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1.
Eur J Orthod ; 46(4)2024 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-39011819

RESUMO

BACKGROUND: Extraction space closure is a challenging phase during orthodontic treatment that affects not only the total treatment duration but also the whole treatment outcome. OBJECTIVE: To compare the efficiency of friction and frictionless mechanics during en-masse retraction of maxillary anterior teeth in adult patients with bimaxillary dentoalveolar protrusion. TRIAL DESIGN: Two-arm parallel group, single-center randomized clinical trial. MATERIALS AND METHODS: Thirty-two adult patients with bimaxillary protrusion were recruited and randomly allocated to two different retraction mechanics. A friction group, using NiTi coil springs and a frictionless group using closing T-loops for en-masse retraction. Randomization in a 1:1 ratio was generated by Microsoft Excel. The randomization numbers were secured in opaque sealed envelopes for allocation concealment. Retraction started in all patients following first premolars extraction using miniscrews as a source of indirect anchorage. Activation was done on a monthly basis until complete retraction of anterior segment. The rate of retraction, amount of anchorage loss, the dental, and soft tissue changes were analyzed on digital models and lateral cephalograms taken before retraction and after space closure. BLINDING: The outcome assessor was blinded through data concealment during assessment. RESULTS: Two patients were lost to follow up, so 30 patients completed the trial. The rate of anterior segment retraction was 0.88 ±â€…0.66 mm/month in the frictionless group compared to 0.72 ±â€…0.36 mm/month in the friction group which was statistically significant. Anchorage loss of 1.18 ±â€…0.72 mm in the friction group compared to 1.29 ±â€…0.55 mm in the frictionless group with no significant difference. Comparable dental and soft tissue changes following en-masse retraction were reported in both groups, with no statistically significant difference. HARM: one patient complained of soft tissue swelling following miniscrew insertion, but the swelling disappeared after one week of using mouth wash. LIMITATION: The study focused only on the maxillary arch. CONCLUSION: Both mechanics have successfully achieved the required treatment objectives in patients with bimaxillary dentoalveolar protrusion. Frictionless group showed a faster rate of retraction than the friction group, which was statistically but not clinically significant. TRIAL REGISTRATION: Clinicaltrials.gov with the identifier NCT03261024.


Assuntos
Fricção , Maxila , Técnicas de Movimentação Dentária , Humanos , Masculino , Feminino , Adulto , Técnicas de Movimentação Dentária/métodos , Técnicas de Movimentação Dentária/instrumentação , Adulto Jovem , Fechamento de Espaço Ortodôntico/métodos , Fechamento de Espaço Ortodôntico/instrumentação , Procedimentos de Ancoragem Ortodôntica/instrumentação , Procedimentos de Ancoragem Ortodôntica/métodos , Má Oclusão Classe I de Angle/terapia , Má Oclusão Classe I de Angle/fisiopatologia , Desenho de Aparelho Ortodôntico , Fios Ortodônticos , Cefalometria/métodos , Resultado do Tratamento , Níquel , Titânio
2.
PLoS One ; 19(7): e0300516, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-39008493

RESUMO

To improve the accuracy of the Hami melon discrete element model, the parameters of the Hami melon seed discrete element model were calibrated by combining practical experiments and simulation tests. The basic physical parameters of Hami melon seeds were obtained through physical experiments, including triaxial size, 100-grain mass, moisture content, density, Poisson's ratio, Young's modulus, shear modulus, angle of repose, suspension speed and various contact parameters. Taking the repose angle of seed simulation as an index, the parameters of each simulation model were significantly screened by the Plackett-Burman test. The results showed that the recovery coefficient, static friction coefficient and rolling friction coefficient of Hami melon seeds had significant effects on repose angle. Based on the steepest climbing test and quadratic regression orthogonal rotation combination test, it was determined that the significant order of the influence of various contact parameters on the angle of repose was static friction coefficient, collision recovery coefficient, and rolling friction coefficient. The optimal parameter combination was obtained through the mathematical regression model between the angle of repose and various contact parameters, namely, the collision recovery coefficient of Hami melon seeds was 0.518, the static friction coefficient of Hami melon seeds was 0.585 and the rolling friction coefficient of Hami melon seeds was 0.337. Under this condition, three static seed-dropping experiments and dynamic rolling accumulation experiments were carried out. The average simulated angle of repose was 31.93°, and the relative error with the actual value was only 1.71%. The average simulated rolling accumulation angle was 51.98°, and the relative error with the actual value was only 1.92%.


