Non-equilibrium Nanoassemblies Constructed by Confined Coordination on a Polymer Chain.

Biological systems employ non-equilibrium self-assembly to create ordered nanoarchitectures with sophisticated functions. However, it is challenging to construct artificial non-equilibrium nanoassemblies due to lack of control over assembly dynamics and kinetics. Herein, we design a series of linear polymers with different side groups for further coordination-driven self-assembly based on shape-complementarity. Such a design introduces a main-chain confinement which effectively slows down the assembly process of side groups, thus allowing us to monitor the real-time evolution of lychee-like nanostructures. The function related to the non-equilibrium nature is further explored by performing photothermal conversion study. The ability to observe and capture non-equilibrium states in this supramolecular system will enhance our understanding of the thermodynamic and kinetic features as well as functions of living systems.

Thiolactone Chemistry-Based Combinatorial Methodology to Construct Multifunctional Polymers for Efficacious Gene Delivery.

Hydrophobic segments and amino moieties in polymeric nonviral gene vectors play important roles in overcoming a cascade of barriers for efficient gene delivery. However, it remains a great challenge to facilely construct well-defined multifunctional polymers through optimization of the amino and hydrophobic groups. Herein, we choose thiolactone chemistry to perform the ring opening reaction of varying hydrophobic groups-modified thiolactones by various amines to generate mercapto groups for further Michael addition reaction with poly[2-(acryloyloxy)ethyl methacrylate] (PAOEMA). Based on the combinatorial methodology, a series of multifunctional polymers were prepared and screened. The polymer (P3D) from tetraethylenepentamine and heptafluorobutyric acid-functionalized thiolactone is the most efficacious one with significantly higher gene transfection efficiency and lower cytotoxicity compared with polyethylenimine (PEI) (branched average Mw ∼ 25 000 Da) and Lipofectamine 2000. Cellular uptake and intracellular distribution studies indicate that P3D complexes show high-efficiency endocytosis and excellent endosomal escape. Accordingly, thiolactone chemistry-based combinatorial methodology allows for facile integration of multifunctional groups to prepare simultaneous efficacious and low-cytotoxic gene delivery vectors.

Measuring the Interactions between Protein-Coated Microspheres and Polymer Brushes in Aqueous Solutions.

Hydrophilic or zwitterionic polymer-functionalized surfaces have become attractive biomaterials in bioscience and technology due to their excellent protein-resistant ability. Understanding the fundamental interactions between proteins and polymers plays an essential role in the surface design of biomaterials. In this work, we studied the interactions between bovine serum albumin (BSA) and two sorts of polymer brushes including zwitterionic poly(carboxybetaine methacrylate) (PCBMA) and hydrophilic poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) in NaCl aqueous solutions directly with a self-established total internal reflection microscope (TIRM) to provide a better understanding of the underlying nonfouling mechanism of polymers. Our results indicate that both the surface charge and brushes length can affect protein adsorption through electrostatic and steric repulsions, respectively. Both PCBMA- and POEGMA-coated surfaces display negative charge properties due to incomplete coverage and ionic adsorption. As a result, strong electrostatic repulsions between proteins and negatively charged polymer-coated surfaces could contribute to the resistance of protein-coated particles in solutions with low ionic strength (0.1, 0.5, and 1 mM) and disappear in solutions with high ionic strength (10 mM). The measured interaction profiles demonstrate that PCBMA brushes could provide apparent steric forces only at high ionic strength (10 mM), where zwitterionic brushes exhibit a relatively extended conformation with a lack of electrostatic forces between intra- and interpolymers. In contrast, the steric repulsion between proteins and POEGMA brushes appears when particles diffuse at low positions in all salt concentrations (0.1-10 mM) with similar steric decay lengths, which results from the unresponsiveness of POEGMA brushes to the salt stimulus.

Multifunctional Polymeric Micelles with Amplified Fenton Reaction for Tumor Ablation.

