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Programmed magnetic manipulation of vesicles into spatially coded prototissue architectures arrays


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In nature, cells self-assemble into spatially coded tissular configurations to execute higher-order biological functions as a collective. This mechanism has stimulated the recent trend in synthetic biology to construct tissue-like assemblies from protocell entities, with the aim to understand the evolution mechanism of multicellular mechanisms, create smart materials or devices, and engineer tissue-like biomedical implant. However, the formation of spatially coded and communicating micro-architectures from large quantity of protocell entities, especially for lipid vesicle-based systems that mostly resemble cells, is still challenging. Herein, we magnetically assemble giant unilamellar vesicles (GUVs) or cells into various microstructures with spatially coded configurations and spatialized cascade biochemical reactions using a stainless steel mesh. GUVs in these tissue-like aggregates exhibit uncustomary osmotic stability that cannot be achieved by individual GUVs suspensions. This work provides a versatile and cost-effective strategy to form robust tissue-mimics and indicates a possible superiority of protocell colonies to individual protocells. To execute higher-order functions, cells self-assemble into spatially coded tissue configurations. Here the authors magnetically assembly giant unilamellar vesicles into three dimensional tissue-mimic structures with collective osmotic stability.
Assembly of giant unilamellar vesicles (GUVs) on stainless steel (SS) mesh under vertical magnetic field. a Schematic illustration of the device for GUVs assembly: a SS mesh placed on the top center of a magnet. b Horizontal (top) and vertical (bottom) central section of the simulated magnetic field distribution across the microwells. The white dash box and the black dash circle respectively indicated the unit of the microwell array and the approximating unit for decentralized microwells. The black dash arrow indicated the preferential localization of GUVs around microwell wall. c Fluorescence images of the GUVs colonies with different extent of occupation of the microwells. The white dash circle indicated microwell wall. d Fluorescence image of GUV colony arrays formed in SS mesh with microwell diameter of 250 μm. e Top view and side view along the yellow dash section line of the GUVs colony taken by a laser confocal microscope. f A 3D image of GUVs colony obtained from serial sections of images in the Z-stacks taken by a laser confocal microscope. g Fluorescence images of GUVs colonies with different morphologies: from left to right, triangular, square, striped, and HITlike assemblies. The dash triangle, rectangle, and line illustrated rough outline of GUVs colonies. h The schematic and simulated magnetic field distribution of SS mesh with densely packed microwells. The white dash box presented the unit of the microwell array. The black arrows indicated the corners. i Fluorescence images of the Chinese ancient coin-like round GUVs colonies with square holes formed using the SS mesh with densely packed microwells. The bottom is the enlarged image in the dash box of top image as indicated by the yellow dash arrow. The white dash box in bottom image indicated the square hole in GUVs colony. The scale bars are 100 μm.
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Programmed magnetic manipulation of vesicles
into spatially coded prototissue architectures
Qingchuan Li1,2, Shubin Li1,2, Xiangxiang Zhang1, Weili Xu1& Xiaojun Han1*
In nature, cells self-assemble into spatially coded tissular congurations to execute higher-
order biological functions as a collective. This mechanism has stimulated the recent trend in
synthetic biology to construct tissue-like assemblies from protocell entities, with the aim to
understand the evolution mechanism of multicellular mechanisms, create smart materials or
devices, and engineer tissue-like biomedical implant. However, the formation of spatially
coded and communicating micro-architectures from large quantity of protocell entities,
especially for lipid vesicle-based systems that mostly resemble cells, is still challenging.
Herein, we magnetically assemble giant unilamellar vesicles (GUVs) or cells into various
microstructures with spatially coded congurations and spatialized cascade biochemical
reactions using a stainless steel mesh. GUVs in these tissue-like aggregates exhibit uncus-
tomary osmotic stability that cannot be achieved by individual GUVs suspensions. This work
provides a versatile and cost-effective strategy to form robust tissue-mimics and indicates a
possible superiority of protocell colonies to individual protocells. OPEN
1State Key Laboratory of Urban Water Resource and Environment, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, 92 West
Da-Zhi Street, Harbin 150001, China.
These authors contributed equally: Qingchuan Li, Shubin Li *email:
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During the evolution of life, one of the major transitions is
the appearance of multicellular systems with spatially coded
cell types1,2, which communicate and cooperate to exhibit
higher-order collective behaviors in the form of tissues or organs.
Mimicking these systems via the controlled assembly of synthetic
cell-like entities is expected to result in important implications for
the fabrication of articial living systems and promising applica-
tions in the eld of tissue engineering3.Sofar,variouskindsof
protocell entities, such as liposomes46, polymersomes7,proteino-
somes8, and water-in-oil emulsion droplets911 have been inte-
grated into rudimentary tissue-like assemblies that exhibit higher-
order behaviors as a collective including communication, defor-
mation, signaling, and differentiation. However, except the series of
breakthrough studies based on water-in-oil emulsion networks,
most of the current tissue-like assemblies are amorphous aggregates
of some protocell entities, especially for the lipid vesicle-based
systems that most closely resemble cells12. In a recent breakthrough,
Ces and coworkers13 sculpted small group of vesicles into dened
spatial organization using optical tweezers. The assembly of large
quantity of vesicle-based protocell entities into spatially coded and
communicating micro-architectures to mimick the existence form
of natural tissues remains a considerable challenge.
As a versatile, noninvasive, and cost-effective strategy, mag-
netic manipulation has been increasingly exploited for the scal-
able assembly of magnetic and nonmagnetic objects into two-
dimensional (2D) or three-dimensional (3D) metastructures
based on their responses to inhomogeneous magnetic eld in two
mechanisms: positive magnetophoresis (moving to areas with
maximized eld intensity) for magnetic objects14,15, and negative
magnetophoresis (moving to areas with minimized eld intensity)
for objects with lower magnetic susceptibility than that of sus-
pension media16,17. Compared with the well-established study
and wide application of the rst mechanism, the investigation of
the second mechanism is still in its infancy, but attracts intense
attentions in recent years because of its universal applicability for
different kinds of inanimate and living materials18,19, and unique
manipulation behaviors for the objects going beyond Earnshaws
theorem20. Early study in this area often required quite high
magnetic eld intensity. However, a recent revolution by intro-
ducing paramagnetic dispersing environment brought up a
magneto-Archimedes effect21, enabling the manipulation of
nonmagnetic objects under weak magnetic eld. Based on this
effect, 2D colloidal particles lattice was assembled on Ni grid with
different morphologies in paramagnetic Ho(NO
Simple 3D structures, for example, the spheroidal tissue-like
models, have also been obtained via magnetic levitation devices in
a more biocompatible gadolinium-based nonionic paramagnetic
solution23. However, the application of this technique for the
formation of more complicated 3D aggregates, for instance, the
spatially coded tissue-like giant unilamellar vesicles (GUVs)
assemblies, has rarely been reported.
Herein, we describe the scalable magnetic assembly of cell-
mimic (GUVs) colonies with tissue-like complex 3D organiza-
tions using a stainless steel (SS) mesh with patterned microwells
in a paramagnetic solution media. The independent and colla-
borative inuences of the microwell parameters (morphology and
arrangement) and directions of external magnetic eld on GUVs
colonies formation with different spatial organizations are
investigated. Cascade enzyme reactions among these spatially
organized structures are engineered. Our work provides a method
to form higher-order tissue-like structures for synthetic biology,
tissue engineering, and the study of spatially compartmented
chemical reactions, and exhibits a further step for the controlled
magnetic manipulation.
