Generated Shear Stress Research Articles

Effect of viscosity of gelatin methacryloyl-based bioinks on bone cells

The viscosity of gelatin methacryloyl (GelMA)-based bioinks generates shear stresses throughout the printing process that can affect cell integrity, reduce cell viability, cause morphological changes, and alter cell functionality. This study systematically investigated the impact of the viscosity of GelMA-gelatin bioinks on osteoblast-like cells in 2D and 3D culture conditions. Three bioinks with low, medium, and high viscosity prepared by supplementing a 5% GelMA solution with different concentrations of gelatin were evaluated. Cell responses were studied in a 2D environment after printing and incubation in non-cross-linked bioinks that caused the gelatin and GelMA to dissolve and release cells for attachment to tissue culture plates. The increased viscosity of the bioinks significantly affected cell area and aspect ratio. Cells printed using the bioink with medium viscosity exhibited greater metabolic activity and proliferation rate than those printed using the high viscosity bioink and even the unprinted control cells. Additionally, cells printed using the bioink with high viscosity demonstrated notably elevated expression levels of alkaline phosphatase and bone morphogenetic protein-2 genes. In the 3D condition, the printed cell-laden hydrogels were photo-cross-linked prior to incubation. The medium viscosity bioink supported greater cell proliferation compared to the high viscosity bioink. However, there were no significant differences in the expression of osteogenic markers between the medium and high viscosity bioinks. Therefore, the choice between medium and high viscosity bioinks should be based on the desired outcomes and objectives of the bone tissue engineering application. Furthermore, the bioprinting procedure with the medium viscosity bioink was used as an automated technique for efficiently seeding cells onto 3D printed porous titanium scaffolds for bone tissue engineering purposes.

Aortic Root Vortex Formation During Left Ventricular Assist Device Support.

The vortex that forms in the aortic sinus plays a vital role in optimizing blood flow. Disruption of the vortex can result in flow stagnation and activate thrombus formation in the aortic root, especially when aortic valve flow is reduced as during left ventricular assist device (LVAD) support. Our goal in this study was to visualize vortex formation in an experimental model of the aortic root as flow is progressively reduced. A mock circulatory loop that reproduces heart failure hemodynamics was combined with a HeartMate II LVAD and velocity measured in a transparent aortic root with a bioprosthetic valve. The aortic valve sinus vortices are clearly visible as counter-rotating structures in the velocity field at baseline and for all conditions with flow through the aortic valve. As LVAD speed increases, the central jet narrows but the vortices persist, disappearing only when the valve is completely closed. The vortices preserve fluid momentum and generate shear stress along the tissue surfaces which disrupts flow stasis. These features underscore the importance of maintaining "intermittent" aortic valve opening, as recommended for LVAD patients. This study is the first to report vortex formation in the aortic root during LVAD support, providing a motivation for further evaluation.

Mid-term Radiographic Outcomes of Anatomic Total Shoulder Arthroplasty in Biplanar Glenoid Deformities

