Permeable polymersomes from temperature and pH dual stimuli-responsive PVCL-b-PLL block copolymers for enhanced cell internalization and lysosome targeting.

A series of dual stimuli-responsive block copolymers comprising temperature-responsive poly(N-vinylcaprolactam) (PVCL) and biodegradable pH-responsive poly(l-lysine) (PLL) of varying chain length were synthesized by a combination of free radical polymerization and ring opening polymerization. The block copolymers formed micelles and vesicles (polymersomes) in response to temperature and pH, respectively, in aqueous solution. The nanoassemblies were characterized by transmission electron microscopy and dynamic light scattering techniques. Encapsulation of both hydrophobic and hydrophilic dyes in the polymersomes was shown. Doxorubicin (DOX) was loaded in the polymersomes and its controlled release in response to the two stimuli, independently and jointly, was studied. The drug was found to be released due to stimuli-induced increased permeability without disassembly of the polymersomes. A significant increase in the cellular uptake of the drug-loaded polymersomes at hyperthermia conditions was demonstrated at 41 °C and release of the drug upon localization in lysosomes was observed. Cellular internalization pathway of the polymersomes was investigated by competitive inhibition assay and a combination of endocytic pathways dominated by caveolae-mediated mechanism was found to be operative.

Poly(N-vinylcaprolactam) containing solid lipid polymer hybrid nanoparticles for controlled delivery of a hydrophilic drug gemcitabine hydrochloride.

Folic acid tagged and hydrophilic polymer containing solid lipid nanoparticles (SLNs) were formulated for the controlled and targeted delivery of gemcitabine, a hydrophilic drug. Drug loaded SLNs were prepared by double emulsion method and optimized by 32 level factorial design. Then, a hydrophilic polymer, namely, poly(N-vinylcaprolactam) (PVCL) was incorporated in the optimized SLN batch in the first aqueous phase (W1) to obtain solid lipid polymer hybrid nanoparticles (SLPHNs) that were further decorated with folic acid (F-SLPHNs). TEM analysis of SLNs and SLPHNs revealed the spherical shape with no aggregation while SLPHNs showed higher % EE. SLPHNs exhibited limited burst release of gemcitabine compared to SLNs as well as lower overall % release. All the formulations showed good cytocompatibility against MDA-MB-231 cell lines and folic acid-tagged hybrid particles (F-SLPHNs) showed remarkably higher cellular uptake.

Amphiphilic Glycopolypeptide Star Copolymer-Based Cross-Linked Nanocarriers for Targeted and Dual-Stimuli-Responsive Drug Delivery.

Glycopolypeptide-based nanocarriers are an attractive class of drug delivery vehicles because of the involvement of carbohydrates in the receptor-mediated endocytosis process. To enhance their efficacy toward controlled and programmable drug delivery, we have prepared stable glycopolypeptide-based bioactive dual-stimuli-responsive (redox and enzyme) micelles for delivery of anticancer drugs specifically to the cancer cells. The amphiphilic biocompatible miktoarm star copolymer, which comprises two hydrophobic poly(ε-caprolactone) blocks, a short poly(propargyl glycine) middle block, and a hydrophilic galactose glycopolypeptide block, was designed and synthesized. The star copolymer is initially self-assembled into un-cross-linked (UCL) micelles, and free alkyne groups at the core-shell interface of the UCL micelles, which were cross-linked by bis(azidoethyl) disulfide (BADS) via click chemistry to form interface cross-linked (ICL) micelles. ICL micelles were found to be stable against dilution. BADS imparted redox-responsive properties to the micelles, while PCL rendered them enzyme-degradable. Dual-stimuli-responsive release behavior with Dox as model drug was studied individually as well as synergistically by applying two stimuli in different sequences. The galactose-containing UCL and ICL micelles were shown to be nontoxic. Intracellular Dox release from UCL and ICL micelles was demonstrated in liver cancer cells (HepG2) by time-dependent cellular uptake studies, and controlled release from ICL micelles compared to UCL micelles was observed. The present report opens a new approach toward targeted and programmable drug delivery in tumor tissues via a specifically targeted (receptor-mediated), dual-responsive, and stable cross-linked nanocarrier system.

