(217fq) Synthesis of Poly(N-vinyl-2-pyrrolidone)/Poly(N-isopropylacrylamide-co-acrylic acid) Colloidosomes Using UV Crosslinking

Abstract: As a kind of microcapsules with the shell
consisting of packed colloidal particles ^[1],colloidosomes
have currently attracted considerable attention because of their promising
applications in the field of medicine ^[2] and biotechnology ^[3].Colloidosomes are usually obtained by 'locking' the colloidal particles
or microgels in Pickering
emulsion together by appropriate technologies. With continued research, a fast
and biocompatible method is required in the application. UV crosslinking is a
desirable method to lock the interfacial particles in Pickering emulsion. ^[4] However,
the photo-crosslinkable microgels are usually obtained through the introduction
of a photo-responsive comonomer into the polymer network which will change the
structure of polymers and cause side effects.

In this work,
photo-crosslinkable microgels were prepared via
photo-responsive polymer coating for colloidosomes preparation. As depicted in Fig. 1, Poly(N-isopropylacrylamide-co-acrylic acid)(P(NIPAM-co-AAc)) was chosen as a template
microgel. Photo-crosslinkable Poly(N-vinyl-2-pyrrolidone) (PVP) ^[5]
layer was formed on the microgel surface via electrostatic adsorption. The PVP/P(NIPAM-co-AAc) composite microgels dispersion
was mixed with an oil phase to get the Pickering
emulsion. The microgels dispersed at liquid/liquid interface owing to their
stabilizing effect. After UV irradiation, the microgels were crosslinked
together resulting in the formation of colloidosomes. Photo-responsive
comonomer or/and chemical crosslinkers are not essential when the
photo-crosslinkable PVP was used in our system. Thus, the proposed method could
avoid the possible side effects associated with the addition of
photo-responsive comonomer. Furthermore, the biocompatible polymer PVP layer
would improve the biocompatibility of the microgels and the performance of
colloidosome in applications such as cell encapsulation and drug controlled
delivery. This novel colloidosomes will give promise in biotechnology and the
synthesis will provide significant contributions to colloidosomes preparation.

As shown in Fig. 2, uniform P(NIPAM-co-AAc) microgels were first prepared by precipitation
polymerization. The mean size of the as-prepared microgels can be controlled by
adjusting the reaction time. A photo-crosslinkable PVP layer was then coated on
the surface of microgels via electrostatic
adsorption. The Pickering
emulsion was further fabricated based on the resulting microgels. The
toluene/water emulsion was verified by confocal laser scanning microscopy
(CLSM). The emulsion was exposed to UV irradiation leading to the formation of
colloidosomes. Since only the microgels on the surface of emulsion droplets
could be crosslinked by UV irradiation, the yield and the mean size of
colloidosomes can be controlled by the amount of toluene used in the
preparation (as shown in Fig. 3 ).

Keywords: PVP; P(NIPAM-co-AAc);
Microgels; Pickering
emulsion; UV crosslinking

References

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[3] Eze,
N. A.; Milam, V. T. Soft Matter, 2013; 9: 2403-2411.

[4] van Rijn,
P.; Mougin, N. C.; Franke, D.;Park, H.;Böker, A. Chem. Commun., 2011;
47: 8376-8378.

[5] Zhang, Q. G.; Hu, W. W.; Zhu, A. M.; Liu, Q. L. RSC Adv., 2013; 3:
1855-1861.