INTRODUCTIONOptimal management of retroversion in anatomic total shoulder arthroplasty (aTSA) remains controversial and limited attention has been directed to the impact of glenoid inclination. Prior biomechanical study suggest that residual glenoid inclination generates shear stresses that may lead to early glenoid loosening. Combined biplanar glenoid deformities may complicate anatomic glenoid reconstruction and affect outcomes. The goal of this matched-cohort analysis was to assess the relationship between biplanar deformities and mid-term radiographic loosening in aTSA. METHODSThe study cohort was identified via an institutional repository of 337 preoperative CT scans from 2010-2017. Glenoid retroversion, inclination, and humeral head subluxation were assessed via 3D-planning software. Patients with retroversion ≥ 20˚ and inclination ≥ 10˚ who underwent aTSA with eccentric reaming and non-augmented components were matched by age, sex, retroversion, and Walch classification to patients with retroversion ≥ 20˚ only. Primary outcome was glenoid component Lazarus radiolucency score. RESULTSTwenty-eight study subjects were matched to 28 controls with retroversion only. No difference in age (61.3 vs. 63.6 years, p=0.26), sex (19 [68%] vs. 19 [68%] male, p=1.0), or follow-up (6.1 vs. 6.4 years, p=0.59). Biplanar deformities had greater inclination (14.5˚ versus 5.3˚, p<0.001), retroversion (30.0˚ versus 25.6˚, p=0.01) and humeral subluxation (86.3% versus 82.1%, p=0.03). Biplanar patients had greater postoperative implant superior inclination (5.9 [4.6] vs. 3.0 [3.6] degrees, p=0.01) but similar rate of complete seating 24 [86%] vs. 24 [86%] p=1.0). At final follow-up, biplanar subjects had higher Lazarus radiolucent scores (2.4 [1.7] vs. 1.6 [1.1], p=0.03) and higher proportion of patients with glenoid radiolucency (19 [68%] vs. 11 [39%], p=0.03). No difference in complete component seating (86% versus 86%, p=0.47) or initial radiolucency grade (0.21 versus 0.29, p=0.55) on immediate postop radiographs. Biplanar patients demonstrated a greater amount of posterior subluxation at immediate postop(3.5% [1.3%] versus 1.8% [0.6%]; p=0.03) and final follow-up (7.6% [2.8%] versus 4.0% [1.8%]; p=0.04). At final radiographic follow-up, biplanar subjects had higher Lazarus radiolucent scores (2.4 [1.7] vs. 1.6 [1.1], p=0.03; ICC=0.82). Bivariate regression analysis demonstrated biplanar deformity was the only significant predictor (OR 3.3, p=0.04) of glenoid radiolucency. CONCLUSIONBiplanar glenoid deformity resulted in time-zero glenoid implant superior inclination and increased mid-term radiographic loosening and posterior subluxation. Attention to glenoid inclination is important for successful anatomical glenoid reconstruction. Future research is warranted to understand the long-term implications of these findings and impact of utilizing augmented implants or reverse shoulder arthroplasty to manage biplanar deformities.

Effects of aeration and centrifugation conditions on omega-3 fatty acid production by the mixotrophic dinoflagellate Gymnodinium smaydae in a semi-continuous cultivation system on a pilot scale

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO2 and O2. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydaeproduction gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000–8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0–4.0 L min-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

Computational insights into colonic motility: Mechanical role of mucus in homeostasis and inflammation

Colonic motility plays a vital role in maintaining proper digestive function. The rhythmic contractions and relaxations facilitate various types of motor functions that generate both propulsive and non-propulsive motility modes which in turn generate shear stresses on the epithelial surface. However, the interplay between colonic mucus, shear stress, and epithelium remains poorly characterized. Here, we present a colonic computational model that describes the potential roles of mucus and shear stress in both homeostasis and ulcerative colitis (UC). Our model integrates several key features, including the properties of the mucus bilayer and faeces, intraluminal pressure, and crypt characteristics to predict the time-space mosaic of shear stress. We show that the mucus thickness which could vary based on the severity of UC, may significantly reduce the amount of shear stress applied to the colonic crypts and effect faecal velocity. Our model also reveals an important spatial shear stress variance in homeostatic colonic crypts that suggests shear stress may have a modulatory role in epithelial cell migration, differentiation, apoptosis, and immune surveillance. Together, our study uncovers the rather neglected roles of mucus and shear stress in intestinal cellular processes during homeostasis and inflammation.

Evaluation of erythrocyte membrane oxidation due to their exposure to shear flow generated by extracorporeal blood pump.

Several similarities have been found between shear stress-induced erythrocyte damage and physiological aging of erythrocytes in terms of elevated mechanical fragility, increased erythrocyte aggregation, and decreased membrane surface charge. Accordingly, we hypothesized that blood pump circulation, which generates shear stress, would accelerate erythrocyte aging, manifesting as oxidation. Therefore, the purpose of this study was to investigate the effect of blood pump circulation on erythrocyte oxidation. Fresh porcine blood was acquired from a slaughterhouse and anticoagulated with sodium citrate. About 500 mL of anticoagulated whole blood was circulated for 180 min in an in vitro test circuit comprising a BP-80 blood pump with a pump speed and a pump pressure head of 100-120 mmHg. A blood sample was taken at the start of the circulation and 180 min afterward. The hemolysis level and oxidation amount of the erythrocyte membrane were analyzed and compared between samples. Hemolysis increased with the prolongation of shear exposure inside the pump circuit. After 180 min of blood pumping in circuit, the oxidation level of the erythrocyte membrane showed an increase of 0.1 nmol/mg protein. Moreover, the membrane oxidation levels of sheared erythrocytes were greater than those of control erythrocytes. These results suggest that blood pump circulation accelerates erythrocyte aging and give us a greater understanding of the effects of blood pump perfusion.

