Self-Assembling Supramolecular Hybrid Hydrogel Beads

Article abstract of DOI:10.1002/anie.201911404

With the goal of imposing shape and structure on supramolecular gels, we combine a low-molecular-weight gelator (LMWG) with the polymer gelator (PG) calcium alginate in a hybrid hydrogel. By imposing thermal and temporal control of the orthogonal gelation methods, the system either forms an extended interpenetrating network or core–shell-structured gel beads—a rare example of a supramolecular gel formulated inside discrete gel spheres. The self-assembled LMWG retains its unique properties within the beads, such as remediating Pd^II and reducing it in situ to yield catalytically active Pd⁰ nanoparticles. A single PdNP-loaded gel bead can catalyse the Suzuki–Miyaura reaction, constituting a simple and easy-to-use reaction-dosing form. These uniquely shaped and structured LMWG-filled gel beads are a versatile platform technology with great potential in a range of applications.

Full text of DOI:10.1002/anie.201911404

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Self-Assembling Supramolecular Hybrid Hydrogel Beads
Authors: Carmen Piras, Petr Slavik, and David K. Smith
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201911404
Angew. Chem. 10.1002/ange.201911404
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RESEARCH ARTICLE
Self-Assembling Supramolecular Hybrid Hydrogel Beads
[
a]
[a]
[a]
Carmen C. Piras, Petr Slavik and David K. Smith*
Abstract: With the goal of imposing shape and structure on
A key strategy that can enhance the behaviour of LMWGs is
supramolecular gels, we combine a low molecular weight gelator
to form hybrid gels,[15] combining them with a polymer gelator (PG)
– such systems can, for example, combine the responsiveness of
a LMWG with the robustness of a PG network, hence enabling
more effective shaping and structuring of the LMWG system.[
Alginic acid is a fascinating PG – biocompatible, biodegradable
and versatile.[16] It is a natural poly-saccharide composed of -D-
mannuronic acid and -L-glucuronic acid units linked through (1-
4) bonds (Fig. 1). Its sodium salt is water-soluble and forms
(LMWG) with the polymer gelator (PG) calcium alginate in a hybrid
hydrogel. By imposing thermal and temporal control of the orthogonal
gelation methods, the system either forms an extended inter-
penetrating network or core-shell structured gel beads – a rare
example of a supramolecular gel formulated inside discrete gel
spheres. The self-assembled LMWG retains its unique properties
within the beads, such as remediating Pd(II) and reducing it in situ to
yield catalytically-active Pd(0) nanoparticles. A single PdNP-loaded
gel bead can catalyse the Suzuki-Miyaura reaction, constituting a
simple and easy-to-use reaction dosing form. These unique shaped
and structured LMWG-filled gel beads are a versatile platform
technology, with great potential in a range of applications.
3]
2
+
hydrogels when mixed with multivalent cations (e.g. Ca ) by
generating ionic interchain bridges. Alginate gel beads can be
obtained by dropwise addition of an aqueous alginate solution to
CaCl
2
.[17] This is a well-known gel system, explored in schools-
level education and exploited in pharmaceutical and food
sectors.[18] More complex core-shell alginate beads, in which the
interior of the bead is filled with a second component, can also be
made.[19] However, to the best of our knowledge, there are no
Supramolecular hydrogels self-assembled from low-molecular-
weight gelator (LMWG) building blocks in water have seen rapid
recent development.[1] A range of gels has been developed
targeting high-tech applications including regenerative medicine,
wound healing, pharmaceutical formulation, optoelectronics,
examples in which
a self-assembled LMWG has been
incorporated within a polymer microgel bead.
[
2]
energy storage, and environmental remediation. The physical
features of a gel (e.g. stiffness or porosity) as well as the chemical
programming inherent within the LMWG scaffold can optimise
gels for specific applications. However, in many cases,
supramolecular gels suffer from rheological weakness meaning
they simply fill the vessel in which they are formed. This can make
it challenging to endow self-assembled gels with desired shapes
and/or structures, yet the ability to shape and pattern such gels
would open up new horizons for LMWGs.[3] Gels with spatially-
Figure 1. Gelator structures – low molecular weight gelator (LMWG) DBS-
CONHNH and polymer gelator (PG) based on alginic acid.
