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We present the integration of amphiphilic block copolymer micelles as nanometer-sized vehicles for hydrophobic drugs within layer-by-layer (LbL) films using alternating hydrogen bond interactions as the driving force for assembly for the first time, thus enabling the incorporation of drugs and pH-sensitive release. The film was constructed based on the hydrogen bonding between poly(acrylic acid) (PAA) as an H-bond donor and biodegradable poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) micelles as the H-bond acceptor when assembled under acidic conditions. By taking advantage of the weak interactions of the hydrogen-bonded film on hydrophobic surfaces, it is possible to generate flexible free-standing films of these materials. A free-standing micelle LbL film of (PEO-b-PCL/PAA)60 with a thickness of 3.1 microm was isolated, allowing further characterization of the bulk film properties, including morphology and phase transitions, using transmission electron microscopy and differential scanning calorimetry. Because of the sensitive nature of the hydrogen bonding employed to build the multilayers, the film can be rapidly deconstructed to release micelles upon exposure to physiological conditions. However, we could also successfully control the rate of film deconstruction by cross-linking carboxylic acid groups in PAA through thermally induced anhydride linkages, which retard the drug release to the surrounding medium to enable sustained release over multiple days. To demonstrate efficacy in delivering active therapeutics, in vitro Kirby-Bauer assays against Staphylococcus aureus were used to illustrate that the drug-loaded micelle LbL film can release significant amounts of an active antibacterial drug, triclosan, to inhibit the growth of bacteria. Because the micellar encapsulation of hydrophobic therapeutics does not require specific chemical interactions, we believe this noncovalent approach provides a new route to integrating active small, uncharged, and hydrophobic therapeutics into LbL thin films for biological and biomedical coatings.
ACS Nano 2008 Feb
PMID:Hydrogen-bonding layer-by-layer-assembled biodegradable polymeric micelles as drug delivery vehicles from surfaces. 1920 41

Polymer vesicles with diameters of ca. 100-600 nm and bearing benzaldehyde functionalities within the vesicular walls were constructed through self-assembly of an amphiphilic block copolymer PEO(45)-b-PVBA(26) in water. The reactivity of the benzaldehyde functionalities was verified by cross-linking the polymersomes and also by a one-pot cross-linking and functionalization approach to further render the vesicles fluorescent, each via reductive amination. In vitro studies found these labeled nanostructures to undergo cell association.
ACS Nano 2009 Mar 24
PMID:Benzaldehyde-functionalized polymer vesicles. 1930 73

Dynamic core-shell-shell-corona micelles are formed between two oppositely charged block copolymer systems. Preformed polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB-P2VPq-PMAA) block terpolymer micelles with a soft polybutadiene core, an interpolyelectrolyte complex (IPEC) shell made out of poly(N-methyl-2-vinylpyridinium) and poly(methacrylic acid), and a negatively charged PMAA corona were mixed in different ratios at high pH with positively charged poly(N-methyl-2-vinylpyridinium)-block-poly(ethylene oxide) (P2VPq-PEO) diblock copolymers. Under these conditions, mixing results in the formation of a second IPEC shell onto the PB-P2VPq-PMAA precursor micelles, surrounded by a PEO corona. The resulting multicompartmented IPECs exhibit dynamic behavior, highlighted by a structural relaxation within a period of 10 days, investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and scanning force microscopy (SFM). After a short mixing time of 1 h, the IPECs exhibit a star-shaped structure, whereas after 10 days, spherical core-shell-shell-corona objects could be observed. To further increase complexity and versatility of the presented systems, the in situ formation of gold nanoparticles (Au NPs) in both the precursor micelles and the equilibrated IPEC was tested. For the PB-P2VPq-PMAA micelles, NP formation resulted in narrowly distributed Au NPs located within the PMAA shell, whereas for the core-shell-shell-corona IPEC, the Au NPs were confined within the IPEC shell and shielded from the outside through the PEO corona.
ACS Nano 2009 Aug 25
PMID:Interpolyelectrolyte complexes of dynamic multicompartment micelles. 1970 20

