A microfluidic-based multi-shear device for investigating the effects of low fluid-induced stresses on osteoblasts

Microsphere-Enabled Modular Formation of Miniaturized In Vitro Breast Cancer Models

In search of effective therapeutics for breast cancers, establishing physiologically relevant in vitro models is of great benefit to facilitate the clinical translation. Despite extensive progresses, it remains to develop the tumor models maximally recapturing the key pathophysiological attributes of their native counterparts. Therefore, the current study aimed to develop a microsphere-enabled modular approach toward the formation of in vitro breast tumor models with the capability of incorporating various selected cells while retaining spatial organization. Poly (lactic-co-glycolic acid) microspheres (150-200 mm) with tailorable pore size and surface topography are fabricated and used as carriers to respectively lade with breast tumor-associated cells. Culture of cell-laden microspheres assembled within a customized microfluidic chamber allowed to form 3D tumor models with spatially controlled cell distribution. The introduction of endothelial cell-laden microspheres into cancer-cell laden microspheres at different ratios would induce angiogenesis within the culture to yield vascularized tumor. Evaluation of anticancer drugs such as doxorubicin and Cediranib on the tumor models do demonstrate corresponding physiological responses. Clearly, with the ability to modulate microsphere morphology, cell composition and spatial distribution, microsphere-enabled 3D tumor tissue formation offers a high flexibility to satisfy the needs for pathophysiological study, anticancer drug screening or design of personalized treatment.

Fluid flow-induced modulation of viability and osteodifferentiation of periodontal ligament stem cell spheroids-on-chip

Developing physiologically relevant in vitro models for studying periodontitis is crucial for understanding its pathogenesis and developing effective therapeutic strategies. In this study, we aimed to integrate the spheroid culture of periodontal ligament stem cells (PDLSCs) within a spheroid-on-chip microfluidic perfusion platform and to investigate the influence of interstitial fluid flow on morphogenesis, cellular viability, and osteogenic differentiation of PDLSC spheroids. PDLSC spheroids were seeded onto the spheroid-on-chip microfluidic device and cultured under static and flow conditions. Computational analysis demonstrated the translation of fluid flow rates of 1.2 μl min-1 (low-flow) and 7.2 μl min-1 (high-flow) to maximum fluid shear stress of 59 μPa and 360 μPa for low and high-flow conditions, respectively. The spheroid-on-chip microfluidic perfusion platform allowed for modulation of flow conditions leading to larger PDLSC spheroids with improved cellular viability under flow compared to static conditions. Modulation of fluid flow enhanced the osteodifferentiation potential of PDLSC spheroids, demonstrated by significantly enhanced alizarin red staining and alkaline phosphatase expression. Additionally, flow conditions, especially high-flow conditions, exhibited extensive calcium staining across both peripheral and central regions of the spheroids, in contrast to the predominantly peripheral staining observed under static conditions. These findings highlight the importance of fluid flow in shaping the morphological and functional properties of PDLSC spheroids. This work paves the way for future investigations exploring the interactions between PDLSC spheroids, microbial pathogens, and biomaterials within a controlled fluidic environment, offering insights for the development of innovative periodontal therapies, tissue engineering strategies, and regenerative approaches.

Emerging Advances in Microfluidic Hydrogel Droplets for Tissue Engineering and STEM Cell Mechanobiology

Hydrogel droplets are biodegradable and biocompatible materials with promising applications in tissue engineering, cell encapsulation, and clinical treatments. They represent a well-controlled microstructure to bridge the spatial divide between two-dimensional cell cultures and three-dimensional tissues, toward the recreation of entire organs. The applications of hydrogel droplets in regenerative medicine require a thorough understanding of microfluidic techniques, the biocompatibility of hydrogel materials, and droplet production and manipulation mechanisms. Although hydrogel droplets were well studied, several emerging advances promise to extend current applications to tissue engineering and beyond. Hydrogel droplets can be designed with high surface-to-volume ratios and a variety of matrix microstructures. Microfluidics provides precise control of the flow patterns required for droplet generation, leading to tight distributions of particle size, shape, matrix, and mechanical properties in the resultant microparticles. This review focuses on recent advances in microfluidic hydrogel droplet generation. First, the theoretical principles of microfluidics, materials used in fabrication, and new 3D fabrication techniques were discussed. Then, the hydrogels used in droplet generation and their cell and tissue engineering applications were reviewed. Finally, droplet generation mechanisms were addressed, such as droplet production, droplet manipulation, and surfactants used to prevent coalescence. Lastly, we propose that microfluidic hydrogel droplets can enable novel shear-related tissue engineering and regeneration studies.

Bone-on-a-Chip: Biomimetic Models Based on Microfluidic Technologies for Biomedical Applications

With the increasing importance of preclinical evaluation of newly developed drugs or treatments, in vitro organ or disease models are necessary. Although various organ-specific on-chip (organ-on-a-chip, or OOC) systems have been developed as emerging in vitro models, bone-on-a-chip (BOC) systems that recapitulate the bone microenvironment have been less developed or reviewed compared with other OOCs. The bone is one of the most dynamic organs and undergoes continuous remodeling throughout its lifetime. The aging population is growing worldwide, and healthcare costs are rising rapidly. Since in vitro BOC models that recapitulate native bone niches and pathological features can be important for studying the underlying mechanism of orthopedic diseases and predicting drug responses in preclinical trials instead of in animals, the development of biomimetic BOCs with high efficiency and fidelity will be accelerated further. Here, we review recently engineered BOCs developed using various microfluidic technologies and investigate their use to model the bone microenvironment. We have also explored various biomimetic strategies based on biological, geometrical, and biomechanical cues for biomedical applications of BOCs. Finally, we addressed the limitations and challenging issues of current BOCs that should be overcome to obtain more acceptable BOCs in the biomedical and pharmaceutical industries.

Controlling Microenvironments with Organs-on-Chips for Osteoarthritis Modelling

Osteoarthritis (OA) remains a prevalent disease affecting more than 20% of the global population, resulting in morbidity and lower quality of life for patients. The study of OA pathophysiology remains predominantly in animal models due to the complexities of mimicking the physiological environment surrounding the joint tissue. Recent development in microfluidic organ-on-chip (OoC) systems have demonstrated various techniques to mimic and modulate tissue physiological environments. Adaptations of these techniques have demonstrated success in capturing a joint tissue's tissue physiology for studying the mechanism of OA. Adapting these techniques and strategies can help create human-specific in vitro models that recapitulate the cellular processes involved in OA. This review aims to comprehensively summarise various demonstrations of microfluidic platforms in mimicking joint microenvironments for future platform design iterations.

