Journal of the Mechanical Behavior of Biomedical Materials

Spinal cord injury (SCI) causes rapid and severe bone loss in the paralysed lower limbs, particularly at the distal femur and proximal tibia, where fragility fracture risk is high. In vitro nanoscale vibration at 1 kHz has been shown to promote osteogenic differentiation and inhibit osteoclastogenesis, suggesting potential as a targeted mechanical intervention. This study aimed to develop and evaluate a wearable device for delivering and monitoring localised nanovibration at the distal femur in individuals with SCI. The device delivered continuous sinusoidal nanoscale stimulation at 1 kHz via a bone-conduction transducer, with an opposing accelerometer used to monitor transmitted vibration in real time. Design and target-site selection were refined through two healthy-volunteer investigations comparing the distal femur, proximal tibia, and distal tibia. Bovine femur experiments characterised vibration transmission under controlled benchtop conditions. Preliminary repeated-use feasibility was assessed in one individual with motor-complete SCI. Healthy volunteer testing showed that although the ankle initially produced the highest transmitted amplitudes, these were highly variable, and positioning was inconsistent. Within the knee region, the distal femur provided the most practical and repeatable site for a wearable application. In bovine femur experiments, scanning laser vibrometry demonstrated measurable vibration on the condylar surface opposite the transducer, and depth-resolved measurements confirmed that nanoscale vibration remained detectable within bone. A gel interface layer reduced the transmitted amplitude. In the feasibility evaluation, 61 sessions were completed over 14 weeks, with logged accelerometry confirming repeated nanoscale vibration transmission. These findings establish feasibility and support further device optimisation and translational studies.

Identification and treatment of pregnancies at risk for preterm birth is a central challenge in obstetric research. Many of the known causes of preterm birth originate from mechanical failure in reproductive tissues. To better understand the biomechanical environment of the gravid uterus and its potential contribution to preterm birth, this computational study presents a parametric method for modeling maternal reproductive anatomy during the early second trimester. A finite element modeling approach was built using existing sonographic measurements from early second-trimester maternal anatomy and material properties from published mechanical tests. We applied the same physiologically relevant intrauterine pressure to all models and quantified the resulting tissue stretch. The sensitivity of the stretch in the proximal cervix was explored by varying material properties and sonographic maternal anatomy dimensions. Cervical material properties, particularly the fiber stiffness modulus and ground substance Youngs modulus, were found to have the greatest effect on proximal cervix stretch compared to other material properties and sonographic dimensions. Among the sonographic dimension measurements, those defining the region surrounding the proximal cervix had the greatest effect on proximal cervix stretch, including the curvature of the posterior uterine wall and the thickness of the lower uterine segment. The computational modeling approach presented here enables future patient-specific studies of gravid reproductive tissues to elucidate differences between individuals who do and do not deliver preterm. Additionally, this study is foundational for building digital twins to support future virtual clinical studies on diagnostic and therapeutic device design to prevent preterm birth.

Poly-L-Lysine (PLL) mediates the non-specific adhesion of cells and is commonly used in Atomic Force Microscopy (AFM) measurements, to ensure that cells remain attached to the substrate. However, it is acknowledged that adhesion affects the measured mechanical properties, in particular in the case Red Blood Cells (RBCs). This results in a wide range of Youngs modulus E reported in the literature. The present study aims at providing a systematic approach to the impact of non-specific adhesion on the rheology of RBCs. It provides a correlation between the topography profile of adherent RBCs and their rheology, from weak (cPLL = 10-3 mg/mL) to strong-adhesion (cPLL = 100 mg/mL) regimes. Using RICM and AFM, we find that there is a continuum of RBC shapes promoted by adhesion, from concave to dome-shaped, as predicted by the theory of vesicle adhesion. Their elastic properties discriminate them into two populations depending on adhesion strength, where stiffer RBCs (E {gtrsim} 100 Pa) correlate with dome-shaped cells. These findings are supported by rheology measurements of the dynamic complex shear modulus G*(f): while the storage modulus increases with cell-substrate adhesion, reflective of an increased membrane shear modulus, the loss modulus remains unchanged. Finally, further analysis inspired by membrane theory shows that different deformation modes may be triggered during indentation of either weakly or strongly adhering RBCs, illustrating the limits of the Hertz model.

