Hydrodynamic damage to animal cells

Effect of impeller type on cellular morphology and production of clavulanic acid by Streptomyces clavuligerus

It is essential to evaluate the effects of operating conditions in submerged cultures of filamentous microorganisms. In particular, the impeller type influences the flow pattern, power consumption, and energy dissipation, leading to differences in the hydrodynamic environment that affect the morphology of the microorganism. This work investigated the effect of different impeller types, namely the Rushton turbine (RT-RT) and Elephant Ear impellers in up-pumping (EEUP) and down-pumping (EEDP) modes, on cellular morphology and clavulanic acid (CA) production by Streptomyces clavuligerus in a stirred-tank bioreactor. At 800 rpm and 0.5 vvm, the cultivations performed using RT-RT and EEUP impellers provided higher shear conditions and oxygen transfer rates than those observed with EEDP. These conditions resulted in higher clavulanic acid production using RT-RT (380.7 mg/L) and EEUP (453.3 mg/L) impellers, compared to EEDP (196.6 mg/L). Although the maximum CA concentration exhibited the same order of magnitude for RT-RT and EEUP impellers, the latter presented 40% of the specific power consumption (4.9 kW/m3) compared to the classical RT-RT (12.0 kW/m3). The specific energy for CA production ( E CA ), defined as the energy cost to produce 1 mg of CA, was 3.5 times lower using the EEUP impeller (1.91 kJ/mgCA) when compared to RT-RT (5.91 kJ/mgCA). Besides, the specific energy for O2 transfer ( E O 2 ), the energy required to transfer 1 mmol of O2, was 2.3 times lower comparing the EEUP impeller (3.28 kJ/mmolO2) to RT-RT (7.65 kJ/mmolO2). The results demonstrated the importance of choosing the most suitable impeller configuration in conventional bioreactors to manufacture bioproducts.

Improving product quality and productivity of an antibody-based biotherapeutic using inverted frustoconical shaking bioreactors

The Chinese hamster ovarian (CHO) cells serve as a common choice in biopharmaceutical production, traditionally cultivated in stirred tank bioreactors (STRs). Nevertheless, the pursuit of improved protein quality and production output for commercial purposes demand exploration into new bioreactor types. In this context, inverted frustoconical shaking bioreactors (IFSB) present unique physical properties distinct from STRs. This study aims to compare the production processes of an antibody-based biotherapeutic in both bioreactor types, to enhance production flexibility. The findings indicate that, when compared to STRs, IFSB demonstrates the capability to produce an antibody-based biotherapeutic with either comparable or enhanced bioprocess performance and product quality. IFSB reduces shear damage to cells, enhances viable cell density (VCD), and improves cell state at a 5-L scale. Consequently, this leads to increased protein expression (3.70 g/L vs 2.56 g/L) and improved protein quality, as evidenced by a reduction in acidic variants from 27.0% to 21.5%. Scaling up the culture utilizing the Froude constant and superficial gas velocity ensures stable operation, effective mixing, and gas transfer. The IFSB maintains a high VCD and cell viability at both 50-L and 500-L scales. Product expression levels range from 3.0 to 3.6 g/L, accompanied by an improved acidic variants attribute of 20.6%-22.7%. The IFSB exhibits superior productivity and product quality, underscoring its potential for incorporation into the manufacturing process for antibody-based biotherapeutics. These results establish the foundation for IFSB to become a viable option in producing antibody-based biotherapeutics for clinical and manufacturing applications.

Advances and Challenges in Cell Biology for Cultured Meat

Cultured meat is an emerging biotechnology that aims to produce meat from animal cell culture, rather than from the raising and slaughtering of livestock, on environmental and animal welfare grounds. The detailed understanding and accurate manipulation of cell biology are critical to the design of cultured meat bioprocesses. Recent years have seen significant interest in this field, with numerous scientific and commercial breakthroughs. Nevertheless, these technologies remain at a nascent stage, and myriad challenges remain, spanning the entire bioprocess. From a cell biological perspective, these include the identification of suitable starting cell types, tuning of proliferation and differentiation conditions, and optimization of cell-biomaterial interactions to create nutritious, enticing foods. Here, we discuss the key advances and outstanding challenges in cultured meat, with a particular focus on cell biology, and argue that solving the remaining bottlenecks in a cost-effective, scalable fashion will require coordinated, concerted scientific efforts. Success will also require solutions to nonscientific challenges, including regulatory approval, consumer acceptance, and market feasibility. However, if these can be overcome, cultured meat technologies can revolutionize our approach to food.

Cell culture design for homogeneous proliferation of cells in three-dimensional nonwoven polymer scaffolds

The objective of this study is to establish strategies to uniformly proliferate cells in a three-dimensional nonwoven polyethylene terephthalate (PET)/ethylene vinyl alcohol (EVOH) scaffold by simple adjustments in seeding and culture methods and the scaffold design. The combined dynamic and static seeding (intermittent agitations at 300 rpm with 1 h interval) resulted in the highest seeding efficiency (71%) comparing to the static and continuous agitating seeding methods. Cell-attached scaffolds were cultivated under different conditions. The stirring culture permitted cells to proliferate to a significantly greater extent than the static or agitating cultures, although faster cell proliferation in the outer region of the scaffold was observed. Next, based on this observation, scaffolds were opened with holes to alleviate the cell aggregation. The effect of hole size and number of scaffolds on the distribution of cells proliferated in the scaffold was evaluated. Two of 1-mm holes showed to be an optimal adjustment to allow cells to proliferate in a homogeneous manner. After 14 days culture, both of the holes were filled by cells proliferated with a fourfold increase in the cell number. The cell viability in the scaffolds was also high upon evaluating the live/dead and 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) staining examinations. Different cell types of 3T3-L1, C3H/10T1/2, and KUM6 cells showed similar behavior of cell proliferation and distribution in the scaffold, indicating the applicability of the established procedure. It is concluded that the nonwoven PET/EVOH scaffold serves as a potential cell culture substrate for an efficient cell proliferation.

