The experimental and finite element analysis data of Cu-UV glue composite materials.

Five different layered-fiber reinforced Cu-UV glue composite structures were prepared, with Cu plate and wire as the reinforcing phase, and UV glue as the substrate. The volume ratio of Cu and UV glue of these structures is the same, but the difference lies in the number and diameter of Cu wires. Three-point bending tests were performed on these structures, and the bending stress-bending strain curves of different structures were measured. At the same time, the finite element method is used to simulate the three-point bending test process of different structures, and the bending stress-bending strain curves of different structures were calculated. Then the experimental and simulated strengths corresponding to different structures were obtained from the stress-strain curves obtained by experiment and simulation. These data are supplementary material for the associated research article [1].

A numerical bone regeneration model incorporating angiogenesis, considering oxygen-induced secretion of vascular endothelial growth factor and vascular remodeling.

Angiogenesis is considered playing an important role in bone regeneration. Studies have shown that angiogenesis is affected by biological factors, oxygen tension, and blood flow. In this paper, we propose a bone regeneration model with angiogenesis based on the theories of mechanobiology regulation, vascular network modeling, oxygen-induced secretion of vascular endothelial growth factor (VEGF), and vascular remodeling. The results showed that this model can describe the distribution and concentration of vascular endothelial growth factor induced by oxygen tension during bone regeneration, the growth and remodeling of vascular tissue under the influence of vascular endothelial growth factor and mechanical loading, and the correspondence between vascular tissue and bone regeneration.

Natural arrangement of micro-strips reduces shear strain in the locust cuticle during power amplification.

As one of the key components in power amplification of locust, semi-lunar process (SLP) cuticle has five different portions where its portion II stores a large amount of strain energy when locusts kick. The SLP portion II is composed of regular chitin micro-strips that non-uniformly arranged in its transverse plane. However, it is still unknown whether the natural arrangement of micro-strips affects the power amplification of the SLP cuticle. To address this, SLP portion II samples of adult locusts were mechanically tested along three orthogonal directions, corresponding to the length, width, and thickness axes of the micro-strips, respectively. Four different arrangements of micro-strips in the portion II were compared using finite element method. It was found that the micro-strip set of the portion II is orthotropic elastic and its elastic modulus is maximal in the length axis of the micro-strip. The inclusion of the micro-strips offers more strain energy than the isotropic portion II (without micro-strips). Compared to the horizontally- and vertically-arrangements of the micro-strips, their natural arrangement does not affect the strain energy but reduces the in-plane shear strain in the portion II. This research helps us deeply understand the power amplification mechanism of locusts and may guide optimization of catapult device design in bioinspired robots.

The Effect of Ground Type on the Jump Performance of Adults of the Locust Locusta migratoria manilensis: A Preliminary Study.

The jump performance of locusts depends on several physiological and environmental factors. Few studies have examined the effects of different ground types on the jump performance of locusts. Here, mature adult locusts (Locusta migratoria manilensis) were examined using a custom-developed measuring system to test their jump performance (including postural features, kinematics, and reaction forces) on three types of ground (sand, soil, and wood). Significant differences were primarily observed in the elevation angle at take-off, the tibial angle at take-off, and the component of the mass-specific reaction force along the aft direction of the insect body between wood and the other two ground types (sand and soil). Slippage of the tarsus and insertion of the tibia were often observed when the locusts jumped on sand and soil, respectively. Nevertheless, comparisons of the different parameters of jump initiation (i.e., take-off speed and mass-specific kinetic energy) did not reveal any differences among the three types of ground, indicating that locusts were able to achieve robust jump performance on various substrates. This study provides insights into the biomechanical basis of the locust jump on different types of ground and enhances our understanding of the mechanism underlying the locust jump.

Time-scale mechanical behaviors of locust semi-lunar process cuticles under power amplification for rapid movements.

The semi-lunar process (SLP) is a key component in the power amplification of locusts to achieve rapid movements. Its mechanical properties determine the amount of the power amplification and the subsequent locomotion performance. As previously reported, the SLP cuticle endures physiological dynamic loadings. However, the time-scale mechanical properties of the SLP are still unknown, especially under stress relaxation and cyclic loadings. In this paper, the SLP cuticles of adult desert locusts (Schistocerca gregaria) were studied using stress relaxation and cyclic tests, with loadings corresponding to the physiological loading conditions of the power amplification. The SLP cuticle was found to show pronounced stress relaxation behavior with the resultant force and an evident time shift between the maximal displacement and the maximal resultant force. The number of loading cycles before mechanical failure (life cycle number) increases when the SLP cuticle is cyclically loaded by a lower stress level. Moreover, the failure strength of the SLP at low cycles equals the physiological stress level in the power amplification, implying that the healing of the cuticle might contribute to the successful performance of numerous jumps in the course of the adult locust life. This study not only deepens our understanding of the power amplification mechanism of locust locomotion but also provides valuable knowledge for the design optimization of bioinspired jumping robots and elastic energy storage devices.

