Intrinsically permeable polymer vesicles based on carbohydrate-conjugated poly(2-oxazoline)s synthesized using a carbohydrate-based initiator system

A thermo-responsive poly(n-propyl oxazoline) block was employed as the hydrophobic segment in an amphiphilic glyco polymer. This approach affords intrinsically permeable polymer vesicles for water-soluble compounds.

Amphiphilic polymers based on polyoxazoline as relevant nanovectors for photodynamic therapy

Coumarin crosslinked polyoxazoline-based vectors developed for efficient photodynamic therapy.

Thermoresponsive hydrogels formed by poly(2-oxazoline) triblock copolymers

Hydrogels are useful materials for drug delivery and tissue engineering. Here, we report the importance of controlling block lengths for making thermoresponsive hydrogels based on ABA triblock copolymers with thermoresponsive outer blocks.

Probing membrane asymmetry of ABC polymersomes

We report the sensitivity of the membrane asymmetry of ABC (PEO-b-PCL-b-PMOXA) polymersomes towards the end-group modification of a shorter C block.

Robust and Biocompatible Functionalization of ZnS Nanoparticles by Catechol-Bearing Poly(2-methyl-2-oxazoline)s

Zinc sulfide (ZnS) nanoparticles (NPs) are particularly interesting materials for their electronic and luminescent properties. Unfortunately, their robust and stable functionalization and stabilization, especially in aqueous media, has represented a challenging and not yet completely accomplished task. In this work, we report the synthesis of colloidally stable, photoluminescent and biocompatible core-polymer shell ZnS and ZnS:Tb NPs by employing a water-in-oil miniemulsion (ME) process combined with surface functionalization via catechol-bearing poly-2-methyl-2-oxazoline (PMOXA) of various molar masses. The strong binding of catechol anchors to the metal cations of the ZnS surface, coupled with the high stability of PMOXA against chemical degradation, enable the formation of suspensions presenting excellent colloidal stability. This feature, combined with the assessed photoluminescence and biocompatibility, make these hybrid NPs suitable for optical bioimaging.

Self-Assembled Thermoresponsive Polymeric Nanogels for 19F MR Imaging

Magnetic resonance imaging using fluorinated contrast agents (¹⁹F MRI) enables to achive highcontrast in images due to the negligible fluorine background in living tissues. In this pilot study, we developed new biocompatible, temperature-responsive, and easily synthesized polymeric nanogels containing a sufficient concentration of magnetically equivalent fluorine atoms for ¹⁹F MRI purposes. The structure of the nanogels is based on amphiphilic copolymers containing two blocks, a hydrophilic poly[ N-(2-hydroxypropyl)methacrylamide] (PHPMA) or poly(2-methyl-2-oxazoline) (PMeOx) block, and a thermoresponsive poly[ N(2,2difluoroethyl)acrylamide] (PDFEA) block. The thermoresponsive properties of the PDFEA block allow us to control the process of nanogel self-assembly upon its heating in an aqueous solution. Particle size depends on the copolymer composition, and the most promising copolymers with longer thermoresponsive blocks form nanogels of suitable size for angiogenesis imaging or the labeling of cells (approximately 120 nm). The in vitro ¹⁹F MRI experiments reveal good sensitivity of the copolymer contrast agents, while the nanogels were proven to be noncytotoxic for several cell lines.

Association and Internal Morphology of Self-Assembled HPPhOx/BSA Hybrid Nanoparticles in Aqueous Solutions

We investigate the formation of hybrid polyelectrolyte/protein nanoparticles by associations between aggregates of partially hydrolyzed poly(2-phenyl-2-oxazoline) (HPPhOx) and bovine serum albumin (BSA) in aqueous solutions. Light scattering experiments show that at conditions of low salt, BSA creates interaggregate bridges and increases the size of the HPPhOx nanoparticles. At high salt contents, breaking of aggregates leads to well-defined nanoparticles. The interior of the formed nanoparticles is probed by small-angle neutron scattering. At low salt, diffuse arrangements are observed, whereas at high salt concentration, scattering is dominated by well-defined hydrophobic domains enhanced by the incorporation of BSA. This system shows that the combination of hydrophobic and electrostatic interactions in random-amphiphilic-polyelectrolyte/protein complexes can be used to determine the properties of self-assembled hybrid multifunctional nanoparticles.

C1q-Mediated Complement Activation and C3 Opsonization Trigger Recognition of Stealth Poly(2-methyl-2-oxazoline)-Coated Silica Nanoparticles by Human Phagocytes

