Attachment kinetics of vero cells onto CT-3 microcarriers

Seed Train Optimization in Microcarrier-Based Cell Culture Post In Situ Cell Detachment through Scale-Down Hybrid Modeling

Microcarrier-based cell culture is a commonly used method to facilitate the growth of anchorage-dependent cells like MA 104 for antigen manufacturing. However, conventionally, static cell culture is employed for cell propagation before seeding the production bioreactor with microcarriers (MCs). This study demonstrates the effective replacement of the conventional method by serial subculturing on MCs with in situ cell detachment under optimal conditions in closed culture units. This study proves that MA 104 can be subcultured at least five times on Cytodex 1 MC without the need for separating cells and MC after cell harvest. Process parameters impacting cell growth were studied post in situ cell detachment in a scaled-down model. Optimization, using augmented Design of Experiments (DoE) combined with hybrid modeling, facilitated rapid screening of the design space for critical process parameters (CPPs). Optimized conditions included an inoculation density of >16 cells/bead, 3.5-4.5 g/L of Cytodex 1, and a controlled agitation speed, starting at Njs (minimum agitation speed) for the first day with a maximum increase of 25% thereafter. With these design spaces for CPPs, a cell density of 2.6 ± 0.5 × 106 cells/mL was achieved after five days. This refined bioprocess methodology offers a reliable and efficient approach for seed training in stirred tank reactors, which is particularly beneficial for viral vaccine production.

Large-Scale Microcarrier Culture of Chinese Perch Brain Cell for Viral Vaccine Production in a Stirred Bioreactor

Mandarin fish (Siniperca chuatsi) is one of the important cultured fish species in China. Infectious spleen and kidney necrosis virus (ISKNV) and Siniperca Chuatsi rhabdovirus (SCRV) have hindered the development of mandarin fish farming industry. Vaccination is the most effective method for control of viral diseases, however viral vaccine production requires the large-scale culture of cells. Herein, a suspension culture system of Chinese perch brain cell (CPB) was developed on Cytodex 1 microcarrier in a stirred bioreactor. Firstly, CPB cells were cultured using Cytodex 1 microcarrier in 125 mL stirring flasks. With the optimum operational parameters, CPB cells grew well, distributed uniformly, and could fully cover the microcarriers. Then, CPB cells were digested with trypsin and expanded step-by-step with different expansion ratios from the 125 mL stirring bottle to a 500 mL stirring bottle, and finally to a 3-L bioreactor. Results showed that with an expansion ratio of 1:3, we achieved a high cell density level (2.25 × 10⁶ cells/mL) with an efficient use of the microcarriers, which also confirmed the data obtained from the 125 mL stirring flask. Moreover, obvious cytopathic effects (CPE) were observed in the suspended CPB cells post-infection with ISKNV and SCRV. This study provided a large-scale culture system of CPB cells for virus vaccine production.

Improved expansion of human bone marrow-derived mesenchymal stem cells in microcarrier-based suspension culture

Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) have potential clinical utility in the treatment of a multitude of ailments and diseases, due to their relative ease of isolation from patients and their capacity to form many cell types. However, hBM-MSCs are sparse, and can only be isolated in very small quantities, thereby hindering the development of clinical therapies. The use of microcarrier-based stirred suspension bioreactors to expand stem cell populations offers an approach to overcome this problem. Starting with standard culture protocols commonly reported in the literature, we have successfully developed new protocols that allow for improved expansion of hBM-MSCs in stirred suspension bioreactors using CultiSpher-S microcarriers. Cell attachment was facilitated by using intermittent bioreactor agitation, removing fetal bovine serum, modifying the stirring speed and manipulating the medium pH. By manipulating these parameters, we enhanced the cell attachment efficiency in the first 8 h post-inoculation from 18% (standard protocol) to 72% (improved protocol). Following microcarrier attachment, agitation rate was found to impact cell growth kinetics, whereas feeding had no significant effect. By serially subculturing hBM-MSCs using the new suspension bioreactor protocols, we managed to obtain cell fold increases of 10³ within 30 days, which was superior to the 200-fold increase obtained using the standard protocol. The cells were found to retain their defining characteristics after several passages in suspension. This new bioprocess represents a more efficient approach for generating large numbers of hBM-MSCs in culture, which in turn should facilitate the development of new stem cell-based therapies.

Polymer-based microparticles in tissue engineering and regenerative medicine

Different types of biomaterials, processed into different shapes, have been proposed as temporary support for cells in tissue engineering (TE) strategies. The manufacturing methods used in the production of particles in drug delivery strategies have been adapted for the development of microparticles in the fields of TE and regenerative medicine (RM). Microparticles have been applied as building blocks and matrices for the delivery of soluble factors, aiming for the construction of TE scaffolds, either by fusion giving rise to porous scaffolds or as injectable systems for in situ scaffold formation, avoiding complicated surgery procedures. More recently, organ printing strategies have been developed by the fusion of hydrogel particles with encapsulated cells, aiming the production of organs in in vitro conditions. Mesoscale self-assembly of hydrogel microblocks and the use of leachable particles in three-dimensional (3D) layer-by-layer (LbL) techniques have been suggested as well in recent works. Along with innovative applications, new perspectives are open for the use of these versatile structures, and different directions can still be followed to use all the potential that such systems can bring. This review focuses on polymeric microparticle processing techniques and overviews several examples and general concepts related to the use of these systems in TE and RE applications. The use of materials in the development of microparticles from research to clinical applications is also discussed.