Relative to normal cells, tumor cells lack adequate capability of reactive oxygen scavenging. Thus, tumor cells can be selectively killed by increasing the concentration of reactive oxygen species in tumor tissue. In this report, we construct an integrated multifunctional polymeric nanoparticle which can selectively improve hydrogen peroxide (H2O2) levels in tumor tissue and convert them into more active hydroxyl radicals by Fenton reaction. First, the diblock copolymers containing polyethylene glycol (PEG) and poly(glutamic acid) modified by ß-cyclodextrin (ß-CD) were synthesized. The block copolymer, ferrocenecarboxylic acid hexadecyl ester (DFc), and ascorbyl palmitate (PA) were coassembled in aqueous solution to obtain stable core-shell micelles through the inclusion complexation between ß-CD moieties in the block copolymer and ferrocene (Fc) groups from DFc. After intravenous injection, the particles achieved significant accumulation in tumor tissue where ascorbic acid at the pharmacological concentration promotes the production of H2O2, and subsequently Fenton reaction was catalyzed by Fc groups to produce hydroxyl radicals to efficiently kill cancer cells and suppress tumor growth. The micellar systems possess great potentials toward cancer therapy through synergistic H2O2 production and conversion into hydroxyl radicals specifically in tumor tissue.

Matrix Metalloproteinase-Responsive Multifunctional Peptide-Linked Amphiphilic Block Copolymers for Intelligent Systemic Anticancer Drug Delivery.

The amphiphilic block copolymer anticancer drug nanocarriers clinically used or in the progress of clinical trials frequently suffer from modest final therapeutic efficacy due to a lack of intelligent features. For example, the biodegradable amphiphilic block copolymer, poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PDLLA) has been approved for clinical applications as a paclitaxel (PTX) nanocarrier (Genexol-PM) due to the optimized pharmacokinetics and biodistribution; however, a lack of intelligent features limits the intracellular delivery in tumor tissue. To endow the mediocre polymer with smart properties via a safe and facile method, we introduced a matrix metalloproteinase (MMP)-responsive peptide GPLGVRGDG into the block copolymer via efficient click chemistry and ring-opening polymerization to prepare PEG-GPLGVRGDG-PDLLA (P1). P1 was further self-assembled into micellar nanoparticles (NPs) to load PTX, which show MMP-2-triggered dePEGylation due to cleavage of the peptide linkage. Moreover, the residual VRGDG sequences are retained on the surface of the NPs after dePEGylation, which can serve as ligands to facilitate the cellular uptake. The cytotoxicity of PTX loaded in P1 NPs against 4T1 cells is significantly enhanced as compared with free PTX or PTX-loaded PEG-GPLGVRG-PDLLA (P2) and PEG-PDLLA (P3) NPs. In vivo studies confirmed that PTX-loaded P1 NPs show prolonged blood circulation, which are similar to P2 and P3 NPs but exhibit more-efficient accumulation in the tumor site. Ultimately, PTX-loaded P1 NPs display statistically significant improvement of antitumor activity against tumor-bearing mice via systemic administration. Therefore, the strategy by facile incorporation of a responsive peptide linkage between PEG and PDLLA is a promising approach to improving the therapeutic efficacy of anticancer-drug-loaded amphiphilic block copolymer micelles.

Measuring the Surface-Surface Interactions Induced by Serum Proteins in a Physiological Environment.

In this work, we applied total internal reflection microscopy (TIRM) to directly measure the interactions between three different kinds of macroscopic surfaces: namely bare polystyrene (PS) particle and bare silica surface (bare-PS/bare-silica), PS particle and silica surfaces both coated with bovine serum albumin (BSA) (BSA-PS/BSA-silica), and PS particle and silica surfaces both modified with polyethylene glycol (PEG) (PEG-PS/PEG-silica) polymers, in phosphate buffer solution (PBS) and fetal bovine serum (FBS). Our results showed that in PBS, all the bare-PS, BSA-PS, and PEG-PS particles were irreversibly deposited onto the bare silica surface or surfaces coated either with BSA or PEG. However, in FBS, the interaction potentials between the particle and surface exhibited both free-diffusing particle and stuck particle profiles. Dynamic light scattering (DLS) and elliposmeter measurements indicated that there was a layer of serum proteins adsorbed on the PS particle and silica surface. TIRM measurement revealed that such adsorbed serum proteins can mediate the surface-surface interactions by providing additional stabilization under certain conditions, but also promoting bridging effect between the two surfaces. The measured potential profile of the stuck particle in FBS thus was much wider than in PBS. These quantitative measurements provide insights that serum proteins adsorbed onto surfaces can regulate surface-surface interactions, thus leading to unique moving behavior and stability of colloidal particles in the serum environment.

Breaking the Limitation of Elevated Coulomb Interaction in Crystalline Carbon Nitride for Visible and Near-Infrared Light Photoactivity.

