Microscale assembly directed by liquid-based template - PubMed (original) (raw)

Microscale assembly directed by liquid-based template

Pu Chen et al. Adv Mater. 2014.

Abstract

A liquid surface established by standing waves is used as a dynamically reconfigurable template to assemble microscale materials into ordered, symmetric structures in a scalable and parallel manner. The broad applicability of this technology is illustrated by assembling diverse materials from soft matter, rigid bodies, individual cells, cell spheroids and cell-seeded microcarrier beads.

Keywords: bottom-up; directed assembly; liquid-based template; microscale materials; tissue engineering.

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Figures

Figure 1

Figure 1. Principle demonstration of liquid-based templated assembly

a, Schematics of assembly based on liquid-based template. b, Top down of the standing waves simulated according to equation (S2) in the supplementary information. Color bar indicates wave amplitude. c, Numerical simulation of drift energy for 200 μm polystyrene divinylbenzene beads on the standing waves based on equation (1). d–e, Assembly of polystyrene divinylbenzene beads on the nodal regions of standing waves with different coverage rate of beads on the air–liquid surface (d, 53% e, 2.5%). f, Numerical simulation of drift energy for 200 μm copper-zinc powder on the standing waves based on Equation (1). g, Assembly of copper-zinc powder on the antinodes of the standing waves. h, Assembly of complementary pattern by using copper-zinc powder (yellow regions) and polystyrene divinylbenzene beads (red regions). Chamber dimensions are 20 mm × 20 mm × 1.5 mm for all the experiments and simulations. Scale bars, 2 mm.

Figure 2

Figure 2

Diversity of the structures created by liquid-based templated assembly. a, Chamber shape effect on the assembly. b, Numerical simulation of the waveforms generated in the square chamber. Square waveform (SQ), stripe waveform (ST) and crystalline waveforms (CR1 and CR2) were obtained using equation S2, S3 and S4 respectively. c–d, Typical assembled structure and corresponding drift energy (numerical simulation) under each waveforms. Each panel in c and d represents the dashed square in the corresponding panel of b. e, Principle demonstration of the symmetric modes within the square waveform. The color bar depicts the amplitude of the standing waves. Each code represents the symmetric modes. λ is the wavelength, and (λ/4, λ/4) indicates translation of the standing waves by λ/4 in both x-axis and y-axis directions. The symmetric axes are indicated with white dash-dotted lines. f, Harmonic order within each symmetric modes. All of the scale bars indicate 2 mm. Codes under the assembled structures are applied in the phase diagrams.

Figure 3

Figure 3. Dynamical reconfigurability of liquid-based templated assembly

a, Schematic demonstration of dynamic reconfiguration of the assembled structures: (_f_A, _a_A) and (_f_B, _a_B) are vibrational frequencies and accelerations for the formation of structures A and B, respectively. By tuning the initial chamber with (_f_A, _a_A) and (_f_B, _a_B), assembly of the structures A and B from dispersed floaters can be performed, as well as the reversible transitions between the structures. b, Dynamic process of the assembly. I–VI show different stages of the assembly: I. before assembly; II. during assembly; III. formation of the ring-shaped structure; IV. intermediate state; V. formation of “H”-shaped structure; VI. restoration of the ring-shaped structure. All of the experiments were performed in10 mm × 10 mm × 1.5 mm chamber using beads with 200 μm in diameter. Scale bars, 2 mm. Note: The snapshots in top-down view and side view were recorded separately and approximately represent the events in the corresponding column. c, Time evolution of the assembly fraction during the assembly process. Vibration was applied at time zero. * Resetting vibrational parameters: the vibrational frequency was first increased from 46 Hz to 60 Hz, and the acceleration was then increased from 1.46 g to 1.9 g. ** Resetting vibrational parameters: the acceleration was first decreased from 1.9 g to 1.46 g, and the vibrational frequency was then decreased from 60 Hz to 46 Hz.

Figure 4

Figure 4. Broad applicability of liquid-based templated assembly

a, Assembly of various materials. From left to right: GelMA hydrogel units (blue) and PDMS blocks (red) on nodal regions; silicon chiplets on antinodes. b, Assembly of size-varied materials. PEG hydrogel units with sizes of 0.5, 1, and 2 mm. c, Scalable assembly. Chamber sizes are 10, 20 and 30 mm respectively. Floater size is 200 μm for all. d, Parallel assembly in a 5-by-5 chamber array. Dimensions of each chamber are 10 mm × 10 mm × 1.5 mm. e, Photo crosslinking of the assembled structure. Once the hydrogels assembled, the crosslinking was performed to immobilize the hydrogels and the assembled pattern. Scale bars: 4 mm.

Figure 5

Figure 5. Liquid-based templated assembly for tissue engineering

a–d, Assembly of cell-seeded microcarrier beads. a, Microcarrier beads with CFSE (Green) stained NIH 3T3 fibroblast cells after assembly and crosslinking. b, Live/dead assays on the cells seeded on the microcarrier beads, 3-day culture after chemical crosslinking. Green color indicates live cells (calcein-AM), red color indicates dead cells (ethidium homodimer-1). c–d, Formation of 3D neural structures on the assembled microcarrier beads after 14-day cell culture. e–h, Scaffold-free assembly of cells spheroids (mean size: 200 μm). f is magnified region in e, marked with red dashed lines. g–h, assembled structures from cell spheroids, bright field recorded by digital SLR camera. i–l, Scaffold-free assembly of fibroblast cells and cytocompatibility tests. i is magnified region in g, marked with red dashed lines. The cells were stained by cell tracker CFSE (Green). k, Cell viability test under assembly onset acceleration at various vibrational frequencies (n = 6); l, Cell proliferation test with Alamar blue. Cells experienced by 15-second agitations at 50, 100 and 200 Hz. The treated cells were seeded in a 64-well plate with a seeding density of 200 cells/well for 11-day cell culture. Data was presented as mean ± S.D. (n = 8).

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