Combined computational analysis and cytology show limited depth osteogenic effect on bone defects in negative pressure wound therapy

Background: The treatment of bone defects remains a clinical challenge. The effect of negative pressure wound therapy (NPWT) on osteogenesis in bone defects has been recognized; however, bone marrow fluid dynamics under negative pressure (NP) remain unknown. In this study, we aimed to examine the marrow fluid mechanics within trabeculae by computational fluid dynamics (CFD), and to verify osteogenic gene expression, osteogenic differentiation to investigate the osteogenic depth under NP. Methods: The human femoral head is scanned using micro-CT to segment the volume of interest (VOI) trabeculae. The VOI trabeculae CFD model simulating the bone marrow cavity is developed by combining the Hypermesh and ANSYS software. The effect of trabecular anisotropy is investigated, and bone regeneration effects are simulated under NP scales of -80, -120, -160, and -200 mmHg. The working distance (WD) is proposed to describe the suction depth of the NP. Finally, gene sequence analysis, cytological experiments including bone mesenchymal stem cells (BMSCs) proliferation and osteogenic differentiation are conducted after the BMSCs are cultured under the same NP scale. Results: The pressure, shear stress on trabeculae, and marrow fluid velocity decrease exponentially with an increase in WD. The hydromechanics of fluid at any WD inside the marrow cavity can be theoretically quantified. The NP scale significantly affects the fluid properties, especially those fluid close to the NP source; however, the effect of the NP scale become marginal as WD deepens. Anisotropy of trabecular structure coupled with the anisotropic hydrodynamic behavior of bone marrow; An NP of -120 mmHg demonstrates the majority of bone formation-related genes, as well as the most effective proliferation and osteogenic differentiation of BMSCs compared to the other NP scales. Conclusion: An NP of -120 mmHg may have the optimal activated ability to promote osteogenesis, but the effective WD may be limited to a certain depth. These findings help improve the understanding of fluid mechanisms behind NPWT in treating bone defects.

Changes in interstitial fluid flow, mass transport and the bone cell response in microgravity and normogravity

In recent years, our scientific interest in spaceflight has grown exponentially and resulted in a thriving area of research, with hundreds of astronauts spending months of their time in space. A recent shift toward pursuing territories farther afield, aiming at near-Earth asteroids, the Moon, and Mars combined with the anticipated availability of commercial flights to space in the near future, warrants continued understanding of the human physiological processes and response mechanisms when in this extreme environment. Acute skeletal loss, more severe than any bone loss seen on Earth, has significant implications for deep space exploration, and it remains elusive as to why there is such a magnitude of difference between bone loss on Earth and loss in microgravity. The removal of gravity eliminates a critical primary mechano-stimulus, and when combined with exposure to both galactic and solar cosmic radiation, healthy human tissue function can be negatively affected. An additional effect found in microgravity, and one with limited insight, involves changes in dynamic fluid flow. Fluids provide the most fundamental way to transport chemical and biochemical elements within our bodies and apply an essential mechano-stimulus to cells. Furthermore, the cell cytoplasm is not a simple liquid, and fluid transport phenomena together with viscoelastic deformation of the cytoskeleton play key roles in cell function. In microgravity, flow behavior changes drastically, and the impact on cells within the porous system of bone and the influence of an expanding level of adiposity are not well understood. This review explores the role of interstitial fluid motion and solute transport in porous bone under two different conditions: normogravity and microgravity.

Application of shear stress for enhanced osteogenic differentiation of mouse induced pluripotent stem cells

The self-organizing potential of induced pluripotent stem cells (iPSCs) represents a promising tool for bone tissue engineering. Shear stress promotes the osteogenic differentiation of mesenchymal stem cells, leading us to hypothesize that specific shear stress could enhance the osteogenic differentiation of iPSCs. For osteogenesis, embryoid bodies were formed for two days and then maintained in medium supplemented with retinoic acid for three days, followed by adherent culture in osteogenic induction medium for one day. The cells were then subjected to shear loading (0.15, 0.5, or 1.5 Pa) for two days. Among different magnitudes tested, 0.5 Pa induced the highest levels of osteogenic gene expression and greatest mineral deposition, corresponding to upregulated connexin 43 (Cx43) and phosphorylated Erk1/2 expression. Erk1/2 inhibition during shear loading resulted in decreased osteogenic gene expression and the suppression of mineral deposition. These results suggest that shear stress (0.5 Pa) enhances the osteogenic differentiation of iPSCs, partly through Cx43 and Erk1/2 signaling. Our findings shed light on the application of shear-stress technology to improve iPSC-based tissue-engineered bone for regenerative bone therapy.

Comprehensive ceRNA network for MACF1 regulates osteoblast proliferation

BACKGROUND

Previous studies have shown that microtubule actin crosslinking factor 1 (MACF1) can regulate osteoblast proliferation and differentiation through non-coding RNA (ncRNA) in bone-forming osteoblasts. However, the role of MACF1 in targeting the competing endogenous RNA (ceRNA) network to regulate osteoblast differentiation remains poorly understood. Here, we profiled messenger RNA (mRNA), microRNA (miRNA), and long ncRNA (lncRNA) expression in MACF1 knockdown MC3TC‑E1 pre‑osteoblast cells.

RESULTS

In total, 547 lncRNAs, 107 miRNAs, and 376 mRNAs were differentially expressed. Significantly altered lncRNAs, miRNAs, and mRNAs were primarily found on chromosome 2. A lncRNA-miRNA-mRNA network was constructed using a bioinformatics computational approach. The network indicated that mir-7063 and mir-7646 were the most potent ncRNA regulators and mef2c was the most potent target gene. Pathway enrichment analysis showed that the fluid shear stress and atherosclerosis, p53 signaling, and focal adhesion pathways were highly enriched and contributed to osteoblast proliferation. Importantly, the fluid shear stress and atherosclerosis pathway was co-regulated by lncRNAs and miRNAs. In this pathway, Dusp1 was regulated by AK079370, while Arhgef2 was regulated by mir-5101. Furthermore, Map3k5 was regulated by AK154638 and mir-466q simultaneously. AK003142 and mir-3082-5p as well as Ak141402 and mir-446 m-3p were identified as interacting pairs that regulate target genes.

CONCLUSION

This study revealed the global expression profile of ceRNAs involved in the differentiation of MC3TC‑E1 osteoblasts induced by MACF1 deletion. These results indicate that loss of MACF1 activates a comprehensive ceRNA network to regulate osteoblast proliferation.

