Multiscale cartilage biomechanics: technical challenges in realizing a high-throughput modelling and simulation workflow

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

Osteoarthritis year in review 2021: mechanics

Osteoarthritis (OA) has a complex, heterogeneous and only partly understood etiology. There is a definite role of joint cartilage pathomechanics in originating and progressing of the disease. Although it is still not identified precisely enough to design or select targeted treatments, the progress of this year's research demonstrates that this goal became much closer. On multiple scales - tissue, joint and whole body - an increasing number of studies were done, with impressive results. (1) Technology based instrument innovations, especially when combined with machine learning models, have broadened the applicability of biomechanics. (2) Combinations with imaging make biomechanics much more precise & personalized. (3) The combination of Musculoskeletal & Finite Element Models yield valid personalized cartilage loads. (4) Mechanical outcomes are becoming increasingly meaningful to inform and evaluate treatments, including predictive power from biomechanical models. Since most recent advancements in the field of biomechanics in OA are at the level of a proof op principle, future research should not only continue on this successful path of innovation, but also aim to develop clinical workflows that would facilitate including precision biomechanics in large scale studies. Eventually this will yield clinical tools for decision making and a rationale for new therapies in OA.

Multiscale biomechanics of the biphasic articular cartilage in the natural hip joint during routine activities

BACKGROUND AND OBJECTIVE

The investigation of the biomechanical behaviour of the articular cartilage (AC) under physiological loading is important to understand the joint function and onset of pathologies. This study aimed to develop a multiscale computational modelling approach and apply the approach to investigate the time-dependant biphasic behaviour of the AC in the natural hip joint under repetitive physiological loading over 80 cycles amongst six routine activities.

METHODS

A subject-specific musculoskeletal multibody dynamics (MBD) model was developed based on the anthropometry and motion capture data collected for a male subject. A corresponding FE model of the natural hip joint with biphasic AC was created based on the bone geometries exported from the MBD model. A multiscale computational modelling was then developed to couple the MBD model and the FE model and used to investigate the time-dependant biphasic behaviour of the AC under subject-specific physiological loading over 80 cycles amongst six routine activities.

RESULTS

The results showed that for all the activities considered, the interstitial fluid pressure in the AC supported over 80% of the loading. The maximum values of the peak contact pressure and peak fluid pressure for the whole cycle increased firstly and then remained stable over time from the 1st cycle to the 80th cycle. At these instants, the contact areas were located at the centre region of the AC. By contrast, when the contact area was located at the edge of the AC, these peak pressures were found to increase over time for some of the activities (squat, ascending stairs, descending stairs) but decrease for the other activities (normal walking, standing up, sitting down).

CONCLUSION

This study for the first time developed a multiscale computational modelling approach to couple a musculoskeletal MBD model of the body and a detailed FE model of the natural hip joint with biphasic AC, which enabled the evaluation of time-dependant biphasic behaviour of the AC under realistic physiological loading conditions. The study may have important implications in biomechanical studies of human cartilage to understand the joint function and biomechanical factors related to joint disease, and to support the development of cartilage substitution.

A Hybrid Microstructural-Continuum Multiscale Approach for Modeling Hyperelastic Fibrous Soft Tissue

The heterogeneous, nonlinear, anisotropic material behavior of biological tissues makes precise definition of an accurate constitutive model difficult. One possible solution to this issue would be to define microstructural elements and perform fully coupled multiscale simulation. However, for complex geometries and loading scenarios, the computational costs of such simulations can be prohibitive. Ideally then, we should seek a method that contains microstructural detail, but leverages the speed of classical continuum-based finite-element (FE) modeling. In this work, we demonstrate the use of the Holzapfel-Gasser-Ogden (HGO) model [1, 2] to fit the behavior of microstructural network models. We show that Delaunay microstructural networks can be fit to the HGO strain energy function by calculating fiber network strain energy and average fiber stretch ratio. We then use the HGO constitutive model in a FE framework to improve the speed of our hybrid model, and demonstrate that this method, combined with a material property update scheme, can match a full multiscale simulation. This method gives us flexibility in defining complex FE simulations that would be impossible, or at least prohibitively time consuming, in multiscale simulation, while still accounting for microstructural heterogeneity.