Large PAMAM Dendron Induces Formation of Unusual P4332 Mesophase in Monoolein/Water Systems.

Compact macromolecular dendrons have previously been shown to induce the formation of discontinuous inverse micellar assemblies with Fd3 m symmetry in monoolein/water systems. Here, we demonstrate that a large PAMAM dendron (G5: fifth generation) induces the formation of a very unusual mesophase with P4332 symmetry. This mesophase had previously been observed in monoolein/water systems only on addition of cytochrome c. The P4332 mesophase can be considered an intermediate phase between the bicontinuous Ia3 d and discontinuous micellar mesophases. We present a detailed investigation of the phase behavior of monoolein/water as a function of G5 concentration and temperature. Addition of 1% G5 in 85/15 monoolein/water system induces a transition from the Lα to Ia3 d phase. Further increase in G5 concentration to above 2% induces the formation of the P4332 phase. In contrast to this, incorporation of lower generation PAMAM dendrons (G2-G4) in monoolein/water yields a qualitatively different phase diagram with the formation of the reverse micellar Fd3 m phase. PAMAM dendrons of all generations, G2-G5, bear terminal amine groups that interact with the monoolein headgroup. The compact molecular architecture of the dendrons and these attractive interactions induce bending of the monoolein bilayer structure. For smaller dendrons, G2-G4, this results in the formation of the Fd3 m phase. However, the large size of the G5 dendron precludes this and a rare intermediate phase between the Ia3 d and discontinuous micellar phase, and the P4332 mesophase forms instead.

Tunable Nanocarrier Morphologies from Glycopolypeptide-Based Amphiphilic Biocompatible Star Copolymers and Their Carbohydrate Specific Intracellular Delivery.

Nanocarriers with carbohydrates on the surface represent a very interesting class of drug-delivery vehicles because carbohydrates are involved in biomolecular recognition events in vivo. We have synthesized biocompatible miktoarm star copolymers comprising glycopolypeptide and poly(ε-caprolactone) chains using ring-opening polymerization and "click chemistry". The amphiphilic copolymers were self-assembled in water into morphologies such as nanorods, polymersomes, and micelles with carbohydrates displayed on the surface. We demonstrate that the formation of nanostructure could be tuned by chain length of the blocks and was not affected by the type of sugar residue. These nanostructures were characterized in detail using a variety of techniques such as TEM, AFM, cryogenic electron microscopy, spectrally resolved fluorescence imaging, and dye encapsulation techniques. We show that it is possible to sequester both hydrophobic as well as hydrophilic dyes within the nanostructures. Finally, we show that these noncytotoxic mannosylated rods and polymersomes were selectively and efficiently taken up by MDA-MB-231 breast cancer cells, demonstrating their potential as nanocarriers for drug delivery.

Visible light-triggered disruption of micelles of an amphiphilic block copolymer with BODIPY at the junction.

A visible light-cleavable polymer is synthesised to overcome the limitations of UV-sensitive polymers. Photocleavable BODIPY functionalized with an ATRP initiator and alkyne was used to obtain an amphiphilic block copolymer by conducting the click reaction and polymerization simultaneously. Micellar assembly of the polymer was disintegrated under visible light irradiation with controlled release of cargo.

Terahertz Spectroscopy and Solid-State Density Functional Theory Calculations of Cyanobenzaldehyde Isomers.

Spectral signatures in the terahertz (THz) frequency region are mainly due to bulk vibrations of the molecules. These resonances are highly sensitive to the relative position of atoms in a molecule as well as the crystal packing arrangement. To understand the variation of THz resonances, THz spectra (2-10 THz) of three structural isomers: 2-, 3-, and 4-cyanobenzaldehyde have been studied. THz spectra obtained from Fourier transform infrared (FTIR) spectrometry of these isomers show that the resonances are distinctly different especially below 5 THz. For understanding the intermolecular interactions due to hydrogen bonds, four molecule cluster simulations of each of the isomers have been carried out using the B3LYP density functional with the 6-31G(d,p) basis set in Gaussian09 software and the compliance constants are obtained. However, to understand the exact reason behind the observed resonances, simulation of each isomer considering the full crystal structure is essential. The crystal structure of each isomer has been determined using X-ray diffraction (XRD) analysis for carrying out crystal structure simulations. Density functional theory (DFT) simulations using CRYSTAL14 software, utilizing the hybrid density functional B3LYP, have been carried out to understand the vibrational modes. The bond lengths and bond angles from the optimized structures are compared with the XRD results in terms of root-mean-square-deviation (RMSD) values. Very low RMSD values confirm the overall accuracy of the results. The simulations are able to predict most of the spectral features exhibited by the isomers. The results show that low frequency modes (<3 THz) are mediated through hydrogen bonds and are dominated by intermolecular vibrations.

