Application Of Compressive Force Research Articles

Surgical Results of Zones I and II Fifth Metatarsal Base Fractures Using Hook Plates

The purpose of this study was to evaluate the results of surgical treatment of fifth metatarsal base fractures using a mini-hook plate. Seventeen patients with Lawrence classification zones I (n=6) and II (n=11) fifth metatarsal base fractures with an initial fracture displacement more than 2 mm and a small (less than 2 mm) comminuted avulsion fragment were included in the study. Patients treated using a mini-hook plate fixation method were prospectively evaluated. A mini-hook tubular plate was designed so that the last hole functioned as a hook for the application of compression force, grasping of comminuted fragments, and rotational stabilization in metatarsal base fractures. Clinically, the American Orthopaedic Foot and Ankle Society (AOFAS) midfoot scale questionnaire was administered preoperatively and 1 year postoperatively. Union was determined by 3-dimensional computed tomography as clinically nontender callus formation. Time to union and return to sports were calculated. Mean AOFAS midfoot scale scores were 48±8 points (range, 35-60 points) preoperatively and 91±7 points (range, 85-100 points) 1 year postoperatively. Mean time to complete union, as determined by computed tomography, was 54±11 days (range, 38-74 days). All patients reported returning to prior activities of daily living at a mean of 74±10 days (range, 63-98 days). One patient reported hardware irritation secondary to inadequate plate bending and screw curving. Mini-hook plate fixation is an effective alternative surgical method for zones I and II displaced fifth metatarsal base fractures or comminuted small fragment fractures.

Effect of Ga‐Al‐As laser irradiation on COX‐2 and cPLA2‐α expression in compressed human periodontal ligament cells

Prostaglandin E(2) (PGE(2)), which has bone-resorptive activity, is produced by human periodontal ligament (PDL) cells in response to mechanical stress. We previously reported that low level laser (LLL) irradiation inhibited PGE(2) production in PDL cells in response to mechanical stress; however, the mechanism underlying this inhibitory effect was unclear. Thus, we sought to determine the mechanism underlying the inhibitory effect of LLL on PGE(2) production in compressed PDL cells. A compressive force of 2.0 g/cm(2) was applied for 24 hours to human PDL cells obtained from premolars extracted for orthodontic treatment. LLL irradiation (Ga-Al-As laser, 830 nm, 3.82 J/cm(2)) was applied 6 hours before, 1 hour before, and immediately after the application of compressive force. The mRNA expression of COX-2 and cPLA(2)-alpha was then examined by real-time PCR. LLL irradiation significantly inhibited COX-2 and cPLA(2)-alpha mRNA expression, which was increased in response to the application of a compressive force. Moreover, LLL irradiation immediately after compression had the strongest inhibitory effect on the expression of these genes. The inhibition of PGE(2) production by LLL irradiation in compressed PDL cells may be due to the inhibition of COX-2 and cPLA(2)-alpha expression and is most pronounced immediately after the application of a compressive force.

Inflammatory response in epithelial cells induced by mechanical stress is suppressed by hyaluronic acid

Hyaluronic acid (HA) is a widely distributed component of the extracellular matrix that has been shown to play regulatory roles in inflammation. In the present study, we examined the inhibitory mechanism of HA related to mechanical stress-induced inflammatory response in mouse gingival epithelial GE1 cells. Application of compressive force in a three-dimensional cell culture system increased the expression of cyclooxygenase-2 (COX-2) mRNA in a force-dependent manner, while COX-2 protein and prostaglandin E2 (PGE2) levels were also increased in a time-dependent manner. Interestingly, we found that HA suppressed the expression of COX-2 and production of PGE2 under the same conditions. Western blotting analysis revealed that mechanical stress induced the phosphorylation of ERK and p38 MAPK at 60 minutes after loading, while that of IκBα was activated at 15 minutes and peaked at 30 minutes. In addition, IκBα degradation was activated at 30 minutes and recovered at 60 minutes. Furthermore, treatment with HA down-regulated the phosphorylation of p38 MAPK, ERK, and IκBα in GE1 cells. These results indicate that mechanical stress enhances the induction of COX-2 and PGE2 in epithelial cells, while HA inhibits those mechanical stress-induced inflammatory responses via MAPKs and the NF-κB signaling pathway.

