Upper Limb Kinematics of Handwriting among Children with and without Developmental Coordination Disorder.

Background: Children with developmental coordination disorder (DCD) often experience difficulties with handwriting legibility and speed. This study investigates the relationship between handwriting and upper limb kinematics to characterize movement patterns of children with DCD and typically developing (TD) children. Methods: 30 children with and without DCD matched for age, gender, and parent education were compared across handwriting abilities using a standardized handwriting assessment of both copied and dictated tasks (A-A Handwriting). The 3D motion capture system (Qualysis) was used to analyze upper limb kinematics and characterize movement patterns during handwriting and contrasted with written output. Results: Children with DCD wrote fewer legible letters in both copying and dictation. Children with DCD also showed poor automatization of key writing concepts. Atypical wrist postures were associated with reduced legibility for children with DCD (F (1,27) 4.71, p = 0.04, p-η2 = 0.15); whereas for TD children, better legibility was associated with greater variations in movement speed, particularly of the wrist (rho = −0.578, p < 0.05). Conclusion: Results reflect different movement parameters influencing handwriting in children with DCD. An improved understanding of the movement characteristics during handwriting of these children may assist intervention design.

Force chains in cell-cell mechanical communication.

Force chains (FCs) are a key determinant of the micromechanical properties and behaviour of heterogeneous materials, such as granular systems. However, less is known about FCs in fibrous materials, such as the networks composing the extracellular matrix (ECM) of biological systems. Using a finite-element computational model, we simulated the contraction of a single cell and two nearby cells embedded in two-dimensional fibrous elastic networks and analysed the tensile FCs that developed in the ECM. The role of ECM nonlinear elasticity on FC formation was evaluated by considering linear and nonlinear, i.e. exhibiting 'buckling' and/or 'strain-stiffening', stress-strain curves. The effect of the degree of cell contraction and network coordination value was assessed. We found that nonlinear elasticity of the ECM fibres influenced the structure of the FCs, facilitating the transition towards more distinct chains that were less branched and more radially oriented than the chains formed in linear elastic networks. When two neighbouring cells contract, a larger number of FCs bridged between the cells in nonlinear networks, and these chains had a larger effective rigidity than the chains that did not reach a neighbouring cell. These results suggest that FCs function as a route for mechanical communication between distant cells and highlight the contribution of ECM fibre nonlinear elasticity to the formation of FCs.

The correlation between upper extremity musculoskeletal symptoms and joint kinematics, playing habits and hand span during playing among piano students.

OBJECTIVE: We aimed to investigate the correlations between Upper Extremity Musculoskeletal Symptoms (MSD) and joint kinematics while playing the piano, as well as correlations between MSD and psychosocial, professional and personal habits, and bio-demographic risk factors of piano students. METHOD: This cross-sectional study included 15 piano students. The research tools included 3D motion capture, anthropometric measurements, and questionnaires for obtaining data about MSD, psychological, and personal factors. RESULTS: The piano students recruited for this study experienced a variety of MSD during the past 12 months, with a particularly high prevalence of neck pain (80%). Extreme wrist extension and/or elbow flexion while playing the piano also correlated with MSD. Additionally, this study identified correlations between MSD and hand span (r = -.69, p≤.004) and number of playing hours per week (r = .58, p≤.024). CONCLUSIONS: Anthropometric factors and playing patterns should be considered together with well-known MSD risk factors, like extreme and repetitive movements. However, considering each joint singularly might not be sufficient to prevent the development of MSD when instructing the piano player; accordingly, joint synchronization should also be considered.

Pressure distributions on the chair seat and backrest correlate with handwriting outcomes of school children.

