Impact of flow shear stress on morphology of osteoblast-like IDG-SW3 cells

β-glycerophosphate, not low magnitude fluid shear stress, increases osteocytogenesis in the osteoblast-to-osteocyte cell line IDG-SW3

AIM

As osteoblasts deposit a mineralized collagen network, a subpopulation of these cells differentiates into osteocytes. Biochemical and mechanical stimuli, particularly fluid shear stress (FSS), are thought to regulate this, but their relative influence remains unclear. Here, we assess both biochemical and mechanical stimuli on long-term bone formation and osteocytogenesis using the osteoblast-osteocyte cell line IDG-SW3.

METHODS

Due to the relative novelty and uncommon culture conditions of IDG-SW3 versus other osteoblast-lineage cell lines, effects of temperature and media formulation on matrix deposition and osteocytogenesis were initially characterized. Subsequently, the relative influence of biochemical (β-glycerophosphate (βGP) and ascorbic acid 2-phosphate (AA2P)) and mechanical stimulation on osteocytogenesis was compared, with intermittent application of low magnitude FSS generated by see-saw rocker.

RESULTS

βGP and AA2P supplementation were required for mineralization and osteocytogenesis, with 33°C cultures retaining a more osteoblastic phenotype and 37°C cultures undergoing significantly higher osteocytogenesis. βGP concentration positively correlated with calcium deposition, whilst AA2P stimulated alkaline phosphatase (ALP) activity and collagen deposition. We demonstrate that increasing βGP concentration also significantly enhances osteocytogenesis as quantified by the expression of green fluorescent protein linked to Dmp1. Intermittent FSS (~0.06 Pa) rocker had no effect on osteocytogenesis and matrix deposition.

CONCLUSIONS

This work demonstrates the suitability and ease with which IDG-SW3 can be utilized in osteocytogenesis studies. IDG-SW3 mineralization was only mediated through biochemical stimuli with no detectable effect of low magnitude FSS. Osteocytogenesis of IDG-SW3 primarily occurred in mineralized areas, further demonstrating the role mineralization of the bone extracellular matrix has in osteocyte differentiation.

Computational fluid dynamics analysis of the fluid environment of 3D printed gradient structure in interfacial tissue engineering

Mass transport properties within three-dimensional (3D) scaffold are essential for tissue regeneration, such as various fluid environmental cues influence mesenchymal stem cells differentiation. Recently, 3D printing has been emerging as a new technology for scaffold fabrication by controlling the scaffold pore geometry to affect cell growth environment. In this study, the flow field within scaffolds in a perfusion system was investigated with uniform structures, single gradient structures and complex gradient structures using computational fluid dynamics (CFD) method. The CFD results from those uniform structures indicate the fluid velocity and fluid shear stress within the scaffold structure increased as the filament diameter increasing, pore width decreasing, pore shape decreased from 90° to 15°, and layer configuration changing from lattice to stagger structure. By assembling those uniform structure as single gradient structures, it is noted that the fluid dynamic characterisation within the scaffold remains the same as the corresponding uniform structures. A complex gradient structure was designed to mimic natural osteochondral tissue by assembly the uniform structures of filament diameter, pore width, pore shape and layer configuration. The results show that the fluid velocity and fluid shear stress within the complex gradient structure distribute gradually increasing and their maximum magnitude were from 1.15 to 3.20 mm/s, and from 12 to 39 mPa, respectively. CFD technique allows the prediction of velocity and fluid shear stress within the designed 3D gradient scaffolds, which would be beneficial for the tissue scaffold development for interfacial tissue engineering in the future.

A quantitative meta-analysis comparing cell models in perfused organ on a chip with static cell cultures

As many consider organ on a chip for better in vitro models, it is timely to extract quantitative data from the literature to compare responses of cells under flow in chips to corresponding static incubations. Of 2828 screened articles, 464 articles described flow for cell culture and 146 contained correct controls and quantified data. Analysis of 1718 ratios between biomarkers measured in cells under flow and static cultures showed that the in all cell types, many biomarkers were unregulated by flow and only some specific biomarkers responded strongly to flow. Biomarkers in cells from the blood vessels walls, the intestine, tumours, pancreatic island, and the liver reacted most strongly to flow. Only 26 biomarkers were analysed in at least two different articles for a given cell type. Of these, the CYP3A4 activity in CaCo2 cells and PXR mRNA levels in hepatocytes were induced more than two-fold by flow. Furthermore, the reproducibility between articles was low as 52 of 95 articles did not show the same response to flow for a given biomarker. Flow showed overall very little improvements in 2D cultures but a slight improvement in 3D cultures suggesting that high density cell culture may benefit from flow. In conclusion, the gains of perfusion are relatively modest, larger gains are linked to specific biomarkers in certain cell types.

