Occupational low back pain (LBP) is an immense burden for both industry and medicine. Ergonomic and personal risk factors result in LBP, but psychosocial factors can influence LBP disability. Epidemiologic studies clearly indicate the role of mechanical loads on the etiology of occupational LBP. Occupational exposures such as lifting, particularly in awkward postures; heavy lifting; or repetitive lifting are related to LBP. Fixed postures and prolonged seating are also risk factors. LBP is found in both sedentary occupations and in drivers as well as those involved in manual materials handling. Any prolonged posture will lead to static loading of the soft tissues and cause discomfort. Standing and sitting have specific advantages and disadvantages for mobility, exertion of force, energy consumption, circulatory demands, coordination, and motion control. The seated posture leads to inactivity causing an accumulation of metabolites, accelerating disk degeneration and leading to disk herniation. Driver's postures can also lead to musculoskeletal problems. Workers in a driving environment are often subjected to postural stress leading to back, neck, and upper extremity pain. This exacerbates the problems due to the vibration. Prevention is by far the treatment of choice. Improved muscle function can be preventative. Poor coordination and motor control systems are as important as endurance and strength. Fixed postures should be avoided. Seats offering good lumbar support should be used in the office. A suspension seat should be used in vehicles whenever possible. Heavy and awkward lifting should be avoided and lifting aids should be made available. Workers should report LBP as early as possible and seek medical advice if they think occupational exposure is harming them. The combined effects of the medical community, labor, and management are required to cause some impact on this problem.
As the key component of the musculoskeletal system, the extracellular matrix of soft connective tissues such as ligaments and tendons is a biological example of fibre-reinforced composite but with a complex hierarchical architecture. To establish a comprehensive structure-function relationship at the respective levels (i.e., from molecule to tissue) of the hierarchical architecture is challenging and requires a multidisciplinary approach, involving the integration of findings from the fields of molecular biology, biochemistry, structural biology, materials science and biophysics. Accordingly, in recent years, some of these fields, namely structural biology, materials science and biophysics, have made significant progress in the microscale and nanoscale studies of extracellular matrix using new tools, such as microelectromechanical systems, optical tweezers and atomic force microscopy, complemented by new techniques in simultaneous imaging and mechanical testing and computer modelling. The intent of this paper is to review the key findings on the mechanical response of extracellular matrix at the respective levels of the hierarchical architecture. The main focus is on the structure and function-the findings are compared across the different levels to provide insights that support the goal of establishing a comprehensive structure-function relationship of extracellular matrix. For this purpose, the review is divided into two parts. The first part explores the features of key structural units of extracellular matrix, namely tropocollagen molecule (the lowest level), microfibril, collagen fibril, collagen fibre and fascicle. The second part examines the mechanics of the structural units at the respective levels. Finally a framework for extracellular matrix mechanics is proposed to support the goal to establish a comprehensive structure-function relationship. The framework describes the integration of the mechanisms of reinforcement by the structural units at the respective levels of the hierarchical architecture in a consistent manner, both to allow comparison of these mechanisms and to make prediction of the interconnection of these mechanisms that can also assist in the identification of effective mechanical pathways. From a design perspective, this is a step in the direction towards the development of effective strategies for engineering materials to replace or repair damaged tissues, and for exogenous cross-linking therapy to enhance the mechanical properties of injured tissues.
Connective tissues are biological composites comprising of collagen fibrils embedded in (and reinforcing) the hydrated proteoglycan-rich (PG) gel within the extracellular matrices (ECMs). Age-related changes to the mechanical properties of tissues are often associated with changes to the structure of the ECM, namely, fibril diameter. However, quantitative attempts to correlate fibril diameter to mechanical properties have yielded inconclusive evidence. Here, we described a novel approach that was based on the rule of mixtures for fiber composites to evaluate the dependence of age-related changes in tendon tensile strength (sigma) and stiffness (E) on the collagen fibril cross-sectional area fraction (rho), which is related to the fibril volume fraction. Tail tendons from C57BL6 mice from age groups 1.6-35.3 months old were stretched to failure to determine sigma and E. Parallel measurements of rho as a function of age were made using transmission electron microscopy. Mathematical models (rule of mixtures) of fibrils reinforcing a PG gel in tendons were used to investigate the influence of rho on ageing changes in sigma and E. The magnitudes of sigma, E, and rho increased rapidly from 1.6 months to 4.0 months (P-values <0.05) before reaching a constant (age independent) from 4.0 months to 29.0 months (P-values >0.05); this trend continued for E and rho (P-values >0.05) from 29.0 months to 35.3 months, but not for sigma, which decreased gradually (P-values <0.05). Linear regression analysis revealed that age-related changes in sigma and E correlated positively to rho (P-values <0.05). Collagen fibril cross-sectional area fraction rho is a significant predictor of ageing changes in sigma and E in the tail tendons of C57BL6 mice.
Scaling relationships have been formulated to investigate the influence of collagen fibril diameter (D) on age-related variations in the strain energy density of tendon. Transmission electron microscopy was used to quantify D in tail tendon from 1.7- to 35.3-mo-old (C57BL/6) male mice. Frequency histograms of D for all age groups were modeled as two normally distributed subpopulations with smaller (D(D1)) and larger (D(D2)) mean Ds, respectively. Both D(D1) and D(D2) increase from 1.6 to 4.0 mo but decrease thereafter. From tensile tests to rupture, two strain energy densities were calculated: 1) u(E) [from initial loading until the yield stress (σ(Y))], which contributes primarily to tendon resilience, and 2) u(F) [from σ(Y) through the maximum stress (σ(U)) until rupture], which relates primarily to resistance of the tendons to rupture. As measured by the normalized strain energy densities u(E)/σ(Y) and u(F)/σ(U), both the resilience and resistance to rupture increase with increasing age and peak at 23.0 and 4.0 mo, respectively, before decreasing thereafter. Multiple regression analysis reveals that increases in u(E)/σ(Y) (resilience energy) are associated with decreases in D(D1) and increases in D(D2), whereas u(F)/σ(U) (rupture energy) is associated with increases in D(D1) alone. These findings support a model where age-related variations in tendon resilience and resistance to rupture can be directed by subtle changes in the bimodal distribution of Ds.
Poly (lactic acid) (PLA)/natural halloysite nanotubes (HNTs) films were prepared by solution casting method to investigate their properties for packaging applications. Tensile test results revealed that the maximum tensile elastic modulus (1.40 ± 0.05 GPa) and tensile strength (52.75 ± 1.80 MPa) were achieved at 5 w/w % of HNTs (in a range of 0–10 w/w % HNT concentrations). A nanoindentation test was performed to confirm the reinforcing effect of HNTs. Analysis of electron micrographs of the fracture surfaces suggested that the reinforcing mechanism was subjected to the interfacial interaction between HNTs and PLA. Infrared spectra revealed that the end hydroxyl groups of PLA chemically interacted with HNTs’ outer surface siloxane groups via hydrogen bonding. In addition, the contact angle test and thermogravimetric analysis were used to investigate the surface wettability and thermal stability of the PLA/HNT films, respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.