BACKGROUND: Postures while sitting are believed to have an important influence on the process of writing and quality of handwriting, but data in this field are sparse. OBJECTIVES: The current study was undertaken to investigate correlations between 'ordinary' children's handwriting skills and their posture and stability while sitting. METHODS: Twenty-nine children with typical development (age 9.2±0.8 years) underwent the Hebrew Handwriting Evaluation, while the pressure distributions on their seats and backrests were recorded using a pressure mapping system. RESULTS: There was an increase in the odds of erasing and overwriting letters in dictation tasks when body displacements of the buttocks increased [Odds Ratio (OR) = 1.01, 95% CI 1.000-1.02, p = 0.050]. Children who did not lean on the backrest were more likely to have legible handwriting in copying tasks (OR = 0.136, 95% CI 0.026-0.723, p = 0.019). CONCLUSIONS: The awareness and involvement of health practitioners in sitting postures of children at school might promote activities such as writing. Further investigation of movement patterns while writing and of the correlations of these patterns with handwriting outcomes is recommended. More research regarding adjustments at the school environment for children with developmental disorders is also warranted.

Nonlinear Elasticity of the ECM Fibers Facilitates Efficient Intercellular Communication.

Biological cells embedded in fibrous matrices have been observed to form intercellular bands of dense and aligned fibers through which they mechanically interact over long distances. Such matrix-mediated cellular interactions have been shown to regulate various biological processes. This study aimed to explore the effects of elastic nonlinearity of the fibers contained in the extracellular matrix (ECM) on the transmission of mechanical loads between contracting cells. Based on our biological experiments, we developed a finite-element model of two contracting cells embedded within a fibrous network. The individual fibers were modeled as showing linear elasticity, compression microbuckling, tension stiffening, or both of the latter two. Fiber compression buckling resulted in smaller loads in the ECM, which were primarily directed toward the neighboring cell. These loads decreased with increasing cell-to-cell distance; when cells were >9 cell diameters apart, no such intercellular interaction was observed. Tension stiffening further contributed to directing the loads toward the neighboring cell, though to a smaller extent. The contraction of two neighboring cells resulted in mutual attraction forces, which were considerably increased by tension stiffening and decayed with increasing cell-to-cell distances. Nonlinear elasticity contributed also to the onset of force polarity on the cell boundaries, manifested by larger contractile forces pointing toward the neighboring cell. The density and alignment of the fibers within the intercellular band were greater when fibers buckled under compression, with tension stiffening further contributing to this structural remodeling. Although previous studies have established the role of the ECM nonlinear mechanical behavior in increasing the range of force transmission, our model demonstrates the contribution of nonlinear elasticity of biological gels to directional and efficient mechanical signal transfer between distant cells, and rehighlights the importance of using fibrous gels in experimental settings for facilitating intercellular communication. VIDEO ABSTRACT.

The infrapatellar fat pad is a dynamic and mobile structure, which deforms during knee motion, and has proximal extensions which wrap around the patella.

PURPOSE: The infrapatellar fat pad (IFP) is a common cause of knee pain and loss of knee flexion and extension. However, its anatomy and behavior are not consistently defined. METHODS: Thirty-six unpaired fresh frozen knees (median age 34 years, range 21-68) were dissected, and IFP attachments and volume measured. The rectus femoris was elevated, suprapatellar pouch opened and videos recorded looking inferiorly along the femoral shaft at the IFP as the knee was flexed. The patellar retinacula were incised and the patella reflected distally. The attachment of the ligamentum mucosum (LMuc) to the intercondylar notch was released from the anterior cruciate ligament (ACL), both menisci and to the tibia via meniscotibial ligaments. IFP strands projecting along both sides of the patella were elevated and the IFP dissected from the inferior patellar pole. Magnetic resonance imaging (MRI) of one knee at ten flexion angles was performed and the IFP, patella, tibia and femur segmented. RESULTS: In all specimens the IFP attached to the inferior patellar pole, femoral intercondylar notch (via the LMuc), proximal patellar tendon, intermeniscal ligament, both menisci and the anterior tibia via the meniscotibial ligaments. In 30 specimens the IFP attached to the anterior ACL fibers via the LMuc, and in 29 specimens it attached directly to the central anterior tibia. Proximal IFP extensions were identified alongside the patella in all specimens and visible on MRI [medially (100% of specimens), mean length 56.2 ± 8.9 mm, laterally (83%), mean length 23.9 ± 6.2 mm]. Mean IFP volume was 29.2 ± 6.1 ml. The LMuc, attached near the base of the middle IFP lobe, acting as a 'tether' drawing it superiorly during knee extension. The medial lobe consistently had a pedicle superomedially, positioned between the patella and medial trochlea. MRI scans demonstrated how the space between the anterior tibia and patellar tendon ('the anterior interval') narrowed during knee flexion, displacing the IFP superiorly and posteriorly as it conformed to the trochlear and intercondylar notch surfaces. CONCLUSION: Proximal IFP extensions are a novel description. The IFP is a dynamic structure, displacing significantly during knee motion, which is, therefore, vulnerable to interference from trauma or repetitive overload. Given that this trauma is often surgical, it may be appropriate that surgeons learn to minimize injury to the fat pad at surgery.

