Force Loading Rate Research Articles

External Validation of Accelerometry-Based Mechanical Loading Prediction Equations

Accurately predicting physical activity-associated mechanical loading is crucial for developing and monitoring exercise interventions that improve bone health. While accelerometer-based prediction equations offer a promising solution, their external validity across different populations and activity contexts remains unclear. This study aimed to validate existing mechanical loading prediction equations by applying them to a sample and testing conditions distinct from the original validation studies. A convenience sample of 49 adults performed walking, running, and jumping activities on a force plate while wearing accelerometers at their hip, lower back, and ankle. Peak ground reaction force (pGRF) and peak loading rate (pLR) predictions were assessed for accuracy. Substantial variability in prediction accuracy was found, with pLR showing the highest errors. These findings highlight the need to improve prediction models to account for individual biomechanical differences, sensor placement, and high-impact activities. Such refinements are essential for ensuring the models’ reliability in real-world applications, particularly in clinical and biomechanical research contexts, where accurate assessments of mechanical loading are critical for designing rehabilitation programs, injury prevention strategies, and optimizing bone health interventions.

The relationships between patellofemoral bone remodeling, cartilage composition, and vertical loading rate: PET/MRI in isolated patellofemoral osteoarthritis

ObjectiveLoading is invariably an important factor of consideration for understanding the causality flow and parallel existence of articular cartilage and subchondral bone changes. The goal of this study was to investigate the patterns of subregional 18NaF-SUV vs. T1p-T2 associations and vertical ground reaction force loading rates; in isolated patellofemoral-joint-osteoarthritis (PFJ-OA) patients. MethodThirty-five isolated PFJ-OA patients, with no tibiofemoral involvement, underwent simultaneous scans in a 3.0T whole-body hybrid PET-MRI scanner. MRI WORMS assessments were performed to identify/confirm isolated PFJ-OA knees from bilateral scans. T1p-T2 relaxation and SUV values were automatically computed for both trochlear and patellar cartilage and subchondral bone subregions (deep, superficial, lateral, and medial). Maximum vertical impact loading rates (Loading-RateNorm) were calculated from walking trials. Relationships were explored between SUV uptake, T1p-T2 values, and Loading-RateNorm via linear mixed-effects modeling. ResultsSignificant and complex association patterns were noted between medial and lateral bone 18NaF-SUV uptakes vs. medial and lateral cartilage sub-regional T1p and T2. SUVMean and SUVMax were positively associated with deep cartilage subregional T1pand T2 values; and negatively associated with superficial cartilage subregional T1p-T2 values in both medial and lateral regions. Both medial and lateral bone 18NaF-SUVMean and SUVMax uptakes remained positively associated with the individual gait characteristics, i.e., peak vertical impact loading rates (Loading-RateNorm). ConclusionEvidence of simultaneous, complementary, cross-sectional associations between T1p-T2 values and peak vertical loading rates with 18NaF-SUV, have been rare in the isolated PFJ-OA cohort. The clinical implications of such novel associations remain of utmost importance from a gait retraining perspective.

Measuring Integrin Force Loading Rates Using a Two-Step DNA Tension Sensor.

Cells apply forces to extracellular matrix (ECM) ligands through transmembrane integrin receptors: an interaction which is intimately involved in cell motility, wound healing, cancer invasion and metastasis. These small (piconewton) integrin-ECM forces have been studied by molecular tension fluorescence microscopy (MTFM), which utilizes a force-induced conformational change of a probe to detect mechanical events. MTFM has revealed the force magnitude for integrin receptors in a variety of cell models including primary cells. However, force dynamics and specifically the force loading rate (LR) have important implications in receptor signaling and adhesion formation and remain poorly characterized. Here, we develop an LR probe composed of an engineered DNA structure that undergoes two mechanical transitions at distinct force thresholds: a low force threshold at 4.7 pN (hairpin unfolding) and a high force threshold at 47 pN (duplex shearing). These transitions yield distinct fluorescence signatures observed through single-molecule fluorescence microscopy in live cells. Automated analysis of tens of thousands of events from eight cells showed that the bond lifetime of integrins that engage their ligands and transmit a force >4.7 pN decays exponentially with a τ of 45.6 s. A subset of these events mature in magnitude to >47 pN with a median loading rate of 1.1 pN s-1 and primarily localize at the periphery of the cell-substrate junction. The LR probe design is modular and can be adapted to measure force ramp rates for a broad range of mechanoreceptors and cell models, thus aiding in the study of molecular mechanotransduction in living systems.