Mechanical characterization of the key portions in locust semi-lunar processes under different strain rates.

The excellent rapid jumping and kicking of locusts are largely attributed to the power amplification mechanisms due to the semi-lunar processes (SLP) at their distal metathoracic femurs, especially dorsal-core (i.e., portion II) and ventral-core parts (i.e., portion III). The physiological range of strain rates at the two portions of locust SLP is quite broad in the periods of energy storage and release (approximately three orders). However, it still remains elusive how the mechanical properties of the two SLP portions change with the strain rate. We identified the elastic moduli and material compositions of SLP portions II and III by using nanoindentation and confocal laser scanning microscope. Apparent and creep-corrected reduced elastic moduli were calculated to represent the total energy absorption and storage, respectively. The results revealed that both portions II and III exhibit strain rate-sensitive elastic moduli, regardless of water content. The efficiency of elastic energy storage is only 51-70% in the case of low strain rate. This work can deepen our understanding in the energy storage and release mechanisms in locust locomotion and further provide guidelines for biomimetic design of power amplification apparatus in jumping robots.

T1ρ-based fibril-reinforced poroviscoelastic constitutive relation of human articular cartilage using inverse finite element technology.

BACKGROUND: Mapping of T1ρ relaxation time is a quantitative magnetic resonance (MR) method and is frequently used for analyzing microstructural and compositional changes in cartilage tissues. However, there is still a lack of study investigating the link between T1ρ relaxation time and a feasible constitutive relation of cartilage which can be used to model complicated mechanical behaviors of cartilage accurately and properly. METHODS: Three-dimensional finite element (FE) models of ten in vitro human tibial cartilage samples were reconstructed such that each element was assigned by material-level parameters, which were determined by a corresponding T1ρ value from MR maps. A T1ρ-based fibril-reinforced poroviscoelastic (FRPE) constitutive relation for human cartilage was developed through an inverse FE optimization technique between the experimental and simulated indentations. RESULTS: A two-parameter exponential relationship was obtained between the T1ρ and the volume fraction of the hydrated solid matrix in the T1ρ-based FRPE constitutive relation. Compared with the common FRPE constitutive relation (i.e., without T1ρ), the T1ρ-based FRPE constitutive relation indicated similar indentation depth results but revealed some different local changes of the stress distribution in cartilages. CONCLUSIONS: Our results suggested that the T1ρ-based FRPE constitutive relation may improve the detection of changes in the heterogeneous, anisotropic, and nonlinear mechanical properties of human cartilage tissues associated with joint pathologies such as osteoarthritis (OA). Incorporating T1ρ relaxation time will provide a more precise assessment of human cartilage based on the individual in vivo MR quantification.

Does the graft-tunnel friction influence knee joint kinematics and biomechanics after anterior cruciate ligament reconstruction? A finite element study.

Graft tissues within bone tunnels remain mobile for a long time after anterior cruciate ligament (ACL) reconstruction. However, whether the graft-tunnel friction affects the finite element (FE) simulation of the ACL reconstruction is still unclear. Four friction coefficients (from 0 to 0.3) were simulated in the ACL-reconstructed joint model as well as two loading levels of anterior tibial drawer. The graft-tunnel friction did not affect joint kinematics and the maximal principal strain of the graft. By contrast, both the relative graft-tunnel motion and equivalent strain for the bone tunnels were altered, which corresponded to different processes of graft-tunnel integration and bone remodeling, respectively. It implies that the graft-tunnel friction should be defined properly for studying the graft-tunnel integration or bone remodeling after ACL reconstruction using numerical simulation.

Quantitative Evaluation of Enzyme-Induced Porcine Articular Cartilage Degeneration Based on Observation of Entire Cartilage Layer Using Ultrasound.