Ascitic fluid shear stress in concert with hepatocyte growth factor drive stemness and chemoresistance of ovarian cancer cells via the c-Met-PI3K/Akt-miR-199a-3p signaling pathway

Overcoming drug resistance is an inevitable challenge to the success of cancer treatment. Recently, in ovarian cancer, a highly chemoresistant tumor, we demonstrated an important role of shear stress in stem-like phenotype and chemoresistance using a three-dimensional microfluidic device, which most closely mimics tumor behavior. Here, we examined a new mechanosensitive microRNA-miR-199a-3p. Unlike most key microRNA biogenesis in static conditions, we found that Dicer, Drosha, and Exportin 5 were not involved in regulating miR-199a-3p under ascitic fluid shear stress (0.02 dynes/cm²). We further showed that hepatocyte growth factor (HGF), but not other ascitic cytokines/growth factors such as epidermal growth factor and tumor necrosis factor α or hypoxia, could transcriptionally downregulate miR-199a-3p through its primary transcript miR-199a-1 and not miR-199a-2. Shear stress in the presence of HGF resulted in a concerted effect via a specific c-Met/PI3K/Akt signaling axis through a positive feedback loop, thereby driving cancer stemness and drug resistance. We also showed that miR-199a-3p expression was inversely correlated with enhanced drug resistance properties in chemoresistant ovarian cancer lines. Patients with low miR-199a-3p expression were more resistant to platinum with a significantly poor prognosis. miR-199a-3p mimic significantly suppressed ovarian tumor metastasis and its co-targeting in combination with cisplatin or paclitaxel further decreased the peritoneal dissemination of ovarian cancer in mice. These findings unravel how biophysical and biochemical cues regulate miR-199a-3p and is important in chemoresistance. miR-199a-3p mimics may serve as a novel targeted therapy for effective chemosensitization.

Engineering multiscale structural orders for high-fidelity embryoids and organoids

Embryoids and organoids hold great promise for human biology and medicine. Herein, we discuss conceptual and technological frameworks useful for developing high-fidelity embryoids and organoids that display tissue- and organ-level phenotypes and functions, which are critically needed for decoding developmental programs and improving translational applications. Through dissecting the layers of inputs controlling mammalian embryogenesis, we review recent progress in reconstructing multiscale structural orders in embryoids and organoids. Bioengineering tools useful for multiscale, multimodal structural engineering of tissue- and organ-level cellular organization and microenvironment are also discussed to present integrative, bioengineering-directed approaches to achieve next-generation, high-fidelity embryoids and organoids.

A new insight into a thermoplastic microfluidic device aimed at improvement of oxygenation process and avoidance of shear stress during cell culture

Keeping the oxygen concentration at the desired physiological limits is a challenging task in cellular microfluidic devices. A good knowledge of affecting parameters would be helpful to control the oxygen delivery to cells. This study aims to provide a fundamental understanding of oxygenation process within a hydrogel-based microfluidic device considering simultaneous mass transfer, medium flow, and cellular consumption. For this purpose, the role of geometrical and hydrodynamic properties was numerically investigated. The results are in good agreement with both numerical and experimental data in the literature. The obtained results reveal that increasing the microchannel height delays the oxygen depletion in the absence of media flow. We also observed that increasing the medium flow rate increases the oxygen concentration in the device; however, it leads to high maximum shear stress. A novel pulsatile medium flow injection pattern is introduced to reduce detrimental effect of the applied shear stress on the cells.

Biofabrication of the osteochondral unit and its applications: Current and future directions for 3D bioprinting

Multiple prevalent diseases, such as osteoarthritis (OA), for which there is no cure or full understanding, affect the osteochondral unit; a complex interface tissue whose architecture, mechanical nature and physiological characteristics are still yet to be successfully reproduced in vitro. Although there have been multiple tissue engineering-based approaches to recapitulate the three dimensional (3D) structural complexity of the osteochondral unit, there are various aspects that still need to be improved. This review presents the different pre-requisites necessary to develop a human osteochondral unit construct and focuses on 3D bioprinting as a promising manufacturing technique. Examples of 3D bioprinted osteochondral tissues are reviewed, focusing on the most used bioinks, chosen cell types and growth factors. Further information regarding the applications of these 3D bioprinted tissues in the fields of disease modelling, drug testing and implantation is presented. Finally, special attention is given to the limitations that currently hold back these 3D bioprinted tissues from being used as models to investigate diseases such as OA. Information regarding improvements needed in bioink development, bioreactor use, vascularisation and inclusion of additional tissues to further complete an OA disease model, are presented. Overall, this review gives an overview of the evolution in 3D bioprinting of the osteochondral unit and its applications, as well as further illustrating limitations and improvements that could be performed explicitly for disease modelling.

Measuring the density and viscosity of culture media for optimized computational fluid dynamics analysis of in vitro devices

Culture medium is frequently modelled as water in computational fluid dynamics (CFD) analysis of in vitro culture systems involving flow, such as bioreactors and organ-on-chips. However, culture medium can be expected to have different properties to water due to its higher solute content. Furthermore, cellular activities such as metabolism and secretion of ECM proteins alter the composition of culture medium and therefore its properties during culture. As these properties directly determine the hydromechanical stimuli exerted on cells in vitro, these, along with any changes during culture must be known for CFD modelling accuracy and meaningful interpretation of cellular responses. In this study, the density and dynamic viscosity of DMEM and RPMI-1640 media supplemented with typical concentrations of foetal bovine serum (0, 5, 10 and 20% v/v) were measured to serve as a reference for computational design analysis. Any changes in the properties of medium during culture were also investigated with NCI-H460 and HN6 cell lines. The density and dynamic viscosity of the media increased proportional to the % volume of added foetal bovine serum (FBS). Importantly, the viscosity of 5% FBS-supplemented RPMI-1640 was found to increase significantly after 3 days of culture of NCI-H460 and HN6 cell lines, with distinct differences between magnitude of change for each cell line. Finally, these experimentally-derived values were applied in CFD analysis of a simple microfluidic device, which demonstrated clear differences in maximum wall shear stress and pressure between fluid models. Overall, these results highlight the importance of characterizing model-specific properties for CFD design analysis of cell culture systems.

