Nanofibrous Electrospun Polymers for Reprogramming Human Cells

Forced expression of transcription factors epigenetically reprograms somatic cells harvested from routine skin biopsies into induced pluripotent stem cells (iPSCs). Human iPSCs are key resources for drug discovery, regenerative medicine and tissue engineering. Here we developed a materials approach to explore how culture substrates could impact factor-mediated reprogramming of human fibroblasts. A materials library consisting of nanofibrous substrates with randomly oriented and aligned structures was prepared by electrospinning four polymers [polylactic acid (PLA), polycaprolactone (PCL), thermoplastic polyurethane (TPU) and polypropylene carbonate (PPC)] into nanofiber orientations. Adsorbing protein to each substrate permitted robust attachment of fibroblasts to all substrates. Fibroblasts on aligned substrates had elongated nuclei, but after reprogramming factor expression, nuclei became more circular. Reprogramming factors could override the nuclear shape constraints imposed by nanofibrous substrates, and the majority of substrates supported full reprogramming. Early culture on PCL and TPU substrates promoted reprogramming, and TGF-b repressed substrate effects. Partial least squares modeling of the biochemical and biophysical cues within our reprogramming system identified TGF-b and polymer identity as important cues governing cellular reprogramming responses. We believe that our approach of using a nanofibrous materials library can be used to dissect molecular mechanisms of reprogramming and generate novel substrates that enhance epigenetic reprogramming. Keywords—Pluripotent stem cells, Reprogramming, Biomaterials, Electrospinning, Nuclear shape.