Electromechanical characterization of cymbal piezocomposites

The aim of this work was to develop a methodology for the characterization of complexpiezocomposites under external mechanical forces. In this specific procedure the sampleswere axially loaded in a universal mechanical test machine and monitored with anelectrometer. The force versus displacement and the generated charge versus the appliedforce were measured. Cymbal piezocomposites were chosen due to their complex designwhich illustrated the effectiveness of the proposed methodology during the application ofcompression force loops.The occurrence of depolarization can be evaluated by measuring the electricalcharge generated during the application of a compression loop. The results showedthe dependence of electromechanical properties on both the PZT ceramics andthe cymbal piezocomposite with the compressive load loops. The depolarizationeffect associated with the mechanical stress induced by switching of a non-180° ferroelectric domain was evaluated.

Pulse propagation in a linear and nonlinear diatomic periodic chain: effects of acoustic frequency band-gap

One-dimensional nonlinear phononic crystals have been assembled from periodic diatomic chains of stainless steel cylinders alternated with Polytetrafluoroethylene spheres. This system allows dramatic changes of behavior (from linear to strongly nonlinear) by application of compressive forces practically without changes of geometry of the system. The relevance of classical acoustic band-gap, characteristic for chain with linear interaction forces and derived from the dispersion relation of the linearized system, on the transformation of single and multiple pulses in linear, nonlinear and strongly nonlinear regimes are investigated with numerical calculations and experiments. The limiting frequencies of the acoustic band-gap for investigated system with given precompression force are within the audible frequency range (20–20,000 Hz) and can be tuned by varying the particle’s material properties, mass and initial compression. In the linear elastic chain the presence of the acoustic band-gap was apparent through fast transformation of incoming pulses within very short distances from the chain entrance. It is interesting that pulses with relatively large amplitude (nonlinear elastic chain) exhibit qualitatively similar behavior indicating relevance of the acoustic band gap also for transformation of nonlinear signals. The effects of an in situ band-gap created by a mean dynamic compression are observed in the strongly nonlinear wave regime.

The influence of increasing sacroiliac joint force closure on the hip and lumbar spine extensor muscle firing pattern

The prone hip extension (PHE) test is commonly used in the evaluation of lumbo-pelvic dysfunction. It has been suggested that altered motor control identified by the PHE test can be improved with the application of compression force across the pelvis, to increase force closure on the sacroiliac joint (SIJ). This repeated measure study design investigated the effect of three levels of pelvis compression (0 N, 50 N, 100 N) on the muscle firing pattern during the PHE test in 20 asymptomatic male subjects tested on two occasions 4-weeks apart. The right gluteus maximus, right semitendinosus and bilateral lumbar erector spinae were analyzed using surface electromyography (EMG). Subjects were instructed to perform right hip extension in prone position while maintaining knee-extension in each measurement condition. Compared with the onset of the semitendinosus muscle, gluteus maximus became active 263.3 ± 99.5 ms later with no pelvic compression, 183.5 ± 77.9 ms later with 50 N compression, 91.5 ± 49.7 ms later with 100 N compression. While significant differences ( α = 0.05) were found in EMG onset for gluteus maximus under different levels of pelvis compression, this was not the case for the erector spinae, which had an inconsistent pattern of temporal onset and was not influenced by the level of pelvis compression force.