Enzyme-induced articular cartilage degeneration resembling osteoarthritis was evaluated using a newly defined acoustic parameter, the "averaged magnitude ratio" (AMR), which has been suggested as an indicator of articular cartilage degeneration. In vitro experiments were conducted on porcine cartilage samples digested with trypsin for 2 h (n = 10) and 4 h (n = 13) and healthy control samples (n = 13). AMR was determined with 15- and 25-MHz ultrasound, and the integrated reflection coefficient (IRC) and apparent integrated backscattering coefficient (AIB) were also calculated for comparison. The Young's modulus of superficial cartilage was measured using atomic force microscopy. Performance of the AMR differs between 15 and 25 MHz, possibly because of frequency-related attenuation and resolution of ultrasound. At the proper settings, AMR exhibited a competence similar to that of IRC and AIB in detecting cartilage degeneration and could also detect differences in deeper positions. Furthermore, AMR has the advantages of being easy to measure and requiring no reference material.

Detection of depth-depend changes in porcine cartilage after wear test using Raman spectroscopy.

Cartilage damage and wear can lead to severe diseases, such as osteoarthritis, thus, many studies on the cartilage wear process have already been performed to better understand the cartilage wear mechanism. However, most characterization methods focus on the cartilage surface or the total wear extent. With the advantages of high spatial resolution and easy characterization, Raman microspectroscopy was employed for the first time to characterize full-depth changes in the cartilage extracellular matrix (ECM) after wear test. Sections from the cartilage samples after wear were compared with sections from the control group. Univariate and multivariate analyses both indicated that collagen content loss at certain depths (20%-30% relative to the cartilage surface) is possibly the dominating alteration during wear rather than changes in collagen fiber orientation or proteoglycan content. These findings are consistent with the observations obtained by scanning electron microscopy and histological staining. This study successfully used Raman microspectroscopy efficiently assess full-depth changes in cartilage ECM after wear test, thus providing new insight into cartilage damage and wear.

The collagen microstructural changes of rat menisci and tibiofemoral cartilages under the influence of mechanical loading: An in vitro wear test of whole joints.

BACKGROUND: Knee osteoarthritis (OA) is suggested to be induced by multi-factors, and mechanical environment is regarded as a risky factor. OBJECTIVE: To investigate the effect of isolated mechanical factor on cartilage. METHODS: An active wear test system was designed to perform parameters-controlled in vitro wear tests on rat knee joints with specific load magnitude, flexion-extension angle, and movement frequency. Six hind limbs of 9-month-old male Sprague-Dawley rats, with an additional spring on the medial side, were worn by using the custom-designed apparatus. Researchers observed both the menisci and tibial cartilages of these hind limbs using multiphoton laser scanning microscopy to analyze the change of the collagen microstructure caused by wear. RESULTS: Collagen microstructure of both the medial and lateral meniscus became disordered under cyclic load. Some tissues on the surface of the medial tibial cartilage were removed and the middle layer of the medial compartment displayed cracks. On the contrary, the lateral tibial cartilage was intact. CONCLUSIONS: The results implied that cyclic load caused menisci microstructure disarrangement prior to tibial cartilage damage and the collagen structure of mid-layer tibial cartilage failed before that of the superficial layer under the kinematics adopted in the study.

Finite element simulations of different hamstring tendon graft lengths and related fixations in anterior cruciate ligament reconstruction.

As one of the most frequently used grafts in anterior cruciate ligament (ACL) reconstruction, hamstring tendon (HT) grafts are prepared with different lengths and fixed by specific fixations in knee joints. However, there are incomplete studies to investigate both the joint kinematics and graft biomechanics in the ACL reconstructions with different HT graft lengths. In this paper, three different graft lengths (i.e., 30, 50, and 70 mm) were developed in the ACL reconstruction and analyzed using finite element method under two usual clinical test loads (i.e., 134 N anterior tibial drawer and pivot shift test load). The different mechanical properties of the corresponding fixations were also considered for each graft length. It was revealed that the change in HT graft length would cause different strain and stress results in the grafts, but did not greatly influence joint stabilities under the two clinical test loads. The graft reaction force at the femoral fixation was always greatly lower than that at the tibial fixation regardless of load and graft length. The comparison of stress and strain results also indicated that more graft tissues inside the femoral and tibial tunnels could decrease the stress and strain values at the femoral and tibial fixation sites, respectively.

Finite element analysis of the effect of medullary contact on fracture healing and remodeling in the intramedullary interlocking nail-fixed tibia fracture.

Intramedullary interlocking nail is an effective treatment for tibial diaphyseal fracture. The contact between medullary rod and diaphyseal cortex is able to enhance fracture stability. However, how and to what degree the contact affects fracture healing and subsequent bone remodeling is still unclear. To investigate this, fracture healing and remodeling algorithms were combined, improved, and used to simulate the healing and remodeling processes in a transverse tibial diaphyseal fracture fixed with an intramedullary interlocking nail device. Two different diaphyseal fracture statuses, three different initial loading levels, and two nail materials were considered. The results showed that the medullary contact could significantly enhance the fixation stability; the strain reduction was up to 80% in the initial granulation callus. However, low initial loading level was found to be a more potential risk factor for the insufficient loading-induced nonunion other than medullary contact and stiffer nail material. Furthermore, the stabilizing effect of medullary contact diminished when stiff bone tissue formed in the callus; thus, the remodeling in the long-term was not affected by medullary contact. Copyright © 2016 John Wiley & Sons, Ltd.