The effect of fresh and used ankle taping on lower limb biomechanics in sports specific movements

ObjectivesWe aimed to investigate the effects of ankle taping on lower extremity biomechanics related to injury development and how these effects change after sports-specific use. DesignRandomized, repeated measures design with three conditions: Barefoot, tape applied fresh, and tape after sports-specific use (between-subject factor: sex). MethodsTwenty-five healthy participants (ten female) performed sports-specific movements, including running, drop jumping, and 180° change of direction, under the three conditions. Kinetic and kinematic data were collected using 3D motion capturing and force platforms. ResultsTape applied fresh and tape after sports-specific use significantly reduced peak ankle inversion. Biomechanical risk factors for anterior cruciate ligament or running overuse injuries were either unchanged or decreased with tape applied fresh, except for the peak loading rate of the resultant ground reaction force, which increased between 4% and 18% between movement types. After 15 minutes of sports-specific use of the tape, the alterations induced by tape applied fresh remained for some biomechanical risk factors while they became closer to barefoot again for others, indicating a differential response to prolonged use of taping for different biomechanical variables. ConclusionsAnkle taping protects the ankle joint by reducing biomechanical risk factors associated with ankle sprains, and most biomechanical risk factors for anterior cruciate ligament or running overuse injuries are not increased. Further research is needed to explore the duration of protective effects, variations across sports, and its impact on patients with chronic ankle instability, contributing to a more comprehensive understanding of ankle taping's influence on lower extremity biomechanics.

DNA-based ForceChrono probes for deciphering single-molecule force dynamics in living cells

Understanding cellular force transmission dynamics is crucial in mechanobiology. We developed the DNA-based ForceChrono probe to measure force magnitude, duration, and loading rates at the single-molecule level within living cells. The ForceChrono probe circumvents the limitations of invitro single-molecule force spectroscopy by enabling direct measurements within the dynamic cellular environment. Our findings reveal integrin force loading rates of 0.5-2 pN/s and durations ranging from tens of seconds in nascent adhesions to approximately 100s in mature focal adhesions. The probe's robust and reversible design allows for continuous monitoring of these dynamic changes as cells undergo morphological transformations. Additionally, by analyzing how mutations, deletions, or pharmacological interventions affect these parameters, we can deduce the functional roles of specific proteins or domains in cellular mechanotransduction. The ForceChrono probe provides detailed insights into the dynamics of mechanical forces, advancing our understanding of cellular mechanics and the molecular mechanisms of mechanotransduction.

Learning effects in over-ground running gait retraining: A six-month follow-up of a quasi-randomized controlled trial

ABSTRACT This study evaluated learning and recall effects following a feedback-based retraining program. A 6-month follow-up of a quasi-randomized controlled trial was performed with and without recall. Twenty runners were assigned to experimental or control groups and completed a 3-week running program. A body-worn system collected axial tibial acceleration and provided real-time feedback on peak tibial acceleration for six running sessions in an athletic training facility. The experimental group received music-based biofeedback in a faded feedback scheme. The controls received tempo-synchronized music as a placebo for blinding purposes. The peak tibial acceleration and vertical loading rate of the ground reaction force were determined in a lab at baseline and six months following the intervention to assess retention and recall. The impacts of the experimental group substantially decreased at follow-up following a simple verbal recall (i.e., run as at the end of the program): peak tibial acceleration:-32%, p = 0.018; vertical loading rate:-34%, p = 0.006. No statistically significant changes were found regarding the retention of the impact variables. The impact magnitudes did not change over time in the control group. The biofeedback-based intervention did not induce clear learning at follow-up, however, a substantial impact reduction was recallable through simple cueing in the absence of biofeedback.

