Linking cortex and contraction-Integrating models along the corticomuscular pathway

Computational models of the neuromusculoskeletal system provide a deterministic approach to investigate input-output relationships in the human motor system. Neuromusculoskeletal models are typically used to estimate muscle activations and forces that are consistent with observed motion under healthy and pathological conditions. However, many movement pathologies originate in the brain, including stroke, cerebral palsy, and Parkinson's disease, while most neuromusculoskeletal models deal exclusively with the peripheral nervous system and do not incorporate models of the motor cortex, cerebellum, or spinal cord. An integrated understanding of motor control is necessary to reveal underlying neural-input and motor-output relationships. To facilitate the development of integrated corticomuscular motor pathway models, we provide an overview of the neuromusculoskeletal modelling landscape with a focus on integrating computational models of the motor cortex, spinal cord circuitry, α-motoneurons  and skeletal muscle in regard to their role in generating voluntary muscle contraction. Further, we highlight the challenges and opportunities associated with an integrated corticomuscular pathway model, such as challenges in defining neuron connectivities, modelling standardisation, and opportunities in applying models to study emergent behaviour. Integrated corticomuscular pathway models have applications in brain-machine-interaction, education, and our understanding of neurological disease.

Modelling motor units in 3D: influence on muscle contraction and joint force via a proof of concept simulation

Functional heterogeneity is a skeletal muscle’s ability to generate diverse force vectors through localised motor unit (MU) recruitment. Existing 3D macroscopic continuum-mechanical finite element (FE) muscle models neglect MU anatomy and recruit muscle volume simultaneously, making them unsuitable for studying functional heterogeneity. Here, we develop a method to incorporate MU anatomy and information in 3D models. Virtual fibres in the muscle are grouped into MUs via a novel “virtual innervation” technique, which can control the units’ size, shape, position, and overlap. The discrete MU anatomy is then mapped to the FE mesh via statistical averaging, resulting in a volumetric MU distribution. Mesh dependency is investigated using a 2D idealised model and revealed that the amount of MU overlap is inversely proportional to mesh dependency. Simultaneous recruitment of a MU’s volume implies that action potentials (AP) propagate instantaneously. A 3D idealised model is used to verify this assumption, revealing that neglecting AP propagation results in a slightly less-steady force, advanced in time by approximately 20 ms, at the tendons. Lastly, the method is applied to a 3D, anatomically realistic model of the masticatory system to demonstrate the functional heterogeneity of masseter muscles in producing bite force. We found that the MU anatomy significantly affected bite force direction compared to bite force magnitude. MU position was much more efficacious in bringing about bite force changes than MU overlap. These results highlight the relevance of MU anatomy to muscle function and joint force, particularly for muscles with complex neuromuscular architecture.

A biophysically guided constitutive law of the musculotendon-complex: modelling and numerical implementation in Abaqus

BACKGROUND AND OBJECTIVE

Many biomedical, clinical, and industrial applications may benefit from musculoskeletal simulations. Three-dimensional macroscopic muscle models (3D models) can more accurately represent muscle architecture than their 1D (line-segment) counterparts. Nevertheless, 3D models remain underutilised in academic, clinical, and commercial environments. Among the reasons for this is a lack of modelling and simulation standardisation, verification, and validation. Here, we strive towards a solution by providing an open-access, characterised, constitutive relation (CR) for 3D musculotendon models.

METHODS

The musculotendon complex is modelled following the state-of-the-art active stress approach and is treated as hyperelastic, transversely isotropic, and nearly incompressible. Furthermore, force-length and -velocity relationships are incorporated, and muscle activation is derived from motor-unit information. The CR was implemented within the commercial finite-element software package Abaqus as a user-subroutine. A masticatory system model with left and right masseters was used to demonstrate active and passive movement.

RESULTS

The CR was characterised by various experimental data sets and was able to capture a wide variety of passive and active behaviours. Furthermore, the masticatory simulations revealed that joint movement was sensitive to the muscle's in-fibre passive response.

