An Overview of Microcarrier Culture Technology

Microcarriers are microbeads with a diameter of 60-250 μm, which are suitable for the growth of adherent cells. It is generally composed of natural dextran or various synthetic polymers.

1. Microcarrier culture application

This technology was used for large-scale cultivation of animal cells in 1967. After more than 30 years of development, the technology has been gradually improved and matured, and is widely used in the production of vaccines and genetic engineering products.

Microcarrier culture is currently recognized as the most promising technology for large-scale animal cell culture. It combines the advantages of suspension culture and adherent culture, and is easy to scale up. At present, microcarrier bead assayculture is widely used to cultivate various types of cells to produce vaccines and protein products, such as 293 cells, myoblasts, Vero cells, and CHO cells.

There are two types of reactors that are commonly used: BIOSTAT?B reactor of Beiran Company, which uses a double-blade bubble-free aeration stirring system; NBS's CelliGen, CelliGen PlusTM, and Bioflo3000 reactors, which use Cell-lift double-screen stirring system. Both systems can achieve effective separation of cultured cells and harvested products.

2. Microcarriers

It refers to microbeads with a diameter of 60-250 μm, which are suitable for the growth of adherent cells. It is generally composed of natural dextran or various synthetic polymers.

Since the first microcarrier developed by Van Wezel with DEAE-Sephadex A 50, there have been more than a dozen types of microcarrier products sold on the international market, including liquid microcarriers, macroporous gelatin microcarriers, and polystyrene. Microcarriers, PHEMA microcarriers, chitin microcarriers, polyurethane foam microcarriers, alginate gel microcarriers, magnetic microcarriers, etc. There are three commonly used commercial microcarriers: Cytodex 1, 2, 3, Cytopore and Cytoline.

The size of the microcarrier: increasing the surface area per unit volume (S/F) is very beneficial to the growth of cells. Keep the diameter of the microcarrier as small as possible, preferably between 100-200μm.

The density of microcarriers is generally 1.03-1.05g/cm2. As the cells attach and grow, the density can gradually increase.

Surface charge of microcarriers: According to research, the basic factor controlling cell adhesion is charge density rather than charge properties. If the charge density is too low, the attachment of cells is insufficient, but if the charge density is too large, it will have a "toxic" effect.

3. Principle and operation of microcarrier culture

1. Principle: The principle is to add the particle-microcarrier, which is harmless to the cells, to the culture solution of the culture container, as a carrier, so that the cells adhere to and grow on the surface of the microcarrier, and at the same time, the microcarrier is always kept suspended by continuous agitation.

The proliferation of adherent-dependent cells on the surface of microcarriers has to go through three stages of adherence, growth, and expansion into a single layer. Cells can only proliferate by attaching to the surface of a solid substrate, so the attachment of cells to the surface of microcarriers is the key to further spreading and growth. Adhesion mainly depends on electrostatic attraction and van der Waals force.

Whether cells can adhere to the surface of microcarriers depends on the contact probability and compatibility of cells and microcarriers.

2. Stirring speed: Because animal cells have no cell wall and are sensitive to shear forces, it is impossible to increase the probability of contact by increasing the stirring speed. The usual method of operation is to use a low stirring speed during the attachment period and stop when stirring; after a few hours, when the cells are attached to the surface of the microcarriers, maintain the set low speed and enter the cultivation stage. The stirring of the microcarrier culture is very slow, the maximum speed is 75r/min.