We report on the fabrication and optical characterization of dense and ordered arrays of metal nanoparticles. The metal arrays are produced by reducing metal salts in block copolymer (BCP) templates made by solvent annealing of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) or poly(styrene-b-ethylene oxide) (PS-b-PEO) diblock copolymer thin films in mixed solvents. The gold and gold/silver composite nanoparticle arrays show characteristic surface plasmon resonances in the visible wavelength range. The patterning can be applied over large areas onto various substrates. We demonstrate that these metal nanoparticle arrays on metal thin films interact with surface plasmon polaritons (SPPs) that propagate at the film/nanoparticle interface and, therefore, modify the dispersion relation of the SPPs.
ACS Nano 2009 Dec 22
PMID:Block-copolymer-based plasmonic nanostructures. 1994 82

Dispersion of an aqueous H(2)PtCl(6) solution into a trifluorotoluene (TFT) solution of a polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) triblock copolymer produced an emulsion-induced hollow micelle (EIHM), comprising a water nanodroplet stabilized by PEO, H(2)PtCl(6)/P2VP, and PS, sequentially. The following addition of an aqueous LiAuCl(4) solution into the dispersion led to a coordination of LiAuCl(4) and PEO. The resulting spherical EIHM structure was transformed to a hollow cylindrical micelle by the fusion of spherical EIHM with the addition of methanol. This structural transition was reversible by the alternative addition of methanol and TFT. Oxygen plasma was used to generate Pt/Au concentric spheres and hollow cylindrical Pt/Au nano-objects.
ACS Nano 2010 Feb 23
PMID:Fabrication of Pt/Au concentric spheres from triblock copolymer. 2011 65

We report a biocompatible polysiloxane containing amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(gamma-methacryloxypropyltrimethoxysilane) (PEO-b-PgammaMPS), for coating and stabilizing nanoparticles for biomedical applications. Such an amphiphilic diblock copolymer that comprises both a hydrophobic segment with "surface anchoring moiety" (silane group) and a hydrophilic segment with PEO (M(n) = 5000 g/mol) was obtained by the reversible addition-fragmentation chain transfer (RAFT) polymerization using the PEO macromolecular chain transfer agent. When used for coating paramagnetic iron oxide nanoparticles (IONPs), copolymers were mixed with hydrophobic oleic acid coated core size uniformed IONPs (D = 13 nm) in cosolvent tetrahydrofuran. After being aged over a period of time, resulting monodispersed IONPs can be transferred into aqueous medium. With proper PgammaMPS block length (M(n) = 10 000 g/mol), polysiloxane containing diblock copolymers formed a thin layer of coating (approximately 3 nm) around monocrystalline nanoparticles as measured by transmission electron microscopy (TEM). Magnetic resonance imaging (MRI) experiments showed excellent T(2) weighted contrast effect from coated IONPs with a transverse relaxivity r(2) = 98.6 mM(-1) s(-1) (at 1.5 T). Such thin coating layer has little effect on the relaxivity when compared to that of IONPs coated with conventional amphiphilic copolymer. Polysiloxane containing diblock copolymer coated IONPs are stable without aggregation or binding to proteins in serum when incubated for 24 h in culture medium containing 10% serum. Furthermore, a much lower level of intracellular uptake by macrophage cells was observed with polysiloxane containing diblock copolymers coated IONPs, suggesting the reduction of nonspecific cell uptakes and antibiofouling effect.
ACS Appl Mater Interfaces 2009 Oct
PMID:Biocompatible polysiloxane-containing diblock copolymer PEO-b-PgammaMPS for coating magnetic nanoparticles. 2016 20