Assuntos
Cucurbitaceae , Sementes , Cucurbitaceae/fisiologia , Sementes/fisiologia , Calibragem , Simulação por Computador , Módulo de Elasticidade , Modelos Teóricos , Fricção
3.
J Oleo Sci ; 73(7): 1015-1026, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38945920

RESUMO

Herein, we evaluated friction dynamics of human skin treated with polyacrylic acid aqueous solutions or gel creams using a sinusoidal motion friction evaluation system to demonstrate the effect of treatment with polymer aqueous solutions on human skin. A polymer aqueous solution or gel cream was applied to the inner forearms of 10 subjects to evaluate temporal changes in friction force under sinusoidal motion. Water content, skin viscoelasticity, and transepidermal water loss were also simultaneously measured to determine the effects on skin conditions. When human skin was treated with the polymer aqueous solution, the friction coefficient immediately after treatment was 0.69-0.99 and the delay time δ, a normalized parameter of the time difference in the delayed response of friction to the movement of the contact probe divided by the friction time T 0 for one round trip, was 0.171-0.179, which was greater than that of untreated skin. This increase was caused by the swelling and softening of the stratum corneum caused by the penetration of water in the polymer aqueous solution, which increased true contact area between the skin and contact probe. A significant difference was observed in the friction coefficient of the skin immediately after treatment with different polymer aqueous solutions. Among polymers (P1-P4), P4, which has a low-salt resistance and low yield stress, had the lowest friction coefficient because of collapsing of the polymer network structures by shearing and reduced viscosity owing to salts on human skin. The skin treated with a gel cream also exhibited a greater friction coefficient than the untreated skin immediately after treatment and 90 min later. This phenomenon can be caused by the occlusive effect of the oil in the gel cream.


Assuntos
Resinas Acrílicas , Fricção , Soluções , Água , Humanos , Viscosidade , Resinas Acrílicas/química , Pele/efeitos dos fármacos , Elasticidade , Adulto , Feminino , Masculino , Polímeros/química , Creme para a Pele/química , Géis , Perda Insensível de Água/efeitos dos fármacos
4.
Sci Rep ; 14(1): 13273, 2024 06 10.
Artigo em Inglês | MEDLINE | ID: mdl-38858470

RESUMO

In this study, we conducted a numerical analysis on catheter sizes using computational fluid dynamics to assess urinary flow rates during intermittent catheterization (IC). The results revealed that the fluid (urine) movement within a catheter is driven by intravesical pressure, with friction against the catheter walls being the main hindrance to fluid movement. Higher-viscosity fluids experienced increased friction with increasing intravesical pressure, resulting in reduced fluid velocity, whereas lower-viscosity fluids experienced reduced friction under similar pressure, leading to increased fluid velocity. Regarding urine characteristics, the results indicated that bacteriuria, with lower viscosity, exhibited higher flow rates, whereas glucosuria exhibited the lowest flow rates. Additionally, velocity gradients decreased with increasing catheter diameters, reducing friction and enhancing fluid speed, while the friction increased with decreasing diameters, reducing fluid velocity. These findings confirm that flow rates increased with larger catheter sizes. Furthermore, in terms of specific gravity, the results showed that a 12Fr catheter did not meet the ISO-suggested average flow rate (50 cc/min). The significance of this study lies in its application of fluid dynamics to nursing, examining urinary flow characteristics in catheterization. It is expected to aid nurses in selecting appropriate catheters for intermittent catheterization based on urinary test results.


