pH-Responsive Polyion Complex Vesicle with Polyphosphobetaine Shells

Robust Electrostatic-Templated Polymerization for Controllable Synthesis of Stable and Permeable Polyelectrolyte Vesicles

Polymer vesicles are of profound interest for designing delivery vehicles and nanoreactors toward a variety of biomedical and catalytic applications, yet robust synthesis of stable and permeable vesicles remains challenging. Here, we propose an electrostatic-templated polymerization that enables fabrication of polyelectrolyte vesicles with simultaneously regulated stability and permeability. In our design, cationic monomers were copolymerized with cross-linkers in the presence of a polyanionic-neutral diblock copolymer as a template. By properly choosing the block length ratio of the template, we fabricated a type of polyion complex vesicle consisting of a cross-linked cationic membrane, electrostatically assembled with the template copolymer which can be removed by sequential dissociation and separation under concentrated salt. We finally obtained stable polyelectrolyte vesicles of regulated size, membrane permeability, and response properties by tuning the synthesis factors including ionic strength, cross-linker type, and fraction as well as different monomers and concentrations. As a proof-of-concept, lipase was loaded in the designed cationic vesicles, which exhibited enhanced enzyme stability and activity. Our study has developed a novel and robust strategy for controllable synthesis of a new class of stable and permeable polymer (polyelectrolyte) vesicles that feature great potential applications as functional delivery carriers and nanoreactors.

Impact of Zwitterions on the Acidity Constant and Glucose Sensitivity of Block Copolymers with Phenylboronic Acid

Molecular assemblies that transform in response to pH and saccharide concentration are promising nanomaterials in the field of biomedicine, and polymeric micelles of amphiphilic polymers with phenylboronic acids (PBAs) have been studied. Herein, we report the impact of zwitterions on the acidity constant for the collapse and the glucose sensitivity of a polymeric micelle produced from a diblock copolymer comprising polyacrylamides with PBA and zwitterionic carboxybetaine (PAEBB-b-PCBAAm). The diblock copolymer was synthesized through reversible addition-fragmentation chain-transfer polymerization followed by deprotection. PAEBB-b-PCBAAm produced micellar aggregates in aqueous solutions at a neutral pH, and the polymeric micelles collapsed at a pH of 11.0 because the PBA transformed into a hydroxyboronate anion. The pKa decreased in the presence of glucose owing to boronate ester formation. The PCBAAm chain significantly increased the pH at which the molecular assemblies dissociated. This is probably because the pKa of boronic acid increased through the dipolar interaction of zwitterions, and/or the zwitterionic polymer corona is valid for screening of PBA ionization and electrostatic repulsion of boronate anions. This study on the modulation of pKa through the zwitterionic interaction can facilitate the molecular design of pH- and saccharide-responsive biomaterials.

Formation of Polyion Complex Aggregate Formed from a Cationic Block Copolymer and Anionic Polysaccharide

Block copolymers (PmMn; P20M101 and P100M98) comprising poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC, P) containing biocompatible phosphorylcholin pendants and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC, M) were synthesized via a controlled radical polymerization method. The degrees of polymerization of the PMPC and PMAPTAC segments are denoted by subscripts (PmMn). The mixture of cationic PmMn and anionic sodium chondroitin sulfate C (CS) with the pendant anionic carboxylate and sulfonate groups formed polyion complex (PIC) aggregates in phosphate-buffered saline. A charge-neutralized mixture of P20M101 with CS formed P20M101/CS PIC vesicles with a hydrodynamic radius (Rh) of 97.2 nm, zeta potential of ca. 0 mV, and aggregation number (Nagg) of 23,044. PMPC shells covered the surface of the PIC vesicles. The mixture of P100M98 and CS formed PIC spherical micelles with the PIC core and hydrophilic PMPC shells. The Rh, zeta potential, and Nagg of the PIC micelles were 26.4 nm, ca. 0 mV, and 404, respectively. At pH < 4, the carboxylate anions in CS were protonated. Thus, the charge balance in the PIC micelles shifted to decrease the core density owing to the electrostatic repulsions of the excess cations in the core. The PIC micelles dissociated at a NaCl concentration ≥0.6 M owing to the charge screening effect. The positively charged PIC micelles with excess P100M98 can encapsulate anionic dyes owing to electrostatic interaction.

pH- and Thermo-Responsive Water-Soluble Smart Polyion Complex (PIC) Vesicle with Polyampholyte Shells