On the role of poroelastic stressing and pore pressure diffusion in discrete fracture and fault system in triggering post-injection seismicity in enhanced geothermal systems

Injection-induced seismicity has become one of the most critical challenges for the widespread deployment of Enhanced Geothermal Systems (EGS). In particular, some EGS development projects have led to large, damaging earthquakes that unexpectedly occurred far off the stimulated reservoir region and, in particular, after stopping fluid injection. Yet, the causative mechanisms of these seismicity patterns remain highly elusive. Here, we identify a combination of mechanisms that could explain delayed seismicity in EGS sites by conducting fully-coupled hydromechanical simulations of the hydraulic stimulation of a naturally-fractured granitic reservoir. The model comprises a sparse network of long, variably-oriented fractures interacting with a nearby, critically-oriented fault. The results show that the presence of fractures introduces notable nonlinearities in the flow field and rock deformation and significantly expands the rock volume affected by fluid injection. First, the stimulated fracture network provides highly-permeable conduits for communicating elevated pore pressure over long distances. Second, the anisotropic expansion of fractures generates shear stress that is transmitted almost instantaneously across the reservoir. The pore pressure and stress perturbations can not only cause slip along fractures, inducing (micro)seismicity during injection, but also affect the stability of nearby faults, which may not necessarily be pressurized during injection. The transferred poroelastic stresses can increase or decrease the slip tendency along different fault segments. However, the fault may reactivate only after several months following injection when a progressive pore pressure diffusion modulated by the transient fault permeability evolution brings a critically-stressed fault segment to failure conditions. We also find that the spatiotemporal evolution of seismicity depends largely on the nearby fault orientation, hydromechanical properties, and hydraulic connection with the fracture network, as well as the initial state of stress. We conclude that accurate subsurface characterization and continuous monitoring during and after injection should allow for managing the risks posed by injection-induced seismicity and safely unlocking the immense potential for clean and sustainable geothermal energy.

Magnetorheological fluids: A comprehensive review

The magnetorheological (MR) fluids contain magnetic micro-sized iron particles, non-magnetic-based fluid, and some additives in order to mitigate sedimentation and agglomeration. The various carrier fluids used in the preparation of MR fluids are mineral oil, silicon oil, castor oil, soybean oil, kerosene, synthetic oils, honge oil, organic oil, water-based oils, etc. However, for obtaining better vibration control, silicone oil is the most preferred one due to its higher viscosity index, lower friction characteristics, higher flash point, and higher shear strength. The MR fluids have various application areas such as dampers, prosthetic knees, valves, brakes, clutches, finishing processes etc. The dampers containing MR fluids are used in automobile cushioning for enhancing passenger comfort and MR suspensions significantly improve steering stability in vehicles. In case of MR brakes, the braking torque on the rotating disks is controlled using the generated shear stress. The carbonyl iron (CI) particles exhibit better rheological characteristics as compared to electrolytic iron (EI) particles. The use of MR fluids produces stable and natural limb movement in orthoses, lower limb prostheses, and exoskeletons. The MR fluids also prove to be very significant in polishing applications. There are various issues with preparation methods and difficulties in the storage of MR fluids. The problems encountered in the synthesis of MR fluids include sedimentation, agglomeration, in-use thickening, corrosion, erosion, etc. The impact of particle proportion, particle shapes, and size has been influential in evaluating MR characteristics. The viscosity and shear stress of MR fluid have been mitigated at higher values of temperature and even CI particles get oxidized at higher temperatures. The CI particles as compared to EI particles are the majority favourable particles used for dispersing state within the MR fluids due to their higher value of saturation magnetization, more availability, and lesser cost. The small-sized particles led to lower wettability, whereas larger-sized particles accounted for an increased sedimentation rate. The currently available MR fluids cost is still on the higher side and the preparation of economical MR fluid is still a big challenge for the researchers. The MR fluids storage is also a big concern. The future scope of MR fluid may be in heavy industries such as nuclear, shipbuilding, oil and gas, space and aviation, etc. to achieve the desired damping response.