The setup for GUVs assembly. The assembly of diamagnetic
GUVs was carried out on a SS mesh (thickness 100 μm) with
patterned microwells (Supplementary Fig. 1) by mixing GUVs
mother dispersion electroformed in 400 mM sucrose solution
(Supplementary Fig. 2) with isotonic paramagnetic MnCl
Gadobutrol solution. The inner volume of GUVs was 400 mM
sucrose solution, and the outside solution was an isotonic mixture
of sucrose and paramagnetic compounds with relative lower
density. The GUVs encapsulated with sucrose solution were
heavier than their surroundings, so when no magnetic eld was
applied, GUVs homogeneously deposited on the microwells and
grids under gravity (Supplementary Fig. 3). After the magnetic
eld was applied from the bottom, the SS mesh exhibited a
paramagnetic response, i.e., magnetic moments parallel to the
external magnetic eld were generated in the SS mesh (Supple-
mentary Fig. 4a), which resulted in the formation of magnetic
eld gradient microenvironments around the SS mesh because of
the interplay between magnetized magnetic eld from SS mesh
and external magnetic eld from the magnets. These micro-
environments drove the aggregation of GUVs that deposited
around the SS mesh under gravity to form tissue-like colonies in
the paramagnetic media containing MnCl
. For a GUV in mag-
netic eld with radius of Rat position r, the magnetostatic
potential energy U(r) was given by22
where μ
is the magnetic permeability of vacuum, χ
and χ
the magnetic susceptibilities of GUVs and paramagnetic solution,
respectively, and H(r) is the magnetic eld at the position of the
GUVs. For diamagnetic GUVs (χ
), the potential energy U(r)
was strictly positive as implied by Eq. (1), so GUVs tended to
move towards regions with minimum magnetic eld in the gra-
dient microenvironments for lower U(r). Therefore, it can be
expected that the spatial organization of GUVs colonies can be
determined by the distribution of magnetic eld around the
microwells. In this work, magnetic elds with three directions
versus the SS mesh surface, i.e., vertical (Fig. 1a), horizontal
(Fig. 2a), and inclined (Fig. 2d) magnetic elds, were adjusted to
modulate the magnetic eld microenvironment around the SS
mesh for the assembly of GUVs in paramagnetic media. The
assembly device contained a cover slip, the SS mesh clinging to
the cover slip, and a Teon cell enclosing the SS mesh (Supple-
mentary Fig. 5).
GUVs assembly under vertical magnetic eld. The vertical
external magnetic eld versus the SS mesh surface was provided
by putting the device on the top center of a permanent magnet
(Fig. 1a). As indicated by the horizontal (top in Fig. 1b) and
vertical (bottom in Fig. 1b) central section of the simulated
magnetic eld distribution across the microwells, local micro-
environments with lower magnetic eld strength than sur-
rounding space were generated in the patterned microwells. So
diamagnetic GUVs tended to aggregate in the microwells under
gravity and negative magnetophoresis. Moreover, the strength of
the magnetic eld in the microwells is also inhomogeneous,
radially decreased from the center to the well walls, which caused
the preferential localization of GUVs around the microwells to
form toroidal microstructures. This phenomenon is more
supercially similar to the traditional manipulation behavior for
magnetic objects rather than diamagnetic entities. In previous
studies related to magnetic levitation or colloidal assembly at 2D
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surfaces, diamagnetic objects tended to run away from the
magnets or the magnetized Ni grids, while magnetic materials
tended to be attracted and collected by them22. The interplay of
the magnetic eld from the magnet and the magnetized SS mesh
resulted in the paramagnetic manipulation-like collection of
GUVs on the microwell walls. With the increase of time and
amount of GUVs, the microwells were gradually occupied by
GUVs from the well walls to the center (Fig. 1c and Supple-
mentary Fig. 6). Complete occupation of the microwells to form
columnar GUVs colonies arrays (Fig. 1d) was realized with
incubation time of 2 h in 0.04 mg mL1GUVs solution (volume
=300 μL, V
GUVs mother solution
=1/4). The top view
and side view from the laser confocal microscope indicated the
close packing of GUVs in the colony (Fig. 1e). The columnar 3D
structure of the tissue-like aggregates can be recognized from a
3D image constructed from serial sections of images in Z-stacks
(Fig. 1f). There existed the adhesive van der Waals force and
different kinds of repulsive forces, including undulation, hydra-
tion, and electrostatic forces, among GUVs. The balance of these
forces determined whether the GUVs were repulsive or adhesive.
However, this had no inuence on the close packing of GUVs.
The adhesive GUVs in assembly solution containing MnCl
, and
the repulsive GUVs in 400 mM nonionic Gadobutrol solution can
both form closely packed GUVs colonies (Supplementary Fig. 7).
The driving forces for GUVs assembly and close packing were the
magnetic force and the gravity. The gravity facilitated the
deposition of GUVs around the mesh and the magnetic force
promoted their aggregation at region with lower magnetic eld
rather than deform them (Supplementary Fig. 8).
As shown by Fig. 1e and Supplementary Fig. 9a, the
electroformed polydisperse GUVs displayed heterogeneous size
distribution in the microwells. From the area close to the
microwell wall to that close to the center, the average diameter of
GUVs gradually decreased. This phenomenon was more
pronounced for the GUVs colony that partially occupied the
microwells via using fewer GUVs (Supplementary Fig. 9b). This is
because larger GUVs settled more quickly under gravity than
smaller ones24. Based on this size-dependent assembly
Top view
SS mesh on magnet
Side view
Magnetic field strength (T)
Magnetic field strength (T)
95% occupation
85% occupation
70% occupation
Top view Side view
Fig. 1 Assembly of giant unilamellar vesicles (GUVs) on stainless steel (SS) mesh under vertical magnetic eld. a Schematic illustration of the device
for GUVs assembly: a SS mesh placed on the top center of a magnet. bHorizontal (top) and vertical (bottom) central section of the simulated magnetic
eld distribution across the microwells. The white dash box and the black dash circle respectively indicated the unit of the microwell array and the
approximating unit for decentralized microwells. The black dash arrow indicated the preferential localization of GUVs around microwell wall.
cFluorescence images of the GUVs colonies with different extent of occupation of the microwells. The white dash circle indicated microwell wall.
dFluorescence image of GUV colony arrays formed in SS mesh with microwell diameter of 250 μm. eTop view and side view along the yellow dash section
line of the GUVs colony taken by a laser confocal microscope. fA 3D image of GUVs colony obtained from serial sections of images in the Z-stacks taken
by a laser confocal microscope. gFluorescence images of GUVs colonies with different morphologies: from left to right, triangular, square, striped, and HIT-
like assemblies. The dash triangle, rectangle, and line illustrated rough outline of GUVs colonies. hThe schematic and simulated magnetic eld distribution
of SS mesh with densely packed microwells. The white dash box presented the unit of the microwell array. The black arrows indicated the corners.
iFluorescence images of the Chinese ancient coin-like round GUVs colonies with square holes formed using the SS mesh with densely packed microwells.
The bottom is the enlarged image in the dash box of top image as indicated by the yellow dash arrow. The white dash box in bottom image indicated the
square hole in GUVs colony. The scale bars are 100 μm.
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phenomenon, we programmed the formation of GUVs colony
with alternating GUVs layers of different average sizes (Supple-
mentary Fig. 9c) via the successive adding of GUVs for two times.
The GUVs in the colony were mutually isolated and retained
the integrity of their compartmentalized interior. No fusion/
hemi-fusion events and leakage of compartmentalized uorescent
molecules were observed in the experiments (Supplementary
Movie 1 and Supplementary Figs. 10, 11). However, these GUVs
displayed no individual transitional motion (Supplementary
Movie 1 and Supplementary Fig. 10), but behaved as a jammed
and consolidated aggregate with collective stability due to their
close packing. When magnetic eld was removed and the SS
mesh was inverted to provide a harmful gravity eld that
promoted the GUVs colony disassembly, the contact forces2527
among the closely packed GUVs kept the GUVs colony stable,
regardless of whether the GUVs were mutually repulsive or
adhesive (Supplementary Fig. 7).
The morphology of the obtained GUVs colonies was directly
related to the shape parameters of the microwells. The size of the
columnar GUVs colonies can be modulated by the diameter of
microwell templates (Supplementary Fig. 12). Columnar GUVs
colonies with aspect ratios (height/diameter) of 0.5 (Fig. 1d), 1.0,
and 1.5 (Supplementary Fig. 13) can be obtained via the variation
of the microwell aspect ratios. Moreover, through varying the
design of the structure of the microwells, GUVs colonies with
different morphologies, including triangular, square, striped, and
HIT-shape assemblies, were obtained (Fig. 1g).