Effect of compressive force on the expression of inflammatory cytokines and their receptors in osteoblastic Saos-2 cells

Objective In orthodontic tooth movement, some cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts on the pressure side can alter the normal processes of bone remodelling, resulting in physiological bone resorption. We examined the effect of compressive force and interleukin (IL)-1 type I receptor antagonist (IL-1ra) on the expression of inflammatory cytokines that promote osteoclast formation, as well as on their receptors, in osteoblastic Saos-2 cells. Design The cells were cultured in Dulbecco's modified Eagle medium containing 10% fetal bovine serum with or without continuous compressive force (0.5–3.0 g/cm 2) and/or IL-1ra for up to 24 h. The gene expression levels of the cytokines and their receptors were estimated by determining mRNA levels using real-time PCR; the protein levels were determined using ELISA or immunohistochemical staining. Results The expression of IL-1β, IL-1 receptor, IL-6, IL-6 receptor, IL-8 receptor, IL-11 and tumor necrosis factor-α (TNFα) increased depending on the strength and duration of the compressive force, whereas the expression of IL-8, IL-11 receptor and TNFα receptor did not change with the application of compressive force. The expression of cytokines and their receptors produced by 3.0 g/cm 2 of compressive force decreased with the simultaneous addition of IL-1ra and the decrease was remarkable in IL-8 receptor, IL-11 and TNFα. Conclusion These results indicate that mechanical stress induces the production of inflammatory cytokines and their receptors in osteoblasts and the phenomenon is enhanced by the autocrine action of IL-1β, which is increased in amount by mechanical stress.

Compressive osseointegration promotes viable bone at the endoprosthetic interface: retrieval study of Compress® implants

The Compress implant (Biomet, Warsaw, IN) is an innovative device developed to enable massive endoprosthetic fixation through the application of compressive forces at the bone-implant interface. This design provides immediate, stable anchorage and helps to avoid the long-term complication of aseptic loosening secondary to stress shielding and particle-induced osteolysis seen in conventional, stemmed megaprostheses. The purpose of our study was to evaluate the in vivo biological effects of the high compressive forces attained. Twelve consecutive Compress patients undergoing revision surgery for infection, periprosthetic fracture, or local tumour recurrence were reviewed in order to exclude the possibility of osteonecrosis at the prosthetic interface. Compressive forces ranged from 400-800 lb. Duration of implantation averaged 3.3 years (range 0.4-12.2 years). Two patients with infection demonstrated loosening at the bone-prosthetic interface; otherwise, there was no radiographic evidence of prosthetic failure in any of the patients. No patient demonstrated histological evidence of osteonecrosis. In fact, new woven bone and other findings consistent with viable bone were noted in all of the retrieved specimens.

Improvement of UV-moulding accuracy by heat and solvent assisted process

A micro-optics replication process with UV-curable liquid pre-polymers is considered. Filling of the master structure is improved by controlling the viscosity of the pre-polymer by heat during the process. A novel process step, solvent-assisted filling, is introduced to avoid the harmful effect of the residual trapped air; a pyramidal retro-reflector structure with the face width of 400 μm is used as an example. Complete filling can be achieved without vacuum assisted replication or without application of compression force in the mould. Material studies showed no signs of chemical changes, solvent inclusion in the replicated structure, or a change of the optical properties of the material during the process. The replication fidelity is compared with conventional UV-moulding and commercial UV-NIL replication. The new heat and solvent assisted replication technique allows the use of high-viscosity pre-polymers with suitable material properties if the process temperature window is optimized.

Role of regulator of G‐protein signaling 2 (RGS2) in periodontal ligament cells under mechanical stress

Mechanical stress is thought to regulate the expression of genes in the periodontal ligament (PDL) cells. Using a microarray approach, we recently identified a regulator of G-protein signaling 2 (RGS2) as an up-regulated gene in the PDL cells under compressive force. The RGS protein family is known to turn off G-protein signaling. G-protein signaling involves the production of cAMP, which is thought to be one of the biological mediators in response to mechanical stress. Here, we investigated the role of RGS2 in the PDL cells under mechanical stress. PDL cells derived from the ligament tissues of human premolar teeth were cultured in collagen gels and subjected to static compressive force. Compressive force application time-dependently enhanced RGS2 expression and intracellular cAMP levels. To examine the interrelationship between RGS2 and cAMP, the PDL cells were treated with 2',5'-dideoxyadenosine (DDA), an inhibitor of adenyl cyclase, or antisense S-oligonucleotide (S-ODN) to RGS2 under compressive force. DDA dose-dependently inhibited RGS2 stimulated by compressive force. Blockage of RGS2 by antisense S-ODN elevated the cAMP levels compared with controls. These results indicate that cAMP stimulates RGS2 expression, which in turn leads to a decrease in the cAMP production by inactivating the G-protein signaling in the mechanically stressed PDL cells.

