Significant Decrease In Stiffness Research Articles

Comparison of the effects of cold water immersion and percussive massage on the recovery after exhausting eccentric exercise: A three-armed randomized controlled trial.

Athletic training requires both challenging stimuli for adaptation and sufficient recovery for improved performance. While cold water immersion (CWI) is already a popular recovery method, handheld percussive massage (PM) devices have also gained popularity in recent years. This study aims to assess the effects of CWI and PM on performance recovery after strenuous eccentric exercises compared to a passive rest (PR) control condition. Thirty-four healthy physically active participants (9 females, 25 males) were randomly divided into three groups: CWI (n = 11), PM (n = 11), and passive rest (PR) (n = 12). They underwent an exhausting eccentric exercise protocol and different measurements at six time points (baseline, POST1, POST2, POST24, POST48, and POST72) over the time course of 72h. These included subjective assessments of muscle soreness and perceived stiffness as well as measures of skin temperature, leg volume, creatine kinase activity, and three different jump tests. The eccentric exercise protocol consisted of 15min downhill running (slope: 12%, speed: 10km/h) and 3 sets of successive depth jumps (dropping height: 0.5m) until individual exhaustion. After POST1 measurements, participants received 12min of either CWI (11 ± 0.5°C), PM (40Hz) or PR (supine posture). No significant group effects were found for the number of depth jumps performed during the exhaustion protocol. All jump tests displayed a significant group × time interaction effect. Post-hoc analysis indicated significant lower jump heights in ΔPOST2 between CWI and both PM and PR. No other significant group effects were observed at any time point. No significant group × time interaction effects were noted for CK, leg volume, and soreness. The perceived stiffness showed a significant group × time interaction effect. Post-hoc analysis revealed a significant decrease in stiffness for PM compared to PR at ΔPOST2. Neither CWI nor PM showed any significant improvement in performance recovery over the 72-h period following strenuous eccentric exercise compared to PR. CWI showed an immediate performance decline which may be attributed to a cold-related reduction in motor nerve conduction velocity.

Comparison of elasticity changes in the paraspinal muscles of adolescent patients with scoliosis treated with surgery and bracing

Scoliosis is a three-dimensional spinal deformity, and paraspinal muscles play an important role as stabilizers of the spinal curve. In this prospective study, we compared elasticity changes in the paraspinal muscles of adolescent patients with scoliosis after surgery or bracing. Elasticity was measured on the concave and convex sides of the paraspinal muscles at the apex of the curve at the beginning of treatment and 6 and 12 months after treatment. Twenty-six patients with correction surgery (n = 15) or bracing (n = 11) were included. At initial evaluation, the Cobb angle was larger in the surgery group (72.3 ± 20.2° in surgery vs. 30.6 ± 5.1° in brace, p < 0.001). The estimated mean elasticity value of the paraspinal muscles was lower in the surgery group at baseline on the convex side (15.8 vs. 22.8 kPa, p = 0.037) and 6 months on both the concave (12.1 vs. 22.7 kPa, p = 0.004) and convex (13.4 vs. 23.8 kPa, p = 0.005) sides. There was a significant stiffness decrease from baseline to 6 months on the concave side in the surgery group (5.9 kPa, p = 0.025). However, the elasticity change recovered at 12 months without significant differences between the two groups.

Investigation of failure behavior of glass fiber reinforced epoxy laminate under fatigue loading

