Development of Three-Stage Bioaerosol Sampler for Size-Selective Sampling

In this study, a three-stage bioaerosol sampler with a sampling flow rate of 170 L/min was designed and fabricated for sampling the bioaerosols released during human breathing and coughing, and its performance was evaluated. The sampler was constructed using a cyclone separator with a cutoff size of 2.5 µm as a preseparator, a multi-nozzle virtual impactor with a cutoff size of 0.34 µm as an aerosol concentrator, and a BioSampler, which is a commercial product, for collecting bioaerosols in a collection fluid. The collection efficiency of the sampler was evaluated through simulations and experiments. Only particles with sizes of 0.1-4 µm were selectively collected in the collection fluid. Bacteriophage bioaerosols were sampled using the developed sampler and ACD-200 Bobcat sampler, which is a commercial product. The amounts of collected bacteriophages were compared using the polymerase chain reaction (PCR) technique. The sampling performance of the developed sampler was similar to that of the ACD-200 Bobcat sampler. Moreover, the developed sampler showed its ability to sample bioaerosols of a specific size-range and collect them directly in a collection fluid for the PCR analysis. Therefore, the developed sampler is expected to be useful for indoor environmental monitoring by effectively sampling the bioaerosols released indoors during human breathing and coughing.

Coronary Artery Stenting Affects Wall Shear Stress Topological Skeleton

Despite the important advancements in the stent technology for the treatment of diseased coronary arteries, major complications still affect the post-operative long-term outcome. The stent-induced flow disturbances, and especially the altered wall shear stress (WSS) profile at the strut level, play an important role in the pathophysiological mechanisms leading to stent thrombosis (ST) and in-stent restenosis (ISR). In this context, the analysis of the WSS topological skeleton is gaining more and more interest by extending the current understanding of the association between local hemodynamics and vascular diseases. The present study aims to analyze the impact that a deployed coronary stent has on the WSS topological skeleton. Computational fluid dynamics simulations were performed in three stented human coronary artery geometries reconstructed from clinical images. The selected cases presented stents with different designs (i.e., two contemporary drug eluting stents and one bioresorbable scaffold) and included regions with stent malapposition or overlapping. A recently proposed Eulerian-based approach was applied to analyze the WSS topological skeleton features. The results highlighted that the presence of single or multiple stents within a coronary artery markedly impacts the WSS topological skeleton. In particular, repetitive patterns of WSS divergence were observed at the luminal surface, highlighting a WSS contraction action proximal to the struts and a WSS expansion action distal to the struts. This WSS action pattern was independent from the stent design. In conclusions, these findings could contribute to a deeper understanding of the hemodynamic-driven processes underlying ST and ISR.

Mechanical Deformation of Peripapillary Retina in Response to Acute Intraocular Pressure Elevation

Elevated intraocular pressure (IOP) may cause mechanical injuries to the optic nerve head (ONH) and the peripapillary tissues in glaucoma. Previous studies have reported the mechanical deformation of the ONH and the peripapillary sclera (PPS) at elevated IOP. The deformation of the peripapillary retina (PPR) has not been well-characterized. Here we applied high-frequency ultrasound elastography to map and quantify PPR deformation, and compared PPR, PPS and ONH deformation in the same eye. Whole globe inflation was performed in ten human donor eyes. High-frequency ultrasound scans of the posterior eye were acquired while IOP was raised from 5 to 30 mmHg. A correlation-based ultrasound speckle tracking algorithm was used to compute pressure-induced displacements within the scanned tissue cross-sections. Radial, tangential, and shear strains were calculated for the PPR, PPS, and ONH regions. In PPR, shear was significantly larger in magnitude than radial and tangential strains. Strain maps showed localized high shear and high tangential strains in PPR. In comparison to PPS and ONH, PPR had greater shear and a similar level of tangential strain. Surprisingly, PPR radial compression was minimal and significantly smaller than that in PPS. These results provide new insights into PPR deformation in response of IOP elevation, suggesting that shear rather than compression was likely the primary mode of IOP-induced mechanical insult in PPR. High shear, especially localized high shear, may contribute to the mechanical damage of this tissue in glaucoma.