CONCLUSIONS

This user-material provides a "plug and play" template for 3D neuro-musculoskeletal finite element modelling. We hope that this reduces modelling effort, fosters exchange, and contributes to the standardisation of such models.

Comparative Study of a Biomechanical Model-based and Black-box Approach for Subject-Specific Movement Prediction. Annu Int Conf IEEE Eng Med Biol Soc 2020;2020:4775-4778. [PMID: 33019058 DOI: 10.1109/embc44109.2020.9176600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The performance and safety of human robot interaction (HRI) can be improved by using subject-specific movement prediction. Typical models include biomechanical (parametric) or black-box (non-parametric) models. The current work aims to investigate the benefits and drawbacks of these approaches by comparing elbow-joint torque predictions based on electromyography signals of the elbow flexors and extensors. To this end, a parameterized biomechanical model is compared to a non-parametric (Gaussian-process) approach. Both models showed adequate results in predicting the elbow-joint torques. While the non-parametric model requires minimal modeling effort, the parameterized biomechanical model can lead to deeper insight of the underlying subject specific musculoskeletal system.

Occlusal load modelling significantly impacts the predicted tooth stress response during biting: a simulation study

Computational models of the masticatory system can provide estimates of occlusal loading during (static) biting or (dynamic) chewing and therefore can be used to evaluate and optimize functional performance of prosthodontic devices and guide dental surgery planning. The modelling assumptions, however, need to be chosen carefully in order to obtain meaningful predictions. The objectives of this study were two-fold: (i) develop a computational model to calculate the stress response of the first molar during biting of a rubber sample and (ii) evaluate the influence of different occlusal load models on the stress response of dental structures. A three-dimensional finite element model was developed comprising the mandible, first molar, associated dental structures, and the articular fossa and discs. Simulations of a maximum force bite on a rubber sample were performed by applying muscle forces as boundary conditions on the mandible and computing the contact between the rubber and molars (GS case). The molar occlusal force was then modelled as a single point force (CF1 case), four point forces (CF2 case), and as a sphere compressing against the occlusal surface (SL case). The peak enamel stress for the GS case was 110 MPa and 677 MPa, 270 MPa and 305 MPa for the CF1, CF2 and SL cases, respectively. Peak dentin stress for the GS case was 44 MPa and 46 MPa, 50 MPa and 63 MPa for the CF1, CF2 and SL cases, respectively. Furthermore, the enamel stress distribution was also strongly correlated to the occlusal load model. The way in which occlusal load is modelled has a substantial influence on the stress response of enamel during biting, but has relatively little impact on the behavior of dentin. The use of point forces or sphere contact to model occlusal loading during mastication overestimates enamel stress magnitude and also influences enamel stress distribution.

A novel computational method to determine subject-specific bite force and occlusal loading during mastication

The evaluation of three-dimensional occlusal loading during biting and chewing may assist in development of new dental materials, in designing effective and long-lasting restorations such as crowns and bridges, and for evaluating functional performance of prosthodontic components such as dental and/or maxillofacial implants. At present, little is known about the dynamic force and pressure distributions at the occlusal surface during mastication, as these quantities cannot be measured directly. The aim of this study was to evaluate subject-specific occlusal loading forces during mastication using accurate jaw motion measurements. Motion data was obtained from experiments in which an individual performed maximal effort dynamic chewing cycles on a rubber sample with known mechanical properties. A finite element model simulation of one recorded chewing cycle was then performed to evaluate the deformation of the rubber. This was achieved by imposing the measured jaw motions on a three-dimensional geometric surface model of the subject's dental impressions. Based on the rubber's deformation and its material behaviour, the simulation was used to compute the resulting stresses within the rubber as well as the contact pressures and forces on the occlusal surfaces. An advantage of this novel modelling approach is that dynamic occlusal pressure maps and biting forces may be predicted with high accuracy and resolution at each time step throughout the chewing cycle. Depending on the motion capture technique and the speed of simulation, the methodology may be automated in such a way that it can be performed chair-side. The present study demonstrates a novel modelling methodology for evaluating dynamic occlusal loading during biting or chewing.