Purpose This study aims to evaluate the failure behavior of glass fiber-reinforced epoxy (GFRE) laminate subjected to cyclic loading conditions. It involves experimental investigation and statistical analysis using Weibull distribution to characterize the failure behavior of the GFRE composite laminate. Design/methodology/approach Fatigue tests were conducted using a tension–tension loading scheme at a frequency of 2 Hz and a loading ratio (R) of 0.1. The tests were performed at five different stress levels, corresponding to 50%–90% of the ultimate tensile strength (UTS). Failure behavior was assessed through cyclic stress-strain hysteresis plots, dynamic modulus behavior and scanning electron microscopy (SEM) analysis of fracture surfaces. Findings The study identified common modes of failure, including fiber pullouts, fiber breakage and matrix cracking. At low stress levels, fiber breakage, matrix cracking and fiber pullouts occurred due to high shear stresses at the fiber–matrix interface. Conversely, at high stress levels, fiber breakage and matrix cracking predominated. Higher stress levels led to larger stress-strain hysteresis loops, indicating increased energy dissipation during cyclic loading. High stress levels were associated with a more significant decrease in stiffness over time, implying a shorter fatigue life, while lower stress levels resulted in a gradual decline in stiffness, leading to extended fatigue life. Originality/value This study makes a valuable contribution to understanding fatigue behavior under tension–tension loading conditions, coupled with an in-depth analysis of the failure mechanism in GFRE composite laminate at different stress levels. The fatigue behavior is scrutinized through stress-strain hysteresis plots and dynamic modulus versus normalized cycles plots. Furthermore, the characterization of the failure mechanism is enhanced by using SEM imaging of fractured specimens. The Weibull distribution approach is used to obtain a reliable estimate of fatigue life.

Full-scale mud pumping test of ballastless trackbed under train loading

This paper presents a full-scale physical modeling investigation on the mud pumping in ballastless trackbed. The physical model was equipped with a rainfall device to simulate the in situ precipitation and various testing sensors were installed to monitor the dynamic response of the track-subgrade system. Results showed that the whipping of the track structure induced by high-speed train passages caused a separation between the track structure and the underlying roadbed, which allowed rainwater to intrude into the roadbed. The intruded rainwater infiltrated vertically and then permeated laterally from the bottom of the roadbed, eventually saturating the entire roadbed. Train moving loads partially promoted this rainwater infiltration. The excess pore water pressure (EPWP) was formed in the saturated roadbed caused by train moving loads, and it increased with train speeds and loading carriages. A noticeable upward EPWP gradient and a slight longitudinal EPWP gradient towards the expansion gap were also created in the saturated roadbed. Accordingly, both the vertical hydraulic gradient (HG) and longitudinal HG increased with train speeds and loading carriages, most of which, especially the vertical HG, exceeded the critical HG for particle migration with a diameter smaller than 7.1 mm. It caused severe upward particle migration and slight longitudinal particle migration towards the expansion gap. This spatial fine particle migration process, known as mud pumping, was driven by the HG-induced seepage force and further promoted by the EPWP amplification induced by high-speed train passages. Mud pumping resulted in a significant decrease in stiffness of the trackbed and a noticeable increase in vibration velocity of the track slab.

Investigating the Flexural Performance of Basalt Fiber Reinforced Polymer (BFRP) Bars at Elevated Temperatures

The FRP-reinforced concrete constructions may be subjected to elevated temperatures, which may compromise the structural integrity of the bars and, finally, the whole structure. As a result, the thermal stability of the FRP bars needs to be properly examined before they can be completely used in the construction field. Flexural strength testing has been utilized as a standard approach for determining the uniaxial tensile strength of brittle materials since it is less costly and easier to perform than the direct tension test. While the findings achieved were not absolute tensile data, they can offer a prediction of the relative tensile strength of the FRP bars. The flexural behavior of basalt fiber-reinforced polymer (BFRP) bars with different nominal diameters (8.0 mm, 10.0 mm, 12.0 mm, and 14.0 mm) exposed to increased temperatures (up to 150 °C) was examined in this research. According to the findings, when the temperature rises, the stiffness and flexural strength of the BFRP bars reduce. As the temperature approached the glass transition temperature (Tg) of the bars, a significant decrease in stiffness and strength was noted. These outcomes were also seen in other studies' pure tension tests of FRP bars. At higher temperatures, bigger nominal diameter bars are superior to smaller nominal diameter bars in terms of flexural strength decaying resistance. Although a comparable flexural stiffness degradation was noted as temperature increased.