Sex- and age-related differences in kinetics and tibial accelerations during military-relevant movement tasks inU.S. Army trainees.

Lower extremity injuries are prevalent in military trainees, especially in female and older trainees. Modifiable factors that lead to higher injury risk in these subgroups are not clear. The purpose of this study was to identify whether external loading variables during military-relevant tasks differ by age and sex in U.S. Army trainees. Data was collected on 915 trainees in the first week of Basic Combat Training. Participants performed running and ruck marching (walking with 18.1kg pack) on a treadmill, as well as double-/single-leg drop landings. Variables included: vertical force loading rates, vertical stiffness, first peak vertical forces, peak vertical and resultant tibial accelerations. Comparisons were made between sexes and age groups (young, ≤19years; middle, 20-24years; older, ≥25years). Significant main effects of sex were found, with females showing higher vertical loading rates during ruck marching, and peak tibial accelerations during running and ruck marching (p≤0.03). Males showed higher vertical stiffness during running and peak vertical tibial accelerations during drop landings (p<0.01). A main effect of age was found for vertical loading rates during running (p=0.03), however no significant pairwise differences were found between age groups. These findings suggest that higher external loading may contribute to higher overall injury rates in female trainees. Further, higher stiffness during running may contribute to specific injuries, such as Achilles Tendinopathy, that are more prevalent in males. The lack of differences between age groups suggests that other factors contribute more to higher injury rates in older trainees.

Highly robust mechanical sensing platform inspired by a scorpion structure for 3D-mechanical signal perception

Three-dimensional force sensors play a crucial role in the aerospace industry and precision mechanical manufacturing. However, the current sensors still lack sufficient stability in the sensing of spatial mechanical forces and struggle to distinguish dynamic and static pressure signals. Coincidentally, scorpions in nature show a remarkable capacity to perceive three-dimensional stress with exceptional stability and sensitivity. This is primarily attributed to the highly sensitive sensing structure and stable multilayer structure in the slit sensilla of a scorpion. Inspired by this design, we develop a biomimetic sensing platform capable of accurately detecting the magnitude, position, and loading rate of a spatial force. This bionic system consists of an alternating combination of carbon fiber board (CFB) and hydroxylated multiwalled carbon nanotubes-styrene–isoprene (HMCNSI). Specifically, the flexible HMCNSI polymer enhances fatigue resistance, while the rigid CFB offers support and protection, resulting in exceptional robustness and stability of the sensing platform. The platform exhibits a rapid response time (14 ms), a fast recovery time (28 ms), and excellent sensitivity (GF = 46 for strain 0–3 %; GF = 118.3 for strain 3–6 %). Furthermore, the mechanical sensing platform can distinguish dynamic and static loads, identify exertion force rates in the range of 0.1–1 m/s and force magnitudes within 30 N, and provide a high positioning accuracy of 1 mm. The proposed biomimetic sensing platform exhibits promising applications in the field of precision detection of spatial forces such as human-machine interactions and intelligent robotics.

Ground reaction force analysis in flexible and rigid flatfoot subjects

BackgroundFlatfoot is a structural and functional deformity of the foot that might change ground reaction force variables of gait. Evaluating the components of ground reaction force in three dimensions during gait is considered clinically important. This study aimed to investigate the components of ground reaction force, impulse, and loading rate during gait in people with flexible and rigid flatfoot compared to healthy subjects. 20 young women with flatfoot in two experimental groups (10 with rigid flatfoot and 10 with flexible flatfoot) and 10 healthy women in the control group participated in this study. Ground reaction force components during gait were measured using two force plates. The peak of ground reaction forces, impulse, and loading rate were then extracted. Data were processed and analyzed using MATLAB and SPSS software. One-way ANOVA with a significant level (P˂0.05) was used for statistical analysis. The results showed that peak braking force was higher in the rigid flatfoot group than in the control group (p = 0.016) and the flexible flatfoot group (p = 0.003). The posterior force loading rate was significantly higher in the rigid flatfoot group than in the flexible flatfoot group (P = 0.04). There was no significant difference in vertical loading rate between groups (P˃0.05). Since the maximal posterior ground reaction force was higher in the subjects with rigid flatfoot than in those with flexible flatfoot and healthy subjects, the increase in posterior ground reaction force is associated with an increase in anterior shear force at the knee.

