This mutation-independent element might be a key factor in promoting development and spread of cancer. Biomechanical forces regulate tumor microenvironment by solid stress, matrix mechanics, interstitial pressure, and flow. Compressive stress by tumor growth and stromal tissue alters cell deformation and recapitulates the biophysical properties of cells to grow, differentiate, spread, or invade. Such solid stress can be introduced externally to change the cell response and to mechanically induce cell lysis by dynamic compression. In this work, we report a microfluidic cell culture platform with an integrated, actively modulated actuator for the application of compressive forces on cancer cells. Our platform is composed of a control microchannel in a top layer for introducing external force and a polydimethylsiloxane (PDMS) membrane with monolithically integrated actuators. The integrated actuator, herein called micro-piston, was used to apply compression on SKOV-3 ovarian cancer cells in a dynamic and controlled manner by modulating applied gas pressure, localization, shape, and size of the micro-piston. We report fabrication of the platform, characterization of the mechanical actuator experimentally and computationally, and cell loading and culture in the device. We further show the use of the actuator to perform both repeated dynamic cell compression at physiological pressure levels and end point mechanical cell lysis, demonstrating suitability for mechanical stimulation to study the role of compressive forces in cancer microenvironments. Finally, we extend cell compression applications in our device to investigating mechanobiologically related protein and nuclear profiles in cyclically compressed cells.

Influence of external forces on actin-dependent T cell protrusions during immune synapse formation.

We have previously observed that in response to antigenic activation, T cells produce actin-rich protrusions that generate forces involved in T cell activation. These forces are influenced by the mechanical properties of antigen-presenting cells (APCs). However, how external forces, which can be produced by APCs, influence the dynamic of the actin protrusion remains unknown. In this study, we quantitatively characterised the effects of external forces in the dynamic of the protrusion grown by activated T cells. Using a micropipette force probe, we applied controlled compressive or pulling forces on primary T lymphocytes activated by an antibody-covered microbead, and measured the effects of these forces on the protrusion generated by T lymphocytes. We found that the application of compressive forces slightly decreased the length, the time at which the protrusion stops growing and retracts and the velocity of the protrusion formation, whereas pulling forces strongly increased these parameters. In both cases, the applied forces did not alter the time required for the T cells to start growing the protrusion (delay). Exploring the molecular events controlling the dynamic of the protrusion, we showed that inhibition of the Arp2/3 complex impaired the dynamic of the protrusion by reducing both its maximum length and its growth speed and increasing the delay to start growing. Finally, T cells developed similar protrusions in more physiological conditions, that is, when activated by an APC instead of an activating microbead. Our results suggest that the formation of the force-generating protrusion by T cells is set by an intracellular constant time and that its dynamic is sensitive to external forces. They also show that actin assembly mediated by actin-related protein Arp2/3 complex is involved in the formation and dynamic of the protrusion. Actin-rich protrusions developed by T cells are sensory organelles that serve as actuators of immune surveillance. Our study shows that forces experienced by this organelle modify their dynamic suggesting that they might modify immune responses. Moreover, the quantitative aspects of our analysis should help to get insight into the molecular mechanisms involved in the formation of the protrusion.

Long Non-coding RNA FER1L4 Mediates the Autophagy of Periodontal Ligament Stem Cells Under Orthodontic Compressive Force via AKT/FOXO3 Pathway

Orthodontic tooth movement is achieved by periodontal tissue remodeling triggered by mechanical force. It is essential to investigate the reaction of periodontal ligament stem cells (PDLSCs) for improving orthodontic therapeutic approaches. Autophagy is an endogenous defense mechanism to prevent mechanical damage of environmental change. Long non-coding RNAs (lncRNAs) are key regulators in gene regulation, but their roles are still largely uncharacterized in the reaction of PDLSCs during orthodontic tooth movement. In this study, we showed that autophagy was significantly induced in PDLSCs under compressive force, as revealed by the markers of autophagy, microtubule-associated protein light chain 3 (LC3) II/I and Beclin1, and the formation of autophagosomes. After the application of compressive force, lncRNA FER1L4 was strongly upregulated. Overexpression of FER1L4 increased the formation of autophagosome and autolysosomes in PDLSCs, while knockdown of FER1L4 reversed the autophagic activity induced by mechanical force. In mechanism, FER1L4 inhibited the phosphorylation of protein kinase B (AKT) and subsequently increased the nuclear translocation of forkhead box O3 (FOXO3) and thus mediated autophagic cascades under compressive strain. In mouse model, the expression of Lc3 as well as Fer1l4 was increased in the pressure side of periodontal ligament during tooth movement. These findings suggest a novel mechanism of autophagy regulation by lncRNA during periodontal tissue remodeling of orthodontic treatment.