A novel characterisation protocol of mechanical interactions between the ground and a tibial prosthesis for long jump

The mechanical study of Running Specific Prostheses (RSPs) is often limited to the blade. The setup developed and presented herein is a simple experiment, based on a mechanical testing machine and a camera, that assesses two indicators relevant to coaches and athletes in the field of athletics: secant stiffness and energy dissipation. The influence of four parameters on global prosthesis behaviour is evaluated: the load line offset, the prosthesis-ground angle, the sole type and the flooring type. The load line offset and the flooring type have little to no influence on their behaviour. The prosthesis-ground angle impacts the stiffness: an increase in the angle brings a significant decrease in stiffness, which strongly impacts the performance. The type of sole modifies the kinematics of the blade tip’s interaction with the ground. However, this effect is less likely to enhance the sports practice since athletics imposes the use of spikes. The camera images allow assessing the local behaviour of the sole, thus enabling to follow its strain through the compression process.

Aggrelyte-2 promotes protein solubility and decreases lens stiffness through lysine acetylation and disulfide reduction: Implications for treating presbyopia.

Aging proteins in the lens become increasingly aggregated and insoluble, contributing to presbyopia. In this study, we investigated the ability of aggrelyte-2 (N,S-diacetyl-L-cysteine methyl ester) to reverse the water insolubility of aged human lens proteins and to decrease stiffness in cultured human and mouse lenses. Water-insoluble proteins (WI) of aged human lenses (65-75 years) were incubated with aggrelyte-2 (500 μM) for 24 or 48 h. A control compound that lacked the S-acetyl group (aggrelyte-2C) was also tested. We observed 19%-30% solubility of WI upon treatment with aggrelyte-2. Aggrelyte-2C also increased protein solubility, but its effect was approximately 1.4-fold lower than that of aggrelyte-2. The protein thiol contents were 1.9- to 4.9-fold higher in the aggrelyte-2- and aggrelyte-2C-treated samples than in the untreated samples. The LC-MS/MS results showed Nε -acetyllysine (AcK) levels of 1.5 to 2.1nmol/mg protein and 0.6 to 0.9nmol/mg protein in the aggrelyte-2- and aggrelyte-2C-treated samples. Mouse (C57BL/6J) lenses (incubated for 24 h) and human lenses (incubated for 72 h) with 1.0 mM aggrelyte-2 showed significant decreases in stiffness with simultaneous increases in soluble proteins (human lenses) and protein-AcK levels, and such changes were not observed in aggrelyte-2C-treated lenses. Mass spectrometry of the solubilized protein revealed AcK in all crystallins, but more was observed in α-crystallins. These results suggest that aggrelyte-2 increases protein solubility and decreases lens stiffness through acetylation and disulfide reduction. Aggrelyte-2 might be useful in treating presbyopia in humans.

Atomic force microscopy reveals involvement of the cell envelope in biomechanical properties of sickle erythrocytes

BackgroundIntracellular hemoglobin polymerization has been supposed to be the major determinant for the elevated rigidity/stiffness of sickle erythrocytes from sickle cell anemia (SCA) patients. However, the contribution of the cell envelope remains unclear.ResultsIn this study, using atomic force microscopy (AFM), we compared the normal and sickled erythrocyte surfaces for stiffness and topography. AFM detected that sickle cells had a rougher surface and were stiffer than normal erythrocytes and that sickle cell ghosts had a rougher surface (for both outer and inner surfaces) and were thicker than normal ghosts, the latter implying a higher membrane-associated hemoglobin content/layer in the sickle cell envelope. Compared to healthy subjects, the SCA patients had lower plasma lipoprotein levels. AFM further revealed that a mild concentration of methyl-β-cyclodextrin (MβCD, a putative cholesterol-depleting reagent) could induce an increase in roughness of erythrocytes/ghosts and a decrease in thickness of ghosts for both normal and sickle cells, implying that MβCD can alter the cell envelope from outside (cholesterol in the plasma membrane) to inside (membrane-associated hemoglobin). More importantly, MβCD also caused a more significant decrease in stiffness of sickle cells than that of normal erythrocytes.ConclusionsThe data reveal that besides the cytosolic hemoglobin fibers, the cell envelope containing the membrane-associated hemoglobin also is involved in the biomechanical properties (e.g., stiffness and shape maintenance) of sickle erythrocytes.

