Mouse embryonic stem cell expansion in a microcarrier-based stirred culture system

Small extracellular vesicles purification and scale-up

Exosomes are small extracellular vesicles (sEVs) secreted by cells. With advances in the study of sEVs, they have shown great potential in the diagnosis and treatment of disease. However, sEV therapy usually requires a certain dose and purity of sEVs to achieve the therapeutic effect, but the existing sEV purification technology exists in the form of low yield, low purity, time-consuming, complex operation and many other problems, which greatly limits the application of sEVs. Therefore, how to obtain high-purity and high-quality sEVs quickly and efficiently, and make them realize large-scale production is a major problem in current sEV research. This paper discusses how to improve the purity and yield of sEVs from the whole production process of sEVs, including the upstream cell line selection and cell culture process, to the downstream isolation and purification, quality testing and the final storage technology.

Technological aspects of manufacturing and analytical control of biological nanoparticles

Extracellular vesicles (EVs) are cell-derived biological nanoparticles that gained great interest for drug delivery. EVs have numerous advantages compared to synthetic nanoparticles, such as ideal biocompatibility, safety, ability to cross biological barriers and surface modification via genetic or chemical methods. On the other hand, the translation and the study of these carriers resulted difficult, mostly because of significant issues in up-scaling, synthesis and impractical methods of quality control. However, current manufacturing advances enable EV packaging with any therapeutic cargo, including DNA, RNA (for RNA vaccines and RNA therapeutics), proteins, peptides, RNA-protein complexes (including gene-editing complexes) and small molecules drugs. To date, an array of new and upgraded technologies have been introduced, substantially improving EV production, isolation, characterization and standardization. The used-to-be "gold standards" of EV manufacturing are now outdated, and the state-of-art requires extensive revision. This review re-evaluates the pipeline for EV industrial production and provides a critical overview of the modern technologies required for their synthesis and characterization.

Milk/colostrum exosomes: A nanoplatform advancing delivery of cancer therapeutics

Chemotherapeutics continue to play a central role in the treatment of a wide variety of cancers. Conventional chemotherapy involving bolus intravenous doses results in severe side effects - in some cases life threatening - delayed toxicity and compromised quality-of-life. Attempts to deliver small drug molecules using liposomes, polymeric nanoparticles, micelles, lipid nanoparticles, etc. have produced limited nanoformulations for clinical use, presumably due to a lack of biocompatibility of the material, costs, toxicity, scalability, and/or lack of effective administration. Naturally occurring small extracellular vesicles, or exosomes, may offer a solution and a viable system for delivering cancer therapeutics. Combined with their inherent trafficking ability and versatility of cargo capacity, exosomes can be engineered to specifically target cancerous cells, thereby minimizing off-target effects, and increasing the efficacy of cancer therapeutics. Exosomal formulations have mitigated the toxic effects of several drugs in murine cancer models. In this article, we review studies related to exosomal delivery of both small molecules and biologics, including siRNA to inhibit specific gene expression, in the pursuit of effective cancer therapeutics. We focus primarily on bovine milk and colostrum exosomes as the cancer therapeutic delivery vehicles based on their high abundance, cost effectiveness, scalability, high drug loading, functionalization of exosomes for targeted delivery, and lack of toxicity. While bovine milk exosomes may provide a new platform for drug delivery, extensive comparison to other nanoformulations and evaluation of long-term toxicity will be required to fully realize its potential.

Viscoelastic Properties of Bioprinted Alginate Microbeads Compared to Their Bulk Hydrogel Analogs

Hydrogel microbeads are engineered spherical microgels widely used for biomedical applications in cell cultures, tissue engineering, and drug delivery. Their mechanical and physical properties (i.e., modulus, porosity, diffusion) heavily influence their utility by affecting encapsulated cellular behavior, biopayload elution kinetics, and stability for longer term cultures. There is a need to quantify these properties to guide microbead design for effective application. However, there are few techniques with the μN-level resolution required to evaluate these relatively small, compliant constructs. To circumvent mechanically testing individual microbeads, researchers often approximate microbead properties by characterizing larger bulk gel analogs of the same material formulation. This approach provides some insight into the hydrogel properties. However, bulk gels possess key structural and mechanical differences compared to their microbead equivalents, which may limit their accuracy and utility as analogs for estimating microbead properties. Herein, we explore how microbead properties are influenced by hydrogel formulation (i.e., alginate concentration, divalent cation crosslinker, and crosslinker concentration), and whether these trends are accurately reflected in bulk gel analogs. To accomplish this, we utilize laser direct-write bioprinting to create 12 × 12 arrays of alginate microbeads and characterize all 144 microbeads in parallel using a commercially available microcompression system. In this way, the compressive load is distributed across a large number of beads, thus amplifying sample signal. Comparing microbead properties to those of their bulk gel analogs, we found that their trends in modulus, porosity, and diffusion with hydrogel formulation are consistent, yet bulk gels exhibit significant discrepancies in their measured values.