Acute subdural hematoma (ASDH) is a prevalent injury with high mortality and morbidity, often resulting from bridging vein (BV) disruption secondary to cortical relative motion. As a thin membrane enveloping the brain surface and anchoring BVs, the pia mater is hypothesized to play a critical mechanical role in cortical response and hence ASDH pathogenesis. Finite element (FE) head models are valuable tools to predict ASDH occurrence during impacts. However, the pia mater is often represented as an elastic material in existing FE head models, despite experimental evidence reporting its nonlinear mechanical behavior. In this study, both linear (Young's modulus of 11.5 MPa) and nonlinear (the stress-strain curve derived from pial tension tests) material models of the pia mater were implemented in one FE head model. The models were subjected to three experimental impact loadings, one of which was known to cause ASDH and two of which were not. Results demonstrated that, across all simulated impacts, the model with nonlinear pia mater properties predicted larger cortical displacements and BV responses than the linear model. For the impact with known ASDH occurrence, the predicted BV strain was 0.17 for the nonlinear model and 0.094 for the linear model, with only the former approaching the reported rupture strain range of the BV-superior sagittal sinus complex (0.29 {+/-} 0.13). These findings verified the mechanical importance of the pia mater in cortical responses and hence the prediction of ASDH, suggesting that conventional linear pia modeling might over-constrain cortical motion, leading to underestimation of BV strain and ASDH risk. The current study supported the adoption of experimentally derived nonlinear pia mater properties in FE head models to improve the reliability of ASDH prediction.

PurposeComputational models of the uterus during pregnancy enable analysis of electro-chemo-mechanical pathways to predict labor timing and guide treatment planning. We aim to develop a robust image-based modeling pipeline to investigate uterine passive mechanics during late pregnancy. MethodsA parametric model of the uterus and cervix was created using a patients MRI measurements at 38 weeks of gestation. Inspired by advances in cardiac mechanics models, we created Laplace-Dirichlet solutions to inform tissue domains, fiber structure within the uterus and cervix, and spatially varying Robin boundary conditions. Prior imaging and mechanical testing data were used to fit material parameters. Boundary condition parameters were tuned to match the displacements of a previously established approach that employed contact with surrounding tissue. The tissue mechanical response to a physiologic load was assessed across varying material properties and fiber architectures. ResultsDiscrepancies in nodal displacements between the current approach and the contact-based model were limited to 3.4 {+/-} 1.8 mm, yielding nearly 90 % computational savings. Uterine tensile strains were more sensitive to ground substance elastic modulus (E) compared to fiber properties. Reduced E and fiber stiffness increased cervical strains and compression. Fiber dispersion and architecture modulated the opening of the cervical internal ostium but had a reduced impact on compression. ConclusionWe developed a novel workflow for modeling passive uterine mechanics, informed by patient-specific measurements and in vitro mechanical tests. The robust workflow may prove useful for studying labor progression and conducting longitudinal studies to enhance our understanding of normal and pathological pregnancies.

Relapse of aligned mandibular anterior teeth and the progressive collapse of the mandibular anterior arch are historically striking problems for orthodontists. The etiology of this collapse, and the cause of mesial molar drift, are unknown. However, light continuous (quasi-continuous) intra-oral pressures and forces applied to the mandibular dentition have been implicated. To explore this further, we use three-dimensional finite element analysis to investigate the influence of these intra-oral loads (tongue pressure, lip-cheek pressure, and interdental force) on mandibular arch collapse and mesial molar drift. Dentitions of three-dimensional finite element mandibular models were subjected to a wide range of simulated tongue pressures, lip-cheek pressures, and transseptal fiber-mediated interdental forces reported in the literature. Resulting crown displacement measurements from these isolated loads were made along with measurements resulting from simultaneous combined application of literature-defined mean tongue pressure, lip-cheek pressure, and interdental force. Our results indicate that tongue pressure alone results in generalized arch expansion and tooth spacing while lip-cheek pressure and interdental force result in generalized arch collapse, anterior crowding, and mesial molar displacement. Simultaneous application of tongue pressure, lip-cheek pressure, and interdental force mean values, as would occur in vivo, results in incisor crowding, intercanine width reduction, and mesial molar displacement. Our results suggest mandibular anterior arch collapse (incisor crowding / intercanine width reduction), and mesial molar displacement result from simultaneous application of tongue pressure, lip-cheek pressure, and interdental force.