Assuntos
Hidrodinâmica , Humanos , Cateteres Urinários , Viscosidade , Cateterismo Urinário/instrumentação , Cateterismo Urinário/métodos , Urina/química , Catéteres , Fricção
5.
Elife ; 122024 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-38864737

RESUMO

Filamentous cyanobacteria are one of the oldest and today still most abundant lifeforms on earth, with manifold implications in ecology and economics. Their flexible filaments, often several hundred cells long, exhibit gliding motility in contact with solid surfaces. The underlying force generating mechanism is not yet understood. Here, we demonstrate that propulsion forces and friction coefficients are strongly coupled in the gliding motility of filamentous cyanobacteria. We directly measure their bending moduli using micropipette force sensors, and quantify propulsion and friction forces by analyzing their self-buckling behavior, complemented with analytical theory and simulations. The results indicate that slime extrusion unlikely generates the gliding forces, but support adhesion-based hypotheses, similar to the better-studied single-celled myxobacteria. The critical self-buckling lengths align well with the peaks of natural length distributions, indicating the importance of self-buckling for the organization of their collective in natural and artificial settings.


Assuntos
Cianobactérias , Cianobactérias/fisiologia , Fenômenos Biomecânicos , Fricção , Movimento
6.
Langmuir ; 40(27): 13810-13818, 2024 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-38918081

RESUMO

The friction of solids is primarily understood through the adhesive interactions between the surfaces. As a result, slick materials tend to be nonstick (e.g., Teflon), and sticky materials tend to produce high friction (e.g., tires and tape). Paradoxically, cartilage, the slippery bearing material of human joints, is also among the stickiest of known materials. This study aims to elucidate this apparent paradox. Cartilage is a biphasic material, and the most cited explanation is that both friction and adhesion increase as load transfers from the pressurized interstitial fluid to the solid matrix over time. In other words, cartilage is slippery and sticky under different times and conditions. This study challenges this explanation, demonstrating the strong adhesion of cartilage under high and low interstitial hydration conditions. Additionally, we find that cartilage clings to itself (a porous material) and Teflon (a nonstick material), as well as other surfaces. We conclude that the unusually strong interfacial tension produced by cartilage reflects suction (like a clingfish) rather than adhesion (like a gecko). This finding is surprising given its unusually large roughness, which typically allows for easy interfacial flow and defeats suction. The results provide compelling evidence that cartilage, like a clingfish, conforms to opposing surfaces and effectively seals submerged contacts. Further, we argue that interfacial sealing is itself a critical function, enabling cartilage to retain hydration, load support, and lubrication across long periods of inactivity.


Assuntos
Cartilagem Articular , Cartilagem Articular/química , Animais , Fricção , Lubrificação , Propriedades de Superfície , Adesividade , Politetrafluoretileno/química
7.
J Dent ; 147: 105120, 2024 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-38857647

RESUMO

OBJECTIVES: To evaluate the wear resistance of three additively manufactured dental crown materials (NextDent C&B MFH, Saremco print CROWNTEC and Bego VarseoSmile Crown) under two environmental conditions (dry and artificial saliva), two loads (49 N and 70 N) and two surface treatments (polished and glazed). METHODS: A total of 120 specimens were divided into 24 groups and tested for wear under two loads (49 N and 70 N), surface treatment (polished or glazed), and environment (dry or submerged in artificial saliva). All samples underwent reciprocating wear testing at 1 Hz using a wear simulator, replicating 48 months of In Vivo conditions with a stainless-steel ball as the antagonist. The coefficient of friction (CoF), surface roughness, volumetric and vertical wear loss were measured and statistically analysed. Confocal microscopy assessed the surface properties of crown materials and the antagonists. RESULTS: The NextDent material demonstrated the most homogenous wear, with relatively low vertical and volumetric loss across all groups (p < 0.004). NextDent and Bego materials performed similarly in artificial saliva regardless of the load type (p > 1.000). The CoF remained below 0.3 for all groups. All groups exhibited significant increases in surface roughness after testing, however, this did not correlate with an increase in the CoF. Confocal analysis revealed material deformities due to load and notable scratch marks on the stainless-steel antagonists. CONCLUSION: It was found that all investigated addtively manufactured materials can be suggested for provisional use. Both vertical loss and volumetric loss results should be included for material evaluation. CoF and surface roughness should be implemented into wear evaluation. CLINICAL SIGNIFICANCE: This study highlights the practical value of additively manufactured dental crown materials, particularly for provisional restorations. However, their extended use requires careful consideration of individual patient needs, emphasising the need for judicious clinical application evaluation.