2
resolved structures could, for example, direct stem cell fate in
regenerative medicine,[4] act as vehicles for controlled drug
delivery,[5] or act as patterned conducting gels in integrated soft
We envisaged a multicomponent gel in which the PG
network would effectively act as a spherical mould to constrain
LMWG self-assembly. To achieve this, spatial control we decided
to combine the alginate PG with 1,3:2,4-di-(4-acylhydrazide)-
electronic devices that may ultimately interface with living
systems.[6] A number of strategies have emerged to shape and
structure supramolecular gels,[3] including photopatterning,[7] 3D-
printing,[8] electrochemistry[9] and surface-mediated processes.[10]
benzylidenesorbitol (DBS-CONHNH2, Fig. 1), a thermally-
responsive gel, demonstrated to be biocompatible and with
potential applications ranging from environmental remediation
and catalysis to drug formulation and tissue engineering.[20] In this
paper, we report how combining the PG and LMWG gives a
multicomponent system. The two networks can be spatially
organised either: (a) as an extended standard vial-filling gel with
interpenetrating networks, or (b) as well-defined core-shell
structured gel beads (or worms). Surprisingly, given the many
uses of alginate and the versatility of LMWGs, reports of hybrid
gels combining an alginate PG with LMWGs are rare, and in all
cases standard gels were made.[21] To the best of our knowledge,
this is the first time a PG has imposed spherical shape onto an
LMWG, thus yielding core-shell supramolecular gel beads (Fig. 2).
Several reports have used controlled diffusion to achieve spatial
resolution.[11] Surprisingly, however, there have been limited
reports of supramolecular gel being formulated as spherical
particles. Miravet and co-workers reported this by dropwise
addition of a DMSO solution of the gelator into an anti-solvent,[12]
while Ulijn and co-workers used microfluidic methods and a water-
in-oil emulsion to form gel microspheres.[13] Spherical nanofibre
shells have also been formed via gelator self-assembly at the
interface of oil-in-water emulsion microspheres.[14]
[
a]
Prof David K. Smith, Dr Carmen C. Piras, Dr Petr Slavik
Department of Chemistry, University of York, Heslington, York,
YO10 5DD, UK
The LMWG, DBS-CONHNH
2
,
was synthesized as
E-mail: david.smith@york.ac.uk
previously reported.[20a] This LMWG forms hydrogels at low
concentrations (0.3% wt/vol) using a heat-cool cycle. Low
Supporting information for this article is given via a link at the end of
the document
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RESEARCH ARTICLE
Figure 2. Schematic representation of the preparation of DBS-CONHNH
2
/alginate multicomponent gels. (1) DBS-CONHNH
2
is suspended in an aqueous solution
of sodium alginate. (2) The suspension is heated until complete dissolution of the LMWG. To obtain a hybrid gel with extended interpenetrating networks, the hot
solution was left to cool to room temperature, allowing the DBS-CONHNH network to form. An aqueous solution of CaCl (5% - 1 ml) was then added on top of the
gel (3a) to diffuse in, crosslink the alginate and form the second gel network (4a). Alternatively, the hot solution was added to an aqueous solution of CaCl dropwise
or as a continuous stream to form gel beads or (3b) worms/strings (4b), respectively. Note: The gels were coloured pink using food colouring to be better visualised.
2
2
2
viscosity sodium alginate PG is commercially available and as
described above, can be triggered to form gels by CaCl . Since
the two gels have orthogonal assembly methods, we reasoned a
specific spatial arrangement of the two networks within the hybrid
LMWG/PG gel could be imposed (Fig. 2).
resistance to strain (brittleness). Tunable mechanical properties
of this type are of great use in cell culture applications.[4]
On the nanoscale, scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) indicated that DBS-
2
2
CONHNH and calcium alginate both formed extended nanofibres,
Initially, to demonstrate the orthogonality of the two gelators,
ca. 20-40 nm and 40-60 nm in diameter respectively (Figs. S8 and
S9). The two-component interpenetrated network gel exhibited
long nanofibers with diameters ca. 20-50 nm, consistent with both
LMWG and PG networks being present – the networks could not
be differentiated because of their relatively similar fibre diameters.