Simulating microgravity using a random positioning machine for inducing cellular responses to mechanotransduction in human osteoblasts

The mechanotransduction pathways that mediate cellular responses to contact forces are better understood than those that mediate response to distance forces, especially the force of gravity. Removing or reducing gravity for significant periods of time involves either sending samples to space, inducing diamagnetic levitation with high magnetic fields, or continually reorienting samples for a period, all in a manner that supports cell culturing. Undesired secondary effects due to high magnetic fields or shear forces associated with fluid flow while reorienting must be considered in the design of ground-based devices. We have developed a lab-friendly and compact random positioning machine (RPM) that fits in a standard tissue culture incubator. Using a two-axis gimbal, it continually reorients samples in a manner that produces an equal likelihood that all possible orientations are visited. We contribute a new control algorithm by which the distribution of probabilities over all possible orientations is completely uniform. Rather than randomly varying gimbal axis speed and/or direction as in previous algorithms (which produces non-uniform probability distributions of orientation), we use inverse kinematics to follow a trajectory with a probability distribution of orientations that is uniform by construction. Over a time period of 6 h of operation using our RPM, the average gravity is within 0.001 23% of the gravity of Earth. Shear forces are minimized by limiting the angular speed of both gimbal motors to under 42 °/s. We demonstrate the utility of our RPM by investigating the effects of simulated microgravity on adherent human osteoblasts immediately after retrieving samples from our RPM. Cytoskeletal disruption and cell shape changes were observed relative to samples cultured in a 1 g environment. We also found that subjecting human osteoblasts in suspension to simulated microgravity resulted in less filamentous actin and lower cell stiffness.

A microfluidics-based method for culturing osteoblasts on biomimetic hydroxyapatite

The reliability of conventional cell culture studies to evaluate biomaterials is often questioned, as in vitro outcomes may contradict results obtained through in vivo assays. Microfluidics technology has the potential to reproduce complex physiological conditions by allowing for fine control of microscale features such as cell confinement and flow rate. Having a continuous flow during cell culture is especially advantageous for bioactive biomaterials such as calcium-deficient hydroxyapatite (HA), which may otherwise alter medium composition and jeopardize cell viability, potentially producing false negative results in vitro. In this work, HA was integrated into a microfluidics-based platform (HA-on-chip) and the effect of varied flow rates (2, 8 and 14 µl/min, corresponding to 0.002, 0.008 and 0.014 dyn/cm², respectively) was evaluated. A HA sample placed in a well plate (HA-static) was included as a control. While substantial calcium depletion and phosphate release occurred in static conditions, the concentration of ions in HA-on-chip samples remained similar to those of fresh medium, particularly at higher flow rates. Pre-osteoblast-like cells (MC3T3-E1) exhibited a significantly higher degree of proliferation on HA-on-chip (8 μl/min flow rate) as compared to HA-static. However, cell differentiation, analysed by alkaline phosphatase (ALP) activity, showed low values in both conditions. This study indicates that cells respond differently when cultured on HA under flow compared to static conditions, which indicates the need for more physiologically relevant methods to increase the predictive value of in vitro studies used to evaluate biomaterials. STATEMENT OF SIGNIFICANCE: There is a lack of correlation between the results obtained when testing some biomaterials under cell culture as opposed to animal models. To address this issue, a cell culture method with slightly enhanced physiological relevance was developed by incorporating a biomaterial, known to regenerate bone, inside of a microfluidic platform that enabled a continuous supply of cell culture medium. Since the utilized biomaterial interacts with surrounding ions, the perfusion of medium allowed for shielding of these changes similarly as would happen in the body. The experimental outcomes observed in the dynamic platform were different than those obtained with standard static cell culture systems, proving the key role of the platform in the assessment of biomaterials.

Tailoring Cellular Function: The Contribution of the Nucleus in Mechanotransduction

Cells sense a variety of different mechanochemical stimuli and promptly react to such signals by reshaping their morphology and adapting their structural organization and tensional state. Cell reactions to mechanical stimuli arising from the local microenvironment, mechanotransduction, play a crucial role in many cellular functions in both physiological and pathological conditions. To decipher this complex process, several studies have been undertaken to develop engineered materials and devices as tools to properly control cell mechanical state and evaluate cellular responses. Recent reports highlight how the nucleus serves as an important mechanosensor organelle and governs cell mechanoresponse. In this review, we will introduce the basic mechanisms linking cytoskeleton organization to the nucleus and how this reacts to mechanical properties of the cell microenvironment. We will also discuss how perturbations of nucleus-cytoskeleton connections, affecting mechanotransduction, influence health and disease. Moreover, we will present some of the main technological tools used to characterize and perturb the nuclear mechanical state.

MAGNETOPHORETIC CIRCUIT BIOCOMPATIBILITY

Recently, we introduced magnetophoretic circuits, composed of overlaid magnetic and metallic layers, as a novel single-cell analysis (SCA) tool. We showed the ability of these circuits in organizing large single-particle and particle-pair arrays. Assembling the cells in microarrays is performed with the ultimate goal of running temporal phenotypic analyses. However, for long-term studies, a suitable microenvironment for the cells to normally grow and differentiate is needed. Towards this goal, in this study, we run required biocompatibility tests, based on which we make the magnetophoretic-based microchip a suitable home for the cells to grow. The results confirm the ability of these chips in cell handling and show no unwanted cell behavior alteration due to the applied shear stress on them, the magnetic labeling, or the microenvironment. After this achievement, this tool would be ready for running important single-cell studies in oncology, virology, and medicine.

Low intermittent flow promotes rat mesenchymal stem cell differentiation in logarithmic fluid shear device

Bone marrow mesenchymal stem cells are an ideal candidate for bone tissue engineering due to their osteogenic potential. Along with chemical, mechanical signals such as fluid shear stress have been found to influence their differentiation characteristics. But the range of fluid shear experienced in vivo is too wide and difficult to generate in a single device. We have designed a microfluidic device that could generate four orders of shear stresses on adherent cells. This was achieved using a unique hydraulic resistance combination and linear optimization to the lesser total length of the circuit, making the device compact and yet generating four logarithmically increasing shear stresses. Numerical simulation depicts that, at an inlet velocity of 160 μl/min, our device generated shear stresses from 1.03 Pa to 1.09 mPa. In this condition, we successfully cultured primary rat bone marrow mesenchymal stem cells (rBMSCs) in the device for a prolonged period of time in the incubator environment (four days). Higher cell proliferation rate was observed in the intermittent flow at 1.09 mPa. At 10 mPa, both upregulation of osteogenic genes and higher alkaline phosphatase activity were observed. These results suggest that the intermittent shear of the order of 10 mPa can competently enhance osteogenic differentiation of rBMSCs compared to static culture.