Comparative evaluation of antimicrobial efficacy of Syzygium aromaticum, Ocimum sanctum and Cinnamomum zeylanicum plant extracts against Enterococcus faecalis: a preliminary study

AIM

To evaluate the antimicrobial efficacy of Ocimum sanctum, Cinnamomum zeylanicum, Syzygium aromaticum and 3% sodium hypochlorite (NaOCl) against Enterococcus faecalis in planktonic suspension and biofilm phenotypes.

METHODOLOGY

The antibacterial efficacy of different concentrations of aqueous ethanolic extracts of O. sanctum, C. zeylanicum and S. aromaticum against E. faecalis at various time intervals was assessed using the agar well diffusion test, microdilution test and biofilm susceptibility assay (BSA) on cellulose nitrate membrane as well as in a tooth model. NaOCl was used as the positive control. Distilled water was used as negative control for agar diffusion and microdilution tests and phosphate-buffered saline for the BSA. The results of the agar diffusion test were analysed statistically using anova and Tukey's tests.

RESULTS

Cinnamomum zeylanicum, S. aromaticum and O. sanctum exhibited minimum bactericidal concentration at 10%, 10% and 40%, respectively. Cinnamomum zeylanicum, S. aromaticum, O. sanctum and NaOCl showed complete bacterial inhibition in planktonic form after exposure of 30, 15, 35 and 1 min, respectively. In BSA on cellulose nitrate membrane, NaOCl was associated with complete bacterial inhibition after contact of 2 min, whilst 10% C. zeylanicum, 10% S. aromaticum and 40% O. sanctum showed cessation of growth after 12, 12 and 24 h, respectively. The results of BSA on tooth model were similar except for O. sanctum, which was not included in the model.

CONCLUSION

Cinnamomum zeylanicum, S. aromaticum and O. sanctum demonstrated antimicrobial activity against planktonic and biofilm forms of E. faecalis with C. zeylanicum and S. aromaticum having better antimicrobial efficacy than O. sanctum. NaOCl had superior antimicrobial efficacy amongst all the groups.

Class Level Test Case Generation in Object Oriented Software Testing

Object-oriented programming consists of several different levels of abstraction, namely, the algorithmic level, class level, cluster level, and system level. In this article, we discuss a testing technique to generate test cases at class level for object-oriented programs. The formal object oriented class specification is used to develop a test model. This test model is based on finite state machine specification. The class specification and the test model is analyzed to select a set of test data for each method of the class, and finally the test cases can be generated using other testing techniques like finite-state testing or data-flow testing.

The development of a membrane-based screening method to detect antibodies to intermediate filament proteins

Autoantibodies directed against the intermediate filament proteins (IF) arise in a variety of disease states. The authors have investigated the binding of the IF to solid membrane supports in a dot blot format in an attempt to develop a simple procedure to detect antibodies (ab) to IF. Commercially obtained, purified IF were utilized. These were: vimentin (VIM), cytokeratin 8 (CYK), glial fibrillary acidic protein (GFA), desmin (DES), and the neurofilament triplet proteins (68, 160, and 200 KDa, respectively designated LMW, MMW, and HMW). Murine monoclonal antibody (mAb) probes were used to detect the presence and immunoreactivity of IF. The mAb were visualized with HRP-anti-mouse conjugates using alpha-chloronaphthol/H 2O 2 as substrate. The membranes studied were nitrocellulose (NC), and two of modified nylon. Nitrocellulose provided the most reproducible binding; no advantage was found to ensue from the use of the other membranes with regard either to quantitative binding or improved capping. Among the IF studied, VIM, GFA, LMW, MMW, and HMW bound well to NC; optimal mass/dot was 1 mug. Filtered, non-fat dry milk is a better capping agent than either albumin or fetal calf serum, but interferes with ab binding to GFA. Binding of CYK and DES is weak at neutral pH. Standard densitometric techniques provide the possibility of quantitation. We conclude that dot and slot blot assays may be practical methods to detect ab to IF antigens.