From abovementioned results, we have demonstrated that the
magnetic eld distribution in the microwells was the result of the
interplay of the magnetized magnetic eld from SS mesh and the
external magnetic eld from the magnets. In microwells, the
magnetized magnetic eld was in opposite direction to the
external magnetic eld, which weakened the magnetic eld
strength. Therefore, the magnetic eld distribution inside each
well can be adjusted by the SS mesh layout. For SS mesh with
decentralized microwells (Fig. 1b), the square unit of the
microwell arrays (white dash box) can be approximately
considered as a circular region (black dash circle). The magnetic
eld was radially decreased from the center to the well walls
(Fig. 1b), resulting in axisymmetric columnar GUVs colonies
(Fig. 1c, d). However, when the microwells were quite hugging
(Fig. 1h), the square corners (indicated by the black arrows)
generated more magnetized magnetic eld, which resulted in the
weakening of magnetic eld strength in greater degree at the part
of microwells adjacent to the corner (bottom image in Fig. 1h).
The magnetic eld microenvironments in the microwells then
guided the assembly of GUVs into Chinese ancient coin-like
round GUVs colonies with square holes (Fig. 1i). GUV colonies
with other morphologies, such as round colonies with oval,
elliptical, heart-shaped, half-round, or hexagonal holes, and
striped colonies with waved edges, can be predicted to generate
by varying the spatial organization of the microwells according to
the simulated results (Supplementary Fig. 14). Taken together,
from abovementioned results, GUVs colonies with various
morphologies were formed by the variation of microwell
morphologies and spatial organization under vertical
magnetic eld.
GUVs assembly under horizontal and inclined magnetic eld.
The above text addressed the inuence of the morphology and
spatial organization of microwells on GUVs colonies formation
under external vertical magnetic eld. The following text will
discuss the inuences of external magnetic eld with other
directions, i.e., horizontal magnetic eld and inclined magnetic
eld, on GUVs colonies formation. Under horizontal external
To the magnet center
Magnetic field strength (T)
Magnetic field strength (T)
Side view
Top view
Top view
To magnet center (1 1)
(4 4)
Fig. 2 Assembly of GUVs on the SS mesh under horizontal and inclined magnetic eld. a The schematic of the device for horizontal magnetic eld.
bSimulated magnetic eld distribution on the top surface of the SS mesh under horizontal magnetic eld. cFluorescence images of the GUVs colonies
formed under horizontal magnetic eld. The right image is the enlarged image in the yellow dash box of the left image. dThe schematic of the device for
inclined magnetic eld (with directions between the vertical and horizontal magnetic elds) by putting the SS mesh on one side of the top of the magnet.
eSimulated magnetic eld distribution at the bottom surface of the SS mesh under inclined magnetic eld. fFluorescence images of the GUVs colonies
under inclined magnetic eld. The right image is the enlarged image in the yellow dash box of the left image. The dash circles in b,c,e, and findicate the
microwells. The scale bars in cand fare 200 μm.
4NATURE COMMUNICATIONS | (2020) 11:232 | |
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magnetic eld by locating the SS mesh between two face-to-face
magnets (Fig. 2a), the region with minimum magnetic eld
strength located on the frame of the SS mesh (Fig. 2b). So
stripped GUVs colonies perpendicular to external magnetic eld
were formed on the frames rather than inside the microwells
(white dash circles) (Fig. 2c). Inclined external magnetic eld
containing both horizontal and vertical components was provided
by putting the SS mesh on one side of magnet top surface
(Fig. 2d), which resulted in Janus distribution of magnetic eld
strength at the bottom surface of the microwells. The part of
individual microwell away from the magnet center was in low
magnetic eld strength (blue), while the opposite part was in high
magnetic eld strength (red) (Fig. 2e). Therefore, as presented by
the uorescence images, GUVs aggregated at the part of indivi-
dual microwell away from the magnet center rather than the
other side (Fig. 2f). Moreover, a gradient occupancy of the
microwells by GUVs was observed in the experiments (Fig. 2f and
Supplementary Fig. 15). From the microwells near the magnet
center to those close to the magnet edge, the amount of GUVs in
microwells gradually decreased. For example, more than half area
of microwell (1 1) in Fig. 2f was lled by GUVs, while microwell
(4 4) away from the magnet center was only occupied for about
one third of the area. We ascribe the gradient location of GUVs to
the non-uniform spatial distribution of the inclined magnetic
eld. As presented by the simulated magnetic eld distribution
around the magnet (Supplementary Fig. 16), the ratio of hor-
izontal component to the vertical component increased from the
magnet center to the edge, which resulted in decreased areas with
low magnet ux density in Fig. 2e for GUVs to occupy.
Formation of hybrid GUVs colonies. Biological tissues are
composed of coded microstructures with different cell types. To
mimic this structural complexity, we magnetically manipulated
the assembly of two kinds of GUVs, i.e., 1,2-dioleoyl-sn-glycero-
(NBD PE) labeled GUVs with green uorescence (gGUVs) and
1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine with
triethylammonium salt (TR DHPE) labeled GUVs with red
uorescence (rGUVs) into congurations with different spatial
organizations. Parallel coding with fully mixed gGUVs and
rGUVs was obtained for the assembly event of pre-mixed GUVs
under vertical magnetic eld (Fig. 3a, Supplementary Fig. 17).
However, higher-order structures with serially coded GUVs
colonies can be obtained via the alternate addition of different
GUVs or the application of different magnetic elds. Firstly,
patterned layer-by-layer gGUVs and rGUVs colonies were
observed via the alternate addition of these two kinds of GUVs
under vertical magnetic eld (Fig. 3b, Supplementary Figs. 18 and
19). The ratio of these two GUVs colonies in the microwells can
be modulated by varying the added amount of different GUVs
(Supplementary Fig. 20) and the structure of the microwells
sculpted morphologies of the microarchitecture (Supplementary
Fig. 21). The top and side view of the microstructures under laser
confocal microscope conrmed their coaxially coded congura-
tion (Supplementary Fig. 22). Secondly, asymmetrically cong-
ured microstructures with two different GUVs colonies were
obtained via the alternate application of two inclined magnetic
elds (Case 1, Fig. 3c and Supplementary Fig. 23) or one inclined
one and another vertical one (Case 2, Fig. 3d and Supplementary
Fig. 23) for the chronological trapping of two GUV types. In case
1, the two inclined magnetic elds had different directions, with
one of them provided by putting the SS mesh on one side of the
top surface of the magnet and the other one provided by putting
it at the opposite side. In case 2, except for the rGUVs colonies
that were located opposite to the pre-trapped gGUVs in the
microwells, an additional rGUVs layer was formed near the pre-
trapped GUVs layer as indicated by the white arrows. This can be
attributed to the shaping effect of the pre-trapped GUVs colonies
on the spatial distribution of magnetic eld in the microwells,
resulting in local weak magnetic eld around them for GUVs
aggregation (Supplementary Fig. 4b). Thirdly, grid-like aggregates
composed of orthogonal gGUVs and rGUVs stripes (Fig. 3e,
Supplementary Fig. 24) can be generated by the successive
application of two horizontal magnetic eld perpendicular to each
other for the respectively trapping of gGUVs and rGUVs. Finally,
through the successive application of one vertical magnetic eld
for gGUVs and two perpendicular horizontal magnetic elds for
rGUVs, we obtained more complex structures containing
columnar gGUVs colonies in the microwells and meshed rGUVs
on the grid (Fig. 3f, Supplementary Fig. 24).