On the molecular-scale, IR spectroscopy (Fig. S2) indicated
that the O-H alginate stretch (3390 cm ), shifted to 3370, 3362
and 3351 cm-1 in the two-component gel obtained using 1.0%,
0.5% and 0.3% wt/vol of alginate, respectively, combined with
the DBS-CONHNH
was obtained using a stepwise approach (Fig. 2 panel 4a)
combining an aqueous suspension of DBS-CONHNH (0.3%
2
/alginate interpenetrating network hydrogel
2
wt/vol) with sodium alginate (0.5% wt/vol). Heating ensured
complete dissolution of the LMWG, with gelation being triggered
-1
on cooling. Once the DBS-CONHNH
2
gel had formed, an
aqueous solution of CaCl (5% wt/vol – 1 mL) was added to the
2
top of the gel and allowed to diffuse through it, causing cross-
linking and gelation of the alginate. The gel properties are briefly
summarised below.
Macroscopically, the thermal stability, evaluated via a
simple tube inversion method indicated that alginate increased
the gel-sol transition temperature (Tgel) from 86°C for DBS-
2
0.3% wt/vol of DBS-CONHNH . As the relative loading of LMWG
increases, the alginate O-H band thus progressively shifts to
smaller wavenumber, suggesting non-covalent interactions
2
between DBS-CONHNH and alginate in the hybrid gel, providing
evidence for interaction between the networks, in support of
-1
CONHNH
2
gel (0.4% wt/vol) to >100°C, i.e., the alginate PG
rheology. In the presence of alginate, the O-H (3282 cm ) and N-
-1
network improves thermal stability. In terms of mechanical
properties, oscillatory rheology using parallel plate geometry
2
H (3167 cm ) stretches of DBS-CONHNH were broadened, also
supportive of interactions with the alginate network.
indicated that the DBS-CONHNH
2
hydrogel (0.4% wt/vol) has an
Having determined these two gel networks could indeed be
assembled in a stepwise manner, we then targeted LMWG/PG
hybrid gels with spatially constrained organisation – specifically
core-shell gel beads (Fig. 2, panel 3b, Fig. 3a). We used the same
elastic modulus (G’) of 800 Pa, the alginate gel (0.4% wt/vol) has
a G’ of 490 Pa, whereas two-component gels at similar loadings
displayed higher G’ values (>5000 Pa) – the two networks thus
support each other, increasing stiffness (Table S2, Figs. S15-
S23). Similar effects are frequently observed for interpenetrated
network polymer gels.[22] Furthermore, hybrid gels obtained using
low alginate concentrations were more resistant to strain than gels
formed by the individual components, with a linear viscoelastic
region (LVR) that extends up to ca. 50% strain in contrast to ca.
quantities of DBS-CONHNH
heating, the resulting hot solution was added dropwise to aqueous
CaCl (5% wt/vol). Small gel beads (Fig. 3b) rapidly formed on
calcium-induced cross-linking of the alginate chains, with
simultaneous self-assembly of DBS-CONHNH on cooling. The
2
and sodium alginate, but after
2
2
beads were then quickly removed from the mixture. To make the
method reproducible and obtain gel beads of similar dimensions,
each gel bead was prepared by adding 20 L of hot alginate/DBS-
6.5% for an equivalent amount of calcium alginate and 25% for
the gel formed only by DBS-CONHNH Higher alginate
2
.
concentrations made the hybrid gels more brittle. The loading of
2 2
CONHNH solution. We combined DBS-CONHNH (0.3% wt/vol)
alginate thus allows optimisation between G’ (stiffness) and
with different alginate concentrations and established that 0.5%
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RESEARCH ARTICLE
2
Figure 3. Images of hybrid DBS-CONHNH /Alginate gel beads. (a) Schematic diagram of hybrid gel bead; (b) Photograph of hybrid gel beads (droplet size 20 l),
adjacent to a ruler (scale, cm); (c) Optical microscopy of cross-section of hybrid gel bead (droplet size 20 l, scale bar 500 m); (d) Optical microscopy of cross-
section of hybrid gel bead (droplet size 1 l, scale bar 150 m); (e) Optical microscopy of cross-section of hybrid gel bead embedded in resin and coloured using
toluidine blue (scale bar 1 mm); (f) SEM image of hybrid gel bead (scale bar 500 m); (g) SEM image of hybrid gel bead surface (scale bar 1 m); (h) SEM image
of interior cross section of hybrid gel bead (scale bar 1 m).
wt/vol was the minimum PG concentration required to isolate
spheroidal gel beads. They could also be made with higher
alginate concentrations (i.e. 0.75% wt/vol and 1.0% wt/vol), but at
lower concentrations (≤0.3% wt/vol) they were more irregular.