Interaction of material stiffness and negative pressure to enhance differentiation of bone marrow-derived stem cells and osteoblast proliferation

Negative pressure wound therapy (NPWT) results in improved wound repair and the combined use of NPWT with elastomeric materials may further stimulate and accelerate tissue repair. No firmly established treatment modalities using both NPWT and biomaterials exist for orthopedic application. The goal of this study was to investigate the response of osteoblasts and bone marrow-derived mesenchymal stem cells to negative pressure and to determine whether a newly developed elastic osteomimetic bone repair material (BRM), a blend of type I collagen, chondroitin 6-sulfate, and poly (octanediol citrate) could enhance the osteoblastic phenotype. The results indicate that proliferation and alkaline phosphatase activity of hFOB1.19 osteoblasts were significantly increased with exposure to 12 hr of negative pressure (-125 mmHg). Follow-on studies with rat and human mesenchymal stem cells confirmed that negative pressure enhanced osteoblastic maturation. In addition, a significant interaction of negative pressure and electrospun BRM resulted in increased mRNA expression of alkaline phosphatase, osteopontin, collagen1α2, and HIF1α, whereas little or no effect on these genes was observed on electrospun collagen or tissue culture plastic. Together, these results suggest that the use of this novel biomaterial, BRM, with NPWT may ultimately translate into a safe and cost-effective clinical application to accelerate bone repair.

Exploring microfluidics as a tool to evaluate the biological properties of a titanium alloy under dynamic conditions

When evaluating the biological properties of titanium under dynamic conditions, cell proliferation was shown to be dominant over cell differentiation.

How Biophysical Forces Regulate Human B Cell Lymphomas

The role of microenvironment-mediated biophysical forces in human lymphomas remains elusive. Diffuse large B cell lymphomas (DLBCLs) are heterogeneous tumors, which originate from highly proliferative germinal center B cells. These tumors, their associated neo-vessels, and lymphatics presumably expose cells to particular fluid flow and survival signals. Here, we show that fluid flow enhances proliferation and modulates response of DLBCLs to specific therapeutic agents. Fluid flow upregulates surface expression of B cell receptors (BCRs) and integrin receptors in subsets of ABC-DLBCLs with either CD79A/B mutations or WT BCRs, similar to what is observed with xenografted human tumors in mice. Fluid flow differentially upregulates signaling targets, such as SYK and p70S6K, in ABC-DLBCLs. By selective knockdown of CD79B and inhibition of signaling targets, we provide mechanistic insights into how fluid flow mechanomodulates BCRs and integrins in ABC-DLBCLs. These findings redefine microenvironment factors that regulate lymphoma-drug interactions and will be critical for testing targeted therapies.

Three-Dimensional Modeling of Avascular Tumor Growth in Both Static and Dynamic Culture Platforms

Microfluidic cell culture platforms are ideal candidates for modeling the native tumor microenvironment because they can precisely reconstruct in vivo cellular behavior. Moreover, mathematical modeling of tumor growth can pave the way toward description and prediction of growth pattern as well as improving cancer treatment. In this study, a modified mathematical model based on concentration distribution is applied to tumor growth in both conventional static culture and dynamic microfluidic cell culture systems. Apoptosis and necrosis mechanisms are considered as the main inhibitory factors in the model, while tumor growth rate and nutrient consumption rate are modified in both quiescent and proliferative zones. We show that such modification can better predict the experimental results of tumor growth reported in the literature. Using numerical simulations, the effects of the concentrations of the nutrients as well as the initial tumor radius on the tumor growth are investigated and discussed. Furthermore, tumor growth is simulated by taking into account the dynamic perfusion into the proposed model. Subsequently, tumor growth kinetics in a three-dimensional (3D) microfluidic device containing a U-shaped barrier is numerically studied. For this case, the effect of the flow rate of culture medium on tumor growth is investigated as well. Finally, to evaluate the impact of the trap geometry on the tumor growth, a comparison is made between the tumor growth kinetics in two frequently used traps in microfluidic cell culture systems, i.e., the U-shaped barrier and microwell structures. The proposed model can provide insight into better predicting the growth and development of avascular tumor in both static and dynamic cell culture platforms.

Spatial presentation of biological molecules to cells by localized diffusive transfer

Cellular decisions in human development, homeostasis, regeneration, and disease are coordinated in large part by signals that are spatially localized in tissues. These signals are often soluble, such that biomolecules produced by one cell diffuse to receiving cells. To recapitulate soluble factor patterning in vitro, several microscale strategies have been developed. However, these techniques often introduce new variables into cell culture experiments (e.g., fluid flow) or are limited in their ability to pattern diverse solutes in a user-defined manner. To address these challenges, we developed an adaptable method that facilitates spatial presentation of biomolecules across cells in traditional open cultures in vitro. This technique employs device inserts that are placed in standard culture wells, which support localized diffusive pattern transmission through microscale spaces between device features and adherent cells. Devices can be removed and cultures can be returned to standard media following patterning. We use this method to spatially control cell labeling with pattern features ranging in scale from several hundred microns to millimeters and with sequential application of multiple patterns. To better understand the method we investigate relationships between pattern fidelity, device geometry, and consumption and diffusion kinetics using finite element modeling. We then apply the method to spatially defining reporter cell heterogeneity by patterning a small molecule modulator of genetic recombination with the requisite sustained exposure. Finally, we demonstrate use of this method for patterning larger and more slowly diffusing particles by creating focal sites of gene delivery and infection with adenoviral, lentiviral, and Zika virus particles. Thus, our method leverages devices that interface with standard culture vessels to pattern diverse diffusible factors, geometries, exposure dynamics, and recipient cell types, making it well poised for adoption by researchers across various fields of biological research.

The Application of Microfluidic Techniques on Tissue Engineering in Orthopaedics

Background:

Tissue engineering (TE) is a promising solution for orthopaedic diseases such as bone or cartilage defects and bone metastasis. Cell culture in vitro and scaffold fabrication are two main parts of TE, but these two methods both have their own limitations. The static cell culture medium is unable to achieve multiple cell incubation or offer an optimal microenvironment for cells, while regularly arranged structures are unavailable in traditional cell-laden scaffolds, which results in low biocompatibility. To solve these problems, microfluidic techniques are combined with TE. By providing 3-D networks and interstitial fluid flows, microfluidic platforms manage to maintain phenotype and viability of osteocytic or chondrocytic cells, and the precise manipulation of liquid, gel and air flows in microfluidic devices leads to the highly organized construction of scaffolds.