Versatility of the magnetic assembly method. Taken together,
via the modulation of SS mesh parameters (microwell morphol-
ogies and organizations) and external magnetic eld, we proposed
a robust and cost-effective method to manipulate large quantity
of GUVs into tissue-mimic microstructures with different
morphologies and spatial organizations. Moreover, this method
can also be applied for the assembly of GUVs on Ni wires to form
1D colonies (Supplementary Fig. 25), on Ni foam to form 3D
networks (Supplementary Fig. 26), and even along the scratch on
a stainless sheet to generate 1D colonies arrays (Supplementary
Fig. 27). Other materials, including gel particles, emulsions,
bubbles and even cells, can all be trapped around the support to
form dened structures (Supplementary Fig. 28). The versatility,
universality, simplicity, and scalability of this method endowed it
with potential boom of applications in synthetic biology, tissue
engineering, photic and electronic devices fabrication, the engi-
neering of electrode surfaces, and the quality control of iron
materials, etc. In this paper, we mainly focus on their potential as
proto-tissues to provide a stable environment for individual cell-
mimic GUVs, and to spatialize biochemical reactions.
Osmotic stability of the GUVs colony. As cell mimics, individual
GUVs suspensions are very fragile. For example, an imbalanced
osmotic (hypotonic or hypertonic) condition can easily cause
their deformation or rupture2830. This impeded their application
in advanced synthetic cells development, cell biology, and bio-
sensing, etc. However, in this work, when GUVs were magneti-
cally gathered to form GUVs colonies, they displayed
uncustomary stability. For colonies composed of GUVs encap-
sulating 400 mM sucrose, no morphology change for individual
GUVs was observed in a hypotonic condition provided by pure
water, and hypertonic conditions provided by 1000 mM glucose,
500 mM NaCl and even 333 mM CaCl
(Supplementary Fig. 29).
The osmotic stability of the GUVs colony originated from the
resistance of the closely packed GUVs in the colony as a collective
to the external osmotic shock. In hypotonic condition provided
by pure water, the reinforced mechanical stability of individual
GUVs from the crowded GUVs surroundings impeded their
rupture and maintained their morphologies. In hypertonic con-
ditions, GUVs in unbalanced osmotic condition experienced a net
force from the high concentration region to the low concentration
region (Supplementary Fig. 30a). In previous studies, this unba-
lanced osmotic condition drove the motion of cancer cells and
GUVs to the region with low osmolyte concentration following
the osmotic engine model31,32. In our case, the forces generated
from the unbalanced osmotic condition compressed the GUVs
colony. This compression was better presented for the colony that
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partially occupied the microwell. Under isotonic condition, the
newly assembly GUVs colony contained some protrusions (yel-
low dash line in the left image of Supplementary Fig. 31). When
external solution was replaced with 1 M glucose solution to
introduce a hypertonic osmotic stress, the GUVs colony was
compressed and the osmotic stress smoothed the interface
between the GUVs colony and external solution (middle image in
Supplementary Fig. 31). Protrusions reappeared when the
hypertonic external solution was replaced with hypotonic pure
water (right image in Supplementary Fig. 31). The compression
from the external hypertonic osmotic stress sealed the voids
among GUVs near the external solution, resulting in the failure of
osmolyte and uorescent dyes to penetrate into the GUVs colony
(Supplementary Fig. 30b) as conrmed by Supplementary
Fig. 30cf. In isosmotic assembly solution containing MnCl
resorun molecules in external solution gradually diffused into
the voids of GUVs colonies, as evidenced by the gradually
enhanced red uorescence intensity of resorun with time in
Supplementary Fig. 30c. In hypertonic glucose, NaCl, or CaCl
solutions, the red uorescence of resorun was not observed
(Supplementary Fig. 30df), indicating its failure to penetrate into
the GUVs colony. The block of the GUVs colony to small
molecules made it behave as an elastic collective under hypertonic
osmotic stress. The osmotic compression increased the elasticity
energy of the GUVs colony, resulting in a negative hydrostatic
energy in the GUVs colony that promoted the entering of water
into the colony. The negative hydrostatic energy (promoting
water in and elasticity energy release) balanced the osmotic stress
(promoting water out) to stabilize the GUVs colony under
hypertonic conditions. This osmotic stability of GUVs colonies
endowed them as robust models for widespread applications.
Moreover, it may also provide a tentative clue for the formation
Parallel coding
Serial coding
magnetic field
magnetic field
magnetic field
Fig. 3 Coding of spatially controlled GUVs colonies. a Schematic and uorescence images of GUVs colonies formed via the parallel coding of giant
unilamellar vesicles with green uorescence (gGUVs) and giant unilamellar vesicles with red uorescence (rGUVs). Schematic and uorescence images of
the serially coded GUVs colonies via application of vertical magnetic eld for the alternative assembly of gGUVs and rGUVs (b), successive application of
two inclined magnetic elds with different directions respectively for gGUVs assembly (putting the SS mesh on one side of the magnet) and rGUVs
(putting the SS mesh on the other side of the magnet) (c), successive application of inclined magnetic eld for gGUVs assembly and vertical magnetic
eld for rGUVs assembly (d), successive application of two perpendicular horizontal magnetic elds for the chronological assembly of gGUVs and rGUVs
(e), and successive application of vertical magnetic eld for gGUVs assembly and two perpendicular horizontal magnetic elds for rGUVs assembly
(f). The dash circles indicated the microwell wall. The scale bars are 100 μm.
6NATURE COMMUNICATIONS | (2020) 11:232 | |
Content courtesy of Springer Nature, terms of use apply. Rights reserved
of proto-tissues from protocells on the early earth, since the
membrane-based protocells aggregates exhibit a mechanical sta-
bility in face of external shock.
Spatialized cascade reaction in the colonies. One unique prop-
erty of cells is their ability to spatialize biochemical reactions
among organelles or tissues for efcient biosynthesis or precise
signaling. In the following part, we evaluated the ability of the
spatially coded GUVs aggregates to mimic the spatialized bio-
chemical process in a simplied model. Two kinds of GUVs, i.e.,
gGUVs with melittin pores encapsulated with glucose oxidase
(GOD) and non-labeled GUVs encapsulated with horseradish
peroxidase (HRP), were magnetically assembled into coaxially
coded colonies in the microwells under vertical magnetic eld
(Fig. 4a, b). With the addition of glucose and Amplex Red in the
external solution, glucose entered gGUVs through melittin pores,
and the uncharged Amplex Red passively diffused across the lipid
bilayers33. The GOD in gGUVs catalyzed the oxidation of glucose
to generate H
, which diffused into the non-labeled GUVs,
where they reacted with Amplex Red under the catalysis of HRP
to generate the product of resorun with red uorescence
(Fig. 4a). The non-labeled GUVs contained no protein pores, and
would also not oxidize the membranes to generate mem-
brane defects34,35 (Supplementary Fig. 32), so the charged
resorun molecules were trapped in the GUVs. With the increase
of time, more resorun molecules were formed, so the uores-
cence intensity increased, until a plateau was achieved above 30
min (Fig. 4c, d). The red uorescence of resorun was mainly
observed in the non-labeled GUVs (Fig. 4e), which indicated the
ability of the magnetically coded GUVs aggregates to compart-
mentalize and spatialize biochemical reactions mimicking natural
tissues. Except for the small molecules mediated chemical com-
munication between articial tissue-like assemblies, this techni-
que can also be utilized to study the chemical process between
GUVs colonies and cell colonies (Fig. 4f, g, and Supplementary
Amplex red
gGUVs with melittin Non-labelled GUVs
0 min 5 min
10 min 15 min
Cell death
Cell colony
GUVs colony
Cell colony
intensity (a.u.)
Time (min)
gGUVs colony Colony of non-labelled
Fig. 4 Spatialized biochemical reactions in tissue-like GUVs aggregates. a Schematic illustration for the chemical communication between the colony of
gGUVs with melittin and the non-labeled GUVs colony. bFluorescence image and bright eld image of the GUVs aggregates with two coaxial GUVs
colonies: uorescence image of the colonies of gGUVs with melittin (left), bright eld image of the two kind of colonies (middle), merged image (right).
cFluorescence images of the GUVs aggregates against time after the biochemical reaction was initiated by the addition of glucose and Amplex Red.
dVariation of the uorescence intensity of the product against time. The error bar represents the standard error of mean (SEM), n=3 independent
experiments. eFluorescence images of the tissue-like GUVs aggregates with uorescent resorun product: uorescent image of gGUVs colony (left),
uorescent image of the product of resorun (middle), merged image (right). fSchematic illustration of the cell death caused by H
that is generated by
the GUVs colonies. gImages for the H
caused cell death: bright eld image of GUVs colonies and cell colonies (the rst one), uorescence image of live
cells (the second one), uorescence image of dead cells (the third one), and merged image (the last one). GOD in aand frepresents glucose oxidase. HRP
in arepresents horseradish peroxidase. The scale bars were 100 μm. Source data are provided as a Source Data le.
