Expansion of Chinese hamster ovary cells via a loose cluster-assisted suspension culture using cell-sized gelatin microcarriers

Cell Adhesion and Local Cytokine Control on Protein-Functionalized PNIPAM-co-AAc Hydrogel Microcarriers

Achieving adequate cell densities remains a major challenge in establishing economic biotechnological and biomedical processes. A possible remedy is microcarrier-based cultivation in stirred-tank bioreactors (STBR), which offers a high surface-to-volume ratio, appropriate process control, and scalability. However, despite their potential, commercial microcarriers are currently limited to material systems featuring unnatural mechanical properties and low adaptability. Because matrix stiffness and ligand presentation impact phenotypical attributes, differentiation potential, and genetic stability, biotechnological processes can significantly benefit from microcarrier systems tailorable toward cell-type specific requirements. This study introduces hydrogel particles co-polymerized from poly(N-isopropylacrylamide) (PNIPAM) and acrylic acid (AAc) as a platform technology for cell expansion. The resulting microcarriers exhibit an adjustable extracellular matrix-like softness, an adaptable gel charge, and functional carboxyl groups, allowing electrostatic and covalent coupling of cell adhesive and cell fate-modulating proteins. These features enable the attachment and growth of L929 mouse fibroblast cells in static microtiter plates and dynamic STBR cultivations while also providing vital growth factors, such as interleukin-3, to myeloblast-like 32D cells over 20 days of cultivation. The study explores the effects of different educt compositions on cell-particle interactions and reveals that PNIPAM-co-AAc microcarriers can provide both covalently coupled and diffusively released cytokine to adjacent cells.

Human Mesenchymal Stem Cells on Size-Sorted Gelatin Hydrogel Microparticles Show Enhanced In Vitro Wound Healing Activities

The demand for innovative therapeutic interventions to expedite wound healing, particularly in vulnerable populations such as aging and diabetic patients, has prompted the exploration of novel strategies. Mesenchymal stem cell (MSC)-based therapy emerges as a promising avenue for treating acute and chronic wounds. However, its clinical application faces persistent challenges, notably the low survivability and limited retention time of engraftment in wound environments. Addressing this, a strategy to sustain the viability and functionality of human MSCs (hMSCs) in a graft-able format has been identified as crucial for advanced wound care. Hydrogel microparticles (HMPs) emerge as promising entities in the field of wound healing, showcasing versatile capabilities in delivering both cells and bioactive molecules/drugs. In this study, gelatin HMPs (GelMPs) were synthesized via an optimized mild processing method. GelMPs with distinct diameter sizes were sorted and characterized. The growth of hMSCs on GelMPs with various sizes was evaluated. The release of wound healing promoting factors from hMSCs cultured on different GelMPs were assessed using scratch wound assays and gene expression analysis. GelMPs with a size smaller than 100 microns supported better cell growth and cell migration compared to larger sizes (100 microns or 200 microns). While encapsulation of hMSCs in hydrogels has been a common route for delivering viable hMSCs, we hypothesized that hMSCs cultured on GelMPs are more robust than those encapsulated in hydrogels. To test this hypothesis, hMSCs were cultured on GelMPs or in the cross-linked methacrylated gelatin hydrogel (GelMA). Comparative analysis of growth and wound healing effects revealed that hMSCs cultured on GelMPs exhibited higher viability and released more wound healing activities in vitro. This observation highlights the potential of GelMPs, especially those with a size smaller than 100 microns, as a promising carrier for delivering hMSCs in wound healing applications, providing valuable insights for the optimization of advanced therapeutic strategies.

Expansion of human mesenchymal stem cells on poly(vinyl alcohol) microcarriers

Microcarriers provide a high surface-area-to-volume ratio that can realize high yields of cell products, including human mesenchymal stem cells (hMSCs). Here, we report a novel poly(vinyl alcohol) (PVA)-based microcarrier for hMSC expansion in suspension culture. PVA microcarriers were prepared as collagen-coated PVA hydrogels 181 μm in size and a high surface-area-to-weight ratio of 2945 cm2/g. The PVA microcarriers supported a 2.6-fold expansion of hMSCs in a 30-mL single-use stirred bioreactor after a 7 d culture period, comparable to that of commercially available microcarriers. Interestingly, we observed that hMSCs on PVA microcarriers adhered to adjacent microcarriers, resulting in the aggregation of hMSC-PVA microcarriers. Therefore, we conducted a long-term expansion culture using a bead-to-bead cell transfer method with PVA microcarriers. Fresh microcarriers were added to the cell-populated microcarriers in the bioreactor on days 7 and 14. hMSCs on PVA microcarriers continued to grow for 21 d using the bead-to-bead cell transfer method. Furthermore, magnetic PVA (PVA-mag) microcarriers were developed by loading magnetic nanoparticles into PVA microcarriers, and we demonstrated that these PVA-mag microcarriers enabled cell recovery by magnetic separation. These results suggest that these PVA microcarriers can contribute to the large-scale culture of hMSCs for regenerative medicine and cell therapy.