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.

Functionalized Particles Designed for Targeted Delivery

Pure bioactive compounds alone can only be exceptionally administered in medical treatment. Usually, drugs are produced as various forms of active compounds and auxiliary substances, combinations assuring the desired healing functions. One of the important drug forms is represented by a combination of active substances and particle-shaped polymer in the nano- or micrometer size range. The review describes recent progress in this field balanced with basic information. After a brief introduction, the paper presents a concise overview of polymers used as components of nano- and microparticle drug carriers. Thereafter, progress in direct synthesis of polymer particles with functional groups is discussed. A section is devoted to formation of particles by self-assembly of homo- and copolymer-bearing functional groups. Special attention is focused on modification of the primary functional groups introduced during particle preparation, including introduction of ligands promoting anchorage of particles onto the chosen living cell types by interactions with specific receptors present in cell membranes. Particular attention is focused on progress in methods suitable for preparation of particles loaded with bioactive substances. The review ends with a brief discussion of the still not answered questions and unsolved problems.

Reduction-responsive double hydrophilic block copolymer nano-capsule synthesized via RCMP-PISA

Double hydrophilic block copolymer vesicles synthesized via RCMP-PISA are degradable under a reductive conditions.

Polysaccharide nanoparticles: from fabrication to applications

The present review highlights the developments in polysaccharide nanoparticles with a particular focus on applications in biomedicine, cosmetics and food.

Pseudo target release behavior of simvastatin through pH-responsive polymer based on dynamic imine bonds: Promotes rapid proliferation of osteoblasts

In this article, a simvastatin loaded pentaerythritol tetra(3-mercaptopropionate)-allylurea-poly(ethylene glycol) (SIM-loaded PETMP-AU-PEG) polymer with excellent biocompatibility by means of in-situ loading method was synthesized. The presence of the imine bonds has given the polymer system an excellent response performance to weak acidic environment. Specifically, for the SIM-loaded polymer, the simvastatin cumulative release dose is only 2.2% in the first 2 h, and the first 32 h of the cumulative release dose is less than 10% in pH 7.4; However, in pH 6.0, the first 2 h of the cumulative release dose is 65.2%, and the first 32 h of the cumulative release dose is almost 100%. MC3T3-E1 osteoblast cell culture experiments show that the SIM-loaded polymer at pH 6.0 can accelerate the proliferation of osteoblasts significantly, which is expected to promote the rapid proliferation of bone cells in clinical applications and accelerate the healing of the lesion region.

Dual Reduction/Acid-Responsive Disassembly and Thermoresponsive Tunability of Degradable Double Hydrophilic Block Copolymer

We report a thermoresponsive double hydrophilic block copolymer degradable in response to dual reduction and acidic pH at dual locations. The copolymer consists of a poly(ethylene oxide) block covalently connected through an acid-labile acetal linkage with a thermoresponsive polymethacrylate block containing pendant oligo(ethylene oxide) and disulfide groups. The copolymer undergoes temperature-driven self-assembly in water to form nanoassemblies with acetal linkages at the core/corona interface and disulfide pendants in the core, exhibiting dual reduction/acid responses at dual locations. The physically assembled nanoaggregates are converted to disulfide-core-crosslinked nanogels through disulfide-thiol exchange reaction, retaining enhanced colloidal stability, yet degraded to water-soluble unimers upon reduction/acid-responsive degradation. Further, the copolymer exhibits improved tunability of thermoresponsive property upon the cleavage of junction acetal and pendant disulfide linkages individually and in combined manner. This work suggests that dual location dual reduction/acid-responsive degradation is a versatile strategy toward effective drug delivery exhibiting disulfide-core-crosslinking capability and disassembly as well as improved thermoresponsive tunability.

Aminolysis induced functionalization of (RAFT) polymer-dithioester with thiols and disulfides

Efficient exchange of the polymer-dithioester end group by aminolysis/functionalization with thiol or disulfide under ambient atmospheric conditions.

