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“Foam Rolling” has been used in sports settings to increase range of motion and decrease muscle stiffness without decreasing muscle strength and athletic performance. However, there has been no study investigating the acute and prolonged effect of different durations of foam rolling intervention on muscle stiffness, and the minimum foam rolling intervention duration required to decrease muscle stiffness is unclear. Therefore, the purpose of this study was to investigate the acute and prolonged effect of different durations of foam rolling intervention on ROM, muscle stiffness, and muscle strength. The 45 participants were randomly allocated to 1 of 3 groups (30 s × 1 times group vs 30 s × 3 times group vs 30 s× 10 times group). The outcome measures were dorsiflexion range of motion, shear elastic modulus of medial gastrocnemius, and muscle strength before, 2 min and 30 min after foam rolling intervention. There were no significant differences before and 2 min after foam rolling intervention in 30 s×1 time group, whereas dorsiflexion range of motion was increased in both 30 s×3 times group (p = 0.042, d = 0.26) and 30 s× 10 times group (p < 0.01, d = 0.33). However, the increase in dorsiflexion range of motion was returned to baseline value after 30 minutes in both 30 s × 3 times group and 30 s × 10 times group. In addition, there were no significant changes in shear elastic modulus and muscle strength in all groups. This study suggested that foam rolling for more than 90 s or more of foam rolling was effective in order to increase the range of motion immediately without changing muscle stiffness and muscle strength.

In this paper, we describe the effects of the combination of topographical, mechanical, chemical and intracellular electrical stimuli on a co-culture of fibroblasts and skeletal muscle cells. The co-culture was anisotropically grown onto an engineered micro-grooved (10 µm-wide grooves) polyacrylamide substrate, showing a precisely tuned Young's modulus (∼ 14 kPa) and a small thickness (∼ 12 µm). We enhanced the co-culture properties through intracellular stimulation produced by piezoelectric nanostructures (i.e., boron nitride nanotubes) activated by ultrasounds, thus exploiting the ability of boron nitride nanotubes to convert outer mechanical waves (such as ultrasounds) in intracellular electrical stimuli, by exploiting the direct piezoelectric effect. We demonstrated that nanotubes were internalized by muscle cells and localized in both early and late endosomes, while they were not internalized by the underneath fibroblast layer. Muscle cell differentiation benefited from the synergic combination of topographical, mechanical, chemical and nanoparticle-based stimuli, showing good myotube development and alignment towards a preferential direction, as well as high expression of genes encoding key proteins for muscle contraction (i.e., actin and myosin). We also clarified the possible role of fibroblasts in this process, highlighting their response to the above mentioned physical stimuli in terms of gene expression and cytokine production. Finally, calcium imaging-based experiments demonstrated a higher functionality of the stimulated co-cultures.

Rutin, a quercetin glycoside is a member of the bioflavonoid family which is known to possess antioxidant properties. In the present study, we aimed to confirm the anti-aging effects of rutin on human dermal fibroblasts (HDFs) and human skin. We examined the effects of rutin using a cell viability assay, senescence-associated-β-galactosidase assay, reverse transcription-quantitative polymerase chain reaction, and by measuring reactive oxygen species (ROS) scavenging activity in vitro. To examine the effects of rutin in vivo, rutin-containing cream was applied to human skin. A double-blind clinical study was conducted in 40 subjects aged between 30-50 years and divided into control and experimental groups. The test material was applied for 4 weeks. After 2 and 4 weeks, dermal density, skin elasticity, the length and area of crow's feet, and number of under-eye wrinkles following the application of either the control or the rutin-containing cream were analyzed. Rutin increased the mRNA expression of collagen, type I, alpha 1 (COL1A1) and decreased the mRNA expression of matrix metallopeptidase 1 (MMP1) in HDFs. We verified that ROS scavenging activity was stimulated by rutin in a dose-dependent manner and we identified that rutin exerted protective effects under conditions of oxidative stress. Furthermore, rutin increased skin elasticity and decreased the length, area and number of wrinkles. The consequences of human aging are primarily visible on the skin, such as increased wrinkling, sagging and decreased elasticity. Overall, this study demonstrated the biological effects of rutin on ROS-induced skin aging.