Most near-infrared (NIR) light-responsive photocatalysts inevitably suffer from low charge separation due to the elevated Coulomb interaction between electrons and holes. Here, an n-type doping strategy of alkaline earth metal ions is proposed in crystalline K+ implanted polymeric carbon nitride (KCN) for visible and NIR photoactivity. The n-type doping significantly increases the electron densities and activates the n→π* electron transitions, producing NIR light absorption. In addition, the more localized valence band (VB) and the regulation of carrier effective mass and band decomposed charge density, as well as the improved conductivity by 1-2 orders of magnitude facilitate the charge transfer and separation. The proposed n-type doping strategy improves the carrier mobility and conductivity, activates the n→π* electron transitions for NIR light absorption, and breaks the limitation of poor charge separation caused by the elevated Coulomb interaction.

Activity and thermal stability improvements of glucose oxidase upon adsorption on core-shell PMMA-BSA nanoparticles.

The interaction and adsorption of enzyme, glucose oxidase (GOx), on poly(methyl methacrylate)-bovine serum albumin (PMMA-BSA) particles were studied by using a quartz crystal microbalance with dissipation (QCM-D) and laser light scattering (LLS). The enzyme was irreversibly immobilized on the PMMA-BSA particle surface. The amount of enzyme immobilized on PMMA-BSA particles and the enzymatic activity were determined by UV/vis measurements. The influences of pH and ionic strength on the adsorption indicate that the electrostatic interaction plays a major role on the immobilization. The adsorbed GOx can retain at least 80% of the free enzyme activity. Thermal stability studies reveal that the adsorbed GOx only losses 28% of its activity in comparison with a 64% activity loss of free GOx when it is incubated at 50 degrees C for 35 h.

BisGMA analogues as monomers and diluents for dental restorative composite materials.

Current commercially available dental composite materials have certain limitations for their use, including high monomer viscosity and high polymerization shrinkage, resulting in residual stresses and interfacial gaps. This study focused on the chemical modification of resin monomer bisphenol A-glycidyl methacrylate (bisGMA), so as to reduce the viscosity and polymerization shrinkage. In this design, the hydroxyl groups of bisGMA were transformed into ester groups with various alkyl chain length and branching. The modified monomers showed promising properties including reduced viscosity, reduced polymerization shrinkage, increased hydrophobicity, increased degree of double bond conversion, and improved mechanical properties of the resulting dental resin composites. The structure/property relationships of the new monomers were investigated, and optimal monomer structures were identified for dental composites with improved properties.

Intracellular glutathione-depleting polymeric micelles for cisplatin prodrug delivery to overcome cisplatin resistance of cancers.

The intrinsic or acquired cisplatin resistance of cancer cells frequently limits the final therapeutic efficacy. Detoxification by the high level of intracellular glutathione (GSH) plays critical roles in the majority of cisplatin-resistant cancers. In this report, we designed an amphiphilic diblock copolymer composed of poly(ethylene glycol) (PEG) and polymerized phenylboronic ester-functionalized methacrylate (PBEMA), PEG-b-PBEMA, which can self-assemble into micelles in aqueous solutions to load hydrophobic cisplatin prodrug (Pt(IV)). Pt(IV)-loaded PEG-b-PBEMA micelles (PtBE-Micelle) reverse cisplatin-resistance of cancer cells through improving cellular uptake efficiency and reducing intracellular GSH level. We found that the cellular uptake amount of platinum from PtBE-Micelle was 6.1 times higher than that of free cisplatin in cisplatin-resistant human lung cancer cells (A549R). Meanwhile, GSH concentration of A549R cells was decreased to 32% upon treatment by PEG-b-PBEMA micelle at the phenyl borate-equivalent concentration of 100µM. PtBE-Micelle displayed significantly higher cytotoxicity toward A549R cells with half maximal inhibitory concentration (IC50) of cisplatin-equivalent 0.20µM compared with free cisplatin of 33.15µM and Pt(IV)-loaded PEG-b-poly(ε-caprolactone) micelles of cisplatin-equivalent 0.75µM. PtBE-Micelle can inhibit the growth of A549R xenograft tumors effectively. Accordingly, PEG-b-PBEMA micelles show great potentials as drug delivery nanocarriers for platinum-based chemotherapy toward cisplatin-resistant cancers.

A robust strategy for preparation of sequential stimuli-responsive block copolymer prodrugs via thiolactone chemistry to overcome multiple anticancer drug delivery barriers.