Assuntos
Coroas , Materiais Dentários , Desgaste de Restauração Dentária , Fricção , Teste de Materiais , Saliva Artificial , Propriedades de Superfície , Saliva Artificial/química , Materiais Dentários/química , Humanos , Polimento Dentário , Aço Inoxidável/química , Microscopia Confocal , Análise do Estresse Dentário
8.
Orthopadie (Heidelb) ; 53(7): 479-486, 2024 Jul.
Artigo em Alemão | MEDLINE | ID: mdl-38833160

RESUMO

This article is intended to highlight one of the key roles in endoprosthetic treatment with artificial implants and the extension of service life. Like every joint, artificial joints are subject to the physical laws of friction and wear-in short, tribology. Material pairings, surfaces and mechanisms of action in particular play a decisive role here. The special features and current findings relating to the three largest synovial joints (hip, knee and shoulder) will be discussed in detail and suggestions will be made for future developments. Continuous developments in the field of the tribology of artificial joints can massively improve care for patients. The revision figures and reasons already show the success of individual improvements in recent years.


Assuntos
Fricção , Prótese Articular , Humanos , Desenho de Prótese , Falha de Prótese , Análise de Falha de Equipamento
9.
J R Soc Interface ; 21(215): 20230696, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38842440

RESUMO

In the area of surgical applications, understanding the interaction between medical device materials and tissue is important since this interaction may cause complications. The interaction often consists of a cell monolayer touching the medical device that can be mimicked in vitro. Prominent examples of this are contact lenses, where epithelial cells interact with the contact lens, or stents and catheters, which are in contact with endothelial cells. To investigate those interactions, in previous studies, expensive microtribometers were used to avoid pressures in the contact area far beyond physiologically relevant levels. Here, we aim to present a new methodology that is cost- and time-efficient, more accessible than those used previously and allows for the application of more realistic pressures, while permitting a quantification of the damage caused to the monolayer. For this, a soft polydimethylsiloxane is employed that better mimics the mechanical properties of blood vessels than materials used in other studies. Furthermore, a technique to account for misalignments within the experiment set-up is presented. This is carried out using the raw spatial and force data recorded by the tribometer and adjusting for misalignments. The methodology is demonstrated using an endothelial cell (human umbilical vein endothelial cells) monolayer.


Assuntos
Células Endoteliais da Veia Umbilical Humana , Humanos , Células Endoteliais da Veia Umbilical Humana/metabolismo , Fricção , Dimetilpolisiloxanos/química
10.
J Food Sci ; 89(6): 3700-3712, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38709880

RESUMO

The densified powder material is convenient for storage and transportation, with broad market application prospects. In this study, the discrete element model parameters required for simulating gluten densification were calibrated using the Hertz-Mindlin with JKR contact model. Initially, physical testing techniques were utilized to assess the size distribution, density, and angle of repose (AoR) of gluten particles. Following this, the Plackett-Burman test, the steepest ascent test, and the Box-Behnken test were conducted, and the significant factors were obtained: The coefficient of rolling friction (P-P) was 1.038, the coefficient of static friction (P-P) was 0.071, and the surface energy (P-P) was 0.047. Finally, the AoR and densification simulations were performed under the optimal parameter combination, along with validation tests. The results showed that the relative error between the simulated and tested AoR was 0.52%. The compression ratio and compression force curves of simulated and actual were similar.


Assuntos
Glutens , Glutens/química , Glutens/análise , Calibragem , Pós/química , Manipulação de Alimentos/métodos , Tamanho da Partícula , Fricção , Modelos Teóricos
11.
Sci Rep ; 14(1): 12243, 2024 05 28.
Artigo em Inglês | MEDLINE | ID: mdl-38806607

RESUMO

Stress shielding and aseptic loosening are complications of short stem total hip arthroplasty, which may lead to hardware failure. Stems with increased porosity toward the distal end were discovered to be effective in reducing stress shielding, however, there is a lack of research on optimized porous distribution in stem's coating. This study aimed to optimize the distribution of the coefficient of friction of a metaphyseal femoral stem, aiming for reducing stress shielding in the proximal area. A finite element analysis model of an implanted, titanium alloy short-tapered wedge stem featuring a porous coating made of titanium was designed to simulate a static structural analysis of the femoral stem's behavior under axial loading in Analysis System Mechanical Software. For computational feasibility, 500 combinations of coefficients of friction were randomly sampled. Increased strains in proximal femur were found in 8.4% of the models, which had decreased coefficients of friction in middle medial areas of porous coating and increased in lateral proximal and lateral and medial distal areas. This study reported the importance of the interface between bone and middle medial and distal lateral areas of the porous coating in influencing the biomechanical behavior of the proximal femur, and potentially reducing stress shielding.