A diblock copolymer (P(VBTAC/NaSS)17-b-PAPTAC50; P(VS)17A50) composed of amphoteric random copolymer, poly(vinylbenzyl trimethylammonium chloride-co-sodium p-styrensunfonate) (P(VBTAC/NaSS); P(VS)) and cationic poly(3-(acrylamidopropyl) trimethylammonium chloride) (PAPTAC; A) block, and poly(acrylic acid) (PAAc49) were prepared via a reversible addition-fragmentation chain transfer radical polymerization. Scrips V, S, and A represent VBTAC, NaSS, and PAPTAC blocks, respectively. Water-soluble polyion complex (PIC) vesicles were formed by mixing P(VS)17A50 and PAAc49 in water under basic conditions through electrostatic interactions between the cationic PAPTAC block and PAAc49 with the deprotonated pendant carboxylate anions. The PIC vesicle collapsed under an acidic medium because the pendant carboxylate anions in PAAc49 were protonated to delete the anionic charges. The PIC vesicle comprises an ionic PAPTAC/PAAc membrane coated with amphoteric random copolymer P(VS)17 shells. The PIC vesicle showed upper critical solution temperature (UCST) behavior in aqueous solutions because of the P(VS)17 shells. The pH- and thermo-responsive behavior of the PIC vesicle were studied using 1H NMR, static and dynamic light scattering, and percent transmittance measurements. When the ratio of the oppositely charged polymers in PAPTAC/PAAc was equal, the size and light scattering intensity of the PIC vesicle reached maximum values. The hydrophilic guest molecules can be encapsulated into the PIC vesicle at the base medium and released under acidic conditions. It is expected that the PIC vesicles will be applied as a smart drug delivery system.

Double hydrophilic copolymers - synthetic approaches, architectural variety, and current application fields

Solubility and functionality of polymeric materials are essential properties determining their role in any application. In that regard, double hydrophilic copolymers (DHC) are typically constructed from two chemically dissimilar but water-soluble building blocks. During the past decades, these materials have been intensely developed and utilised as, e.g., matrices for the design of multifunctional hybrid materials, in drug carriers and gene delivery, as nanoreactors, or as sensors. This is predominantly due to almost unlimited possibilities to precisely tune DHC composition and topology, their solution behavior, e.g., stimuli-response, and potential interactions with small molecules, ions and (nanoparticle) surfaces. In this contribution we want to highlight that this class of polymers has experienced tremendous progress regarding synthesis, architectural variety, and the possibility to combine response to different stimuli within one material. Especially the implementation of DHCs as versatile building blocks in hybrid materials expanded the range of water-based applications during the last two decades, which now includes also photocatalysis, sensing, and 3D inkjet printing of hydrogels, definitely going beyond already well-established utilisation in biomedicine or as templates.

Recent progress and perspectives in applications of 2-methacryloyloxyethyl phosphorylcholine polymers in biodevices at small scales

Bioinspired materials have attracted attention in a wide range of fields. Among these materials, a polymer family containing 2-methacryloyloxyethyl phosphorylcholine (MPC), which has a zwitterionic phosphorylcholine headgroup inspired by the...

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

Complex Formation of Sulfobetaine Surfactant and Ionic Polymers and Their Stimuli Responsivity

We investigated the kinds of complexes sulfobetaine surfactant and ionic polymer formed using lauramidopropyl hydroxysultane (LAPHS) as a sulfobetaine surfactant, poly(sodium styrenesulfonate) (PSSNa) as the anionic polymer and poly[3-(methacrylamido)propyl trimethylammonium chloride] (PMAPTAC) as the cationic polymer. The fundamental properties of LAPHS at various salt concentrations were estimated by various measurements, and it was confirmed that the LAPHS micelles alone did not show temperature responsiveness. The presence of large aggregates in addition to LAPHS micelles was confirmed in the aggregates prepared by adding PSSNa to LAPHS at a charge ratio of 1:0.5, 1:1, and 1:2. However, the aggregates could not be formed when the salt concentration was high or when a monomer was added instead of the polymer. This revealed that the cation part of sulfobetaine, which is the shell of LAPHS micelles, and the anion part of PSSNa electrostatically interacted with each other to form a large aggregate. On the other hand, unlike the case of LAPHS micelles alone and the aggregate consisting of LAPHS micelles and PSSNa, the aggregate of LAPHS micelles and PMAPTAC showed an unprecedented phenomenon of "clear → opaque → clear" with increasing concentration in the concentration range above CMC. The change in the transition temperature due to the change of concentration was a factor. Additionally, we confirmed that the transition temperature was lowered when the concentration was higher than CMC or the salt concentration was increased, and the transition temperature was increased when the PMAPTAC with a high degree of polymerization was added. These results suggested that the LAPHS micelles and the ionic polymer form an aggregate, and the temperature responsivity can be expressed by the interaction with the cationic polymer.

