Effect Of Cell Density Research Articles

Numerical study on flow and pressure drop characteristics of a novel type asymmetric wall-flow diesel particulate filter

In order to reduce the pressure drop and regeneration cost of diesel particulate filters (DPFs), and improve the power and economic performance of the diesel engines, a novel type of asymmetric channel wall-flow filter was proposed, including the regular hexagonal and triangular channels, as well as the rectangular channels. A one-dimensional mathematical model was built to study the flow characteristics, especially pressure drop performance, for this type of particulate filter, as well as a square symmetric and a square asymmetric channel filter for comparison. The effects of exhaust gas flow rate, cell density, wall thickness, and aspect ratio were numerically accessed. The results show that the novel asymmetric channel filter can effectively reduce the lifetime pressure drop by increasing the utilization ratio of the filtration wall and the filtration area. Specially, with the novel asymmetric channel structure, the wall pressure drop is considerably reduced owing to a lower mean wall penetration velocity. Furthermore, the depth layer and soot layer pressure drops of the novel type filter are much lower than those of the square symmetric channel filter owing to the smaller penetration velocity and thinner thickness of the soot layer, nearly the same as those of the square asymmetric channel filter. Additionally, the filter with a smaller aspect ratio can slightly reduce the pressure drop, so it can be practically applied if the distribution of the inlet gas is uniform. The novel asymmetric channel filter can meet the current and future demand for miniaturization and light-weighting of particulate filters, and has excellent market adaptability.

Multiplexed Quantitative Proteomic Analysis of HEK293 Provides Insights into Molecular Changes Associated with the Cell Density Effect, Transient Transfection, and Virus-Like Particle Production.

The production of virus-like particles (VLPs) has gained importance over the last few years owing to the benefits they provide compared to conventional vaccines. The biopharmaceutical industry is currently searching for safer candidates based on VLPs for new and existing vaccines and implementing new methods of manufacturing, thus allowing a more sustainable, effective, and species-specific production. Despite achieving lower yields compared to traditional platforms, the use of mammalian cells provides the right post-translational modifications, and consequently, the intensification of bioprocesses using mammalian cell platforms has become a matter of pressing concern. One of the methods subjected to intensification is transient gene expression, which has been proven to be highly effective regarding VLP production for preclinical or even clinical trials. In this work, a multiplexed quantitative proteomic approach has been applied to study the molecular characteristics of HEK293 cell cultures when growing at cell densities higher than 4 × 106 cells/mL and to study the effects related to cell transfection and VLP production. The obtained results revealed a set of functional and metabolic profiles of HEK293 under these three different conditions that allowed the identification of physiological bottlenecks regarding VLP production. Regarding the cell density effect, molecular alterations in the cell biology were proposed to help explain the difficulty for the cells to be transfected at higher densities. In addition, an overall disruption of cellular homeostasis after transfection was observed based on altered biological processes, and after identifying potential pathways liable to be optimized via metabolic engineering, different solutions were proposed to improve VLP production.

Cell encapsulation in gelatin bioink impairs 3D bioprinting resolution

Recent advances in three-dimensional (3D) bioprinting technologies have enabled precise patterning of cellular components along with biomimetic constructs for tissue engineering and regenerative medicine. The viscoelasticity of bioinks regulate printability and the smallest feature size in 3D bioprinted constructs. The impact of cellular components is typically neglected when choosing 3D bioprinting parameters. In this short communication, we quantified the effect of cell densities on the printability of hydrogel bioinks. Unexpectedly, our results show that encapsulated cells reduced the steady shear viscosity of gelatin-based bioinks by approximately 50% and the minimum force for onset of flow by approximately 30%. These results may justify the lower spatial resolution in 3D bioprinted cell-laden hydrogels.

