The central focus of tissue engineering is the re-creation of complexities found in cells and cellular microenvironments. We have developed biomembrane-microsphere constructs that are capable of presenting ligands/bound factors to stem cells, mimicking in vivocell-cell interactions that occur in the stem cell niche. Our platform, termed proteolipobeads (PLBs), features laterally-mobile proteins and peptides integrated within a synthetic biomembrane. While well established in 2D systems, biomimetic cell-cell communication involving model cell membranes has not taken hold in 3D stem cell culture systems.
We present results on three aspects of this study: 1) the fabrication and characterization of PLBs displaying surface-functional molecules, 2) the construction and characterization of hydrogel/PLB hybrid scaffolds, and 3) preliminary experiments of human mesenchymal stem cells (hMSCs) microencapsulated into matrix/PLB hybrid scaffolds. Special attention was given to the viability of hMSCs and the frequency and extent of hMSC-PLB interactions within these hybrid scaffolds. We will also describe the development of peptide-cadherin fusion protein conjugates that promote cellular interactions and peptide-based biomembrane anchoring to the microsphere surface. Finally, we will discuss recent progress in creating a fully biocompatible platform featuring biodegradable PLBs.
Confocal microscopy studies were conducted to assess the diffusivity of laterally mobile PLB constituents (via FRAP) and to visualize N-cadherin-mediated PLB interactions with hMSCs in situ. Immunohistochemical staining was used to detect N-Cadherin within the hybrid matrices relative to counterstained supported lipid bilayers. This work constitutes a new, physiologically relevant method for displaying mobile membrane proteins and signaling molecules to live cells within 3D matrices.