Block copolymer prodrugs (BCPs) have attracted considerable attentions in clinical translation of nanomedicine owing to their self-assembly into well-defined core-shell nanoparticles for improved pharmacokinetics, stability in blood circulation without drug leakage, and optimized biodistribution. However, a cascade of physiological barriers against specific delivery of drugs into tumor cells limit the final therapeutic efficacy. Herein, we report a robust and facile strategy based on thiolactone chemistry to fabricate well-defined BCPs with sequential tumor pH-promoted cellular internalization and intracellular stimuli-responsive drug release. A series of BCPs were prepared through one-pot synthesis from clinically used small molecule anticancer drugs. The ring-opening reaction of drug-conjugated thiolactones releases mercapto groups via aminolysis by N-(3-aminopropyl)-imidazole, which further react with poly(ethylene glycol)-block-poly(pyridyldisulfide ethylmethacrylate) (PEG-PDSEMA) to produce imidazole and disulfide bonds-incorporated BCPs. Taking paclitaxel (PTX) for example, PTX BCPs exhibited high drug-loading content (>50%) and low critical micellization concentration (5 × 10-3 g/L), which can self-assemble into micellar nanoparticles in aqueous solution with a small size (∼40 nm). The nanoparticles showed high tumor accumulation and uniform distribution in hypopermeable tumors via systemic administration. Meanwhile, imidazole moieties endow nanoparticles tumor pH-sensitive charge transition from nearly neutral to positive, which promoted cellular internalization. Disulfide bonds can be cleaved by intracellular glutathione (GSH) of cancer cells, which accelerate the release of active PTX drug inside cells. Finally, highly aggressive murine breast cancer 4T1 tumor and hypopermeable human pancreatic adenocarcinoma BxPC3 tumor were completely ablated after treatment by PTX BCP nanoparticles. Consequently, the robust and facile preparation strategy based on thiolactone chemistry represents an efficient approach to construct multifunctional BCPs for better therapeutic efficacy via addressing multiple physiological barriers.

Smart Asymmetric Vesicles with Triggered Availability of Inner Cell-Penetrating Shells for Specific Intracellular Drug Delivery.

Smart nanocarriers attract considerable interest in the filed of precision nanomedicine. Dynamic control of the interaction between nanocarriers and cells offers the feasibility that in situ activates cellular internalization at the targeting sites. Herein, we demonstrate a novel class of enzyme-responsive asymmetric polymeric vesicles self-assembled from matrix metalloproteinase (MMP)-cleavable peptide-linked triblock copolymer, poly(ethylene glycol)-GPLGVRG-b-poly(ε-caprolactone)-b-poly(3-guanidinopropyl methacrylamide) (PEG-GPLGVRG-PCL-PGPMA), in which the cell-penetrating PGPMA segments asymmetrically distribute in the outer and inner shells with fractions of 9% and 91%, respectively. Upon treatment with MMP-2 to cleave the stealthy PEG shell, the vesicles undergo morphological transformation into fused multicavity vesicles and small nanoparticles, accompanied by redistribution of PGPMA segments with 76% exposed to the outside. The vesicles after dePEGylation show significantly increased cellular internalization efficiency (∼10 times) as compared to the original ones due to the triggered availability of cell-penetrating shells. The vesicles loading hydrophobic anticancer drug paclitaxel (PTX) in the membrane exhibit significantly enhanced cytotoxicity against MMP-overexpressing HT1080 cells and multicellular spheroids. The proposed vesicular system can serve as a smart nanoplatform for in situ activating intracellular drug delivery in MMP-enriched tumors.

Preparation of well-defined core-shell particles by Cu2+-mediated graft copolymerization of methyl methacrylate from bovine serum albumin.

Small well-defined core-shell poly(methyl methacrylate)-bovine serum albumin (PMMA-BSA) particles have been prepared in a direct one-step graft copolymerization of MMA from BSA at 75 degrees C in water with a trace amount of Cu2+ (5 microM). Initially, BSA generates free radicals and acts as a multifunctional macroinitiator, which leads to the formation of an amphiphilic PMMA-BSA grafting copolymer. Such formed copolymer chains act as a polymeric stabilizer to promote further emulsion polymerization of MMA inside, resulting in surfactant-free stable core-shell particles, confirmed by a transmission electron microscopic (TEM) analysis. The PMMA-BSA copolymers as well as PMMA homopolymer inside the particles were isolated by Soxhlet extraction and characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). The highest grafting efficiency was approximately 80%. Effects of the reaction temperature, the MMA/BSA ratio, and the concentrations of Cu2+ and BSA on such core-shell particle formation have been systematically studied. Due to their inert PMMA core and biocompatible BSA shell, these small polymer particles are potentially useful in biomedical applications.