Biotransformation of Acetaminophen by intact cells and crude enzymes of bacteria: A comparative study and modelling

Acetaminophen (APAP), which is an active ingredient of many analgesic drugs, is one of the contaminants of emerging concern in the environment. Although APAP is biodegradable, it is frequently detected in treatment plant effluents, surface water and soil suggesting that there are factors affecting the fate of APAP in the environment. In this study, four strains of bacteria that can degrade APAP were isolated from soil. Those strains belonged to Rhodococcus, Pseudomonas, Flavobacterium, and Sphingobium genera of Bacteria. A series of kinetic experiments were performed on the isolates in shake-flasks to determine biodegradation rate constant as well as the effect of temperature, APAP concentration and cell density on the biodegradation rates. APAP biodegradation follows the first order reaction kinetics which is coupled with cell growth. The specific APAP biodegradation rate constant (k) for all strains was similar and equal to 0.19 ± 0.01 h−1. The temperature, at which APAP biodegradation rate was maximum, was 35 °C. APAP biodegradation rate was linearly correlated with both the initial APAP concentration and the cell density. Initial step of the APAP biodegradation was hydrolysis of the amide bond which resulted in formation and accumulation of p-aminophenol suggesting that aryl acylamidase enzyme is responsible for the biotransformation. In addition, free and immobilized crude enzymes of the isolates transformed APAP at similar rates, comparable to the intact cells. This study showed that APAP biodegradation is achieved by a diverse group of bacteria having a similar enzyme operating at a constant kinetics which is very slow at environmentally relevant APAP concentrations. Natural removal of APAP in the environment is limited by kinetics, therefore APAP-bearing waste streams should be treated in adsorption enhanced biological systems before discharged into the environment.

Effect of propagation cell density and use of a nursery stage on plant growth of ‘Rex’ lettuce in hydroponic production

Effect of propagation cell density and use of a nursery stage on plant growth of ‘Rex’ lettuce in hydroponic production

A Multiscale Agent-Based Model of Ductal Carcinoma In Situ.

Objective:we present a multiscale agent-based model of Ductal Carcinoma in Situ (DCIS) in order to gain a detailed understanding of the cell-scale population dynamics, phenotypic distributions, and the associated interplay of important molecular signaling pathways that are involved in DCIS ductal invasion into the duct cavity (a process we refer to as duct advance rate here).Methods:DCIS is modeled mathematically through a hybridized discrete cell-scale model and a continuum molecular scale model, which are explicitly linked through a bidirectional feedback mechanism.Results:we find that duct advance rates occur in two distinct phases, characterized by an early exponential population expansion, followed by a long-term steady linear phase of population expansion, a result that is consistent with other modeling work. We further found that the rates were influenced most strongly by endocrine and paracrine signaling intensity, as well as by the effects of cell density induced quiescence within the DCIS population.Conclusion:our model analysis identified a complex interplay between phenotypic diversity that may provide a tumor adaptation mechanism to overcome proliferation limiting conditions, allowing for dynamic shifts in phenotypic populations in response to variation in molecular signaling intensity. Further, sensitivity analysis determined DCIS axial advance rates and calcification rates were most sensitive to cell cycle time variation.Significance:this model may serve as a useful tool to study the cell-scale dynamics involved in DCIS initiation and intraductal invasion, and may provide insights into promising areas of future experimental research.

High density cell seeding affects the rheology and printability of collagen bioinks

An advantage of bioprinting is the ability to incorporate cells into the hydrogel bioink allowing for precise control over cell placement within a construct. Previous work found that the printability of collagen bioinks is highly dependent on their rheological properties. The effect of cell density on collagen rheological properties and, therefore, printability has not been assessed. Therefore, the objective of this study was to determine the effects of incorporating cells on the rheology and printability of collagen bioinks. Primary chondrocytes, at densities relevant to cartilage tissue engineering (up to 100 × 106 cells ml−1), were incorporated into 8 mg ml−1 collagen bioinks. Bioink rheological properties before, during, and after gelation as well as printability were assessed. Cell-laden printed constructs were also cultured for up to 14 d to assess longer-term cell behavior. The addition of cells resulted in an increase in the storage modulus and viscosity of the collagen before gelation. However, the storage modulus after gelation and the rate of gelation decreased with increasing cell density. Theoretical models were compared to the rheological data to suggest frameworks that could be used to predict the rheological properties of cell-laden bioinks. Printability testing showed that improved printability could be achieved with higher cell densities. Fourteen-day culture studies showed that the printing process had no adverse effects on the viability or function of printed cells. Overall, this study shows that collagen bioinks are conducive to bioprinting with a wide range of cell densities while maintaining high printability and chondrocyte viability and function.

