From drug delivery1, 2 to chemical and biological catalysis3 and cosmetics4, the need for efficient fabrication pathways for particles over a wide range of sizes, from a variety of materials, and in many different structures has been well established5. Here we harness the inherent scalability of fibre production6 and an in-fibre Plateau–Rayleigh capillary instability7 for the fabrication of uniformly sized, structured spherical particles spanning an exceptionally wide range of sizes: from 2 mm down to 20 nm. Thermal processing of a multimaterial fibre8 controllably induces the instability9, resulting in a well-ordered, oriented emulsion10 in three dimensions. The fibre core and cladding correspond to the dispersed and continuous phases, respectively, and are both frozen in situ on cooling, after which the particles are released when needed. By arranging a variety of structures and materials in a macroscopic scaled-up model of the fibre, we produce composite, structured, spherical particles, such as core–shell particles, two-compartment ‘Janus’ particles11, and multi-sectioned ‘beach ball’ particles. Moreover, producing fibres with a high density of cores allows for an unprecedented level of parallelization. In principle, 108 50-nm cores may be embedded in metres-long, 1-mm-diameter fibre, which can be induced to break up simultaneously throughout its length, into uniformly sized, structured spheres.
Figures at a glance
Figure 1: Fluid capillary instabilities in multimaterial fibres as a route to size-tunable particle fabrication. 
a, A macroscopic preform is thermally drawn into a fibre. Subsequent thermal processing of the fibre induces the PRI, which results in the breakup of the intact core into spherical droplets that are frozen in situ on cooling. b, Reflection optical micrograph of a fibre cross-section with 20-μm-diameter core; inset shows the core (scale bar, 20 μm). The fibre consists of an As2Se3 glass core (G), encased in a PES polymer cladding (P). c, Transmission optical micrograph of the fibre side-view in b after a temperature (T) gradient is applied along the axis to induce the PRI at the core–cladding interface. d, Calculated instability time, τ, for various temperatures T and core diameters D (see Supplementary Information). e, SEM images of microparticles with diameters of ~1.4 mm, 200 μm, 18 μm and 2.7 μm. f, SEM images of nanoparticles with diameters of ~920, 560, 62 and 20 nm.
Figure 2: Scalable fabrication of micro- and nano-scale spherical particles. 
a, SEM micrograph of 12 20-μm intact glass cores (G, As2Se3), exposed from a 1-mm-diameter fibre after dissolving the polymer cladding (P, PES). An SEM micrograph of the fibre cross-section is shown in Supplementary Fig. 3. b, Transmission optical micrograph of the fibre side-view, showing the cores after global heating of the fibre, which results in the simultaneous breakup of the cores into an ordered distribution of particles in three dimensions held in the polymer cladding. c, SEM micrograph of a large number of 40-μm (average diameter) glass particles released from the fibre in b by dissolving the polymer cladding. d, SEM micrograph of 27,000 200-nm-diameter intact glass cores exposed from a 1-mm-diameter fibre. An SEM micrograph of the fibre cross-section is shown in Supplementary Figs 4, 5. e, SEM micrograph of a large number of 400-nm (average diameter) glass particles. f, SEM micrograph of a few particles from e. See Supplementary Fig. 2 for the particle-size distribution.
Figure 3: Polymer-core/glass-shell spherical particle fabrication. 
a, Schematic of the fibre structure (P, G as in Figs 1, 2). b, c, SEM images of fibre cross-sections. d, SEM image of the glass-shell outer surface, showing the modulation characteristic of the PRI. e, SEM image of the structure in d after sectioning off half of the glass shell using a focused ion beam (FEI 200 THP; current ~10–100 pA), revealing the correlated modulations on the two interfaces (inner polymer/glass and outer glass/polymer interfaces), and resulting ultimately in two concentric spherical surfaces as shown in g and h. f, Three snapshots from a three-dimensional simulation of the Stokes equations using a representative fibre structure (full movie available online; see Supplementary Information), illustrating the full breakup process. Time progresses from top to bottom. Scale bar, 50 μm. Dark green, polymer core; light green, glass shell; the outer polymer scaffold cladding is made transparent for clarity. g, Top and h, front (tilted) SEM views of four differently sized core–shell particles (outer diameters 34 μm, 7 μm, 1.2 μm and 650 nm, respectively). Scale bars in the corresponding top and front views are the same length.
- Figure 4: Broken-symmetry Janus particle and ‘beach ball’ particle fabrication.
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