Silk nanospheres and microspheres and methods of making same

1. A method comprising:

(a) dissolving in water a silk/polyvinyl alcohol (PVA) blend film, wherein the silk/PVA blend film comprises silk fibroin and PVA; and

(b) removing at least a portion of the PVA, thereby forming silk spheres having a size in a range of nanometers to micrometers.

2. The method of claim 1 , wherein the silk/PVA blend film is produced by drying an aqueous blend solution comprising silk fibroin and PVA to form the silk/PVA film.

3. The method of claim 1 , further comprising applying a constraint on the silk/PVA blend film before dissolving the film in water to change the shape of the silk spheres.

4. The method of claim 1 , further comprising stretching the silk/PVA blend film before dissolving the film in water, thereby forming a spindle-shaped silk sphere.

5. The method of claim 1 , further comprising water-annealing the silk/PVA blend film before dissolving the film in water, thereby forming a disk-shaped silk sphere.

6. The method of claim 2 , wherein the size of the silk spheres is controlled by adjusting one or more of (a) the weight ratio of silk fibroin and PVA in the blend solution, (b) the concentrations of silk fibroin and PVA in the blend solution; (c) molecular weight of PVA; or (d) energy output of sonification applied on the silk/PVA blend solution before drying the solution to form the film.

7. The method of claim 2 , wherein the sphere size is controlled by one or more of (a) adding glycerin or other hydroxyl groups-rich compounds or polymers in the silk/PVA blend solution; (b) adjusting pH of the silk/PVA blend solution; or (c) adding salt to the silk/PVA blend solution and optionally adjusting the salt concentration.

8. The method of claim 2 , wherein the concentration of silk fibroin in the blend solution is from about 0.02% to about 15 wt %.

9. The method of claim 8 , wherein the concentration of silk in the blend solution ranges from about 0.2% to about 5 wt %.

10. The method of claim 2 , further comprising sonicating the blend solution before drying the solution to form the film.

11. The method of claim 10 , wherein the energy output of the sonication is no less than about 4 watts.

12. The method of claim 1 , further comprising selecting the formed silk spheres of a desired size.

13. The method of claim 2 , wherein the concentration of silk fibroin in the solution is up to about 0.2 wt %.

14. The method of claim 10 , wherein the silk spheres have a mean sphere size of less than 330 nm, and a PDI of below 0.4, and no spheres is larger than 2 μm.

15. The method of claim 1 , wherein the silk/PVA blend film further comprises an active agent encapsulated in the silk fibroin.

16. The method of claim 15 , wherein the active agent is selected from the group consisting of proteins and peptides, nucleic acids, nucleic acid analogues, nucleotides, viruses, and combinations thereof.

17. The method of claim 1 , wherein the PVA has an average molecular weight of 30,000-124,000.

18. The method of claim 2 , wherein the concentration ratio of silk fibroin: PVA in the blend solution ranges from about 1:1 to about 1:4.

19. The method of claim 8 , wherein the size of the formed silk spheres ranges from about 1 μm to about 30 μm.

20. The method of claim 13 , wherein the concentration of PVA is up to about 0.8 wt %, thereby forming silk spheres with a mean sphere size of less than 500 nm and a polydispersity index (PDI) of below 0.3, wherein no spheres is larger than 2 μm.

21. The method of claim 16 , wherein the active agent is selected from the group consisting of antibodies, oligonucleotides, peptide nucleic acids, aptamers, and combinations thereof.

22. The method of claim 15 , where in the active agent is selected from the group consisting of hormones, hormone antagonists, growth factors or recombinant growth factors and fragments and variants thereof, cytokines, enzymes, antibiotics, antivirals, toxins, chemotherapeutic agents, and combinations thereof.