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We thank the staff of the Center for Cancer Genome Discovery and
the Molecular Biology Core Facility at Dana-Farber Cancer Institute
(DFCI) for DNA sequencing. D.P. is a Cancer Research Institute–
Robertson Foundation Fellow; L.F.d.A. was funded by a Friends
for Life Neuroblastoma Fellowship, and R.E. T. was supported by an
A*STAR Graduate Fellowship. A.M.L. is a Research Fellow of the
Training Program in Cancer Immunology at DFCI (NIH grant
1T32CA207021-01). This work was supported by a Transformative
R01 grant from the National Cancer Institute, NIH (R01CA173750)
(K. W. W.) and NIH (U24CA224316) (X.S.L.), and by a sponsored
research agreement with Astellas Pharma. X.S.L. is a cofounder of
and is on the scientific advisory board of GV20 Oncotherapy, a
precision cancer medicine company. X.S.L. is also on the scientific
advisory board of 3DMedCare and is a paid consultant for Genentech.
J.D. is a paid consultant for Tango Therapeutics. K. W. W. and D.P.
are inventors on patent application DFS-190.6 submitted by DFCI,
which covers new targets for cancer immunotherapy. RNA-seq
data have been deposited at the Gene Expression Omnibus under
accession number GSE107670.
Materials and Methods
Figs. S1 to S15
Tables S1 to S5
21 June 2017; resubmitted 30 October 2017
Accepted 14 December 2017
Published online 4 January 2018
Wrapping with a splash: High-speed
encapsulation with ultrathin sheets
Deepak Kumar,1,2 Joseph D. Paulsen,3 Thomas P. Russell,2,4,5,6 Narayanan Menon1*
Many complex fluids rely on surfactants to contain, protect, or isolate liquid drops in an
immiscible continuous phase. Thin elastic sheets can wrap liquid drops in a spontaneous
process driven by capillary forces. For encapsulation by sheets to be practically viable, a
rapid, continuous, and scalable process is essential. We exploit the fast dynamics of
droplet impact to achieve wrapping of oil droplets by ultrathin polymer films in a water
phase. Despite the violence of splashing events, the process robustly yields wrappings that
are optimally shaped to maximize the enclosed fluid volume and have near-perfect seams.
We achieve wrappings of targeted three-dimensional (3D) shapes by tailoring the 2D
boundary of the films and show the generality of the technique by producing both
oil-in-water and water-in-oil wrappings.
Many liquid-phase technologies require the ncapsulation of one liquid in another. In the stabilization of emulsions, drug delivery, and remediation of oil spills, liquid droplets are separated from the
surrounding liquid by a fluid monolayer of mo-
lecular or particulate surfactants (1–3). By con-
trast, we typically wrap solid contents, such as
chocolates or the filling in a dumpling, with solid
elastic sheets. Solid wrappings of liquids would
allow new possibilities, such as drops with non-
spherical shapes, designed permeability, and me-
chanical shear rigidity. Sufficiently thin planar
sheets will spontaneously wrap liquid droplets by
balancing the elastic energy of curving the sheet
with the reduction in interfacial surface energies.
Elastomer films of thickness t 100 mm were
shown to bend around a water droplet by this
mechanism (4, 5). For much thinner films, the
energetic cost of bending becomes negligible compared with the surface energies (6). Paulsen et al.
(7) found that in this regime of highly bendable
sheets (8), the wrappings are optimal in the sense
that they enclose the maximum volume within
a fixed area of sheet. However, those experiments
changed the volume of the liquid quasistati-cally and required controlled initial conditions
that are not scalable for the rapid production
of wrapped drops.
Here, we establish a fast, dynamic route to
wrapping in the high-bendability regime, exploit-
ing the dynamics generated by the impact of a
drop of oil on an ultrathin polymer sheet floating
on a pool of water. Polystyrene films of thickness
t from 46 to 372 nm are cut into circular discs
of radius W = 1.6 to 3.2 mm and placed on the
water surface in a cuvette (9) as shown in Fig. 1.
A drop of fluorinated oil of radius R = 0.6 to
1.2 mm, density roil = 1800 kg/m3, and surface
tension goil = 16 mN/m is released from a height
h = 10 to 300 mm above the surface. The drop
hits the surface with a kinetic energy propor-
tional to h. Immediately after the impact, a cra-
ter begins to form, which reaches a maximum
depth and then retracts back toward a flat inter-
face. During the retraction, the drop separates
from the water-air interface while the sheet wraps
around the drop. Despite the uncontrolled dy-
namics of the splash, the drop achieves optimal
wrapping, both in terms of the three-dimensional
(3D) shape of the wrapped drop (7) and in the
near-perfect closure achieved along the seam. This
sequence of events takes tens of milliseconds to
complete (movie S1). Once the wrapped oil sepa-
rates from the water surface, it sinks under gravity.
The static 3D shape is optimal when the ex-
posed area of the fluid interface is minimized,
as in Eq. 1 (7)
U ¼ gAfree ð1Þ
where the only dimensionless control parameter is W/R, the ratio of the sheet radius to the
droplet radius. In the dynamical splashing process, the energies of the initial and final state
involve the surface energy of the partially or
fully wrapped drop, as well as the energies of all
other interfaces between the air, oil, water, and
sheet. The final energy is higher, which implies
that an energy barrier (9) must be overcome by
the kinetic energy of the drop. As is typically done
in splashing problems (10), we take the ratio of
the kinetic energy at impact to the initial surface
energy of the drop to form the dimensionless
Weber number, We ¼ roilv2R
. If the oil drop does
not carry sufficient kinetic energy to overcome
1Department of Physics, University of Massachusetts,
Amherst, MA 01003, USA. 2Polymer Science and Engineering
Department, University of Massachusetts, Amherst, MA
01003, USA. 3Department of Physics, Syracuse University,
Syracuse, NY 13244, USA. 4Materials Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, CA 94720,
USA. 5Beijing Advanced Innovation Center for Soft Matter
Science and Engineering, Beijing University of Chemical
Technology, Beijing 100029, China. 6Advanced Institute for
Materials Research, Tohoku University, 2-1-1 Katehira,
Aoba, Sendai 980-8577, Japan.
*Corresponding author. Email: firstname.lastname@example.org