Total ankle replacement design and positioning affect implant-bone micromotion and bone strains.

Implant loosening - commonly linked with elevated initial micromotion - is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning - previously linked with higher failure rates - remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.

The influence of muscle pennation angle and cross-sectional area on contact forces in the ankle joint.

Data about a muscle's fibre pennation angle and physiological cross-sectional area are used in musculoskeletal modelling to estimate muscle forces, which are used to calculate joint contact forces. For the leg, muscle architecture data are derived from studies that measured pennation angle at the muscle surface, but not deep within it. Musculoskeletal models developed to estimate joint contact loads have usually been based on the mean values of pennation angle and physiological cross-sectional area. Therefore, the first aim of this study was to investigate differences between superficial and deep pennation angles within each muscle acting over the ankle and predict how differences may influence muscle forces calculated in musculoskeletal modelling. The second aim was to investigate how inter-subject variability in physiological cross-sectional area and pennation angle affects calculated ankle contact forces. Eight cadaveric legs were dissected to excise the muscles acting over the ankle. The mean surface and deep pennation angles, fibre length and physiological cross-sectional area were measured. Cluster analysis was applied to group the muscles according to their architectural characteristics. A previously validated OpenSim model was used to estimate ankle muscle forces and contact loads using architecture data from all eight limbs. The mean surface pennation angle for soleus was significantly greater (54%) than the mean deep pennation angle. Cluster analysis revealed three groups of muscles with similar architecture and function: deep plantarflexors and peroneals, superficial plantarflexors and dorsiflexors. Peak ankle contact force was predicted to occur before toe-off, with magnitude greater than five times bodyweight. Inter-specimen variability in contact force was smallest at peak force. These findings will help improve the development of experimental and computational musculoskeletal models by providing data to estimate force based on both surface and deep pennation angles. Inter-subject variability in muscle architecture affected ankle muscle and contact loads only slightly. The link between muscle architecture and function contributes to the understanding of the relationship between muscle structure and function.

The effect of compressive deformations on the rate of build-up of oxygen in isolated skeletal muscle cells.

In this study we integrated between confocal-based cell-specific finite element (FE) modeling and Virtual Cell (VC) transport simulations in order to determine trends of relationship between externally applied compressive deformations and build-up rates of oxygen in myoblast cells, and to further test how mild culture temperature drops (~3°C) might affect such trends. Geometries of two different cells were used, and each FE cell model was computationally subjected to large compressive deformations. Build-up of oxygen concentrations within the deformed cell shapes over time were calculated using the VC software. We found that the build-up of oxygen in the cells was slightly but consistently hindered when compressive cell deformations were applied. Temperature drops characteristic to ischemic conditions further hinder the oxygen built-up in cells. In a real-world condition, a combination of the deformation and temperature factors should be anticipated, and their combined effect might substantially impair cell respiration functions.