Rapid, label-free enrichment of lymphocytes in a closed system using a flow-through microfluidic device

The majority of adoptive cellular therapies are produced from peripheral mononuclear cells obtained via leukapheresis and further enriched for the cells of interest (e.g., T cells). Here, we present a first-of-its-kind closed system, which effectively removes ~85% of monocytes and ~88% of platelets, while recovering ~88% of concentrated T cells in a separate output stream, as the leukapheresis sample flows through a microfluidic device at 5 mL/min. The system is driven by a common peristaltic pump, enabled by a novel pressure wave dampener, and operates in a closed bag-to-bag configuration, without requiring any specialized, dedicated equipment. When compared to standard density gradient centrifugation on paired samples, the new system demonstrated a 1.5-fold increase in T cell recovery and a 2-fold reduction in inter-sample variability for this separation outcome. The T cell-to-monocyte ratio of the leukapheresis sample was increased to 20:1, whereas with density gradient processing it decreased to 2:1. As a result of superior purity and/or gentler processing, T cells enriched by the system showed a 2.7-times higher fold expansion during subsequent culture, and an overall 3.5-times higher cumulative yield. This centrifugation-free and label-free closed system for enriching lymphocytes could significantly simplify and standardize the manufacturing of life-saving cellular therapies.

In-droplet cell lysis of AC16 human cardiomyocyte cells via surface acoustic waves

Although several lysis methods are available, biomedical applications are pushing the demand for miniaturised systems and thus for new ways to lyse cells in small volumes. In this work, we demonstrate in-droplet cell lysis of AC16 human cardiomyocyte cells in 20 μL droplets using high frequency surface acoustic waves. The acoustic streaming leads to high shear flow creating porous or breaking the cell membrane and releasing intracellular material. Contrary to previous work where the lysis efficiency is measured by a cell-permeant dye that can be used to determine cell viability, here we propose to quantify the DNA extracted from the cells as a measure of the lysis efficiency. This reagent-free method provides a valuable cell lysis alternative for many biological and biomedical applications, particularly for the development of point-of-care platforms.

Scale-up analysis of geometrically dissimilar single-use bioreactors

Cell culture scale-up is a challenging task due to the simultaneous change of multiple hydrodynamic process characteristics and their different dependencies on the bioreactor size as well as variation in the requirements of individual cell lines. Conventionally, the volumetric power input is the most common parameter to select the impeller speed for scale-up, however, it is well reported that this approach fails when there are huge differences in bioreactor scales. In this study, different scale-up criteria are evaluated. At first, different hydrodynamic characteristics are assessed using computational fluid dynamics data for four single-use bioreactors, the Mobius® CellReady 3 L, the Xcellerex™ XDR-10, the Xcellerex™ XDR-200, and the Xcellerex™ XDR-2000. On the basis of this numerical data, several potential scale-up criteria such as volumetric power input, impeller tip speed, mixing time, maximum hydrodynamic stress, and average strain rate in the impeller zone are evaluated. Out of all these criteria, the latter is found to be most appropriate, and the successful scale-up from 3 to 10 L bioreactor and to 200 L bioreactor is confirmed with cell culture experiments using Chinese Hamster Ovary cell cultivation.

The role of biomechanical stress in extracellular vesicle formation, composition and activity

Extracellular vesicles (EVs) are cornerstones of intercellular communication with exciting fundamental, clinical, and more broadly biotechnological applications. However, variability in EV composition, which results from the culture conditions used to generate the EVs, poses significant fundamental and applied challenges and a hurdle for scalable bioprocessing. Thus, an understanding of the relationship between EV production (and for clinical applications, manufacturing) and EV composition is increasingly recognized as important and necessary. While chemical stimulation and culture conditions such as cell density are known to influence EV biology, the impact of biomechanical forces on the generation, properties, and biological activity of EVs remains poorly understood. Given the omnipresence of these forces in EV preparation and in biomanufacturing, expanding the understanding of their impact on EV composition-and thus, activity-is vital. Although several publications have examined EV preparation and bioprocessing and briefly discussed biomechanical stresses as variables of interest, this review represents the first comprehensive evaluation of the impact of such stresses on EV production, composition and biological activity. We review how EV biogenesis, cargo, efficacy, and uptake are uniquely affected by various types, magnitudes, and durations of biomechanical forces, identifying trends that emerge both generically and for individual cell types. We also describe implications for scalable bioprocessing, evaluating processes inherent in common EV production and isolation methods, and propose a path forward for rigorous EV quality control.

Microbubbles in Food Technology

Microbubbles are largely unused in the food industry yet have promising capabilities as environmentally friendly cleaning and supporting agents within products and production lines due to their unique physical behaviors. Their small diameters increase their dispersion throughout liquid materials, promote reactivity because of their high specific surface area, enhance dissolution of gases into the surrounding liquid phase, and promote the generation of reactive chemical species. This article reviews techniques to generate microbubbles, their modes of action to enhance cleaning and disinfection, their contributions to functional and mechanical properties of food materials, and their use in supporting the growth of living organisms in hydroponics or bioreactors. The utility and diverse applications of microbubbles, combined with their low intrinsic ingredient cost, strongly encourage their increased adoption within the food industry in coming years.