EFFECTIVENESS OF PLATELET RICH PLASMA IN PAIN MANAGEMENT OF OSTEOARTHRITIS KNEE: RANDOMIZED COMPARATIVE STUDY

Background: Intra-articular injections of platelet-rich plasma to treat symptoms of knee osteoarthritis have been successfully used in young patients. However, in most of these studies the control and test knees were present in different patients thus incorporating a large amount of bias in the results. Therefore, the present study was designed in which patients with bilateral osteoarthritis knee were included and platelet-rich plasma was administered in one knee and normal saline in another knee of same patient. 20 patients aged 30---65 years with bilateral osteoar Methods: thritis knees (ASA class I and II) of either gender were included in the study. Patients were randomized to receive platelet-rich plasma and normal saline in one of the two knees. The primary outcome was VAS and WOMAC score at 6 months after procedure. The secondary outcome included changes in joint stiffness, physical function, any adverse effects noted during the course of study.p The baseline VAS score in platelet-rich plasma knee was 8.7±0.1which i Results: mproved significantly to 6.4±0.11 (p &lt; 0.001) at 6 months as compared to normal saline knee (p = 0.017). The WOMAC pain score also improved from baseline (17.7±0.15) to over 6 month 14.0±0.11 ( &lt; 0.001) in platelet-rich plasma knee while in the normal saline knee, no significant change occurred from baseline to six months (14.4±0.1 to 14.4±0.1). There was also significant decrease in stiffness and improvement of physical activity in the platelet-rich plasma knee as compared to normal saline knee. The present study showed significant decrease in pain and stiffness and improveme Conclusion: nt of physical functions of knee joint with intra-articular platelet-rich plasma injection as compared to normal saline.

Stiffness and fatigue evaluation in cyclic tests with rest periods for asphalt mixtures with or without fly ash

Fatigue of asphalt materials is evaluated in the laboratory by continuous cyclic loading tests, whereas in the field loading is intermittent. Due to such distinction in the nature of loading and possible differences in material behaviour, further study of the effect of rest periods (RPs) on stiffness and fatigue life is of paramount importance. This paper aimed to investigate the effects of rest periods (RPs) on the fatigue life and on the stiffness evolution of asphalt mixtures, including the use of fly ash. The materials used in this research are: three asphalt binders; two granitic aggregate sources from different quarries; fly ash from a thermal power plant. Stiffness and fatigue tests were performed using a servo-hydraulic press. Stiffness characterisation was performed using complex modulus tests at five different temperatures and six different frequencies. Fatigue tests were performed at 19 °C, considering different maximum strain amplitudes in the specimen. Tests with recovery time (5 RPs of 4 h each) were performed. Complex modulus during all fatigue tests was tracked using small, short-period loadings (compared to fatigue loading) during rest. The results show that after significant stiffness decrease during loading, there is a great (about 90% of the total decrease) stiffness recovery during the 4 h RPs, but this recovery is not associated with an increase in the number of cycles to failure in tests with rest. This indicates other phenomena, probably reversible, are responsible for part of the stiffness change during loading.

Evaluation of exhumed HDPE geomembranes used as a liner in Brazilian shrimp farming ponds

The present work evaluated three high-density polyethylene (HDPE) geomembranes exhumed from two shrimp farming ponds in the northeast of Brazil with nominal thicknesses of 0.8 mm. The CAM sample was exhumed from the bottom liner, and the CAM1 sample was exhumed from the slope liner, both after 8.25 years of field exposure in the same pond. The third sample, called CAM2, was exhumed from another shrimp farming pond after 3.0 years of service. It can be observed that the environmental exposure changed the CAM1 sample’s behavior compared to the CAM sample. Changes in viscosity, stress cracking, and polymer unprotection by the antioxidants demonstrated that the environmental exposure in the field changed the initial conditions of the CAM1 sample. The CAM2 sample presented a high-density value, brittle tensile behavior, and a different thermal behavior from the other samples, as observed by the thermogravimetry (TG). Moreover, the CAM2 sample showed an event in dynamic mechanical analysis (DMA) presenting a significant decrease in stiffness. The first heating of differential scanning calorimetry (DSC) analysis showed an event before the melting points for all samples analyzed. Finally, the application of CAM1 and CAM2 samples as a liner can cause a system failure.