The human spine is a complex, coordinated biomechanical system. Physiologically, its tissues are also highly interdependent in terms of function and viability. The interaction between mechanical stress and biological/biochemical activity over time constitutes a key driver of spinal degeneration. Research to date providing mechanistic insights into this process has focused on individual components (vertebra and disc tissue analogues), in isolation or as basic functional units. However, many observations from individual units will not translate to whole spine behaviour. The intricate complexity of the spine requires novel experimental models (synthetic and biotic), which must consider the spine at an organ level and adopt an integrative approach that can capture the dynamics which govern its function. Here, we report the development of a biomimetic spinal model prototype, amenable to cellular integration, which is miniaturised to the in vitro scale to provide a controlled environment and testbed for axial biological mechanics. The research presented here encompasses more than a decade of systematic investigations during which the gradual emergence of key manufacturing innovations progressively enabled addressing an exceptionally complex bioengineering challenge - organotypic spine engineering. The model comprises the full anatomical range of spinal vertebrae/bones (C1 to Sacrum & Coccyx), reproduced using bioceramic materials, assembled in sequence into a relevant columnar architecture and mechanically connected end-to-end by biochemically active interfaces. A range of assessments examining anatomical design, material behaviour and manufacturing processes is presented. The work explores concepts such as longitudinal mechanobiology and multi-segment coupling as well as manufacturing strategies using autonomous materials and instrumentation. This prototype introduces for the first time columnar level behaviour and the ability to study time dependent adaptations. This model is important because it can support tissue maturation, evolving mechanical properties and adaptive behaviour and it represents an intermediate step between isolated skeletal tissue models and future organ-level spinal constructs.

The surface layer of articular cartilage provides for low-friction joint movement and protects the tissue from mechanical wear. The superficial zone chondrocytes (SZCs) of the surface layer produce proteoglycan-4 (PRG4), which is a lubricant that is necessary to reduce friction. Articular cartilage has limited capacity for self-repair and cell-based therapies, such as autologous chondrocyte implantation (ACI), is used to stimulate repair. However, in ACI, cells are expanded on tissue culture polystyrene where SZC poorly attach, proliferate slowly and dedifferentiate. Consequently, expanded SZC produce fibrocartilage tissue with insufficient PRG4. We previously demonstrated that culturing SZC on chondrocyte-derived decellularized extracellular matrix (CM) enhances SZC attachment and preserves phenotype. Since fibronectin (FN) was identified as the most abundant matrix protein within CM, here we tested the hypothesis that FN-coated culture surfaces would partially reproduce the beneficial effects of CM. We found that, similar to CM, SZC on FN-coated polystyrene increased SZC attachment and proliferation. However, unlike CM, SZCs expanded on FN-coated polystyrene remained more dedifferentiated as indicated by spread cells, elevated fibroblastic and contractile mRNA levels, and increased formation of SMA positive stress fibers. Consistent with the dedifferentiated phenotype, SZC on FN-coated polystyrene displayed extensive stress fibers, and higher nuclear myocardin-related-transcription-factor-a (MRTF-A). In contrast, CM reduced stress fiber formation and diminished nuclear MRTF-A in SZC. CM provides matrix cues beyond FN that suppress dedifferentiation and preserve the SZC phenotype. Identifying the matrix cues necessary to improve SZC expansion could lead to the generation of a superior surface in ACI repair tissue.