Hybrid de-icing method combining electrothermal system and ultrasonic guided waves

A novel hybrid de-icing method combining an electrothermal system and ultrasonic guided waves is proposed for the leading edge structure of wind turbine blades. The adhesion strength between the ice layer and the leading-edge structure is reduced by the electrothermal system. Piezoelectric ultrasonic transducers are used to generate shear stresses to crack and remove ice. The heating resistance wires and transducers are pasted onto the inner surface of the leading-edge structure. The spacing of the resistance wires was calculated by a theoretical thermal model. A temperature recorder was used to measure the temperature changes at different measuring points on the leading-edge surface under electric heating. This study conducted ultrasonic guided waves de-icing, electrothermal de-icing, and combined electrothermal–ultrasonic de-icing experiments in a freezer with an airfoil leading edge model. The results reveal that the combined electrothermal–ultrasonic method is feasible and has great potential for ice shedding acceleration.

Shear stress induces autophagy in Schlemm's canal cells via primary cilia-mediated SMAD2/3 signaling pathway.

The Schlemm's canal (SC) is a circular, lymphatic-like vessel located at the limbus of the eye that participates in the regulation of aqueous humor drainage to control intraocular pressure (IOP). Circumferential flow of aqueous humor within the SC lumen generates shear stress, which regulates SC cell behaviour. Using biochemical analysis and real-time live cell imaging techniques, we have investigated the activation of autophagy in SC cells by shear stress. We report, for the first time, the primary cilium (PC)-dependent activation of autophagy in SC cells in response to shear stress. Moreover, we identified PC-dependent shear stress-induced autophagy to be positively regulated by phosphorylation of SMAD2 in its linker and C-terminal regions. Additionally, SMAD2/3 signaling was found to transcriptionally activate LC3B, ATG5 and ATG7 in SC cells. Intriguingly, concomitant to SMAD2-dependent activation of autophagy, we also report here the activation of mTOR pathway, a classical autophagy inhibitor, in SC cells by shear stress. mTOR activation was found to also be dependent on the PC. Moreover, pharmacological inhibition of class I PI3K increased phosphorylation of SMAD2 at the linker and activated autophagy. Together, our data indicates an interplay between PI3K and SMAD2/3 signaling pathways in the regulation of PC-dependent shear stress-induced autophagy in SC cells.

Effects of Shear Stress Waves on Meat Tenderness: Ultrasonoporation.

Meat is an important part of the food pyramid in Mexico, to such an extent that it is included in the basic food basket. In recent years, there has been great interest in the application of so-called emerging technologies, such as high-intensity ultrasound (HIU), to modify the characteristics of meat and meat products. The advantages of the HIU in meat such as pH, increased water-holding capacity, and antimicrobial activity are well documented and conclusive. However, in terms of meat tenderization, the results are confusing and contradictory, mainly when they focus on three HIU parameters: acoustic intensity, frequency, and application time. This study explores via a texturometer the effect of HIU-generated acoustic cavitation and ultrasonoporation in beef (m. Longissimus dorsi). Loin-steak was ultrasonicated with the following parameters: time tHIU = 30 min/each side; frequency fHIU = 37 kHz; acoustic intensity IHIU = ~6, 7, 16, 28, and 90 W/cm2. The results showed that acoustic cavitation has a chaotic effect on the loin-steak surface and thickness of the rib-eye due to Bjerknes force, generating shear stress waves, and acoustic radiation transmittance via the internal structure of the meat and the modification of the myofibrils, in addition to the collateral effect in which the collagen and pH generated ultrasonoporation. This means that HIU can be beneficial for the tenderization of meat.

