Cyclic Compression Research Articles

Experimental assessment of damage and microplastic release during cyclic loading of clear aligners.

The widespread adoption of clear aligners in orthodontic treatments in recent years has necessitated a more precise examination of the mechanical properties of the devices currently available in orthodontics. Recent studies indicate that aligners, when exposed to the forces exerted during swallowing, undergo fatigue-like phenomena, leading to chip formation and cracks. The cumulative damage results in a compromised fit between the tooth and aligner, which is crucial for the effective execution of orthodontic treatment. Additionally, the formation of chips poses a potential risk to patients, as there is a possibility of inadvertently ingesting microplastics that become detached from the aligner over time. This study attempts to assess the release of microplastics from the aligners subjected to cyclic compressive loading. Three different aligners (Essix Ace, Ghost Aligner and Invisalign) are tested to simulate swallowing conditions over the aligner usage period. The mechanical performance is studied in terms of the energy absorbed by the aligner, which shows that the Essix Ace has a stable energy absorption behaviour, while the energy absorbed by the Invisalign is significantly higher than their counterparts. Ghost Aligner did not perform well in the cyclic compression tests. The microplastics (MPs) released by the aligners are examined under an optical microscope. A dimensional analysis based on k-means image segmentation and edge detection algorithm is developed to analyse the MPs. The dimensional analysis of the MPs revealed that the ingestion of the MPs released by all the three aligners does not pose a health risk.

An investigation of the mechanism of adjacent segment disease in a porcine spine model.

Fusion changes the biomechanics of the spine leading to the potential development of adjacent segment disease. Despite many studies on adjacent segment disease, it is largely unknown how spinal fixation affects the mechanical properties of the adjacent disc. The purpose of this study was to assess whether axial compression causes mechanical disruption to the annulus when the caudal spinal level is immobilized or injured. Fifty-two porcine spines were assigned to one of four conditions: 1) control; 2) injured (18.5-gauge needle inserted into the nucleus of cervical 4/5); 3) immobilized (18-gauge steel wire wrapped around the transverse and spinous processes of cervical 4/5); and 4) injured+immobilized. Each specimen was then subjected to 0.5Hz cyclic compression (300-1200N) for two hours. Post-compression, three annular samples were dissected from the cervical 3/4 disc (adjacent to immobilized and/or injured level) and mechanically tested. The same loading protocol and annular testing was also conducted in eight human cadaveric lumbar spines. Immobilization and injury resulted in a reduction in adjacent disc lamellar strength including toe region stress (p<0.001), initial failure stress (p=0.03), and ultimate stress (p=0.004), with immobilization having the greatest impact. Similar findings were observed in the human cadaver samples with reduced toe region strength in the injured+ immobilized samples compared to the control (p=0.049). The current study provides empirical evidence of decreased lamellar strength in the disc adjacent to an immobilized and/or injured level following prolonged cyclic axial loading, lending mechanistic insight into the development of adjacent segment disease.

Mechanical Properties and Vibrational Behavior of 3D-Printed Carbon Fiber-Reinforced Polyphenylene Sulfide and Polyamide-6 Composites with Different Infill Types

The aim of the present study is to investigate the performance of two carbon fiber-reinforced composite polymers used to manufacture end-use parts via the fused filament fabrication (FFF) method. The materials under investigation were carbon fiber-reinforced Polyamide-6 (PA6-CF15) and carbon fiber-reinforced polyphenylene sulfide (PPS-CF15). To evaluate their mechanical properties and vibrational behavior, specimens were fabricated with four distinct infill patterns: grid, gyroid, triangle and hexagon. In particular, the vibrational behavior of the 3D-printed composites was determined by conducting cyclic compression testing, as well as modal tests. Additionally, the mechanical behavior of the reinforced polymers was determined by conducting both uniaxial tensile and compression tests, as well as three-point bending tests. The results of the mechanical experiments revealed that the grid pattern exhibited the best overall performance, while the gyroid pattern exhibited the greatest strength-to-weight ratio, making it the most durable infill for use with composite filaments. In vibration experiments, PA6-CF15 structures exhibited higher damping ratios than PPS-CF15, indicating superior damping capacity. Among the infill patterns, the hexagon pattern provided the greatest vibration isolation performance.

