A cost-effective and enhanced mesenchymal stem cell expansion platform with internal plasma-activated biofunctional interfaces.

Mesenchymal stem cells (MSCs) used for clinical applications require expansion to achieve therapeutically relevant numbers. However, conventional planar cell expansion approaches using tissue culture vessels are inefficient, costly, and can trigger MSC phenotypic and functional decline. Here we present a one-step dry plasma process to modify the internal surfaces of three-dimensional (3D) printed, high surface area to volume ratio (high-SA:V) porous scaffolds as platforms for stem cell expansion. To address the long-lasting challenge of uniform plasma treatment within the micrometre-sized pores of scaffolds, we developed a packed bed plasma immersion ion implantation (PBPI) technology by which plasma is ignited inside porous materials for homogeneous surface activation. COMSOL Multiphysics simulations support our experimental data and provide insights into the role of electrical field and pressure distribution in plasma ignition. Spatial surface characterisation inside scaffolds demonstrates the homogeneity of PBPI activation. The PBPI treatment induces radical-containing chemical structures that enable the covalent attachment of biomolecules via a simple, non-toxic, single-step incubation process. We showed that PBPI-treated scaffolds biofunctionalised with fibroblast growth factor 2 (FGF2) significantly promoted the expansion of MSCs, preserved cell phenotypic expression, and multipotency, while reducing the usage of costly growth factor supplements. This breakthrough PBPI technology can be applied to a wide range of 3D polymeric porous scaffolds, paving the way towards developing new biomimetic interfaces for tissue engineering and regenerative medicine.