Block Copolymer Self-assembly: Exploitation of Hydrogen Bonding for Nanoparticle Morphology Control via Incorporation of Triazine Based Comonomers by RAFT Polymerization.

Synthesis of polymeric nanoparticles of controlled non-spherical morphology is of profound interest for a wide variety of potential applications. Self-assembly of amphiphilic diblock copolymers is an attractive bottom-up approach to prepare such nanoparticles. In the present work, RAFT polymerization is employed to synthesize a variety of poly(N,N-dimethylacrylamide)-b-poly[butyl acrylate-stat-GCB] copolymers, where GCB represents vinyl monomer containing triazine based Janus guanine-cytosine nucleobase motifs featuring multiple hydrogen bonding arrays. Hydrogen bonding between the hydrophobic blocks exert significant influence on the morphology of the resulting nanoparticles self-assembled in water. The Janus feature of the GCB moieties makes it possible to use a single polymer type in self-assembly, unlike previous work exploiting, e.g., thymine-containing polymer and adenine-containing polymer. Moreover, the strength of the hydrogen bonding interactions enables use of a low molar fraction of GCB units, thereby rendering it possible to use the present approach for copolymers based on common vinyl monomers for the development of advanced nanomaterials.

Polymeric Nanofibers of Various Degrees of Cross-Linking as Fillers in Poly(styrene-stat-n-butyl acrylate) Nanocomposites: Overcoming the Trade-Off between Tensile Strength and Stretchability.

Synthesis of light polymer nanocomposites with high strength and toughness has been a significant interest for its potential applications in industry. Herein, the authors have synthesized polymerization-induced self-assembly (PISA) derived nanodimensional polymeric worm (fiber) reinforced polymer nanocomposites by a simple and environmentally friendly synthesis process without the addition of volatile organic compounds. PISA-derived worms with a core-forming block of low glass transition temperature (Tg  ≈ 27.1 °C) comprising poly(styrene-stat-n-butyl acrylate) have been employed as reinforcing filler. The influence of core-segment cross-linking on reinforcement efficiency has been explored by comparing noncross-linked worms, and worms cross-linked with a small amount of ethylene glycol diacrylate introduced at t = 0 h or t = 2 h of polymerization. Upon addition of 1 wt% of noncross-linked, t = 0 h cross-linked, and t = 2 h cross-linked worms, toughness of polymer nanocomposites can be enhanced by 62%, 114%, and 120%, respectively. The results suggest that the reinforcement efficiency of worms is significantly influenced by the cross-linking of core-segments regardless of cross-linking methods. This work broadens the understanding in application of PISA-derived worms as reinforcing filler by demonstrating the efficient reinforcement with low Tg worms.

Development of a spatiotemporal method to control molecular function by using silica-based photodegradable nanoparticles.

To effectively and safely use molecules, it is important to be able to control the timing and site of molecule activation. We developed a spatiotemporal method to control molecular function by using silica-based photodegradable nanoparticles that can be prepared under mild conditions. The function of various molecules, such as rhodamine B, Nile blue A, propidium iodide (PI), and rhodamine 110, bis-(N-CBZ-l-arginine amide), dihydrochloride (BZAR), was restricted by wrapping in the network structure of the nanoparticle gel. The encapsulated molecule was released from the gel by the light stimulus and its function was restored. Hence, this technique is applicable to the functional control of various molecules. The PI-encapsulated nanoparticles were internalized by the cells after being conjugated with the cell membrane permeability peptide, octaarginine, and were localized to the cytoplasm. Short-term irradiation (20 s) induced PI release from the nanoparticles and the rapid movement (less than 2 min) of the released PI to the nucleus. These nanoparticles are thus useful tools for the spatiotemporal control of various molecular functions because they permit the quick and transient release of encapsulated molecules after short-term irradiation and can be prepared under mild conditions.

Delivery, stabilization, and spatiotemporal activation of cargo molecules in cells with positively charged nanoparticles.

Positively charged photodegradable nanoparticles that simultaneously encapsulated various compounds including small and large molecules were prepared. The nanoparticles were internalized to the cell by endocytosis and were stable within the cells for at least 4 days. The encapsulated molecules were released into the cytosol using light stimuli.

Small mesh size hydrogel for functional photocontrol of encapsulated enzymes and small probe molecules.

Previously, we developed the "protein activation and release from cage by external light" (PARCEL) method for controlling the function of proteins by encapsulating them in a photodegradable hydrogel and subsequently releasing them by ultraviolet (UV) irradiation of the gel. However, controlling small proteins is difficult because small proteins can leak from the gap (ca. 12.4 nm) of the mesh structure of the hydrogel without irradiation. Here, we developed a photodegradable gel with a smaller mesh size (~3.6 nm) and used the new gel to control the function of three small enzymes (trypsin, chymotrypsin, and elastase) and several small nonprotein molecules. The new gel showed reduced leakage of the proteins without irradiation, and tryptic activity increased approximately 78-fold upon irradiation of gel-encapsulated trypsin. The new gel also permitted encapsulation and release of 4',6-diamidino-2-phenylindole (DAPI, molecular weight 277), a small DNA-specific fluorescent probe. After irradiation to the gel-encapsulated DAPI and subsequent addition of DNA, strong fluorescence of the DAPI-DNA complex was observed. Our results indicate that reducing the gel mesh size from 12.4 to 3.6 nm should allow the encapsulation of various proteins and small molecules in an inactive state and their subsequent light-induced release. We expect this method to be useful in preparation of photoactivated biosensors, drug delivery systems, and catalysis.