Template-Thermally Induced Phase Separation-Assisted Microporous Regulation in Poly(lactic acid) Aerogel for Sustainable Radiative Cooling.

Herein, an eco-friendly and degradable poly(lactic acid) aerogel was prepared by combining a poly(ethylene glycol) template material with thermally induced phase separation. Due to the tailored pore size introduced by the template material, the aerogel exhibits high solar reflectance (92.0%), excellent thermal emittance (90.5%), low thermal conductivity (52.0 mW m-1 K-1), and high compressive strength (0.15 MPa). Cooling tests demonstrate that the aerogel can achieve temperature drops of 3.7 °C during the day and of 6.2 °C at night. Furthermore, simulations of building cooling energy systems reveal that the aerogel can reduce energy consumption by 2.2 to 10.2 MJ m-2 per year in various cities, achieving energy savings ranging from 8.2 to 24.3%. Meanwhile, the aerogel cooler demonstrates excellent self-cleaning performance (WCA = 149.1°) and cyclic compression performance. This research will promote the field of passive radiative cooling toward a greener and more sustainable direction.

Optimizing Recovery Strategies in Elite Speedskating: A Comparative Analysis of Different Modalities.

Background/Objectives: As short-track speed skaters have to race multiple races to achieve success during competition, optimizing the recovery between efforts is a noteworthy performance determinant. Therefore, we compared three different recovery modalities (active cycling recovery, pneumatic compression boots, and isocapnic breathing protocol) in the context of perceived subjective pain and recovery variables, multiple biochemical and biomechanical indices, CMJ height and power, as well as repeated efforts on the ice track. Methods: Fifteen elite short-track speed skaters (eight males and seven females; age 18.3 ± 1.0 years, height 175.6 ± 7.5 cm, weight 73.7 ± 7.7 kg, 23.8 kg/m2, VO2max 55.5 mL·kg-1·min-1: ♂ 58 20 ± 3.6 mL·kg-1·min-1; and ♀ 53 ± 4.5 mL·kg-1·min-1) completed the study experiment and were included in the analyses. Repeated measures ANOVA with optional post hoc Bonferroni correction was used to assess the association magnitude of changes in variables across the recovery methods. Results: All the investigated protocols were associated with significant changes in multiple recovery indices observed within all the investigated protocols (p ≤ 0.05). However, for this sample, they resulted in analogous effects on subjective variables, hormonal response, creatine kinase, CMJ parameters, and on-ice performance (between-protocol effect: p ≥ 0.002). Changes in creatine kinase were generally higher in males than females (p = 0.05), which might suggest that optimal recovery protocols in short-track are gender-dependent. Conclusions: Since compression and active cycling remain gold standard recovery protocols, a similar response from isocapnic breathing suggests it may be a modality particularly useful in real-world settings.

Fatigue behaviors and cellular damages of bead-welded foam of poly(ether-b-amide) under cyclic compression

Fatigue behaviors and cellular damages of bead-welded foam of poly(ether-b-amide) under cyclic compression

Mechanical-dielectric optimized graphene aerogels with strain-tunable microwave attenuation and shielding functions

We developed graphene aerogels with bridge-lamellar microstructures that provide strain-tunable microwave attenuation and shielding, achieving stable efficiency after cyclic compression and harsh conditions, which is ideal for practical usages.

Mechanical properties and damage characteristics of modified polyurethane concrete under uniaxial and cyclic compression

Mechanical properties and damage characteristics of modified polyurethane concrete under uniaxial and cyclic compression

Precursory characteristics of coal failure using acoustic emission and computed tomography under uniaxial monotonic and cyclic compression

Precursory characteristics of coal failure using acoustic emission and computed tomography under uniaxial monotonic and cyclic compression

A Mechanically Stimulated Co-culture in 3-Dimensional Composite Scaffolds Promotes Osteogenic and Anti-osteoclastogenic Activity and M2 Macrophage Polarization.

