The anterior cruciate ligament is one of the six ligaments in the human knee joint that provides stability during articulations. It is relatively prone to acute and chronic injuries as compared to ...other ligaments. Repair and self-healing of an injured anterior cruciate ligament are time-consuming processes. For personnel resuming an active sports life, surgical repair or replacement is essential. Untreated anterior cruciate ligament tear results frequently in osteoarthritis. Therefore, understanding of the biomechanics of injury and properties of the native ligament is crucial. An abridged summary of the prominent literature with a focus on key topics on kinematics and kinetics of the knee joint and various loads acting on the anterior cruciate ligament as a function of flexion angle is presented here with an emphasis on the gaps. Briefly, we also review mechanical characterization composition and anatomy of the anterior cruciate ligament as well as graft materials used for replacement/reconstruction surgeries. The key conclusions of this review are as follows: (a) the highest shear forces on the anterior cruciate ligament occur during hyperextension/low flexion angles of the knee joint; (b) the characterization of the anterior cruciate ligament at variable strain rates is critical to model a viscoelastic behavior; however, studies on human anterior cruciate ligament on variable strain rates are yet to be reported; (c) a significant disparity on maximum stress/strain pattern of the anterior cruciate ligament was observed in the earlier works; (d) nearly all synthetic grafts have been recalled from the market; and (e) bridge-enhanced repair developed by Murray is a promising technique for anterior cruciate ligament reconstruction, currently in clinical trials. It is important to note that full extension of the knee is not feasible in the case of most animals and hence the loading pattern of human ACL is different from animal models. Many of the published reviews on the ACL focus largely on animal ACL than human ACL. Further, this review article summarizes the issues with autografts and synthetic grafts used so far. Autografts (patellar tendon and hamstring tendon) remains the gold standard as nearly all synthetic grafts introduced for clinical use have been withdrawn from the market. The mechanical strength during the ligamentization of autografts is also highlighted in this work.
The progenitor cells of the developing liver can differentiate toward both hepatocyte and biliary cell fates. In addition to the established roles of TGFβ and Notch signaling in this fate ...specification process, there is increasing evidence that liver progenitors are sensitive to mechanical cues. Here, we utilized microarrayed patterns to provide a controlled biochemical and biomechanical microenvironment for mouse liver progenitor cell differentiation. In these defined circular geometries, we observed biliary differentiation at the periphery and hepatocytic differentiation in the center. Parallel measurements obtained by traction force microscopy showed substantial stresses at the periphery, coincident with maximal biliary differentiation. We investigated the impact of downstream signaling, showing that peripheral biliary differentiation is dependent not only on Notch and TGFβ but also E-cadherin, myosin-mediated cell contractility, and ERK. We have therefore identified distinct combinations of microenvironmental cues which guide fate specification of mouse liver progenitors toward both hepatocyte and biliary fates.
BACKGROUND: Critical care for exploration space missions may require intravenous (IV) fluid resuscitation therapy. Resource constraints may limit availability of standard, Earth-based infusion ...technologies. The effect of variable acceleration on infusion flow rates using simple
fluid resuscitation supplies was investigated.METHODS: Infusions of water or blood analog (40% glycerol) from a 1 L IV bag were performed using pressure bag augmentation at 0, 150, or 300 mmHg. The solution bag rested on an adjustable mount, configured to different
heights to simulate relevant gravitational accelerations (1 G, Martian G, lunar G, and 0 G). The bag emptied through an IV line with a 14- or 20-gauge angiocath into a 3-mmHg venous pressure reservoir. Flow rates were measured using an in-line flow probe. Three determinations
were made for each test condition.RESULTS: Temporal flow rate data for all test conditions displayed one-phase exponential decay. At 300 mmHg pressurization, maximum infusion rates ranged from 92–222 mL ⋅ min−1 for water and from 21–49 mL
⋅ min−1 for blood analog. All reduced gravity conditions had significantly longer infusion times in comparison to 1 G for both test solutions.DISCUSSION: Reduced acceleration significantly altered flow rates and infusion times for fluid resuscitation.
