Supramolecular Additive Screening to Engineer Microfibrous Rafts for Expansion of Pluripotent Stem Cells in Dynamic Suspension

Segmented PCL-bisurea (BU) polymers and BU-peptide conjugate additives assemble into fibrous superstructures at the nanoscale through a mix-and-matching strategy. Different bioactivities are incorporated through variation of peptide sequences. The resulting materials are screened for their effect on stem cell adhesion and pluripotency. Screening hits are electrospun into microfibrous rafts and applied as scaffolds for dynamic suspension culture of pluripotent stem cells.

Abstract

Human induced pluripotent stem cells (hiPSCs) hold the potential to generate any human tissue for transplantation in regenerative therapies. These complex cell therapies require billions of cells, which is challenging to acquire in planar adherent cultures. Transitioning hiPSCs to 3D suspension culture on microcarrier materials, often bead-shaped, improves the total surface area accessible to cells, thereby enabling culture scale-up. However, bead-shaped microcarriers do not have the optimal shape configuration, because it is the lowest surface-to-volume ratio of all geometrical shapes, and it also induces uncontrolled cell clumping. Application of synthetic, microfibrous rafts as a replacement for bead-shaped microcarriers potentially solves these issues. Here, microfibrous rafts are engineered by first screening a supramolecular biomaterial library composed of bisurea (BU)-peptide conjugate additives for its ability to induce hiPSC adhesion and maintenance of its pluripotent state, followed by electrospinning the screening-hit into raft-like structures. The resulting rafts contain cylinder-like microfibers, which have a higher surface-to-volume ratio compared to conventional bead-shaped microcarriers, and the flat configuration of the rafts prevents clumping.