Bone is subjected to a plethora of mechanical stresses, which have been found to directly influence the equilibrium between bone resorption and formation. Taking this into account, we present herein a novel biomimicking 3-dimensional model that applies cyclic uniaxial compression onto cells co-cultured on 3-dimensionally printed scaffolds consisting of poly L-lactic acid/poly(ε-caprolactone)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Sr-nanohydroxyapatite. The aim is to investigate how compression can modulate the balance between osteogenesis and osteoclastogenesis in co-culture, as well as the polarization of macrophages. One of the key aspects of the current study is the unprecedented development of a growth-factor-free co-culture, sustainable solely by the cross talk between human bone marrow mesenchymal stem cells and human peripheral blood mononuclear cells for their survival and osteogenic/osteoclastogenic differentiation capacity, respectively. Real-time polymerase chain reaction gene expression analysis of the mechanically stimulated constructs revealed up-regulation of the osteogenesis-related markers osteocalcin, osteoprotegerin, and runt-related transcription factor 2, with concurrent down-regulation of the osteoclastogenic markers dendritic-cell-specific transmembrane protein, nuclear factor of activated T cells 1, and tartrate acid phosphatase. The secretion of the receptor activator of nuclear factor kappa-Β ligand and macrophage colony-stimulating factor, as determined from enzyme-linked immunosorbent assay, was also found to depict lower levels compared to static conditions. Finally, macrophage polarization was examined via confocal imaging of tumor necrosis factor-α and interleukin-10 secretion levels, as well as through nitric oxide synthase and arginase 1 markers' gene expression, with the results indicating stronger commitment toward the M2 phenotype after mechanical stimulation.

On-chip non-contact mechanical cell stimulation - quantification of SKOV-3 alignment to suspended microstructures.

Although the accumulation of random genetic mutations has been traditionally viewed as the main cause of cancer progression, altered mechanobiological profiles of the cells and microenvironment also play a major role as a mutation-independent element. To probe the latter, we have previously reported a microfluidic cell-culture platform with an integrated flexible actuator and its application for sequential cyclic compression of cancer cells. The platform is composed of a control microchannel in a top layer for introducing external pressure, and a polydimethylsiloxane (PDMS) membrane from which a monolithically-integrated actuator protrudes downwards into a cell-culture microchannel. When actuated, the integrated actuator, referred to as micro-piston, transfers the pressure from the control channel as a mechanical force to the cells underneath. When not actuated, the micro-piston remains suspended above cells, separated from the latter via a liquid-filled gap of ∼108 μm. Despite the lack of direct physical contact between the micro-piston and cells in the latter arrangement, we observed distinct alignment of SKOV-3 ovarian cancer cells to the piston shape. To characterize this observation, micro-piston localization, shape, and size were adjusted and the directionality of a mono-layer of SKOV-3 cells relative to the suspended structure was probed. Cell alignment analysis was performed in a novel, label-free approach by measuring elongation angles of whole cell bodies with respect to micro-piston peripheries. Alignment of SKOV-3 cells to the structure outline was significant for circular, triangular and square micro-piston when compared to control areas without micro-piston on the same chip. The effect was present irrespective of whether cells were loaded with micro-pistons in static position (∼108 μm gap) or actively retracted using vacuum (>108 μm gap). Similar alignment was not observed for MCF7 cancer cells and MCF10A non-cancerous epithelial cells. The reported observation of directional movement and growth of SKOV-3 cells towards the region under micro-pistons point towards a to-date unexplored mechanotactic behavior of these cells, warranting future investigations regarding the mechanisms involved and the role these may play in cancer.