Sutures are the primary sites of cranial bone growth, allowing the skull to accommodate the growing brain. External mechanical stimulus has been shown to delay suture fusion and induce tissue remodelling. Recent studies suggest that in vivo cyclic bone loading increased proliferation of mesenchymal stem cells (MSC) in the coronal suture. The overall aim of this study was to understand how many loading sessions (exposure-response) and how long after loading (time-course) did MSC proliferation increase in the coronal suture. In the exposure-response analysis, mice underwent 1, 3, or 5 loading sessions between Postnatal day 7 (P7) and P11, and in the time-course analysis, treated mice underwent 10 loading sessions between P7 and P21. Loading sessions were 10 minutes at a frequency of 1 Hz and a force of 10 g (0.1 N). The loading tip was positioned on the posterior aspect of the left frontal bone, dorsal to the coronal suture. The EdU marker shows a statistically significant increase in proliferation after one loading session and a decrease after three loading sessions. The PCNA marker shows a statistically significant increase after three and five loading sessions. The exposure-response analysis showed that when the results of both markers are combined, levels of proliferation cannot be interpreted until at least five loading sessions have been completed, after which a clear increase in proliferation was observed. In the time-course analysis, proliferation was highest immediately after the final treatment session and 24 hours after the final loading session the effects of mechanical bone loading gradually returned to baseline.

Distal radius fractures (DRFs) can delay return to activities of daily living and social participation because of postoperative pain, temporary joint immobilization, and limited wrist and forearm range of motion. The Ghost System developed at Saitama Prefectural University, Japan, combines visual action observation with tendon vibration stimulation and has shown potential as an adjunct to conventional rehabilitation. This Study Protocol describes a modified Ghost system intended to improve clinical implementation by replacing the head-mounted virtual reality display with iPad-based action observation and by using a wristband-type vibrator. This single-center, single-arm, open-label feasibility trial will enroll 10 adults after palmar locking plate fixation for DRF. The intervention will be delivered twice weekly during outpatient rehabilitation follow-up sessions from the early postoperative period (postoperative days 2-10 after enrollment) through the approved early postoperative rehabilitation period (generally up to postoperative week 8), in parallel with standard rehabilitation practices. Primary feasibility and preliminary clinical outcomes include device fit and acceptability, pain assessed using a 100-mm Visual Analog Scale, and wrist/forearm range of motion. Secondary implementation and safety outcomes include Disabilities of the Arm, Shoulder and Hand (DASH), Patient-Rated Wrist Evaluation (PRWE), Hand20 Questionnaire (HANDS-20), EuroQol 5 Dimensions 5 Levels (EQ-5D-5L), body ownership and hand-illusion questionnaires, setup time, setup errors, adherence, adverse events, and device incidents. We hypothesize that the modified Ghost system will be feasible and acceptable for early postoperative outpatient rehabilitation and will be delivered without serious device-related adverse events. Clinical outcomes will be summarized descriptively to inform a future controlled study rather than to establish efficacy.

Background: Cutaneous microvascular responses to local heating and acetylcholine perfusion are widely used to assess nitric oxide (NO)-mediated endothelium-dependent dilation in human health and disease. Despite the increasingly common usage of these approaches, no studies have directly compared responses to these stimuli within individuals. Therefore, we assessed endothelium- and NO-dependent dilation in 80 young adults (40 males/40 females; 22{+/-}3 years) to determine the extent to which microvascular responses to these endothelium-dependent stimuli are comparable within an individual. Methods: We examined cutaneous vascular conductance responses to (1) standardized local heating protocols to 39{degrees}C and 42{degrees}C, and (2) graded infusions of acetylcholine (10-10-10-1 M) alone or with 15 mM NG-nitro-l-arginine methyl ester (L-NAME; NO synthase inhibitor). Endothelium- and NO-dependent dilation were calculated and expressed in multiple ways based on commonly published analyses to allow for a thorough comparison within and between each stimulus. Results: Local heating-induced endothelium- and NO-dependent dilation were lower at 39{degrees}C compared with 42{degrees}C (P<0.001). The magnitude of local heating-induced endothelium-dependent dilation was significantly related to the NO-dependent contribution of that response at 39{degrees}C (R2= 0.79) and 42{degrees}C (R2= 0.56). Local heating-induced NO-dependent dilation at 39{degrees}C was not related to that at 42{degrees}C (P>0.05). Acetylcholine-induced endothelium- and NO-dependent dilation were not related to local heating-induced responses (all P>0.05). Conclusions: These data demonstrate that while local heating and acetylcholine perfusion produce robust endothelium- and NO-dependent cutaneous vasodilation, these responses are not comparable within an individual.