Effects of different culture media, cell densities and adhesion periods on stem cells from human exfoliated deciduous teeth after photobiomodulation

This study aimed to evaluate different culture media, cell densities and adhesion periods on stem cells from human exfoliated deciduous teeth (SHED) after photobiomodulation (PBM). SHED was cultured in either MEMα or DMEM with 10% Fetal Bovine Serum (FBS), let to adhere for 24 h or 48 h, submitted to 1%FBS, and irradiated. The following densities were tested: 2 × 103 (G1, G2), 1 × 104 (G3, G4), and 2 × 104 (G5, G6). PBM was applied at 20 mW for 10 s (5.0 J cm−2). Control groups were not irradiated (G2, G4, G6). MTT assay evaluated cell viability at 6 h, 12 h and 24 h. The comparison between different culture media revealed statistically significant differences among periods (p < 0.05) and no difference among groups at all periods. The statistical analysis showed the interaction between cell density, period, and adhesion (p < 0.001). The comparison between adhesion periods revealed that after PBM, at the first period G3 and G4 showed greater cell viability at 48 h of adhesion, while G5 and G6 had greater cell viability at 24 h of adhesion than at 48 h at both periods. G3, G5 and G6 had greater cell viability 24 h after PBM at 24 h of adhesion than at 48 h. Based on this study, the culture medium type MEMα or DMEM did not change the SHED viability after PBM. The adhesion period of 24 h, 6 and 24 h after PBM, the SHED density of 2 × 104 exhibited greater viability. However, with the adhesion period of 48 h, this SHED density showed a decreasing in viability, 6 and 24 h after PBM. Higher cell density (1 × 104 and 2 × 104) and shorter adhesion period (24 h) led to greater cell viability after PBM.

Mesenchymal stromal cells contract collagen more efficiently than dermal fibroblasts: Implications for cytotherapy.

BackgroundStem cell therapy is the next generation a well-established technique. Cell therapy with mesenchymal stem cells (MSC) has been demonstrated to enhance wound healing in diabetic mice, at least partly due to improved growth factor production. However, it is unclear whether MSC can biomechanically affect wound closure. Utilizing the well-established cell-populated collagen gel contraction model we investigated the interactions between MSC and the extracellular matrix.MethodsMurine fetal liver-derived Mesenchymal Stem Cells (MSCs) or fetal Dermal Fibroblasts (DFs) were cultured in cell–populated collagen gels (CPCGs). The effect of cell density, conditioned media, growth factors (TGF-B1, FGF, PDGF-BB), cytoskeletal disruptors (colchicine, cytochalasin-D), and relative hypoxia on gel contraction were evaluated. Finally, we also measured the expression of integrin receptors and some growth factors by MSCs within the contracting gels.ResultsOur results show that at different densities, MSCs induced a higher gel contraction compared to DFs. Higher cell density resulted in faster and more complete contraction of CPCGs. Cytoskeletal inhibitors either inhibited or prevented MSC-mediated contraction in a dose dependent fashion. Growth factors, conditioned media from both MSC and DF, and hypoxia all influenced CPCG contraction.DiscussionThe results suggest that MSCs are capable of directly contributing to wound closure through matrix contraction, and they are more effective than DF. In addition, this study demonstrates the importance of how other factors such as cell concentration, cytokines, and oxygen tension can provide potential modulation of therapies to correct wound healing impairments.

