Synthesis of stable elastomeric negative acoustic contrast particles
We describe methods for synthesis and formulations of stable elastomeric negative acoustic contrast particles with controllable compressibility and density. These elastomeric negative acoustic contrast particles have a density/compressibility ratio that is less than that of water and therefore exhibit negative acoustic contrast under acoustic radiation exposure. This negative acoustic contrast allows our elastomeric negative acoustic contrast particles to be acoustically manipulated (e.g. separated) differently from other components (e.g. cells) within an aqueous solution. This disclosure also describes methods for biofunctionalization of the elastomeric negative acoustic contrast particles and as an example their use as platforms for bioassays. Potential applications of these elastomeric negative acoustic contrast particles include sensitive bioassays based on acoustic flow cytometry and other types of techniques that utilize acoustic fields, including ultrasound imaging and ultrasound triggered drug delivery.
1. A method for synthesizing elastomeric negative acoustic contrast microparticles comprising:
emulsifying an elastomer pre-polymer with a crosslinking agent in the presence of an amphiphillic surfactant under sufficient conditions to produce emulsion droplets; and
curing the emulsions droplets under sufficient conditions to form stable elastomeric negative acoustic contrast particles.
2. The method of claim 1 wherein the step of emulsifying comprises:
introducing the elastomer pre-polymer and crosslinking agent into a first channel of a microfluidic device at a first flow rate; and
introducing the aqueous phase with amphiphillic surfactant into a second channel of a microfluidic device at a second flow rate.
3. The method of claim 1 wherein the elastomer pre-polymer and crosslinking agent are released from an ink jet printer nozzle into an aqueous phase comprising the amphiphillic surfactant.
4. The method of claim 1 wherein the elastomer pre-polymer is a dielectric silicone gel.
5. The method of claim 4 wherein the soft compressible dielectric silicone gel is low viscosity polydimethylsiloxane.
6. The method of claim 1 wherein the elastomer is a high viscosity elastomer.
7. The method of claim 1 wherein the elastomer pre-polymer is emulsified with at least 50% volume crosslinking agent.
8. The method of claim 1 wherein the elastomer pre-polymer and crosslinking agent are provided in a 1:1 (w:w) mixture.
9. The method of claim 1 wherein the emulsion droplets are cured for at least 12 hours.
10. The method of claim 1 further comprising functionalizing the elastomeric negative acoustic contrast particles.
11. The method of claim 1 further comprising selecting the amount of crosslinking agent to be emulsified with the elastomeric precursor based on a desired behavior of the particle within an acoustic radiation field.
12. A method comprising:
determining a specific desired behavior for an elastomeric acoustic contrast particle within an acoustic radiation field;
selecting a weight percent of cross-linking agent to be emulsified with an elastomeric precursor based on the determined specific desired behavior;
emulsifying an elastomer pre-polymer with the selected weight percent of the cross-linking agent in the presence of an amphiphillic surfactant under sufficient conditions to produce emulsion droplets; and
curing the emulsions droplets under sufficient conditions to form stable elastomeric negative acoustic contrast particles.
13. The method of claim 12 wherein the desired behavior is a time-averaged drift force moving the particles to acoustic pressure antinodes.