Assuntos
Artroplastia de Quadril , Fêmur , Análise de Elementos Finitos , Fricção , Prótese de Quadril , Titânio , Humanos , Fêmur/fisiologia , Porosidade , Artroplastia de Quadril/métodos , Titânio/química , Estresse Mecânico , Desenho de Prótese , Materiais Revestidos Biocompatíveis/química , Fenômenos Biomecânicos , Ligas/química
12.
J Oleo Sci ; 73(5): 801-811, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38692901

RESUMO

Hair shape affects the frictional properties and tactile sensation of hair. In this study, we evaluated the friction associated with the rubbing of straight, curly, or wavy hair by a contact probe equipped in a sinusoidal motion friction evaluation system. This system provides dynamic information such as the velocity dependence and hysteresis of the frictional force. In the case of hair fibers fixed at 1 mm intervals on a glass plate, a stable friction pattern was observed, in which the friction coefficient was almost constant during the dynamic friction process. The friction coefficients in the inward direction toward the hair root for straight, curly, and wavy hair were 0.47 ± 0.04, 0.51 ± 0.02, and 0.54 ± 0.04, respectively. As wavy hair is thick and has a larger true contact area with the contact probe, the friction coefficient was larger. When the finger model rubbed the straight or curly hair bundle in the inward direction, an oscillation pattern was observed, with the friction coefficient fluctuating at 20 ms intervals and the kinetic friction coefficient evaluated at 0.67 and 0.64, respectively. For the surface of straight hair, containing densely arranged cuticles, a large oscillation was observed in the direction against the cuticles. Meanwhile, no oscillation phenomenon was observed in wavy hair, which is characterized by a smooth cuticle and complex hair flow. Because wavy hair, which is frizzy, has fewer points of contact between hairs, impeding the occurrence of cooperative fluctuations in the frictional force.


Assuntos
Fricção , Cabelo , Cabelo/fisiologia , Humanos , Tato/fisiologia
13.
J Mech Behav Biomed Mater ; 155: 106566, 2024 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-38729087

RESUMO

The objective of this study is to develop a reliable tribological model to enable a more thorough investigation of the frictional behavior of fascia tissues connected to non-specific lower back pain. Several models were designed and evaluated based on their coefficient of friction, using a low-frequency, low-load reciprocating motion. The study found that two technical elastomers, layered on PDMS to simulate the fascia and underlying muscle, are suitable substitutes for biological tissue in the model. The influence of tribopair geometry was also examined, and the results showed that greater conformity of contact leads to a lower COF, regardless of the material combination used. Finally, the friction properties of HA of various molecular weights and concentrations were tested.


Assuntos
Fáscia , Fricção , Teste de Materiais , Fáscia/fisiologia , Dimetilpolisiloxanos/química , Fenômenos Biomecânicos , Modelos Biológicos , Elastômeros/química
14.
PLoS One ; 19(4): e0297912, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38573995

RESUMO

The bulkhead additional thrust during shield tunneling, the force of friction between shield and soil, and the additional grouting pressure can cause additional stress in the surrounding soil, thereby disturbing existing buildings and structures. However, few studies focused on the disturbance situation when the shield tunneling machine approaches the receiving well. If the additional stress and deformation of the receiving well are too excessive, it could result in the collapse of the receiving well. Based on the two-stage method, this study derived the calculation formula of the additional stress and deformation of the receiving well enclosure structure caused by shield tunneling. Taking a shield machine receiving engineering as the context, this study established a numerical simulation model and compared theoretical calculation, the results of numerical simulation model and on-site monitoring data. Finally, the additional stress of the receiving well is analyzed. The research findings demonstrate that the theoretical prediction results, numerical simulation calculation results, and on-site monitoring data exhibit relatively small calculation errors, which validated the applicability of the theoretical prediction formula and numerical simulation model. As the distance between the shield machine and the receiving well decreases, the disturbance to the receiving well increases sharply. When the distance between the cutter head and the receiving well is less than three times the shield length, it is crucial to enhance the deformation monitoring of the receiving well. The primary factors affecting the additional load and deformation of the receiving well enclosure structure are the force of friction between shield and soil and the additional thrust of the cutterhead. The disturbance caused by the additional grouting pressure on the enclosure structure can be ignored.