Engineered cell-laden thermosensitive poly(N-isopropylacrylamide)-immobilized gelatin microspheres as 3D cell carriers for regenerative medicine

Several studies have focused on using cell carriers to solve the problem of mesenchymal stem cell expansion on regenerative medicine. However, the disadvantages of using prolonged enzymatic treatment and low cell harvest efficiency still trouble researchers. In this study, PNIPAAm-immobilized gelatin microspheres (abbreviated as GNMS) were synthesized using a simple power-driven flow-focusing microinjection system. The developed thermosensitive GNMS can allow easier harvesting of cells from the microspheres, requiring only 10 ​min of low-temperature treatment and 5 ​min of trypsin treatment. The developed GNMS was characterized by Fourier-transform infrared spectroscopy, optical microscopy, and scanning electron microscopy. Further, live/dead staining, F-actin staining, and PrestoBlue cell viability assays were used to evaluate cytotoxicity, cell morphology, cell proliferation, and harvest efficiency. The gene expression of stem cell markers was determined by real-time quantitative PCR (Q-PCR) analysis to investigate the stemness and phenotypic changes in Wharton's jelly-derived mesenchymal stem cells. The results showed that the engineered cell-laden thermosensitive GNMS could significantly increase the cell harvest rate with over 99% cell survival rate and no change in the cell phenotype. Thus, the described strategy GNMS could be the suitable 3D cell carriers in the therapeutic application and opens new avenues for regenerative medicine.

Overcoming bioprocess bottlenecks in the large-scale expansion of high-quality hiPSC aggregates in vertical-wheel stirred suspension bioreactors

BACKGROUND

Human induced pluripotent stem cells (hiPSCs) hold enormous promise in accelerating breakthroughs in understanding human development, drug screening, disease modeling, and cell and gene therapies. Their potential, however, has been bottlenecked in a mostly laboratory setting due to bioprocess challenges in the scale-up of large quantities of high-quality cells for clinical and manufacturing purposes. While several studies have investigated the production of hiPSCs in bioreactors, the use of conventional horizontal-impeller, paddle, and rocking-wave mixing mechanisms have demonstrated unfavorable hydrodynamic environments for hiPSC growth and quality maintenance. This study focused on using computational fluid dynamics (CFD) modeling to aid in characterizing and optimizing the use of vertical-wheel bioreactors for hiPSC production.

METHODS

The vertical-wheel bioreactor was modeled with CFD simulation software Fluent at agitation rates between 20 and 100 rpm. These models produced fluid flow patterns that mapped out a hydrodynamic environment to guide in the development of hiPSC inoculation and in-vessel aggregate dissociation protocols. The effect of single-cell inoculation on aggregate formation and growth was tested at select CFD-modeled agitation rates and feeding regimes in the vertical-wheel bioreactor. An in-vessel dissociation protocol was developed through the testing of various proteolytic enzymes and agitation exposure times.

RESULTS

CFD modeling demonstrated the unique flow pattern and homogeneous distribution of hydrodynamic forces produced in the vertical-wheel bioreactor, making it the opportune environment for systematic bioprocess optimization of hiPSC expansion. We developed a scalable, single-cell inoculation protocol for the culture of hiPSCs as aggregates in vertical-wheel bioreactors, achieving over 30-fold expansion in 6 days without sacrificing cell quality. We have also provided the first published protocol for in-vessel hiPSC aggregate dissociation, permitting the entire bioreactor volume to be harvested into single cells for serial passaging into larger scale reactors. Importantly, the cells harvested and re-inoculated into scaled-up vertical-wheel bioreactors not only maintained consistent growth kinetics, they maintained a normal karyotype and pluripotent characterization and function.

CONCLUSIONS

Taken together, these protocols provide a feasible solution for the culture of high-quality hiPSCs at a clinical and manufacturing scale by overcoming some of the major documented bioprocess bottlenecks.

Therapeutic application of extracellular vesicles for musculoskeletal repair & regeneration

Traumatic musculoskeletal injuries are common in both the civilian and combat care settings. Significant barriers exist to repairing these injuries including fracture nonunion, muscle fibrosis, re-innervation, and compartment syndrome, as well as infection and inflammation. Recently, extracellular vesicles (EVs), including exosomes and microvesicles, have attracted attention in the field of musculoskeletal regeneration. These vesicles are released by different cell types and play a vital role in cell communication by delivering functional cargoes such as proteins and RNAs. Many of these cargo molecules can be utilized for repair purposes in skeletal disorders such as osteoporosis, osteogenesis imperfecta, sarcopenia, and fracture healing. There are, however, some challenges to overcome in order to advance the successful application of these vesicles in the therapeutic setting. These include large-scale production and isolation of exosomes, long-term storage, in vivo stability, and strategies for tissue-specific targeting and delivery. This paper reviews the general characteristics of exosomes along with their physiological roles and contribution to the pathogenesis of musculoskeletal diseases. We also highlight new findings on the use of synthetic exosomes to overcome the limitations of native exosomes in treating musculoskeletal injuries and disorders.

