Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability

Herein,
we describe capsule polymer particles with precisely controlled
pH-responsive release properties prepared directly via the interfacial
photo-cross-linking of spherical poly­(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P­(DEAEMA-CEMA)) particles.
In the interfacial photo-cross-linking, photoreactive cinnamoyl groups
in the polymer particles were cross-linked via [2π + 2π]
cycloaddition reactions at the polymer/water interface, showing that
the shell-cross-linked hollow polymer particles can be directly prepared
from spherical polymer particles. The approach has fascinating advantages
such as using minimal components, simplicity, and not requiring sacrificial
template particles and toxic solvents. The following important observations
are made: (I) encapsulated materials were stably retained in the capsule
particles under neutral pH conditions; (II) encapsulated materials
were released from the capsule particles under acidic pH conditions;
(III) the release kinetics of encapsulated materials were controlled
by the pH conditions; i.e., immediate and sustained release was achieved
by varying the acidity of the aqueous media; (IV) the photoirradiation
time did not significantly affect the release kinetics under different
pH conditions; and (V) the pH-responsive release properties were regulated
by changing the polymer composition in P­(DEAEMA-CEMA). Furthermore,
by exploiting the pH-responsiveness, capsule particles are successfully
obtained via an all-aqueous process from spherical polymer particles.
The advantages of the all-aqueous encapsulation process allowed the
water-soluble biomacromolecules such as DNA and saccharides to be
successfully encapsulated in the P­(DEAEMA-CEMA) hollow particles.
With this simple interfacial photo-cross-linking strategy, we envision
the ready synthesis of sophisticated particulate materials for broad
application in advanced research fields.