The influence of foot posture, support stiffness, heel pad loading and tissue mechanical properties on biomechanical factors associated with a risk of heel ulceration.

Heel ulcers (HU) are the second most common type of pressure ulcers. In this work, we developed the first anatomically-realistic three-dimensional finite element model of the posterior heel for studying the risk for HU in bedridden patients. We specifically simulated a heel that is resting on supports with different stiffnesses at upright and inclined foot postures. Our objective was to examine the effects of foot posture and stiffness of the support on strains and stresses within the fat pad of the resting heel. We found that strains and stresses in the fat pad of the heel are considerably reduced when the foot is positioned so that its lateral aspect is at 90° with respect to the horizon compared to an abducted (60°) foot posture. The study therefore indicates that theoretically, an inclined foot posture puts a bedridden patient at a higher risk for HU with respect to an upright foot posture, which may be explained by the anatomy of the heel that faces a lower curvature and better cushioned region against the support when the foot is upright.

Effects of intramuscular fat infiltration, scarring, and spasticity on the risk for sitting-acquired deep tissue injury in spinal cord injury patients.

Sitting-acquired deep tissue injury (DTI) is a severe form of pressure ulcer (PU) often affecting patients with spinal cord injury (SCI) who also tend to suffer from intramuscular fat infiltration, soft tissue scarring (due to previous PU), and/or muscle spasticity in their buttocks. We previously used finite element (FE) modeling to evaluate whether abnormal bodyweight is a risk factor for sitting-acquired DTI. Here we hypothesize that fat infiltration, scarring, or spasms increase internal loads in the gluteus muscles in the vicinity of the ischial tuberosities during sitting, which consequently put SCI patients with these conditions at a higher risk for DTI. Our objective was to determine changes in gluteal strains and stresses and tissue volumes exposed to elevated strains/stresses associated with these factors. Thirty-five FE models of coronal slices through the seated buttocks, simulating these conditions at different severities, were developed. We calculated peak strains and stresses in glutei and percentage volumes of muscle tissue exposed to above-critical strains/stresses (compression strain≥50%, compression/von Mises stress≥2 kPa, and strain energy density≥0.5 kPa). Progressive intramuscular fat infiltration increased all the aforementioned outcome measures. Increase in size of scar patterns that were contained in both muscle and fat tissues similarly elevated the outcome measures. Spasms increased muscle stresses and volumetric exposures to stress, but tissue volumes at risk were ∼1-2% and increases due to spasticity were slight. We conclude that the above potential risk factors can be listed according to the following order of importance: (i) fat infiltration, (ii) scars contained in both muscle and fat tissues, and (iii) spasms. This information should be considered when prioritizing prevention means and resources for patients with SCI.

Effects of skin wrinkles, age and wetness on mechanical loads in the stratum corneum as related to skin lesions.

Finite element models of skin were developed to determine the effects of wetness, age, and wrinkles on mechanical strains and stresses in the stratum corneum (SC) as related to skin lesions. We modeled two geometries, young (0.12-mm-deep wrinkles) and aged (0.18-mm-deep wrinkles), and for each geometry, three loading conditions were applied (compression in a dry environment, compression and shear in dryness, and compression with shear in wetness). Effects of skin wrinkling were studied independently or while coupled with age-related mechanical property changes. For each simulation, we calculated the peak maximal shear strain and stress in the SC, peak shear stress on the skin surface, and volumetric exposure of the SC to potentially injurious shear stresses (<70 kPa). Compression and shear with wetness produced the highest skin surface loads. Volumetric exposure of aged skin to potentially injurious shear stresses was six times greater than in the young skin for these conditions. Deeper wrinkles caused elevated loads in the SC consistently for all outcome measures and independently of the age factor. Thinning and/or stiffening the SC increased both the surface and internal SC stresses. Our findings indicate that theoretically, wetness, skin aging, and/or skin wrinkling are all risk factors for skin lesions such as superficial pressure ulcers.