Hybrid fluorescence-AFM explores articular surface degeneration in early osteoarthritis across length scales

Atomic force microscopy (AFM) has become a powerful tool for the characterization of materials at the nanoscale. Nevertheless, its application to hierarchical biological tissue like cartilage is still limited. One reason is that such samples are usually millimeters in size, while the AFM delivers much more localized information. Here a combination of AFM and fluorescence microscopy is presented where features on a millimeter sized tissue sample are selected by fluorescence microscopy on the micrometer scale and then mapped down to nanometer precision by AFM under native conditions. This served us to show that local changes in the organization of fluorescent stained cells, a marker for early osteoarthritis, correlate with a significant local reduction of the elastic modulus, local thinning of the collagen fibers, and a roughening of the articular surface. This approach is not only relevant for cartilage, but in general for the characterization of native biological tissue from the macro- to the nanoscale. STATEMENT OF SIGNIFICANCE: Different length scales have to be studied to understand the function and dysfunction of hierarchically organized biomaterials or tissues. Here we combine a highly stable AFM with fluorescence microscopy and precisely motorized movement to correlate micro- and nanoscopic properties of articular cartilage on a millimeter sized sample under native conditions. This is necessary for unraveling the relationship between microscale organization of chondrocytes, micrometer scale changes in articular cartilage properties and nanoscale organization of collagen (including D-banding). We anticipate that such studies pave the way for a guided design of hierarchical biomaterials.

Prediction of patellofemoral joint kinematics and contact through co-simulation of rigid body dynamics and nonlinear finite element analysis

Joint-level rigid body dynamics simulations, when coupled with tissue-level finite element analyses, can simultaneously provide movement and tissue deformation metrics to understand mechanical interactions within the joint on a multi-scale level. In this study, a co-simulation workflow of a joint-level rigid body model that predicts the relative motion as a function of the non-linear cartilage response predicted by a non-linear implicit finite element solver is presented. Predictions are compared to in-vitro measurements (The Open Knee(s) project) in terms of the mean error and level-of-agreement: pressure_error = 0.46 MPa (level-of-agreement, -0.23 - 1.1 MPa); area_error = -89 mm² (level-of-agreement, -280 - 98 mm²) and contact force_error = 93 N (level-of-agreement, 7.8 - 180 N). The automated co-simulation control algorithm enables multiscale coupling between joint and tissue-level models with real-time two-way communication as opposed to the traditional feed-forward approach of multi-scale models.

Use of Computational Modeling to Study Joint Degeneration: A Review

Osteoarthritis (OA), a degenerative joint disease, is the most common chronic condition of the joints, which cannot be prevented effectively. Computational modeling of joint degradation allows to estimate the patient-specific progression of OA, which can aid clinicians to estimate the most suitable time window for surgical intervention in osteoarthritic patients. This paper gives an overview of the different approaches used to model different aspects of joint degeneration, thereby focusing mostly on the knee joint. The paper starts by discussing how OA affects the different components of the joint and how these are accounted for in the models. Subsequently, it discusses the different modeling approaches that can be used to answer questions related to OA etiology, progression and treatment. These models are ordered based on their underlying assumptions and technologies: musculoskeletal models, Finite Element models, (gene) regulatory models, multiscale models and data-driven models (artificial intelligence/machine learning). Finally, it is concluded that in the future, efforts should be made to integrate the different modeling techniques into a more robust computational framework that should not only be efficient to predict OA progression but also easily allow a patient’s individualized risk assessment as screening tool for use in clinical practice.