Fluid resuscitation protocols specify a desired volume to infuse for a target time (e.g., 20–30 mL ⋅ min−1 for a 75-kg adult). This data demonstrates that this protocol parameter can be achieved with infusion pressure bag augmentation alone and provides information
for the refinement of fluid resuscitation protocols for exploration space missions.Pantalos GM, Heidel JS, Jain IM, Warner SE, Barefoot TL, Baker RO, Hailey M. Intravenous fluid resuscitation capabilities in simulated reduced gravity. Aerosp Med Hum Perform. 2023; 94(8):596–603.
Nonalcoholic fatty liver disease affects 30% of the United States population and its progression can lead to nonalcoholic steatohepatitis (NASH), and increased risks for cirrhosis and hepatocellular ...carcinoma. NASH is characterized by a highly heterogeneous liver microenvironment created by the fibrotic activity of hepatic stellate cells (HSCs). While HSCs have been widely studied in 2D, further advancements in physiologically relevant 3D culture platforms for the in vitro modeling of these heterogeneous environments are needed. In this study, the use of stiffness‐variable, extracellular matrix (ECM) protein‐conjugated polyethylene glycol microgels as 3D cell culture scaffolds to modulate HSC activation is demonstrated. These microgels as a high throughput ECM screening system to identify HSC matrix remodeling and metabolic activities in distinct heterogeneous microenvironmental conditions are further employed. The 6 kPa fibronectin microgels are shown to significantly increase HSC matrix remodeling and metabolic activities in single or multiple‐component microenvironments. Overall, heterogeneous microenvironments consisting of multiple distinct ECM microgels promoted a decrease in HSC matrix remodeling and metabolic activities compared to homogeneous microenvironments. The study envisions this ECM screening platform being adapted to a broad number of cell types to aid the identification of ECM microenvironments that best recapitulate the desired phenotype, differentiation, or drug efficacy.
The development and utility of stiffness‐variable, ECM protein‐conjugated polyethylene glycol microgels as 3D cell culture scaffolds to modulate human hepatic stellate cell activation is demonstrated. The study envisions this ECM screening platform being adapted to a broad number of cell types to aid the identification of ECM microenvironments that best recapitulate the desired phenotype, differentiation, or drug efficacy.
Vertically stacked nanowire field effect transistors currently dominate the race to become mainstream devices for 7-nm CMOS technology node. However, these devices are likely to suffer from the issue ...of nanowire stack position dependent drain current. In this paper, we show that the nanowire located at the bottom of the stack is farthest away from the source/drain silicide contacts and suffers from higher series resistance as compared to the nanowires that are higher up in the stack. It is found that upscaling the diameter of lower nanowires with respect to the upper nanowires improved uniformity of the current in each nanowire, but with the drawback of threshold voltage reduction. We propose to increase source/drain trench silicide depth as a more promising solution to this problem over the nanowire diameter scaling, without compromising on power or performance of these devices.
Abstract only Endothelial-mesenchymal transition (EndoMT) is a biological process in which vascular endothelial cells (ECs) acquire a mesenchymal identity that give rise to lineages like fibroblasts ...and smooth muscle-like cells. Pathologically, EndoMT is involved in the progression of cardiovascular diseases such as atherosclerosis, in which ECs give rise to smooth muscle-like cells within the plaque. However, there is essentially a dearth of knowledge of how the biochemical and biomechanical cues from the extracellular matrix (ECM) milieu directly influence the progression of EndoMT. To address the limited knowledge of ECM effects on EndoMT, we aim to develop a 3D tissue engineered model with independently tunable biochemical and biomechanical cues, including stiffness, stress relaxation rate and ECM composition to study EndoMT progression in 3D. Alginate hydrogels were prepared at 2% w/v final concentration and crosslinked using calcium sulfate and different concentrations. Human primary coronary artery endothelial cells (HCAECs, Lonza) were formed into spheroids and then co-encapuslated with fibroblasts in the alginate hydrogels for 7 days. EndoMT was induced by using media with no supplements such as VEGF and bFGF (that inhibit EndoMT) and using TGFb treatment. We successfully fabricated a family of alginate hydrogels with different mechanical and viscoelastic properties. HCAEC spheroids survived well in the 3D alginate hydrogel system and actively interacted with the fibroblasts in the hydrogels. Additionally, we observed viscoelasticity dependent migration of ECs from the spheroid into the alginate hydrogel and vessel like tube formation in the 3D model. Lastly, we quantified higher expression of the mesenchymal marker, SM22, in ECs in slow relaxing hydrogels, pointing towards viscoelasticity dependent progression of EndoMT. These results underscore the importance of mechanical factors such viscoelasticity in addition to stiffness in progression of diseases like atherosclerosis. Future work involves performing transcriptomics analysis to uncover the mechanism behind viscoelasticity dependent EndoMT progression.