Methods:

In this review, we focus on the recent advances of microfluidic techniques applied in the field of tissue engineering, especially in orthropaedics. An extensive literature search was done using PubMed. The introduction describes the properties of microfluidics and how it exploits the advantages to the full in the aspects of TE. Then we discuss the application of microfluidics on the cultivation of osteocytic cells and chondrocytes, and other extended researches carried out on this platform. The following section focuses on the fabrication of highly organized scaffolds and other biomaterials produced by microfluidic devices. Finally, the incubation and studying of bone metastasis models in microfluidic platforms are discussed.

Conclusion:

The combination of microfluidics and tissue engineering shows great potentials in the osteocytic cell culture and scaffold fabrication. Though there are several problems that still require further exploration, the future of microfluidics in TE is promising.

[Establishment of a 3D printing system for bone tissue engineering scaffold fabrication and the evaluation of its controllability over macro and micro structure precision]

OBJECTIVE

To establish a 3D printing system for bone tissue engineering scaffold fabrication based on the principle of fused deposition modeling, and to evaluate the controllability over macro and micro structure precision of polylactide (PLA) and polycaprolactone (PCL) scaffolds.

METHODS

The system was composed of the elements mixture-I bioprinter and its supporting slicing software which generated printing control code in the G code file format. With a diameter of 0.3 mm, the nozzle of the bioprinter was controlled by a triaxial stepper motor and extruded melting material. In this study, a 10 mm×10 mm×2 mm cuboid CAD model was designed in the image ware software and saved as STL file. The file was imported into the slicing software and the internal structure was designed in a pattern of cuboid pore uniform distribution, with a layer thickness of 0.2 mm. Then the data were exported as Gcode file and ready for printing. Both polylactic acid (PLA) and polycaprolactone (PCL) filaments were used to print the cuboid parts and each material was printed 10 times repeatedly. After natural cooling, the PLA and PCL scaffolds were removed from the platform and the macro dimensions of each one were measured using a vernier caliper. Three scaffolds of each material were randomly selected and scanned by a 3D measurement laser microscope. Measurements of thediameter of struts and the size of pores both in the interlayer overlapping area and non-interlayer overlapping area were taken.

RESULTS

The pores in the printed PLA and PCL scaffolds were regular and interconnected. The printed PLA scaffolds were 9.950 (0.020) mm long, 9.950 (0.003) mm wide and 1.970 (0.023) mm high, while the PCL scaffolds were 9.845 (0.025) mm long, 9.845 (0.045) mm wide and 1.950 (0.043) mm high. The struts of both the PLA and PCL parts became wider inthe interlayer overlapping area, and the former was more obvious. The difference between the designed size and the printed size was greatest in the pore size of the PLA scaffolds in interlayer overlapping area [(274.09 ± 8.35) μm)], which was 26.91 μm. However, it satisfied the requirements for research application.

CONCLUSION

The self-established 3D printing system for bone tissue engineering scaffold can be used to print PLA and PCL porous scaffolds. The controllability of this system over macro and micro structure can meet the precision requirements for research application.

Matrix architecture plays a pivotal role in 3D osteoblast migration: The effect of interstitial fluid flow

Osteoblast migration is a crucial process in bone regeneration, which is strongly regulated by interstitial fluid flow. However, the exact role that such flow exerts on osteoblast migration is still unclear. To deepen the understanding of this phenomenon, we cultured human osteoblasts on 3D microfluidic devices under different fluid flow regimes. Our results show that a slow fluid flow rate by itself is not able to alter the 3D migratory patterns of osteoblasts in collagen-based gels but that at higher fluid flow rates (increased flow velocity) may indirectly influence cell movement by altering the collagen microstructure. In fact, we observed that high fluid flow rates (1 µl/min) are able to alter the collagen matrix architecture and to indirectly modulate the migration pattern. However, when these collagen scaffolds were crosslinked with a chemical crosslinker, specifically, transglutaminase II, we did not find significant alterations in the scaffold architecture or in osteoblast movement. Therefore, our data suggest that high interstitial fluid flow rates can regulate osteoblast migration by means of modifying the orientation of collagen fibers. Together, these results highlight the crucial role of the matrix architecture in 3D osteoblast migration. In addition, we show that interstitial fluid flow in conjunction with the matrix architecture regulates the osteoblast morphology in 3D.

3D bone models to study the complex physical and cellular interactions between tumor and the bone microenvironment

As the complexity of interactions between tumor and its microenvironment has become more evident, a critical need to engineer in vitro models that veritably recapitulate the 3D microenvironment and relevant cell populations has arisen. This need has caused many groups to move away from the traditional 2D, tissue culture plastic paradigms in favor of 3D models with materials that more closely replicate the in vivo milieu. Creating these 3D models remains a difficult endeavor for hard and soft tissues alike as the selection of materials, fabrication processes, and optimal conditions for supporting multiple cell populations makes model development a nontrivial task. Bone tissue in particular is uniquely difficult to model in part because of the limited availability of materials that can accurately capture bone rigidity and architecture, and also due to the dependence of both bone and tumor cell behavior on mechanical signaling. Additionally, the bone is a complex cellular microenvironment with multiple cell types present, including relatively immature, pluripotent cells in the bone marrow. This prospect will focus on the current 3D models in development to more accurately replicate the bone microenvironment, which will help facilitate improved understanding of bone turnover, tumor-bone interactions, and drug response. These studies have demonstrated the importance of accurately modelling the bone microenvironment in order to fully understand signaling and drug response, and the significant effects that model properties such as architecture, rigidity, and dynamic mechanical factors have on tumor and bone cell response.

Prediction of Necrotic Core and Hypoxic Zone of Multicellular Spheroids in a Microbioreactor with a U-Shaped Barrier

Microfluidic devices have been widely used for biological and cellular studies. Microbioreactors for three-dimensional (3D) multicellular spheroid culture are now considered as the next generation in in vitro diagnostic tools. The feasibility of using 3D cell aggregates to form multicellular spheroids in a microbioreactor with U-shaped barriers has been demonstrated experimentally. A barrier array is an alternative to commonly used microwell traps. The present study investigates oxygen and glucose concentration distributions as key parameters in a U-shaped array microbioreactor using finite element simulation. The effect of spheroid diameter, inlet concentration and flow rate of the medium are systematically studied. In all cases, the channel walls are considered to be permeable to oxygen. Necrotic and hypoxic or quiescent regions corresponding to both oxygen and glucose concentration distributions are identified for various conditions. The results show that the entire quiescent and necrotic regions become larger with increasing spheroid diameter and decreasing inlet and wall concentration. The shear stress (0.5⁻9 mPa) imposed on the spheroid surface by the fluid flow was compared with the critical values to predict possible damage to the cells. Finally, optimum range of medium inlet concentration (0.13⁻0.2 mM for oxygen and 3⁻11 mM for glucose) and flow rate (5⁻20 μL/min) are found to form the largest possible multicellular spheroid (500 μm), without any quiescent and necrotic regions with an acceptable shear stress. The effect of cell-trap types on the oxygen and glucose concentration inside the spheroid was also investigated. The levels of oxygen and glucose concentration for the microwell are much lower than those for the other two traps. The U-shaped barrier created with microposts allows for a continuous flow of culture medium, and so improves the glucose concentration compared to that in the integrated U-shaped barrier. Oxygen concentration for both types of U-shaped barriers is nearly the same. Due to the advantage of using U-shaped barriers to culture multicellular spheroids, the results of this paper can help to choose the experimental and design parameters of the microbioreactor.

