Efficient
synthesis of functionalized, uniform polymer nano-objects
in water with controlled morphologies in one step and at high concentrations
is extremely attractive, from perspectives of both materials applications
and industrial scale-up. Herein, we report a novel formulation for
aqueous reversible addition–fragmentation chain transfer (RAFT)
dispersion polymerization based on polymerization-induced self-assembly
(PISA) to synthesize ketone-functionalized nanospheres and vesicles.
Significantly, the core-forming block was composed entirely of a ketone-containing
polymer from a commodity monomer diacetone acrylamide (DAAM), resulting
in a high density of ketone functionality in the nano-objects. Producing
uniform vesicles represents another challenge both in PISA and in
the traditional self-assembly process. Aiming at producing uniform
nano-objects, especially vesicles, in such a highly efficient aqueous
PISA process, we devised strategies to allow sufficient time for the
in
situ generated polymers to relax and reorganize into vesicles with
a remarkably low polydispersity. Specifically,
both reducing the radical initiator concentration and lowering the
polymerization temperature were shown to be effective for improving
the uniformity of vesicles. Such an efficient, aqueous PISA to produce
functionalized and uniform nano-objects with controlled morphologies
at solid contents up to 20% represents important progress in the field.
Efficient
preparation of multifunctional nano-objects with controlled
morphologies in one step at high concentrations is synthetically challenging,
yet is highly desirable, in a broad range of materials applications.
Herein, we address this synthetic hurdle by introducing a single commodity
monomer 2-(acetoacetoxy)ethyl methacrylate (AEMA) to realize multiple
functions. Facile preparation of both nanospheres and vesicles via
polymerization induced self-assembly at concentrations of 20–30%
provided defined polymeric nanomaterials with reactive handles inherent
to the AEMA units. High-yielding keto-alkoxylamine chemistry was utilized
to decorate and cross-link the nano-objects. Nanoparticle loading
into the designated location within both nano-objects was exemplified
with in situ formation of silver nanoparticles. The concept of using
a single monomer capable of both morphology control and multifunctionalization
is expected to offer significant opportunities in functional nanomaterials.
BackgroundDegummed silk fibroin from Bombyx mori (silkworm) has potential carrier capabilities for drug delivery in humans; however, the processing methods have yet to be comparatively analyzed to determine the differential effects on the silk protein properties, including crystalline structure and activity.MethodsIn this study, we treated degummed silk with four kinds of calcium-alcohol solutions, and performed secondary structure measurements and enzyme activity test to distinguish the differences between the regenerated fibroins and degummed silk fibroin.ResultsGel electrophoresis analysis revealed that Ca(NO3)2-methanol, Ca(NO3)2-ethanol, or CaCl2-methanol treatments produced more lower molecular weights of silk fibroin than CaCl2-ethanol. X-ray diffraction and Fourier-transform infrared spectroscopy showed that CaCl2-ethanol produced a crystalline structure with more silk I (α-form, type II β-turn), while the other treatments produced more silk II (β-form, anti-parallel β-pleated sheet). Solid-State 13C cross polarization and magic angle spinning-nuclear magnetic resonance measurements suggested that regenerated fibroins from CaCl2-ethanol were nearly identical to degummed silk fibroin, while the other treatments produced fibroins with significantly different chemical shifts. Finally, enzyme activity test indicated that silk fibroins from CaCl2-ethanol had higher activity when linked to a known chemotherapeutic drug, L-asparaginase, than the fibroins from other treatments.ConclusionsCollectively, these results suggest that the CaCl2-ethanol processing method produces silk fibroin with biomaterial properties that are appropriate for drug delivery.
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