Effects of Smad4 on the expression of caspase‑3 and Bcl‑2 in human gingival fibroblasts cultured on 3DPLGA scaffolds induced by compressive force.

Human gingival fibroblasts (HGFs) are the main cells that comprise gingival tissue, where they transfer mechanical signals under physiological and pathological conditions. The exact mechanism underlying gingival tissue reconstruction under compressive forces remains unclear. The present study aimed to explore the effects of Smad4, caspase-3 and Bcl-2 on the proliferation of HGFs induced by compressive force. HGFs were cultured on poly(lactide-co-glycolide) (PLGA) scaffolds under an optimal compressive force of 25 g/cm2. Cell viability was determined via Cell Counting Kit-8 assays at 0, 12, 24, 48 and 72 h. The expression levels of Smad4, caspase-3 and Bcl-2 were measured via reverse transcription-quantitative PCR and western blotting. The application of compressive force on HGFs for 24 h resulted in a significant increase in cell proliferation and Bcl-2 expression, but a significant decrease in the expression of Smad4 and caspase-3; however, inverse trends were observed by 72 h. Subsequently, a lentivirus was used to overexpress Smad4 in HGFs, which attenuated the effects of compressive force on HGF proliferation and Bcl-2 expression, but enhanced caspase-3 expression, suggesting that Smad4 may regulate compressive force-induced apoptosis in HGFs. In conclusion, these findings increased understanding regarding the mechanisms of compressive force-induced HGF proliferation and apoptosis, which may provide further insight for improving the efficacy and stability of orthodontic treatment.

A Human Periodontal Ligament Fibroblast Cell Line as a New Model to Study Periodontal Stress.

The periodontal ligament (PDL) is exposed to different kinds of mechanical stresses such as bite force or orthodontic tooth movement. A simple and efficient model to study molecular responses to mechanical stress is the application of compressive force onto primary human periodontal ligament fibroblasts via glass disks. Yet, this model suffers from the need for primary cells from human donors which have a limited proliferative capacity. Here we show that an immortalized cell line, PDL-hTERT, derived from primary human periodontal ligament fibroblasts exhibits characteristic responses to glass disk-mediated compressive force resembling those of primary cells. These responses include induction and secretion of pro-inflammatory markers, changes in expression of extracellular matrix-reorganizing genes and induction of genes related to angiogenesis, osteoblastogenesis and osteoclastogenesis. The fact that PDL-hTERT cells can easily be transfected broadens their usefulness, as molecular gain- and loss-of-function studies become feasible.

VNUT/SLC17A9, a vesicular nucleotide transporter, regulates osteoblast differentiation.

Osteoblasts release adenosine triphosphate (ATP) out of the cell following mechanical stress. Although it is well established that extracellular ATP affects bone metabolism via P2 receptors [such as purinergic receptor P2X7 (P2X7R) and purinergic receptor P2Y2 (P2Y2R)], the mechanism of ATP release from osteoblasts remains unknown. Recently, a vesicular nucleotide transporter [VNUT, solute carrier family 17 member 9 (SLC17A9)] that preserves ATP in vesicles has been identified. The purpose of this study was to elucidate the role of VNUT in osteoblast bone metabolism. mRNA and protein expression of VNUT were confirmed in mouse bone and in osteoblasts by quantitative real‐time PCR (qPCR) and immunohistochemistry. Next, when compressive force was applied to MC3T3‐E1 cells by centrifugation, the expression of Slc17a9, P2x7r, and P2y2r was increased concomitant with an increase in extracellular ATP levels. Furthermore, compressive force decreased the osteoblast differentiation capacity of MC3T3‐E1 cells. shRNA knockdown of Slc17a9 in MC3T3‐E1 cells reduced levels of extracellular ATP and also led to increased osteoblast differentiation after the application of compressive force as assessed by qPCR analysis of osteoblast markers such as Runx2, Osterix, and alkaline phosphatase (ALP) as well as ALP activity. Consistent with these observations, knockdown of P2x7r or P2y2r by siRNA partially rescued the downregulation of osteoblast differentiation markers, caused by mechanical loading. In conclusion, our results demonstrate that VNUT is expressed in osteoblasts and that VNUT inhibits osteoblast differentiation in response to compressive force by mechanisms related to ATP release and P2X7R and/or P2Y2R activity.