Internal Tibial Forces and Moments During Graded Running

This note is to correct errata in the paper "Internal Tibial Forces and Moments During Graded Running" published in Journal of Biomechanical Engineering, Vol. 144, p. 011009 (2021), DOI: 10.1115/1.4051924. In the Data Analysis section, it was stated that, "The joint moments used in the optimization were the flexion-extension and abduction-adduction moments at the hip and ankle, and the flexion-extension moment at the knee." However, it has come to our attention that this is incorrect, and instead the joint moments used in the static optimization routine were the flexion-extension and abduction-adduction moments at the hip, and the flexion-extension moment at the knee and ankle. Please accept our apologies for the error.

Bioink Rheology Regulates Stability of Bioprinted Strands

Extrusion three-dimensional (3D) bioprinting typically requires an ad-hoc trial-and-error optimization of the bioink composition towards enhanced resolution. The bioink solutions are solidified after leaving cone-shaped or cylindrical nozzles. The presence of bioink instability not only hampers the extrusion resolution but also affects the behavior of embedded cellular components. This is a key factor in selecting bioinks and bioprinting design parameters for well-established desktop and handheld bioprinters. In this work, we developed an analytical solution for the process of bioink deposition and compared its predictions against numerical simulations of the deposition. We estimated the onset of bioink instability as a function of bioink rheological properties and nozzle geometry. Both analytical and simulation results demonstrated that enhancing shear-thinning behavior of the bioink stabilizes the printing process whereas bioink shear-thickening behavior induces an opposite effect through extending the toe region of the deposition. The present study serves as a benchmark for detailed simulations of the extrusion process for optimal bioprinting.

Investigating the Effect of Real-Time Center of Pressure (CoP) Feedback Training on the Swing Phase of Lower Limb Kinematics in Transfemoral Prostheses with SACH foot

Transfemoral amputee often encounters reduced toe clearance resulting in trip-related falls. Swing phase joint angles have been shown to influence the toe clearance therefore, training intervention that targets shaping the swing phase joint angles can potentially enhance toe clearance. The focus of this study was to investigate the effect of the shift in the location of the center of pressure (CoP) during heel strike on modulation of the swing phase joint angles in able-bodied participants (n=6) and transfemoral amputees (n=3). We first developed a real-time CoP-based visual feedback system such that participants could shift the CoP during treadmill walking. Next, the kinematic data were collected during two different walking sessions- baseline (without feedback) and feedback (shifting the CoP anteriorly/posteriorly at heel strike to match the target CoP location). Primary swing phase joint angle adaptations were observed with feedback such that during the mid-swing phase, posterior CoP shift feedback significantly increases (p<0.05) the average hip and knee flexion angle by 11.55 degrees and 11.86 degrees respectively in amputees, whereas a significant increase (p<0.05) in ankle dorsiflexion, hip and knee flexion angle by 3.60 degrees, 3.22 degrees, and 1.27 degrees respectively compared to baseline was observed in able-bodied participants. Moreover, an opposite kinematic adaptation was seen during anterior CoP shift feedback. Overall, results confirm a direct correlation between the CoP shift and the modulation in the swing phase lower limb joint angles.

Development and Multi-Site Assessment of a Novel Shoulder Motion Joint Simulator

Background: Multiple biomechanical shoulder simulators have been described in the literature, with a trend toward increasing complexity to better simulate clinical scenarios. Our objective was to develop an advanced, novel shoulder joint simulator and compare outcomes at two separate institutions, for a typical shoulder joint motion simulation. Methods: Identical shoulder simulators were developed & deployed at both institutions. Eight cadaveric upper extremities were tested by simulating actively controlled, arm elevation in the plane of the scapula for two sequential test conditions (intact and non-destructive simulated cuff-tear), each repeated for a total of five trials. Muscle forces and joint translations were recorded for both conditions. The intact condition was repeated following simulated cuff-tear to assess effect of testing order. Statistical analyses were aimed at assessing repeatability and reproducibility of results within specimens, between specimens, and between institutions. Results: The highest average forces were observed for the middle deltoid (233N or 32.5% body weight), followed by infraspinatus (99.0N), and posterior deltoid (93.7N) muscles. Differentiation between test conditions was unhindered by variability between repeated trials. Data from testing repeated over time, and between the two institutions were not significantly different. Conclusions: The novel shoulder simulator produced repeatable results with low trial-to-trial variation and outcomes were comparable between the two institutions. The results demonstrated a consistent response in muscle forces and humeral translation for the simulated rotator cuff tear condition. Such advanced shoulder simulators could thus be used for evaluating and optimizing surgical interventions and implant strategies.