Mechanomics analysis of hESCs under combined mechanical shear, stretch, and compression

Human embryonic stem cells (hESCs) can differentiate to three germ layers within biochemical and biomechanical niches. The complicated mechanical environments in vivo could have diverse effects on the fate decision and biological functions of hESCs. To globally screen mechanosensitive molecules, three typical types of mechanical stimuli, i.e., tensile stretch, shear flow, and mechanical compression, were applied in respective parameter sets of loading pattern, amplitude, frequency, and/or duration, and then, iTRAQ proteomics test was used for identifying and quantifying differentially expressed proteins in hESCs. Bioinformatics analysis identified 37, 41, and 23 proteins under stretch pattern, frequency, and duration, 13, 18, and 41 proteins under shear pattern, amplitude, and duration, and 4, 0, and 183 proteins under compression amplitude, frequency, and duration, respectively, where distinct parameters yielded the differentially weighted preferences under each stimulus. Ten mechanosensitive proteins were commonly shared between two of three mechanical stimuli, together with numerous proteins identified under single stimulus. More importantly, functional GSEA and WGCNA analyses elaborated the variations of the screened proteins with loading parameters. Common functions in protein synthesis and modification were identified among three stimuli, and specific functions were observed in skin development under stretch alone. In conclusion, mechanomics analysis is indispensable to map actual mechanosensitive proteins under physiologically mimicking mechanical environment, and sheds light on understanding the core hub proteins in mechanobiology.

Therapeutic Potentials of Extracellular Vesicles for the Treatment of Diabetes and Diabetic Complications

Extracellular vesicles (EVs), including exosomes and microvesicles, are nano-to-micrometer vesicles released from nearly all cellular types. EVs comprise a mixture of bioactive molecules (e.g., mRNAs, miRNAs, lipids, and proteins) that can be transported to the targeted cells/tissues via the blood or lymph circulation. Recently, EVs have received increased attention, owing to their emerging roles in cell-to-cell communication, or as biomarkers with the therapeutic potential to replace cell-based therapy. Diabetes comprises a group of metabolic disorders characterized by hyperglycemia that cause the development of life-threatening complications. The impacts of conventional clinical treatment are generally limited and are followed by many side effects, including hypoglycemia, obesity, and damage to the liver and kidney. Recently, several studies have shown that EVs released by stem cells and immune cells can regulate gene expression in the recipient cells, thus providing a strategy to treat diabetes and its complications. In this review, we summarize the results from currently available studies, demonstrating the therapeutic potentials of EVs in diabetes and diabetic complications. Additionally, we highlight recommendations for future research.

Expansion of Transdifferentiated Human Hepatocytes in a Serum-Free Microcarrier Culture System

BACKGROUND AND AIMS

Bioartificial livers (BALs) have attracted much attention as potential supportive therapies for liver diseases. A serum-free microcarrier culture strategy for the in vitro high-density expansion of human-induced hepatocyte-like cells (hiHeps) suitable for BALs was studied in this article.

METHODS

hiHeps were transdifferentiated from human fibroblasts by the lentiviral overexpression of FOXA3, HNF1A, and HNF4A. Cells were cultured on microcarriers, their proliferation was evaluated by cell count and CCK-8 assays, and their function was evaluated by detecting liver function parameters in the supernatant, including urea secretion, albumin synthesis, and lactate dehydrogenase levels. The expressions of hepatocyte function-associated genes of hiHeps were measured by qRT-PCR in 2D and 3D conditions. The expression of related proteins during fibronectin promotes cell adhesion, and proliferation on microcarrier was detected by western blotting.

RESULTS

During microcarrier culture, the optimal culture conditions during the adherence period were the use of half-volume high-density inoculation, Cytodex 3 at a concentration of 3 mg/mL, a cell seeding density of 2.0 × 10⁵ cells/mL, and a stirring speed of 45 rpm. The final cell density in self-developed, chemically defined serum-free medium (SFM) reached 2.53 × 10⁶ cells/mL, and the maximum increase in expansion was 12.61-fold. In addition, we found that fibronectin (FN) can promote hiHep attachment and proliferation on Cytodex 3 microcarriers and that this pro-proliferative effect was mediated by the integrin-β1/FAK/ERK/CyclinD1 signaling pathway. Finally, the growth and function of hiHeps on Cytodex 3 in SFM were close to those of hiHeps on Cytodex 3 in hepatocyte maintenance medium (HMM), and cells maintained their morphology and function after harvest on microcarriers.

CONCLUSIONS

Serum-free microcarrier culture has important implications for the expansion of a sufficient number of hiHeps prior to the clinical application of BALs.

An effective detachment system for human induced pluripotent stem cells cultured on multilayered cultivation substrates using resonance vibrations

Clinical application of human induced pluripotent stem cells (hiPSCs) has been hampered by the lack of a practical, scalable culture system. Stacked culture plates (SCPs) have recently attracted attention. However, final cell yields depend on the efficiency of cell detachment, and inefficient cell recovery from SCPs presents a major challenge to their use. We have developed an effective detachment method using resonance vibrations (RVs) of substrates with sweeping driving frequency. By exciting RVs that have 1–3 antinodes with ultra-low-density enzyme spread on each substrate of SCPs, 87.8% of hiPSCs were successfully detached from a 5-layer SCP compared to 30.8% detached by the conventional enzymatic method. hiPSC viability was similar after either method. Moreover, hiPSCs detached by the RV method maintained their undifferentiated state. Additionally, hiPSCs after long-term culture (10 passages) kept excellent detachment efficiency, had the normal karyotypes, and maintained the undifferentiated state and pluripotency. These results indicated that the RV method has definite advantages over the conventional enzymatic method in the scalable culture of hiPSCs using SCPs.