Quorum sensing inPseudomonas syringaepv.actinidiae(Psa)

Quorum sensing (QS) is a complex bacterial intra and interspecific communication system that is regulated by signaling molecules produced by cell density-dependent mechanisms. QS may regulate different phenotypes such as virulence, motility and biofilm production. The aim of this research was to investigate the existence of a QS system in Pseudomonas syringae pv. actinidiae (Psa). Psa lacks the canonical QS system based on N-acyl homoserine lactone (AHL) production and detection. However, at least three signal receptors (PsaR1, PsaR2, PsaR3) were recently identified. The present study was conducted in order to clarify the effects of different cell densities on the intraspecific communication in Psa cultures, and the interspecific interaction between Psa and other bacteria associated with the plant host (i.e. in the phyllosphere) or known to have an active QS system. A bioinformatic research was conducted for the identification of genes putatively involved in Psa QS system. About 30 genes were selected due to their involvement in influencing specific phenotypes such as virulence, density perception, biofilm formation and motility. Motility and biofilm formation are crucial phenotypes in the early stages of host colonization under the control of QS circuitries. The experiments conducted demonstrated Psa ability to produce biofilm in LB liquid media depending on population density. Psa motility resulted particularly enhanced in the supernatants of bacteria with a AHL-based QS system, such as Pseudomonas fluorescens, or an AHL-overproducing strain of Pseudomonas putida. Quantitative expression of QS-related genes was analyzed by qPCR. In conclusion, from our preliminary studies we observed that QS-phenotypes seem to be influenced not only by the cell density, but also by the microbial community that may share the same environment with Psa. Presumably, only by considering the multiple interactions with both the plant host and other bacterial species, the functionality of Psa QS-system will be fully elucidated.

Modeling intraphase and interphase mass transfer limitations for NH3–SCR over Cu–ZSM–5

A model describing NH3 selective catalytic reduction (NH3-SCR) over Cu-ZSM-5 to investigate the effects of intraphase and interphase mass transfer on standard SCR reaction is developed and further verified with the synthetic gas bench. The correlation between tortuosity and porosity has been analyzed by least squares method and applied to the sinuousoidal capillary bundle model. The effects of washcoat thicknesses, lengths, cell densities and channel widths on the standard SCR reaction are analyzed in temperature range of 150–500 °C. It is found that deNOx efficiency is affected by intraphase diffusion limitations at 200–500 °C and by interphase mass transfer limitation at intermediate (250–400 °C) and high temperatures (400–500 °C). As the temperature increases, the reaction is firstly controlled by kinetics, with the kinetics resistance decreasing and then increasing until the maximum among three processes. Furthermore, intake flow rates (GHSVs) play an important role impacting NO conversion on NH3–SCR.

Microengineered human amniotic ectoderm tissue array for high-content developmental phenotyping

During early post-implantation human embryogenesis, the epiblast (EPI) within the blastocyst polarizes to generate a cyst with a central lumen. Cells at the uterine pole of the EPI cyst then undergo differentiation to form the amniotic ectoderm (AM), a tissue essential for further embryonic development. While the causes of early pregnancy failure are complex, improper lumenogenesis or amniogenesis of the EPI represent possible contributing factors. Here we report a novel AM microtissue array platform that allows quantitative phenotyping of lumenogenesis and amniogenesis of the EPI and demonstrate its potential application for embryonic toxicity profiling. Specifically, a human pluripotent stem cell (hPSC)-based amniogenic differentiation protocol was developed using a two-step micropatterning technique to generate a regular AM microtissue array with defined tissue sizes. A computer-assisted analysis pipeline was developed to automatically process imaging data and quantify morphological and biological features of AM microtissues. Analysis of the effects of cell density, cyst size and culture conditions revealed a clear connection between cyst size and amniogenesis of hPSC. Using this platform, we demonstrated that pharmacological inhibition of ROCK signaling, an essential mechanotransductive pathway, suppressed lumenogenesis but did not perturb amniogenic differentiation of hPSC, suggesting uncoupled regulatory mechanisms for AM morphogenesis vs. cytodifferentiation. The AM microtissue array was further applied to screen a panel of clinically relevant drugs, which successfully detected their differential teratogenecity. This work provides a technological platform for toxicological screening of clinically relevant drugs for their effects on lumenogenesis and amniogenesis during early human peri-implantation development, processes that have been previously inaccessible to study.

