# Efficient and high-density immobilization of animal cells by a microfiber with both swelling and cell adhesion properties and its application to exosome production

## TL;DR

Researchers developed a new microfiber material that can efficiently immobilize animal cells for high-density culture and exosome production.

## Contribution

A novel microfiber (CPG) combining swelling and adhesion properties was developed for high-density cell immobilization and exosome production.

## Key findings

- The CPG microfiber immobilized nearly all supplied cells with minimal loss.
- The immobilized cells achieved a high density of 3.2 × 109 cells per gram of microfiber.
- Exosome production reached 6–7 × 1010 particles per milliliter after 8–16 hours of culture.

## Abstract

For high-density cell culture, we studied the development of optimal microfibers (MFs) with a 0.1–10 μm diameter, which due to their large surface area can serve as an immobilization carrier for animal cells. To date, few studies have used MFs as scaffolding for high-density cell culturing.

Using six types of nonsoluble synthetic polymers, MF sheets were fabricated by electrospinning. The cellulose acetate, polyketone, and polyvinyl acetate MFs exhibited swelling and water retention capacities. Next, the six types of MF fragments were examined for immobilizing TKD2 mouse vascular endothelial cells. Although most cells were taken into the three MFs characterized by swelling, most leaked from the MFs without adhesion. To solve this, the MF sheets comprising cellulose acetate and polyketones were coated with gelatin. Although the adhesive capacity was enhanced, the swelling capacity decreased and almost all the immobilized mouse cells remained on the sheets’ surfaces. Based on these results, we produced a novel MF sheet comprising a gelatin, cellulose acetate, and polyketone mixture (CPG). Since the cells were taken into the MFs by swelling and attached by the gelatin, the CPG fragment immobilized almost all the supplied cells with little loss and reached a high density of 3.2 × 109 MF-g−1, Furthermore, the immobilized cells continuously produced exosomes with a high productivity of 6–7 × 1010 particles ml−1 after either 8 h or 16 h of culturing.

CPG-based MFs are expected to have a wide range of future applications, including exosome production from animal cells.