In this work, we synthesized chiral mesoporous silica (CMS) spheres, which can be used as a potential candidate for chiral separation. The CMS spheres with controllable pore sizes (of 2-3 nm) and high surface areas of ca. 614 m(2) g(-1) were synthesized by chiral templating with chiral block copolymers based on poly(ethylene oxide) and dl-glutamic acid [PEO(113)-b-(GluA)(10)]. The ordered structure of the chiral mesopores was characterized by high-resolution transmission electron microscopy, and the average pore diameters of chiral mesopores were estimated from the nitrogen adsorption-desorption measurements. The enantioselectivity properties and chiral resolution kinetics of the mesopores of silica spheres, after extraction of chiral polymers of PEO(113)-b-(l/d-GluA)(10), were scrutinized using a racemic solution of valine and measuring the circular dichroism and optical polarimetery. A chiral selectivity factor of 5.22 was found with a specific enantiomer of valine adsorbed preferably. These results raise the new possibilities of CMS spheres for enantiomeric separation and other enantioselective applications.
ACS Appl Mater Interfaces 2009 Aug
PMID:Enantioselective separation using chiral mesoporous spherical silica prepared by templating of chiral block copolymers. 2035 1

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol-gel process where a ethylene oxide and propylene oxide triblock polymer (PEO-PPO-PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m(2) x h x bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.
ACS Appl Mater Interfaces 2009 Jul
PMID:Fabrication of supported mesoporous TiO2 membranes: matching the assembled and interparticle pores for an improved ultrafiltration performance. 2035 68

Concentrated solutions of poly(styrene-b-ethylene oxide) (PS-PEO) diblock copolymers were prepared using the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMI][TFSI] as the solvent. The self-assembled microstructures adopted by the copolymer solutions have been characterized using small-angle X-ray scattering. Lyotropic mesophase transitions were observed, with a progression from hexagonally packed cylinders of PEO, to lamellae, to hexagonally packed cylinders of PS upon increasing [EMI][TFSI] content. The change in lamellar domain spacing with ionic liquid concentration was found to be comparable to that reported for other block copolymers in strongly selective solvents. The ionic conductivity of the concentrated PS-PEO/[EMI][TFSI] solutions was measured via impedance spectroscopy, and ranged from 1 x 10(-7) to 1 x 10(-3) S/cm at temperatures from 25 - 100 degrees C. Additionally, the ionic conductivity of the solutions was found to increase with both ionic liquid concentration and molecular weight of the PEO blocks. The ionic conductivity of PEO homopolymer/[EMI][TFSI] solutions was also measured in order to compare the conductivity of the PS-PEO solutions to the expected limit for a lamellar sample with randomly oriented microstructure grains.
ACS Appl Mater Interfaces 2009 Dec
PMID:Phase behavior and ionic conductivity of concentrated solutions of polystyrene-poly(ethylene oxide) diblock copolymers in an ionic liquid. 2035 61

Hierarchically structured titania films for application in hybrid solar cells are prepared by combining microsphere templating and sol-gel chemistry with an amphiphilic diblock copolymer as a structure-directing agent. The films have a functional structure on three size scales: (1) on the micrometer scale a holelike structure for reduction of light reflection, (2) on an intermediate scale macropores for surface roughening and improved infiltration of a hole transport material, and (3) on a nanometer scale a mesoporous structure for charge generation. Poly(dimethyl siloxane)-block-methyl methacrylate poly(ethylene oxide) (PDMS-b-MA(PEO)) is used as a structure-directing agent for the preparation of the mesopore structure, and poly(methyl methacrylate) (PMMA) microspheres act as a template for the micrometer-scale structure. The structure on all levels is modified by the method of polymer extraction as well as by the addition of PMMA particles to the sol-gel solution. Calcination results in structures with increased size and a higher degree of order than extraction with acetic acid. With addition of PMMA a microstructure is created and the size of the mesopores is reduced. Already moderate microstructuring results in a strong decrease in film reflectivity; a minimum reflectivity value of less than 0.1 is obtained by acetic acid treatment and subsequent calcination.
ACS Appl Mater Interfaces 2009 Dec
PMID:Hierarchically structured titania films prepared by polymer/colloidal templating. 2035 68


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