Compensating for Soft-Tissue Artifact Using the Orientation of Distal Limb Segments During Electromagnetic Motion Capture of the Upper Limb

Most motion capture measurements suffer from soft-tissue artifacts (STA). Especially affected are rotations about the long axis of a limb segment, such as humeral internal-external rotation (HIER) and forearm pronation-supination (FPS). Unfortunately, most existing methods to compensate for STA were designed for optoelectronic motion capture systems. We present and evaluate a STA compensation method that 1) compensates for STA in HIER and/or FPS, 2) is developed specifically for electromagnetic motion capture systems, and 3) does not require additional calibration or data. To compensate for STA, calculation of HIER angles rely on forearm orientation, and calculation of FPS angles rely on hand orientation. To test this approach, we recorded whole-arm movement data from eight subjects and compared their joint angle trajectories calculated according to progressive levels of STA compensation. Compensated HIER and FPS angles were significantly larger than uncompensated angles. Although the effect of STA compensation on other joint angles (besides HIER and FPS) was usually modest, significant effects were seen in certain DOF under some conditions. Overall, the method functioned as intended during most of the range of motion of the upper limb, but it becomes unstable in extreme elbow extension and extreme wrist flexion-extension. Specifically, this method is not recommended for movements within 20° of full elbow extension, full wrist flexion, or full wrist extension. Since this method does not require additional calibration of data, it can be applied retroactively to data collected without the intent to compensate for STA.

Reaction Forces and Flexion-Extension Moments Imposed On Functional Spinal Units with Constrained and Unconstrained in Vitro Testing Systems

A mechanical goal of in vitro testing systems is to minimize differences between applied and actual forces and moments experienced by spinal units. This study quantified the joint reaction forces and reaction flexion-extension moments during dynamic compression loading imposed throughout the physiological flexion-extension range-of-motion. Constrained (fixed base) and unconstrained (floating base) testing systems were compared. Sixteen porcine spinal units were assigned to both testing groups. Following conditioning tests, specimens were dynamically loaded for 1 cycle with a 1 Hz compression waveform to a peak load of 1 kN and 2 kN while positioned in five different postures (neutral, 100% and 300% of the flexion and extension neutral zone), totalling ten trials per FSU. A six degree-of-freedom force and torque sensor was used to measure peak reaction forces and moments for each trial. Shear reaction forces were significantly greater (25.5 N - 85.7 N) when the testing system was constrained compared to unconstrained (p < 0.029). The reaction moment was influenced by posture (p = 0.037), particularly in C5C6 spinal units. In 300% extension (C5C6), the reaction moment was, on average, 9.9 Nm greater than the applied moment in both testing systems and differed from all other postures (p < 0.001). The reaction moment error was, on average, 0.45 Nm at all other postures. In conclusion, these findings demonstrate that comparable reaction moments can be achieved with unconstrained systems, but without inducing appreciable shear reaction forces.

Mesoscale Simulation-based Parametric Study of Damage Potential in Brain Tissue Using Hyperelastic and Internal State Variable Models

Two-dimensional mesoscale finite element analysis (FEA) of a multi-layered brain tissue was performed to calculate the damage related average stress triaxiality and local maximum von Mises strain in the brain. The FEA was integrated with rate dependent hyperelastic and internal state variable (ISV) models respectively describing the behaviors of wet and dry brain tissues. Using the finite element results, a statistical method of design of experiments (DOE) was utilized to independently screen the relative influences of seven parameters related to brain morphology (sulcal width/depth, gray matter (GM) thickness, cerebrospinal fluid (CSF) thickness and brain lobe) and loading/environment conditions (strain rate and humidity) with respect to the potential damage growth/coalescence in the brain tissue. The results of the parametric study illustrated that the GM thickness and humidity were the two most crucial parameters affecting average stress triaxiality. For the local maximum von Mises strain at the depth of brain sulci, the brain lobe/region was the most influential factor. The conclusion of this investigation gives insight for the future development and refinement of a macroscale brain damage model incorporating information from lower length scale