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

Abstract 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.