The osteocyte network in bone is believed to play an important role for how bone tissues sense and respond to mechanical stimulation. Yet, bone adaptation to mechanical loads is often conceptualised as a simple response to mechanical stimuli, such as Wolffs law, which is based on mechanical variables only and takes no account of the cellular basis of mechanosensation. Wolffs law presumes the existence of a reference mechanical stimulus, the mechanical setpoint, above which bone is consolidated, and under which bone is removed. In this paper, we develop a theory of bone tissue sensing and adaptation based on osteocytes to provide new understanding of the role played by osteocyte signals in mechanical adaptation. In this theory, the mechanical setpoint of Frosts mechanostat is explicitly embodied as osteocyte properties involved in mechanotransduction. The mechanical setpoint is allowed to adapt due to the replacement of osteocytes during remodelling, making the setpoint space and time dependent. We propose a mathematical model to implement this new theory of bone adapation and present numerical simulations of this model to explore how mechanobiological response curves (effective Wolffs laws) are modulated by setpoint adaptation during remodelling. By accounting for varying osteocyte populations within bone tissue, we explore bone adaptation under osteocyte disruptions, which is particularly relevant to age-related bone loss. Our model suggests that biological disruptions of remodelling balance cannot always be compensated by mechanical feedback, and that setpoint adaptation during remodelling may have significant observable consequences, such as hysteresis in bone response signatures that resemble lazy zones.

Objective: To identify brain injury metrics suitable for supporting sports head injury assessment by evaluating their association with brain tissue strain and consistency across sports. Methods: Head kinematics from 3,139 impacts in boxing, mixed martial arts, and rugby matches were recorded using instrumented mouthguards and used to calculate nine brain injury metrics. Impacts were simulated using an anatomically detailed finite element brain model to estimate peak 95th-percentile maximum principal strain (MPS) in the brain and brainstem, a measure of tissue deformation associated with long-term pathology. Sport-specific ordinary least squares models estimated xE, the metric value equivalent to a reference MPS of 0.21. Metric-MPS correlations and xE uncertainties were quantified using 5000 bootstrap resamples. Cross-sport consistency was assessed using the coefficient of variation (CV) of sport-specific median xE values, and uncertainty using the normalised confidence interval size (NCIS). Results: XGB, an extreme gradient boosting strain-prediction model, showed the strongest and most consistent correlations with whole-brain (r=0.924-0.974) and brainstem MPS (r=0.887-0.954) across all sports. PRV, BrIC and UBrIC also correlated strongly with whole-brain (r=0.724-0.930) and brainstem MPS (r=0.739-0.900), whereas HIC15 and HARM showed weaker correlation with MPS, particularly in rugby. XGB showed the lowest cross-sport variability (CV=0.034) and uncertainty (median NCIS=0.056). HARM, DAMAGE and HIC15 showed the greatest sport dependence (CV=0.575-0.588) and uncertainty (median NCIS=0.331-0.791). Conclusions: XGB, BrIC, and UBrIC demonstrated the strongest associations with brain tissue strain and the greatest consistency across sports. This study provides a biomechanically informed framework for selecting suitable metrics for sports HIA protocols.

Introduction: Critical-sized bone defects cannot heal spontaneously, requiring additional, often burdensome, treatment. Thus, various synthetic substitute materials have been investigated regarding their treatment capacity. Poly-L-lactic acid (PLLA) and polyglycolic acid (PGA) have emerged as promising biodegradable scaffold materials. The addition of inorganic materials such as calcium carbonate (CC) has also been shown to be advantageous. This study investigates the effect on bone regeneration of PLLA-PGA-CC scaffolds in critical-sized bone defects over a two-year observation period using sheep as an animal model. Methods: Critical-sized mandible angle defects were created in twelve female merino sheep. Mandibular defects were reconstructed with PLLA-PGA-CC scaffolds in four sheep, while the remaining eight served as negative control (defects left empty). The scaffolds were manufactured using computer-aided design and manufacturing, incorporating an interconnected porous structure and fixated with polyether ether ketone cages. Bone regeneration was evaluated using computed tomography (CT) imaging at 3, 12, and 24 months postoperatively. Bone volume was assessed quantitatively. Additionally, a histological analysis was performed. Results: Surgical procedures were successful and without major complications. CT assessment showed more bone regeneration in the scaffold group (mean volume: 7,472 mm3) than in the control group (4,168 mm3, p = 0.1) at 24 months postoperatively. Resorption of the scaffolds and formation of compact lamellar bone tissue were confirmed by histological analysis. However, the osteoconductive properties of the scaffolds were limited, with only minimal ingrowth of bone tissue into the porous structure. In both groups, fibrous tissue infiltration and the formation of cyst-like cavities in the defect region were observed. Conclusion: PLLA-PGA-CC scaffolds were found to be biocompatible and enhanced bone regeneration compared to the control group. Due to fibrous tissue infiltration and the lack of osteoconductivity, the suitability of the material for critical-sized bone defect reconstruction is limited.