Cues to land softly and quietly result in acute reductions in ground reaction force loading rates in runners

BackgroundA common gait retraining goal for runners is reducing vertical ground reaction force (GRF) loading rates (LRs), which have been associated with injury. Many gait retraining programs prioritize an internal focus of attention, despite evidence supporting an external focus of attention when a specific outcome is desired (e.g., LR reduction). Research QuestionDoes an external focus of attention (using cues for quiet, soft landings) result in comparable reductions in LRs to those achieved using a common internal focus (forefoot striking while barefoot)? MethodsThis observational study included 37 injured runners (18 male; mean age 36 (14) years) at the OMITTED Running Center. Runners wore inertial measurement units over the distal-medial tibia while running on an instrumented treadmill at a self-selected speed. Data were collected for three conditions: 1) Shod-Control (wearing shoes, without cues); 2) Shod-Quiet (wearing shoes, cues for quiet, soft landings); and 3) Barefoot-FFS (barefoot, cues for forefoot strike (FFS)). Within-subject variables were compared across conditions: vertical instantaneous loading rate (LR, primary outcome); vertical stiffness during initial loading; peak vertical GRF; peak vertical tibial acceleration (TA); and cadence. ResultsVertical LR, stiffness, and TA were lower in the Shod-Quiet compared to Shod-Control p < 0.001). Peak vertical GRF and cadence were not different between Shod-Quiet and Shod-Control. Reductions in stiffness and LR were similar between Shod-Quiet and Barefoot-FFS, and GRF in Barefoot-FFS remained similar to both shod conditions. However, runners demonstrated additional reductions in TA and increased cadence when transitioning from Shod-Quiet to the Barefoot-FFS condition (p < 0.05). SignificanceThese results suggests that a focus on quiet, soft landings may be an effective gait retraining method for future research.

Biomechanical effects of foot orthoses on jump landing performance: A systematic review

Jumping is involved in a wide range of sports and activities, and foot orthoses (FO) are suggested to enhance performance and prevent injury. The aim of this systematic review was to investigate whether using FO with different modifications affects jump landing biomechanics and improves performance in healthy individuals. The search strategy included 7 databases that identified 19 studies. The study quality was evaluated using a modified Downs and Black index. The primary outcome measures were joint kinematics, kinetics, muscle activity, vertical jump height, and horizontal jump distance. Our findings indicated that incorporating arch support with a rearfoot post and softer forefoot region into FO may improve several biomechanical variables during jump landing activities. Improvements in vertical ground reaction force loading rates, knee and ankle kinematics, and muscle cocontraction during jumping with FO could enhance jumping performance. In addition, improvements in hip, knee, ankle, and tibial kinematics and vertical ground reaction force loading rates during landing could reduce impact forces and related injuries. Although a limited number of studies have addressed the effects of FO on vertical jump height and horizontal jump distance, inserting such FO inside shoes with optimum bending stiffness could facilitate jumping performance. A rigorous exploration of the effect and mechanism of FO designs on jumping performance could benefit jumping-related activities and prevent ankle and knee injuries.