Cell Density Effects in Different Cell Culture Media and Their Impact on the Propagation of Foot-And-Mouth Disease Virus.

Foot-and-mouth disease virus (FMDV) is endemic in many parts of the world. Vaccination is an important control measure, limits viral spread, and can help to eradicate the disease. However, vaccination programs are cost-intensive because of the short shelf life of vaccines and the need for frequent re-vaccination. Animal-component-free (ACF) or chemically defined media (CDM) at high cell densities are a promising approach for the production of inexpensive high-quality vaccines, but the occurrence of cell density effects has been reported for various virus-cell systems in vaccine production. For FMDV, the use of CDM or ACF media for vaccine production has not been studied and no information about cell density effects is available. This work describes the propagation of FMDV in ACF or in CDM. Cells were grown at increasing cell densities and either 100% media exchange or addition of 30% fresh media was performed before infection with FMDV. Increasing cell densities reduced the viral titer and increased yield variability in all media except BHK300G. This effect can be mitigated by performing a 100% media exchange before infection or when using the controlled environment of a bioreactor. The media composition and also a fragile relationship between virus and cell metabolism seem to be causal for that phenomenon.

Controlled temp for cell plating eliminates room temp cell settling in 96-well plates, reducing Edge Effect and improving cell conditions

Abstract The “edge effect” has always limited the use of edge wells of widely-used 96-well plates, reduced useable assay space by 37%, increased materials, time, and costs for these assays. Methods reported to reduce edge effect include leaving the plates at room temperature (RT) for extended cell settling times (30–120 min). We previously reported that controlling conditions to 37° C during cell plating prevents thermal currents and non-random distribution of cells seen during cell settling in edge wells. Here we report studies with human A549 lung carcinoma cells, used for in vitro viral assays, and human bone marrow mesenchymal stromal cells (MSC). Our null hypothesis is that there would be no difference in cell density or viability between cells plated/settled at constant 37° C and extended cell settling times at RT conditions. We plated A549 or MSC under controlled conditions in modular cell handling and incubation chambers in the Xvivo System. We pre-incubated plates for 30, 60, 90, and 120 min at RT and compared these with cells handled at constant 37 degrees. We used the HoloMonitor M4 (PHI, Inc) to monitor cell settling and assessed cell density at 24 and 48 hrs later using crystal violet. We found that cell settling at RT resulted in delayed cell attachment, delayed time to first division, and different cell densities as compared with cell handling at 37° C. Cell agitation and thermal variation was still seen between center and edge wells during cell settling with medium warmed to 37 degrees before traditional cell plating at RT. We concluded that full-time control of 37° C during cell plating is necessary to prevent cell density and cell viability edge effect that occurs during routine handling of cells under RT conditions.

Proteomic analysis of the effects of cell culture density on the metastasis of breast cancer cells.

Cancer cell progression and proliferation increase cell density, resulting in changes to the tumour site, including the microenvironment. What is not known is if increased cell density influences the aggressiveness of cancer cells, especially their proliferation, migration, and invasion capabilities. In this study, we found that dense cell culture enhances the aggressiveness of the metastatic cancer cell lines, 4T1 and ZR-75-30, by increasing their proliferation, migration, and invasion capabilities. However, a less metastatic cell line, MCF-7, did not show an increase in aggressiveness, following dense cell culture conditions. We conducted a differential proteomic analysis on 4T1 cells cultured under dense or sparse conditions and identified an increase in expression for proteins involved in migration, including focal adhesion, cytoskeletal reorganization, and transendothelial migration. In contrast, 4T1 cells grown under sparse conditions had higher expression levels for proteins involved in metabolism, including lipid and phospholipid binding, lipid and cholesterol transporter activity, and protein binding. These results suggest that the high-density tumour microenvironment can cause a change in cellular behaviour, leading towards more aggressive cancers. SIGNIFICANCE OF THE STUDY: Metastasis of cancer cells is an obstacle to the clinical treatment of cancer. We found that dense cultures made metastatic cancer cells more potent in terms of proliferation, migration, and invasion. The proteomic and bioinformatic analyses provided some valuable clues for further intensive studies about the effects of cell density on cancer cell aggressiveness, which were associated with events such as pre-mRNA splicing and RNA transport, focal adhesion and cytoskeleton reorganization, ribosome biogenesis, and transendothelial migration, or associated with proteins, such as JAM-1 and S100A11. This investigation gives us new perspectives to investigate the metastasis mechanisms related to the microenvironment of tumour sites.