Background: The saphenous vein (SV) remains the most widely used graft in coronary artery bypass grafting (CABG). However, graft failure over the years has compromised long-term outcomes. Preservation of the vascular endothelium is fundamental for vein graft patency, and hydrogen sulfide (H2S) a protective gasotransmitter, plays a significant role in vascular homeostasis. This study evaluated how different intraoperative preservation solutions modulate H2S-synthesizing enzymes and endothelial integrity. Methods: SV segments from 20 CABG patients were subdivided into five groups: Control (immediate fixation), normal saline (NS; 0.9% NaCl), autologous heparinized arterial blood (AHB), histidine-tryptophan-ketoglutarate (HTK) solution, and a damage group (no solution for 30 minutes). Structural integrity was evaluated by measuring endothelial coverage using light microscopy, and the expression of eNOS, CD31, and H2S pathway enzymes (CSE, CBS, and 3-MPST) was assessed by immunofluorescence (IF) and confocal microscopy to determine mean fluorescence intensity (MFI). Results: LM analysis revealed that AHB (89.66% {+/-} 3.02) and HTK (88.72% {+/-} 3.07) preserved endothelial coverage significantly better than NS (78.06% {+/-} 4.48) and the Damage Group (76.82% {+/-} 4.90; p < 0.001). In IF, all interventions reduced eNOS and CD31 expression compared to the control, but AHB and HTK maintained significantly higher levels than NS (p < 0.001). All three H2S-producing enzymes were detected in the GSV endothelium, with CSE being the most expressed isoform. The use of NS caused a marked depletion of these enzymes, while AHB and HTK showed specific superiority in preserving H2S synthesizing enzymes. Conclusions: The choice of preservation solution significantly affects endothelial integrity and the modulation of enzymatic H2S synthesis. NS proved to be deleterious to the endothelium, whereas AHB and HTK better preserved vascular structure and function, suggesting their clinical superiority for the preparation of venous grafts during CABG.

ObjectiveReliable animal models of tracheal stenosis are necessary for the development and translational testing of anti-fibrotic and regenerative therapies, but existing rabbit models frequently demonstrate substantial variability in stenosis severity, which limits their translational utility. The objective of our study was to determine whether airway diameter-matched mechanical injury improves the severity and reproducibility of experimental tracheal stenosis in a rabbit model, and to evaluate whether rabbit body weight is a reliable surrogate for tracheal luminal diameter during model creation. MethodsFourteen male New Zealand White rabbits (weight range, 2.7-3.5 kg) underwent tracheal injury using steel-bristle brushes introduced through a tracheotomy. Animals were assigned to receive either airway diameter-matched injury, in which brush size was selected to closely approximate the directly measured tracheal lumen diameter, or non-matched injury, in which brush size was selected without regard to measured lumen diameter. At postoperative day 21 (POD21), the injured tracheal segment and a native uninjured segment from the same animal were harvested and compared. Stenosis degree was quantified grossly, and lamina propria-to-cartilage (LP:C) ratio was quantified histologically by three blinded reviewers. The relationship between rabbit weight and airway diameter was assessed, and inter-rater reliability was calculated using the intraclass correlation coefficient (ICC). ResultsTwelve of fourteen rabbits reached the POD21 endpoint; two were euthanized early for severe airway compromise meeting humane endpoint criteria, both with approximately 80% stenosis. Injured tracheas demonstrated significantly greater stenosis than native controls (66.0 {+/-} 13.0% vs 16.0 {+/-} 2.7%; p = 0.00012), with a corresponding increase in LP:C ratio (p = 0.031). Airway diameter-matched injury produced significantly greater stenosis than non-matched injury (74.6 {+/-} 6.1% vs 50.6 {+/-} 4.0%; p = 0.001), while LP:C ratio did not differ between injury techniques (p = 1.0). Rabbit weight did not correlate with airway diameter (r = 0.176, p = 0.515; R2 = 0.031). Inter-rater reliability was excellent for both stenosis degree (ICC = 0.989) and LP:C ratio (ICC = 0.992). ConclusionsDirect measurement and matching of injury instrument diameter to native airway diameter substantially improves both the severity and the reproducibility of stenosis in a rabbit tracheal injury model, whereas body weight is an unreliable surrogate for airway size. This optimized, standardized protocol offers a reproducible platform for future translational studies of airway fibrosis and anti-fibrotic or regenerative therapies.