Intercellular Crosstalk Via Extracellular Vesicles in Tumor Milieu as Emerging Therapies for Cancer Progression

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Increasing evidence has suggested that extracellular vesicles (EV) mediated bidirectional transfer of functional molecules (such as proteins, different types of RNA, and lipids) between cancer cells and tumor stromal cells (immune cells, endothelial cells, fibroblasts, stem cells) and strongly contributed to the reinforcement of cancer progression. Thus, intercellular EV-mediated signaling in tumor microenvironment (TME) is essential in the modulation of all processes that support and promote tumor development like immune suppression, angiogenesis, invasion and metastasis, and resistance of tumor cells to anticancer treatments.

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Besides EV potential to revolutionize our understanding of the cancer cell-stromal cells crosstalk in TME, their ability to selectively transfer different cargos to recipient cells has created excitement in the field of tumortargeted delivery of specific molecules for anticancer treatments. Therefore, in tight connection with previous findings, this review brought insight into the dual role of EV in modulation of TME. Thus, on one side EV create a favorable phenotype of tumor stromal cells for tumor progression; however, as a future new class of anticancer drug delivery systems EV could re-educate the TME to overcome main supportive processes for malignancy progression.

P34HB electrospun fibres promote bone regeneration in vivo

Objective

Bone tissue engineering was introduced in 1995 and provides a new way to reconstruct bone and repair bone defects. However, the design and fabrication of suitable bionic bone scaffolds are still challenging, and the ideal scaffolds in bone tissue engineering should have a three‐dimensional porous network, good biocompatibility, excellent biodegradability and so on. The purpose of our research was to investigate whether a bioplasticpoly3‐hydroxybutyrate4‐hydroxybutyrate (P34HB) electrospun fibre scaffold is conducive to the repair of bone defects, and whether it is a potential scaffold for bone tissue engineering.

Materials and methods

The P34HB electrospun fibre scaffolds were prepared by electrospinning technology, and the surface morphology, hydrophilicity, mechanical properties and cytological behaviour of the scaffolds were tested. Furthermore, a calvarial defect model was created in rats, and through layer‐by‐layer paper‐stacking technology, the P34HB electrospun fibre scaffolds were implanted into the calvarial defect area and their effect on bone repair was evaluated.

Results

The results showed that the P34HB electrospun fibre scaffolds are interwoven with several fibres and have good porosity, physical properties and chemical properties and can promote cell adhesion and proliferation with no cytotoxicity in vitro. In addition, the P34HB electrospun fibre scaffolds can promote the repair of calvarial defects in vivo.

Conclusions

These results demonstrated that the P34HB electrospun fibre scaffold has a three‐dimensional porous network with good biocompatibility, excellent biosafety and ability for bone regeneration and repair; thus, the P34HB electrospun fibre scaffold is a potential scaffold for bone tissue engineering.

Physiological Microenvironmental Conditions in Different Scalable Culture Systems for Pluripotent Stem Cell Expansion and Differentiation

Human Pluripotent Stem Cells (PSCs) are a valuable cell type that has a wide range of biomedical applications because they can differentiate into many types of adult somatic cell. Numerous studies have examined the clinical applications of PSCs. However, several factors such as bioreactor design, mechanical stress, and the physiological environment have not been optimized. These factors can significantly alter the pluripotency and proliferation properties of the cells, which are important for the mass production of PSCs. Nutritional mass transfer and oxygen transfer must be effectively maintained to obtain a high yield. Various culture systems are currently available for optimum cell propagation by maintaining the physiological conditions necessary for cell cultivation. Each type of culture system using a different configuration with various advantages and disadvantages affecting the mechanical conditions in the bioreactor, such as shear stress. These factors make it difficult to preserve the cellular viability and pluripotency of PSCs. Additional limitations of the culture system for PSCs must also be identified and overcome to maintain the culture conditions and enable large-scale expansion and differentiation of PSCs. This review describes the different physiological conditions in the various culture systems and recent developments in culture technology for PSC expansion and differentiation.

Stem cell niche: Dynamic neighbor of stem cells

Stem cell niche is a specialized and dynamic microenvironment around the stem cells which plays a critical role in maintaining the stemness properties of stem cells. Over the years, advancement in the research activity has revealed the various important aspects of stem cell niche including cell-cell interaction, cell-extracellular matrix interaction, a large number of soluble signaling factors and various biochemical and biophysical cues (such as oxygen tension, flow, and shear and pore size). Stem cells have the potential to be a powerful tool in regenerative medicine due to their self-renewal property and immense differentiation potential. Recent progresses in in vitro culture conditions of embryonic stem cells, adult stem cells and induced pluripotent stem cells have enabled the researchers to investigate and understand the role of the microenvironment in stem cell properties. The engineered artificial stem cell niche has led to a better execution of stem cells in regenerative medicine. Here we elucidate the key components of stem cell niche and their role in niche engineering and stem cell therapeutics.

Modulating cell state to enhance suspension expansion of human pluripotent stem cells

Efficient manufacturing is critical for the translation of cell-based therapies to clinical applications. To date, high-yield expansion of human pluripotent stem cells (hPSC) in suspension bioreactors has not been reported. Here, we present a strategy to shift suspension-grown hPSC to a high-yield state without compromising their ability to differentiate to all three germ layers. In this new state, hPSC expand to densities 5.7 ± 0.2-fold higher than conventional hPSC each passage in suspension bioreactors. High-density suspension cultures enable process intensification, cost reduction, and more efficient manufacturing. This work advances cell-state engineering as a valuable tool to overcome current challenges in therapeutic cell production and processing.