NATURE COMMUNICATIONS | (2020) 11:232 | | 7
Content courtesy of Springer Nature, terms of use apply. Rights reserved
Fig. 33). The GUVs encapsulated with GOD generated H
which diffused to the cell colony and caused cell death. The live
cells were stained with uorescein diacetate (FDA) with green
uorescence, and dead cells were labeled by propidium iodide
(PI) with red uorescence. After 6 h of incubation in 400 mM
glucose solution, almost all the cells died as indicated by the
negligible green uorescence in the second image of Fig. 4g and
the evident red uorescence in the third image of Fig. 4g. As a
control, GUVs colonies contained no cell death because of the
absence of red uorescence (Supplementary Fig. 34). According
to the above experimental result, this technique holds great
potential in the investigation of more complicated biological
processes for the study of cell biology and the development of
tissue models with higher-order collective behaviors.
In summary, we obtained tissue-mimicking GUVs aggregates
arrays with different morphologies and spatially coded cong-
urations using a SS mesh under magnetic eld. GUVs in these
aggregates exhibited uncustomary stability in hypotonic or
hypertonic conditions in comparison with individual GUVs
suspensions, which made them robust models for application in
synthetic biology and cell biology, and suggests possible clues for
the evolution of multicellular cells on early earth. Via the spatial
coding of GUVs or cells, designated GUVs were illumined and
cell death was triggered by enzyme reactions, proving the ability
of the model to mimic the spatialized biochemical processes in
natural tissues. This work paved the way for the study of higher-
order tissue behaviors via the groundbreaking manipulation of
diamagnetic objects into dened 3D structures.
Materials. 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmi-
toyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-dioleoyl-sn-glycero-3-phos-
pho-L-serine (sodium salt) (DOPS) were purchased from Avanti Polar Lipids
(USA). 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzox-
adiazol-4-yl) (NBD PE) and Texas red labeled 1,2-dihexadecanoyl-sn-glycero-3-
phosphoethanolamine, triethylammonium salt (TR-DHPE) were obtained from
Invitrogen (China). Sucrose, glucose, HRP, GOD, Amplex Red, melittin, FDA, PI,
manganese (II) chloride, and Gadobutrol were purchased from Sigma (China).
Cylindrical NdFeb magnets (1T, diameter =3 cm, thickness =1 cm) were bought
from Gates Qiangci Company (Shanghai, China). The square SS mesh (1 cm ×1
cm) with thickness of 100 μm was custom-made by RGRS Company (Shenzhen,
China). Indium tin oxide (ITO) electrode was purchased from Hangzhou Yuhong
technology Co. Ltd (China). Millipore Milli-Q water with a resistivity of 18.2 MΩ
cm was used in the experiments.
Giant unilamellar vesicles (GUVs) formation. Two kinds of mother GUVs
samples, i.e., DMPC/NBD PE (w/w, 95/5) GUVs and DMPC/DOPS/TR-DHPE
(w/w/w, 95/4.5/0.5) GUVs, were formed using electroformation method in 400 mM
sucrose solution using two face-to-face electrode layout of ITO electrodes. Lipid
thin lms were formed in the following procedure: 20 μL of lipid solution (5.0 mg
mL1) was deposited on ITO electrode, and spread using a needle, followed by
drying in a vacuum desiccator for 2 h. The two slides of ITO electrodes were then
assembled with a 2 mm thick Teon spacer with a 2 cm × 1 cm hole, as reported
elsewhere28,36,37. To form GUVs, the electroformation instrument was placed on a
hot plate with temperat ure of 45 °C, and an AC electric eld with amplitude of 5 V
and frequency of 10 Hz was applied for 2 h. The GUVs were observed under the
uorescence microscope.
GUVs colonies formation. GUVs colonies were formed under magnetic eld in a
home-made device (Supplementary Fig. 5). The device was assembled by adhering
a square Teon cell with opening size of ~1.1 cm × 1.1 cm to a cover slip using
vacuum grease, followed by putting the SS mesh on the top of the cover slip in the
cell. Before using it for GUVs assembly, the device was rstly treated in below
procedure to avoid GUVs rupture during GUVs entrapment experiments. A total
of 200 μL of DPPC ethanol-water solution with ethanol volume percentage of 40%
and DPPC concentration of 0.10 mg mL1(similar composition used for bicelles
formation3840 by us) were added in the cell. The device was then heated at 50 °C
for 5 min, and washed using 133 mM MnCl
solution for at least three times,
resulting in the formation of supported DPPC membranes on the cover slip and SS
mesh. To form GUVs colony arrays, GUVs mother dispersion in 400 mM sucrose
solution was mixed with isotonic MnCl
(133 mM) solution to obtain a mixture
with volume of 300 μL. The mixture was added in the cell, and then the device was
put in magnetic eld generated by NdFeB magnets. The GUVs concentration was
controlled by varying the volume ratio of GUVs sucrose solution and 133 mM
solution with xed nal solution volume of 300 μL. Magnetic elds with
three different directions were used in the GUVs colonies formation experiments.
The vertical magnetic eld was provided by putting the SS mesh on the top center
of the magnet. The horizontal magnetic eld was provided by putting the SS mesh
between two face-to-face magnets. An inclined magnetic eld was provided by
putting the SS mesh on one side of the top of the magnet. To obtain colonies with
coded GUVs assemblies, GUVs solution containing different GUVs were
successively added, or magnetic elds with different directions were successively
applied. The most GUVs magnetic entrapment experiments were lasting more
than 2 h.
Spatialized chemical communications. The communication between two GUVs
populations or one GUVs population and one cell colony was investigated. For the
study of communication between two GUVs populations, gGUVs and non-labeled
GUVs were electroformed in 400 mM sucrose solution containing 12 μgmL
GOD and 1.2 μgmL
1HRP, respectively. gGUVs encapsulated with GOD was
rstly magnetically trapped in the microwells under vertical magnetic eld, incu-
bated in solution with 12 μgmL
1melittin for 2 h, and carefully washed with
excess MnCl
solution to remove the non-encapsulated GOD and free melittin.
Then the non-labeled GUVs encapsulated with HRP were added and trapped in the
microwells under vertical magnetic eld followed by the remove of non-
encapsulated HRP via careful washing with MnCl
solution. To initiate the reac-
tions, the external solution was replaced with 400 mM glucose containing 50 μM
Amplex Red. The uorescent product of the cascade reaction was monitored using
uorescence microscope. For the investigation of the communication between
GUVs population and cell colony, non-labeled GUVs encapsulated with GOD were
trapped in microwells, incorporated with melittin, and washed with excess
Gadobutrol solution. Then HEPG2 cells were added to form coaxial aggregates of
GUVs population (encapsulated with GOD) and cell colony. For comparison,
coaxial aggregates of GUVs population with no GOD and cell colony were also
fabricated. The two microstructures were then incubated in 400 mM glucose
solution for 6 h. The communication between GUVs and cells was veried via the
check of cell viability. Live and dead cells were stained with FDA and PI,
Characterization. The topology of the SS mesh was characterized by uorescence
microscope (Olympus IX73, Japan) and scanning electron microscopy (Quanta 200
FEG, Netherlands). The uorescence images of the GUVs colonies were obtained
by uorescence microscope and laser confocal microscope (Olympus FV 3000,
Simulation. The magnetic eld distribution around the SS mesh was simulated
using COMSOL Multiphysics 4.3 software. The magnetic susceptibilities of GUVs,
SS mesh, and 133 mM MnCl
solution were 1.0 × 105, 2, and 0.03, respectively.
The external magnetic eld generated by magnets magnetized the SS mesh for
GUVs assembly.