Compact polar moieties induce lipid-water systems to form discontinuous reverse micellar phase.

The role of molecular interactions in governing lipid mesophase organization is of fundamental interest and has technological implications. Herein, we describe an unusual pathway for monoolein/water reorganization from a bicontinuous mesophase to a discontinuous reverse micellar assembly, directed by the inclusion of polar macromolecules. This pathway is very different from those reported earlier, wherein the Fd3m phase formed only upon addition of apolar oils. Experiments and molecular dynamics simulations indicate that hydrophilic ternary additives capable of inducing discontinuous phase formation must (i) interact strongly with the monoolein head group and (ii) have a compact molecular architecture. We present a detailed investigation that contrasts a monoolein-water system containing polyamidoamine (PAMAM) dendrons with one containing their linear analogs. The Fd3m phase forms only on the addition of PAMAM dendrons but not their linear analogs. Thus, the dendritic architecture of PAMAM plays an important role in determining lipid mesophase behavior. Both dendrons and their linear analogs interact strongly with monoolein through their amine groups. However, while linear polymers adsorb and spread on monoolein, dendrons form aggregates that interact with the lipid. Dendrons induce formation of an intermediate reverse hexagonal phase, which subsequently restructures into the Fd3m phase. Finally, we demonstrate that other additives with compact structures that are known to interact with monoolein, such as branched polyethylenimine and polyhedral silsesquioxane cages, also induce the formation of the Fd3m phase.

Multiple topologies from glycopolypeptide-dendron conjugate self-assembly: nanorods, micelles, and organogels.

Glycopolypeptides (GPs) were synthesized by ring-opening polymerization of glycosylated N-carboxyanhydride monomer and attached to hydrophobic dendrons at one chain end by "click" reaction to obtain amphiphilic anisotropic macromolecules. We show that by varying polypeptide chain length and dendron generation, an organogel was obtained in dimethylsulfoxide, while nanorods and micellar aggregates were observed in aqueous solutions. Assemblies in water were characterized by electron microscopy and dye encapsulation. Secondary structure of the GP chain was shown to affect the morphology, whereas the chain length of the poly(ethylene glycol) linker between the GP and dendron did not alter rod-like assemblies. Bioactive surface chemistry of these assemblies displaying carbohydrate groups was demonstrated by interaction of mannose-functionalized nanorods with ConA.

Main-chain supramolecular block copolymers.

Block copolymers are key building blocks for a variety of applications ranging from electronic devices to drug delivery. The material properties of block copolymers can be tuned and potentially improved by introducing noncovalent interactions in place of covalent linkages between polymeric blocks resulting in the formation of supramolecular block copolymers. Such materials combine the microphase separation behavior inherent to block copolymers with the responsiveness of supramolecular materials thereby affording dynamic and reversible materials. This tutorial review covers recent advances in main-chain supramolecular block copolymers and describes the design principles, synthetic approaches, advantages, and potential applications.

Supramolecular ABC triblock copolymers via one-pot, orthogonal self-assembly.

