Shell click-crosslinked (SCC) nanoparticles: a new methodology for synthesis and orthogonal functionalization

Bioresponsive mesoporous silica nanoparticles for triggered drug release

Mesoporous silica nanoparticles (MSNPs) have garnered a great deal of attention as potential carriers for therapeutic payloads. However, achieving triggered drug release from MSNPs in vivo has been challenging. Here, we describe the synthesis of stimulus-responsive polymer-coated MSNPs and the loading of therapeutics into both the core and shell domains. We characterize MSNP drug-eluting properties in vitro and demonstrate that the polymer-coated MSNPs release doxorubicin in response to proteases present at a tumor site in vivo, resulting in cellular apoptosis. These results demonstrate the utility of polymer-coated nanoparticles in specifically delivering an antitumor payload.

Facile Preparation of Nanogels Using Activated Ester Containing Polymers

A facile methodology to prepare water-dispersible nanogels based on pentafluorophenyl acrylate and polyethylene glycol methacrylate random copolymer and diamine cross-linkers has been developed. Cross-linking reaction was characterized by FTIR and 19F NMR. We show that those nanogels : (i) are water-dispersible; (ii) can conveniently encapsulate lipophilic guest molecules; (iii) can be prepared with different nanosizes; (iv) are engineered to allow for surface decoration with additional functional groups.

PEG-detachable and acid-labile cross-linked micelles based on orthoester linked graft copolymer for paclitaxel release

Polyethylene glycol detachable graft copolymer, mPEG-g-p(NAS-co-BMA), was synthesized by grafting 2-(ω-methoxy)PEGyl-1,3-dioxan-5-ylamine onto poly(N-(acryloyloxy)succinimide-co-butyl methacrylate). Pseudo in situ cross-linking of the mPEG-g-p(NAS-co-BMA) was performed in dimethylformamide phosphate buffer (v/v = 1/1) by an acid-labile diamine cross-linker bearing two symmetrical cyclic orthoesters. The cross-linked (CL) micelles with different contents of mPEG segments represented different morphologies. The CL micelles containing approximately one mPEG segment exhibited 'echini' morphology whereas the CL micelle with approximately three mPEG segments formed nanowires. The hydrolysis rate of the CL micelles is highly pH-dependent and much more rapid at mild acid than physiological conditions. Hydrolyzates of the CL micelles formed vesicles because new amphiphilic copolymers were formed. Paclitaxel (PTX) was successfully loaded into the CL micelles and a controlled and pH-dependent release behavior was observed. No obvious cytotoxicity was found for the CL micelles at concentration as high as 800  mg l( - 1).

Engineering of amphiphilic block copolymers for polymeric micellar drug and gene delivery

The use of nano-delivery systems formed through assembly of synthetic amphiphilic block copolymers (ABCs) in experimental medicine and pharmaceutical sciences is experiencing rapid development. This rapid development is driven by a crucial need in improving the performance of existing therapeutic agents, as well as the necessity for the development of advanced delivery systems for complex new entities such as genes, proteins and other cellular components. The flexibility in the construction of appropriate carriers for the delivery requirements of these complex new "drugs" offered by versatile polymer chemistry provides an undeniable advantage for polymer based nano-delivery systems compared to other colloids in this regard. With seven formulations already in different stages of clinical trials, polymeric micelles are in the front line of drug development among different ABC-based nano-carriers. The success in rapid advancement of polymeric micelles from bench to bedside is owed to the rational engineering of core/shell structure so that the polymeric micellar carrier can meet the requirements for optimum delivery of specific drug(s) in certain disease condition(s). The engineering efforts in this regard have mostly been aimed at providing efficient drug loading, micellar stabilization, and sustained and/or site specific drug release. The objective of this review is to provide an update on different engineering strategies employed to achieve optimum polymeric micellar formulations.

Catechol Redox Induced Formation of Metal Core-Polymer Shell Nanoparticles

A novel strategy was developed to synthesize polymer-coated metal nanoparticles (NPs) through reduction of metal cations with 3,4-dihydroxyphenylalanine (DOPA)-containing polyethylene glycol (PEG) polymers. Catechol redox chemistry was used to both synthesize metal NPs and simultaneously form a cross-linked shell of PEG polymers on their surfaces. DOPA reduced gold and silver cations into neutral metal atoms, producing reactive quinones that covalently cross-linked the PEG molecules around the surface of the NP. Importantly, these PEG-functionalized metal NPs were stable in physiological ionic strengths and under centrifugation, and hold broad appeal since they absorb and scatter light in aqueous solutions.

Poly(Acrylic Acid-b-Styrene) Amphiphilic Multiblock Copolymers as Building Blocks for the Assembly of Discrete Nanoparticles

In order to expand the utility of current polymeric micellar systems, we have developed amphiphilic multiblock copolymers containing alternating blocks of poly(acrylic acid) and poly(styrene). Heterotelechelic poly(tert-butyl acrylate-b-styrene) diblock copolymers containing an α-alkyne and an ω-azide were synthesized by atom transfer radical polymerization (ATRP), allowing control over the molecular weight while maintaining narrow polydispersity indices. The multiblock copolymers were constructed by copper-catalyzed azide-alkyne cycloaddition of azide-alkyne end functional diblock copolymers which were then characterized by (1)H NMR, FT-IR and SEC. The tert-butyl moieties of the poly(tert-butyl acrylate-b-styrene) multiblock copolymers were easily removed to form the poly(acrylic acid-b-styrene) multiblock copolymer ((PAA-PS)(9)), which contained up to 9 diblock repeats. The amphiphilic multiblock (PAA-PS)(9) (M(n) = 73.3 kg/mol) was self-assembled by dissolution into tetrahydrofuran and extensive dialysis against deionized water for 4 days. The critical micelle concentration (CMC) for (PAA-PS)(9) was determined by fluorescence spectroscopy using pyrene as a fluorescent probe and was found to be very low at 2 × 10(-4) mg/mL. The (PAA-PS)(9) multiblock was also analyzed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The hydrodynamic diameter of the particles was found to be 11 nm. Discrete spherical particles were observed by TEM with an average particle diameter of 14 nm. The poly(acrylic acid) periphery of the spherical particles should allow for future conjugation of biomolecules.

Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and "click" chemistry

A straightforward approach to the synthesis of "clickable" thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N(3)) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via "click" chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.

Development of benzothiazole 'click-on' fluorogenic dyes

'Click-on' fluorogenic reaction: a non-fluorescent benzothiazole with an electron-deficient alkyne group at 2-position reacts with azide containing molecules could form fluorescent adducts.

Analysis of Thiol-sensitive Core-cross-linked Polymeric Micelles Carrying Nucleoside Pendant Groups using 'On-line' Methods: Effect of Hydrophobicity on Cross-linking and Degradation

Amphiphilic block copolymers were prepared via reversible–addition fragmentation chain transfer (RAFT) polymerization and their synthesis, cross-linking, and degradation were studied using on-line monitoring. The focus of this work is the systematic alteration of the hydrophobic block using copolymers based on 5′-O-methacryloyluridine (MAU) and styrene at different compositions to determine the effect of the copolymer composition on the properties of the micelle. A poly(poly(ethylene glycol) methyl ether methacrylate) (PEGMA) macroRAFT agent was chain extended with a mixture of styrene and MAU. In both systems, an increasing fraction of styrene was found to reduce the rate of polymerization, but the functionality of the RAFT system was always maintained. The amphiphilic block copolymers were dialyzed against water to generate micelles with sizes between 17 and 25 nm according to dynamic light scattering (DLS). Increasing styrene content lead to smaller micelles (determined by DLS and transmission electron microscopy) and to lower critical micelle concentrations, which was measured using surface tensiometry. The micelles were further stabilized via core-cross-linking using bis(2-methacroyloxyethyl) disulfide as crosslinker. NMR analysis revealed a faster consumption of crosslinker with higher styrene content. These stable cross-linked micelles were investigated regarding their ability to degrade in the presence of dithiothreitol as a model reductant. Increasing the styrene content resulted in a faster degradation of the cross-linked micelles into unimers.

Core-clickable PEG-branch-azide bivalent-bottle-brush polymers by ROMP: grafting-through and clicking-to

The combination of highly efficient polymerizations with modular "click" coupling reactions has enabled the synthesis of a wide variety of novel nanoscopic structures. Here we demonstrate the facile synthesis of a new class of clickable, branched nanostructures, polyethylene glycol (PEG)-branch-azide bivalent-brush polymers, facilitated by "graft-through" ring-opening metathesis polymerization of a branched norbornene-PEG-chloride macromonomer followed by halide-azide exchange. The resulting bivalent-brush polymers possess azide groups at the core near a polynorbornene backbone with PEG chains extended into solution; the structure resembles a unimolecular micelle. We demonstrate copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click-to" coupling of a photocleavable doxorubicin (DOX)-alkyne derivative to the azide core. The CuAAC coupling was quantitative across a wide range of nanoscopic sizes (∼6-∼50 nm); UV photolysis of the resulting DOX-loaded materials yielded free DOX that was therapeutically effective against human cancer cells.

Challenging nature's monopoly on the creation of well-defined nanoparticles

Nature has selected and fine-tuned the physical and chemical properties of natural objects, such as size, shape, mechanical properties and surface chemistry, at the molecular level in order to modulate biological functions. A new particle fabrication process, particle replication in nonwetting templates (PRINT), has recently begun to attempt to emulate nature's ability to control those physical and chemical traits. The PRINT technology, which combines modern soft lithography with the unique properties of perfluoropolyether molds, enables the production of nanoparticles with unprecedented control of size, shape, chemical composition, deformability and surface functionality. This scalable 'top-down' fabrication process allows for the generation of well-defined nanostructures without the need for molecular assembly. The ability to flexibly engineer various matrix materials offers unique opportunities for the development of nanomedicines with desired functionality. The strength and versatility of PRINT makes it a powerful platform in nanomedicine for elucidating the role of physical and chemical properties of nanodelivery vehicles on the behavior and fate at the cellular, tissue and whole organism level. Utilizing the PRINT technology, we are generating well-defined nanomedicines with tailored properties for preclinical studies against a variety of human diseases.

Application of nanogel systems in the administration of local anesthetics

Nanogels are robust nanoparticles that could be used to deliver active drug compounds in controlled drug delivery applications. This review discusses the design, synthesis, loading, and release of local anesthetics using polymeric nanoparticles produced via various types of polymerization techniques. The strategy of using layer-by-layer approach to control the burst release of procaine hydrochloride (PrHy; a local anesthetic drug of the amino ester group) is described and discussed.

Efficient synthesis of fluorescent squaraine rotaxane dendrimers

A squaraine rotaxane scaffold with four alkyne groups is readily converted into a range of dendritic architectures using high-yielding copper-catalyzed alkyne azide cycloaddition (CuAAC) chemistry. A convergent synthesis approach is more efficient than a divergent pathway. Dendritic squaraine rotaxanes with peripheral amine groups can be further functionalized to produce multivalent deep-red fluorescent derivatives that exhibit high brightness and outstanding chemical stability in biological solution. The surface groups on these functionalized fluorescent dendrimers include guanidinium, mannose, and phosphatidylcholine.