RESUMO
Colloidal supraparticles are finite, spherical assemblies of many primary particles. To take advantage of their emergent functionalities, such supraparticles must retain their structural integrity. Here, we investigate their size-dependent mechanical properties via nanoindentation. We find that the deformation resistance inversely scales with the primary particle diameter, while the work of deformation is dependent on the supraparticle diameter. We adopt the Griffith theory to such particulate systems to provide a predictive scaling to relate the fracture stress to the geometry of supraparticles. The interplay between primary particle material and cohesive interparticle forces dictates the mechanical properties of supraparticles. We find that enhanced stability, associated with ductile fracture, can be achieved if supraparticles are engineered to dissipate more energy via deformation of primary particles than breaking of interparticle bonds. Our work provides a coherent framework to analyze, predict, and design the mechanical properties of colloidal supraparticles.
RESUMO
Quantum size-confined CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.
RESUMO
Multi-potent adult mesenchymal stem cells (MSCs) derived from bone marrow have therapeutic potential for bone diseases and regenerative medicine. However, an intrinsic heterogeneity in their phenotype, which in turn results in various differentiation potentials, makes it difficult to predict the response of these cells. The aim of this study is to investigate initial cell-surface interactions of human MSCs on modified titanium alloys. Gold nanoparticles deposited on ß-type Ti-40Nb alloys by block copolymer micelle nanolithography served as nanotopographical cues as well as specific binding sites for the immobilization of thiolated peptides present in several extracellular matrix proteins. MSC heterogeneity persists on polished and nanopatterned Ti-40Nb samples. However, cell heterogeneity and donor variability decreased upon functionalization of the gold nanoparticles with cyclic RGD peptides. In particular, the number of large cells significantly decreased after 24 h owing to the arrangement of cell anchorage sites, rather than peptide specificity. However, the size and number of integrin-mediated adhesion clusters increased in the presence of the integrin-binding peptide (cRGDfK) compared with the control peptide (cRADfK). These results suggest that the use of integrin ligands in defined patterns could improve MSC-material interactions, not only by regulating cell adhesion locally, but also by reducing population heterogeneity.