Characterization of three-dimensional bone-like tissue growth and organization under influence of directional fluid flow

The transition in the field of bone tissue engineering from bone regeneration to in vitro models has come with the challenge of recreating a dense and anisotropic bone-like extracellular matrix (ECM). Although the mechanism by which bone ECM gains its structure is not fully understood, mechanical loading and curvature have been identified as potential contributors. Here, guided by computational simulations, we evaluated cell and bone-like tissue growth and organization in a concave channel with and without directional fluid flow stimulation. Human mesenchymal stromal cells were seeded on donut-shaped silk fibroin scaffolds and osteogenically stimulated for 42 days statically or in a flow perfusion bioreactor. After 14, 28, and 42 days, constructs were investigated for cell and tissue growth and organization. As a result, directional fluid flow was able to improve organic tissue growth but not organization. Cells tended to orient in the tangential direction of the channel, possibly attributed to its curvature. Based on our results, we suggest that organic ECM production but not anisotropy can be stimulated through the application of fluid flow. With this study, an initial attempt in three-dimensions was made to improve the resemblance of in vitro produced bone-like ECM to the physiological bone ECM.

Effects of different physical factors on osteogenic differentiation

Osteoblasts are essential for bone formation and can perceive external mechanical stimuli, which are translated into biochemical responses that ultimately alter cell phenotypes and respond to environmental stimuli, described as mechanical transduction. These cells actively participate in osteogenesis and the formation and mineralisation of the extracellular bone matrix. This review summarises the basic physiological and biological mechanisms of five different physical stimuli, i.e. light, electricity, magnetism, force and sound, to induce osteogenesis; further, it summarises the effects of changing culture conditions on the morphology, structure and function of osteoblasts. These findings may provide a theoretical basis for further studies on bone physiology and pathology at the cytological level and will be useful in the clinical application of bone formation and bone regeneration technology.

Effects of compound stimulation of fluid shear stress plus ultrasound on stem cell proliferation and osteogenesis

Bone tissue with strong adaptability is often in a complex dynamical microenvironment in vivo, which is associated with the pathogenesis and treatment of orthopedic diseases. Therefore, it is of great significance to investigate the effects of corresponding compound stimulation on cell behaviors. Herein, a fluid shear stress (FSS) plus ultrasound stimulation platform suitable for cell studies based on a microfluidic chip was constructed and bone marrow mesenchymal stem cell (BMSC) was chosen as a model cell. The proliferation and osteogenesis of BMSCs under the compound stimulation of FSS plus ultrasound in growth medium without any soluble induction factors were firstly investigated. Single FSS stimulation and static culture conditions were also examined. Results illustrated that suitable single FSS stimulation (about 0.06 dyn/cm²) could significantly enhance cell proliferation and osteogenesis simultaneously when compared to the static control, while greater FSS mitigated or even restricted these enhancing effects. Interestingly, ultrasound stimulation combined with this suitable FSS stimulation further accelerated cell proliferation as the intensity of ultrasound increasing. As for the osteogenesis under compound stimulation, it was relatively restricted under lower ultrasound intensity (about 0.075 W/cm²), while promoted when the intensity became higher (about 1.75 W/cm²). This study suggests that both the cell proliferation and osteogenesis are very responsive to the magnitudes of FSS and ultrasound stimulations and can be both significantly enhanced by proper combination strategies. Moreover, these findings will provide valuable references for the construction of effective cell bioreactors and also the treatment of orthopedic diseases.

Mineral deposition intervention through reduction of phosphorus intake suppresses osteoarthritic lesions in temporomandibular joint

OBJECTIVE

To explore the suppressing impact of low phosphorus intake on osteoarthritic temporomandibular joint and the possible mechanisms of nuclear acid injury in the insulted chondrocytes.

