Biodegradable Proteolipobeads for Dynamic Ligand Display in Cell Microenvironments

Biomaterials and biomedical research are often focused on the re-creation of complexities found in cells and cellular microenvironments. We hypothesize that biomembrane-microsphere assemblies are a viable biomimetic means to present ligands/bound factors to stem cells and mimic cellular communication in the stem cell niche. Supported lipid bilayers (SLBs) are ideally suited for the study of biomembrane−biomembrane interactions and for the biomimicry of cell-to-cell communication, allowing for surface ligand displays that contain laterally mobile elements. However, the SLB paradigm does not include three-dimensionality and biocompatibility. As a way to bypass these limitations, we have developed a biodegradable form of microsphere SLBs, also known as proteolipobeads (PLBs), using PLGA microspheres. Microspheres were synthesized using solvent evaporation and size selected with fluorescence activated cell sorting (FACS). Biomembranes were covalently tethered upon fusion to microsphere supports via short-chain PEG spacers connecting membrane-integrated α-helical peptides and the microsphere surface, affecting membrane diffusivity and mobility as indicated by confocal FRAP analysis. Membrane heterogeneities, which are attributed to PLGA hydrophobicity and rough surface topography, are curtailed by the addition of PEG tethers. This method allows for the presentation of tethered, laterally mobile biomembranes in three dimensions with functionally embedded attachment peptides for mobile ligand displays.