Prolonged Prothrombin Time in DIC: Contributions of Excess Thrombin and Fibrinogen Degradation Products

BackgroundProthrombin time (PT) is a clot-based assay that remains the clinical standard for diagnosis of coagulopathy. Prolongation of PT can be attributed to decreased fibrinogen (Fg) and dysfibrinogenemia but is commonly interpreted as a deficiency in thrombin (FIIa) generation. Paradoxically, conditions in which PT becomes prolonged (e.g., DIC, trauma) are associated with increased FIIa generation. This suggests that prolonged PT may be misleading, and efforts to improve PT in hypocoagulopathy by promoting FIIa generation may be misguided. We modeled the effects on fibrin polymerization related to varying FIIa, Fg, and Fg degradation products (FDPs, such as D-Dimer) in vitro as a platform for understanding the mechanisms underlying hypocoagulopathy.MethodsIn vitro studies were conducted using prothrombin-deficient plasmas, synthetic plasma (Fg and coagulation factors in HEPES buffered saline), and re-assembled whole blood (plasma with fresh RBCs and platelets). Concentrations of synthetic plasma components were varied to model coagulopathic states (Shaz et al. J Trauma 2011;70(6):1401-7; Johansson et al. Crit Care. 2011;15(6):R272). Assays included thromboelastography (TEG), fibrin polymerization (turbidimetry), FIIa generation (calibrated automated thrombogram, CAT), rheology, and PT/INR (Stago STA-R Evolution).ResultsIn vitro simulations of coagulopathy illustrated the significance of each factor on coagulation function. A dose response of FIIa (50-1000 nM) in prothrombin-deficient plasma demonstrated that beyond the normal FIIa range (100-200 nM), excess FIIa did not enhance clot characteristics; in fact, TEG maximum amplitude (clot strength) decreased in a FIIa dose-dependent fashion versus the equivalent dose of prothrombin (p < .001).In synthetic plasma, a similar dose-dependent FIIa effect on fibrin polymerization peak was shown at Fg concentrations of 5 and 3 mg/ml; depleting Fg to 1 mg/ml also showed this effect, but at this level clot formation was extremely poor even with optimal FIIa (Figure 1). The exponential turbidity rise as Fg converts to fibrin resulted in a time-to-peak of ~60 s for all FIIa conc. (time-to-half-peak was < 15 s). For equivalent Fg, increasing FIIa from 120 nM (peak in normal pooled blood) to 250 nM (peak in hemorrhaged coagulopathic patient; Cardenas et al. J Trauma. 2014;77(6):839-45) resulted in decreased total fibrin polymerization (p < .001 between 120 and 250 nM FIIa for all Fg values ≥ 150 mg/dl; Figure 2). With rheology, 150 nM FIIa resulted in rapidly formed clots with a significant decrease in stiffness vs. clots allowed to form by contact activation (135 Pa vs. 4.5 Pa with FIIa; p < .001).When RBCs and platelets were present, the same FIIa dose-dependent effect existed but was highly mitigated with increasing hematocrit (from 0 to 40%). The inhibitory effect of increased FIIa on fibrin polymerization was enhanced by addition of exogenous FDPs in a model of hyperfibrinolysis.ConclusionsProthrombin levels typically drop following severe hemorrhage but are sufficient to produce the active enzyme. These in vitro studies show that the prolongation of PT found in hypocoagulopathy may be a misleading diagnostic; increasing FIIa levels may improve PT but does not improve clot function. The addition of excess FIIa, while rapidly initiating clot formation, results in poorly formed clots.Excess FIIa generated during injury and hemorrhage combined with production of FDPs is mimicked in these in vitro studies, leading to a hypocoagulable state. Additionally, changes in Fg have profound effects on coagulation within the range of 100-300 mg/dl. The inhibitory effects of excess FIIa are worsened with insufficient Fg, aggravated further by D-dimer. Therefore, increases in PT under these circumstances may be attributed to poor fibrin polymerization.Hyperfibrinolysis is problematic, not just because of the breakdown of hemostasis-providing clots, but also due to the effects that FDPs have on future clot formation, particularly amplified at low Fg levels. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Screw-blade fixation systems for implant anchorage in the femoral head: Horizontal blade orientation provides superior stability