Fluidic Culture and Analysis of Pulmonary Artery Smooth Muscle Cells for the Study of Pulmonary Hypertension

There is an urgent need to develop novel in-vitro models to mimic the disease conditions in pulmonary hypertension (PH). We developed a microfluidic cell culture device for PH studies that withstood high shear stress. Techniques were also developed for cell recovery from the microchannel and mRNA isolation from the collected cells. Using this device, we found that shear stress caused a 7.5-fold increase in the transcription levels of a PH-related molecule, Cyclin D1.

Microfluidics approach to investigate the role of dynamic similitude in osteocyte mechanobiology

Fluid flow is an important regulator of cell function and metabolism in many tissues. Fluid shear stresses have been used to level the mechanical stimuli applied in vitro with what occurs in vivo. However, these experiments often lack dynamic similarity, which is necessary to ensure the validity of the model. For interstitial fluid flow, the major requirement for dynamic similarity is the Reynolds number (Re), the ratio of inertial to viscous forces, is the same between the system and model. To study the necessity of dynamic similarity for cell mechanotransduction studies, we investigated the response of osteocyte-like MLO-Y4 cells to different Re flows at the same level of fluid shear stress. Osteocytes were chosen for this study as flows applied in vitro and in vivo have Re that are orders of magnitude different. We hypothesize that osteocytes' response to fluid flow is Re dependent. We observed that cells exposed to lower and higher Re flows developed rounded and triangular morphologies, respectively. Lower Re flows also reduced apoptosis rates compared to higher Re flows. Furthermore, MLO-Y4 cells exposed to higher Re flows had stronger calcium responses compared to lower Re flows. However, by also controlling for flow rate, the lower Re flows induced a stronger calcium response; while degradation of components of the osteocyte glycocalyx reversed this effect. This work suggests that osteocytes are highly sensitive to differences in Re, independent of just shear stresses, supporting the need for improved in vitro flow platforms that better recapitulate the physiological environment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:663-671, 2018.

Fluid shear stress induces osteoblast differentiation and arrests the cell cycle at the G0 phase via the ERK1/2 pathway

Numerous studies have demonstrated that fluid shear stress (FSS) may promote the proliferation and differentiation of osteoblast cells. However, proliferation and differentiation are mutually exclusive processes and are unlikely to be promoted by FSS simultaneously. Cell proliferation and differentiation induced by FSS has rarely been reported. In order to provide an insight into this process, the present study investigated the effects of FSS on osteoblast‑like MC3T3 cells in the G0/G1 phase, the period during which the fate of a cell is determined. The results of the present study demonstrated that FSS promoted alkaline phosphatase (ALP) activity, and the mRNA expression and protein expression of osteocalcin, collagen type I and runt‑related transcription factor 2 (Runx2), while inhibiting DNA synthesis and arresting the cell cycle at the G0/G1 phase. The increase in Runx2 and ALP activity was accompanied by the activation of calcium/calmodulin‑dependent protein kinase type II (CaMK II) and extracellular signal‑regulated kinases 1/2 (ERK1/2), which was completely abolished by treatment with KN93 and U0126, respectively. In addition, the inhibition of ERK1/2, although not CaMK II, decreased p21Cip/Kip activity, resulting in an increase in cell number and S phase re‑entry. The results of the present study indicated that in the G0/G1 phase, FSS promoted osteoblast differentiation via the CaMK II and ERK1/2 signaling pathways, and blocked the cell cycle at the G0/G1 phase via the ERK1/2 pathway only. The present findings provided an increased understanding of osteoblastic mechanobiology.

Development and Characterization of a Parallelizable Perfusion Bioreactor for 3D Cell Culture

The three dimensional (3D) cultivation of stem cells in dynamic bioreactor systems is essential in the context of regenerative medicine. Still, there is a lack of bioreactor systems that allow the cultivation of multiple independent samples under different conditions while ensuring comprehensive control over the mechanical environment. Therefore, we developed a miniaturized, parallelizable perfusion bioreactor system with two different bioreactor chambers. Pressure sensors were also implemented to determine the permeability of biomaterials which allows us to approximate the shear stress conditions. To characterize the flow velocity and shear stress profile of a porous scaffold in both bioreactor chambers, a computational fluid dynamics analysis was performed. Furthermore, the mixing behavior was characterized by acquisition of the residence time distributions. Finally, the effects of the different flow and shear stress profiles of the bioreactor chambers on osteogenic differentiation of human mesenchymal stem cells were evaluated in a proof of concept study. In conclusion, the data from computational fluid dynamics and shear stress calculations were found to be predictable for relative comparison of the bioreactor geometries, but not for final determination of the optimal flow rate. However, we suggest that the system is beneficial for parallel dynamic cultivation of multiple samples for 3D cell culture processes.

Modeling Ovarian Cancer Multicellular Spheroid Behavior in a Dynamic 3D Peritoneal Microdevice

Ovarian cancer is characterized by extensive peritoneal metastasis, with tumor spheres commonly found in the malignant ascites. This is associated with poor clinical outcomes and currently lacks effective treatment. Both the three-dimensional (3D) environment and the dynamic mechanical forces are very important factors in this metastatic cascade. However, traditional cell cultures fail to recapitulate this natural tumor microenvironment. Thus, in vivo-like models that can emulate the intraperitoneal environment are of obvious importance. In this study, a new microfluidic platform of the peritoneum was set up to mimic the situation of ovarian cancer spheroids in the peritoneal cavity during metastasis. Ovarian cancer spheroids generated under a non-adherent condition were cultured in microfluidic channels coated with peritoneal mesothelial cells subjected to physiologically relevant shear stress. In summary, this dynamic 3D ovarian cancer-mesothelium microfluidic platform can provide new knowledge on basic cancer biology and serve as a platform for potential drug screening and development.

