Patent Number: 
Section: claims

1. A composite material, comprising a polymer, a plurality of metal nanoparticles, and a surface-modifying agent, wherein:the polymer is selected from the group consisting of polydimethylsiloxane (PDMS), polyamide, polyacrylonitrile, polyethylene, polypropylene, polyvinyl chloride, epoxy resin, polyimide, polyurethane, polyurethane polyvinylidene fluoride, and polyvinylidene difluoride;the surface-modifying agent is nanocellulose;the surface-modifying agent and the polymer form an interpenetrating network; andthe plurality of metal nanoparticles comprises metal nanoparticles selected from the group consisting of lead nanoparticles, tungsten nanoparticles, bismuth nanoparticles, and uranium nanoparticles. 2. The composite material of claim 1, wherein the polymer is PDMS. 3. The composite material of claim 1, wherein the plurality of metal nanoparticles comprises bismuth nanoparticles. 4. The composite material of claim 1, wherein the average size of the plurality of metal nanoparticles is from 1 nm to 40,000 nm. 5. The composite material of claim 1, wherein the average size of the plurality of metal nanoparticles is 5 nm. 6. The composite material of claim 1, wherein the amount of the plurality of metal nanoparticles in the composite material is from 0.5 wt. % to 40 wt. %. 7. The composite material of claim 1, wherein the amount of the plurality of metal nanoparticles in the composite is 2 wt. %. 8. The composite material of claim 1, wherein nanocellulose comprises cellulose nanofibers. 9. The composite material of claim 1, wherein nanocellulose comprises cellulose nanocrystals. 10. The composite material of claim 1, wherein the amount of nanocellulose in the composite material is from 0.5 wt. % to 40 wt. %. 11. A film comprising at least one composite material of claim 1. 12. A method for shielding a subject from electromagnetic radiation, comprising placing at least one composite material of claim 1 between the subject and a source of electromagnetic radiation, thereby reducing a dose of electromagnetic radiation received by the subject. 13. The method of claim 12, wherein the dose of electromagnetic radiation received by the subject is reduced by an amount from 95% to 99%. 14. The method of claim 12, wherein the dose of electromagnetic radiation received by the subject is reduced by at least 96%. 15. The method of claim 12, wherein the electromagnetic radiation is X-ray radiation.