2022年3月课题组在JCR一区期刊“Computers in Biology and Medicine”发表研究论文

2022年3月，课题组博士生孙仲伟以第一作者身份在JCR一区期刊“Computers in Biology and Medicine”第145卷（2022）发表题为“A finite element study on the effects of follower load on the continuous biomechanical responses of subaxial cervical spine”的研究论文，谨致热烈祝贺！论文官方网页和摘要如下。

论文官方网页：

https://www.sciencedirect.com/science/article/pii/S0010482522002670?via%3Dihub

论文摘要：

In spine biomechanics, follower loads are used to mimic the in vivo muscle forces acting on a human spine. However, the effects of the follower load on the continuous biomechanical responses of the subaxial cervical spines (C2-T1) have not been systematically clarified. This study aims at investigating the follower load effects on the continuous biomechanical responses of C2-T1. A nonlinear finite element model is reconstructed and validated for C2-T1. Six levels follower loads are considered along the follower load path that is optimized through a novel range of motion-based method. A moment up to 2 Nm is subsequently superimposed to produce motions in three anatomical planes. The continuous biomechanical responses, including the range of motion, facet joint force, intradiscal pressure and flexibility are evaluated for each motion segment. In the sagittal plane, the change of the overall range of motion arising from the follower loads is less than 6%. In the other two anatomical planes, both the magnitude and shape of the rotation-moment curves change with follower loads. At the neutral position, over 50% decrease in flexibility occurs as the follower load increases from zero to 250 N. In all three anatomical planes, over 50% and 30% decreases in flexibility occur in the first 0.5 Nm for small (≤100 N) and large (≥150 N) follower loads, respectively. Moreover, follower loads tend to increase both the facet joint forces and the intradiscal pressures. The shape of the intradiscal pressure-moment curves changes from nonlinear to roughly linear with increased follower load, especially in the coronal and transverse planes. The results obtained in this work provide a comprehensive understanding on the effects of follower load on the continuous biomechanical responses of the C2-T1.

关键词：

Follower load; Continuous biomechanical response; Subaxial cervical spine; Finite element modeling; Logarithmic rotation-moment relation

2023年3月课题组在JCR一区期刊“Computer Methods and Programs in Biomedicine”发表研究论文

2023年3月，课题组博士生孙仲伟以第一作者身份在JCR一区期刊“Computer Methods and Programs in Biomedicine”第235卷（2023）发表题为“A swelling-based biphasic analysis on the quasi-static biomechanical behaviors of healthy and degenerative intervertebral discs”的研究论文，谨致热烈祝贺！论文官方网页和摘要如下：

论文官方网页：

https://www.sciencedirect.com/science/article/pii/S0169260723001785?via%3Dihub

论文摘要：

Background and Objective

The degeneration of intervertebral discs is significantly dependent of the changes in tissue composition ratio and tissue structure. Up to the present, the effects of degeneration on the quasi-static biomechanical responses of discs have not been well understood. The goal of this study is to quantitatively analyze the quasi-static responses of healthy and degenerative discs.

Methods

Four biphasic swelling-based finite element models are developed and quantitatively validated. Four quasi-static test protocols, including the free-swelling, slow-ramp, creep and stress-relaxation, are implemented. The double Voigt and double Maxwell models are further used to extract the immediate (or residual), short-term and long-term responses of these tests.

Results

Simulation results show that both the swelling-induced pressure in the nucleus pulposus and the initial modulus decrease with degeneration. In the free-swelling test of discs possessing healthy cartilage endplates, simulation results show that over 80% of the total strain is contributed by the short-term response. The long-term response is dominant for discs with degenerated permeability in cartilage endplates. For the creep test, over 50% of the deformation is contributed by the long-term response. In the stress-relaxation test, the long-term stress contribution occupies approximately 31% of total response and is independent of degeneration. Both the residual and short-term responses vary monotonically with degeneration. In addition, both the glycosaminoglycan content and permeability affect the engineering equilibrium time constants of the rheologic models, in which the determining factor is the permeability.

Conclusions

The content of glycosaminoglycan in intervertebral soft tissues and the permeability of cartilage endplates are two critical factors that affect the fluid-dependent viscoelastic responses of intervertebral discs. The component proportions of the fluid-dependent viscoelastic responses depend also strongly on test protocols. In the slow-ramp test, the glycosaminoglycan content is responsible for the changes of the initial modulus. Since existing computational models simulate disc degenerations only by altering disc height, boundary conditions and material stiffness, the current work highlights the significance of biochemical composition and cartilage endplates permeability in the biomechanical behaviors of degenerated discs.

关键词：

Degenerative intervertebral discs；Biphasic swelling model；Quantitative validation；Quasi-static biomechanics；Rheologic modeling

2023年7月课题组在生物力学权威期刊“Journal of Biomechanics”发表论文

2023年7月，课题组博士生孙仲伟以第一作者身份在生物力学权威期刊“Journal of biomechanics”第157卷（2023）发表题为“On the identification of the ultra-structural organization of elastic fibers and their effects on the integrity of annulus fibrosus”的研究论文，谨致热烈祝贺！论文官方网页和摘要如下。

论文官方网页：

https://www.sciencedirect.com/science/article/pii/S002192902300297X?via%3Dihub

论文摘要：

Due to the complicated structure of the elastic fiber network in annulus fibrosus, existing in-silico studies either simplified or just overlooked its distribution pattern. Nonetheless, experimental and simulation results have proven that elastic fibers are of great importance to maintaining the structural integrity of annulus fibrosus and therefore to ensuring the load-bearing ability of intervertebral discs. Such needs call for a fine model. This work aims at developing a biphasic annulus fibrosus model by incorporating the accurate distribution pattern of collagen and elastic fibers. Both the structural parameters and intrinsic mechanical parameters were successfully identified using single lamella and inter-lamella microscopy anatomy and micromechanical testing data. The proposed model was then used to implement finite element simulations on various anterior and posterolateral multi-lamellae annulus fibrosus specimens. In general, simulation results agree well with available experimental and simulation data. On this basis, the effects of elastic fibers on the integrity of annulus fibrosus were further investigated. It was found that elastic fibers significantly influence the free swelling, radial stretching and circumferential shear performances of annulus fibrosus. Nonetheless, no significant effects were found for the circumferential stretching capability. The proposed biphasic model considers for the first time the distribution characteristics of elastic fiber at two levels, for both the principal orientation of each fiber family and the distribution of fiber within each fiber family. Better understandings on the functions of collagen and elastic fibers can therefore be realized. To further enhance its prediction capability, the current model can be extended in the future by taking the fiber-matrix interaction as well as progressive damages into consideration.

关键词：

Annulus fibrosus; Elastic fiber distribution; Collagen fiber distribution; Constitutive modeling; Finite element simulation