Cell growth and differentiation on feeder layers is predicted to be influenced by bioreactor geometry

Consumer Acceptance and Production of In Vitro Meat: A Review

In vitro meat (IVM) is a recent development in the production of sustainable food. The consumer perception of IVM has a strong impact on the commercial success of IVM. Hence this review examines existing studies related to consumer concerns, acceptance and uncertainty of IVM. This will help create better marketing strategies for IVM-producing companies in the future. In addition, IVM production is described in terms of the types of cells and culture conditions employed. The applications of self-organising, scaffolding, and 3D printing techniques to produce IVM are also discussed. As the conditions for IVM production are controlled and can be manipulated, it will be feasible to produce a chemically safe and disease-free meat with improved consumer acceptance on a sustainable basis.

Biomanufacturing of Therapeutic Cells: State of the Art, Current Challenges, and Future Perspectives

Stem cells and other functionally defined therapeutic cells (e.g., T cells) are promising to bring hope of a permanent cure for diseases and disorders that currently cannot be cured by conventional drugs or biological molecules. This paradigm shift in modern medicine of using cells as novel therapeutics can be realized only if suitable manufacturing technologies for large-scale, cost-effective, reproducible production of high-quality cells can be developed. Here we review the state of the art in therapeutic cell manufacturing, including cell purification and isolation, activation and differentiation, genetic modification, expansion, packaging, and preservation. We identify current challenges and discuss opportunities to overcome them such that cell therapies become highly effective, safe, and predictively reproducible while at the same time becoming affordable and widely available.

Unilineage model of hematopoiesis predicts self-renewal of stem and progenitor cells based on ex vivo growth data

Stem cell models are used to describe the function of several tissues. We present unilineage kinetic description of stem cell models and their application to the analysis of ex vivo hematopoietic cell expansion data. This model has the capability to simulate the total cell number and the number of cells at each stage of differentiation over time as a function of the stem cell self-renewal probability, the growth rate of each subpopulation, and the mature cell death rate. The model predicts experimental observations in perfusion-based hematopoietic bioreactor systems. To obtain net cell expansion ex vivo, the model simulations show that the stem cell self-renewal probability must exceed one-half, thus resulting in net expansion of the stem cell population. Experimental data on long-term culture-initiating cells (LTC-IC) confirm this prediction and the probability of self-renewal is estimated to be 0.62 to 0.73. This self-renewal probability, along with the death rate, define a relationship in which the apparent overall growth rate is less than the compartmental growth rate. Finally, the model predicts that cells beyond the stem cell stage of differentiation must self-renew to achieve the level of expansion within the time frame observed in experimental systems. (c) 1996 John Wiley & Sons, Inc.

MECHANICS OF ACTIVE POROUS MEDIA: BONE TISSUE ENGINEERING APPLICATION

In orthopedics, a currently developed technique for large graft hybrid implants consists of using porous and biocompatible scaffolds seeded with a patient's bone cells. Successful culture in such large implants remains a challenge for biologists, and requires strict control of the physicochemical and mechanical environments achieved by perfusion within a bioreactor for several weeks. This perfusion, with a nutritive fluid carrying solute ingredients, is necessary for the active cells to grow, proliferate, differentiate, and produce extracellular matrices. An understanding and control of these processes, which lead to substrate degradation and extracellular matrix remodeling during the in vitro culture phase, depend widely on the success in the realization of new orthopedic biomaterials. Within this context, the analysis of the interactions between convective phenomena of hydrodynamic origin and chemical reactions of biological order which are associated to these processes is a fundamental challenge in the framework of bone tissue engineering. In order to better account for the different intricate processes taking place in such a sample and to design a relevant experimental protocol leading to the definition of an optimal tissue implant, we propose one- and two-dimensional theoretical models based on transport phenomena in porous active media.

Stem cell cultivation in bioreactors

Cell-based therapies have generated great interest in the scientific and medical communities, and stem cells in particular are very appealing for regenerative medicine, drug screening and other biomedical applications. These unspecialized cells have unlimited self-renewal capacity and the remarkable ability to produce mature cells with specialized functions, such as blood cells, nerve cells or cardiac muscle. However, the actual number of cells that can be obtained from available donors is very low. One possible solution for the generation of relevant numbers of cells for several applications is to scale-up the culture of these cells in vitro. This review describes recent developments in the cultivation of stem cells in bioreactors, particularly considerations regarding critical culture parameters, possible bioreactor configurations, and integration of novel technologies in the bioprocess development stage. We expect that this review will provide updated and detailed information focusing on the systematic production of stem cell products in compliance with regulatory guidelines, while using robust and cost-effective approaches.