Enhanced directional cell migration induced by vaccinia virus on a microfluidic-based multi-shear cell migration assay platform

An integrated mcirofluidic-based cell migration platform was developed to explore the vaccinia virus-induced cell migration in different shear stress environments.

In Vitro Bone Cell Models: Impact of Fluid Shear Stress on Bone Formation

This review describes the role of bone cells and their surrounding matrix in maintaining bone strength through the process of bone remodeling. Subsequently, this work focusses on how bone formation is guided by mechanical forces and fluid shear stress in particular. It has been demonstrated that mechanical stimulation is an important regulator of bone metabolism. Shear stress generated by interstitial fluid flow in the lacunar-canalicular network influences maintenance and healing of bone tissue. Fluid flow is primarily caused by compressive loading of bone as a result of physical activity. Changes in loading, e.g., due to extended periods of bed rest or microgravity in space are associated with altered bone remodeling and formation in vivo. In vitro, it has been reported that bone cells respond to fluid shear stress by releasing osteogenic signaling factors, such as nitric oxide, and prostaglandins. This work focusses on the application of in vitro models to study the effects of fluid flow on bone cell signaling, collagen deposition, and matrix mineralization. Particular attention is given to in vitro set-ups, which allow long-term cell culture and the application of low fluid shear stress. In addition, this review explores what mechanisms influence the orientation of collagen fibers, which determine the anisotropic properties of bone. A better understanding of these mechanisms could facilitate the design of improved tissue-engineered bone implants or more effective bone disease models.

Stemness and chemoresistance in epithelial ovarian carcinoma cells under shear stress

One of greatest challenges to the successful treatment of cancer is drug resistance. An exciting approach is the eradication of cancer stem cells (CSCs). However, little is known about key signals regulating the formation and expansion of CSCs. Moreover, lack of a reliable predictive preclinical model has been a major obstacle to discover new cancer drugs and predict their clinical activity. Here, in ovarian cancer, a highly chemoresistant tumor that is rapidly fatal, we provide the first evidence demonstrating the causal involvement of mechanical stimulus in the CSC phenotype using a customizable microfluidic platform and three-dimensional spheroids, which most closely mimic tumor behavior. We found that ovarian cancer cells significantly acquired the expression of epithelial-to-mesenchymal transition and CSC markers and a remarkable chemoresistance to clinically relevant doses of frontline chemotherapeutic drugs cisplatin and paclitaxel when grown under fluid shear stress, which corroborates with the physiological attainable levels in the malignant ascites, but not under static condition. Furthermore, we uncovered a new link of microRNA-199a-3p, phosphatidylinositol 3-kinase/Akt, and multidrug transporter activation in shear stress-induced CSC enrichment. Our findings shed new light on the significance of hydrodynamics in cancer progression, emphasizing the need of a flow-informed framework in the development of therapeutics.

Long range microfluidic shear device for cellular mechanotransduction studies

Cells sense external mechanical stimulus and respond to it through mechanotransduction mechanism. Fluid shear stress (FSS) has been found to be an important element among the mechanical stimuli. Recent advancements in microfluidics made mechanotransduction studies possible in near physiological conditions using microfluidic devices. FSS on human cells covers a broad range from very low level experienced due to interstitial flows (0.1 mPa) to very high level in aorta (10 Pa). In the present communication, we have designed a novel microfluidic device which can generate FSS on cells of five different orders with single inflow of fluid which can cover the whole range of physiological fluid shear stresses in one run. The dimensions of the device were calculated taking a resistance model for the micro channels. Flow velocities and wall shear stress were predicted through computer simulation. Shear stress values were analyzed for two different depths of channels and different inlet flow rates ranging from 50 to 0.5 μl/s. FSS was found to increase linearly with inlet flow rate and the stress profile was flatter for lesser depth of channel.

Flow-induced stress on adherent cells in microfluidic devices

Transduction of mechanical forces and chemical signals affect every cell in the human body. Fluid flow in systems such as the lymphatic or circulatory systems modulates not only cell morphology, but also gene expression patterns, extracellular matrix protein secretion and cell-cell and cell-matrix adhesions. Similar to the role of mechanical forces in adaptation of tissues, shear fluid flow orchestrates collective behaviours of adherent cells found at the interface between tissues and their fluidic environments. These behaviours range from alignment of endothelial cells in the direction of flow to stem cell lineage commitment. Therefore, it is important to characterize quantitatively fluid interface-dependent cell activity. Common macro-scale techniques, such as the parallel plate flow chamber and vertical-step flow methods that apply fluid-induced stress on adherent cells, offer standardization, repeatability and ease of operation. However, in order to achieve improved control over a cell's microenvironment, additional microscale-based techniques are needed. The use of microfluidics for this has been recognized, but its true potential has emerged only recently with the advent of hybrid systems, offering increased throughput, multicellular interactions, substrate functionalization on 3D geometries, and simultaneous control over chemical and mechanical stimulation. In this review, we discuss recent advances in microfluidic flow systems for adherent cells and elaborate on their suitability to mimic physiologic micromechanical environments subjected to fluid flow. We describe device design considerations in light of ongoing discoveries in mechanobiology and point to future trends of this promising technology.

The inter-sample structural variability of regular tissue-engineered scaffolds significantly affects the micromechanical local cell environment

Rapid prototyping techniques have been widely used in tissue engineering to fabricate scaffolds with controlled architecture. Despite the ability of these techniques to fabricate regular structures, the consistency with which these regular structures are produced throughout the scaffold and from one scaffold to another needs to be quantified. Small variations at the pore level can affect the local mechanical stimuli sensed by the cells thereby affecting the final tissue properties. Most studies assume rapid prototyping scaffolds as regular structures without quantifying the local mechanical stimuli at the cell level. In this study, a computational method using a micro-computed tomography-based scaffold geometry was developed to characterize the mechanical stimuli within a real scaffold at the pore level. Five samples from a commercial polycaprolactone scaffold were analysed and computational fluid dynamics analyses were created to compare local velocity and shear stress values at the same scaffold location. The five samples did not replicate the computer-aided design (CAD) scaffold and velocity and shear stress values were up to five times higher than the ones calculated in the CAD scaffold. In addition high variability among samples was found: at the same location velocity and shear stress values could be up to two times higher from sample to sample. This study shows that regular scaffolds need to be thoroughly analysed in order to quantify real cell mechanical stimuli so inspection methods should be included as part of the fabrication process.