Poly(2-methyl-2-oxazoline) (PMOXA) is an alternative promising polymer to poly(ethylene glycol) (PEG) for design and engineering of macrophage-evading nanoparticles (NPs). Although PMOXA-engineered NPs have shown comparable pharmacokinetics and in vivo performance to PEGylated stealth NPs in the murine model, its interaction with elements of the human innate immune system has not been studied. From a translational angle, we studied the interaction of fully characterized PMOXA-coated vinyltriethoxysilane-derived organically modified silica NPs (PMOXA-coated NPs) of approximately 100 nm in diameter with human complement system, blood leukocytes, and macrophages and compared their performance with PEGylated and uncoated NP counterparts. Through detailed immunological and proteomic profiling, we show that PMOXA-coated NPs extensively trigger complement activation in human sera exclusively through the classical pathway. Complement activation is initiated by the sensing molecule C1q, where C1q binds with high affinity ( K_d = 11 ± 1 nM) to NP surfaces independent of immunoglobulin binding. C1q-mediated complement activation accelerates PMOXA opsonization with the third complement protein (C3) through the amplification loop of the alternative pathway. This promoted NP recognition by human blood leukocytes and monocyte-derived macrophages. The macrophage capture of PMOXA-coated NPs correlates with sera donor variability in complement activation and opsonization but not with other major corona proteins, including clusterin and a wide range of apolipoproteins. In contrast to these observations, PMOXA-coated NPs poorly activated the murine complement system and were marginally recognized by mouse macrophages. These studies provide important insights into compatibility of engineered NPs with elements of the human innate immune system for translational steps.

Human plasma proteome association and cytotoxicity of nano-graphene oxide grafted with stealth polyethylene glycol and poly(2-ethyl-2-oxazoline)

Polyethylene glycol (PEG) is a gold standard against protein fouling. However, recent studies have revealed surprising adverse effects of PEG, namely its immunogenicity and shortened bio-circulation upon repeated dosing. This highlights a crucial need to further examine 'stealth' polymers for controlling the protein 'corona', a new challenge in nanomedicine and bionanotechnology. Poly(2-ethyl-2-oxazoline) (PEtOx) is another primary form of stealth polymer that, despite its excellent hydrophilicity and biocompatibility, has found considerably less applications compared with PEG. Herein, we performed label-free proteomics to compare the associations of linear PEG- and PEtOx-grafted nano-graphene oxide (nGO) sheets with human plasma proteins, complemented by cytotoxicity and haemolysis assays to compare the cellular interactions of these polymers. Our data revealed that nGO-PEG enriched apolipoproteins, while nGO-PEtOx displayed a preferred binding with pro-angiogenic and structural proteins, despite high similarities in their respective top-10 enriched proteins. In addition, nGO-PEG and nGO-PEtOx exhibited similar levels of enrichment of complement proteins. Both PEG and PEtOx markedly reduced nGO toxicity to HEK 293 cells while mitigating nGO haemolysis. This study provides the first detailed profile of the human plasma protein corona associated with PEtOx-grafted nanomaterials and, in light of the distinctions of PEtOx in chemical adaptability, in vivo clearance and immunogenicity, validates the use of PEtOx as a viable stealth alternative to PEG for nanomedicines and bionanotechnologies.

The Power of Shielding: Low Toxicity and High Transfection Performance of Cationic Graft Copolymers Containing Poly(2-oxazoline) Side Chains

We show the potential of oligo(2-ethyl-2-oxazoline) (Ox_n)-shielded graft copolymers of (2-aminoethyl)-methacrylate and N-methyl-(2-aminoethyl)-methacrylate for pDNA delivery in HEK cells. For the effect of grafting density and side chain length concerning improved transfection properties through the concept of shielding to be investigated, copolymers were synthesized via the macromonomer method using a combination of cationic ring opening polymerization and reversible addition-fragmentation chain transfer polymerization to vary the degree of grafting (DG = 10 and 30%) as well as the side chain degree of polymerization (DP = 5 and 20). Investigations of the polyplex formation, in vitro flow cytometry, and confocal laser scanning microscopy measurements on the copolymer library revealed classical shielding properties of the Ox side chains, including highly reduced cytotoxicity and a partial decrease in transfection efficiency, as also reported for polyethylene glycol shielding. In terms of the transfection efficiency, the best performing copolymers (A- g-Ox₅(10) and M- g-Ox₅(10)) revealed equal or better performances compared to those of the corresponding homopolymers. In particular, the graft copolymers with low DG and side chain DP transfected well with over 10-fold higher IC₅₀ values. In contrast, a DG of 30% resulted in a loss of transfection efficiency due to missing ability for endosomal release, and a side chain DP of 20 hampered the cellular uptake.

Renewable (Bis)pyrrolidone Based Monomers as Components for Thermally Curable and Enzymatically Depolymerizable 2-Oxazoline Thermoset Resins

In this study we describe the synthesis of bis(pyrrolidone) based dicarboxylic acids from itaconic acid and their application in 2-oxazoline resins for fully renewable thermoset materials. The monomers are obtained using a bulk aza-Michael addition of a diamine and two itaconic acid molecules using a catalytic amount of water. The monomers can be isolated in high purity after recrystallization, though their yield proved to be highly dependent on the selected diamine spacer length: In general, only the dicarboxylic acids containing diamines with an even number of methylene spacers are isolated in high yields. Through NMR, GPC, and FTIR analysis we demonstrate that these bis(pyrrolidone) based dicarboxylic acids exhibit significantly enhanced curing rates in 2-oxazoline resins compared to resins containing aliphatic dicarboxylic acids such as sebacic acid. Overall, we demonstrate that the rate of 2-oxazoline ring-opening addition with carboxylic acid functionalities is determined by the used dicarboxylic acid, whereas the ring-opening addition of the 2-oxazoline functionality with amide groups is determined by the used bis(2-oxazoline) compound. The thermosets obtained after curing proved to be readily plasticized by water, opening up possibilities for enzymatic degradation.