DESIGN

Chondrocytes were loaded with fluid flow shear stress (FFSS) with or without low phosphorus medium. Seventy-two mice (sampled at 3-, 7- and 11-wk, n = 6) and forty-eight rats (sampled at 12-wks for different testing purpose, n = 6) were applied with unilateral anterior crossbite (UAC) with or without low phosphorus diet. In the FFSS model, the Ca and P content, molecules related to nucleic acid degradation and the mineral-producing responses in chondrocytes were detected. The effect of culture dish stiffness on chondrocytes osteogenic differentiation was measured. In the UAC model, the content of Ca and P in serum were tested. The condylar cartilage ossification and stiffness were detected using micro-CT, scanning electron microscope and atomic force microscope.

RESULTS

FFSS induced nucleic acid degradation, Pi accumulation and mineral-producing responses in the cultured chondrocytes, all were alleviated by low P medium. Stiffer dish bottoms promoted the osteogenic differentiation of the cultured chondrocytes. UAC stimulated cartilage degeneration and chondrocytes nucleic acid damage, increased PARP 1 and serum P content, and enhanced ossification and stiffening of the cartilage, all were suppressed by low phosphorus diet (all, P < 0.05).

CONCLUSION

Nucleic acid damage takes a role in phosphorus production in osteoarthritic cartilage, contributing to the enhanced mineralization and stiffness of the cartilage that in turn promotes cartilage degradation, which can be alleviated by low phosphorus intake.

Adsorption Force of Fibronectin: A Balance Regulator to Transmission of Cell Traction Force and Fluid Shear Stress

Osteoblasts actively generate cell traction force (CTF) to sense chemical and mechanical microenvironments. Fluid shear stress (FSS) is a principle mechanical stimulus for bone modeling/remodeling. FSS and CTF share common interconnected elements for force transmission, among which the role of the protein-material interfacial force (F_ad) remains unclear. Here, we found that, on the low F_ad surface (5.47 ± 1.31 pN/FN), CTF overwhelmed F_ad to partially desorb FN, and FSS exacerbated the desorption, resulting in disassembly of the actin cytoskeleton and focal adhesions (FAs) to reduce CTF and establishment of a new mechanical balance at the FN-material interface. Contrarily, on the high F_ad surface (27.68 ± 5.24 pN/FN), pure CTF or the combination of CTF and FSS induced no FN desorption, and FSS promoted assembly of actin cytoskeletons and disassembly of FAs, regaining new mechanical balance at the cell-FN interface. These results indicate that F_ad is a mechanical regulator for transmission of CTF and FSS, which has never been reported before.

Progress in the mechanical modulation of cell functions in tissue engineering

In mammals, mechanics at multiple stages-nucleus to cell to ECM-underlie multiple physiological and pathological functions from its development to reproduction to death. Under this inspiration, substantial research has established the role of multiple aspects of mechanics in regulating fundamental cellular processes, including spreading, migration, growth, proliferation, and differentiation. However, our understanding of how these mechanical mechanisms are orchestrated or tuned at different stages to maintain or restore the healthy environment at the tissue or organ level remains largely a mystery. Over the past few decades, research in the mechanical manipulation of the surrounding environment-known as substrate or matrix or scaffold on which, or within which, cells are seeded-has been exceptionally enriched in the field of tissue engineering and regenerative medicine. To do so, traditional tissue engineering aims at recapitulating key mechanical milestones of native ECM into a substrate for guiding the cell fate and functions towards specific tissue regeneration. Despite tremendous progress, a big puzzle that remains is how the cells compute a host of mechanical cues, such as stiffness (elasticity), viscoelasticity, plasticity, non-linear elasticity, anisotropy, mechanical forces, and mechanical memory, into many biological functions in a cooperative, controlled, and safe manner. High throughput understanding of key cellular decisions as well as associated mechanosensitive downstream signaling pathway(s) for executing these decisions in response to mechanical cues, solo or combined, is essential to address this issue. While many reports have been made towards the progress and understanding of mechanical cues-particularly, substrate bulk stiffness and viscoelasticity-in regulating the cellular responses, a complete picture of mechanical cues is lacking. This review highlights a comprehensive view on the mechanical cues that are linked to modulate many cellular functions and consequent tissue functionality. For a very basic understanding, a brief discussion of the key mechanical players of ECM and the principle of mechanotransduction process is outlined. In addition, this review gathers together the most important data on the stiffness of various cells and ECM components as well as various tissues/organs and proposes an associated link from the mechanical perspective that is not yet reported. Finally, beyond addressing the challenges involved in tuning the interplaying mechanical cues in an independent manner, emerging advances in designing biomaterials for tissue engineering are also explored.