Interleukin 17 (IL-17) and interleukin 23 (IL-23) levels are modulated by compressive orthodontic forces in humans

ObjectiveThe purpose of the investigation was to evaluate whether the application of compression forces exerted on the periodontal ligament during orthodontic movement is reflected at the level of interleukin (IL)-17 and IL-23. Materials and methodsThe gingival crevicular fluid (GCF) samples from the compression sites of 32 molars from 16 patients prescribed with modified Hyrax appliance were collected. The GCF were analyzed for IL-17, IL-23, and IL-1β (Control) at baseline and at 1, 7, and 14 days of active wear of the appliance. ResultsOrthodontic forces resulted in increased levels of IL-17 and IL-23 in the GCF, which were statistically significant at 7 days of force application at compression sites. At day 14, levels decreased to baseline; IL-1β levels (positive control) were more elevated at all times after force application. IL-17 and IL-23 levels were significantly lower than IL-1β, and undetectable in some samples. ConclusionUpregulation of IL-17 and IL-23 occurred in response to the force application in compression sites. Monitoring the levels of inflammatory mediators might be a clinically useful procedure, as they may help to define optimal forces to produce the most rapid tooth movement.

IMPLEMENTATION OF CONNECTION SYSTEM OF WOODEN PLATE AND WOODEN CLAMP ON JOINT MODEL OF BAMBOO TRUSS STRUCTURES

The study of wooden plate bamboo connection system with the addition of wooden clamp was carried out taking into account the variety the angle of the stems at the joint. The loading was preceded through the application of compressive force at the joint’s member understudied up to reaching the maximum load and the connection was collapsed. It is known that the strength of bamboo not parallel to the direction of the fiber is lower than those parallel to fiber. Therefore, the strength of connection must be determined considering the strength of bamboo not parallel to the fiber direction. The experiment was carried out under static loading on the bamboo truss connections model with the various angle of connection stems of 0o, 30o and 45o toward bamboo fiber direction. From the test result, it was found that there is a decrease in the connection strength at stem angle of 30o and 45o for about 16,80% and 12,21%, respectively, compared to the strength of the stem angle of 0o. The test results also resulted the value of average elastic stiffness (Se) of the connection also indicates a decrease in the of elastic stiffness value (Se) of the connection for the stem’s angle 30o and 45o for about 42,62% and 82,95%, respectively, compared to stem angle of 0o. It can be concluded that there is a decrease in the strength and stiffness of the joints along with the increase in stem’s angle of the bamboo truss connection system using wooden plate and clamp.

Compressive force-induced autophagy in periodontal ligament cells downregulates osteoclastogenesis during tooth movement.

Autophagy has recently emerged as a protective mechanism in response to compressive force and an important process in maintenance of bone homeostasis. It appears to be involved in the degradation of osteoclasts, osteoblasts, and osteocytes. The aim of this study was to investigate the role of compressive force-induced autophagy in periodontal ligament (PDL) cells in regulating osteoclastogenesis of orthodontic tooth movement (OTM). An OTM model and compressive force on PDL cells were employed to investigate the expression of autophagy markers in vivo and in vitro, respectively. Autophagosomes and autolysosomes were observed in PDL cells by transmission electron microscope (TEM) and autophagy LC3 double labelling. 3-Methyladenine (3-MA) and rapamycin were respectively used to inhibit and promote autophagy, and the effect of autophagy on osteoclastogenesis was explored via microcomputed tomography, hematoxylin and eosin (H&E) staining, histochemistry of titrate-resistant acid phosphatase, and real-time polymerase chain reaction (RT-PCR) in vivo. Receptor activator of nuclear factor-kappa B ligand/osteoprotegerin (RANKL/OPG) was investigated by RT-PCR and ELISA in vitro. Orthodontic force-induced autophagy was prominent on the pressured side of PDL tissues. Administration of 3-MA downregulated bone density and upregulated osteoclasts, while rapamycin had reverse results in OTM. The autophagy activity increased initially then decreased in PDL cells during compressive force application and responded to light force. In PDL cells, administration of 3-MA upregulated while rapamycin downregulated the RANKL/OPG ratio. Autophagy is activated by compressive force in PDL cells. Besides, it could modulate OTM by negatively regulating osteoclastogenesis and keep bone homeostasis via RANKL/OPG signaling.