Loading leads to tendon adaptation but the influence of load-intensity and contraction type is unclear. Clinicians need to be aware of the type and intensity of loading required for tendon adaptation when prescribing exercise. The aim of this study was to investigate the influence of contraction type and load-intensity on patellar tendon mechanical properties. Load intensity was determined using the 1 repetition maximum (RM) on a resistance exercise device at baseline and fortnightly intervals in four randomly allocated groups of healthy, young males: (1) control (no training); (2) concentric (80% of concentric–eccentric 1RM, 4×7–8); (3) standard load eccentric only (80% of concentric-eccentric 1RM, 4×12–15 repetitions) and (4) high load eccentric (80% of eccentric 1RM, 4×7–8 repetitions). Participants exercised three times a week for 12 weeks on a leg extension machine. Knee extension maximum torque, patellar tendon CSA and length were measured with dynamometry and ultrasound imaging. Patellar tendon force, stress and strain were calculated at 25%, 50%, 75% and 100% of maximum torque during isometric knee extension contractions, and stiffness and modulus at torque intervals of 50–75% and 75–100%. Within group and between group differences in CSA, force, elongation, stress, strain, stiffness and modulus were investigated. The same day reliability of patellar tendon measures was established with a subset of eight participants. Patellar tendon modulus increased in all exercise groups compared with the control group (p<0.05) at 50–75% of maximal voluntary isometric contraction (MVIC), but only in the high eccentric group compared with the control group at 75–100% of MVIC (p<0.05). The only other group difference in tendon properties was a significantly greater increase in maximum force in the high eccentric compared with the control group (p<0.05). Five repetition maximum increased in all groups but the increase was significantly greater in the high load eccentric compared with the other exercise groups (p<0.05). Load at different intensity levels and contraction types increased patellar tendon modulus whereas muscle strength seems to respond more to load-intensity. High load eccentric was, however, the only group to have significantly greater increase in force, stiffness and modulus (at the highest torque levels) compared with the control group. The effects and clinical applicability of high load interventions needs to be investigated further.

Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe's principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction.

PurposeTo determine the interrelation of different elastic moduli of the cornea and to investigate their dependency on corneal hydration.MethodsRabbit eyes were divided into four groups. Corneas were excised and mounted into a Barron artificial anterior chamber. Various corneal hydration steady states were achieved with different dextran T-500 concentrations in the anterior chamber, as well as on the corneal anterior surface. The treatment-solutions of each group contained either 5, 10, 15, or 20% w/w dextran. Ultrasound pachymetry was used to measure central corneal thickness. Brillouin microscopy of the central cornea determined the longitudinal bulk modulus by means of Brillouin frequency shift. Subsequently, a 5-mm-wide central strip was taken for extensiometry to measure the tangential elastic modulus.ResultsThe longitudinal bulk modulus was 1.2-times higher in corneas dehydrated with 20% dextran compared to those hydrated with 5% dextran. In contrast, the tangential elastic modulus increased by 4.4 times. The obtained longitudinal bulk moduli were two orders of magnitude bigger than the tangential elastic moduli. Regression analysis of longitudinal bulk modulus and tangential elastic modulus revealed a quadratic relation. The bulk modulus seemed to be independent of tension, whereas the elastic modulus was tension-dependent. Greater corneal hydration led to significantly thicker pachymetry.ConclusionCorneal biomechanics are highly dependent on the level of corneal hydration. Surprisingly, tangential elastic moduli were more sensitive to hydration changes than longitudinal bulk moduli. A quadratic relation was found between both moduli.

Children born with a small or absent ears undergo surgical reconstruction to restore their auricle. Currently, rib (costal) cartilage is used to carve the auricle. However as alternative, tissue engineered and synthetic materials are being developed to restore the auricle shape to overcome donor site morbidity and limited availability of rib cartilage. However, to date there is limited knowledge regarding the mechanical properties of the auricular and costal cartilage to optimise the required compressive properties of the graft. The remnant auricular and costal cartilage from 20 patients undergoing stage-1 microtia surgery was harvested. On the day of surgery, the cartilage was evaluated in compression, with each sample loaded to 300 g at 1 mm/s. The costal cartilage was observed to have a significantly higher Young’s Elastic Modulus than auricular cartilage (average costal cartilage 11.43 MPa vs average auricular cartilage 2 MPa, p < 0.0001). The auricular cartilage showed a significantly higher relaxation rate than costal cartilage (average costal cartilage 0.72 MPa10-4 vs average auricular cartilage 1.93 MPa10-4, p < 0.05). The final absolute relaxation was significantly lower for elastic cartilage than costal cartilage (average costal cartilage 3.35 MPa vs average auricular cartilage 0.2 MPa, p < 0.0001). Alloplastic cartilage replacements used as alternatives for reconstruction were also evaluated. Silicone, Gore-Tex and Medpor were observed to have significantly higher Young’s Elastic Modulus than costal and auricular cartilage. Costal cartilage has a higher Young’s Elastic Modulus in compression compared to auricular cartilage. Current synthetic materials used to replace synthetic cartilage do not mimic costal cartilage, which should be addressed in the future.