ObjectivesDespite continual improvement in the methods and devices used for treatment of proximal femoral fractures, unacceptably high failure rates remain. Novel screw-blade implant systems, combining a lag screw with a blade – the latter adding rotational stability to the femoral head – offer improvement of osseous purchase, especially in osteoporotic bone. The aim of this study was to compare biomechanically the head element (HE) anchorage of two screw-blade implant systems differing in blade orientation in the femoral head – vertical versus horizontal. MethodsTwenty paired human cadaveric femoral heads were assigned to four groups (n = 10), implanted with either Rotationally Stable Screw-Anchor HE (RoSA-HE, vertical blade orientation) or Gamma3 Rotation Control Lag Screw (Gamma-RC, horizontal blade orientation) in center or off-center position, and biomechanically tested until failure under progressively increasing cyclic loading at 2 Hz. ResultsCycles to failure and failure load were significantly higher for Gamma-RC versus RoSA-HE in center position and not significantly different between them in off-center position, p = 0.03 and p = 0.22, respectively. In center position, the progression of both rotation around implant axis and varus deformation over time demonstrated superiority of the implant with horizontal versus vertical blade orientation. Compared with center positioning, off-center implant placement led to a significant decrease in stiffness, cycles to failure and failure load for Gamma-RC, but not for RoSA-HE, p < 0.01 and p = 0.99, respectively. ConclusionHorizontal blade orientation of screw-blade implant systems demonstrates better anchorage in the femoral head versus vertical blade orientation in center position. As the stability of the implant system with horizontal blade orientation drops sharply in off-center position, central insertion is its placement of choice.

Immediate decrease of muscle biomechanical stiffness following dry needling in asymptomatic participants

BackgroundBiomechanical muscle stiffness has been linked to musculoskeletal disorders. Assessing changes in muscle stiffness following DN may help elucidate a physiologic mechanism of DN. This study characterizes the effects of dry needling (DN) to the infraspinatus, erector spinae, and gastrocnemius muscles on biomechanical muscle stiffness. Method60 healthy participants were randomized into infraspinatus, erector spinae, or gastrocnemius groups. One session of DN was applied to the muscle in standardized location. Stiffness was assessed using a MyotonPRO at baseline, immediately post DN, and 24 h later. The presence of a localized twitch response (LTR) during DN was used to subgroup participants. ResultsA statistically significant decrease in stiffness was observed in the gastrocnemius, the LTR gastrocnemius, and the LTR erector spinae group immediately following DN treatment. However, stiffness increased after 24 h. No significant change was found in the infraspinatus group. ConclusionsDN may cause an immediate, yet transitory change in local muscle stiffness. It is unknown whether these effects are present in a symptomatic population or related to improvements in clinical outcomes. Future studies are necessary to determine if a decrease in biomechanical stiffness is related to improvement in symptomatic individuals.

Exercise training to increase stress?