Reporting summary. Further information on research design is available in
the Nature Research Reporting Summary linked to this article.
Data availability
The source data underlying Fig. 4d and Supplementary Figs. 6b, 9a, b, c, 11b, 32b, and d
are provided as a Source Data le. The data that support the ndings of this study are
available within the paper and its supplementary information. All other relevant data are
available from the authors upon reasonable request.
Received: 22 July 2019; Accepted: 11 December 2019;
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This work was supported by the National Natural Science Foundation of China (Grant
No. 21773050), the Natural Science Foundation of Heilongjiang Province for Dis-
tinguished Young Scholars (JC2018003).
Author contributions
X.J.H. supervised the research. X.J.H., Q.C.L., and S.B.L. conceived and designed the
experiments. Q.C.L., S. B. L., X. X. Z, and W. L. X. performed experiments. X.J.H., Q.C.L.,
S. B. L., X. X. Z, and W. L. X. analyzed the data. X.J.H., Q.C.L., and S. B. L wrote the
paper, and all authors commented on the paper. Q. C. L and S. B. L contributed equally
to this work.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at
Correspondence and requests for materials should be addressed to X.H.
Peer review information Nature Communications thanks Atul Parikh and the other,
anonymous, reviewer(s) for their contribution to the peer review of this work. Peer
reviewer reports are available.
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... Due to differences in magnetic susceptibilities, paramagnetic agents are typically divided into two groups, paramagnetic and superparamagnetic substances. Manganese (II) chloride (MnCl 2 ) 81 and Gd 3þ chelates (Gadolinium, 20,82 Gadabutrol 83 etc.) are two of the most commonly used paramagnetic agents for diamagnetic objects manipulation with magnetic susceptibilities in the range of 10 À3 (dimensionless), 84 while SPIONs attain two orders of larger magnetic susceptibilities (Fig. 4). 85 ...
... Interestingly, the authors found that particle size was an important factor that dictated movement, where colloidal particles with larger sizes tended to move to the center of the hole within the nickel grid, which is the field maximum. Following this work, in 2020, Han et al. 81 leveraged magnetized stainless-steel meshes to assemble vesicles into different geometries [ Fig. 6(a)]. The stainless-steel mesh was positioned at different spots of the magnet to generate heterogeneous magnetic fields. ...
... For example, magnetized metal plates with holes can generate magnetic gradients across the hole to effect spatial assembly of cells within each hole. 81 Future explorations in this field could include alternative designs to further broaden the applications of diamagnetic cell manipulation. For instance, a magnetized metal plate featuring a rectangular aperture could be employed to create structures using endothelial cells, thus facilitating the generation of vessel-like structures. ...
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Cell manipulation techniques such as those based on three-dimensional (3D) bioprinting and microfluidic systems have recently been developed to reconstruct complex 3D tissue structures in vitro. Compared to these technologies, magnetic force-based cell manipulation is a simpler, scaffold- and label-free method that minimally affects cell viability and can rapidly manipulate cells into 3D tissue constructs. As such, there is increasing interest in leveraging this technology for cell assembly in tissue engineering. Cell manipulation using magnetic forces primarily involves two key approaches. The first method, positive magnetophoresis, uses magnetic nanoparticles (MNPs) which are either attached to the cell surface or integrated within the cell. These MNPs enable the deliberate positioning of cells into designated configurations when an external magnetic field is applied. The second method, known as negative magnetophoresis, manipulates diamagnetic entities, such as cells, in a paramagnetic environment using an external magnetic field. Unlike the first method, this technique does not require the use of MNPs for cell manipulation. Instead, it leverages the magnetic field and the motion of paramagnetic agents like paramagnetic salts (Gadobutrol, MnCl2, etc.) to propel cells toward the field minimum, resulting in the assembly of cells into the desired geometrical arrangement. In this Review, we will first describe the major approaches used to assemble cells in vitro—3D bioprinting and microfluidics-based platforms—and then discuss the use of magnetic forces for cell manipulation. Finally, we will highlight recent research in which these magnetic force-based approaches have been applied and outline challenges to mature this technology for in vitro tissue engineering.
... The application of an alternating current proposed by Anglova can promote the hydration and swelling of phospholipid membrane [14,53]. The phospholipid membrane layer should be uniformly deposited on special electrode surfaces, such as Pt wire [55], indium tin oxide (ITO) electrode [56,57] and stainless steel electrode [58]. Giant unilamellar vesicles (GUVs) with diameters in the range of 5-200 μm were prepared using an alternating current (frequency: 10 Hz; voltage of 1-7 V; time: 2 h) produced by the electrodes submerged in an aqueous solution [59]. ...
Artificial cells have received much attention in recent years as cell mimics with typical biological functions that can be adapted for therapeutic and diagnostic applications, as well as having an unlimited supply. Although remarkable progress has been made to construct complex multifunctional artificial cells, there are still significant differences between artificial cells and natural cells. It is therefore important to understand the techniques and challenges for the fabrication of artificial cells and their applications for further technological advancement. The key concepts of top-down and bottom-up methods for preparing artificial cells are summarized, and the advantages and disadvantages of the bottom-up methods are compared and critically discussed in this review. Potential applications of artificial cells as drug carriers (microcapsules), as signaling regulators for coordinating cellular communication and as bioreactors for biomolecule fabrication, are further discussed. The challenges and future trends for the development of artificial cells simulating the real activities of natural cells are finally described.
... The spatial distribution of species in communities is important for communication among species and for species to execute their functions. Spatially coded three-species communities were constructed inside each well of a steel mesh (Supplementary Fig. 17) under a magnetic field using the Magneto-Archimedes principle with a homemade device 45,46 (Supplementary Fig. 18). Gadobutrol is a paramagnetic contrast agent used in magnetic resonance imaging 47 . ...
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Constructing a synthetic community system helps scientist understand the complex interactions among species in a community and its environment. Herein, a two-species community is constructed with species A (artificial cells encapsulating pH-responsive molecules and sucrose) and species B (Saccharomyces cerevisiae), which causes the environment to exhibit pH oscillation behaviour due to the generation and dissipation of CO2. In addition, a three-species community is constructed with species A′ (artificial cells containing sucrose and G6P), species B, and species C (artificial cells containing NAD⁺ and G6PDH). The solution pH oscillation regulates the periodical release of G6P from species A′; G6P then enters species C to promote the metabolic reaction that converts NAD⁺ to NADH. The location of species A′ and B determines the metabolism behaviour in species C in the spatially coded three-species communities with CA′B, CBA′, and A′CB patterns. The proposed synthetic community system provides a foundation to construct a more complicated microecosystem.
... In the same context, Li et al. used lipid-based vesicles to fabricate artificial prototissue models by magnetic field-driven assembly approach. [80] Their paramagnetic MnCl 2 or gadobutrol-containing GUVs were spatially distributed on a stainless steel mesh, where the applied magnetic field affected the particles through the grids of the mesh. Liu et al. used lipid-stabilized coacervate-based artificial cells to create tubular structures that resemble vasculature. ...
The fast‐growing pace of regenerative medicine research has allowed the development of a range of novel approaches to tissue engineering applications. Until recently, the main points of interest in the majority of studies have been to combine different materials to control cellular behavior and use different techniques to optimize tissue formation, from 3‐D bioprinting to in situ regeneration. However, with the increase of the understanding of the fundamentals of cellular organization, tissue development, and regeneration, has also come the realization that for the next step in tissue engineering, a higher level of spatiotemporal control on cell‐matrix interactions is required. It is proposed that the combination of artificial cell research with tissue engineering could provide a route toward control over complex tissue development. By equipping artificial cells with the underlying mechanisms of cellular functions, such as communication mechanisms, migration behavior, or the coherent behavior of cells depending on the surrounding matrix properties, they can be applied in instructing native cells into desired differentiation behavior at a resolution not to be attained with traditional matrix materials.