Fluorescently labeled 1 nm thin nanomembranes.

Fluorescent labeling of self-assembled monolayers (SAMs) has a great potential for chemical and biotechnological sensing. However, its use is limited by the quenching of the fluorescence in the proximity of the conducting substrates. We show that this quenching can be overcome by the labeling of a cross-linked aromatic SAM (nanosheet) and its subsequent transfer onto a non-conducting substrate. We demonstrate the successful labeling of nanosheets with a fluorophore (tetramethylrhodamine) and its subsequent transfer to oxidized silicon, where they are detected by optical as well as fluorescence microscopy. Fluorescently labeled freestanding nanosheets, i.e. nanomembranes were obtained by a similar transfer of the nanosheets to TEM grids.

Quantitative monitoring of lipid accumulation over time in cultured adipocytes as function of culture conditions: toward controlled adipose tissue engineering.

Adipose tissue engineering is investigated for native fat substitutes and wound healing model systems. Research and clinical applications of bioartificial fat require a quantitative and objective method to continuously measure adipogenesis in living cultures as opposed to currently used culture-destructive techniques that stain lipid droplet (LD) accumulation. To allow standardization, automatic quantification of LD size is further needed, but currently LD size is measured mostly manually. We developed an image processing-based method that does not require staining to monitor adipose cell maturation in vitro nondestructively using optical micrographs taken consecutively during culturing. We employed our method to monitor LD accumulation in 3T3-L1 and mesenchymal stem cells over 37 days. For each cell type, percentage of lipid area, number of droplets per cell, and droplet diameter were obtained every 2-3 days. In 3T3-L1 cultures, high insulin concentration (10 microg/mL) yielded a significantly different (p < 0.01) time course of all three outcome measures. In mesenchymal stem cell cultures, high fetal bovine serum concentration (12.5%) produced significantly more lipid area (p < 0.01). Our method was able to successfully characterize time courses and extents of adipogenesis and is useful for a wide range of applications testing the effects of biochemical, mechanical, and thermal stimulations in tissue engineering of bioartificial fat constructs.

Exposure to internal muscle tissue loads under the ischial tuberosities during sitting is elevated at abnormally high or low body mass indices.

Deep tissue injury (DTI) is a severe pressure ulcer characteristic of chairfast or bedfast individuals, such as those with impaired mobility or neurological disorders. A DTI differs from superficial pressure ulcers in that the onset of DTI occurs under intact skin, in skeletal muscle tissue overlying bony prominences, and progression of the wound continues subcutaneously until skin breakdown. Due to the nature of this silently progressing wound, it is highly important to screen potentially susceptible individuals for their risk of developing a DTI. Abnormally low and high values of the body mass index (BMI) have been proposed to be associated with pressure ulcers, but a clear mechanism is lacking. We hypothesize that during sitting, exposure to internal muscle tissue loads under the ischial tuberosities (IT) is elevated at abnormally high or low body mass indices. Our aims in this study were: (a) to develop biomechanical models of the IT region in the buttocks that represent an individual who is gaining or losing weight drastically. (b) To determine changes in internal tissue load measures: principal compression strain, strain energy density (SED), principal compression stress and von Mises stress versus the BMI. (c) To determine percentage volumes of muscle tissue exposed to critical levels of the above load measures, which were defined based on our previous animal and tissue engineered model experiments: strain>or=50%, stress>or=2 kPa, SED>or=0.5 kPa. A set of 21 finite element models, which represented the same individual, but with different BMI values within the normal range, above it and below it, was solved for the outcome measures listed above. The models had the same IT shape, size, distance between the IT, and (non-linear) mechanical properties for all soft tissues, but different thicknesses of gluteus muscles and fat tissue layers, corresponding to the BMI level. The resulted data indicated a trend of progressive increase in internal tissue loading, particularly in volumetric exposure to critical loading for BMI values outside the 17