Quantitative assessment and optimization of parallel contact model for flexible paddy straw: a definitive screening and central composite design approach using discrete element method

To simulate the bending behaviour of paddy straw at varied moisture contents after crop harvesting, we created a flexible paddy straw specimen model based on the Hertz–Mindlin with parallel contact bonding model using the discrete element model (DEM) approach. The research presented in this study aims to investigate a new approach called Definitive Screening Design (DSD) for parameterizing and screening the most significant parameters of the DEM model. This investigation will specifically focus on the three-point bending test as a means of parameterization, and the shear plate test will be used for validation purposes. In addition, the most influential DEM parameters were optimized using another Design of Experiments approach called Central Composite Design. The findings from the DSD indicated that parameters such as bonded disk scale, normal stiffness, and shear stiffness have the highest impact on the bending force, while the coefficient of static friction (Straw-Steel) has the least effect. The three bonding parameters were respectively calibrated with the loading rate (0.42, 0.5, and 0.58 mm s−1) and a good agreement between actual and simulated shear force at moisture content M1—35 ± 3.4%, M2—24 ± 2.2% and M3—17 ± 2.6%. Modelled stem helps simulate the straw with low error and increases the accuracy of the simulation. The validated model, with an average relative error of 5.43, 7.63, and 8.86 per cent, produced reasonable agreement between measured and simulated shear force value and loading rate.

Spring-Mass Characteristics in Runners Before and After a 56-km Road Ultramarathon.

Ultramarathons are a unique model to study the effects of systemic fatigue in athletes. This investigation applied the spring-mass template to study runners before and 2days after a road ultramarathon to characterize the effects of fatigue on systemic gait patterns. Overground kinetics were captured 7days before and 2days after the event in 14 runners. Traditional kinetic and spring-mass parameters were calculated, along with nonlinear regression-derived parameters and spring-mass model fit metrics. After the ultramarathon, vertical force magnitudes and loading rates were unchanged, but impact peaks increased (1.88 ± 0.08-1.95 ± 0.10 bodyweight). Ground contact times were modestly shorter (-3 ± 1ms), resulting in increased leg stiffness (10.0 ± 0.5-10.3 ± 0.5kN/m) with equivocal vertical stiffnesses. The deviation from the modeled spring-mass kinetics also increased (171.3 ± 15.0-181.4 ± 16.5N). Overall, the systemic mechanical behaviors of the runners persisted despite the fatigue and stress induced by a road ultramarathon. These findings support previous observations that runners maintain gross mechanical behavior when fatigued with small compensatory changes in spatiotemporal and traditional spring-mass characteristics. However, these findings also suggest that the variability within that gross behavior may increase after stress, suggesting new opportunities for quantifying those deviations.

Post-stroke deficits in the anticipatory control and bimanual coordination during naturalistic cooperative bimanual action

BackgroundUnilateral stroke leads to asymmetric deficits in movement performance; yet its effects on naturalistic bimanual actions, a key aspect of everyday functions, are understudied. Particularly, how naturalistic bimanual actions that require the two hands to cooperatively interact with each other while manipulating a single common object are planned, executed, and coordinated after stroke is not known. In the present study, we compared the anticipatory planning, execution, and coordination of force between individuals with left and right hemisphere stroke and neurotypical controls in a naturalistic bimanual common-goal task, lifting a box.MethodThirty-three individuals with chronic stroke (15 LCVA, 18 RCVA) and 8 neurotypical age-matched controls used both hands to lift a box fitted with force transducers under unweighted and weighted conditions. Primary dependent variables included measures of anticipation (peak grip and load force rate), execution (peak grip force, load force), and measures of within-hand (grip-load force coordination) and between-hand coordination (force rate cross-correlations). Primary analyses were performed using linear mixed effects modeling. Exploratory backward stepwise regression examined predictors of individual variability within participants with stroke.ResultsParticipants with stroke, particularly the RCVA group, showed impaired scaling of grip and load force rates with the addition of weight, indicating deficits in anticipatory control. While there were no group differences in peak grip force, participants with stroke showed significant impairments in peak load force and in grip-load force coordination with specific deficits in the evolution of load force prior to object lift-off. Finally, there were differences in spatial coordination of load force rates for participants with stroke, and especially the RCVA group, as compared to controls. Unimanual motor performance of the paretic arm and hemisphere of lesion (right hemisphere) were the key predictors of impairments in anticipatory planning of grip force and bimanual coordination among participants with stroke.ConclusionsThese results suggest that individuals with stroke, particularly those with right hemisphere damage, have impairments in anticipatory planning and interlimb coordination of symmetric cooperative bimanual tasks.