The development of cell-based therapies to replace missing or damaged tissues within the body or generate cells with a unique biological activity requires a reliable and accessible source of cells. Human pluripotent stem cells (hPSC) have emerged as a strong candidate cell source capable of extended propagation in vitro and differentiation to clinically relevant cell types. However, the application of hPSC in cell-based therapies requires overcoming yield limitations in large-scale hPSC manufacturing. We explored methods to convert hPSC to alternative states of pluripotency with advantageous bioprocessing properties, identifying a suspension-based small-molecule and cytokine combination that supports increased single-cell survival efficiency, faster growth rates, higher densities, and greater expansion than control hPSC cultures. ERK inhibition was found to be essential for conversion to this altered state, but once converted, ERK inhibition led to a loss of pluripotent phenotype in suspension. The resulting suspension medium formulation enabled hPSC suspension yields 5.7 ± 0.2-fold greater than conventional hPSC in 6 d, for at least five passages. Treated cells remained pluripotent, karyotypically normal, and capable of differentiating into all germ layers. Treated cells could also be integrated into directed differentiated strategies as demonstrated by the generation of pancreatic progenitors (NKX6.1+/PDX1+ cells). Enhanced suspension-yield hPSC displayed higher oxidative metabolism and altered expression of adhesion-related genes. The enhanced bioprocess properties of this alternative pluripotent state provide a strategy to overcome cell manufacturing limitations of hPSC.

Manufacturing Exosomes: A Promising Therapeutic Platform

Extracellular vesicles, in particular the subclass exosomes, are rapidly emerging as a novel therapeutic platform. However, currently very few clinical validation studies and no clearly defined manufacturing process exist. As exosomes progress towards the clinic for treatment of a vast array of diseases, it is important to define the engineering basis for their manufacture early in the development cycle to ensure they can be produced cost-effectively at the appropriate scale. We hypothesize that transitioning to defined manufacturing platforms will increase consistency of the exosome product and improve their clinical advancement as a new therapeutic tool. We present manufacturing technologies and strategies that are being implemented and consider their application for the transition from bench-scale to clinical production of exosomes.

Pitch-tunable pillar arrays for high-throughput culture and immunohistological analysis of tumor spheroids

Tumor spheroids are multicellular, three-dimensional (3D) cell culture models closely mimicking the microenvironments of human tumors in vivo, thereby providing enhanced predictability, clinical relevancy of drug efficacy and the mechanism of action. Conventional confocal microscopic imaging remains inappropriate for immunohistological analysis due to current technical limits in immunostaining using antibodies and imaging cells grown in 3D multicellular contexts. Preparation of microsections of these spheroids represents a best alternative, yet their sub-millimeter size and fragility make it less practical for high-throughput screening. To address these problems, we developed a pitch-tunable 5 × 5 mini-pillar array chip for culturing and sectioning tumor spheroids in a high throughput manner. Tumor spheroids were 3D cultured in an alginate matrix using a twenty-five mini-pillar array which aligns to a 96-well. At least a few tens of spheroids per pillar were cultured and as many as 25 different treatment conditions per chip were evaluated, which indicated the high throughput manner of the 5 × 5 pillar array chip. The twenty-five mini-pillars were then rearranged to a transferring pitch so that spheroid-containing gel caps from all pillars can be embedded into a specimen block. Tissue array sections were then prepared and stained for immunohistological examination. The utility of this pitch-tunable pillar array was demonstrated by evaluating drug distribution and expression levels of several proteins following drug treatment in 3D tumor spheroids. Overall, our mini-pillar array provides a novel platform that can be useful for culturing tumor spheroids as well as for immunohistological analysis in a multiplexed and high throughput manner.

A pitch-tunable 5 × 5 mini-pillar array chip was developed for culturing and sectioning tumor spheroids (TSs) in a high throughput manner. TSs were cultured on the chip aligned to 96-well. TS array sections were prepared following pitch rearrangement.

Bionic Design, Materials and Performance of Bone Tissue Scaffolds

Design, materials, and performance are important factors in the research of bone tissue scaffolds. This work briefly describes the bone scaffolds and their anatomic structure, as well as their biological and mechanical characteristics. Furthermore, we reviewed the characteristics of metal materials, inorganic materials, organic polymer materials, and composite materials. The importance of the bionic design in preoperative diagnosis models and customized bone scaffolds was also discussed, addressing both the bionic structure design (macro and micro structure) and the bionic performance design (mechanical performance and biological performance). Materials and performance are the two main problems in the development of customized bone scaffolds. Bionic design is an effective way to solve these problems, which could improve the clinical application of bone scaffolds, by creating a balance between mechanical performance and biological performance.