Tendons are series elastic structures that connect bone to muscle and transmit energy by absorbing, transferring, and dissipating energy. Remodeling can be induced from overuse, disuse, or aging, and as a result may change the tendon’s stiffness over an individual’s lifetime. The rate and degree of intrinsic changes in tendons are not well understood. In this study, we investigate the effects of different exercise types on tendon remodeling. We measured tendon gross morphology and mechanics in mice (Mus musculus) using exercise regimens with varying mechanical loading: voluntary wheel running, treadmill running, and repeated jumping. After 4 weeks of training, tendons were harvested for mechanical testing. When individuals were pooled across exercise treatments, there was a significant decrease in stiffness with increasing cross‐sectional area (CSA). Surprisingly, although jump mice had the smallest CSA of the three training regimens, they exhibited the greatest failure stress and stiffness. Treadmill‐training mice had the largest CSA but also the lowest failure stress and stiffness. These data suggest that exercise contributes to physical remodeling of tendon in mice, but the mechanical properties are not correlated strictly with CSA. Our future work will investigate the role of remodeling on intrinsic tendon structure and material properties.

Mechanical properties of polymeric implant materials produced by extrusion-based additive manufacturing

The application of material extrusion-based additive manufacturing methods has recently become increasingly popular in the medical sector. Thereby, thermoplastic materials are likely to be used. However, thermoplastics are highly dependent on the temperature and loading rate in comparison to other material classes. Therefore, it is crucial to characterise these influences on the mechanical properties. On this account, dynamic mechanical analyses to investigate the application temperature range, and tensile tests at different crosshead speeds (103, 101, 10-1 and 10-3 mms-1) were performed on various 3D-printable polymers, namely polyetheretherketone (PEEK), polylactide (PLA), poly(methyl methacrylate) (PMMA), glycol-modified poly(ethylene terephthalate) (PETG), poly(vinylidene fluoride) (PVDF) and polypropylene (PP). It was found that the mechanical properties of PEEK, PLA, PMMA and PETG hardly depend on temperature changes inside the human body. PVDF and PP show a significant decrease in stiffness with increasing body temperatures. Additionally, the dependency of the stiffness on the strain-rate is increasing between PLA, PP, PEEK, PETG, PMMA and PVDF. Besides the mechanical integrity of these materials (strength, stiffness and its strain-rate and temperature dependency inside the body), the materials were further ranked considering their filling density as a measure of their processability. Hence, useful information for the selection of possible medical applications for each material and the design process of 3D-printed implants are provided.

Repair of microdamage caused by cyclic loading in insect cuticle.

It is well known that repeated loading cycles can reduce the strength of a material and cause eventual failure by the gradual build-up of damage. Previous work has shown that mammalian bone is able to extend its life almost indefinitely by continuously repairing microdamage, preventing the development of macroscopic cracks. However, no study has been conducted until now to investigate repair of microdamage in any other biological material. We applied cyclic bending loads to the hind tibiae of desert locusts (Schistocerca gregaria). We observed a significant decrease in the elastic stiffness (Young's modulus) of the cuticle during the five applied loading cycles, indicating that microdamage had been induced. The tibiae were then left to rest for various time periods: 1 hr, 24 hr, 1 week, and 4 weeks. When tested again after up to 24 hr, there was still a significant decrease in stiffness, showing that some microdamage remained. However, in the samples left for 1 week or 4 weeks before retesting, this decrease in stiffness had disappeared, indicating that the microdamage had been repaired. This is the first ever indication that insects are capable of repairing microdamage. It is a highly significant finding-insects such as locusts rely on the stiffness and strength of their hind legs for jumping. This study suggests that, within a time period of order of a few days, the insect can fully restore the mechanical function of an overloaded leg and thus return to normal activities.

Effectiveness of platelet rich plasma in pain management of osteoarthritis knee: double blind, randomized comparative study

