Self-Assembly of RGD-Functionalized Recombinant Spider Silk Protein into Microspheres in Physiological Buffer and in the Presence of Hyaluronic Acid

Biomaterials made of self-assembling protein buildingblocks arewidely explored for biomedical applications, for example, as drugcarriers, tissue engineering scaffolds, and functionalized coatings.It has previously been shown that a recombinant spider silk proteinfunctionalized with a cell binding motif from fibronectin, FN-4RepCT(FN-silk), self-assembles into fibrillar structures at interfaces,i.e., membranes, fibers, or foams at liquid/air interfaces, and fibrillarcoatings at liquid/solid interfaces. Recently, we observed that FN-silkalso assembles into microspheres in the bulk of a physiological buffer(PBS) solution. Herein, we investigate the self-assembly process ofFN-silk into microspheres in the bulk and how its progression is affectedby the presence of hyaluronic acid (HA), both in solution and in across-linked HA hydrogel. Moreover, we characterize the size, morphology,mesostructure, and protein secondary structure of the FN-silk microspheresprepared in PBS and HA. Finally, we examine how the FN-silk microspherescan be used to mediate cell adhesion and spreading of human mesenchymalstem cells (hMSCs) during cell culture. These investigations contributeto our fundamental understanding of the self-assembly of silk proteininto materials and demonstrate the use of silk microspheres as additivesfor cell culture applications.