Microcarriers with Synthetic Hydrogel Surfaces for Stem Cell Expansion

Microcarriers are scalable support surfaces for cell growth that enable high levels of expansion, and are particularly relevant for expansion of human mesenchymal stem cells (hMSCs). The goal of this study is to develop a poly(ethylene glycol) (PEG)-based microcarrier coating for hMSC expansion. Commercially available microcarriers do not offer customizability of microcarrier surface properties, including elastic modulus and surface cell adhesion ligands. The lab has previously demonstrated that tuning these material properties on PEG-based hydrogels can modulate important cellular growth characteristics, such as cell attachment and expansion, which are important in microcarrier-based culture. Eosin-Y is adsorbed to polystyrene microcarriers and used as a photoinitiator for thiol-ene polymerization under visible light. Resultant PEG coatings are over 100 µm thick and localized to microcarrier surfaces. This thickness is relevant for cells to react to mechanical properties of the hydrogel coating, and coated microcarriers support hMSC attachment and expansion. hMSC expansion is highly favorable on coated microcarriers in serum-free media, with doubling times under 25 h in the growth phase, and retained osteogenic and adipogenic differentiation capacity after culture on microcarriers. These microcarriers with defined, synthetic coatings enable tailorable surfaces for cell expansion that may be suitable for a variety of biomanufacturing applications.

Stirred tank bioreactor culture combined with serum-/xenogeneic-free culture medium enables an efficient expansion of umbilical cord-derived mesenchymal stem/stromal cells

Mesenchymal stem/stromal cells (MSC) are being widely explored as promising candidates for cell-based therapies. Among the different human MSC origins exploited, umbilical cord represents an attractive and readily available source of MSC that involves a non-invasive collection procedure. In order to achieve relevant cell numbers of human MSC for clinical applications, it is crucial to develop scalable culture systems that allow bioprocess control and monitoring, combined with the use of serum/xenogeneic (xeno)-free culture media. In the present study, we firstly established a spinner flask culture system combining gelatin-based Cultispher(®) S microcarriers and xeno-free culture medium for the expansion of umbilical cord matrix (UCM)-derived MSC. This system enabled the production of 2.4 (±1.1) x10(5) cells/mL (n = 4) after 5 days of culture, corresponding to a 5.3 (±1.6)-fold increase in cell number. The established protocol was then implemented in a stirred-tank bioreactor (800 mL working volume) (n = 3) yielding 115 million cells after 4 days. Upon expansion under stirred conditions, cells retained their differentiation ability and immunomodulatory potential. The development of a scalable microcarrier-based stirred culture system, using xeno-free culture medium that suits the intrinsic features of UCM-derived MSC represents an important step towards a GMP compliant large-scale production platform for these promising cell therapy candidates.

Cell confluency analysis on microcarriers by micro-flow imaging

The productivity of cell culture-derived vaccines grown in anchorage-dependent animal cells is limited by bioreactor surface area. One way to increase the available surface area is by growing cells as monolayers on small spheres called microcarriers, which are approximately 100-250 μm in diameter. In order for microcarrier-based cell culture to be a success, it is important to understand the kinetics of cell growth on the microcarriers. Micro-flow imaging (MFI) is a simple and powerful technique that captures images and analyzes samples as they are drawn through a precision flow cell. In addition to providing size distribution and defect frequency data to compare microcarrier lots, MFI was used to generate hundreds of images to determine cell coverage and confluency on microcarriers. Same-day manual classification of these images provided upstream cell culture teams with actionable data that informed in-process decision making (e.g. time of infection). Additionally, an automated cell coverage algorithm was developed to increase the speed and throughput of the analyses.

Stem cell niche engineering through droplet microfluidics

Stem cells reside in complex niches in which their behaviour is tightly regulated by various biochemical and biophysical signals. In order to unveil some of the crucial stem cell-niche interactions and expedite the implementation of stem cells in clinical and pharmaceutical applications, in vitro methodologies are being developed to reconstruct key features of stem cell niches. Recently, droplet-based microfluidics has emerged as a promising strategy to build stem cell niche models in a miniaturized and highly precise fashion. This review highlights current advances in using droplet microfluidics in stem cell biology. We also discuss recent efforts in which microgel technology has been interfaced with high-throughput analyses to engender screening paradigms with an unparalleled potential for basic and applied biological studies.

Insoluble fibrinogen particles for harvesting and expanding attachment-dependent cells and for trapping suspended cancer cells in the presence of blood

Fibrinogen has the potential of being used as a material to harvest and grow normal mesenchymal cells (fibroblasts, endothelial cells) or to trap cancer cells from a suspension with blood as a potential circulatory trap.Insoluble fibrinogen particles (iFP) were prepared from commercial Cohn fraction I paste (source: Kedrion). The sized iFP (~60-180 µm) were not soluble in physiologic buffers, exhibited a density of 1.2 ± 0.02, and did not aggregate or clump when mixed with whole blood or thrombin, but were degraded in lytic solutions.Cell culture studies indicated that the iFP could be used to harvest, expand and transfer normal, mammalian, attachment-dependent cells, notably fibroblasts and stem cells from bone marrow, as well as numerous cancer lines. Cells attached to iFP underwent logarithmic growth kinetics and could be transferred without trypsinization. Transplanted cancer cells-on-iFP generated characteristic tumors and retained their surface marker (by Western immuno-blot). An iFP 'cell-affinity' batch column was shown to trap MCF-7 cancer cells in the presence of red blood cells (RBCs) or serum.The scalable process for fabricating iFP retained the cell attachment properties of native fibrinogen. The results indicate that iFP has the potential to be used as a 3D cell culture matrix, and possibly to trap cancer cells from blood.