Hydrodynamic dissection of Stentor coeruleus in a microfluidic cross junction

Stentor coeruleus, a single-cell ciliated protozoan, is a model organism for wound healing and regeneration studies. Despite Stentor's large size (up to 2 mm in extended state), microdissection of Stentor remains challenging. In this work, we describe a hydrodynamic cell splitter, consisting of a microfluidic cross junction, capable of splitting Stentor cells in a non-contact manner at a high throughput of ∼500 cells per minute under continuous operation. Introduction of asymmetry in the flow field at the cross junction leads to asymmetric splitting of the cells to generate cell fragments as small as ∼8.5 times the original cell size. Characterization of cell fragment viability shows reduced 5-day survival as fragment size decreases and as the extent of hydrodynamic stress imposed on the fragments increases. Our results suggest that cell fragment size and composition, as well as mechanical stress, play important roles in the long-term repair of Stentor cells and warrant further investigations. Nevertheless, the hydrodynamic splitter can be useful for studying phenomena immediately after cell splitting, such as the closure of wounds in the plasma membrane which occurs on the order of 100-1000 seconds in Stentor.

A star shaped acoustofluidic mixer enhances rapid malaria diagnostics via cell lysis and whole blood homogenisation in 2 seconds

Malaria is a life-threatening disease caused by a parasite, which can be transmitted to humans through bites of infected female Anopheles mosquitoes. This disease plagues a significant population of the world, necessitating the need for better diagnostic platforms to enhance the detection sensitivity, whilst reducing processing times, sample volumes and cost. A critical step in achieving improved detection is the effective lysis of blood samples. Here, we propose the use of an acoustically actuated microfluidic mixer for enhanced blood cell lysis. Guided by numerical simulations, we experimentally demonstrate that the device is capable of lysing a 20× dilution of isolated red blood cells (RBCs) with an efficiency of ∼95% within 350 ms (0.1 mL). Further, experimental results show that the device can effectively lyse whole blood irrespective of its dilution factor. Compared to the conventional method of using water, this platform is capable of releasing a larger quantity of haemoglobin into plasma, increasing the efficiency without the need for lysis reagents. The lysis efficiency was validated with malaria infected whole blood samples, resulting in an improved sensitivity as compared to the unlysed infected samples. Partial least squares-regression (PLS-R) analysis exhibits cross-validated R² values of 0.959 and 0.98 from unlysed and device lysed spectral datasets, respectively. Critically, as expected, the root mean square error of cross validation (RMSECV) value was significantly reduced in the acoustically lysed datasets (RMSECV of 0.97), indicating the improved quantification of parasitic infections compared to unlysed datasets (RMSECV of 1.48). High lysis efficiency and ultrafast processing of very small sample volumes makes the combined acoustofluidic/spectroscopic approach extremely attractive for point-of-care blood diagnosis, especially for detection of neonatal and congenital malaria in babies, for whom a heel prick is often the only option for blood collection.

3D In Vitro Platform for Cell and Explant Culture in Liquid-like Solids

Existing 3D cell models and technologies have offered tools to elevate cell culture to a more physiologically relevant dimension. One mechanism to maintain cells cultured in 3D is by means of perfusion. However, existing perfusion technologies for cell culture require complex electronic components, intricate tubing networks, or specific laboratory protocols for each application. We have developed a cell culture platform that simply employs a pump-free suction device to enable controlled perfusion of cell culture media through a bed of granular microgels and removal of cell-secreted metabolic waste. We demonstrated the versatile application of the platform by culturing single cells and keeping tissue microexplants viable for an extended period. The human cardiomyocyte AC16 cell line cultured in our platform revealed rapid cellular spheroid formation after 48 h and ~90% viability by day 7. Notably, we were able to culture gut microexplants for more than 2 weeks as demonstrated by immunofluorescent viability assay and prolonged contractility.

CFD-Based and Experimental Hydrodynamic Characterization of the Single-Use Bioreactor XcellerexTM XDR-10

Understanding the hydrodynamic conditions in bioreactors is of utmost importance for the selection of operating conditions during cell culture process development. In the present study, the two-phase flow in the lab-scale single-use bioreactor XcellerexTM XDR-10 is characterized for working volumes from 4.5 L to 10 L, impeller speeds from 40 rpm to 360 rpm, and sparging with two different microporous spargers at rates from 0.02 L min-1 to 0.5 L min-1. The numerical simulations are performed with the one-way coupled Euler-Lagrange and the Euler-Euler models. The results of the agitated liquid height, the mixing time, and the volumetric oxygen mass transfer coefficient are compared to experiments. For the unbaffled XDR-10, strong surface vortex formation is found for the maximum impeller speed. To support the selection of suitable impeller speeds for cell cultivation, the surface vortex formation, the average turbulence energy dissipation rate, the hydrodynamic stress, and the mixing time are analyzed and discussed. Surface vortex formation is observed for the maximum impeller speed. Mixing times are below 30 s across all conditions, and volumetric oxygen mass transfer coefficients of up to 22.1 h-1 are found. The XDR-10 provides hydrodynamic conditions which are well suited for the cultivation of animal cells, despite the unusual design of a single bottom-mounted impeller and an unbaffled cultivation bioreactor.

Effect of Hyaluronic Acid on the Differentiation of Mesenchymal Stem Cells into Mature Type II Pneumocytes

Hyaluronic acid (HA) is an essential component of the extracellular matrix (ECM) of the healthy lung, playing an important role in the structure of the alveolar surface stabilizing the surfactant proteins. Alveolar type II (ATII) cells are the fundamental element of the alveolus, specializing in surfactant production. ATII cells represent the main target of lung external lesion and a cornerstone in the repair process of pulmonary damage. In this context, knowledge of the factors influencing mesenchymal stem cell (MSC) differentiation in ATII cells is pivotal in fulfilling therapeutic strategies based on MSCs in lung regenerative medicine. To achieve this goal, the role of HA in promoting the differentiation of MSCs in mature Type II pneumocytes capable of secreting pulmonary surfactant was evaluated. Results demonstrated that HA, at a specific molecular weight can greatly increase the expression of lung surfactant protein, indicating the ability of HA to influence MSC differentiation in ATII cells.

