Stress Relaxation Behavior of Collagen Type II- Silk Fibroin Composite Cartilage Scaffold under Different Degradation Cycles / 医用生物力学

Objective To study stress relaxation behaviors of cartilage scaffolds under different degradation cycles by using finite element analysis combined with theoretical models. Methods Based on the established degradation theoretical model, the elastic modulus of the scaffold was calculated under different degradation cycles. The finite element model of cartilage scaffolds was established and stress relaxation simulation was performed to analyze the variation of scaffold relaxation stress with time. The stress relaxation constitutive model was established to predict mechanical properties of the scaffold. Results The elastic modulus of cartilage scaffolds at 14 th, 28th, 42nd, 56th day after degradation was 32. 35, 31. 12, 29. 91, 28. 74 kPa, respectively. The upper layer for cartilage scaffolds was the largest. The overall relaxation stress of the scaffold decreased rapidly with time and then tended to be stable. At 8th week after degradation, the stress which the scaffold couldwithstand was still within the physiological load range of the cartilage. The predicted results of the stress relaxation constitutive model were in good agreement with the finite element simulation results. Conclusions The elastic modulus of the scaffold gradually decreases with the increase of degradation time. The longer the degradation period is, the less stress the scaffold can withstand. At the same degradation period, the larger the applied compressive strain, the larger the stress on the scaffold. Both the finite element simulation and stress relaxation constitutive model can effectively predict stress variations of cartilage scaffolds under degradation

Influencing Factors of Renal Blunt Impact Injury: A Finite Element Method Study / 医用生物力学

Objective To study influencing factors of renal blunt impact injury by using finite element (FE) method. Methods Based on CT images of the kidney, the kidney FE models for different age groups were constructed. The renal blunt impact test was reconstructed, and the influence of kidney material constitutive parameters, kidney tissue structure, kidney size, impact position and impact velocity on injury severity were analyzed. Results Under the same impact condition, the stress of renal cortex decreased with the kidney mass increasing, and increased with the impact velocity of the hammer increasing. The renal capsule had a certain energy absorption effect, so as to reduce the kidney stress. When the kidney was impacted, the stress of renal cortex under side impact was significantly higher than that under frontal impact. Conclusions Compared with viscoelastic constitutive model, Mooney Rivlin material constitutive model is more suitable for FE evaluation on renal injury severity. The renal injury decreases with the kidney mass increasing. The increase of impact velocity will intensify the renal injury severity. Renal capsule will reduce renal injury to a certain extent, so the existence of renal capsule structure must be considered in FE modeling of the kidney. Compared with frontal and rear impact, the renal injury severity is greater when the kidney is impacted from the lateral side.

Reverse and Optimization for Constitutive Parameters of Adipose Tissues Based on Feasible Direction Method / 医用生物力学

Objective To study the constitutive model of adipose tissue at medium strain rate and its parameter inversion. Methods Based on experiments of adipose tissue mechanical properties, the compression experiment of adipose tissues was reconstructed by finite element method, and the parameters for characterizing constitutive models of adipose tissues were screened. Combined with the method of feasible direction (MFD) in optimization method, the reverse calculation for parameters of fat tissue constitutive model at medium strain rate was conducted. ResultsCompared with Ogden constitutive model, the viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate (260 s-1). The parameters of the constitutive model suitable for simulation were obtained using the reverse method. Conclusions The viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate. The results provide references for studying the influence of human adipose tissues on body injury in finite element simulation of vehicle collisions.

Numerical Model for Calculating Active and Passive Properties of Muscles with High Strain Rate / 医用生物力学

Objective On the basis of explicit dynamics calculation theory, a numerical model for calculating active and passive properties of muscles with high strain rate was proposed. Methods In the process of calculating the motion equation of muscle element with high strain rate, Hill’s three-factor muscle model with high strain rate was introduced into the noda force formula to modify the node force in each time step. Results As Hill’s three-factor muscle model was introduced in numerical calculation, the muscle element had the passive characteristics of the general structural constitutive model and its proprietary active characteristics. Conclusions The research findings will contribute to numerical calculation for dynamic response and damage of muscles with high strain rate.

Research progress in biomechanical properties and numerical simulation of periodontal ligament during orthodontic tooth movement / 国际生物医学工程杂志

Orthodontic tooth movement is achieved by remodeling periodontal ligament, alveolar bone and other periodontal tissues in response to mechanical loading. The periodontal ligament is the fibrous connective tissue connecting cementum and alveolar bone, which plays an important role in the transmission, absorption and dispersion of supporting teeth and biting force. When orthodontic forces are applied to the teeth, load transfer occurs from the tooth through the periodontal ligament to the alveolar bone. The remodeling of periodontal ligament interacts with the alveolar bone formation and absorption alternately. As the initial factor of orthodontic tooth movement, the stress/strain of periodontal ligament is involved in the process of alveolar bone remodeling and affects the direction and speed of tooth movement. Therefore, the biomechanical properties of the periodontal ligament have received extensive attention. In this paper, the related researches on the structural changes and biomechanical characteristics of the periodontal ligament during orthodontic tooth movement were reviewed as well as the researches on the mechanical constitutive model of the periodontal ligament. The mechanical response and biomechanical mechanism of the periodontal ligament were discussed in order to provide a theoretical basis for accurate numerical simulation of orthodontic tooth movement.