Flow characterization of a spinner flask for induced pluripotent stem cell culture application

We present detailed quantitative measurement analyses for flow in a spinner flask with spinning rates between 20 to 45 RPM, utilizing the optical velocimetry measurement technique of Particle Image Velocimetry (PIV). A partial section of the impeller was immersed in the working fluid to reduce the shear forces induced on the cells cultured on microcarriers. Higher rotational speeds improved the mixing effect in the medium at the expense of a higher shear environment. It was found that the mouse induced pluripotent stem (iPS) cells achieved the optimum number of cells over 7 days in 25 RPM suspension culture. This condition translates to 0.0984 Pa of maximum shear stress caused by the interaction of the fluid flow with the bottom surface. However, inverse cell growth was obtained at 28 RPM culture condition. Such a narrow margin demonstrated that mouse iPS cells cultured on microcarriers are very sensitive to mechanical forces. This study provides insight to biomechanical parameters, specifically the shear stress distribution, for a commercially available spinner flask over a wide range of Reynolds number.

Optimization of agitation speed in spinner flask for microcarrier structural integrity and expansion of induced pluripotent stem cells

In recent times, the study and use of induced pluripotent stem cells (iPSC) have become important in order to avoid the ethical issues surrounding the use of embryonic stem cells. Therapeutic, industrial and research based use of iPSC requires large quantities of cells generated in vitro. Mammalian cells, including pluripotent stem cells, have been expanded using 3D culture, however current limitations have not been overcome to allow a uniform, optimized platform for dynamic culture of pluripotent stem cells to be achieved. In the current work, we have expanded mouse iPSC in a spinner flask using Cytodex 3 microcarriers. We have looked at the effect of agitation on the microcarrier survival and optimized an agitation speed that supports bead suspension and iPS cell expansion without any bead breakage. Under the optimized conditions, the mouse iPSC were able to maintain their growth, pluripotency and differentiation capability. We demonstrate that microcarrier survival and iPS cell expansion in a spinner flask are reliant on a very narrow range of spin rates, highlighting the need for precise control of such set ups and the need for improved design of more robust systems.

Scalable expansion of human-induced pluripotent stem cells in xeno-free microcarriers

The expansion of human-induced pluripotent stem cells (hiPSCs) is commonly performed using feeder layers of mouse embryonic fibroblasts or in feeder-free conditions in two-dimensional culture platforms, which are associated with low production yields and lack of process control. Robust large-scale production of these cells under defined conditions has been one of the major challenges to fulfil the large cell number requirement for drug screening applications, toxicology assays, disease modeling and potential cellular therapies. Microcarrier-based systems, in particular, are a promising culture format since they provide a high surface-to-volume ratio and allow the scale-up of the process to stirred suspension bioreactors. In this context, this chapter describes a detailed methodology for the scalable expansion of hiPSCs in spinner flasks and using xeno-free microcarriers to allow further translation to Good Manufacturing Practice (GMP) conditions.

Improving embryonic stem cell expansion through the combination of perfusion and Bioprocess model design

BACKGROUND

High proliferative and differentiation capacity renders embryonic stem cells (ESCs) a promising cell source for tissue engineering and cell-based therapies. Harnessing their potential, however, requires well-designed, efficient and reproducible expansion and differentiation protocols as well as avoiding hazardous by-products, such as teratoma formation. Traditional, standard culture methodologies are fragmented and limited in their fed-batch feeding strategies that afford a sub-optimal environment for cellular metabolism. Herein, we investigate the impact of metabolic stress as a result of inefficient feeding utilizing a novel perfusion bioreactor and a mathematical model to achieve bioprocess improvement.

METHODOLOGY/PRINCIPAL FINDINGS

To characterize nutritional requirements, the expansion of undifferentiated murine ESCs (mESCs) encapsulated in hydrogels was performed in batch and perfusion cultures using bioreactors. Despite sufficient nutrient and growth factor provision, the accumulation of inhibitory metabolites resulted in the unscheduled differentiation of mESCs and a decline in their cell numbers in the batch cultures. In contrast, perfusion cultures maintained metabolite concentration below toxic levels, resulting in the robust expansion (>16-fold) of high quality 'naïve' mESCs within 4 days. A multi-scale mathematical model describing population segregated growth kinetics, metabolism and the expression of selected pluripotency ('stemness') genes was implemented to maximize information from available experimental data. A global sensitivity analysis (GSA) was employed that identified significant (6/29) model parameters and enabled model validation. Predicting the preferential propagation of undifferentiated ESCs in perfusion culture conditions demonstrates synchrony between theory and experiment.

CONCLUSIONS/SIGNIFICANCE

The limitations of batch culture highlight the importance of cellular metabolism in maintaining pluripotency, which necessitates the design of suitable ESC bioprocesses. We propose a novel investigational framework that integrates a novel perfusion culture platform (controlled metabolic conditions) with mathematical modeling (information maximization) to enhance ESC bioprocess productivity and facilitate bioprocess optimization.