The gel beads had diameters of 3.0-3.6 mm (Fig. 3b). The
theoretical diameter (d) of a sphere of a known volume (V) is
Our data are consistent with a model in which, as the hot
solution is added dropwise into calcium chloride, the periphery is
rapidly converted into a calcium alginate crosslinked shell. As the
system cools, the LMWG then assembles within this sphere (or
worm) to form a self-assembled gel interior. In this way, the
calcium alginate PG effectively acts as a ‘vessel’ or mould that
contains the self-assembling LMWG. This prevents the LMWG
from uncontrolled assembly into an extended vial-filling gel, and
hence yields discrete shaped and structured LMWG/PG objects.
ꢀ
obtained using: d = 2 ∗ √3푉/4휋. Since for each gel bead a
3
volume of 0.020 mL (= 0.02 cm ) was used, spheres of 0.336 cm
(
3.36 mm) diameter were predicted – the observed bead
diameters therefore agree with expectations. The diameter was
varied by simply changing the volume of liquid added dropwise to
2
To quantify the amount of DBS-CONHNH incorporated into
each gel bead, a simple 1H NMR experiment was used. Ten
beads were isolated and dried under vacuum. The resulting solid
CaCl . Using 5 and 1 L volumes, we obtained gel beads with
2
diameters of 1.6-2.0 mm and 0.75-1.0 mm respectively (Fig. 3d).
Simple optical microscopy clearly indicated core-shell structures
was dissolved in DMSO-d
not alginate, so the LMWG can be determined by 1H NMR.
Acetonitrile (CH CN) was used as an internal standard, and the
concentration of LMWG was hence calculated by comparing the
6 2
, dissolving all the DBS-CONHNH but
(
Figs. 3c and 3d). Further optical microscopy on the gel beads
3
cut in half, embedded in resin and dyed with toluidine blue
indicated a clear difference between the interior volume and the
outer shell in the hybrid gel bead cross section (Fig. 3e). This was
not seen for the beads formed from alginate alone (Fig. S7).
Scanning electron microscopy (SEM, Fig. 3f) provided insight
into the nanoscale morphologies of the bead surface (Fig. 3g) and
cross-section (Fig. 3h). Samples were prepared by freeze-drying
integrals of relevant resonances (DBS-CONHNH
protons:  = 7.53 and 7.83 ppm, and the acetonitrile CH
2
aromatic
group: 
3
= 2.09 ppm) (Fig. S1). In principle, 50 gel beads (20 l volume
each) could be prepared from 1 mL of water containing DBS-
CONHNH
wt/vol). If the DBS-CONHNH
2
(0.3% wt/vol, 6.32 moles) and sodium alginate (0.5%
was fully incorporated and evenly
2
to minimise drying effects. DBS-CONHNH
2
/alginate and alginate
distributed into the gel beads, each bead should contain ca. 0.12
moles of LMWG. The NMR study showed that the amount of
LMWG in each gel bead was ca. 0.11 moles. This experiment
was highly reproducible, and we therefore reason that >90% of
the LMWG is incorporated within the LMWG/PG gel beads
demonstrating the efficiency of this fabrication method.
gel bead surfaces appeared ‘wrinkled’ (Figs. 3g, S12 and S13)
and densely packed consistent with a highly crosslinked calcium
alginate shell. The SEM image of the cross-section of the hybrid
gel beads shows an extended nanofibrillar network in the core of
the bead (Fig. 3h), consistent with incorporation of the LMWG in
self-assembled form inside the bead.
IR spectroscopy (Figs. S2 and S3) indicated that in the hybrid
By varying the mode of addition of the hot solution containing
2
gel beads, the O-H and N-H stretches of DBS-CONHNH were
the LMWG/PG mixture to CaCl
other shapes, e.g. worms (Fig. 2, panel 4b). Worms were
prepared by adding the hot alginate/DBS-CONHNH solution to
the CaCl solution as a thin stream rather than dropwise. Stupp
2
, the gels could be formed into
broadened, and the alginate O-H stretch shifts from 3390 cm-1 to
3352 and 3341 cm-1 (with 1.0% and 0.5% wt/vol of alginate,
respectively). These shifts are similar to those described for the
interpenetrated gels described above.