Moisture effects on the transverse compressive behaviour of single flax fibres

Studying the effects of moisture on the mechanical behaviour of single flax fibres, particularly in the transverse direction, is of key importance for the reliable use of biobased composites exposed to varying humidity levels. In this study, the apparent transverse Young’s modulus evolution of single flax fibres is recorded through repeated compressive load/unload cycles conducted at three Relative Humidity (RH) levels— 40%, 60%, and 80%. No significant changes in the apparent Young’s modulus, determined from the unloading, were observed during transverse compression cycling or under increasing humidity conditions. The absence of apparent softening with the rise in RH is attributed to the expression of two antagonistic mechanisms: wall softening due to plasticisation and structural stiffening linked to fibre compaction. Intriguingly, a noteworthy transverse stiffening is recorded at 40% RH following the humidification and drying of the fibre. This outcome is ascribed to a hornification phenomenon.

Evaluation of 3D robotic spray parameters on the performance of the developed sensing functional cementitious coating

ABSTRACT This study explores the innovative use of 3D robotic spray for applying self-sensing cementitious coating, emphasising its potential for multifunctional smart concrete applications. The effects of spray parameters on the performance of self-sensing cementitious composites were investigated by systematically examining the impact of nozzle travel speed, air injection pressure, nozzle standoff distance, and spray direction on the self-sensing coating. In-depth analyses were conducted on mechanical strength, coating adhesion properties, and sensing performance. Micro-CT was performed to investigate the coating's inherent porosity. This study evaluated the sensing performance of the coatings by analysing their piezoresistive behaviour under cyclic compression and bending. Furthermore, it demonstrated the coating's capacity for real-time structural health monitoring by evaluating its performance under compressive and bending stresses until failure. This research underscores the significant impact of spray parameters on optimising the sensing capabilities of the self-sensing spray coating, highlighting its potential for advanced real-time structural health monitoring.

Degradation study of gas-diffusion layers in proton exchange membrane fuel cell through acid dissolution and oxidation

ABSTRACT Durability is one of the key factors influencing the commercialization of fuel cells. Since the gas-diffusion layer (GDL) in fuel cells operates in a high-temperature, high-humidity, acidic environment, performance deterioration occurs over time due to the dissolution and corrosion. This study carried out an aging degradation for 500 h at 80°C in a 1 mol/L H2SO4 and 15% H2O2 solution, and comprehensive experimental investigations were conducted on multiple parameters including the characteristic (thickness, density), mechanical (tensile, cyclic compression), electrical and permeability properties before and after the aging test. It was discovered that the GDL exhibited varying degrees of changes in a range of physicochemical characteristics, including thickness thinning, significant mechanical property attenuation, decreased hydrophobicity, increased electrical conductivity, etc. Microstructural characterization techniques were utilized to investigate the aging morphological features and pore size distributions in order to further explicate these variations. This analysis supports the degradation of the macroscopic physicochemical attributes from the microscopic level. This study is of great practical significance for revealing the durability degradation mechanism of GDL and optimizing the structural design and material screen.

In Vitro Induction of Hypertrophic Chondrocyte Differentiation of Naïve MSCs by Strain.

In the context of bone fractures, the influence of the mechanical environment on the healing outcome is widely accepted, while its influence at the cellular level is still poorly understood. This study explores the influence of mechanical load on naïve mesenchymal stem cell (MSC) differentiation, focusing on hypertrophic chondrocyte differentiation. Unlike primary bone healing, which involves the direct differentiation of MSCs into bone-forming cells, endochondral ossification uses an intermediate cartilage template that remodels into bone. A high-throughput uniaxial bioreactor system (StrainBot) was used to apply varying percentages of strain on naïve MSCs encapsulated in GelMa hydrogels. This research shows that cyclic uniaxial compression alone directs naïve MSCs towards a hypertrophic chondrocyte phenotype. This was demonstrated by increased cell volumes and reduced glycosaminoglycan (GAG) production, along with an elevated expression of hypertrophic markers such as MMP13 and Type X collagen. In contrast, Type II collagen, typically associated with resting chondrocytes, was poorly detected under mechanical loading alone conditions. The addition of chondrogenic factor TGFβ1 in the culture medium altered these outcomes. TGFβ1 induced chondrogenic differentiation, as indicated by higher GAG/DNA production and Type II collagen expression, overshadowing the effect of mechanical loading. This suggests that, under mechanical strain, hypertrophic differentiation is hindered by TGFβ1, while chondrogenesis is promoted. Biochemical analyses further confirmed these findings. Mechanical deformation alone led to a larger cell size and a more rounded cell morphology characteristic of hypertrophic chondrocytes, while lower GAG and proteoglycan production was observed. Immunohistology staining corroborated the gene expression data, showing increased Type X collagen with mechanical strain. Overall, this study indicates that mechanical loading alone drives naïve MSCs towards a hypertrophic chondrocyte differentiation path. These insights underscore the critical role of mechanical forces in MSC differentiation and have significant implications for bone healing, regenerative medicine strategies and rehabilitation protocols.