Engineering stem cell fate with biochemical and biomechanical properties of microcarriers

Microcarriers have been widely used for various biotechnology applications because of their high scale-up potential, high reproducibility in regulating cellular behavior, and well-documented compliance with current Good Manufacturing Practices (cGMP). Recently, microcarriers have been emerging as a novel approach for stem cell expansion and differentiation, enabling potential scale-up of stem cell-derived products in large bioreactors. This review summarizes recent advances of using microcarriers in mesenchymal stem cell (MSC) and pluripotent stem cell (PSC) cultures. From the reported data, efficient expansion and differentiation of stem cells on microcarriers rely on their ability to modulate cell shape (i.e. round or spreading) and cell organization (i.e. aggregate size). Nonetheless, current screening of microcarriers remains empirical, and accurate understanding of how stem cells interact with microcarriers still remains unknown. This review suggests that accurate characterization of biochemical and biomechanical properties of microcarriers is required to fully exploit their potential in regulating stem cell fate decision. Due to the variety of microcarriers, such detailed analyses should lead to the rational design of application-specific microcarriers, enabling the exploitation of reproducible effects for large scale biomedical applications.

Oxygen-controlled automated neural differentiation of mouse embryonic stem cells

Automation and oxygen tension control are two tools that provide significant improvements to the reproducibility and efficiency of stem cell production processes.

AIM

the aim of this study was to establish a novel automation platform capable of controlling oxygen tension during both the cell-culture and liquid-handling steps of neural differentiation processes.

MATERIALS & METHODS

We built a bespoke automation platform, which enclosed a liquid-handling platform in a sterile, oxygen-controlled environment. An airtight connection was used to transfer cell culture plates to and from an automated oxygen-controlled incubator.

RESULTS

Our results demonstrate that our system yielded comparable cell numbers, viabilities, metabolism profiles and differentiation efficiencies when compared with traditional manual processes. Interestingly, eliminating exposure to ambient conditions during the liquid-handling stage resulted in significant improvements in the yield of MAP2-positive neural cells, indicating that this level of control can improve differentiation processes.

CONCLUSION

This article describes, for the first time, an automation platform capable of maintaining oxygen tension control during both the cell-culture and liquid-handling stages of a 2D embryonic stem cell differentiation process.

Ex vivo expansion of cord blood haematopoietic stem/progenitor cells under physiological oxygen tensions: clear-cut effects on cell proliferation, differentiation and metabolism

Physiologically low O(2) tensions are believed to regulate haematopoietic stem cell (HSC) functions in the bone marrow (BM; 0-5%). In turn, placenta and umbilical cord are characterized by slightly higher physiological O(2) tensions (3-10%). We hypothesized that O(2) concentrations within this range may be exploited to augment the ex vivo expansion/maintenance of HSCs from umbilical cord (placental) blood (UCB). The expansion of UCB CD34(+) -enriched cells was studied in co-culture with BM mesenchymal stem/stromal cells (MSCs) under 2%, 5%, 10% and 21% O(2). 2% O(2) resulted in a significantly lower CD34(+) cell expansion (25-fold vs 60-, 64- and 92-fold at day 10 for 5%, 21%, 10% O(2), respectively). In turn, 10% O(2) promoted the highest CD34(+) CD90(+) cell expansion, reaching 22 ± 5.4- vs 5.6 ± 2.4- and 5.7 ± 2.0-fold for 2%, 5% and 21% O(2), respectively, after 14 days. Similar differentiation patterns were observed under different O(2) tensions, being primarily shifted towards the neutrophil lineage. Cell division kinetics revealed a higher proliferative status of cells cultured under 10% and 21% vs 2% O(2). Expectedly, higher specific glucose consumption and lactate production rates were determined at 2% O(2) when compared to higher O(2) concentrations (5-21%). Overall, these results suggest that physiological oxygen tensions, in particular 10% O(2), can maximize the ex vivo expansion of UCB stem/progenitor cells in co-culture with BM MSCs. Importantly, these studies highlight the importance of exploiting knowledge of the intricate microenvironment of the haematopoietic niche towards the definition of efficient and controlled ex vivo culture systems capable of generating large HSCs numbers for clinical applications.

Stem cell bioengineering strategies to widen the therapeutic applications of haematopoietic stem/progenitor cells from umbilical cord blood

Umbilical cord blood (UCB) transplantation has observed a significant increase in recent years, due to the unique features of UCB haematopoietic stem/progenitor cells (HSCs) for the treatment of blood-related disorders. However, the low cell numbers available per UCB unit significantly impairs the widespread use of this source for transplantation of adult patients, resulting in graft failure, delayed engraftment and delayed immune reconstitution. In order to overcome this issue, distinct approaches are now being considered in clinical trials, such as double-UCB transplantation, intrabone injection or ex vivo expansion. In this article the authors review the current state of the art, future trends and challenges on the ex vivo expansion of UCB HSCs, focusing on culture parameters affecting the yield and quality of the expanded HSC grafts: novel HSC selection schemes prior to cell culture, cytokine/growth factor cocktails, the impact of biochemical factors (e.g. O2 ) or the addition of supportive cells, e.g. mesenchymal stem/stromal cell (MSC)-based feeder layers) were addressed. Importantly, a critical challenge in cellular therapy is still the scalability, reproducibility and control of the expansion process, in order to meet the clinical requirements for therapeutic applications. Efficient design of bioreactor systems and operation modes are now the focus of many bioengineers, integrating the increasing 'know-how' on HSC biology and physiology, while complying with the GMP standards for the production of cellular products, i.e. through the use of commercially available, highly controlled, disposable technologies.