Advanced biomaterial systems for local control of fate decisions in pluripotent stem cell cultures

Abstract

The promise of regenerative therapies is currently hindered by the availability of large-scale, homogeneous populations of desired cell types. The in vitro differentiation efficiency of human pluripotent stem cell (PSC)-derived cell types could be enhanced with robust biomimetic stem cell culture systems that recapitulate the dynamic interplay between a cell and its extracellular matrix (ECM). We have therefore leveraged novel biomedical engineering technologies for improving the local and sustained delivery of bioactive molecules.

As cells precisely regulate matrix metalloproteinase (MMP) expression and activity, they spatially and temporally control ECM remodelling and degradation when transitioning from a pluripotent phenotype. Here, in vitro MMP expression profiles were studied in human and murine PSCs cultured in feeder-free conditions. MMP2 is up-regulated and released directly to the ECM during spontaneous differentiation, but is minimally produced in OCT4 expressing cells, making it an ideal candidate for a differentiation-sensitive material.

A new biomaterial is reported for in vitro stem cell culture that is sensitive to differentiation through a dynamic nano-vesicle biomolecule delivery system, exploiting natural enzymatic mechanisms, with 3D tissue design. Thermo-responsive polymersomes, composed of poly(ethylene glycol), poly(acrylic acid) and poly(N-isopropylacrylamide) block copolymer, ranging in diameter from 120-220 nm, can be cross-linked with various peptide linkers and reliably encapsulate large bioactive molecules. Incorporating MMP2-degradable peptide cross-links within these particles affords site-directed controlled release of cell-instructive morphogens. This enzyme-activated reciprocal response system is shown by ultra-centrifugal and ELISA-based platforms. As proof-of-concept, the platform function and specificity were validated with encapsulated cell-surface receptor antibodies, triggered to release by cell-secreted MMP2 during spontaneous differentiation in murine and human PSCs. In both 2D and 3D, local delivery of soluble cues is initiated to highly heterogeneous PSC-derived populations, having the potential to enhance differentiation efficiencies for a wide variety of regenerative strategies.