Structural and Biochemical Features of Human Serum Albumin Essential for Eukaryotic Cell Culture

Serum albumin physically interacts with fatty acids, small molecules, metal ions, and several other proteins. Binding with a plethora of bioactive substances makes it a critical transport molecule. Albumin also scavenges the reactive oxygen species that are harmful to cell survival. These properties make albumin an excellent choice to promote cell growth and maintain a variety of eukaryotic cells under in vitro culture environment. Furthermore, purified recombinant human serum albumin is mostly free from impurities and modifications, providing a perfect choice as an additive in cell and tissue culture media while avoiding any regulatory constraints. This review discusses key features of human serum albumin implicated in cell growth and survival under in vitro conditions.

Enhancing Peptide Biomaterials for Biofabrication

Biofabrication using well-matched cell/materials systems provides unprecedented opportunities for dealing with human health issues where disease or injury overtake the body’s native regenerative abilities. Such opportunities can be enhanced through the development of biomaterials with cues that appropriately influence embedded cells into forming functional tissues and organs. In this context, biomaterials’ reliance on rigid biofabrication techniques needs to support the incorporation of a hierarchical mimicry of local and bulk biological cues that mimic the key functional components of native extracellular matrix. Advances in synthetic self-assembling peptide biomaterials promise to produce reproducible mimics of tissue-specific structures and may go some way in overcoming batch inconsistency issues of naturally sourced materials. Recent work in this area has demonstrated biofabrication with self-assembling peptide biomaterials with unique biofabrication technologies to support structural fidelity upon 3D patterning. The use of synthetic self-assembling peptide biomaterials is a growing field that has demonstrated applicability in dermal, intestinal, muscle, cancer and stem cell tissue engineering.

Alginate-chitosan core-shell microcapsule cultures of hepatic cells in a small scale stirred bioreactor: impact of shear forces and microcapsule core composition

A small scale stirred bioreactor was designed and the effect of different agitation rates (30, 60 and 100 rpm) was investigated on HepG2 cells cultured in alginate-chitosan (AC) core-shell microcapsule in terms of the cell proliferation and liver-specific function. The microencapsulated hepatic cells could proliferate well when they were cultured for 10 days at 30 rpm while the cell-laden microcapsules showed no cell proliferation at 100 rpm in the bioreactor system. Albumin production rate, as an important liver function, increased also 1.8- and 1.5- fold under stirring rate of 30 rpm compared to the static culture and 60 rpm of agitation, respectively. Moreover, In comparison with the static culture, about 1.5-fold increment in urea production was observed at 30 rpm. Similarly, the highest expressions of albumin and P450 genes were found at 30 rpm stirring rate, which were 4.9- and 19.2-fold of the static culture. Addition of collagen to the microcapsule core composition (ACol/C) could improve the cell proliferation and functionality at 60 rpm in comparison with the cell-laden microcapsules without collagen. The study demonstrated the hepatic cell-laden ACol/C microcapsule hydrogel cultured in the small scale stirred bioreactor at low mixing rate has a great potential for mass production of the hepatic cells while maintaining liver-specific functions.

Microdroplet-based one-step RT-PCR for ultrahigh throughput single-cell multiplex gene expression analysis and rare cell detection

Gene expression analysis of individual cells enables characterization of heterogeneous and rare cell populations, yet widespread implementation of existing single-cell gene analysis techniques has been hindered due to limitations in scale, ease, and cost. Here, we present a novel microdroplet-based, one-step reverse-transcriptase polymerase chain reaction (RT-PCR) platform and demonstrate the detection of three targets simultaneously in over 100,000 single cells in a single experiment with a rapid read-out. Our customized reagent cocktail incorporates the bacteriophage T7 gene 2.5 protein to overcome cell lysate-mediated inhibition and allows for one-step RT-PCR of single cells encapsulated in nanoliter droplets. Fluorescent signals indicative of gene expressions are analyzed using a probabilistic deconvolution method to account for ambient RNA and cell doublets and produce single-cell gene signature profiles, as well as predict cell frequencies within heterogeneous samples. We also developed a simulation model to guide experimental design and optimize the accuracy and precision of the assay. Using mixtures of in vitro transcripts and murine cell lines, we demonstrated the detection of single RNA molecules and rare cell populations at a frequency of 0.1%. This low cost, sensitive, and adaptable technique will provide an accessible platform for high throughput single-cell analysis and enable a wide range of research and clinical applications.

Cell spheroids as a versatile research platform: formation mechanisms, high throughput production, characterization and applications

Three-dimensional cell culture has tremendous advantages to closely mimic the in vivo architecture and microenvironment of healthy tissue and organs, as well as of solid tumors. Spheroids are currently the most attractive 3D model to produce uniform reproducible cell structures as well as a potential basis for engineering large tissues and complex organs. In this review we discuss, from an engineering perspective, processes to obtain uniform 3D cell spheroids, comparing dynamic and static cultures and considering aspects such as mass transfer and shear stress. In addition, computational and mathematical modelling of complex cell spheroid systems are discussed. The non-cell-adhesive hydrogel-based method and dynamic cell culture in bioreactors are focused in detail and the myriad of developed spheroid characterization techniques is presented. The main bottlenecks and weaknesses are discussed, especially regarding the analysis of morphological parameters, cell quantification and viability, gene expression profiles, metabolic behavior and high-content analysis. Finally, a vast set of applications of spheroids as tools for in vitro study model systems is examined, including drug screening, tissue formation, pathologies development, tissue engineering and biofabrication, 3D bioprinting and microfluidics, together with their use in high-throughput platforms.