Numerical Study on Electromechanics in Cartilage Tissue with Respect to Its Electrical Properties

Hyaline cartilage undergoes many substantial age-related physiochemical and biomechanical changes that reduce its ability to overcome the effects of mechanical stress and injury. In quest of therapeutic options, magnetic stimulation and electrical stimulation (ES) have been proposed for improving tissue engineering approaches for the repair of articular cartilage. The aim of this study is to summarize in silico investigations involving induced electrical properties of cartilage tissue due to various biophysical stimuli along their respective mathematical descriptions. Based on these, a preliminary numerical study involving electromechanical transduction in bovine cartilage tissue has been carried out using an open source finite element computational software. The simulation results have been compared to experimental results from the literature. This study serves as a basis for further in silico studies to better understand the behavior of hyaline cartilage tissue due to ES and to find an optimal stimulation protocol for the cartilage regeneration. Moreover, it provides an overview of the basic models along with mathematical description and scope for future research regarding electrical behavior of the cartilage tissue using open source software.

Multiscale mechanics of the cervical facet capsular ligament, with particular emphasis on anomalous fiber realignment prior to tissue failure

The facet capsular ligaments encapsulate the bilateral spinal facet joints and are common sources of painful injury due to afferent innervation. These ligaments exhibit architectural complexity, which is suspected to contribute to the experimentally observed lack of co-localization between macroscopic strain and microstructural tissue damage. The heterogeneous and multiscale nature of this ligament, combined with challenges in experimentally measuring its microscale mechanics, hinders the ability to understand sensory mechanisms under normal or injurious loading. Therefore, image-based, subject-specific, multiscale finite-element models were constructed to predict the mechanical responses of the human cervical facet capsular ligament under uniaxial tensile stretch. The models precisely simulated the force-displacement responses for all samples ([Formula: see text]) and showed promise in predicting the magnitude and location of peak regional strains at two different displacements. Yet, there was a loss of agreement between the model and experiment in terms of fiber organization at large tissue stretch, possibly due to a lack of accounting for tissue failure. The mean fiber stretch ratio predicted by the models was found to be significantly higher in regions that exhibited anomalous fiber realignment experimentally than in regions with normal realignment ([Formula: see text]). The development of microstructural abnormalities was associated with the predicted fiber-level stretch ([Formula: see text]), but not with the elemental maximum principal stress or maximum principal strain by logistic regression. The multiscale models elucidate a potential mechanical basis for predicting injury-prone tissue domains and for defining the relationships between macroscopic ligament stretch and microscale pathophysiology in the subfailure regime.

Comparison of the effects of exercise with chondroitin sulfate on knee osteoarthritis in rabbits

Background

The aim of the study is to compare the effects of exercise therapy with chondroitin sulfate (CS) therapy in an experimental model of osteoarthritis (OA).

Methods

Twenty-one New Zealand rabbits were randomly divided into four groups: normal group (N group, n = 3); OA control group (C group, n = 6); OA plus medication group (CS group, n = 6); and OA plus exercise group (E group, n = 6). Four weeks after modeling, the rabbits were subjected to exercise (artificial, 30 min/time, 4 times/week) or medicated with CS (2% CS, 0.3 ml/time, once/week) for 4 weeks. Histopathological changes in treated joints were examined after staining. X-ray and scanning electron microscopy was used to evaluate the different therapies by examining the surfaces and joint spaces of the articular cartilage. RT-qPCR was used to assess chondrogenic gene expression including Col2, Col10, mmp-13, il-1β, adamats-5, and acan in the experimental groups.

Results

Histology showed both treatment groups resulted in cartilage that was in good condition, with increased numbers of chondrocytes, and the results of X-ray and scanning electron microscopy showed the therapeutic effect of exercise therapy is equivalent to CS therapy, surface articular cartilage was flat, and the of cartilage layer was thinning. All treated groups induced the expression of Col10 and Col2 and decreased expression of mmp-13, il-1β, and adamats-5 compared with the control groups. The expression of acan was upregulated in the E group and downregulated in the CS group. Furthermore, expression of Col10 was higher and il-1β was lower in the exercise group compared to that of the CS group.