Although muscle–tendon slack length is a crucial parameter used in muscle models, this is one of the most difficult measures to estimate in vivo. The aim of this study was to determine the onset of the rise in tension (i.e., slack length) during passive stretching in both Achilles tendon and gastrocnemius medialis. Muscle and tendon shear elastic modulus was measured by elastography (supersonic shear imaging) during passive plantarflexion (0° and 90° of knee angle, 0° representing knee fully extended, in a random order) in 9 participants. The within-session repeatability of the determined slack length was good at 90° of knee flexion (SEM=3.3° and 2.2° for Achilles tendon and gastrocnemius medialis, respectively) and very good at 0° of knee flexion (SEM=1.9° and 1.9° for Achilles tendon and gastrocnemius medialis, respectively). The slack length of gastrocnemius medialis was obtained at a significantly lower plantarflexed angle than for Achilles tendon at both 0° (P<0.0001; mean difference=19.4±3.8°) and 90° of knee flexion (P<0.0001; mean difference=25.5±7.6°). In conclusion, this study showed that the joint angle at which the tendon falls slack can be experimentally determined using supersonic shear imaging. The slack length of gastrocnemius medialis and Achilles tendon occurred at different joint angles. Although reporting this result is crucial to a better understanding of muscle–tendon interactions, further experimental investigations are required to explain this result.

Introduction The elastic behavior of mortars, conforming to ASTM standards, incorporating up to 10% recycled rubber with and without interfacial compatibilizing additives, was investigated through quasi-static and dynamic testing methods. Materials and Methods Various thermosetting resins (epoxy, phenol–formaldehyde, and unsaturated polyester) were employed as interfacial compatibilizing additives to enhance rubber's performance as an aggregate. Mechanical tests (TM) including axial compression and flexion, longitudinal and torsional impulse excitation technique (IET), and dynamic mechanical thermal analysis (DMTA) were conducted to assess properties such as quasi-static (QEM) and dynamic elastic moduli (DEM), storage moduli (E′), and loss factors (Tan δ). Results The study revealed significant enhancements in the composites, particularly in terms of elastic modulus performance, as a result of interfacial compatibilization. The materials developed in this study hold promise for applications in engineering and construction sectors, facilitating improved dissipation and damping of energy in the form of vibration in mortar composites while also addressing environmental concerns by integrating recycled materials. Conclusion Incorporating interfacial compatibilizing additives into mortars with recycled rubber offers notable improvements in elastic behavior, presenting opportunities for applications in various industries concerned with materials performance and sustainability.

In many geological conditions, obtaining the static elastic moduli of crustal rocks is an essential subject for accurate mechanical analyses of crust. The elastic wave method may be the best choice if rock specimens cannot be taken since elastic wave propagation can be applied to in-situ environments. Although many signs of progress have been made in the elastic wave method, some issues still restrict the accurate extraction of static moduli and its applications. A review of this method and its further research prospect is urgently needed. With this purpose, this paper summarized and analyzed the published experimental data about the relationship between the static and dynamic Young’s moduli of rock, and the frequency dependence of wave velocities and dynamic elastic moduli. P- and S-wave velocities, Young’s, and bulk moduli of rock, especially the saturated rock, have strong frequency dependence in a wide frequency range of 10 –6 –10 6  Hz. Different rocks or conditions (such as water content, amplitude, and pressure), have different frequency-dependent characteristics. The current elastic wave method can be classified into two methods: the empirical correlation method and the multifrequency ultrasonic method. The basic principle, advantages, and disadvantages of both methods are analyzed. Especially, the reasonability of the multifrequency ultrasonic method was elaborated given the nonlinear elasticity, strain level/rate, and pores/cracks in rock materials. Existing problems and prospects on the two methods are also pointed out, such as the choice of a proper empirical correlation, accurate determination of the critical P- and S-wave velocities, the prediction of Young’s modulus at each strain level, and the reasonability of the method under various water contents and fracture structures.