Effect of microfluidic processing on the viability of boar and bull spermatozoa

The use of microfluidics in artificial reproductive technologies for manipulation or assessment of spermatozoa is unique in the sense that it is not always an end point measurement and the sample may be used afterward. During microfluidic processing, spermatozoa are exposed to shear stress, which may harm viability and functioning of spermatozoa. The shear stresses during general microfluidic processing steps were calculated and compared to estimated shear stresses during ejaculation. The viability of boar and bull spermatozoa after microfluidic processing was studied and compared to the typical handling method (centrifugation) and to a control (the sample in a tube at the same temperature). The boar spermatozoa showed a small but significant decrease in viability of 6% after microfluidic handling. Bull spermatozoa proved to be less susceptible to shear stress and were not significantly affected by microfluidic processing. These data indicate that the impact of microfluidic processing on the viability of boar and bull spermatozoa is less than the literature values reported for flow cytometry and comparable to the impact of centrifugation.

A microfluidic platform culturing two cell lines paralleled under in-vivo like fluidic microenvironment for testing the tumor targeting of nanoparticles

Nanoparticles are attractive in medicine because their surfaces can be chemically modified for targeting specific disease cells, especially for cancer. Providing an in-vivo like platform is crucial to evaluate the biological behaviours of nanoparticles. This paper presents a microfluidic device that could culture two cell lines in parallel in in-vivo like fluidic microenvironments and be used for testing the tumor targeting of folic acid - cholesterol - chitosan (FACC) nanoparticles. The uniformity and uniformity of flow fields inside the cell culture units are investigated using the finite element method and particle tracking technology. HeLa and A549 cells are cultured in the microfluidic chip under continuous media supplementation, mimicking the fluid microenvironment in vivo. Cell introducing processes are presented by the flow behaviours of inks with different colours. The two cell lines are identified by detecting folate receptors on the cellular membranes. The growth curves of the two cell lines are measured. The two cell lines cultured paralleled inside the microfluidic device are treated with FITC-FACC to investigate the targeting of FACC. The tumor targeting of FACC are also detected by in vivo imaging of HeLa cells growth in nude mice models. The results indicate that the microfluidic device could provide a dynamic, uniform and stable fluidic microenvironment to test the tumor targeting of FACC nanoparticles.

Microfluidic Device for Localized Electroporation

Electroporation is a common method of transfection due to its relatively low risk and high transfection efficiency. The most common method of electroporation is bulk electroporation which is easily performed on large quantities of cells yet results in variable levels of viability and transfection efficiency across the population. Localized electroporation is an alternative that can be administered on a similar scale but results in much more consistent with higher quality transfection and higher cell viability. This chapter discusses the creation and use of a simple and cost-effective device using porous membrane for performing localized electroporation.

A microfluidics-based wound-healing assay for studying the effects of shear stresses, wound widths, and chemicals on the wound-healing process

Collective cell migration plays important roles in various physiological processes. To investigate this collective cellular movement, various wound-healing assays have been developed. In these assays, a “wound” is created mechanically, chemically, optically, or electrically out of a cellular monolayer. Most of these assays are subject to drawbacks of run-to-run variations in wound size/shape and damages to cells/substrate. Moreover, in all these assays, cells are cultured in open, static (non-circulating) environments. In this study, we reported a microfluidics-based wound-healing assay by using the trypsin flow-focusing technique. Fibroblasts were first cultured inside this chip to a cellular monolayer. Then three parallel fluidic flows (containing normal medium and trypsin solution) were introduced into the channels, and cells exposed to protease trypsin were enzymatically detached from the surface. Wounds of three different widths were generated, and subsequent wound-healing processes were observed. This assay is capable of creating three or more wounds of different widths for investigating the effects of various physical and chemical stimuli on wound-healing speeds. The effects of shear stresses, wound widths, and β-lapachone (a wound healing-promoting chemical) on wound-healing speeds were studied. It was found that the wound-healing speed (total area healed per unit time) increased with increasing shear stress and wound width, but under a shear stress of 0.174 mPa the linear healing speed (percent area healed per unit time) was independent of the wound width. Also, the addition of β-lapachone up to 0.5 μM did not accelerate wound healing. This microfluidics-based assay can definitely help in understanding the mechanisms of the wound-healing process and developing new wound-healing therapies.

Characterization of the Metabolic Response of Streptomyces clavuligerus to Shear Stress in Stirred Tanks and Single-Use 2D Rocking Motion Bioreactors for Clavulanic Acid Production

Streptomyces clavuligerus is a gram-positive filamentous bacterium notable for producing clavulanic acid (CA), an inhibitor of β-lactamase enzymes, which confers resistance to bacteria against several antibiotics. Here we present a comparative analysis of the morphological and metabolic response of S. clavuligerus linked to the CA production under low and high shear stress conditions in a 2D rocking-motion single-use bioreactor (CELL-tainer ^®) and stirred tank bioreactor (STR), respectively. The CELL-tainer^® guarantees high turbulence and enhanced volumetric mass transfer at low shear stress, which (in contrast to bubble columns) allows the investigation of the impact of shear stress without oxygen limitation. The results indicate that high shear forces do not compromise the viability of S. clavuligerus cells; even higher specific growth rate, biomass, and specific CA production rate were observed in the STR. Under low shear forces in the CELL-tainer^® the mycelial diameter increased considerably (average diameter 2.27 in CELL-tainer^® vs. 1.44 µm in STR). This suggests that CA production may be affected by a lower surface-to-volume ratio which would lead to lower diffusion and transport of nutrients, oxygen, and product. The present study shows that there is a strong correlation between macromorphology and CA production, which should be an important aspect to consider in industrial production of CA.