Conclusion

These results indicate that exercise has a positive effect on OA compare with CS, and it also supplies reference for the movement mode to improve function.

Study of the Mechanical Environment of Chondrocytes in Articular Cartilage Defects Repaired Area under Cyclic Compressive Loading

COMSOL finite element software was used to establish a solid-liquid coupling biphasic model of articular cartilage and a microscopic model of chondrocytes, using modeling to take into account the shape and number of chondrocytes in cartilage lacuna in each layer. The effects of cyclic loading at different frequencies on the micromechanical environment of chondrocytes in different regions of the cartilage were studied. The results showed that low frequency loading can cause stress concentration of superficial chondrocytes. Moreover, along with increased frequency, the maximum value of stress response curve of chondrocytes decreased, while the minimum value increased. When the frequency was greater than 0.2 Hz, the extreme value stress of response curve tended to be constant. Cyclic loading had a large influence on the distribution of liquid pressure in chondrocytes in the middle and deep layers. The concentration of fluid pressure changed alternately from intracellular to peripheral in the middle layer. Both the range of liquid pressure in the upper chondrocytes and the maximum value of liquid pressure in the lower chondrocytes in the same lacunae varied greatly in the deep layer. At the same loading frequency, the elastic modulus of artificial cartilage had little effect on the mechanical environment of chondrocytes.

Bioinspired Technologies to Connect Musculoskeletal Mechanobiology to the Person for Training and Rehabilitation

Musculoskeletal tissues respond to optimal mechanical signals (e.g., strains) through anabolic adaptations, while mechanical signals above and below optimal levels cause tissue catabolism. If an individual's physical behavior could be altered to generate optimal mechanical signaling to musculoskeletal tissues, then targeted strengthening and/or repair would be possible. We propose new bioinspired technologies to provide real-time biofeedback of relevant mechanical signals to guide training and rehabilitation. In this review we provide a description of how wearable devices may be used in conjunction with computational rigid-body and continuum models of musculoskeletal tissues to produce real-time estimates of localized tissue stresses and strains. It is proposed that these bioinspired technologies will facilitate a new approach to physical training that promotes tissue strengthening and/or repair through optimal tissue loading.

The potential for intercellular mechanical interaction: simulations of single chondrocyte versus anatomically based distribution

Computational studies of chondrocyte mechanics, and cell mechanics in general, have typically been performed using single cell models embedded in an extracellular matrix construct. The assumption of a single cell microstructural model may not capture intercellular interactions or accurately reflect the macroscale mechanics of cartilage when higher cell concentrations are considered, as may be the case in many instances. Hence, the goal of this study was to compare cell-level response of single and eleven cell biphasic finite element models, where the latter provided an anatomically based cellular distribution representative of the actual number of cells for a commonly used [Formula: see text] edge cubic representative volume in the middle zone of cartilage. Single cell representations incorporated a centered single cell model and eleven location-corrected single cell models, the latter to delineate the role of cell placement in the representative volume element. A stress relaxation test at 10% compressive strain was adopted for all simulations. During transient response, volume- averaged chondrocyte mechanics demonstrated marked differences (up to 60% and typically greater than 10%) for the centered single versus the eleven cell models, yet steady-state loading was similar. Cell location played a marked role, due to inhomogeneity of the displacement and fluid pressure fields at the macroscopic scale. When the single cell representation was corrected for cell location, the transient response was consistent, while steady-state differences on the order of 1-4% were realized, which may be attributed to intercellular mechanical interactions. Anatomical representations of the superficial and deep zones, where cells reside in close proximity, may exhibit greater intercellular interactions, but these have yet to be explored.