Background: Acute pulmonary embolism (PE) is a leading cause of morbidity and mortality with persistent difficulties in choosing interventions and predicting outcomes for patients defined clinically as intermediate risk. Computational fluid dynamics (CFD) tools have been used to understand the hemodynamic environment and plan interventions in the pulmonary arteries across a variety of disease conditions. Several biomechanical metrics have been used to evaluate risk in narrowed vessels, including hemodynamic resistance, power dissipation, and fractional flow reserve (FFR). In this study, we evaluate differences in these CFD-derived biomarkers between healthy controls (HC) and intermediate risk, acute PE patients. Additionally, we examine the response of patient hemodynamics to mechanical thrombectomy and compare values of these biomarkers across post-intervention pressure status. Methods: A CFD framework was developed to simulate patient-specific hemodynamics within the pulmonary vasculature identifiable from clinical imaging. The pipeline involved reconstructing three-dimensional (3D) structures of the pulmonary arteries and modeling blood flow with the finite element method. Patient-specific boundary conditions were derived from matching pre-intervention inlet mPAP to the patient's measured value given their measured CO as steady inflow. Converged simulations allowed for precise quantification of primary hemodynamic characteristics (flow and pressure) as well as secondary flow phenomena, primarily wall shear stress (WSS) and simulated pressure metrics such as fractional flow reserve (FFR). Results: Our simulations revealed significant elevations in resistance, power dissipation, and the number of vessels with low FFR in those patients with acute PE (n=6) compared to HC (n=3). Occlusions of hemodynamic significance were generally found in segmental pulmonary arteries. For patients with normalized pulmonary pressures post-thrombectomy (n=3), we found significantly higher proximal power dissipation and counts of low FFR vessels in comparison to those with elevated pressures after intervention (n=3). Distal resistance, which was derived from the portion of resistance attributed to the outflow boundary conditions, was significantly higher in patients with elevated pressures post-intervention. Across all PE patients, FFR count was significantly correlated with post-thrombectomy pulmonary pressure and cardiac index. Discussion: CFD-derived biomarkers offer a promising tool for understanding disease severity in acute PE. Differences between HCs and acute PE patients reveal expected increases in metrics associated with proximal disease burden. Yet, in examining acute PE patients with varying post-intervention hemodynamics, we found that these metrics of proximal disease burden could also be useful to predict the efficacy of mechanical thrombectomy. Those patients with normalized pressures had higher values for proximal disease metrics and lower values for distal disease metrics than those with continued elevations in pressure. This suggests that accessibility of hemodynamically-significant emboli to thrombectomy may be useful as a predictor for outcomes.

