Abstract: The present invention provides fibrin nanoparticles having a mean diameter of 200-2000 nm. The present invention provides also methods for preparing fibrin particles of various sizes, including fibrin nanoparticles and fibrin microbeads. The present invention further provides compositions comprising fibrin particles and an agent, wherein the agent is coupled to the amine or carboxy moieties on the surface of the fibrin particles. In addition the present invention provides a composition comprising fibrin nanoparticles and an agent, wherein the agent is admixed with the fibrin nanoparticles. Still further, the present invention provides a method for introducing an agent into a cell, a method for isolating stem and/or progenitor cells from a biological sample, as well as a composition comprising fibrin particles bound to stem and/or progenitor cells.