Synthesis and self assembly of eosin functionalized amphiphilic block-random copolymers prepared by ring opening metathesis polymerization: Synthesis and Assembly of Rom-Block Copolymers

Reverse Hexosome Dispersions in Alkanes-The Challenge of Inverting Structures

Monoglycerides form lipophilic liquid-crystalline (LC) phases when mixed with water. The corresponding LC nanostructures coexist with excess water, which is a necessary condition for the formation of internally nanostructured dispersed particles. These nanostructures comprise bicontinuous cubic phases, inverted hexagonal phases, and inverted micellar cubic phases. The dispersed particles are therefore named cubosomes, hexosomes, or micellar cubosomes. Such dispersions are usually stabilized by hydrophilic high-molecular-weight triblock (TB) copolymers. Another way to stabilize such dispersions is by forming the so-called Pickering or Ramsden emulsions using nanoparticles as stabilizers. In this contribution, we explore the possibility of forming and stabilizing inverted or reverse systems, that is, dispersions of hydrophilic LC phases in an excess oil phase like tetradecane. Our aim was to change from oil-in-water emulsions to water-in-oil emulsions, where the water phase is a LC phase in equilibrium with excess oil and where the oil is nonpolar, for example, an alkane. This work consists of three parts: (1) to find a hexagonal hydrophilic LC phase that can not only incorporate a certain amount of tetradecane but can also coexist with excess tetradecane in the case of higher oil concentration, (2) to find a suitable stabilizer-either polymeric or nanoparticle type-that can stabilize the emulsion without destroying the hexagonal LC phase, and finally (3) to check the stability of this reverse hexosome emulsion. We discovered that it is possible to create a hexagonal hydrophilic LC phase with short-chain nonionic surfactants such as polyethylene glycol alkyl ethers or with high-molecular-weight TB copolymers of type A-B-A. Furthermore, it is possible to successfully stabilize the reverse hexosomes with low hydrophilic-lipophilic balance TB copolymers-either synthesized in our laboratory or commercially available ones-as well as with hydrophobized, commercially available silica nanoparticles.

Fluorescent ROMP Monomers and Copolymers for Biomedical Applications

The synthesis and characterization of a series of green, blue and red-fluorescent exo-oxanorbornene acid and imide monomers carrying nitrobenzofurazan, coumarin, and Rhodamin B, respectively, as fluorophores is presented. These monomers carry oxanorbornene as polymerizable unit, and were readily copolymerized with bioactive functional oxanorbornene monomers by ring-opening metathesis polymerization (ROMP), as demonstrated by gel permeation chromatography and NMR spectroscopy. Due to the ease of synthesis of these monomers, and their cost-effectiveness compared many to other fluorescent probes, they are useful for biomaterials applications.

Thermo- and pH-Responsive Copolymers Bearing Cholic Acid and Oligo(ethylene glycol) Pendants: Self-Assembly and pH-Controlled Release

A family of block and random copolymers of norbornene derivatives bearing cholic acid and oligo(ethylene glycol) pendants were prepared in the presence of Grubbs' catalyst. The phase transition temperature of the copolymers in aqueous solutions may be tuned by the variation of comonomer ratios and pH values. Both types of copolymers formed micellar nanostructures with a hydrophilic poly(ethylene glycol) shell and a hydrophobic core containing cholic acid residues. The micellar size increased gradually with increasing pH due to the deprotonation of the carboxylic acid groups. These micelles were capable of encapsulating hydrophobic compounds such as Nile Red (NR). A higher hydrophobicity/hydrophilicity ratio in both copolymers resulted in a higher loading capacity for NR. With similar molecular weights and monomer compositions, the block copolymers showed a higher loading capacity for NR than the random copolymers. The NR-loaded micelles exhibited a pH-triggered release behavior. At pH 7.4 within 96 h, the micelles formed by the block and random of copolymers released 56 and 97% NR, respectively. Therefore, these micelles may have promise for use as therapeutic nanocarriers in drug delivery systems.

Block and random copolymers bearing cholic acid and oligo(ethylene glycol) pendant groups: aggregation, thermosensitivity, and drug loading

A series of block and random copolymers consisting of oligo(ethylene glycol) and cholic acid pendant groups were synthesized via ring-opening metathesis polymerization of their norbornene derivatives. These block and random copolymers were designed to have similar molecular weights and comonomer ratios; both types of copolymers showed thermosensitivity in aqueous solutions with similar cloud points. The copolymers self-assembled into micelles in water as shown by dynamic light scattering and transmission electron microscopy. The hydrodynamic diameter of the micelles formed by the block copolymer is much larger and exhibited a broad and gradual shrinkage from 20 to 54 °C below its cloud point, while the micelles formed by the random copolymers are smaller in size but exhibited some swelling in the same temperature range. Based on in vitro drug release studies, 78% and 24% paclitaxel (PTX) were released in 24 h from micelles self-assembled by the block and random copolymers, respectively. PTX-loaded micelles formed by the block and random copolymers exhibited apparent antitumor efficacy toward the ovarian cancer cells with a particularly low half-maximal inhibitory concentration (IC50) of 27.4 and 40.2 ng/mL, respectively. Cholic acid-based micelles show promise as a versatile and potent platform for cancer chemotherapy.