Adhesion and Proliferation of Human Adipose-Derived Stem Cells on Titania Nanotube Surfaces

When a biomaterial is implanted, the body reacts similar to an injury and stem cells are recruited to the implant site. Since, stem cells play an important role in tissue repair in the body, their interaction with biomaterials is critical for long-term success of medical devices. Surfaces with nanostructured features have been shown to alter cellular functionality in vitro and even improve fixation of the implant to the surrounding bone tissues in vivo. In this study, the effect of titania nanotube (NT) size and cell density on the adhesion and proliferation of human adipose-derived stem cells (ASCs) was evaluated. Although many studies have evaluated mesenchymal stem cells response on nanostructured surfaces, very few studies have explored the response of adipose-derived stem cells on titanium nanotube surfaces and none have explored the effect of cell density concurrent with nanotube size on ASC proliferation. Proliferation behavior of ASCs on NT surfaces and titanium control were investigated for a week using three different cell densities. The optimal cell density was 2500 cells/well and the smaller diameter NT exhibited higher ASC proliferation. This study confirms that NT surfaces promote ASC adhesion and proliferation. By more fully understanding the effect of nanostructure size on adhesion and proliferation of stem cells, implants could be specifically designed to achieve the optimal stem cell response from the tissue in which they are implanted. Additionally, the favorable response of ASC to these NT surfaces and determination of optimal cell density suggests a potential use in orthopedic tissue regeneration. When a biomaterial is implanted, the body reacts similar to an injury and stem cells are recruited to the implant site. Since, stem cells play an important role in tissue repair in the body, their interaction with biomaterials is critical for long-term success of medical devices. This study confirms that nanotube surfaces promote stem cell adhesion and proliferation.

Effect of cell density on formation of three-dimensional cartilaginous constructs using fibrin & human osteoarthritic chondrocytes.

Background & objectives:Seeding density is one of the major parameters affecting the quality of tissue-engineered cartilage. The objective of this study was to evaluate different seeding densities of osteoarthritis chondrocytes (OACs) to obtain the highest quality cartilage.Methods:The OACs were expanded from passage 0 (P0) to P3, and cells in each passage were analyzed for gross morphology, growth rate, RNA expression and immunochemistry (IHC). The harvested OACs were assigned into two groups: low (1×107 cells/ml) and high (3×107 cells/ml) cell density. Three-dimensional (3D) constructs for each group were created using polymerised fibrin and cultured for 7, 14 and 21 days in vitro using chondrocyte growth medium. OAC constructs were analyzed with gross assessments and microscopic evaluation using standard histology, IHC and immunofluorescence staining, in addition to gene expression and biochemical analyses to evaluate tissue development.Results:Constructs with a high seeding density of 3×107 cells/ml were associated with better quality cartilage-like tissue than those seeded with 1×107 cells/ml based on overall tissue formation, cell association and extracellular matrix distribution. The chondrogenic properties of the constructs were further confirmed by the expression of genes encoding aggrecan core protein and collagen type II.Interpretation & conclusions:Our results confirmed that cell density was a significant factor affecting cell behaviour and aggregate production, and this was important for establishing good quality cartilage.

Optimization of macrophage isolation from the Persian sturgeon and the Caspian kutum fish: a comparative study.