Systems approaches in osteoarthritis: Identifying routes to novel diagnostic and therapeutic strategies

Systems orientated research offers the possibility of identifying novel therapeutic targets and relevant diagnostic markers for complex diseases such as osteoarthritis. This review demonstrates that the osteoarthritis research community has been slow to incorporate systems orientated approaches into research studies, although a number of key studies reveal novel insights into the regulatory mechanisms that contribute both to joint tissue homeostasis and its dysfunction. The review introduces both top-down and bottom-up approaches employed in the study of osteoarthritis. A holistic and multiscale approach, where clinical measurements may predict dysregulation and progression of joint degeneration, should be a key objective in future research. The review concludes with suggestions for further research and emerging trends not least of which is the coupled development of diagnostic tests and therapeutics as part of a concerted effort by the osteoarthritis research community to meet clinical needs. © 2017 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1573-1588, 2017.

In Vivo Multiscale and Spatially-Dependent Biomechanics Reveals Differential Strain Transfer Hierarchy in Skeletal Muscle

Biological tissues have a complex hierarchical architecture that spans organ to subcellular scales and comprises interconnected biophysical and biochemical machinery. Mechanotransduction, gene regulation, gene protection, and structure-function relationships in tissues depend on how force and strain are modulated from macro to micro scales, and vice versa. Traditionally, computational and experimental techniques have been used in common model systems (e.g., embryos) and simple strain measures were applied. But the hierarchical transfer of mechanical parameters like strain in mammalian systems is largely unexplored in vivo. Here, we experimentally probed complex strain transfer processes in mammalian skeletal muscle tissue over multiple biological scales using complementary in vivo ultrasound and optical imaging approaches. An iterative hyperelastic warping technique quantified the spatially-dependent strain distributions in tissue, matrix, and subcellular (nuclear) structures, and revealed a surprising increase in strain magnitude and heterogeneity in active muscle as the spatial scale also increased. The multiscale strain heterogeneity indicates tight regulation of mechanical signals to the nuclei of individual cells in active muscle, and an emergent behavior appearing at larger (e.g. tissue) scales characterized by dramatically increased strain complexity.

Osteoarthritis year in review 2016: mechanics

Inappropriate biomechanics, namely wear-and-tear, has been long believed to be a main cause of osteoarthritis (OA). However, this view is now being re-evaluated, especially when examined alongside mechanobiology and new biomechanical studies. These are multiscale experimental and computational studies focussing on cell- and tissue-level mechanobiology through to organ- and whole-body-level biomechanics, which focuses on the biomechanical and biochemical environment of the joint tissues. This review examined papers from April 2015 to April 2016, with a focus on multiscale experimental and computational biomechanical studies of OA. Assessing the onset or progression of OA at organ- and whole-body-levels, gait analysis, medical imaging and neuromusculoskeletal modelling revealed the extent to which tissue damage changes the view of inappropriate biomechanics. Traditional gait analyses studies reported that conservative treatments can alter joint biomechanics, thereby improving pain and function experienced by those with OA. Results of animal models of OA were consistent with these human studies, showing interactions among bone, cartilage and meniscus biomechanics and the onset and/or progression OA. Going down size scales, experimental and computational studies probed the nanosize biomechanics of molecules, cells and extracellular matrix, and demonstrated how the interactions between biomechanics and morphology affect cartilage dynamic poroelastic behaviour and pathways to OA. Finally, integration of multiscale experimental data and computational models were proposed to predict cartilage extracellular matrix remodelling and the development of OA. Summarising, experimental and computational methods provided a nuanced biomechanical understanding of the sub-cellular, cellular, tissue, organ and whole-body mechanisms involved in OA.