Aging stimulates cyclooxygenase‐2 expression and prostaglandin E2 production in human periodontal ligament cells after the application of compressive force

Some clinical studies show that alveolar crestal bone loss is higher in adults than in young patients during orthodontic treatment, but the causes of such a phenomenon have not been elucidated. It is known that prostaglandin E2 (PGE2) is a proinflammatory agent and one of the potent osteoclast-inducing factors, and is produced by human periodontal ligament cells in response to orthodontic force. The aim of this study was to investigate age-related change in the biosynthetic capacity of PGE2 and its regulatory gene, cyclooxygenase 2 (COX-2) from periodontal ligament cells in response to mechanical stress. Compressive force of 2 g/cm2 was applied for 3-48 h to periodontal ligament cells obtained from human donors aged 9-50 years, and COX-2 mRNA expression in and PGE2 production by the periodontal ligament cells in response to the compressive force were examined. Application of a compressive force of 2 g/cm2 for 3-48 h significantly stimulated these factors in both time- and age-dependent manners. Furthermore, these increases were dramatically larger in periodontal ligament cells obtained from donors over the age of 35. Periodontal ligament cells obtained from old donors have significantly greater COX-2 expression and PGE2 production in response to compressive force than those from younger donors. The turning point of aging, where significantly larger amounts of theses factors begin production, appears to be around the age of 35. These results may be positively related to the acceleration of alveolar crestal bone loss during orthodontic treatment in adult patients.

Bonding of articular cartilage using a combination of biochemical degradation and surface cross-linking

After trauma, articular cartilage often does not heal due to incomplete bonding of the fractured surfaces. In this study we investigated the ability of chemical cross-linkers to facilitate bonding of articular cartilage, either alone or in combination with a pre-treatment with surface-degrading agents. Articular cartilage blocks were harvested from the femoropatellar groove of bovine calves. Two cartilage blocks, either after pre-treatment or without, were assembled in a custom-designed chamber in partial apposition and subjected to cross-linking treatment. Subsequently, bonding of cartilage was measured as adhesive strength, that is, the maximum force at rupture of bonded cartilage blocks divided by the overlap area. In a first approach, bonding was investigated after treatment with cross-linking reagents only, employing glutaraldehyde, 1-ethyl-3-diaminopropyl-carbodiimide (EDC)/N-hydroxysuccinimide (NHS), genipin, or transglutaminase. Experiments were conducted with or without compression of the opposing surfaces. Compression during cross-linking strongly enhanced bonding, especially when applying EDC/NHS and glutaraldehyde. Therefore, all further experiments were performed under compressive conditions. Combinations of each of the four cross-linking agents with the degrading pre-treatments, pepsin, trypsin, and guanidine, led to distinct improvements in bonding compared to the use of cross-linkers alone. The highest values of adhesive strength were achieved employing combinations of pepsin or guanidine with EDC/NHS, and guanidine with glutaraldehyde. The release of extracellular matrix components, that is, glycosaminoglycans and total collagen, from cartilage blocks after pre-treatment was measured, but could not be directly correlated to the determined adhesive strength. Cytotoxicity was determined for all substances employed, that is, surface degrading agents and cross-linkers, using the resazurin assay. Taking the favourable cell vitality after treatment with pepsin and EDC/NHS and the cytotoxic effects of guanidine and glutaraldehyde into account, the combination of pepsin and EDC/NHS appeared to be the most advantageous treatment in this study. In conclusion, bonding of articular cartilage blocks was achieved by chemical fixation of their surface components using cross-linking reagents. Application of compressive forces and prior modulation of surface structures enhanced cartilage bonding significantly. Enzymatic treatment in combination with cross-linkers may represent a promising addition to current techniques for articular cartilage repair.

