Polyhedral Particles with Controlled Concavity by Indentation Templating

Abstract

Current methods for fabricating microparticles offer limited control over size and shape. Here, we demonstrate a droplet microfluidic method to form polyhedral microparticles with controlled concavity. By manipulating Laplace pressure, buoyancy, and particle rheology, we generate microparticles with diverse shapes and curvatures. Additionally, we demonstrate the particles provide increased capture efficiency when used for particle-templated emulsification. Our approach enables microparticles with enhanced chemical and biological functionality.

Figure 1

Indentation templating produces particles with controlled concavity. (Left) Microfluidics produces spherical droplets of controlled size containing gelling agents. (Top) Gelling the droplets yields common spherical particles. (Middle) By compressing the emulsion via centrifugation, the spherical droplets are deformed into polyhedra, yielding polyhedral particles upon gelation. (Bottom) To produce particles with concave interfaces, we add solid “indenter particles” and compress the emulsion during gelation.

Figure 2

Indentation templating generates particles with controlled size and surface curvature. (a) Small (45 μm) and large (135 μm) spherical particles produced by gelling an uncompressed emulsion. (b) Polyhedral particles produced by compressing and gelling an emulsion. (c) Particles with concave faces produced by adding indenter particles to the emulsion prior to compression and gelation. The plots on the right are the particle size distributions, as measured for the particle longest axis. Even though the particles have low volume dispersity (<5%), the longest axes vary due to differences in particle shape. Scale bar: 100 μm.

Figure 3

Indentation templating generates particles with controlled surface shape. (a) Effect of centrifugal force on droplet geometry. (b) Map depicting particles generated by varying the ratio of droplets and indenter particles in the solidified emulsion. (c) Minimal deformation observed under 100 rcf for polyhedral particles (N_i/N_p = 0). (d) Similarly minimal deformation observed under 500 rcf for polyhedral particles. (e) Deformation observed at 2000 rcf for polyhedral particles. (f) Polyhedral particle deformation at 5000 rcf. (g) Deformation at 10000 rcf, notably similar to both 5000 and 2000 rcf. (h) Spherical particles (N_p = 0), (i) polyhedral particles (N_i = 0), (j) partial particles (V_i = V_p and N_i = N_p), (k) small indented particles (V_i < V_p and N_i > N_p), and (l) large, indented particles (V_i > V_p and N_i > N_p. Scale bar: 100 μm

Figure 4

Templating particle shape affects emulsification. (a) Example templating particle shapes and (b–d) images of resultant emulsions. (e) Fraction of fluorescent beads encapsulated in droplets versus number of templating particles per droplet. (f) Fraction of droplets that contain fluorescent beads vs number of templating particles per droplet. Scale bar: 100 μm

Figure 5

Droplet digital PCR using polyhedral and indented particles. (a) We encapsulate both yeast genomic DNA and ddPCR reagents in droplets using PTE. Observation of positive ddPCR droplets associated with (b) spherical, (c) polyhedral, and (d) indented particles allows for calculation of the targets within samples. Scale bar: 200 μm.