ABA-type triblock copolymer micellar system with lower critical solution temperature-type sol-gel transition

A temperature sensitive sol-gel transition induced by the self-assembly of amphiphilic copolymers and its application in industry have been the objects of increasing study. We demonstrate here a two-step, reversible addition-fragmentation chain transfer (RAFT) polymerization of an ABA-type copolymer consisting of poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-dimethylacrylamide) (PDMAA-b-PDAAM-b-PDMAA). This copolymer can be easily dispersed in water, and this dispersion is critical for its lower critical solution temperature (LCST)-type sol-gel transition, which was monitored using dynamic light scattering (DLS), transmission electron microscopy (TEM), and rheology analysis, in addition to temperature-dependent ¹H nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). Results revealed an abnormal sphere-to-worm micellar transition of this ABA copolymer at the LCST point, which could be affected by the length of the PDAAM block (B-block), the length as well as the distribution of the PDMAA block (A-block), and the concentration of the copolymer dispersion. Thus, copolymer dispersion could be feasibly used for drug loading at a low temperature, which could then be transformed into a gel at an elevated temperature. The loading and controllable release of the model drug of paracetamol into and out of a copolymer gel was further determined. The sustained release behavior was also studied using the Rigter-Peppas model.

Tannic Acid-Mediated Aggregate Stabilization of Poly(N-vinylpyrrolidone)-b-poly(oligo (ethylene glycol) methyl ether methacrylate) Double Hydrophilic Block Copolymers

The self-assembly of block copolymers in aqueous solution is an important field in modern polymer science that has been extended to double hydrophilic block copolymers (DHBC) in recent years. In here, a significant improvement of the self-assembly process of DHBC in aqueous solution by utilizing a linear-brush macromolecular architecture is presented. The improved self-assembly behavior of poly(N-vinylpyrrolidone)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PVP-b-P(OEGMA)) and its concentration dependency is investigated via dynamic light scattering (DLS) (apparent hydrodynamic radii ≈ 100-120 nm). Moreover, the DHBC assemblies can be non-covalently crosslinked with tannic acid via hydrogen bonding, which leads to the formation of small aggregates as well (apparent hydrodynamic radius ≈ 15 nm). Non-covalent crosslinking improves the self-assembly and stabilizes the aggregates upon dilution, reducing the concentration dependency of aggregate self-assembly. Additionally, the non-covalent aggregates can be disassembled in basic media. The presence of aggregates was studied via cryogenic scanning electron microscopy (cryo-SEM) and DLS before and after non-covalent crosslinking. Furthermore, analytical ultracentrifugation of the formed aggregate structures was performed, clearly showing the existence of polymer assemblies, particularly after non-covalent crosslinking. In summary, we report on the completely hydrophilic self-assembled structures in solution formed from fully biocompatible building entities in water.

A facile synthesis of pH stimuli biocompatible block copolymer poly(methacrylic acid)-block-poly(N-vinylpyrrolidone) utilizing switchable RAFT agents

Synthesis of block copolymer PMAA-b-PNVP utilizing switchable RAFT agents and its self-assembly.

Poly(ethylene glycol) brush-b-poly(N-vinylpyrrolidone)-based double hydrophilic block copolymer particles crosslinked via crystalline α-cyclodextrin domains

Self-assembly of block copolymers is a significant area of polymer science. The self-assembly of completely water-soluble block copolymers is of particular interest, albeit a challenging task. In the present work the self-assembly of a linear-brush architecture block copolymer, namely poly(N-vinylpyrrolidone)-b-poly(oligoethylene glycol methacrylate) (PVP-b-POEGMA), in water is studied. Moreover, the assembled structures are crosslinked via α-CD host/guest complexation in a supramolecular way. The crosslinking shifts the equilibrium toward aggregate formation without switching off the dynamic equilibrium of double hydrophilic block copolymer (DHBC). As a consequence, the self-assembly efficiency is improved without extinguishing the unique DHBC self-assembly behavior. In addition, decrosslinking could be induced without a change in concentration by adding a competing complexation agent for α-CD. The self-assembly behavior was followed by DLS measurement, while the presence of the particles could be observed via cryo-TEM before and after crosslinking.

Self-assembly of the double hydrophilic block copolymer poly(N-vinylpyrrolidone)-b-poly(oligoethylene glycol methacrylate) and supramolecular crosslinking via α-cyclodextrin in water is presented.