2
2
and co-workers also used calcium chloride solution to induce the
formation of gel worms,[23] although in their case, a peptide
amphiphile was used as the self-assembling unit, that was, itself
stiffened as a result of interactions with calcium ions – no PG was
present to mediate the process.
To demonstrate one possible use of these spatially-
constrained hybrid gels, we explored catalysis. Gels have great
potential in catalysis as a result of their solvated nature, and the
ability of small molecule reagents to diffuse through them – indeed
gels can be considered intermediate between homogeneous and
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RESEARCH ARTICLE
heterogeneous catalytic systems, combining the advantages of
coupling reaction between 4-iodotoluene and phenylboronic acid
(0.8 mmol scale).[25] When we used the whole amount of
both.[24] We recently reported that DBS-CONHNH
hydrogels
2
achieve efficient in situ reduction of precious metals to yield gels
with embedded metal nanoparticles (NPs).[20c] Furthermore gels
with embedded palladium nanoparticles (PdNPs) can catalyse
Suzuki-Miyaura cross-coupling reactions.[25] We were interested
to see if the presence of alginate influenced Pd uptake or catalysis
and demonstrate advantages of the gel bead formulation.
extended interpenetrating network DBS-CONHNH
2
/alginate gel
(3 mg of DBS-CONHNH and 1 mL of 1% alginate) containing ca.
2
12 µmol of Pd (1.2 mol%), and performed the reaction in the vial
in which the gel was formed, we obtained the desired product 2a
in 98% yield after stirring at 50°C for 24 h – however, we note that
under these stirred conditions, the gel was broken down. The
reaction was then performed without stirring, using just one single
hybrid gel bead as catalyst (ca. 0.4 µmol of Pd, 0.05 mol%).
Pleasingly, product 2a was obtained in 99% yield after 24 h. This
clearly demonstrates that these hybrid gel beads have high
catalytic potential, and that even a single bead can effectively
catalyse the Suzuki-Miyaura reaction (molar ratio of
catalyst:reagent = 1:2000). The conversions obtained using these
DBS/CONHNH
4 h using 0.05 mol% Pd) were very similar to those obtained and
reported previously using simple DBS-CONHNH /agarose hybrid
gels (93% after 18 with 0.05 mol% Pd), suggesting
2
/alginate hybrid LMWG/PG gel beads (99% after
2
2
h
encapsulation within the gel bead is not having an adverse effect
on catalytic performance. To demonstrate some scope of these
catalytic gel beads, we also performed reactions with a range of
other substrates to give 2b-2f in good yield (Scheme 1).
Figure 4. (a) UV-Vis spectra of Pd uptake by Pd-hybrid gel beads (3.00 mg DBS-
CONHNH in 0.5 mL H O, 0.5 mL 1% alginate, 1 mL 5% CaCl ); (b) Amount of
2 2 2
Pd embedded within the gel beads; (c) TEM image of hybrid gel beads with
PdNPs, scale bar 200 nm; (d) SEM image of hybrid gel beads with PdNPs, scale
bar 0.5 µm.
Gel samples were left to interact with aqueous PdCl
approx. 5 mM), and at specified times, the supernatant PdCl
2
(3 mL,
was
2
analysed by UV-Vis (Figs. 4a and S25-27) to determine the
remaining concentration of Pd(II) and thus, the amount of Pd
incorporated within the gel. The calcium alginate gel itself could
also incorporate Pd(II), in agreement with literature reports.[26]
However, based on the colour of the Pd-loaded calcium alginate
gel being yellow, the incorporated Pd is clearly still in the +2
oxidation state (Fig. S30). On the other hand, when DBS-
2
CONHNH was present in the hybrid gel, the gel changed to dark
brown/black suggesting not only Pd(II) incorporation, but in situ
reduction to Pd(0) (Fig. S30). When the gel was prepared as
hybrid gel beads, Pd uptake was faster compared with the
extended interpenetrating network gel in vials, presumably due to
the greater relative surface area of the beads – a black colour,
consistent with reduction of Pd(II) to Pd(0) NPs was again
Scheme 1. Suzuki cross-coupling reaction using a single Pd-hybrid gel bead.