Validation of a novel 3D flow model for the optimization of construct perfusion in radial-flow packed-bed bioreactors (rPBBs) for long-bone tissue engineering

Osteogenic cell culture in three-dimensional (3D) hollow cylindrical porous scaffolds in radial-flow packed-bed bioreactors (rPBBs) may overcome the transport limitations of static and axial perfusion bioreactors in the engineering of long-bone substitutes. Flow models of rPBBs help optimize radial flux distribution of medium and tissue maturation in vitro. Only a 2D model is available for steady flow transport in rPBBs with axisymmetric inlet and outlet accounting for the fluid dynamics of void spaces, assessed against literature information. Here, a novel 3D model is proposed for steady flow transport in the three compartments of rPBBs with a more practical lateral outlet. A 3D model of transient tracer transport was developed based on the flow model to predict bioreactor residence time distribution (RTD). Model-predicted flow patterns were validated in terms of RTD against tracer experiments performed with bioreactor prototypes equipped with commercial scaffolds for bone tissue engineering. Bioreactors were challenged with a step change in entering tracer concentration in an optimized set-up under conditions promoting uniform radial flux distribution and typical shunt flows. Model-predicted RTDs agreed well with those experimentally determined. In conclusion, tracer experiments validate the use of the 3D flow model for optimizing construct perfusion in rPBBs to engineer long-bone substitutes.

Aeration and Shear Stress Are Critical Process Parameters for the Production of Oncolytic Measles Virus

Oncolytic Measles virus is a promising candidate for cancer treatment, but clinical studies have shown that extremely high doses (up to 1011 TCID50 per dose) are required to effect a cure. Very high titers of the virus must therefore be achieved during production to ensure an adequate supply. We have previously shown that Measles virus can be produced in Vero cells growing on a Cytodex 1 microcarrier in serum-containing medium using a stirred-tank reactor (STR). However, process optimization and further process transfer or scale up requires the identification of critical process parameters, particularly because the use of STRs increases the risk of cell damage and lower product yields due to shear stress. Using a small-scale STR (0.5 L working volume) we found that Measles virus titers are sensitive to agitator-dependent shear, with shear stress ≥0.25 N m-2 reducing the titer by more than four orders of magnitude. This effect was observed in both serum-containing and serum-free medium. At this scale, virus of titers up to 1010 TCID50 mL-1 could be achieved with an average shear stress of 0.1 N m-2. We also found that the aeration method affected the virus titer. Aeration was necessary to ensure a sufficient oxygen supply to the Vero cells, and CO2 was also needed to regulate the pH of the sodium bicarbonate buffer system. Continuous gassing with air and CO2 reduced the virus titer by four orders of magnitude compared to head-space aeration. The manufacture of oncolytic Measles virus in a STR can therefore be defined as a shear-sensitive process, but high titers can nevertheless be achieved by keeping shear stress levels below 0.25 N m-2 and by avoiding extensive gassing of the medium.

A Continuous Flow-through Microfluidic Device for Electrical Lysis of Cells

In contrast to the delicate 3D electrodes in the literature, a simple flow-through device is proposed here for continuous and massive lysis of cells using electricity. The device is essentially a rectangular microchannel with a planar electrode array built on its bottom wall, actuated by alternating current (AC) voltages between neighboring electrodes, and can be incorporated easily into other biomedical systems. Human whole blood diluted 10 times with phosphate-buffered saline (about 6 108 cells per mL) was pumped through the device, and the cells were completely lysed within 7 s after the application of a 20 V peak-to-peak voltage at 1 MHz, up to 400 μL/hr. Electric field and Maxwell stress were calculated for assessing electrical lysis. Only the lower half-channel was exposed to an electric field exceeding the irreversible threshold value of cell electroporation (Eth2), suggesting that a cross flow, proposed here primarily as the electro-thermally induced flow, was responsible for bringing the cells in the upper half-channel downward to the lower half-channel. The Maxwell shear stress associated with Eth2 was one order of magnitude less than the threshold mechanical stresses for lysis, implying that an applied moderate mechanical stress could aid electrical lysis.

Morphological and electrical disturbances after split-flow fractionation in murine macrophages

Split-flow fractionation (SPLITT) is a family of techniques that separates in the absence of labeling using very low flow rates and force fields, and is therefore expected to minimize cell damage. Although it has been documented that separation methods cause physiological changes in immune cells that are attributable to mechanical stress and antibody labeling, SPLITT has not yet been examined for possible damaging effects of hydrodynamic stress, partly because it is assumed that the low flow rates and weak forces used in this technique do not generate significant mechanical stress. The aim of this study was to investigate the effects of SPLITT on cell function of a murine macrophage cell, and to compare these effects with those induced by centrifugation. Macrophages J774.2 were cultured in RPMI-enriched media, then detached from the culture flask and resuspended for 12 h. Cell suspensions were diluted in a buffered saline solution and exposed to SPLITT (flow rates 1-10 ml/min) or centrifugation (100-1500g) for 10 min. Cell viability, diameter, membrane potential, and nitric oxide production were measured. Under the operating conditions employed, cell viability was above 98% after SPLITT and centrifugation but cells suffered immediate hydrodynamic cell damage, including decreased cell diameter and membrane hyperpolarization which was inhibitable by 4-aminopyridine; nitric oxide production was not affected. Pressure values during SPLITT and centrifugation correlated with diameter and membrane potential. Our data do not support the assumption that SPLITT is innocuous to cell function. Some changes in SPLITT channel design are suggested to minimize cell damage. Membrane potential and cell diameter are sensitive indicators for the evaluation of sublethal damage in different cell models, and allow identification of optimal operating conditions on different scales.