Influence of shear stress on the intracellular bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) level within an MBR biofilm

Biofilms are inevitable and typically adhere on solid surfaces such as the membrane surfaces in membrane bioreactors. Aeration has been widely used in the aerobic stage of water treatment to hydrodynamically generate shear stress to disrupt biofilm formation. The current study quantified the influence of shear stress on mature biofilms by examining its influence on bacteria Quorum Sensing behaviour which involves c-di-GMP molecules. The level of external shear stress was determined via validated Computational Fluid Dynamics simulation and the level of c-di-GMP was measured directly. It was found that bacteria are very sensitive to environmental shear stress; a small change of 0.05 Pa can lead to an intracellular c-di-GMP fluctuation of 5.6 pmol/mg protein. The mediating effect of shear stress on c-di-GMP level is nonlinear. In MBR systems, a time-averaged shear stress exceeding 0.72 Pa is indicated as it generates lower c-di-GMP and a looser biofilm that has low biodiversity.

The regulation and functions of the matricellular CCN proteins induced by shear stress.

Shear stress is a frictional drag generated by the flow of fluid, such as blood or interstitial fluid, and plays a critical role in regulating cellular gene expression and functional phenotype. The matricellular CCN family proteins are dynamically regulated by shear stress of different flow patterns, and their expression significantly alters the microenvironment of cells. Secreted CCN proteins mainly bind to several cell surface integrin receptors to mediate their diverse functions in regulating cell survival, function, and behavior. Gene-knockout studies indicate major functions of CCN proteins in the cardiovascular and skeletal systems, the two primary systems in which CCN expressions are regulated by shear stress. In the cardiovascular system, the endothelium is directly exposed to vascular shear stress. Unidirectional laminar blood flow generates laminar shear stress, which promotes a mature endothelial phenotype and upregulates anti-inflammatory CCN3 expression. In contrast, disturbed flow generates oscillatory shear stress, which induces endothelial dysfunction through the induction of CCN1 and CCN2. Shear-induced CCN1 binds to integrin α6β1 and promotes superoxide production, NF-κB activation, and inflammatory gene expression in endothelial cells. Although the interaction between shear stress and CCN4-6 is not clear, CCN 4 exhibits a proinflammatory property and CCN5 inhibits vascular cell growth and migration. The crucial roles of CCN proteins in cardiovascular development, homeostasis, and disease are evident but not fully understood. In the skeletal system, mechanical loading on bone generates shear stress from interstitial fluid in the lacuna-canalicular system and promotes osteoblast differentiation and bone formation. CCN1 and CCN2 are induced and potentially mediate fluid shear stress mechanosensing in osteocytes. However, the exact roles of interstitial shear stress-induced CCN1 and CCN2 in bone are still not clear. In contrast to other CCN family proteins, CCN3 inhibits osteoblast differentiation, although its regulation by interstitial shear stress in osteocytes has not been reported. The induction of CCN proteins by shear stress in bone and their functions remain largely unknown and merit further investigation. This review discusses the expression and functions of CCN proteins regulated by shear stress in physiological conditions, diseases, and cell culture models. The roles between CCN family proteins can be compensatory or counteractive in tissue remodeling and homeostasis.

Microvascular no reflow in acute MI—Mechanistic studies of sonoreperfusion

Congestive heart failure (CHF) following acute myocardial infarction (AMI) is on the rise. Microvascular obstruction (MVO) is the single most important contributor to post-AMI CHF; it occurs in up to 80% of patients with AMI and is associated with worse outcomes. To address this unmet need, we have been developing ultrasound targeted microbubble cavitation (UTMC) to achieve “sonoreperfusion” (SRP) for MVO. During SRP, US is applied to intravenously administered MBs as they transit the coronary microcirculation, which causes MBs to oscillate and generate shear stress. We have previously shown that SRP therapy restores perfusion during MVO through direct mechanical “chiseling” effects of MBs on microthrombi. However, MVO is more than just physical obstruction from microemboli; it is characterized by a milieu of inflammation and oxidative stress, a state of imbalance between the formation of damaging reactive oxygen species (ROS) and antioxidant defenses. One such defense is nitric oxide (NO), which has multi-level therapeutic potential for MVO. We have demonstrated that UTMC releases NO from endothelial cells through mechanotransduction, and that NO is a major contributor to the efficacy of SRP. We are now actively pursuing strategies to optimize SRP, not only through mechanical mechanisms but also by addressing oxidative stress.