... Specically, magnetic elds can induce directional magnetic dipolar interactions, facilitating precise regulation of the position and orientation of building blocks. 202 Meanwhile, the high controllability of magnetic interactions in both time and space provides opportunities to design or dynamically adjust the structure and properties of the macroscopic assemblies. 203 Recently, our group constructed large-scale patterns of magnetic potential traps generated by a ferromagnetic microstructure array to assemble polymeric microspheres suspended in ferrouids (Fig. 7a). ...
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Hierarchical self-assembly of organic molecules or assemblies is of great importance for organic photonics to move from fundamental research to integrated and practical applications. Magnetic fields with the advantages of high controllability, non-contact manipulation, and instantaneous response have emerged as an elegant way to prepare organic hierarchical nanostructures. In this perspective, we outline the development history of organic photonic materials and highlight the importance of organic hierarchical nanostructures for a wide range of applications, including microlasers, optical displays, information encoding, sensing, and beyond. Then, we will discuss recent advances in magnetically controlled assembly for creating organic hierarchical nanostructures, with a particular focus on their potential for enabling the development of integrated photonic devices with unprecedented functionality and performance. Finally, we present several perspectives on the further development of magnetically controlled assembly strategies from the perspective of performance optimization and functional design of organic integrated photonics.
... Microgels with MNPs embedded can be manipulated remotely by an external magnetic field. Iron oxide particles are biocompatible with low toxicity, [17] and photo-crosslinking of GelMA allows the biomaterial inks to be solidified, which is essential for in vivo implanting, [18] To investigate the reconfigurability and stability of the molded droplets, we characterized the interfacial assembly dynamics and apparent surface coverage (SC) of the alginate-surfactants. The interfacial tension and SC were measured by pendant drop tensiometry. ...
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All‐liquid molding can be used to transform a liquid into free‐form solid constructs, while maintaining internal fluidity. Traditional biological scaffolds, such as cured pre‐gels, are normally processed in solid state, sacrificing flowability and permeability. However, it is essential to maintain the fluidity of the scaffold to truly mimic the complexity and heterogeneity of natural human tissues. Here, this work molds an aqueous biomaterial ink into liquid building blocks with rigid shapes while preserving internal fluidity. The molded ink blocks for bone‐like vertebrae and cartilaginous‐intervertebral‐disc shapes, are magnetically manipulated to assemble into hierarchical structures as a scaffold for subsequent spinal column tissue growth. It is also possible to join separate ink blocks by interfacial coalescence, different from bridging solid blocks by interfacial fixation. Generally, aqueous biomaterial inks are molded into shapes with high fidelity by the interfacial jamming of alginate surfactants. The molded liquid blocks can be reconfigured using induced magnetic dipoles, that dictated the magnetic assembly behavior of liquid blocks. The implanted spinal column tissue exhibits a biocompatibility based on in vitro seeding and in vivo cultivating results, showing potential physiological function such as bending of the spinal column.
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The exponential growth of research on artificial cells and organelles underscores their potential as tools to advance the understanding of fundamental biological processes. The bottom–up construction from a variety of building blocks at the micro‐ and nanoscale, in combination with biomolecules is key to developing artificial cells. In this review, artificial cells are focused upon based on compartments where polymers are the main constituent of the assembly. Polymers are of particular interest due to their incredible chemical variety and the advantage of tuning the properties and functionality of their assemblies. First, the architectures of micro‐ and nanoscale polymer assemblies are introduced and then their usage as building blocks is elaborated upon. Different membrane‐bound and membrane‐less compartments and supramolecular structures and how they combine into advanced synthetic cells are presented. Then, the functional aspects are explored, addressing how artificial organelles in giant compartments mimic cellular processes. Finally, how artificial cells communicate with their surrounding and each other such as to adapt to an ever‐changing environment and achieve collective behavior as a steppingstone toward artificial tissues, is taken a look at. Engineering artificial cells with highly controllable and programmable features open new avenues for the development of sophisticated multifunctional systems.
An important goal for bottom-up synthetic biology is to construct tissue-like structures from artificial cells. The key is the ability to control the assembly of the individual artificial cells. Unlike most methods resorting to external fields or sophisticated devices, inspired by the hanging drop method used for culturing spheroids of biological cells, we employ a capillary-driven approach to assemble giant unilamellar vesicles (GUVs)-based protocells into colonized prototissue arrays by means of a coverslip with patterned wettability. By spatially confining and controllably merging a mixed population of lipid-coated double-emulsion droplets that hang on a water/oil interface, an array of synthetic tissue-like constructs can be obtained. Each prototissue module in the array comprises multiple tightly packed droplet compartments where interfacial lipid bilayers are self-assembled at the interfaces both between two neighboring droplets and between the droplet and the external aqueous environment. The number, shape, and composition of the interconnected droplet compartments can be precisely controlled. Each prototissue module functions as a processer, in which fast signal transports of molecules via cell-cell and cell-environment communications have been demonstrated by molecular diffusions and cascade enzyme reactions, exhibiting the ability to be used as biochemical sensing and microreactor arrays. Our work provides a simple yet scalable and programmable method to form arrays of prototissues for synthetic biology, tissue engineering, and high-throughput assays.
The bottom‐up fabrication of synthetic cells (protocells) from molecules and materials, is a major challenge of modern chemistry. A significant breakthrough has been the engineering of protocells capable of chemical communication using bio‐derived natural molecules and ex situ stabilised cell machineries. These, however, suffer from short shelf‐lives, high costs, and require mild aqueous conditions. In this Concept Article we analyse the chemistry at the heart of protocell communication to highlight new opportunities for synthetic chemists in protocell engineering. Specifically, we (i) categorise the main bio‐derived chemical communication machineries in enzyme cascades, DNA strand displacement, and gene‐mediated communication; (ii) review the chemistries of these signal transduction machineries; and (iii) introduce new types of bio‐inspired, fully synthetic artificial enzymes to replace their natural counterparts. Developing protocells that incorporate synthetic analogues of bio‐derived signal transduction machineries will improve the robustness, stability and versatility of protocells, and broaden their applications to highly strategic fields such as photocatalysis and fine chemicals production.
In metazoans, living cells achieve capabilities beyond individual cell functionality by assembling into multicellular tissue structures. These higher-order structures represent dynamic, heterogeneous, and responsive systems that have evolved to regenerate and coordinate their actions over large distances. Recent advances in constructing micrometer-sized vesicles, or synthetic cells, now point to a future where construction of synthetic tissue can be pursued, a boon to pressing material needs in biomedical implants, drug delivery systems, adhesives, filters, and storage devices, among others. To fully realize the potential of synthetic tissue, inspiration has been and will continue to be drawn from new molecular findings on its natural counterpart. In this review, we describe advances in introducing tissue-scale features into synthetic cell assemblies. Beyond mere complexation, synthetic cells have been fashioned with a variety of natural and engineered molecular components that serve as initial steps toward morphological control and patterning, intercellular communication, replication, and responsiveness in synthetic tissue. Particular attention has been paid to the dynamics, spatial constraints, and mechanical strengths of interactions that drive the synthesis of this next-generation material, describing how multiple synthetic cells can act as one.
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The process of crystallization is difficult to observe for transported, out-of-equilibrium systems, as the continuous energy injection increases activity and competes with ordering. In emerging fields such as microfluidics and active matter, the formation of long-range order is often frustrated by the presence of hydrodynamics. Here we show that a population of colloidal rollers assembled by magnetic fields into large-scale propelling carpets can form perfect crystalline materials upon suitable balance between magnetism and hydrodynamics. We demonstrate a field-tunable annealing protocol based on a controlled colloidal flow above the carpet that enables complete crystallization after a few seconds of propulsion. The structural transition from a disordered to a crystalline carpet phase is captured via spatial and temporal correlation functions. Our findings unveil a novel pathway to magnetically anneal clusters of propelling particles, bridging driven systems with crystallization and freezing in material science.