Growth behavior of number distributed adherent MDCK cells for optimization in microcarrier cultures

An assay for measuring the number of adherent cells on microcarriers that is independent from dilution errors in sample preparation was used to investigate attachment dynamics and cell growth. It could be shown that the recovery of seeded cells is a function of the specific rates of cell attachment and cell death, and finally a function of the initial cell-to-bead ratio. An unstructured, segregated population balance model was developed that considers individual classes of microcarriers covered by 1-220 cells/bead. The model describes the distribution of initially attached cells and their growth in a microcarrier system. The model distinguishes between subpopulations of dividing and nondividing cells and describes in a detailed way cell attachment, cell growth, density-dependent growth inhibition, and basic metabolism of Madin-Darby canine kidney cells used in influenza vaccine manufacturing. To obtain a model approach that is suitable for process control applications, a reduced growth model without cell subpopulations, but with a formulation of the specific cell growth rate as a function of the initial cell distribution on microcarriers after seeding was developed. With both model approaches, the fraction of growth-inhibited cells could be predicted. Simulation results of two cultivations with a different number of initially seeded cells showed that the growth kinetics of adherent cells at the given cultivation conditions is mainly determined by the range of disparity in the initial distribution of cells on microcarriers after attachment.

A 3D collagen microsphere culture system for GDNF-secreting HEK293 cells with enhanced protein productivity

Mammalian cell culture technology has been used for decades in mass production of therapeutic proteins. However, unrestricted cell proliferation usually results in low-protein productivity. Controlled proliferation technologies such as metabolism intervention and genetic manipulation are therefore applied to enhance the productivity. Nevertheless, these strategies induced growth arrest with reduced viability and increased apoptosis. In this study, we report a new controlled proliferation technology by encapsulating human embryonic kidney (HEK) 293 cells over-expressing glial-derived neurotrophic factor (GDNF) in 3D collagen microspheres for extended culture. We investigated the viability, proliferation, cell cycle and GDNF productivity of HEK293 cells in microspheres as compared to monolayer culture. This system provides a physiologically relevant tissue-like environment for cells to grow and exerts proliferation control throughout the culture period without compromising the viability. A significant increase in the production rate of GDNF was found in the 3D microsphere system comparing with the monolayer culture. GDNF productivity was also significantly affected by the initial cell number and the serum concentration. The secreted GDNF was still bioactive as it induced neurite extension in PC12 cells. In summary, the 3D collagen microsphere system presents a cost-effective controlled growth technology for protein production in pharmaceutical manufacturing.

Polyethylene glycol-based cationically charged hydrogel beads as a new microcarrier for cell culture

A new polyethylene glycol (PEG) based microcarrier was designed and examined by the attachment and growth of mouse fibroblast cells. In the design of microcarrier, a PEG-based macromonomer, polyethyleneglycol methacrylate (PEGMA), was selected as the main component of hydrogel beads since PEG is known as a nontoxic and biocompatible material. A relatively new cationic comonomer, N-[3-(dimethylamino)propyl]methacrylamide (DMAPM), with higher ionization ability with respect to the similar comonomers was used for providing cationic charge to the hydrogel structure. In the first part, a suspension copolymerization method was developed for the production of cationically charged hydrogel beads as a potential microcarrier for cell culturing. The suspension copolymerization by using ethylene dimethacrylate (EDM) as cross-linking agent and cyclohexanol as the diluent provided spherical, polydisperse poly(PEGMA-DMAPM-EDM) hydrogel beads with an average size of 121 microm. The hydrogel beads exhibited a pH-dependent swelling behavior. The L929 mouse fibroblast cells were cultured on poly(PEGMA-DMAPM-EDM) hydrogel beads with an initial concentration of 200,000 cells/mL. The cells were incubated in Dulbecco's modified Eagle's medium during 5 days and the cell proliferation was investigated at every 24 h. An effective cell attachment and growth up to 3.5 x 10(6) cells/mL were observed with the poly(PEGMA-DMAPM-EDM) hydrogel beads. The results indicated that the proposed microcarrier was a significant alternative to the hydrogel beads obtained by the copolymerization of 2-hydroxyethyl methacrylate and 2-dimethylaminoethylmethacrylate commonly used in microcarrier-facilitated cell culturing studies.

Effects of mixing intensity on cell seeding and proliferation in three-dimensional fibrous matrices

Nonwoven fibrous matrices have been widely used in cell and tissue cultures because their three-dimensional (3-D) structures with large surface areas and pore spaces can support high-density cell growth. Although cell adherence and growth on 2-D surfaces have been thoroughly investigated, very little is known for cells cultured in 3-D matrices. The effects of mixing intensity on cell seeding, adherence, and growth in fibrous matrices were thus investigated. Chinese Hamster Ovary and osteosarcoma cells were inoculated into nonwoven polyethylene terephthalate matrices by dynamic and static seeding methods, of which the former was found to be superior in seeding efficiency and cell distribution in the matrices. Dynamic seeding increased seeding efficiency from approximately 40% to more than 90%. When higher mixing intensities were applied, both cell attachment and detachment rates increased. Cell attachment was transport limited, as indicated by the increased attachment rate with increasing the mass transfer coefficient of the cells. Meanwhile, cell detachment from the 3-D matrix can be described by the Bell model. The effects of matrix pore size on cell adherence and proliferation were also investigated. In general, the smaller pore size is favorable to cell attachment and proliferation. Further analysis revealed that the interaction between mixing intensity and pore size played a vital role in hydrodynamic damage to cells, which was found to be significant when the Kolomogorov eddy size was smaller than the matrix pores. Increasing mixing intensity also increased oxygen transfer, decreased the lactate yield from glucose, and improved cell growth.