Osteoarthritis year in review 2015: mechanics

Motivated by the conceptual framework of multi-scale biomechanics, this narrative review highlights recent major advances with a focus on gait and joint kinematics, then tissue-level mechanics, cell mechanics and mechanotransduction, matrix mechanics, and finally the nanoscale mechanics of matrix macromolecules. A literature review was conducted from January 2014 to April 2015 using PubMed to identify major developments in mechanics related to osteoarthritis (OA). Studies of knee adduction, flexion, rotation, and contact mechanics have extended our understanding of medial compartment loading. In turn, advances in measurement methodologies have shown how injuries to both the meniscus and ligaments, together, can alter joint kinematics. At the tissue scale, novel findings have emerged regarding the mechanics of the meniscus as well as cartilage superficial zone. Moving to the cell level, poroelastic and poro-viscoelastic mechanisms underlying chondrocyte deformation have been reported, along with the response to osmotic stress. Further developments have emerged on the role of calcium signaling in chondrocyte mechanobiology, including exciting findings on the function of mechanically activated cation channels newly found to be expressed in chondrocytes. Finally, AFM-based nano-rheology systems have enabled studies of thin murine tissues and brush layers of matrix molecules over a wide range of loading rates including high rates corresponding to impact injury. With OA acknowledged to be a disease of the joint as an organ, understanding mechanical behavior at each length scale helps to elucidate the connections between cell biology, matrix biochemistry and tissue structure/function that may play a role in the pathomechanics of OA.

Multiscale cartilage biomechanics: technical challenges in realizing a high-throughput modelling and simulation workflow

Understanding the mechanical environment of articular cartilage and chondrocytes is of the utmost importance in evaluating tissue damage which is often related to failure of the fibre architecture and mechanical injury to the cells. This knowledge also has significant implications for understanding the mechanobiological response in healthy and diseased cartilage and can drive the development of intervention strategies, ranging from the design of tissue-engineered constructs to the establishment of rehabilitation protocols. Spanning multiple spatial scales, a wide range of biomechanical factors dictate this mechanical environment. Computational modelling and simulation provide descriptive and predictive tools to identify multiscale interactions, and can lead towards a greater comprehension of healthy and diseased cartilage function, possibly in an individualized manner. Cartilage and chondrocyte mechanics can be examined in silico, through post-processing or feed-forward approaches. First, joint-tissue level simulations, typically using the finite-element method, solve boundary value problems representing the joint articulation and underlying tissue, which can differentiate the role of compartmental joint loading in cartilage contact mechanics and macroscale cartilage field mechanics. Subsequently, tissue-cell scale simulations, driven by the macroscale cartilage mechanical field information, can predict chondrocyte deformation metrics along with the mechanics of the surrounding pericellular and extracellular matrices. A high-throughput modelling and simulation framework is necessary to develop models representative of regional and population-wide variations in cartilage and chondrocyte anatomy and mechanical properties, and to conduct large-scale analysis accommodating a multitude of loading scenarios. However, realization of such a framework is a daunting task, with technical difficulties hindering the processes of model development, scale coupling, simulation and interpretation of the results. This study aims to summarize various strategies to address the technical challenges of post-processing-based simulations of cartilage and chondrocyte mechanics with the ultimate goal of establishing the foundations of a high-throughput multiscale analysis framework. At the joint-tissue scale, rapid development of regional models of articular contact is possible by automating the process of generating parametric representations of cartilage boundaries and depth-dependent zonal delineation with associated constitutive relationships. At the tissue-cell scale, models descriptive of multicellular and fibrillar architecture of cartilage zones can also be generated in an automated fashion. Through post-processing, scripts can extract biphasic mechanical metrics at a desired point in the cartilage to assign loading and boundary conditions to models at the lower spatial scale of cells. Cell deformation metrics can be extracted from simulation results to provide a simplified description of individual chondrocyte responses. Simulations at the tissue-cell scale can be parallelized owing to the loosely coupled nature of the feed-forward approach. Verification studies illustrated the necessity of a second-order data passing scheme between scales and evaluated the role that the microscale representative volume size plays in appropriately predicting the mechanical response of the chondrocytes. The tools summarized in this study collectively provide a framework for high-throughput exploration of cartilage biomechanics, which includes minimally supervised model generation, and prediction of multiscale biomechanical metrics across a range of spatial scales, from joint regions and cartilage zones, down to that of the chondrocytes.