Assuntos
Engenharia , Equipamentos de Proteção , Simulação por Computador , Fricção , Solo
15.
J Environ Manage ; 357: 120717, 2024 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-38579466

RESUMO

Household food waste is increasingly recognised as a global wicked problem for its greenhouse gas emissions, economic damage, and resource loss. Although targeted in the UN's Sustainable Development Goals, countries can only respond according to their capacity. For Australia, national policy has put the pressure on states and territories to divert food waste away from landfill into a nascent circular economy. For councils, this increasingly means implementing a FOGO (Food Organics/Garden Organics) kerbside collection. Despite funding and infrastructure development, many are resisting. Framed by the tenets of policy diffusion, this paper presents the results of a nationwide exploratory survey aimed at identifying how and why council-based waste services staff resist, emulate or lead FOGO implementation. By assessing participants current kerbside systems and their attitudes towards household food waste management, the survey found costs, contamination, and capacity and were key concerns. However, responses to these varied considerably despite similarities of situation, often relating more to collaborative attitudes across waste services, council, and councillors. This paper recognises that a conducive environment for change is urgently needed for Australia to achieve organics diversion targets and shift household food towards a circular economy. It provides a starting point for further research into the complex and nuanced dynamics between council waste services and FOGO implementations, from external drivers and council paradigms to individual attitudes and perceptions.


Assuntos
Eliminação de Resíduos , Gerenciamento de Resíduos , Humanos , Eliminação de Resíduos/métodos , Perda e Desperdício de Alimentos , Alimentos , Fricção , Gerenciamento de Resíduos/métodos , Austrália , Políticas
16.
Int Wound J ; 21(4): e14871, 2024 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-38591160

RESUMO

Pressure ulcers including heel ulcers remain a global healthcare concern. This study comprehensively evaluates the biomechanical effectiveness of the market-popular ALLEVYN® LIFE multilayer dressing in preventing heel ulcers. It focuses on the contribution of the frictional sliding occurring between the non-bonded, fully independent layers of this dressing type when the dressing is protecting the body from friction and shear. The layer-on-layer sliding phenomenon, which this dressing design enables, named here the frictional energy absorber effectiveness (FEAE), absorbs approximately 30%-45% of the mechanical energy resulting from the foot weight, friction and shear acting to distort soft tissues in a supine position, thereby reducing the risk of heel ulcers. Introducing the novel theoretical FEAE formulation, new laboratory methods to quantify the FEAE and a review of relevant clinical studies, this research underlines the importance of the FEAE in protecting the heels of at-risk patients. The work builds on a decade of research published by our group in analysing and evaluating dressing designs for pressure ulcer prevention and will be useful for clinicians, manufacturers, regulators and reimbursing bodies in assessing the effectiveness of dressings indicated or considered for prophylactic use.


Assuntos
Úlcera por Pressão , Humanos , Úlcera por Pressão/prevenção & controle , Fricção , Úlcera , Bandagens , Higiene da Pele , Calcanhar
17.
J Phys Chem B ; 128(16): 3856-3869, 2024 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-38606880