BackgroundIntra-articular injections of platelet-rich plasma to treat symptoms of knee osteoarthritis have been successfully used in young patients. However in most of these studies the control and test knees were present in different patients thus incorporating a large amount of bias in the results. Therefore, the present study was designed in which patients with bilateral osteoarthritis knee were included and platelet-rich plasma was administered in one knee and normal saline in another knee of same patient. Methods20 patients aged 30–65 years with bilateral osteoarthritis knees (ASA class I and II) of either gender were included in the study. Patients were randomized to receive platelet-rich plasma and normal saline in one of the two knees. The primary outcome was VAS and WOMAC score at 6 months after procedure. The secondary outcome included changes in joint stiffness, physical function, any adverse effects noted during the course of study. ResultsThe baseline VAS score in platelet-rich plasma knee was 8.4±0.88 which improved significantly to 4.85±2.48 (p<0.001) at 6 months as compared to normal saline knee (p=0.017). The WOMAC pain score also improved from baseline (14.5±1.3) to over 6 month 7.00±4.24 (p<0.001) in platelet-rich plasma knee while in the normal saline knee, no significant change occurred from baseline to six months (10.2±1.2 to 10.05±1.23). There was also significant decrease in stiffness and improvement of physical activity in the platelet-rich plasma knee as compared to normal saline knee. ConclusionThe present study showed significant decrease in pain and stiffness and improvement of physical functions of knee joint with intra-articular platelet-rich plasma injection as compared to normal saline.

Efetividade do plasma rico em plaquetas no tratamento da dor em osteoartrite de joelho: estudo comparativo randômico e duplo‐cego

BackgroundIntra‐articular injections of platelet‐rich plasma to treat symptoms of knee osteoarthritis have been successfully used in young patients. However in most of these studies the control and test knees were present in different patients thus incorporating a large amount of bias in the results. Therefore, the present study was designed in which patients with bilateral osteoarthritis knee were included and platelet‐rich plasma was administered in one knee and normal saline in another knee of same patient. Methods20 patients aged 30‐65 years with bilateral osteoarthritis knees (ASA class I and II) of either gender were included in the study. Patients were randomized to receive platelet‐rich plasma and normal saline in one of the two knees. The primary outcome was VAS and WOMAC score at 6months after procedure. The secondary outcome included changes in joint stiffness, physical function, any adverse effects noted during the course of study. ResultsThe baseline VAS score in platelet‐rich plasma knee was 8.4 ± 0.88 which improved significantly to 4.85 ± 2.48 (p < 0.001) at 6months as compared to normal saline knee (p = 0.017). The WOMAC pain score also improved from baseline (14.5 ± 1.3) to over 6month 7.00 ± 4.24 (p < 0.001) in platelet‐rich plasma knee while in the normal saline knee, no significant change occurred from baseline to six months (10.2 ± 1.2 to 10.05 ± 1.23). There was also significant decrease in stiffness and improvement of physical activity in the platelet‐rich plasma knee as compared to normal saline knee. ConclusionThe present study showed significant decrease in pain and stiffness and improvement of physical functions of knee joint with intra‐articular platelet‐rich plasma injection as compared to normal saline.

Effect of setting accelerator additive on short- and long-term properties of cold recycled mixture containing bitumen emulsion–cement composites

Cold recycled layers have low early stiffness and are prone to rutting at initial days of curing. In this research, it was tried to resolve these issues by concurrent use of cement and chloride-free sodium carbonate-based accelerator. The cement content was fixed to 2% by weight of dry reclaimed asphalt pavement. The accelerator contents varied from 0% to 15% of the cement weight at 5% intervals. Experimental study was conducted on recycled mixes and emulsion–cement pastes. The partial and full curing protocols have been used to simulate the short- and long-term field curing processes, respectively. Marshall stability, indirect tensile strength and resilient modulus tests were accomplished on recycled mixes after both curing protocols and indirect tensile fatigue test was performed after the full curing process. Micro-structural analysis including the X-ray diffraction and scanning electron microscopy were conducted on cured pastes. Furthermore, the hydration heat release was measured by isothermal calorimetric procedure. It was concluded that the existence of emulsion in cement paste to some extent hindered the cement–water reactions. The addition of accelerator evidently increased the rate of cement hydration at initial days of curing and compensated the retarding effects of emulsion. For partially cured specimens, the strength and stiffness of recycled mixes containing accelerator was higher than the conventional mixture. However, a significant decrease in stiffness occurred after finishing the curing process for accelerator containing mixes. The retardation in portlandite development and growth of calcium carbonate crystals were the main reasons for stiffness decrease in these mixes after the full curing process.