Do biodegradable magnesium alloy intramedullary interlocking nails prematurely lose fixation stability in the treatment of tibial fracture? A numerical simulation.

Intramedullary interlocking nailing is an effective technique used to treat long bone fractures. Recently, biodegradable metals have drawn increased attention as an intramedullary interlocking nailing material. In this study, numerical simulations were implemented to determine whether the degradation rate of magnesium alloy makes it a suitable material for manufacturing biodegradable intramedullary interlocking nails. Mechano-regulatory and bone-remodeling models were used to simulate the fracture healing process, and a surface corrosion model was used to simulate intramedullary rod degradation. The results showed that magnesium alloy intramedullary rods exhibited a satisfactory degradation rate; the fracture healed and callus enhancement was observed before complete dissolution of the intramedullary rod. Delayed magnesium degradation (using surface coating techniques) did not confer a significant advantage over the non-delayed degradation process; immediate degradation also achieved satisfactory healing outcomes. However, delayed degradation had no negative effect on callus enhancement, as it did not cause signs of stress shielding. To avoid risks of individual differences such as delayed union, delayed degradation is recommended. Although the magnesium intramedullary rod did not demonstrate rapid degradation, its ability to provide high fixation stiffness to achieve earlier load bearing was inferior to that of the conventional titanium alloy and stainless steel rods. Therefore, light physiological loads should be ensured during the early stages of healing to achieve bony healing; otherwise, with increased loading and degraded intramedullary rods, the fracture may ultimately fail to heal.

Structures, properties, and energy-storage mechanisms of the semi-lunar process cuticles in locusts.

Locusts have excellent jumping and kicking abilities to survive in nature, which are achieved through the energy storage and release processes occurring in cuticles, especially in the semi-lunar processes (SLP) at the femorotibial joints. As yet, however, the strain energy-storage mechanisms of the SLP cuticles remain unclear. To decode this mystery, we investigated the microstructure, material composition, and mechanical properties of the SLP cuticle and its remarkable strain energy-storage mechanisms for jumping and kicking. It is found that the SLP cuticle of adult Locusta migratoria manilensis consists of five main parts that exhibit different microstructural features, material compositions, mechanical properties, and biological functions in storing strain energy. The mechanical properties of these five components are all transversely isotropic and strongly depend on their water contents. Finite element simulations indicate that the two parts of the core region of the SLP cuticle likely make significant contributions to its outstanding strain energy-storage ability. This work deepens our understanding of the locomotion behaviors and superior energy-storage mechanisms of insects such as locusts and is helpful for the design and fabrication of strain energy-storage devices.

The effect of healing in the medial collateral ligament of human knee joint: A three-dimensional finite element analysis.

The medial collateral ligament (MCL) is one of the main ligaments that provide knee joint with major restraints against valgus, internal, and external torque loads. The MCL injury most frequently occurs near its femoral attachment but can be healed spontaneously. Hence, the usual clinical treatment for MCL injury is conservative therapy with early controlled rehabilitation motion. However, the effect of the variations in the healing conditions of the MCL portion (i.e. near the femoral insertion) is still unclear. In this study, finite element tibiofemoral joint models with three different MCL healing conditions were analyzed under six kinds of joint loads, such as 10 and 20 N·m valgus tibial torques, 5 and 10 N·m internal tibial torques, and 5 and 10 N·m external tibial torques. The three healing conditions corresponded to the early, medium, and final (i.e. healthy) stages of the healing period, respectively. It was found that different MCL healing conditions greatly affected the main joint kinematics under valgus tibial torques, but neither the reaction force nor stress results of the MCL. The peak strain values in the MCL healing portion changed greatly under all the six loads. Moreover, all the joint kinematics, strain results, and reaction force of the MCL at the medium stage were similar to those in the healthy joint, that is, at the final healing stage. These imply that the partially healed MCL might be enough for providing the restraints for knee joints and would not lead to some high strains occurring in the MCL.

An update on the constitutive relation of ligament tissues with the effects of collagen types.