A heterotelechelic poly(norbornene imide) containing two terminal and orthogonal hydrogen-bonding receptors, N,N'-bis[6-(alkanoylamino)pyridin-2-yl] isophthalamide (often referred to as the Hamilton receptor or Wedge) and 2,7-diamido-1,8-naphthyridine (DAN), at the opposite ends of the polymer was synthesized via ring-opening metathesis polymerization (ROMP) through the employment of a Hamilton receptor-functionalized ruthenium initiator and a DAN-based chain-terminator. In parallel, two monotelechelic polymers containing either cyanuric acid (CA)- or ureidoguanosine (UG)-end groups that are complementary to the hydrogen-bonding receptors along the poly(norbornene imide) were synthesized either also via ROMP by terminating the polymerization of norbornene octyl ester with a CA-based chain-terminator or by the reaction of poly(ethylene oxide) with UG. Complete incorporations of the hydrogen-bonding receptors at the chain-ends of all polymers were confirmed by (1)H NMR spectroscopy. The telechelic polymers can be self-assembled into ABC triblock copolymers following either a stepwise or a one-pot, orthogonal self-assembly protocol. The self-assembly process was monitored by (1)H NMR spectroscopy, revealing full orthogonality of the two recognition pairs, Hamilton receptor-CA and DAN-UG. The resulting supramolecular ABC triblock copolymers were further characterized by a series of methods including 2-D NOESY, isothermal titration calorimetry, and viscometry, proving that the two orthogonal hydrogen-bonding interactions are strong enough to hold the three polymer chains together. We suggest that a self-assembly methodology solely based on the fully orthogonal hydrogen-bonding recognition motifs will allow for an easy and rapid synthesis of architecturally controlled supramolecular polymeric assemblies with a high degree of complexity.

Orthogonally self-assembled multifunctional block copolymers.

We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring-opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen-bonding moiety along the polymer side-chains, together with a single hydrogen-bonding-based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side-chain-functionalized AB and ABA block copolymers through self-assembly. The orthogonal natures of all side- and main-chain self-assembly events were demonstrated by (1)H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side- and main-chain self-assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self-assembly structures found in nature.

Supramolecular alternating block copolymers via metal coordination.

A bimetallic ruthenium olefin metathesis initiator was synthesized and used to polymerize functionalized norbornenes, affording polymers that are living at both polymer chain-ends. Using this bis-ruthenium initiator strategy and combining it with functional chain-terminators, highly-efficient syntheses of either SCS-Pd(II) pincer- or pyridine-functionalized symmetrical telechelic polymers were developed. The terminal functional group incorporation was confirmed by 1H NMR spectroscopy analyses. The telechelic polymers were self-assembled into block copolymers by means of metal coordination between corresponding terminal recognition units. The self-assembly process was monitored by 1H NMR spectroscopy revealing nearly quantitative functionalization. The resulting supramolecular block copolymers were further characterized by viscometry and dynamic light scattering.

Supramolecular ABC triblock copolymers.

Just add it! Ruthenium initiators functionalized with hydrogen-bonding sites were utilized in ring-opening metathesis polymerization to prepare heterotelechelic polymers with hydrogen-bonding and metal-coordination units in a single step. Supramolecular ABC triblock copolymers were then self-assembled in one pot by simply adding complementary telechelic polymers to a solution of the heterotelechelic polymer (see picture).

Smaller building blocks form larger assemblies: aggregation behavior of biaryl-based dendritic facial amphiphiles.

Synthesis and micellar behavior of biaryl-based benzyl ether dendritic molecules prepared from a new biaryl building block are described. The key objective of the study is to tune the size of individual dendritic molecules and investigate its effect on aggregation behavior of the resulting micelle-like assemblies. We show that the functional group placement in the building block influences flexibility of the dendritic backbone and interior volume available for packing the hydrophobic groups, which is reflected in different aggregation behavior and aggregate size of the two types of micellar assemblies.

Self-assembly of facially amphiphilic dendrimers on surfaces.

Facially amphiphilic dendrimers have been shown to provide significant difference in surface behavior due to subtle changes in structure. The monodendrons are capable of providing hydrophobic surfaces, while the didendrons provide superhydrophobic surfaces. This provides an example of how a molecular level change could result in significant changes in surface behavior. This difference is attributed to the conformational differences exhibited by these dendrimers on surfaces.

Dendrimeric micelles for controlled drug release and targeted delivery.

This review highlights the developments in dendrimer-based micelles for drug delivery. Dendrimers, the perfectly branched monodisperse macromolecules, have certain structural advantages that make them attractive candidates as drug carriers for controlled release or targeted delivery. As polymeric micelle-based approaches precede the work in dendrimers, these are also discussed briefly. The review concludes with a perspective on possible applications of biaryl-based dendrimeric micelles that exhibit environment-dependent conformations, in drug delivery.