Establishing a quick screening method by using a microfluidic chip to evaluate cytotoxicity of metal contaminants

Due to rapid industrialization and urbanization, the environment is exposed to many chemicals from natural or anthropogenic sources. The contaminants impact eco-system and human health via food chain. Animals, including humans, are likely to accumulate contaminants in their bodies from direct exposure or feeding behavior, resulting in toxicity. Therefore, evaluation of the toxicity of contaminants is an important issue. Metals are highly toxic but the toxicity depends on many factors, including the valance and the complex form of metals, the organic matter level in the environment, the reducing/oxidizing condition of the environment, and etc. Since the level of metal amount does not directly correlate to bioavailability, cell culture is usually used for toxicity evaluation. In this study, a microfluidic chip was developed to evaluate the cell toxicity from exposure to metals, copper and thallium. Compared to traditional cytotoxicity assay using static state culture with tetrazolium reagent, this microfluidic chip can generate various shear stresses by changing geometry of culture areas or flow rate. Enhancement of shear stresses could increase cell sensitivity toward metal exposure. Therefore, this platform provides a more sensitive platform for quantitative analysis of cell toxicity and could be applied to evaluate toxicity from environmental samples.

Using CFD simulations and statistical analysis to correlate oxygen mass transfer coefficient to both geometrical parameters and operating conditions in a stirred-tank bioreactor

Optimization of a bioreactor design can be an especially challenging process. For instance, testing different bioreactor vessel geometries and different impeller and sparger types, locations, and dimensions can lead to an exceedingly large number of configurations and necessary experiments. Computational fluid dynamics (CFD), therefore, has been widely used to model multiphase flow in stirred-tank bioreactors to minimize the number of optimization experiments. In this study, a multiphase CFD model with population balance equations are used to model gas-liquid mixing, as well as gas bubble distribution, in a 50 L single-use bioreactor vessel. The vessel is the larger chamber in an early prototype of a multichamber bioreactor for mammalian cell culture. The model results are validated with oxygen mass transfer coefficient (k_L a) measurements within the prototype. The validated model is projected to predict the effect of using ring or pipe spargers of different sizes and the effect of varying the impeller diameter on k_L a. The simulations show that ring spargers result in a superior k_L a compared to pipe spargers, with an optimum sparger-to-impeller diameter ratio of 0.8. In addition, larger impellers are shown to improve k_L a. A correlation of k_L a is presented as a function of both the reactor geometry (i.e., sparger-to-impeller diameter ratio and impeller-to-vessel diameter ratio) and operating conditions (i.e., Reynolds number and gas flow rate). The resulting correlation can be used to predict k_L a in a bioreactor and to optimize its design, geometry, and operating conditions.

Harnessing stem cells and biomaterials to promote neural repair

With the limited capacity for self-repair in the adult CNS, efforts to stimulate quiescent stem cell populations within discrete brain regions, as well as harness the potential of stem cell transplants, offer significant hope for neural repair. These new cells are capable of providing trophic cues to support residual host populations and/or replace those cells lost to the primary insult. However, issues with low-level adult neurogenesis, cell survival, directed differentiation and inadequate reinnervation of host tissue have impeded the full potential of these therapeutic approaches and their clinical advancement. Biomaterials offer novel approaches to stimulate endogenous neurogenesis, as well as for the delivery and support of neural progenitor transplants, providing a tissue-appropriate physical and trophic milieu for the newly integrating cells. In this review, we will discuss the various approaches by which bioengineered scaffolds may improve stem cell-based therapies for repair of the CNS.

Addressing the Manufacturing Challenges of Cell-Based Therapies

Exciting developments in the cell therapy field over the last decades have led to an increasing number of clinical trials and the first cell products receiving marketing authorization. In spite of substantial progress in the field, manufacturing of cell-based therapies presents multiple challenges that need to be addressed in order to assure the development of safe, efficacious, and cost-effective cell therapies.The manufacturing process of cell-based therapies generally requires tissue collection, cell isolation, culture and expansion (upstream processing), cell harvest, separation and purification (downstream processing), and, finally, product formulation and storage. Each one of these stages presents significant challenges that have been the focus of study over the years, leading to innovative and groundbreaking technological advances, as discussed throughout this chapter.Delivery of cell-based therapies relies on defining product targets while controlling process variable impact on cellular features. Moreover, commercial viability is a critical issue that has had damaging consequences for some therapies. Implementation of cost-effectiveness measures facilitates healthy process development, potentially being able to influence end product pricing.Although cell-based therapies represent a new level in bioprocessing complexity in every manufacturing stage, they also show unprecedented levels of therapeutic potential, already radically changing the landscape of medical care.

3D bioprinting of heterogeneous bi- and tri-layered hollow channels within gel scaffolds using scalable multi-axial microfluidic extrusion nozzle

One of the primary focuses in recent years in tissue engineering has been the fabrication and integration of vascular structures into artificial tissue constructs. However, most available methodologies lack the ability to create multi-layered concentric conduits inside natural extracellular matrices (ECMs) and gels that replicate more accurately the hierarchical architecture of biological blood vessels. In this work, we present a new microfluidic nozzle design capable of multi-axial extrusion in order to 3D print and pattern bi- and tri-layered hollow channel structures. This nozzle allows, for the first time, for these structures to be embedded within layers of gels and ECMs in a fast, simple and low-cost manner. By varying flow rates (1-6 ml min^-1), printspeeds (1-16 m min^-1), and material concentration (25-175 mM and 1.5%-2.5% for calcium chloride and alginate, respectively) we are able to accurately determine the operational printing range as well as achieve a wide range of conduit dimensions (0.69-2.31 mm) that can be printed within a few seconds. Our scalable design allows for multi-axial extrusion and versatility in material incorporation in order to create heterogeneous structures. We demonstrate the ability to print distinct concentric layers of different cell types, namely endothelial cells and fibroblasts. By incorporating various layers of different cell-friendly materials (such as collagen and fibrin) alongside materials with high mechanical strength (i.e. alginate), we were able to increase long-term cell viability and growth without compromising the structural integrity. In this way, we can improve cellular adhesion in our biocompatible constructs as well as allow them to remain structurally sound. We are able to realize complex heterogeneous, hierarchical architectures that have strong potential for use not only in vascular tissue applications, but also in other artificially fabricated tubular or fiber-like structures such as skeletal muscle or nerve conduits.