The musculoskeletal ligament is a kind of multiscale composite material with collagen fibers embedded in a ground matrix. As the major constituent in ligaments to bear external loads, collagens are composed mainly of two collagen contents with different mechanical properties, i.e., types I and III collagen. The constitutive relation of ligaments plays a critical role in the stability and normal function of human joints. However, collagen types have not been distinguished in the previous constitutive relations. In this paper a constitutive relation for ligament tissues was modified based on the previous constitutive relation by considering the effects of collagen types. Both the collagen contents and the mechanical properties of sixteen ligament specimens from four cadaveric human knee joints were measured for determining their material coefficients in the constitutive relation. The mechanical behaviors of ligaments were obtained from both the uniaxial tensile and simple shear tests. A linear regression between joint kinematic results from in vitro and in silico experiments was made to validate the accuracy of this constitutive relation. The high correlation coefficient (R(2)=0.93) and significance (P<0.0001) of the regression equation revealed that this modified constitutive relation of ligaments was accurate to be used in studying joint biomechanics. Another finite element analysis with collagen contents changing demonstrated that the effect of variations in collagen ratios on both joint kinematics and ligament biomechanics could be simulated by this constitutive relation.

A quantitative study of the relationship between the distribution of different types of collagen and the mechanical behavior of rabbit medial collateral ligaments.

The mechanical properties of ligaments are key contributors to the stability and function of musculoskeletal joints. Ligaments are generally composed of ground substance, collagen (mainly type I and III collagen), and minimal elastin fibers. However, no consensus has been reached about whether the distribution of different types of collagen correlates with the mechanical behaviors of ligaments. The main objective of this study was to determine whether the collagen type distribution is correlated with the mechanical properties of ligaments. Using axial tensile tests and picrosirius red staining-polarization observations, the mechanical behaviors and the ratios of the various types of collagen were investigated for twenty-four rabbit medial collateral ligaments from twenty-four rabbits of different ages, respectively. One-way analysis of variance was used in the comparison of the Young's modulus in the linear region of the stress-strain curves and the ratios of type I and III collagen for the specimens (the mid-substance specimens of the ligaments) with different ages. A multiple linear regression was performed using the collagen contents (the ratios of type I and III collagen) and the Young's modulus of the specimens. During the maturation of the ligaments, the type I collagen content increased, and the type III collagen content decreased. A significant and strong correlation (R2 = 0.839, P < 0.05) was identified by multiple linear regression between the collagen contents (i.e., the ratios of type I and type III collagen) and the mechanical properties of the specimens. The collagen content of ligaments might provide a new perspective for evaluating the linear modulus of global stress-strain curves for ligaments and open a new door for studying the mechanical behaviors and functions of connective tissues.

The effect of the material property change of anterior cruciate ligament by ageing on joint kinematics and biomechanics under tibial varus/valgus torques.

It is known that the anterior cruciate ligament (ACL) plays a role in providing joint stabilities under tibial varus/valgus torques and the material behavior of the ACL has changed with ageing. However, the effect of this variation of the ACL material property on joint kinematics and biomechanics under tibial varus/valgus torques has still not been clarified.In this paper, three finite element (FE) models of an intact tibiofemoral joint were reconstructed with different ACL material properties, corresponding to the ACL on the younger, middle and older ages, respectively. The joint kinematics, the stress distribution and resultant force of the ACL were obtained under a tibial varus or valgus torque load. It was found that the variation in the ACL material property would result in great changes in some joint displacements (i.e., the tibial anterior translation and external rotation). The maximal stress value in the ACL had also altered while the stress distribution did not varied obviously. The great change in the tibial anterior translation illustrated that ACL played an important role against varus/valgus torques by controlling the coupled tibial anterior translation//external rotation rather than the corresponding varus/valgus rotation.

A comparison of material characterizations in frequently used constitutive models of ligaments.

Longitudinal tensile and simple shear stress-strain curves of human medial collateral ligaments (MCL) were fitted by six frequently used constitutive relations of ligaments using two different fitting methods for determining which was the best fitting method and the most preferable constitutive model for describing the ligament properties. According to the results of fitting goodness, two typical constitutive models were further analyzed by FEM to investigate the effect of the variation in MCL constitutive models under some physiological loads (i.e., 4.5 Nm external tibial and 10 Nm valgus tibial torques). It was found that different fitting methods induced great variations in describing the simple shear behavior whereas no obvious difference in the longitudinal tensile behavior. The most accurate description of both the longitudinal tensile and simple shear behaviors was obtained from the constitutive model with ground substance defined by an exponential function when the parameters were fitted by the two test data, respectively. Although the distributions of maximal principal stress were almost the same, the variation in MCL constitutive models affected the highest value of the stress greatly when MCL was under the complex physiological loads.