RESUMO

We have studied in silico the effect of proline, a model cosolvent, on local and global friction coefficients in (un)folding of several typical alanine-based α-helical peptides. Local friction is related to dwell times of a single, ensemble-averaged hydrogen bond (HB) within each peptide. Global friction is related to energy dissipated in a series of configurational changes of each peptide experienced by increasing the number of HBs during folding. Both of these approaches are important in relation to future atomic force microscopic-based measurements of internal friction via force-clamp single-molecule force spectroscopy. Molecular dynamics (MD) simulations for six peptides, namely, ALA5, ALA8, ALA15, ALA21, (AAQAA)3, and H2N-GN(AAQAA)2G-COONH2, have been conducted at 2 and 5 M proline solutions in water. Using previously obtained MD data for these peptides in pure water as well as upgraded theoretical models, we obtained variations of local and global internal friction coefficients as a function of solution viscosity. The results showed the substantial role of proline in stabilizing the folded state and slowing the overall folding dynamics. Consequently, larger friction coefficients were obtained at larger viscosities. The local and global internal friction, i.e., respective, friction coefficients approximated to zero viscosity, was also obtained. The evolution of friction coefficients with viscosity was weakly dependent on the number of concurrent folding pathways but was rather dominated by a stabilizing effect of proline on the folded states. Obtained values of local and global internal friction showed qualitatively similar results and a clear dependency on the structure of the studied peptide.


Assuntos
Simulação de Dinâmica Molecular , Peptídeos , Prolina , Dobramento de Proteína , Prolina/química , Peptídeos/química , Conformação Proteica em alfa-Hélice , Alanina/química , Ligação de Hidrogênio , Fricção
18.
Int J Mol Sci ; 25(7)2024 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-38612749

RESUMO

A large amount of primary energy is lost due to friction, and the study of new additive materials to improve friction performance is in line with the concept of low carbon. Carbon nanotubes (CNTs) have advantages in drag reduction and wear resistance with their hollow structure and self-lubricating properties. This review investigated the mechanism of improving friction properties of blocky composites (including polymer, metal, and ceramic-based composites) with CNTs' incorporation. The characteristic tubular structure and the carbon film make low wear rate and friction coefficient on the surface. In addition, the effect of CNTs' aggregation and interfacial bond strength on the wear resistance was analyzed. Within an appropriate concentration range of CNTs, the blocky composites exhibit better wear resistance properties. Based on the differences in drag reduction and wear resistance in different materials and preparation methods, further research directions of CNTs have been suggested.


Assuntos
Nanotubos de Carbono , Cerâmica , Fricção , Polímeros , Software
19.
J Orthop Surg Res ; 19(1): 259, 2024 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-38659060

RESUMO

PURPOSE: The purpose of the study was to describe a novel growth guidance system, which can avoid metal debris and reduce the sliding friction forces, and test the durability and glidability of the system by in vitro test. METHOD: Two major modifications were made to the traditional Shilla system, including the use of ultra-high molecular weight polyethylene (UHMWPE) gaskets to avoid direct contact between the screw and rod, and polishing the surface of the sliding part of the rod. We tested the durability of the system by a fatigue test, which the samples were test on the MTS system for a 10 million cycle of a constant displacement. Pre and post-testing involved weighing the UHMWPE gaskets and observing the wear conditions. The sliding ability were measured by a sliding displacement test. The maximum sliding displacement of the system was measured after a 300 cycles of dynamic compressive loads in a sinusoidal waveform. RESULTS: After the fatigue test, all the UHMWPE gaskets samples showed some of the fretting on the edge of the inner sides, but its still isolated and avoided the friction between the screws and rods. There was no production of metallic fretting around the sliding screws and rods. The average wear mass of the UHMWPE gaskets was 0.002 ± 0.001 g, less than 1.7% of the original mass. In the sliding test, the novel growth guidance system demonstrated the best sliding ability, with an average maximum sliding distance(AMSD) of 35.75 ± 5.73 mm, significantly better than the group of the traditional Shilla technique(AMSD 3.65 ± 0.46 mm, P < 0.0001). CONCLUSION: In conclusion, we modified the Shilla technique and designed a novel growth guidance system by changing the friction interface of sliding screw and rod, which may significantly reduce the metallic debris and promote spine growth. The fatigue test and sliding dislocation test demonstrated the better durability and glidability of the system. An in vivo animal experiment should be performed to further verify the system.


Assuntos
Teste de Materiais , Polietilenos , Escoliose , Humanos , Teste de Materiais/métodos , Fricção , Parafusos Ósseos , Técnicas In Vitro
20.
Acta Biomater ; 178: 196-207, 2024 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-38428511

RESUMO

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.


Assuntos
Cartilagem Articular , Osteoartrite , Animais , Bovinos , Lubrificação , Estresse Mecânico , Líquido Sinovial , Osteoartrite/terapia , Fricção , Digestão
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