Time-Resolved SAXS Studies of the Kinetics of Thermally Triggered Release of Encapsulated Silica Nanoparticles from Block Copolymer Vesicles

Abstract

Silica-loaded poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles are prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). As the concentration of silica nanoparticles present during the PISA synthesis is increased up to 35% w/w, higher degrees of encapsulation of this component within the vesicles can be achieved. After centrifugal purification to remove excess non-encapsulated silica nanoparticles, SAXS, DCP, and TGA analysis indicates encapsulation of up to hundreds of silica nanoparticles per vesicle. In the present study, the thermally triggered release of these encapsulated silica nanoparticles is examined by cooling to 0 °C for 30 min, which causes in situ vesicle dissociation. Transmission electron microscopy studies confirm the change in diblock copolymer morphology and also enable direct visualization of the released silica nanoparticles. Time-resolved small-angle X-ray scattering is used to quantify the extent of silica release over time. For an initial silica concentration of 5% w/w, cooling induces a vesicle-to-sphere transition with subsequent nanoparticle release. For higher silica concentrations (20 or 30% w/w) cooling only leads to perforation of the vesicle membranes, but silica nanoparticles are nevertheless released through the pores. For vesicles prepared in the presence of 30% w/w silica, the purified silica-loaded vesicles were cooled to 0 °C for 30 min, and SAXS patterns were collected every 15 s. A new SAXS model has been developed to determine both the mean volume fraction of encapsulated silica within the vesicles and the scattering length density. Satisfactory data fits to the experimental SAXS patterns were obtained using this model.

Toward Sulfur-Free RAFT Polymerization Induced Self-Assembly

“…Note that PGMA-PHPMA block copolymers have been widely studied in aqueous dispersion PISA using benzodithioate transfer agents, showing effective chain-extension and access to higher order morphologies. 13,39,40 In our case, polymerizations using these batch conditions resulted in low monomer conversion, no observable chain-extension ( Figure S5A), and a lot of coagulation along with the formation of a milky white suspension. This result was not unexpected though.…”

Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization‐Induced Self‐Assembly

“…In addition to small molecule drugs, controlled release of large payloads (e.g., proteins, antibodies) offers considerable scope for targeted drug delivery applications. To that end, various chemistries have been explored to induce the release of large cargos from PISA particles . For example, Armes’ group carried out RAFT aqueous dispersion polymerization of HPMA in the presence of 5–35 wt% silica nanoparticles as a model of large payloads .…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…SAXS has been used to follow the evolution of these morphologies and gain insight into their formation mechanism depending on the reaction conditions [59]. It is possible to encapsulate large amounts of nanoparticles in these large block copolymer vesicles during the synthesis and trigger their release over slower time scales by temperature or pH change [60]. SAXS studies showed that at lower loading densities, the complete release of particles is associated with a block copolymer vesicle to micelle transition, whereas at higher loading, the release is via perforations on the vesicles and remaining particles stabilize the vesicle structure [60].…”