Evidence for the cumulene cyclo[n]carbon formation in a compression reactor during the pyrolysis of acetylene in neon atmosphere

The article is dedicated to the experimental study of ultra-small carbon particles, containing from several to several tens of carbon atoms. In the absence of sufficient experimental data in this area, the theoretical notion considers carbon polyene structures as of flat rings with alternating triple and single bonds between carbon atoms and an even number of carbon atoms in ring structures as being the more favorable energy-wise. However, currently reliable evidence of the true structure of carbon rings that can occur naturally is lacking. Here, we show that the carbon nanoparticle synthesis by pyrolysis of gaseous hydrocarbons in a cyclic piston-cylinder compression reactor produces carbon rings with double bonds between carbon atoms, i.e. with a cumulene structure, contrary to the current theoretical notion. We believe that the cumulene structures are more favorable energy-wise due to the specific shape of carbon rings, which appear as a Grover washer or a helix turn. Our results are corroborated by MALDI-TOF mass spectrometry, IR spectroscopy, and high-resolution transmission electron microscopy of the samples obtained, as well as by density functional theory calculations. We believe that our work will bring more clarity to the issues surrounding the formation of carbon particles of the smallest sizes.

PH-responsive antibacterial emulsion gel based on cinnamaldehyde and carboxymethyl chitosan for fruits preservation applications.

Although the natural antibacterial agent, cinnamaldehyde, has been extensively studied in the field of food packaging, its water solubility and instability limit its further applications. The controllable responsive release can be achieved through encapsulation in responsive emulsion systems based on carboxymethyl chitosan. Herein, a pH-responsive antibacterial emulsion gel was constructed from cinnamaldehyde-loaded oil-in-water emulsion templates. The interfacial imidization between carboxymethyl chitosan and cinnamaldehyde forms a pH-responsive Schiff base and further stabilizes the emulsion. To immobilize the droplets, acrylamide was subsequently added and polymerized. Such a double network design gives materials adjustable mechanical strength in addition to sealing off the cinnamaldehyde droplets in the network to postpone their release. According to the results of the tensile and compressive cycle, this material has good fatigue resistance. Furthermore, the antibacterial results showed that this material has a 15-day antibacterial cycle and long-lasting antibacterial qualities. In practical applications, acidic moisture from the fruits' respiration decomposes Schiff base bonds and accelerates the release of cinnamaldehyde. The results of cinnamaldehyde release proved that the emulsion gel was pH-responsive, and the dynamic covalent network and emulsion encapsulation technology prolonged the release period of cinnamaldehyde. The mechanical test results proved that the acrylamide network structure gave the material good mechanical properties. Using longan and citrus fruits as examples, we found emulsion gel can significantly prolong the life of fruits by two to three times.

A Flexible Sensing Material with High Force and Thermal Sensitivity Based on GaInSn in Capillary Embedded in PDMS.