Reaction conditions: 4-Iodoarene (0.80 mmol), phenylboronic acid (0.96 mmol),
K
2 3 2
CO (1.60 mmol), EtOH (3 mL), H O (1 mL) and Pd-Hybrid Gel Bead
(prepared using 1 mL of 1% alginate; containing ~ 0.05 mol% of Pd). The
reaction was carried out without stirring at 50°C for 24 h. Compound 2a was
1
made using a single gel bead recycled 5 times. Conversions by H NMR.
observed.
CONHNH
The total amount of Pd within the DBS-
/alginate gels was ca. 33% of that in our previously
2
Although the PdNP gels showed excellent catalytic activity,
they could not be easily removed from the reaction. We
attempted to increase their mechanical stability by increasing the
amount of alginate (1 mL of 2% alginate solution) or using high
viscosity alginate (1 mL of 1% alginate solution), but the gel bead
could not be removed with a spatula after reaction. We therefore
simply left the gel bead in the reaction vial, removed the reaction
mixture by Pasteur pipette, washed the gel bead with diethyl ether
and water, and charged the reaction vial with fresh starting
materials. In this way, it was possible to re-use a single Pd-hybrid
gel bead five times (Scheme 1), with high conversion and yield,
prepared DBS-CONHNH
proposal above that there are interactions between DBS-
CONHNH and alginate networks – we suggest these somewhat
2
/agarose gels.[25] This agrees with the
2
limit the ability of the acylhydrazide to reduce Pd(II) to Pd(0). The
formation of PdNPs was confirmed by TEM and SEM (Figs. 4c,
4d S28 and S29), with the NPs being attached to the gel fibres
(
where the acyl hydrazide groups are located) and mostly
spherical with diameters <5 nm.
The catalytic activity of DBS-CONHNH /alginate gels loaded
2
with PdNPs was studied in a standard Suzuki-Miyaura cross-
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
pleasingly demonstrating the recyclabillity and reuse of these gel Acknowledgements
beads.
We tested the Pd-leaching from these beads (ESI Section
S11) and found some palladium was leached into the solvent
during reaction. At the end of reaction, if the solution was
removed from the bead and charged with different Suzuki reaction
substrates, then the second Suzuki reaction would proceed to
We thank EPSRC for funding (EP/P03361X/1) and Meg Stark
(
Bioscience Technology Facility, Department of Biology,
University of York) for SEM and TEM imaging. PS acknowledges
the Experientia Foundation and University of York (Pump Priming
Funding) for a research fellowship.
>90%, even in the absence of the bead. Leaching is greater than
from our previously reported agarose hybrid hydrogels (34%
Suzuki coupling achieved using the filtrate).[25] We suggest this
results from Pd in the alginate shell being less effectively-bound,
and the greater relative surface area of the small beads used here.
Nonetheless, a significant amount of Pd is clearly retained within
the beads, because, as described above, they can be reused in
the reaction 5 times (an overall molar ratio of catalyst:reagent =
Keywords: catalysis • gel • self-assembly • supramolecular
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Overall, it is evident the LMWG retains its fundamental Pd
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structured core-shell beads. As such, this fabrication method is a
very simple way of imposing shape onto an active and functional
self-assembled gelator. The core-shell hybrid gel beads are a
straightforward and efficient dosing form for these catalytic gels –
one single bead can be placed into the reaction vessel to facilitate
the Suzuki-Miyaura cross coupling and the product easily
extracted. This would therefore be an effective way of supplying
catalytic gels in a simple physical form, which is easy for the end-
user to employ in synthesis. This clearly demonstrates the
advantage of combining a functional LMWG with a PG that plays
the role of imposing defined shape and structure onto the overall
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In conclusion, we report spatial control over LMWG assembly
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2
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–
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RESEARCH ARTICLE
Entry for the Table of Contents
RESEARCH ARTICLE
Supramolecular gel beads – alginate
can be used to enforce spherical core
shell structures onto catalytic gels
self-assembled from low-molecular-
weight gelators
Carmen C. Piras, Petr Slavik and David
K. Smith*
Page No. – Page No.
Self-Assembling Supramolecular
Hybrid Hydrogel Beads
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