Engineered bone culture in a perfusion bioreactor: a 2D computational study of stationary mass and momentum transport

Successful bone cell culture in large implants still is a challenge to biologists and requires a strict control of the physicochemical and mechanical environments. This study analyses from the transport phenomena viewpoint the limiting factors of a perfusion bioreactor for bone cell culture within fibrous and porous large implants (2.5 cm in length, a few cubic centimetres in volume, 250 microm in fibre diameter with approximately 60% porosity). A two-dimensional mathematical model, based upon stationary mass and momentum transport in these implants is proposed and numerically solved. Cell oxygen consumption, in accordance theoretically with the Michaelis-Menten law, generates non linearity in the boundary conditions of the convection diffusion equation. Numerical solutions are obtained with a commercial code (Femlab 3.1; Comsol AB, Stockholm, Sweden). Moreover, based on the simplification of transport equations, a simple formula is given for estimating the length of the oxygen penetration within the implant. Results show that within a few hours of culture process and for a perfusion velocity of the order of 10(-4) m s(-1), the local oxygen concentration is everywhere sufficiently high to ensure a suitable cell metabolism. But shear stresses induced by the fluid flow with such a perfusion velocity are found to be locally too large (higher than 10(-3) Pa). Suitable shear stresses are obtained by decreasing the velocity at the inlet to around 2 x 10(-5) m s(-1). But consequently hypoxic regions (low oxygen concentrations) appear at the downstream part of the implant. Thus, it is suggested here that in the determination of the perfusion flow rate within a large implant, a compromise between oxygen supply and shear stress effects must be found in order to obtain a successful cell culture.

Theoretical analysis of engineered cartilage oxygenation: influence of construct thickness and media flow rate

A novel parallel-plate bioreactor has been shown to modulate the mechanical and biochemical properties of engineered cartilage by the application of fluid-induced shear stress. Flow or perfusion bioreactors may improve tissue development via enhanced transport of nutrients or gases as well as the application of mechanical stimuli, or a combination of these factors. The goal of this study was to complement observed experimental responses to flow by simulating oxygen transport within cartilage constructs of different thicknesses (250 microm or 1 mm). Using numerical computation of convection-diffusion equations, the evaluation of the tissue oxygenation is performed. Four culture conditions are defined based on tissue thickness and flow rates ranging from 0 to approximately 25 mL min(-1). Under these experimental conditions results show a mean oxygen concentration within the tissue varying from 0.01 to 0.19 mol m(-3) as a function of the tissue thickness and the magnitude of the applied shear stress. More generally, the influence of shear stress varying (via flow rate modification) from 10(-3) to 10 dynes cm(-2) on the tissue oxygenation is studied. The influence on the results of important physical parameters such as the maximal oxygen consumption rate of cells is discussed. Lastly, the importance of oxygen concentration in the lower chamber and its relevance to tissue oxygenation are highlighted by the model results.

Ex vivo expansion of hematopoietic stem cells derived from umbilical cord blood in rotating wall vessel

Expansion of umbilical cord blood mononuclear cells (UCB MNCs) was carried out in a rotating wall vessel (RWV) bioreactor and tissue culture flasks (T-flasks) in serum-containing medium supplemented with relatively low doses of purified recombinant human cytokines (5.33 ng/ml IL-3, 16 ng/ml SCF, 3.33 ng/ml G-CSF, 2.13 ng/ml GM-CSF, 7.47 ng/ml FL and 7.47 ng/ml TPO) for 8 days. The cell density, pH and osmolality of the culture medium in the two culture systems were measured every 24h. Flow cytometric assay for CD34+ cells was carried out at 0, 144 and 197 h and methylcellulose colony assays were performed at 0, 72, 144 and 197 h. The pH and osmolality of the medium in the two culture systems were maintained in the proper ranges for hematopoietic stem cells (HSCs) and progenitors culture. The RWV bioreactor, combined with a cell-dilution feeding protocol, was efficient to expand UCB MNCs. At the end of 200 h culture, the total cell number was multiplied by 435.5+/-87.6 times, and CD34+ cells 32.7+/-15.6 times, and colony-forming units of granulocyte-macrophage (CFU-GM) 21.7+/-4.9 times. While in T-flasks, however, total cells density changed mildly, CD34+ cells and CFU-GM decreased in number. It is demonstrated that the RWV bioreactor can provide a better environment for UCB MNCs expansion, enhance the contact between HSCs and accessory cells and make the utilization of cytokines more effective than T-flask.

Hematopoietic stem cells: from the bone to the bioreactor

The ex vivo expansion of human hematopoietic stem cells is a rapidly developing area with a broad range of biomedical applications. The mechanisms of renewal, differentiation and plasticity of stem cells are currently under intense investigation. However, the complexity of hematopoiesis, the heterogeneity of the culture population and the complex interplay between the culture parameters that significantly influence the proliferation and differentiation of hematopoietic cells have impaired the translation of small scale results to the highly demanded large-scale applications. The better understanding of these mechanisms is providing the basis for more rational approaches to the ex vivo expansion of hematopoietic stem cells. Efforts are now being made to establish a rational design of bioreactor systems, allowing the modeling and control of large-scale production of stem cells and the study of their proliferation and differentiation, under conditions as similar as possible to those in vivo.