A Continuum Constitutive Model of skeletal Muscle at Variable Strain Rate / 医用生物力学

Objective Aiming at the problem that mechanical properties for the continuum of muscle tissues cannot be considered in active and passive behaviors of different structurally coupled muscles, a method of passive and active coupling in the same constitutive equation was proposed to construct ahyperelastic active and passive constitutive model of skeletal muscle continuum. Methods In order to calibrate parameters of the passive constitutive model, the uniaxial tensile experiment method and conditions were given, and through theoretical derivation, the specific method of using experimental data to solve the passive model parameters was introduced. In order to verify effectiveness of the active model, the model was verified with an example. Results The curves predicted by the model were in good agreement with the experimental output stress-stretch ratio curves. At the same strain, the maximum error of passive stress and total stress were only 20 kPa and 40 kPa. Conclusions The continuum hyperelastic constitutive model can better simulate active and passive behavior of skeletal muscles, which is beneficial for modeling and simulation of human muscles in further study.

Experimental measurement and modeling analysis of active and passive mechanical properties of arterial vessel wall / 生物医学工程学杂志

Coronary artery diseases (CAD) have always been serious threats to human health. The measurement, constitutive modeling, and analysis of mechanical properties of the blood vessel wall can provide a tool for disease diagnosis, stent implantation, and artificial artery design. The vessel wall has both active and passive mechanical properties. The passive mechanical properties are mainly determined by elastic and collagen fibers, and the active mechanical properties are determined by the contraction of vascular smooth muscle cells (VSMC). Substantial studies have shown that, the two-layer model of the vessel wall can feature the mechanical properties well, and the circumferential, axial and radial strain and stress are of great significance in arterial wall mechanics. This study reviewed recent investigations of mechanical properties of the vessel wall. Challenges and opportunities in this area are discussed relevant to the clinical treatment of coronary artery diseases.

Experiments study on mechanical behavior of porcine lumbar intervertebral disc after nucleotomy under compression / 生物医学工程学杂志

In order to study the mechanical behavior of degeneration and nucleotomy of lumbar intervertebral disc, compression experiments with porcine lumbar intervertebral discs were carried out. The lumbar intervertebral discs with trypsin-treated and nucleus nucleotomy served as the experimental group and the normal discs as the control group. Considering the effects of load magnitude and loading rate, the relationship between stress and strain, instantaneous elastic modulus and creep property of intervertebral disc were obtained. The creep constitutive model was established. The results show that the strain and creep strain of the experimental group increase significantly with the increase of compression load and loading rate, whereas the instantaneous elastic modulus decreases obviously, compared with the control group. It indicates that the effect of load magnitude and loading rate on load-bearing capacity of intervertebral disc after nucleotomy is larger obviously than that of normal disc. The creep behavior of the experimental group can be still predicted by the Kelvin three-parameter solid model. The results will provide theoretical foundation for clinical treatment and postoperative rehabilitation of intervertebral disc disease.

The elimination method of preloading force for soft tissue based on the linear loading region / 生物医学工程学杂志

Aiming at the problem of the influence of preloading force on its mechanical response in soft tissue compression experiments, an elimination method of preloading force based on linear loading region is proposed. Unconfined compression experiments under a variety of different preloading forces are performed. The influence of the preloading force on the parameters of constitutive model is analyzed. In the preload phase, the mechanical response of the soft tissue is taken as a linear model. The preloading force is eliminated by taking the preloading phase into account throughout the response process. According to five different preloading forces of the unconfined compression experiments, the elimination method is validated with two different constitutive models of soft tissue, and the error between the models obtained by the preloading force elimination method and the traditional method with the experimental results is compared. The results show that the error obtained by preloading force elimination method is significantly smaller than the traditional method. The preloading force elimination method can eliminate the influence of preloading force on mechanical response to a certain extent, and constitutive model parameters which are closer to the true properties of soft tissue can be obtained.

Testing of Mechanical Properties of Ballistic Gelatin / 医用生物力学

Objective To study the mechanical properties of ballistic gelatin and establish a dynamic constitutive model by a numerical method to lay the foundation for the related research on wound ballistics. Methods First, 20% ballistic gelatin samples at 10°C were prepared, and then, the quasi static and dynamic compressive mechanical properties of the ballistic gelatin were tested using a universal material testing machine and an aluminum Hopkinson bar, respectively. Results The quasi-static and dynamic compressive stress-strain curves of 20% ballistic gelatin at 10 ℃ were obtained. When the strain was 0.45, the true stress was 0.041, 0.083, 0.194, 14.515, 31.496, 55.597, and 96.678 MPa at a strain rate of 10-3, 10-2, 10-1, 5 800, 7 900, 10 400, and 13 000 s-1, respectively. When the strain rate was 13 000 s-1 and the strain increased from 0.4 to 0.5, the stress increased rapidly from 53.558 MPa to 164.417 MPa, equivalent to an increase by over 3.07 times. Conclusions The ballistic gelatin had a remarkable strain rate effect in the range of both low and high strain rates. The constitutive model with strain rate was established based on the experimental results with the form of σ=kε·mεn, and the material constants of 20% ballistic gelatin were obtained.

Analysis on constitutive models and biomechanical properties of brain / 医用生物力学

Brain injury has become the most severe injury in traffic accident due to its high incidence and high fatality rate. The brain injury model plays a critical role in researches on brain injury. The constitutive model and the material properties used in the model are key factors in determining the accuracy of injury prediction. The present paper aims to review the application of constitutive models and material properties in brain simulation so as to better understand biomechanical properties of brain and provide references for finite element researches on brain injury.

Development of a nonlinear 3D solid finite element model for the calculation of bending moments of flexural members / 药物分析学报

A numerical model is developed in this paper to calculate the bending moments of flexural members through integration in 3D solid finite element analyses according to the nonlinear constitutive model of concrete and the elastoplastic constitutive model of steel, utilizing the stress condition of the cross-section, considering the destruction characteristic of reinforced concrete members, and based on the plane cross-section assumption. The results of this model give good agreement with those of the classical method. Consequently, we can also deduce the corresponding numerical expression for eccentrically loaded members according to the analysis method.