The Measurement and Analysis of Impedance Response of HeLa Cells to Distinct Chemotherapy Drugs

Electric cell–substrate impedance sensing exhibits a real-time and label-free feature to monitor the response of cells stimulated by various biochemical and mechanical signals. Alterations in the currents passing through the cell–electrode system characterize the impedance variations of cells. The impedance responses of HeLa cells under distinct chemotherapy drugs combine the effects of cell proliferation and cell–substrate adhesion. Optimal interdigitated electrodes were selected to explore the impedance responses of HeLa cells. Measurements of impedance of cells in response to three widely used chemotherapy drugs in clinical practice, namely cisplatin, doxorubicin, 5-fluorouracil, were performed. The results demonstrated that distinct impedance responses of HeLa cells to drugs were exhibited and a decrease in measured impedance was observed after drug treatment, accompanied by alterations in the distribution and intensity of the adhesion-related protein vinculin and the rate of cell proliferation. The link between the impedance profiles of HeLa cells and their biological functions was developed based on the circuit model. This study demonstrated the weights of cell proliferation and adhesion of HeLa cells under the treatments of DDP, DOX, and 5-FU, resulted in distinct impedance responses of cells, providing an impedance-based evaluation methodology for cervical cancer treatment.

Loading history changes the morphology and compressive force-induced expression of receptor activator of nuclear factor kappa B ligand/osteoprotegerin in MLO-Y4 osteocytes

BACKGROUND

In this study, we investigated the effect of the mechanical loading history on the expression of receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) in MLO-Y4 osteocyte-like cells.

METHODS

Three hours after MLO-Y4 osteocytes were seeded, a continuous compressive force (CCF) of 31 dynes/cm2 with or without additional CCF (32 dynes/cm2) was loaded onto the osteocytes. After 36 h, the additional CCF (loading history) was removed for a recovery period of 10 h. The expression of RANKL, OPG, RANKL/OPG ratio, cell numbers, viability and morphology were time-dependently examined at 0, 3, 6 and 10 h. Then, the same additional CCF was applied again for 1 h to all osteocytes with or without the gap junction inhibitor to examine the expression of RANKL, OPG, the RANKL/OPG ratio and other genes that essential to characterize the phenotype of MLO-Y4 cells. Fluorescence recovery after photobleaching technique was also applied to test the differences of gap-junctional intercellular communications (GJIC) among MLO-Y4 cells.

RESULTS

The expression of RANKL and OPG by MLO-Y4 osteocytes without a loading history was dramatically decreased and increased, respectively, in response to the 1-h loading of additional weight. However, the expression of RANKL, OPG and the RANKL/OPG ratio were maintained at the same level as in the control group in the MLO-Y4 osteocytes with a loading history but without gap junction inhibitor treatment. Treatment of loading history significantly changed the capacity of GJIC and protein expression of connexin 43 (Cx43) but not the mRNA expression of Cx43. No significant difference was observed in the cell number or viability between the MLO-Y4 osteocyte-like cells with and without a loading history or among different time checkpoints during the recovery period. The cell morphology showed significant changes and was correlated with the expression of OPG, Gja1 and Dmp1 during the recovery period.

CONCLUSION

Our findings indicated that the compressive force-induced changes in the RANKL/OPG expression could be habituated within at least 11 h by 36-h CCF exposure. GJIC and cell morphology may play roles in response to loading history in MLO-Y4 osteocyte-like cells.

Tailoring of the rheological properties of bioinks to improve bioprinting and bioassembly for tissue replacement

BACKGROUND

Tissue replacement is among the most important challenges in biotechnology worldwide.