Compressive Force Induces Osteoblast Apoptosis via Caspase-8

Periodontal remodeling during orthodontic tooth movement is a result of mechanical stresses. The application of excessive orthodontic force induces cell death. However, the nature of compressive force-induced cell death is unclear. We examined whether the in vitro application of continuous compressive force would induce apoptosis in human osteoblast-like cells (MG-63 cells), and investigated the mechanism by which apoptosis was initiated. The cells became aligned irregularly, and cell viability decreased, indicating that the compressive force caused cell death. According to the TUNEL analysis, the number of apoptotic cells increased significantly in a time-and force-dependent manner. Caspase-3 activity increased with the magnitude of the compressive force, and this effect was reduced significantly by a caspase-8 inhibitor, whereas a caspase-9 inhibitor had no such effect. We conclude that the in vitro application of compressive force can induce apoptosis in MG-63 cells through the activation of caspase-3 via the caspase-8 signaling cascade.

Reliability-based preform shape design in forging

A reliability-based optimization method is developed for preform shape design in forging. Forging is a plastic deformation process that transforms a simple shape of workpiece into a predetermined complex shape through a number of intermediate shapes by the application of compressive forces. Traditionally, these intermediate shapes are designed in a deterministic manufacturing domain. In reality, there exist various uncertainties in the forging environment, such as variations in process conditions, billet/die temperatures, and material properties. Randomness in these parameters could lead to variations in product quality and often induce heavy manufacturing losses. In this research, a robust preform design methodology is developed in which various randomnesses in parameters are quantified and incorporated through reliability analysis and uncertainty quantification techniques. The stochastic response surface approach is used to reduce computation time by establishing a relationship between the process performance and shape and random parameters. Finally, reliability-based optimization is utilized for preform shape design of an engine component to improve the product quality and robustness. Copyright © 2005 John Wiley & Sons, Ltd.

Mental development after modified pi procedure: dynamic cranioplasty for sagittal synostosis.

A prospective developmental assessment was performed on 26 patients operated on with dynamic cranioplasty for sagittal synostosis. Because this technique entails the application of compressive force, it was of great concern to assess the effect of surgery on development and mental status. The surgical technique used was a modified pi procedure. Perioperative variables were recorded. Six patients underwent preoperative intracranial pressure (ICP) measurements. To evaluate objectively the developmental outcome, the Griffiths' Mental Development Scales was used for analysis before and after surgery. A parental questionnaire was used for subjective outcome measurement. Preoperative ICP recordings during sleep ranged from 12.8 to 22.8 mmHg (mean, 16.1 mmHg). The mean age at the time for surgery was 6.9 months (range, 4-16 months; standard deviation [SD], 2.32 months). The surgical technique included shortening of the anteroposterior diameter of the skull by a mean of 16.6 mm. The mean global development quotient (GDQ) preoperatively was 104.5 (range, 82-144; SD, 12.4) and the mean GDQ postoperatively was 101.4 (range, 62-129; SD, 13.6). Mean age at follow-up was 16.3 months (range, 9-40 months; SD, 4.04 months). There was no significant correlation between the amount of intraoperative shortening and mental development. In comparison of means, the GDQ preoperatively did not differ significantly from the GDQ postoperatively. The modified pi procedure is safe and efficient. When surgery was performed before 1 year of age, no significant (p = 0.33) effect on mental development-either detrimental or beneficial-was demonstrated.