Impacts of mobile phone texting on vertical ground reaction forces during stair negotiation

Stairs are one of the most dangerous places for accidental falls in both daily life and occupational settings. Knowledge about ground reaction force (GRF) characteristics during stair negotiation can facilitate a better understanding of the causal mechanisms for stair falls. The objective of this study was to investigate the effects of mobile phone texting on GRF during stair negotiation and reveal their implications associated with the safety during stair negotiation. Twelve young male adults were involved in an experimental study. They were instructed to carry out texting tasks with different levels of cognitive load while performing stair negotiation. Vertical GRF (vGRF) parameters accounting for force amplitude and loading/unloading rates were compared between texting conditions. Texting tasks resulted in slower force loading and unloading rates during stair ascent, while weight acceptance force during stair descent decreased with the application of texting tasks. These findings suggested that mobile phone texting can compromise postural stability and increase the risk of falls during stair negotiation. The findings from the present study highlight the necessity of avoiding mobile phone usage during stair negation to prevent accidental stair falls. They also have practical implications for developing effective fall prevention interventions.

Effect of Purposely Induced Asymmetric Walking Perturbations on Limb Loading After Anterior Cruciate Ligament Reconstruction.

Patients often sustain prolonged neuromuscular dysfunction after anterior cruciate ligament reconstruction (ACLR). This dysfunction can present as interlimb loading rate asymmetries linked to reinjury and knee osteoarthritis progression. To evaluate how asymmetric walking protocols can reduce interlimb loading rate asymmetry in patients after ACLR. It was hypothesized that asymmetric walking perturbations would (1) produce a short-term adaptation of interlimb gait symmetry and (2) induce the temporary storage of these new gait patterns after the perturbations were removed. Descriptive laboratory study. Fifteen patients who had undergone ACLR were asked to perform an asymmetric walking protocol during the study period (2022-2023). First, to classify each limb as overloaded or underloaded based on the vertical ground-reaction force loading rate for each limb, participants were asked to perform baseline symmetric walking trials. Participants then performed an asymmetric walking trial for 10 minutes, where one limb was moving 0.5 m/s faster than the other limb (1 vs 1.5 m/s), followed by a 2-minute 1 m/s symmetric deadaptation walking trial. This process was repeated with the limb speeds switched for a second asymmetric trial. Participants adopted a new, symmetric interlimb loading rate gait pattern over time in response to the asymmetric trial, where the overloaded limb was set at 1 m/s. A linear mixed-effects model detected a significant change in gait dynamics (P < .001). The participants exhibited negative aftereffects after this asymmetric perturbation, indicating the temporary storage of the new gait pattern. No positive short-term gait adaptation or storage was observed when the overloaded limb was set to a faster speed. Asymmetric walking successfully produced the short-term adaptation of interlimb loading rate symmetry in patients after ACLR and induced the temporary storage of these gait patterns in the initial period when the perturbation was removed. These findings are promising, as they suggest that asymmetric walking could serve as an effective gait retraining protocol that has the potential to improve long-term outcomes in patients after ACLR.

Foot Strike Run Retraining forPatients With Patellofemoral Chondral Defects: A Case Series.

Military service members (SMs) demonstrate high rates of patellofemoral chondral defects (PFCDs) that are difficult to diagnosis and, if untreated, result in a cascade of events eventually leading to osteoarthritis. Running is an essential occupational task for SMs; however, there is little evidence regarding techniques to maintain running ability in individuals with cartilage defects. The purpose of this case series was to assess the clinical application of foot strike run retraining in patients with PFCDs. This case series included two active duty U.S. Marine Corps SMs who presented to outpatient physical therapy with PFCD, diagnosed via MRI. Both patients attended eight foot strike run retraining sessions. Running mechanics and patient-reported outcomes were recorded pre-training, post-training, and at a 1-month follow-up visit. Both patients successfully converted their strike pattern from a rearfoot to a non-rearfoot strike pattern with training and retained this strategy at 1-month follow-up. Post-intervention, both patients demonstrated increased running tolerance, and improvements in Numeric Pain Rating Scale and Lower Extremity Functional Scale scores. Biomechanical analysis showed that both patients demonstrated a 63% to 70% reduction in average and peak vertical ground reaction force loading rates post-treatment. Modification of foot strike pattern from rear to non-rearfoot strike during running for individuals with PFCD can reduce the magnitude of impact loading, which potentially limits disease progression. These findings suggest that foot strike run retraining may be a feasible strategy to reduce pain and improve function in SMs with PFCD who are required to run for occupational responsibilities.