SCOPE OF REVIEW

We aim to highlight the importance of the intricate feedback between rheological properties and materials science and cell biological parameters in order to obtain an efficient bioink design, supported by various practical examples.

MAJOR CONCLUSIONS

Viscoelastic properties of bioink formulas, rheological properties, injection speed and printing nozzle diameter must be considered in bioink design. These properties are related to cell behavior and the survival rate during and after printing. Mechanosensing can strongly influence epigenetics to modify the final cell phenotype, which can affect the replacement tissue.

GENERAL SIGNIFICANCE

In tissue engineering, biotechnologists must consider the biophysical properties and biological conditions of the materials used, as well as the material delivery mode (in a case or tissue) and maturation mode (curing or biomass), to ensure the development off appropriate materials mimicking the native tissue.

Pumpless microfluidic device with open top cell culture under oscillatory shear stress

Here we developed a 96-well plate-based pumpless microfluidic device to mimic bidirectional oscillatory shear stress experienced by osteoblasts at the endosteal niche located at the interface between bone and bone marrow. The culture device was designed to be high-throughput with 32 open top culture chambers for convenient cell seeding and staining. Mathematical modeling was used to simulate the control of oscillatory shear stress with the peak stress in the range of 0.3 to 50 mPa. Osteoblasts, cultured under oscillatory shear stress, were found to be highly viable and significantly aligned along the direction of flow. The modeling and experimental results demonstrate for the first time that cells can be cultured under controllable oscillatory shear stress in the open top culture chamber and pumpless configurations.

IDG-SW3 Osteocyte Differentiation and Bone Extracellular Matrix Deposition Are Enhanced in a 3D Matrix Metalloproteinase-Sensitive Hydrogel

Osteocytes reside within a heavily mineralized matrix making them difficult to study in vivo and to extract for studies in vitro. IDG-SW3 cells are capable of producing mineralized collagen matrix and transitioning from osteoblasts to mature osteocytes, thus offering an alternative to study osteoblast to late osteocyte differentiation in vitro. The goal for this work was to develop a 3D degradable hydrogel to support IDG-SW3 differentiation and deposition of bone ECM. In 2D, the genes Mmp2 and Mmp13 increased during IDG-SW3 differentiation and were used as targets to create a MMP-sensitive poly(ethylene glycol) hydrogel containing the peptide crosslink GCGPLG-LWARCG and RGD to promote cell attachment. IDG-SW3 differentiation in the MMP-sensitive hydrogels improved over non-degradable hydrogels and standard 2D culture. Alkaline phosphatase activity at day 14 was higher, Dmp1 and Phex were 8.1-fold and 3.8-fold higher, respectively, and DMP1 protein expression was more pronounced in the MMP-sensitive hydrogels compared to non-degradable hydrogels. Cell-encapsulation density (cells/ml precursor) influenced formation of dendrite-like cellular process and mineral and collagen deposition with 80×10⁶ performing better than 2×10⁶ or 20×10⁶, while connexin 43 was not affected by cell density. The cell density effects were more pronounced in the MMP-sensitive hydrogels over non-degradable hydrogels. This study identified that high cell encapsulation density and a hydrogel susceptible to cell-mediated degradation enhanced mineralized collagen matrix and osteocyte differentiation. Overall, a promising hydrogel is presented that supports IDG-SW3 cell maturation from osteoblasts to osteocytes in 3D.

Online Analysis of Drug Toxicity to Cells with Shear Stress on an Integrated Microfluidic Chip

Mechanical stimulation, especially fluid shear stress (FSS), is essential for a cell to regulate regular behaviors. A high-throughput platform to provide varying FSS for cell research is desperately required for better mimicking of the complex fluidic microenvironment. This work reports an integrated microfluidic chip that could afford five different FSS gradients consistently to investigate drug toxicity on cells with the stimulation of FSS. Compared with traditional methods to provide FSS, this device would be easier to operate, have higher throughput, and could eliminate interference factors from the culture environment for cells (apart from the unique variable FSS). On such a multi-FSS platform, effects of drugs toxicity on cells were exhibited, which would be more intense than that under static conditions. The results indicated that FSS enhanced the drug toxicity. The designed biochip provides an easy and high-throughput platform to evaluate the toxicity of drugs in the more authentic microenvironment and could be promisingly applied in future drug screening tests.