Differences in RUNX2 and P2RX7 gene expression between mono- and coculture of human periodontal ligament cells and human osteoblasts under compressive force application.

Objectives were (a) to establish an in vitro coculture model of human PDL-derived fibroblasts (HPDFs) and human alveolar bone-derived osteoblasts (HABOs), and (b) to measure RUNX2 and P2RX7 gene expression at multiple time points after compressive force (CF) stimulation for different durations. Human PDL-derived fibroblasts and HABOs from two individuals isolated from extracted teeth of healthy donors due to orthodontic reasons at LMU's Dental School were used. Mono- and cocultured cells were subjected to CF by centrifugation (47.4g/cm2 ) for 1, 2 and 4hours at 30°C. Total RNA was isolated before and 2, 4, 8, 16minutes after CF application. Expression of RUNX2 and P2RX7 was determined using quantitative real-time polymerase chain reaction. In monocultured cells, an upregulation of RUNX2 and P2RX7 expression was found after all CF durations: RUNX2 twofold in HPDFs after 4hours (P=0.002) and 1.7-fold in HABOs after 1hour (P=0.009) or 2hours (P=0.002) of CF. P2RX7 was significantly upregulated following 1hour (P=0.004) and 2hours (P=0.002) of CF application in HPDFS. In HABOs, a transient regulation was observed. In cocultured cells, a significant alleviation in gene expression was found for both loci after CF application. In both cell types, RUNX2 expression was significantly reduced in cocultured cells compared to cells in monoculture. P2RX7 expression showed significant attenuation in HPDFs only. Cocultivation attenuated the CF induced increase of RUNX2 and P2RX7 gene expression in comparison to monoculture in both cell types. This suggests that intercellular communication may exist between HPDFs and HABOs.

Effects of ethanol on human periodontal ligament fibroblasts subjected to static compressive force.

Consumption of toxic substances such as alcohol is widespread in the general population and thus also in patients receiving orthodontic treatment. Since human periodontal ligament (hPDL) fibroblasts play a key role in orthodontic tooth movement (OTM) by expressing cytokines and chemokines, we wanted to clarify whether ethanol modulates the physiological activity and expression pattern of hPDL fibroblasts during static compressive force application. We pre-incubated hPDL fibroblasts for 24h with different ethanol concentrations, corresponding to casual (0.041% blood alcohol concentration [BAC], % by volume) and excessive (0.179%) alcohol consumption. At each ethanol concentration, we incubated the cells for another 48h with and without an additional physiological compressive force of 2g/cm2 occurring during orthodontic tooth movement in compression areas of the periodontal ligament. Thereafter, we analyzed expression and secretion of genes and proteins involved in OTM regulation by RT-qPCR and ELISA. We also performed co-culture experiments to observe hPDL-fibroblast-mediated osteoclastogenesis. We observed no effects of ethanol on cytotoxicity or cell viability of hPDL fibroblasts in the applied concentrations. Ethanol showed an enhancing effect on angiogenesis and activity of alkaline phosphatase. Simultaneously, ethanol reduced the induction of IL-6 and increased prostaglandin E2 synthesis as well as hPDL-fibroblast-mediated osteoclastogenesis without affecting the RANK-L/OPG-system. hPDL fibroblasts thus seem to be a cell type quite resistant to ethanol, as no cytotoxic effects or influence on cell viability were detected. High ethanol concentrations, however, seem to promote bone formation and angiogenesis. Ethanol at 0.179% also enhanced hPDL-induced osteoclastogenesis, indicating increased bone resorption and thus tooth movement velocity to be expected during orthodontic therapy.

Tuning frequency band gaps of tensegrity mass-spring chains with local and global prestress

This work studies the acoustic band structure of tensegrity mass-spring chains, and the possibility to tune the dispersion relation of such systems by suitably varying local and global prestress variables. Building on established results of the Bloch–Floquet theory, the paper first investigates the linearized response of chains composed of tensegrity units and lumped masses, which undergo small oscillations around an initial equilibrium state. The stiffness of the units in such a state varies with an internal self-stress induced by prestretching the cables forming the tensegrity units, and the global prestress induced by the application of compression forces to the terminal bases. The given results show that frequency band gaps of monoatomic and biatomic chains can be effectively altered by the fine tuning of local and global prestress parameters, while keeping material properties unchanged. Numerical results on the wave dynamics of chains under moderately large displacements confirm the presence of frequency band gaps of the examined systems in the elastically hardening regime. Novel engineering uses of the examined systems are discussed.