Polyelectrolyte-coated gold nanorods and their interactions with type I collagen.

Gold nanorods (AuNRs) have unique optical properties for numerous biomedical applications, but the interactions between AuNRs and proteins, particularly those of the extracellular matrix (ECM), are poorly understood. Here the effects of AuNRs on the self-assembly, mechanics, and remodeling of type I collagen gels were examined in vitro. AuNRs were modified with polyelectrolyte multilayers (PEMs) to minimize cytotoxicity, and AuNRs with different terminal polymer chemistries were examined for their interactions with collagen by turbidity assays, rheological tests, and microscopy. Gel contraction assays were used to examine the effects of the PEM-coated AuNRs on cell-mediated collagen remodeling. Polyanion-terminated AuNRs significantly reduced the lag (nucleation) phase of collagen self-assembly and significantly increased the dynamic shear modulus of the polymerized gels, whereas polycation-terminated AuNRs had no effect on the mechanical properties of the collagen. Both polyanion- and polycation-terminated AuNRs significantly inhibited collagen gel contraction by cardiac fibroblasts, and the nanoparticles were localized in intra-, peri-, and extracellular compartments, suggesting that PEM-coated AuNRs influence cell behavior via multiple mechanisms. These results demonstrate the significance of nanoparticle-ECM interactions in determining the bioactivity of nanoparticles.