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Multicellularity enables the growth of complex life forms as it allows for the specialization of cell types, differentiation and large-scale spatial organization. In a similar way, modular construction of synthetic multicellular systems will lead to dynamic biomimetic materials that can respond to their environment in complex ways. To achieve this goal, artificial cellular communication and developmental programs still have to be established. Here, we create geometrically controlled spatial arrangements of emulsion-based artificial cellular compartments containing synthetic in vitro gene circuitry, separated by lipid bilayer membranes. We quantitatively determine the membrane pore-dependent response of the circuits to artificial morphogen gradients, which are established via diffusion from dedicated organizer cells. Utilizing different types of feedforward and feedback in vitro gene circuits, we then implement artificial signalling and differentiation processes, demonstrating the potential for the realization of complex spatiotemporal dynamics in artificial multicellular systems.
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Although several new types of synthetic cell-like entities are now available, their structural integration into spatially interlinked prototissues that communicate and display coordinated functions remains a considerable challenge. Here we describe the programmed assembly of synthetic prototissue constructs based on the bio-orthogonal adhesion of a spatially confined binary community of protein–polymer protocells, termed proteinosomes. The thermoresponsive properties of the interlinked proteinosomes are used collectively to generate prototissue spheroids capable of reversible contractions that can be enzymatically modulated and exploited for mechanochemical transduction. Overall, our methodology opens up a route to the fabrication of artificial tissue-like materials capable of collective behaviours, and addresses important emerging challenges in bottom-up synthetic biology and bioinspired engineering. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.
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Nature has evolved elaborate, dynamic organelle morphologies for optimal organelle functions. Among them, cisternae stacks are the universal structure for most organelles. However, compared with the well-studied spherical cell/organelle membrane mimic, the fabrication of the ubiquitously present cisternal organelle-like membrane structures for organelle mimic remains a challenging task. Herein, rough endoplasmic reticulum (RER)-like helicoidal cisternae stacks were assembled to mimic the enzyme crowded environment in spatially confined RER cisternae. RER-like single helicoid, multiple helicoids, and secondary helix are all observed. Membrane electrostatics drives their formation and controls the percentages, which indicates the possible role of membrane electrostatics in RER shaping. The organelle-like cisternae stacks can reversibly expand and compress, which provides modulated crowded or de-crowded enzyme environment for biochemical reactions. This work provides advanced membrane models, and novel mechanisms for organelle shaping and helicoids formation, and holds great potential in biomimetics, cell biology, and advanced materials design. : Biomaterials; Materials Science; Molecular Self-Assembly Subject Areas: Biomaterials, Materials Science, Molecular Self-Assembly
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Cells are integral to all forms of life due to their compartmentalization by the plasma membrane. However, living organisms are immensely complex. Thus there is a need for simplified and controllable models of life for a deeper understanding of fundamental biological processes and man-made applications. This is where the bottom-up approach of synthetic biology comes from: a stepwise assembly of biomimetic functionalities ultimately into a protocell. A fundamental feature of such an endeavor is the generation and control of model membranes such as liposomes and polymersomes. We compare and contrast liposomes and polymersomes for a better a priori choice and design of vesicles and try to understand the advantages and shortcomings associated with using one or the other in many different aspects (properties, synthesis, self-assembly, applications) and which aspects have been studied and developed with each type and update the current development in the field.
Self-propelled underwater microrobots that locomote without external sources of energy have potential application as drug carriers and probes in narrow spaces. In this study, we focused on an osmotic engine model, which is a migration mechanism, and applied it as a negative chemotaxis mechanism to induce liposome displacement. First, we confirmed the osmotic flow across the lipid bilayer and calculated the osmotic flow velocity to be 8.5 fL/(min·μm2) when a salt concentration difference was applied to the lipid bilayer. Next, we designed and fabricated a microchannel that can trap a giant liposome and apply a salt concentration difference to the front and rear of the liposome. Then, we demonstrated the movement of a liposome by flowing it to the microchannel. The liposome successfully moved in the direction of the lower ion concentration at a speed of 0.6 μm/min owing to the osmotic pressure difference. Finally, we visualized the inner flow in a liposome by encapsulating microbeads in the liposome and observed the movement of the microbeads to verify that an osmotic flow was generated on the liposome. As a result, we observed the circulation of the microbeads in the liposome when the concentration difference was applied to the front and rear of the liposome, suggesting that the movement of the liposome was driven by the osmotic flow generated by the osmotic pressure difference. These results indicate that the osmotic-pressure-based migration mechanism has the potential to be utilized as the actuator of molecular robots.
The chemical signal communication among organelles in the cell is extremely important for life. We hereby demonstrated that the chemical signal communication between two protoorganelles using cascade enzyme reactions in a lipid based artificial cell. Two protoorganelles inside the artificial cell are the large unilamellar vesicles containing glucose oxidase (GOx-LUVs) and the vesicle containing (horseradish peroxidase (HRP) and Amplex red), respectively. The glucose molecules outside the artificial cell penetrate the lipid bilayer through mellitin pores and enter into one protoroganelle (GOx-LUVs) to produce H2O2, which subsequently transport to the other protoorganelle to oxidize Amplex red into red resorufin catalyzed by HRP. The number of GOx-LUVs in an artificial cell is controlled by using GOx-LUVs solution with different density during the electroformation. The reaction rate for resorufin in the protoorganelle increases with more GOx-LUVs inside the artificial cell. The artificial cell developed here paves the way for more complicated signal transduction mechanism study in a eukaryocyte.
Recent years have seen a rising class of methods and technologies in magnetic manupulation. Magneto-Archimedes effect, a less intuitive way to direct nonmagnetic matter without binding them to magnetic particles, has emerged as a preferred candidate for label-free manipulation of inanimate and living matters at macroscale and microscale. Due to its simplicity, low cost, broad applicability as well as potential biocompatibility, a sudden burst of technological advances have been diversified for both non-microfluidic and microfluidic manipulations. This review introduces a theoretical basis associated with label-free manipulation by distinguishing magnetic matter and magnetic medium. A state-of-the-art review is presented on manipulation techniques ranging from levitation to orientation, separation, trapping, self-assembly in 3D at both macroscale and microscale. Finally, the review concludes with a brief outlook and future perspectives.
Topological defects are crucial to the shaping of the crystalline membrane systems such as lipid bilayers, virus capsids, graphene, as well as the arrangement of cells in tissues. In a typical case, the introduction of disclination defects elastically buckles the crystalline membranes into conical shapes. However, how planar membranes transform to cones triggered by disclinations is still rarely observed in the experiments. Herein, we experimentally observe the transformation from phospholipid bicelles to cones in response to disclinations. During the transformation process, the wall thickness increases, while the conical generatrix length remains the same with respect to the radius of bicelles. The cones with apex angles of 112.8o, 83.6o, 60o, 39o, and 19.2o are observed when 1, 2, 3, 4, and 5 pentagon defects are introduced, respectively. Monodispersed microcones are obtained by adjusting aging temperature and time. These microcones are then used as templates to form platinum conical micromotors with open tips or closed tips, which display different heading directions in H2O2 solution. Our work provides a shape evolution pathway of planar membranes in response to disclinations. The homogeneous microcones can find wide applications in micromotors fabrication, the study of curvature dependent processes, and the formation of advanced materials.
This work describes the development of magnetic levitation (MagLev) using ring magnets and a configuration (which we call “axial MagLev”) to remove the physical barriers to physical sampling in the magnetic field present in “standard MagLev” and to simplify the procedures used to carry out density-based analyses, separations, and manipulations. The optimized, linear magnetic field generated between the two ring magnets (coaxially aligned and like-poles facing) enables the levitation of diamagnetic (and weakly paramagnetic, e.g., aluminum) materials in a paramagnetic suspending medium and makes density measurements more straightforward. This “axial” configuration enables (i) simple procedures to add samples and paramagnetic medium from an open end and to retrieve samples while levitating in the magnetic field (e.g., a subpopulation of a cluster of small particles); (ii) simple accesses and the abilities to view the samples 360° around the sample container and from the top and bottom; and (iii) convenient density measurements of small quantities (as small as a single submillimeter particle as demonstrated) of samples. The compact design, portability, affordability, and simplicity in use of the “axial MagLev” device will broaden the uses of magnetic methods in analyzing, separating, and manipulating different types of samples (solids, liquids, powders, pastes, gels, and also biological entities) in areas such as materials sciences, chemistry, and biochemistry.