Experimental measurements and CFD modelling of hydroxyapatite scaffolds in perfusion bioreactors for bone regeneration.

In the field of bone tissue engineering, particular interest is devoted to the development of 3D cultures to study bone cell proliferation under conditions similar to in vivo ones, e.g. by artificially producing mechanical stresses promoting a biological response (mechanotransduction). Of particular relevance in this context are the effects generated by the flow shear stress, which governs the nutrients delivery rate to the growing cells and which can be controlled in perfusion reactors. However, the introduction of 3D scaffolds complicates the direct measurement of the generated shear stress on the adhered cells inside the matrix, thus jeopardizing the potential of using multi-dimensional matrices. In this study, an anisotropic hydroxyapatite-based set of scaffolds is considered as a 3D biomimetic support for bone cells deposition and growth. Measurements of sample-specific flow resistance are carried out using a perfusion system, accompanied by a visual characterization of the material structure. From the obtained results, a subset of three samples is reproduced using 3D-Computational Fluid Dynamics (CFD) techniques and the models are validated by virtually replicating the flow resistance measurement. Once a good agreement is found, the analysis of flow-induced shear stress on the inner B-HA structure is carried out based on simulation results. Finally, a statistical analysis leads to a simplified expression to correlate the flow resistance with the entity and extensions of wall shear stress inside the scaffold. The study applies CFD to overcome the limitations of experiments, allowing for an advancement in multi-dimensional cell cultures by elucidating the flow conditions in 3D reactors.

Structural analysis of unreinforced masonry spiral staircases using Discrete Element modelling

Unreinforced masonry spiral staircases have been built for more than two thousand years in castles, churches and palaces, and these staircases require structural assessment. For a few decades, the structural behaviour of “cantilever” staircases has been debated among scholars. Several structural methods have been used, but due to the complex 3D geometry and the substantial number of treads, a priori assumptions have been made about the magnitude and point of application of the contact forces between the treads and the wall-tread connections. These assumptions influence the calculation of torsional moment, which, in some methods, reaches high values that could generate shear stresses greater than the material’s strength. In this paper, a 3D model based on one helix of the “cantilever” spiral staircase of San Domingo de Bonaval, in Spain, has been analysed using the Discrete Element Method. The entire stair is analysed without making assumptions on the magnitude and location of the resultant contact forces, which are calculated for each tread using customised Python-based functions. The wall-tread connections have been modelled using rigid blocks, and several contact conditions have been investigated. Moreover, different friction angles and the influence of geometrical imperfections are analysed to simulate material tolerances and assembly imprecisions. The simulation results indicate that perfect wall-tread contact conditions lead to conservative predictions of the torsional moment. Instead, gaps and imperfections allow small displacements, which reduce the torque and increase compression forces in the inner helical ring of the stair. Low friction angles could increase the torsional moment values, while vertical settlements do not cause a significant effect. Cantilever situations could still occur due to not perfect contact conditions between consecutive treads, which suggests that the tread-tread contact area should be carefully inspected during restoration. More generally, this paper demonstrates the potential variability of the structural behaviour of highly indeterminate structures when boundary conditions are uncertain, while providing valuable context to inform restoration strategies.

Enhancing cell survival in 3D printing of organoids using innovative bioinks loaded with pre-cellularized porous microscaffolds

Extrusion bioprinting is a relevant 3D technology to create biological systems in regenerative medicine, pharmaceutical development and cancer research. Bioink is the necessary component to incorporate the cells that will be printed by extrusion bioprinting. However, bioinks and extrusion printing can generate shear stresses mechanically unfavorable for cell survival. We thus developed a bioink, based on methacrylated collagen and hyaluronic acid, in combination with porous poly(D,L-lactic-co-glycolic acid) solid microscaffolds to protect cells against mechanical stress during extrusion printing. We found that porosities of the microscaffolds allowed human chondosarcoma cells to colonize the structure. Moreover, metabolic activity of these chondrosarcoma cells, fibroblast cells, and dental pulp stem cells (DPSCs) incorporated within bioink (before printing) increased 4-fold in presence of a polylysine- or collagen-coated microscaffolds compared with those cultured without microscaffolds. Their survival increased by 10% either by hand deposition or by bioprinting extrusion (bioprinter BioBot®Basic) compared to cells in bioink without microscaffolds. In addition to the mechanoshield properties provided by microscaffolds, they allow the migration of DPSCs stem cells towards HCS-2/8 cancer cells after 7 days of co-culture in an organoid created by bioprinting extrusion while without microscaffolds the cells aggregated and remained static.

