Nanoparticles Harmlessly Connect With Cells

An illustration of nanoparticles with striations of water loving and water repelling molecules appears superimposed above a fluorescence microscopy image of cells.  One of the main challenges in biology is to understand the molecular mechanisms that regulate the interaction of cell membranes with the outside world.  When a cell membrane recognizes a foreign object it 'wraps' around it, generating an endosome that is internalized inside the cell, eventually leading to the object being eliminated. This happens with both synthetic and biological materials.  Some synthetic materials (typically positively charged ones) are able to transiently create pores in cell membranes and gain contact with the true cell machinery, the cytosol.

The problem is that pores are intrinsically toxic to the cell because they allow ions to enter in higher concentrations than normal. A few biological materials (cell-penetrating and cell-fusing peptides) are able to penetrate the cell membrane without generating pores, though the exact mechanism is still unknown.  Ayush Verma, Oktay Uzun, Darrell Irvine and Francesco Stellacci of the Massachusetts Institute of Technology have discovered the first synthetic material that penetrates cell membranes without creating pores. These are striped particles with an alternating negatively charged and water repelling ligand molecules.

The researchers discovered that the ability of the particles to enter the cell depends on the extent of order or disorder for the molecules on the particle surface; particles with the same shell composition as penetrating particles, yet have disordered surfaces, do not penetrate. 

Credit: Ayush Verma, Oktay Uzun, Darrell Irvine, Francesco Stellacci, Massachusetts Institute of Technology