Mark S. Thompson

Reliably and accurately estimating joint/segmental kinematics from optical motion capture data has remained challenging. Studies objectively characterizing human movement patterns have typically involved inverse kinematics and inverse dynamics techniques. Subsequent research has included scaled cadaver-based musculoskeletal (MSK) modeling for noninvasively estimating joint and muscle loads. As one of the ways to enhance confidence in the validity of MSK model predictions, the kinematics from the preceding step that drives such a model needs to be checked for agreement or compared with established/widely used models. This study rigorously compares the upper extremity (UE) joint kinematics calculated by the Dutch Shoulder Model implemented in the AnyBody Managed Model Repository (involving multibody kinematics optimization (MKO)) with those estimated by the Vicon Plug-in Gait model (involving single-body kinematics optimization (SKO)). Ten subjects performed three trials of (different types of) reaching tasks in a three-dimensional marker-based optical motion capture laboratory setting. Joint angles, processed marker trajectories, and reconstruction residuals corresponding to both models were compared. Scatter plots and Bland–Altman plots were used to assess the agreement between the two model outputs. Results showed the largest differences between the two models for shoulder, followed by elbow and wrist, with all root-mean-squared differences less than 10 deg (although this limit might be unacceptable for clinical use). Strong-to-excellent Spearman's rank correlation coefficients were found between the two model outputs. The Bland–Altman plots showed a good agreement between most of the outputs. In conclusion, results indicate that these two models with different kinematic algorithms broadly agree with each other, albeit with few key differences.

The study presented in this paper details the development and experimental testing of a novel, magnetic, tactile feedback device that is able to deliver a stimulus to a patch of skin on the lower arm of a user. The device utilizes magnets to deliver a sensation that is not dependent on controlling specific frequency bands to stimulate the mechanoreceptors, as is the case with vibro-tactile methods. The device was tested on human volunteers to evaluate its ability to induce a response from the user through the magnetic interface. The study aims to quantify the ability of the user to sense the stimulus by analysis of the receiver operating characteristic (ROC) and delay in response under different experimental conditions. Three different speeds and two different distances were explored for the magnetic interface. A two-way, repeated-measures ANOVA with post-hoc analysis was performed for the percentage of correct responses, delay in response time, and area under the curve (AUC) of the obtained ROCs. The results showed that the different conditions had a significant effect on the number of correct responses and the AUC, but not on the delay. The magnetic interface thus needs to be optimized across different parameters to deliver the best detectable stimulus to the user. Future work includes further development of the device and working towards a comparative trial with other tactile feedback approaches.

Peripheral nerves, subject to continuous elongation and compression during everyday movement, contain neuron fibers vital for movement and sensation. At supraphysiological strains resulting from trauma, chronic conditions, aberrant limb positioning, or surgery, conduction blocks occur which may result in chronic or temporary loss of function. Previous in vitro stretch models, mainly focused on traumatic brain injury modelling, have demonstrated altered electrophysiological behavior during localized deformation applied by pipette suction. Our aim was to evaluate the changes in voltage‐activated ion channel function during uniaxial straining of neurons applied by whole‐cell deformation, more physiologically relevant model of peripheral nerve trauma. Here, we quantified experimentally the changes in inwards and outwards ion currents and action potential (AP) firing in dorsal root ganglion‐derived neurons subject to uniaxial strains, using a custom‐built device allowing simultaneous cell deformation and patch clamp recording. Peak inwards sodium currents and rectifying potassium current magnitudes were found to decrease in cells under stretch, channel reversal potentials were found to be left‐shifted, and half‐maximum activation potentials right‐shifted. The threshold for AP firing was increased in stretched cells, although neurons retained the ability to fire induced APs. Overall, these results point to ion channels being damaged directly and immediately by uniaxial strain, affecting cell electrophysiological activity, and can help develop prevention and treatment strategies for peripheral neuropathies caused by mechanical trauma.

Peripheral nerves are continuously subjected to mechanical strain during everyday movements, but excessive stretch can lead to damage and neuronal cell functionality can also be impaired. To better understand cellular processes triggered by stretch, it is necessary to develop in vitro experimental methods that allow multiple concurrent measurements and replicate in vivo mechanical conditions. Current commercially available cell stretching devices do not allow flexible experimental design, restricting the range of possible multi-physics measurements. Here, we describe and characterise a custom-built uniaxial substrate-straining device, with which neurons cultured on aligned patterned surfaces (50 µm wide grooves) can be strained up to 70% and simultaneously imaged with widefield and confocal imaging (up to 100x magnification). Furthermore, direct and indirect electrophysiological measurements by patch clamping and calcium imaging can be made during strain application. We characterise the strain applied to cells cultured in deformable wells by using finite element method simulations and experimental data, showing local surface strains of up to 60% with applied strains of up to 25%. We also show how patterned substrates do not alter the mechanical properties of the system compared to unpatterned surfaces whilst still inducing a homogeneous cell response to strain. The characterisation of this device will be useful for research into investigating the effect of whole-cell mechanical stretch on neurons at both single cell and network scales, with applications found in peripheral neuropathy modelling and in platforms for preventive and regenerative studies.