Traumatic axonal injury: neuropathological features, postmortem diagnostic methods, and strategies.

Traumatic brain injury (TBI) has high morbidity and poor prognosis and imposes a serious socioeconomic burden. Traumatic axonal injury (TAI), which is one of the common pathological changes in the primary injury of TBI, is often caused by the external force to the head that causes the white matter bundles to generate shear stress and tension; resulting in tissue damage and leading to the cytoskeletal disorder. At present, the forensic pathological diagnosis of TAI-caused death is still a difficult problem. Most of the TAI biomarkers studied are used for the prediction, evaluation, and prognosis of TAI in the living state. The research subjects are mainly humans in the living state or model animals, which are not suitable for the postmortem diagnosis of TAI. In addition, there is still a lack of recognized indicators for the autopsy pathological diagnosis of TAI. Different diagnostic methods and markers have their limitations, and there is a lack of systematic research and summary of autopsy diagnostic markers of TAI. Therefore, this study mainly summarizes the pathological mechanism, common methods, techniques of postmortem diagnosis, and corresponding biomarkers of TAI, and puts forward the strategies for postmortem diagnosis of TAI for forensic cases with different survival times, which is of great significance to forensic pathological diagnosis.

Viscoplastic effects of Newtonian fluids in nanopores: a molecular dynamics study

Understanding the influence of fluid–solid interactions on low-velocity non-Darcy flow in ultra-low permeability reservoirs is essential for enhanced oil recovery. The Poiseuille flows of C12H26 and argon under different pressure gradients in a nanopore are simulated using the molecular dynamics method. The results demonstrate that the confined fluids behave as elastic solids under lower pressure gradient but as viscous fluids under higher pressure gradient in the simulation. With increase of the external pressure gradient, the generated shear stress exceeds the yield stress related to the fluid-solid interaction and leads to a transition. This phenomenon indicates that the confined fluids in the nanopore exhibit apparent viscoplasticity. According to the viscoplastic hypothesis, the confined fluid can be divided into elastic and viscous layers, depending on the competition between the shear and yield stresses. The simulation results also indicate the yield stress increases near the wall. Assuming that the yield stress is inversely proportional to the distance from the wall, a non-Darcy flow model is proposed to calculate the flow rate by pressure gradient. The predictions of the model are consistent with the simulations for both C12H26 and argon, indicating the similarity of viscoplastic effects on the seepage of both fluid-nanopore systems.

Impact of Fluid Flow Shear Stress on Osteoblast Differentiation and Cross-Talk with Articular Chondrocytes.

Bone cells, in particular osteoblasts, are capable of communication with each other during bone growth and homeostasis. More recently it has become clear that they also communicate with other cell-types; including chondrocytes in articular cartilage. One way that this process is facilitated is by interstitial fluid movement within the pericellular and extracellular matrices. This stimulus is also an important mechanical signal in skeletal tissues, and is known to generate shear stresses at the micron-scale (known as fluid flow shear stresses (FFSS)). The primary aim of this study was to develop and characterize an in vitro bone–cartilage crosstalk system, to examine the effect of FFSS on these cell types. Specifically, we evaluated the response of osteoblasts and chondrocytes to FFSS and the effect of FFSS-induced soluble factors from the former, on the latter. This system will ultimately be used to help us understand the role of subchondral bone damage in articular cartilage degeneration. We also carried out a comparison of responses between cell lines and primary murine cells in this work. Our findings demonstrate that primary cells produce a more reliable and reproducible response to FFSS. Furthermore we found that at lower magnitudes , direct FFSS produces anabolic responses in both chondrocytes and osteoblasts, whereas higher levels produce more catabolic responses. Finally we show that exposure to osteoblast-derived factors in conditioned media experiments produced similarly catabolic changes in primary chondrocytes.