Silicon Carbide Nanoparticles as an Effective Bioadhesive to Bond Collagen Containing Composite Gel Layers for Tissue Engineering Applications

Additive manufacturing via layer-by-layer adhesive bonding holds much promise for scalable manufacturing of tissue-like constructs, specifically scaffolds with integrated vascular networks for tissue engineering applications. However, there remains a lack of effective adhesives capable of composite layer fusion without affecting the integrity of patterned features. Here, the use of silicon carbide is introduced as an effective adhesive to achieve strong bonding (0.39 ± 0.03 kPa) between hybrid hydrogel films composed of alginate and collagen. The techniques have allowed us to fabricate multilayered, heterogeneous constructs with embedded high-resolution microchannels (150 µm-1 mm) that are precisely interspaced (500-600 µm). Hydrogel layers are effectively bonded with silicon carbide nanoparticles without blocking the hollow microchannels and high cell viability (90.61 ± 3.28%) is maintained within the scaffold. Nanosilica is also tested and found to cause clogging of smaller microchannels when used for interlayer bonding, but is successfully used to attach synthetic polymers (e.g., Tygon) to the hydrogels (32.5 ± 2.12 mN bond strength). This allows us to form inlet and outlet interconnections to the gel constructs. This ability to integrate hollow channel networks into bulk soft material structures for perfusion can be useful in 3D tissue engineering applications.

Large-scale culture of a megakaryocytic progenitor cell line with a single-use bioreactor system

The increasing application of regenerative medicine has generated a growing demand for stem cells and their derivatives. Single-use bioreactors offer an attractive platform for stem cell expansion owing to their scalability for large-scale production and feasibility of meeting clinical-grade standards. The current work evaluated the capacity of a single-use bioreactor system (1 L working volume) for expanding Meg01 cells, a megakaryocytic (MK) progenitor cell line. Oxygen supply was provided by surface aeration to minimize foaming and orbital shaking was used to promote oxygen transfer. Oxygen transfer rates (k_L a) of shaking speeds 50, 100, and 125 rpm were estimated to be 0.39, 1.12, and 10.45 h^-1 , respectively. Shaking speed was a critical factor for optimizing cell growth. At 50 rpm, Meg01 cells exhibited restricted growth due to insufficient mixing. A negative effect occurred when the shaking speed was increased to 125 rpm, likely caused by high hydrodynamic shear stress. The bioreactor culture achieved the highest growth profile when shaken at 100 rpm, achieving a total expansion rate up to 5.7-fold with a total cell number of 1.2 ± 0.2 × 10⁹ cells L^-1 . In addition, cells expanded using the bioreactor system could maintain their potency to differentiate following the MK lineage, as analyzed from specific surface protein and morphological similarity with the cells grown in the conventional culturing system. Our study reports the impact of operational variables such as shaking speed for growth profile and MK differentiation potential of a progenitor cell line in a single-use bioreactor. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:362-369, 2018.

A novel microfluidic microelectrode chip for a significantly enhanced monitoring of NPY-receptor activation in live mode

Lab-on-a-chip devices that combine, e.g. chemical synthesis with integrated on-chip analytics and multi-compartment organ-on-a-chip approaches, are a fast and attractive evolving research area. While integration of appropriate cell models in microfluidic setups for monitoring the biological activity of synthesis products or test compounds is already in focus, the integration of label-free bioelectronic analysis techniques is still poorly realized. In this context, we investigated the capabilities of impedance spectroscopy as a non-destructive real-time monitoring technique for adherent cell models in a microfluidic setup. While an initial adaptation of a microelectrode array (MEA) layout from a static setup revealed clear restrictions in the application of impedance spectroscopy in a microfluidic chip, we could demonstrate the advantage of a FEM simulation based rational MEA layout optimization for an optimum electrical field distribution within microfluidic structures. Furthermore, FEM simulation based analysis of shear stress and time-dependent test compound distribution led to identification of an optimal flow rate. Based on the simulation derived optimized microfluidic MEA, comparable impedance spectra characteristics were achieved for HEK293A cells cultured under microfluidic and static conditions. Furthermore, HEK293A cells expressing Y1 receptors were used to successfully demonstrate the capabilities of impedimetric monitoring of cellular alterations in the microfluidic setup. More strikingly, the maximum impedimetric signal for the receptor activation was significantly increased by a factor of 2.8. Detailed investigations of cell morphology and motility led to the conclusion that cultivation under microfluidic conditions could lead to an extended and stabilized cell-electrode interface.

The recent development and applications of fluidic channels by 3D printing

The technology of “Lab-on-a-Chip” allows the synthesis and analysis of chemicals and biological substance within a portable or handheld device. The 3D printed structures enable precise control of various geometries. The combination of these two technologies in recent years makes a significant progress. The current approaches of 3D printing, such as stereolithography, polyjet, and fused deposition modeling, are introduced. Their manufacture specifications, such as surface roughness, resolution, replication fidelity, cost, and fabrication time, are compared with each other. Finally, novel application of 3D printed channel in biology are reviewed, including pathogenic bacteria detection using magnetic nanoparticle clusters in a helical microchannel, cell stimulation by 3D chemical gradients, perfused functional vascular channels, 3D tissue construct, organ-on-a-chip, and miniaturized fluidic “reactionware” devices for chemical syntheses. Overall, the 3D printed fluidic chip is becoming a powerful tool in the both medical and chemical industries.