Methods of generating microparticles and porous hydrogels using microfluidics

1. A method of preparing a plurality of microparticles in a microfluidics device in an oxygen-controlled environment comprising the steps of:

(a) providing a continuous phase comprising a non-aqueous liquid and an aqueous phase comprising a polyethylene glycol (PEG)-based photodegradable macromer having a molecular weight selected from the range of 200 to 20,000 Daltons, a biological material, and an initiator;

(b) forming a composition comprising microdroplets of said aqueous phase dispersed in said non-aqueous liquid;

(c) controlling oxygen concentration in the microdroplets to enhance viability of the biological material, wherein the controlling comprises:

(i) providing said composition comprising said microdroplets and said non-aqueous liquid in a first channel of said microfluidics device;

(ii) flowing said oxygen-free gas through a second channel, adjacent to said first channel;

(iii) diffusing at least some of said oxygen-free gas into a region of the microfluidics device between the first and second channels; and

(iv) varying a supply pressure of the oxygen-free gas in order to vary the oxygen concentration within the microdroplets; and

(d) partially polymerizing said monomer or said macromer in said microdroplets, wherein, as polymerization is impeded by dissolved oxygen, only a fraction of a radial volume of each microdroplet is polymerized and the rest remains as a liquid film of un-polymerized aqueous phase on a polymerized core thereby generating microparticles within said aqueous phase having a smaller radius than said microdroplets; wherein the partially polymerizing step is at least partially controlled via the controlling oxygen concentration step (c); and wherein the microparticles have a mean diameter of less than or equal to 1000 μm.

2. The method of claim 1 , wherein said oxygen-free gas is nitrogen.

3. The method of claim 1 , wherein said oxygen-free gas is varied within the range of 0.1 atm to 10 atm.

4. The method of claim 1 , where said initiator is a photoinitiator and said step of polymerizing said monomer or macromer is carried out in the presence of ultraviolet light.

5. The method of claim 4 , wherein said photoinitiator is lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) or Irgacure 1173.

6. The method of claim 1 , wherein said non-aqueous liquid comprises a fluorocarbon oil.

7. The method of claim 6 , wherein said fluorocarbon oil is a segregated hydrofluoroether.

8. The method of claim 1 , wherein said non-aqueous liquid further comprises a surfactant and said surfactant is provided at a concentration selected from the range of 0.1% to 4%.

9. The method of claim 8 , wherein said surfactant is a Dolomite FluoroPEG surfactant, RAN Biotechnologies FluoroPEG surfactant or Krytox FSL 157.

10. The method of claim 1 , wherein said microparticles are hydrogel microparticles.

11. The method of claim 1 , wherein said microparticles are photodegradable.

12. The method of claim 1 , wherein said macromer is a PEG-diacrylate (PEGDA) macromer.

13. The method of claim 1 , wherein said step (c) of controlling oxygen concentration in the microdroplets reduces the amount of oxygen in the composition to a preselected concentration selected from the range of 1% to 90%.

14. The method of claim 1 , wherein said step(c) of controlling oxygen concentration in the microdroplets reduces the amount of oxygen in the non-aqueous liquid to a preselected concentration selected from the range of 1% to 90%.

15. The method of claim 1 , wherein said step (c) of controlling oxygen concentration in the microdroplets comprises providing a membrane between said composition and said oxygen-free gas.

16. The method of claim 15 , wherein said membrane is a polydimethylsiloxane membrane.

17. The method of claim 1 , further comprising the steps of:

(e) at least partially encapsulating said microparticles within a non-photodegradable polymer, wherein said microparticles are photodegradable; and

(f) photodegrading said photodegradable microparticles to produce a composite porous hydrogel.

18. The method of claim 1 , wherein said biological material comprises cells.

19. The method of claim 18 , wherein said pores of said composite porous hydrogel have a lateral dimension to receive an individual cell.

20. The method of claim 1 wherein said biological material is selected from the group consisting of: mesenchymal stem cells, ß cells, satellite muscle cells, proteins, therapeutic small molecules, imaging molecules, secondary nanoparticles and any combination thereof.

21. The method of claim 1 , wherein said composition is a water in oil emulsion.

22. The method of claim 1 , wherein said microparticles are photodegradable microparticles and further comprising:

(e) at least partially encapsulating said photodegradable microparticles within a non-photodegradable polymer;

(f) photodegrading said photodegradable microparticles to produce a composite porous hydrogel; and

(g) contacting said composite porous hydrogel with a biological material, thereby capturing a portion of said biologically material in said composite porous hydrogel.

23. The method of claim 1 , wherein the step of regulating oxygen exposure (c)(iv) comprises varying a residence time of the microdroplets in the first channel of said microfluidics device.

24. The method of claim 18 , comprising tuning viability of the cells via the step of controlling oxygen concentration in the microdroplets.

25. The method of claim 1 comprising removing the un-polymerized liquid film from the microparticles.

26. The method of claim 1 comprising removing the non-aqueous phase from the microparticles to induce self-assembly of a hexagonal matrix of microparticles surrounded by un-polymerized aqueous phase.

27. The method of claim 26 comprising polymerizing the un-polymerized aqueous phase of the hexagonal matrix to form an ordered structure.