Formation of Sulfobetaine-Containing Entirely Ionic PIC (Polyion Complex) Micelles and Their Temperature Responsivity

Sulfobetaine, a type of zwitterionic polymer, is highly biocompatible with temperature responsiveness of the upper critical solution temperature (UCST) type. The objective of this research was to construct polyion complex (PIC) micelles in the shell of sulfobetaine that had these properties. We used poly(sulfopropyl dimethylammonium propylacrylamide) (PSPP) as sulfobetaine, poly(sodium styrenesulfonate) (PSSNa) as the anionic polymer, and poly[3-(methacrylamido)propyl trimethylammonium chloride] (PMAPTAC) as the cationic polymer. The fundamental properties of the sulfobetaine-containing polymer and the complex were investigated to construct micelles in which the corona expands and contracts in response to temperature changes. Changes in the cloud point were observed from the transmittance for sulfobetaine homopolymers with different degrees of polymerization and concentration and aqueous solution of temperature-responsive diblock copolymers with different concentrations. The concentration and degree of polymerization dependencies on temperature responsivity were determined. Then we mixed two diblock copolymer aqueous solutions that did not have temperature responsivity so that the charge number of anions and cations became equal, and the temperature responsivity and the formation of micelles were confirmed from ¹H NMR, DLS, and transmittance. This confirmed the formation of PIC micelles with temperature responsivity. The diblock copolymer did not have temperature responsivity due to the influence of the block ratio by introduction of the ionic chain. However, it is considered to have temperature responsivity because the ionic chain becomes the core when PIC micelles are formed. Furthermore, the PIC micelles with temperature responsivity also had a degree of polymerization and concentration dependencies.

Polymaleimide-Based Polysulfobetaines Bearing Functional and Nonfunctional Hydrophobic Units and Its Aggregation Behavior in Aqueous Media

Copolymaleimide-based zwitterionic polysulfobetaines (PM-SBs) were prepared by a "top down" method for the first time. Interfacial studies of these polymers showed many interesting characteristics. These PM-SBs did not require any salt in the form of sodium chloride (NaCl) to dissolve in water and exhibited exceptional salt tolerance. PM-SBs showed very mild thermogelling behavior. The viscosity of 5 wt % aqueous solution of polymers increased with increasing concentration of salt without showing any limits within the salt concentrations studied [200g/L of NaCl (3.4 M)] in contrast to other reported zwitterionic polysulfobetaines. Dynamic light scattering (DLS) studies also indicated a structure-dependent particle size with varying concentrations of NaCl solution. The uniformity of particles of 5 wt % aqueous solution of PM-SBs increased with increasing concentration of NaCl. At 0.1 wt % concentration, even in the absence of NaCl, mild aggregation was noticed. The concentration of aggregated particles increased with the increasing concentration of NaCl. Because of the exceptionally high salt tolerance, these polymers are potentially suitable for applications in antifouling, oil field, personal care formulations, and water purification.

Zwitterionic shielded polymeric prodrug with folate-targeting and pH responsiveness for drug delivery

Zwitterionic polymers are a class of polymers that acts as both Lewis base and Lewis acid in solution. These polymers not only have excellent properties of hydration, anti-bacterial adhesion, charge reversal and easy chemical modification, but also have characteristics of long-term circulation and suppress nonspecific protein adsorption in vivo. Here, we describe a novel folate-targeted and acid-labile polymeric prodrug under the microenvironment of tumor cells, abbreviated as FA-P(MPC-co-PEGMA-BZ)-g-DOX, which was synthesized via a combination of reversible addition-fragmentation chain transfer (RAFT) copolymerization, Schiff-base reaction, Click chemistry, and a reaction between the amine group of doxorubicin (DOX) and aldehyde functionalities of P(MPC-co-PEGMA-BZ) pendants, wherein MPC and PEGMA-BZ represent 2-(methacryloyloxy)ethyl phosphorylcholine and polyethylene glycol methacrylate ester benzaldehyde, respectively. The polymeric prodrug could self-assemble into nanoparticles in an aqueous solution. The average particle size and morphologies of the prodrug nanoparticles were observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. We also investigated the in vitro drug release behavior and observed rapid prodrug nanoparticle dissociation and drug release under a mildly acidic microenvironment. The methyl thiazolyl tetrazolium (MTT) assay verified that the P(MPC-co-PEGMA-BZ) copolymer possessed good biocompatibility and the FA-P(MPC-co-PEGMA-BZ)-g-DOX prodrug nanoparticles showed higher cellular uptake than those prodrug nanoparticles without the FA moiety. The results of cytotoxicity and the intracellular uptake of non-folate/folate targeted prodrug nanoparticles further confirmed that FA-P(MPC-co-PEGMA-BZ)-g-DOX could be efficiently accumulated and rapidly internalized by HeLa cells due to the strong interaction between multivalent phosphorylcholine (PC) groups and cell membranes. This kind of multifunctional FA-P(MPC-co-PEGMA-BZ)-g-DOX prodrug nanoparticle with combined target-ability and pH responsiveness demonstrates promising potential for cancer chemotherapy.