A method of forming articles having closed microchannels includes the steps of providing a substrae including a composite material, the composite having metal nanoparticles dispersed in a polymer matrix. The substrate is irradiated with a laser beam at an intensity and time sufficient to selectively remove the polymer below a surface of said substrate to form at least one microchannel, wherein the intensity and time is low enough to avoid removing the polymer above the microchannel, wherein an article having at least one closed microchannel is formed. A metal nanoparticle/polyer composite composition can have functionality that can undergo addition reactions to seal or join pieces of polymers or composites upon irradiation of the composition placed on one or more pieces