Flexible sensing materials have become a hot topic due to their sensitive electrical response to external force or temperature and their promising applications in flexible wear and human-machine interaction. In this study, a PDMS/capillary GaInSn flexible sensing material with high force and thermal sensitivity was prepared utilizing liquid metal (LM, GaInSn), flexible silicone capillary, and polydimethylsiloxane (PDMS). The resistance (R) of the flexible sensing materials under the action of different forces and temperatures was recorded in real-time. The electrical performance results confirmed that the R of the sensing material was responsive to temperature changes and increased with the increasing temperature, indicating its ability to transmit temperature signals into electrical signals. The R was also sensitive to the external force, such as cyclic stretching, cyclic compression, cyclic bending, impact and rolling. The ΔR/R0 changed periodically and stably with the cyclic stretching, cyclic compression and cyclic bending when the conductive pathway diameter was 0.5-1.0 mm, the cyclic tensile strain ≤ 20%, the cyclic tensile rate ≤ 2.0 mm/min, the compression ratio ≤ 0.5, and the relative bending curvature ≤ 0.16. Moreover, the material exhibited sensitivity in detecting biological signals, such as the joint movements of the finger, wrist, elbow and the stand up-crouch motion. In conclusion, this work provides a method for preparing a sensing material with the capillary structure, which was confirmed to be sensitive to force and heat, and it produced different types of R signals under different deformations and different temperatures.

The role of loading-induced convection versus diffusion on the transport of small molecules into the intervertebral disc

PurposeLimited nutrient transport is hypothesized to be involved in intervertebral disc (IVD) degeneration. It is widely recognized that the dominant mode of transport of small molecules such as glucose is via diffusion, rather than convection. However, recent findings suggest a role for convection-induced by fast (motion-related) and slow (diurnal) dynamic loading in molecular transport of even such small solutes. The aim of this study was to investigate whether fluid exchange induced by simulated physiological loading (composed of both fast cyclic or slower diurnal loading) can influence the molecular transport of a small molecule through the cartilage endplate (CEP) into the nucleus pulposus (NP) of IVDs. MethodsThe molecular transport of fluorescein through the CEP and into the NP was studied in a bovine CEP/NP explant model and loading was applied by an axial compression bioreactor. The loaded explants (convection and diffusion) were compared to unloaded explants (diffusion alone).ResultsIn the initial 24 h, there were no differences between loaded and unloaded explants, indicating that convection did not enhance molecular transport of small solutes over diffusion alone. Notably, after 48 h which corresponds to two complete diurnal cycles of tissue compression, fluid exudation/imbibing and redistribution, the fluorescein concentration was significantly increased in the top and bottom layer of the explant, when compared to the unloaded explant.ConclusionsSlower diurnal cyclic compression of the IVD might enhance the transport of small molecules into the IVD although it could not be discerned whether this was due to diffusion/convection or a combination.

A Composite Foam of Dermal Matrix-Demineralized Bone Matrix for Enhanced Bone Regeneration.

Allogenic demineralized bone matrix (DBM) is widely used for bone repair and regeneration due to its osteoinductivity and osteoconductivity. The present study utilized acellular dermis microfibers to improve the DBM's clinical handling properties and to enhance bone regeneration. Donated human cadaver skin was de-epidermized and decellularized to be acellular dermal matrix (ADM), which was further processed into microfibers. Donated human bone was micronized and partially demineralized (∼30% calcium removal) for optimal bone regeneration. A flexible ADM/DBM composite foam was fabricated with ADM microfibers and DBM particles. Structural analysis found that the ADM/DBM composite foam had proper porosity with interconnected micropores and rapid wettability, and good stability upon cyclic compressions, whereas cytotoxicity test, in vitro collagenase degradation, and rat subcutaneous implantation showed good biocompatibility and biodegradability. The composite foam, used for in vitro coculture, significantly increased the alkaline phosphatase activity of C2C12 cells and upregulated the expression of osteogenesis-related genes of human umbilical cord mesenchymal stem cells. Using the rat Φ8 mm calvarium defect repair model, the ADM/DBM composite foam demonstrated superior osteogenicity by rapidly inducing new bone formation and achieving complete closure of the bone defects, as compared with the commercially available bone graft for skull repair (SkuHeal). Therefore, the ADM/DBM composite foam holds promise as a superior DBM-based product for repairing critical bone defects.