Perfusion culture of hepatocytes within galactose-derivatized biodegradable poly(lactide-co-glycolide) scaffolds prepared by gas foaming of effervescent salts

Galactose, a specific ligand for asialoglycoprotein receptor in hepatocytes, was immobilized onto the internal surface of highly porous biodegradable poly(D,L-lactic-co-glycolic acid) scaffolds prepared by gas foaming of effervescent salts. Rat hepatocytes seeded within the scaffolds were cultivated by using a continuous flow and perfusion reactor system. Flow rate of medium circulating through the closed loop bioreactor system was optimized to minimize the extent of cell washout from the scaffold/cell construct while satisfying the oxygen transport rate to the seeded hepatocytes. Using the flow culture system, the scaffolds immobilized with galactose onto its internal surface retained a greater number of hepatocytes than those with unmodified or immobilized with glucose due to specific interactions between seeded hepatocytes and galactose moieties exposed onto the surface of the scaffolds. The perfusion culture system based on galactose-modified macroporous scaffolds, under optimal flow conditions, resulted in much higher albumin secretion rate, approximately 70 pg/cell/day for 7 days, compared to that with glucose modified scaffolds used as a negative control. The enhanced functional activity of hepatocytes seeded within the galactose modified scaffolds was likely caused by the formation of aggregated hepatocytes within the scaffolds.

Effective intercellular communication distances are determined by the relative time constants for cyto/chemokine secretion and diffusion

A cell's ability to effectively communicate with a neighboring cell is essential for tissue function and ultimately for the organism to which it belongs. One important mode of intercellular communication is the release of soluble cyto- and chemokines. Once secreted, these signaling molecules diffuse through the surrounding medium and eventually bind to neighboring cell's receptors whereby the signal is received. This mode of communication is governed both by physicochemical transport processes and cellular secretion rates, which in turn are determined by genetic and biochemical processes. The characteristics of transport processes have been known for some time, and information on the genetic and biochemical determinants of cellular function is rapidly growing. Simultaneous quantitative analysis of the two is required to systematically evaluate the nature and limitations of intercellular signaling. The present study uses a solitary cell model to estimate effective communication distances over which a single cell can meaningfully propagate a soluble signal. The analysis reveals that: (i) this process is governed by a single, key, dimensionless group that is a ratio of biological parameters and physicochemical determinants; (ii) this ratio has a maximal value; (iii) for realistic values of the parameters contained in this dimensionless group, it is estimated that the domain that a single cell can effectively communicate in is approximately 250 micron in size; and (iv) the communication within this domain takes place in 10-30 minutes. These results have fundamental implications for interpretation of organ physiology and for engineering tissue function ex vivo.

Importance of parenchymal:stromal cell ratio for the ex vivo reconstitution of human hematopoiesis

Many new developments in tissue engineering rely on the culture of primary tissues which is composed of parenchymal and mesenchymal (stromal) cell populations. Because stroma regulates parenchymal function, the parenchymal:stromal cell (P:S) ratio will likely influence culture behavior. To investigate parenchymal-stromal cell interactions, the P:S ratio was systematically varied in a human bone marrow (BM) culture system, measuring the output of mature cells, immature progenitors (colony forming units-granulocyte/macrophage [CFU-GM]), and primitive stem cells (long-term culture-initiating cells [LTC-IC]). When parenchymal CD34-enriched cells were grown without stroma, cell and CFU-GM output increased linearly as inoculum density was increased, resulting in constant cell and CFU-GM expansion ratios. On irradiated preformed stroma (IPFS), culture output was significantly higher and less dependent on CD34-enriched cell inoculum density, resulting in greater expansion ratios at lower inoculum densities. The number of IPFS cells required to support CD34-enriched cells was independent of the CD34-enriched cell number, suggesting that IPFS did not provide discrete niches, but instead acted through soluble signals. Experiments using conditioned medium (CM) from IPFS confirmed the presence of soluble signals, but CM did not completely substitute for direct contact between CD34-enriched cells and IPFS. Because of known differences between IPFS and stroma growing within BM mononuclear cell (MNC) cultures, experiments were next performed using mixtures of CD34-enriched and CD34-depleted fractions of MNC. When inoculated with a fixed CD34+lin- cell number, culture output was optimal near the P:S ratio of the unmanipulated MNC sample and declined as CD34- cell number was increased or decreased. In cultures inoculated with a fixed total cell number, CFU-GM output increased as CD34+lin- cell number was increased, whereas LTC-IC output reached a plateau. These data suggest that a limited number of LTC-IC supportive niches were present in MNC stroma, whereas IPFS lacks these niches and acts predominantly through a less potent soluble mechanism. These studies underscore the importance of parenchymal-stromal cell interactions in the ex vivo reconstitution of tissue function and offer insight into the nature of these interactions in the human BM culture system.