The aim of this research was a comparative study on the isolation and culture of head kidney macrophages derived from Acipenser persicous and Rutilus frisii kutum as teleost and chondrostei species of fish. The macrophages were isolated by density gradient sedimentation, followed by adherence to a plastic surface. They exhibited strong phagocytic activity against bacteria. The effect of cell density, incubation time, FBS percentage, pH and temperatures on the cell number and viability were determined and compared. Also, the effect of light/dark regimen on viability, adherence, release of reactive oxygen species (ROS) and nitric oxide (NO) in the macrophages was determined. The results showed that the Caspian kutum macrophages were more sensitive to FBS percentage and cell density whereas the Persian sturgeon macrophages were more sensitive to pH of the cell culture media. The adherence and viability of the macrophages from both fish species firstly increased (P < 0.05) after exposure to a light/dark regimen, but then significantly decreased as did ROS and NO productions. For the first time, this study has determined the optimal conditions for primary culture of macrophages derived from sturgeons, and shows the unique effect of light on the biology of fish immune cells.

Initial cell plating density affects properties of human primary synovial mesenchymal stem cells

ABSTRACTSynovial mesenchymal stem cells (MSCs) appear to be an attractive cell source in cartilage and meniscus regeneration because of their high proliferative and chondrogenic potentials. Two methods are used to culture synovial nucleated cells in the preparation of primary synovial MSCs. In one method, the cells are plated at low density to make cell colonies. In the other method, the cells are plated at high density. We investigated the effects of initial cell density on proliferation, surface markers, and multipotentiality, including chondrogenesis in primary synovial MSCs. Human synovium was obtained from the knee joints of patients with osteoarthritis after total knee arthroplasty. Immediately after enzyme digestion, the synovial nucleated cells were plated in densities of 103, 104, or 105 cells/60‐cm2 dish and cultured for 14 days. Proliferation, surface markers, chondrogenesis, adipogenesis, and calcification were examined in three populations. The cell colonies were distinct in the 103 cells/dish group, faint in the 104 cells/dish group, and obscure in the 105 cells/dish group. The total number of cells/dish was positively related to plating density, whereas the fold increase was negatively related to plating density (n = 13). Among 12 surface markers, a negative relation to plating density was distinct in CD105. The cartilage pellet weight was negatively related to the initial plating density. The oil red‐o positive area and alizarin red positive area were positively related to the initial plating density. The initial cell plating density affected the properties of primary synovial MSCs. Synovial nucleated cells proliferated better when plated at low density, and the synovial MSCs obtained by this method contained a high chondrogenic potential. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 37:1358–1367, 2019.

Effect of flow on ATP/ADP concentration at the endothelial cell surface: interplay between shear stress and mass transport

The nucleotides ATP and ADP regulate many aspects of endothelial cell (EC) biology, including intracellular calcium concentrations, focal adhesion activation, cytoskeletal organization, and cellular motility. In vivo, ECs are constantly under flow, and the concentration of ATP/ADP on the EC surface is determined by the combined effects of nucleotide convective and diffusive transport as well as hydrolysis by ectonucleotidases on the EC surface. In addition, experiments have demonstrated that flow induces ATP release from the cells. Previously computational models have incorporated the above effects and thus described concentration at the EC surface. However, it remains unclear what physical processes are responsible for nucleotide regulation. While some EC responses to flow have been shown to be directly driven by shear stress, others appear to also involve a non-negligible contribution of transport. In the present work, we develop a mathematical model and perform numerical simulations to investigate the relative contributions of shear stress and transport to nucleotide concentration at the EC surface, with the effect of cell density. Because in vitro experiments are performed by using confluent cells in some cases and subconfluent cells in other cases, we also investigate the effect of cell density on the results. The outcomes of the simulations demonstrate a complex interplay between shear stress and transport such that transport has a significant contribution at certain shear stress values but not at others. The effect of transport on nucleotide concentration increases with cell density. The present findings enhance our understanding of the mechanisms that govern the regulation of such molecules at the EC surface under flow. The implications of these findings for downstream responses such as cellular motility merit future investigation.