Acceleration-Based Estimation of Vertical Ground Reaction Forces during Running: A Comparison of Methods across Running Speeds, Surfaces, and Foot Strike Patterns.

Twenty-seven methods of estimating vertical ground reaction force first peak, loading rate, second peak, average, and/or time series from a single wearable accelerometer worn on the shank or approximate center of mass during running were compared. Force estimation errors were quantified for 74 participants across different running surfaces, speeds, and foot strike angles and biases, repeatability coefficients, and limits of agreement were modeled with linear mixed effects to quantify the accuracy, reliability, and precision. Several methods accurately and reliably estimated the first peak and loading rate, however, none could do so precisely (the limits of agreement exceeded ±65% of target values). Thus, we do not recommend first peak or loading rate estimation from accelerometers with the methods currently available. In contrast, the second peak, average, and time series could all be estimated accurately, reliably, and precisely with several different methods. Of these, we recommend the 'Pogson' methods due to their accuracy, reliability, and precision as well as their stability across surfaces, speeds, and foot strike angles.

Single-Cell Measurements Using Acoustic Force Spectroscopy (AFS).

Single-molecule force spectroscopy is a powerful tool to investigate the forces and motions related to interactions of biological molecules. Acoustic force spectroscopy (AFS) is a developed measurement tool to study single molecules or cells making use of acoustic standing waves. AFS permits high experimental throughput because many individual molecules can be manipulated and tracked in parallel. Moreover, a wide range of forces can be applied as well as a force loading rate with range of six orders of magnitude. At the same time, AFS stands out because of its simplicity and the compactness of the experimental setup. Even though the AFS setup is simple, it can still be challenging to perform high-quality measurements. Here we describe, in detail, how to setup, perform, and analyze an AFS measurement to determine cell adhesion.

Effect of Femoral Head Material, Surgeon Experience, and Assembly Technique on Simulated Head-Neck Total Hip Arthroplasty Impaction Forces

BackgroundThere is no standard method for assembling the femoral head onto the femoral stem during total hip arthroplasty (THA). This study aimed to measure and record dynamic 3-dimensional (3D) THA head-neck assembly loads from residents, fellows, and attending surgeons, for metal and ceramic femoral heads. MethodsAn instrumented apparatus measured dynamic 3D forces applied through the femoral stem taper in vitro for 31 surgeons (11 attendings, 14 residents, 6 fellows) using their preferred technique (ie, number of hits or mallet strikes). Outcome variables included peak axial force, peak resultant force, impulse of the resultant force, loading rate of the resultant force, and off-axis angle. They were compared between femoral head material, surgeon experience level, and the number of hits per trial. ResultsAverage peak axial force was 6.92 ± 2.11kN for all surgeons. No significant differences were found between femoral head material. Attendings applied forces more “on-axis” as compared to both residents and fellows. Nine surgeons assembled the head with 1 hit, 3 with 2 hits, 14 with 3 hits, 2 with 4 hits, and 3 with ≥5 hits. The first hit of multihit trials was significantly lower than single-hit trials for all outcome measures except the off-axis angle. The last hit of multihit trials had a significantly lower impulse of resultant force than single-hit trials. ConclusionDifferences in applied 3D force-time curve dynamic characteristics were found between surgeon experience level and single and multihit trials. No significant differences were found between femoral head material.