Mechanical forces have a major effect on cell behavior. Most cells in vitro are grown under static conditions on hard tissue culture plastic, conditions that do not accurately reflect living tissues. The ability of cells to sense and respond to mechanical forces is essential for key biological processes, including development, proliferation, and migration. Disruption of the ability to respond to mechanical forces are known to be a critical factor in many diseases, including cardiovascular disease, progeria, and cancer. Here, we present the design, fabrication, and biological testing of a custom-built cell-stretching device that applies controlled biaxial strain to cells cultured on a polydimethylsiloxane (PDMS) membrane. We then used this device to examine how cells respond to strain. In response to biaxial strain, MCF-7 cells activated the mechanosensitive immediate early gene (IEX-1), with its expression increasing significantly after 1 and 3 hours of stretching. Cells exposed to mechanical strain also remodeled their cytoskeleton in a direction-dependent manner. Under uniaxial strain, actin filaments reoriented perpendicular to the stretch direction, whereas biaxially stretched cells do not promote directional reorientation, but instead appear to reinforce actin at the cell periphery. Similarly, cells under uniaxial strain exhibited changes in nuclear orientation and shape that were not observed under biaxial strain. Nuclear area remained unchanged in either strain condition. These results highlight that the biaxial stretcher can be used to apply strain to cells, and that cells respond differently to biaxial strain compared to what has been reported for uniaxial strain.

Cooling the skin may increase its tolerance to mechanical loading and decrease the risk of developing pressure ulcers. Yet, the mechanisms of action (e.g. cooling-modulation of cytotoxic, post-occlusive hyperaemia), and their individual variability, remain unclear. We investigated the effects of different cooling levels (24{degrees}C and 16{degrees}C) on microvascular, inflammatory and perceptual responses to mechanical loading of the sacrum in healthy young (N=23) and older adults (N=19), and in spinal cord injury patients (SCI; N=10). Healthy participants underwent 45-min loading (~60 mmHg) and 20-min unloading of the sacrum, using an instrumented indenter probe set at either 38{degrees}C (control condition), 24{degrees}C or 16{degrees}C. SCI participants completed a more conservative protocol (i.e. 25min, ~45mmHg loading, 38{degrees}C and 16{degrees}C conditions). Pre-insult skin structure was characterised with optical coherence tomography; skin blood flow (SkBF) at the loading site was continuously measured, alongside thermal acceptability; and post-insult inflammatory responses were determined via skin-sebum cytokines analyses. Compared to control, 24{degrees}C- and 16{degrees}C-cooling induced a similar ~8-fold decrease in peak post-occlusive reactive hyperaemia in healthy participants, with similar temperature-related differences observed in SCI. Pro-inflammatory cytokines decreased post-insult; yet this occurred similarly across all temperatures and groups. The majority of participants ([&ge;]70%) rated both 24{degrees}C- and 16{degrees}C-cooling as thermally acceptable. We conclude that cooling is a potent modulator of the skin microvascular response to mechanical loading in younger, older, and vulnerable skin (SCI). These findings can inform design parameters for thermal technology aimed at preventing the loss of skin integrity (e.g. integrating 24{degrees}C-cooling in support surfaces and skin wearables).

Background: Despite the common use of local heating and intradermal microdialysis perfusion of acetylcholine (ACh) to probe cutaneous endothelium and nitric oxide (NO)-dependent dilation, sex differences in microvascular responsiveness to these stimuli in healthy young adults remain incompletely understood. Methods: Cutaneous vasodilation was assessed in response to local heating to 39{degrees}C and 42{degrees}C and graded perfusion of ACh (10-10 to 10-1 mol/L) alone or concurrently with 15 mM NG-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor) using laser-Doppler flowmetry coupled with intradermal microdialysis in 80 young adults (40 females). Results: Local heating to 42{degrees}C elicited greater endothelium- and NO-dependent dilation than heating to 39{degrees}C in both groups (p<0.001), but no sex differences were observed at either temperature (p=0.65). ACh-induced endothelium-dependent dilation also was not different between sexes (p=0.08), but the NO-dependent component was greater in females than in males (p=0.01). In young females, menstrual cycle day (range: day 2-33) was not associated with endothelium- or NO-dependent dilation in response to any stimulus (all p[&ge;]0.19), regardless of hormonal contraceptive use. Conclusions: Taken together, these findings suggest that sex differences in microvascular NO bioavailability in healthy young adults depend on the stimulus used to elicit cutaneous vasodilation and, in females, microvascular endothelium- and NO-dependent dilation are not meaningfully influenced by menstrual cycle phase.