Prostacyclin (PGI2): a potential mediator of c‐fos expression induced by hydrostatic pressure in osteoblastic cells

Application of compressive forces to osteoblastic cells is known to cause specific cellular responses. We report that hydrostatic pressure increased c-fos mRNA expression in MC3T3-E1 cells after 15, 30 and 60 min. This effect was absent when 5 x 10(-7) mol L-1 indomethacin, an inhibitor of prostaglandin synthesis, was present in the culture medium during pressurization. Using radioimmunoassay, a significant increase in the concentrations of 6-keto-PGF1 alpha, the stable conversion product of prostacyclin (PGI2), in the conditioned medium of pressurized cells, was measured after 60 min. In contrast, PGE2 levels were not significantly changed and we therefore assume that under these experimental conditions PGE2 is not responsible for the transduction of the hydrostatic force. However, we also found that PGE2 has the capacity to induce c-fos mRNA in MC3T3-E1 cells. Furthermore, we show for the first time that the stable prostacyclin analogue, Iloprost-Trometamol (Ilomedin), is a potent activator of c-fos gene transcription. Our data suggest that prostacyclin is a likely candidate in mediating the effect of hydrostatic compressive stress on bone cells by regulating the level of c-fos mRNA, a member of the activator protein (AP-1) complex and potent regulator of osteoblastic proliferation and differentiation.

Breast compression: a preliminary study

X-Ray mammography is the technique employed to image breast tumours; it is the gold standard for both diagnosis and screening 1. To increase the sensitivity of the test and to reduce the dose of X-radiation, breast compression is used. The effect of squeezing a simple model of a breast in which there is an idealized spherical tumour volume is investigated; the cases where the lesion has both a smaller, and a larger compressibility than the surrounding tissues are considered. Surface strain is computed as a function of the deformation of the lesion from its spherical shape. Evidence from earlier studies is adduced to show that when the lesion is malignant care should be exercised to avoid the possibility of disseminating cancer cells by the application of compressive forces.

The lumbar spine in backward bending.

Cadaveric lumbar motion segments were loaded to simulate backward bending (extension) movements of the lumbar spine. The motion segments' resistance was measured initially, and after the spinous processes and apophyseal joints had been cut through in turn. Compression tests were then performed on the discs while they were wedged in full extension. The results showed that extension is resisted mainly by the disc and spinous processes, and that, in hyperextension, damage usually occurs first in the spinous processes (or the soft tissue squashed between them). However, if the spinous processes are particularly widely spaced, then the apophyseal joints can become damaged first. The protection offered the disc by the neural arch is greater in young people, and after the disc height has been reduced by creep loading. The disc can be damaged in hyperextension if the spine is subjected to high compressive forces at the same time. A sudden application of compressive force can cause an anterior disc prolapse, while a cyclic (fatigue) compressive force can increase the posterior bulging of the lamellas in the posterior annulus.

A simplified viscoelastic constitutive equation applied to a dynamic finite deformation problem

A single integral type of constitutive equation for finite viscoelastic deformation is proposed. A special case, which is a viscoelastic generalization of the constitutive equation for a neo-Hookean elastic solid, is used to consider the finite deformation problem of shock wave propagation resulting from the sudden application of compressive force at the end of a semi-infinite viscoelastic bar. An approximate method is used to determine the shock front path and shock strength when the viscoelastic dissipative effect is small.

Determination of crystal structure of metastable anthracene by a novel method

A combination of transmission electron microscopy (TEM) and ‘atom–atom’ computational procedures1,2 developed for molecular crystals has led to the discovery and the determination of the crystal structure and lattice dynamics of a metastable, triclinic phase (hereafter designated, II) of anthracene. The new form, which is only 2 kJ mol−1 less stable than the monoclinic, thermodynamically stable parent phase (I), may be generated by the application of compressive force or shear stress approximately perpendicualr to the basal plane of I. In essence, the size and shape of the unit cell into which molecules of anthracene are packed is determined from the electron diffraction patterns of the new phase. From the symmetry and space group, determined by TEM, assuming that the individual molecules are as undistorted in II as in I, A ‘trial structure’ of the ‘new’ phase may be computed by minimising the total energy as a function of the moleculear packing characteristics, knowing the empirically determined3 atom–atom potentials between all pairs of non-bonded atoms. The structure is refined by varying the molecular coordinates, as described below, so as to arrive at a set of lattice vibrations4,5 all of which are real in the entire Brillouin zone. The enhanced photo reactivity of phase II compared with I is explicable in terms of the resulting crystal structure.