Controlled in vitro multicellular culture systems with defined biophysical microenvironment have been used to elucidate the role of Notch signaling in the spatiotemporal regulation of stem and ...progenitor cell differentiation. In addition, computational models incorporating features of Notch ligand-receptor interactions have provided important insights into Notch pathway signaling dynamics. However, the mechanistic relationship between Notch-mediated intercellular signaling and cooperative microenvironmental cues is less clear. Here, liver progenitor cell differentiation patterning was used as a model to systematically evaluate the complex interplay of cellular mechanics and Notch signaling along with identifying combinatorial mechanisms guiding progenitor fate. We present an integrated approach that pairs a computational intercellular signaling model with defined microscale culture configurations provided within a cell microarray platform. Specifically, the cell microarray-based experiments were used to validate and optimize parameters of the intercellular Notch signaling model. This model incorporated the experimentally established multicellular dimensions of the cellular microarray domains, mechanical stress-related activation parameters, and distinct Notch receptor-ligand interactions based on the roles of the Notch ligands Jagged-1 and Delta-like-1. Overall, these studies demonstrate the spatial control of mechanotransduction-associated components, key growth factor and Notch signaling interactions, and point towards a possible role of E-Cadherin in translating intercellular mechanical gradients to downstream Notch signaling.
Hepatic stellate cells (HSCs) are one of the primary drivers of liver fibrosis in non-alcoholic fatty liver disease. Although HSC activation in liver disease is associated with changes in ...extracellular matrix (ECM) deposition and remodeling, it remains unclear how ECM regulates the phenotypic state transitions of HSCs. Using high-throughput cellular microarrays, coupled with genome-wide ATAC and RNA sequencing within engineered ECM microenvironments, we investigated the effect of ECM and substrate stiffness on chromatin accessibility and resulting gene expression in activated primary human HSCs. Cell microarrays demonstrated the cooperative effects of stiffness and ECM composition on H3K4 and H3K9 methylation/acetylation. ATAC sequencing revealed higher chromatin accessibility in HSCs on 1kPa compared to 25kPa substrates for all ECM conditions. Gene set enrichment analysis using RNA sequencing data of HSCs in defined ECM microenvironments demonstrated higher enrichment of NAFLD and fibrosis-related genes in pre-activated HSCs on 1kPa relative to 25kPa. Overall, these findings are indicative of a microenvironmental adaptation response in HSCs, and the acquisition of a persistent activation state. Combined ATAC/RNA sequencing analyses enabled identification of candidate regulatory factors, including HSD11B1 and CEBPb. siRNA-mediated knockdown of HSD11b1 and CEBPb demonstrated microenvironmental controlled reduction in fibrogenic markers in HSCs.
Hepatic stellate cells (HSCs) are one of the primary drivers of liver fibrosis in non-alcoholic fatty liver disease. Although HSC activation in liver disease is associated with changes in extracellular matrix (ECM) deposition and remodeling, it remains unclear how ECM regulates the phenotypic state transitions of HSCs. Using high-throughput cellular microarrays, coupled with genome-wide ATAC and RNA sequencing within engineered ECM microenvironments, we investigated the effect of ECM and substrate stiffness on chromatin accessibility and resulting gene expression in activated primary human HSCs. Overall, these findings were indicative of a microenvironmental adaptation response in HSCs, and the acquisition of a persistent activation state. Combined ATAC/RNA sequencing analyses enabled identification of candidate regulatory factors, including HSD11B1 and CEBPb. siRNA-mediated knockdown of HSD11b1 and CEBPb demonstrated microenvironmental controlled reduction in fibrogenic markers in HSCs.
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