What are Microcarriers?
In cell culture, "microcarriers" embody a class of minuscule beads measuring a modest 60-250 μm diameter. Comprising a medley of natural glucan or a diverse array of synthetic polymers, these microscopic entities serve as nurturing grounds for the growth and sustenance of adherent cells. Distinctly catering to the intricate demands of certain cell types reliant on adhesion for their proliferation, microcarriers play a pivotal role within animal cell culture. Originating with the inception of the first microcarrier, the global market has since burgeoned, now boasting an extensive repertoire of microcarrier variations, including liquid microcarriers, macroporous gel microcarriers, polystyrene microcarriers, PHEMA microcarriers, chitosan microcarriers, polyurethane foam microcarriers, alginate gel microcarriers, and magnetic microcarriers, among others.
Microcarrier Culture Technique
The inception of the microcarrier culture technique dates back to the year 1967, marking its pioneering implementation in the realm of large-scale animal cell cultivation. Over the span of more than three decades, this method has undergone a comprehensive evolution, gradually attaining a state of refined maturity and witnessing extensive applications in diverse domains, prominently in the realm of vaccine production and gene engineering products, among others.
At its core, microcarriers, characterized by minuscule particles serving as carriers for cells, are suspended within the culture medium through a process of meticulous agitation. This intricate mechanism enables cells to proliferate in the form of monolayers coating the surfaces of these carriers. The present-day understanding of the microcarrier culture technique positions it as a pivotal player among the array of large-scale animal cell cultivation methodologies, effectively amalgamating the inherent strengths of both suspension and adherent cultures. The versatility of this technique is underscored by its successful application in cultivating a wide spectrum of cell types, including the cultivation of 293 cells, Vero cells, and CHO cells.
Preparation Methods of Microcarriers
Studies have found that the cell adhesion rate, drug sustained release rate and self-degradation rate of microcarriers are closely related to the materials and preparation methods of the microcarriers. In recent years, many studies have optimized and innovated the traditional preparation methods of microcarriers to prepare microcarriers with a narrower diameter distribution range and more controllable properties.
Droplet Method
The dropwise method stands as a prevalent avenue for the fabrication of microcarriers, frequently resorted to in various scientific domains. The crux of this methodology lies in the forceful ejection of material for microcarrier preparation through a nozzle, inducing the material to coalesce into spherical configurations under the compelling influence of surface tension. The subsequent phase involves the consolidation of these droplets into stable structures, accomplished through their immersion in a curing bath. While the dropwise approach finds its niche primarily within the realm of small-scale microsphere generation in laboratory settings, its adoption is often impeded by its inherent limitations. These constraints manifest in the form of lackluster preparation efficiency, compromised spherical uniformity, and a confined ability to exercise precision control over the resultant sphere quality.
Emulsification Method
The emulsification method involves mixing two or more immiscible solutions, followed by mechanical stirring to form an emulsion. External forces are then applied to allow the solvent in the dispersed phase to pass through the external aqueous phase, resulting in the solidification of the droplets' outer surfaces to form microspheres. Compared to traditional emulsification methods, microspheres prepared by the membrane emulsification method have a narrower diameter distribution range and a more uniform shape.
Microfluidics-Based Preparation Methods
Microfluidics-based preparation methods are similar to the emulsion method, entailing a delicate interplay of interfacial tension and internal channel pressure to meticulously fragment the dispersed phase, culminating in the formation of meticulously uniform monodisperse microspheres. However, distinct from its emulsion counterpart, microfluidics-based preparation methods present an array of tantalizing advantages. Foremost among them is the unparalleled precision it offers in the control of microsphere diameter, coupled with an elevated efficacy that allows for the generation of thousands of droplet microspheres within the span of a single second. This accentuates the low consumption and high throughput intrinsic of these microfluidic chips.
Electrospray Method
The electrospray method utilizes the potential difference between a high-voltage needle and a zero-potential surface within a device. This potential difference causes the drug-loaded electrolyte solution emitted from the needle to form Taylor cones. These microdroplets are sprayed toward the zero-potential surface under the influence of electric field forces, ultimately falling into a shaping pool to form microspheres. Research has shown that increasing the voltage and reducing the flow rate results in smaller microsphere diameters. Conversely, decreasing the voltage and increasing the flow rate lead to a wider diameter distribution range for the microspheres.
Applications of Microcarriers
Microcarriers are widely used in cell culture and biological product production. Here are some of the main application areas:
Viral vaccine production: Microcarrier technology assumes a central role in the intricate process of viral vaccine synthesis. Acting as a robust scaffold, it orchestrates the conducive milieu necessary for viral replication and subsequent high-caliber production. The consequence is a notable upsurge in both the yield and the purity of the resultant vaccine, underlining its paramount significance.
Recombinant protein production: Not confining themselves to the confines of vaccine synthesis, the application of microcarriers extends to the field of recombinant protein production. Embracing the likes of antibodies, growth factors, and a myriad of other vital proteins, these carriers serve as veritable catalysts and provide an efficient cell culture environment that helps increase protein production.
Cell Research: Microcarriers are also widely used in the field of cell research. It can provide a three-dimensional cell growth environment that is closer to the in vivo environment, promoting multi-layer growth of cells and research on physiological processes.
Gene therapy: Within the intricate domain of gene therapy, microcarriers assume a pivotal role in facilitating the intricate task of gene delivery. They shoulder the responsibility of transporting crucial genetic material, be it genes, RNA, or other therapeutic molecules, into the patient's cellular architecture to repair or replace damaged genes.
References
- Blüml, G. Microcarrier cell culture technology. Animal Cell Biotechnology: Methods and Protocols. 2007, 149-178.
- Shao C.; et al. Droplet microfluidics-based biomedical microcarriers. Acta Biomaterialia. 2022, 138: 21-33.
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