PMMA-g-OEtOx Graft Copolymers: Influence of Grafting Degree and Side Chain Length on the Conformation in Aqueous Solution

Depending on the degree of grafting (DG) and the side chain degree of polymerization (DP), graft copolymers may feature properties similar to statistical copolymers or to block copolymers. This issue is approached by studying aqueous solutions of PMMA-g-OEtOx graft copolymers comprising a hydrophobic poly(methyl methacrylate) (PMMA) backbone and hydrophilic oligo(2-ethyl-2-oxazoline) (OEtOx) side chains. The graft copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of methyl methacrylate (MMA) and OEtOx-methacrylate macromonomers of varying DP. All aqueous solutions of PMMA-g-OEtOx (9% ≤ DG ≤ 34%; 5 ≤ side chain DP ≤ 24) revealed lower critical solution temperature behavior. The graft copolymer architecture significantly influenced the aggregation behavior, the conformation in aqueous solution and the coil to globule transition, as verified by means of turbidimetry, dynamic light scattering, nuclear magnetic resonance spectroscopy, and analytical ultracentrifugation. The aggregation behavior of graft copolymers with a side chain DP of 5 was significantly affected by small variations of the DG, occasionally forming mesoglobules above the cloud point temperature (T_cp), which was around human body temperature. On the other hand, PMMA-g-OEtOx with elongated side chains assembled into well-defined structures below the T_cp (apparent aggregation number (N_agg = 10)) that were able to solubilize Disperse Orange 3. The thermoresponsive behavior of aqueous solutions thus resembled that of micelles comprising a poly(2-ethyl-2-oxazoline) (PEtOx) shell (T_cp > 60 °C).

Mechanochemical Preparation of Stable Sub-100 nm γ-Cyclodextrin:Buckminsterfullerene (C60) Nanoparticles by Electrostatic or Steric Stabilization

Buckminster fullerene (C₆₀ )'s main hurdle to enter the field of biomedicine is its low bioavailability, which results from its extremely low water solubility. A well-known approach to increase the water solubility of C₆₀ is by complexation with γ-cyclodextrins. However, the formed complexes are not stable in time as they rapidly aggregate and eventually precipitate due to attractive intermolecular forces, a common problem in inclusion complexes of cyclodextrins. In this study we attempt to overcome the attractive intermolecular forces between the complexes by designing custom γ-cyclodextrin (γCD)-based supramolecular hosts for C₆₀ that inhibit the aggregation found in native γCD-C₆₀ complexes. The approach entails the introduction of either repulsive electrostatic forces or increased steric hindrance to prevent aggregation, thus enhancing the biomedical application potential of C₆₀ . These modifications have led to new sub-100 nm nanostructures that show long-term stability in solution.

Beyond PEGylation: Alternative surface-modification of nanoparticles with mucus-inert biomaterials

Mucus is a highly hydrated viscoelastic gel present on various moist surfaces in our body including the eyes, nasal cavity, mouth, gastrointestinal, respiratory and reproductive tracts. It serves as a very efficient barrier that prevents harmful particles, viruses and bacteria from entering the human body. However, the protective function of the mucus also hampers the diffusion of drugs and nanomedicines, which dramatically reduces their efficiency. Functionalisation of nanoparticles with low molecular weight poly(ethylene glycol) (PEGylation) is one of the strategies to enhance their penetration through mucus. Recently a number of other polymers were explored as alternatives to PEGylation. These alternatives include poly(2-alkyl-2-oxazolines), polysarcosine, poly(vinyl alcohol), other hydroxyl-containing non-ionic water-soluble polymers, zwitterionic polymers (polybetaines) and mucolytic enzymes. This review discusses the studies reporting the use of these polymers or potential application to facilitate mucus permeation of nanoparticles.

Computational studies of micellar and nanoparticle nanomedicines

The review highlights recent computational modeling of micellar and nanoparticle nanomedicines, which elucidates their functional roles in atomistic details.

Conformational properties of biocompatible poly(2-ethyl-2-oxazoline)s in phosphate buffered saline

The Kuhn segment length of PEtOx as a flexible macromolecule under physiological conditions is undoubtedly decreasing when approaching the LCST.

Poly(2-oxazoline)s with pendant cubane groups

The synthesis and properties of poly(2-oxazoline)s with cubane side chains are explored in this work.

Dual stimuli-responsive viologen-containing poly(2-isopropyl-2-oxazoline) and its multi-modal electrochromic phase transition

A viologen-containing thermo-responsive poly(2-isopropyl-2-oxazoline) (PiPOx-V) showed a multi-modal electrochromic phase transition behavior.

Poly(2-ethyl-2-oxazoline) conjugates with doxorubicin for cancer therapy: In vitro and in vivo evaluation and direct comparison to poly[N-(2-hydroxypropyl)methacrylamide] analogues

We designed and synthesized a new delivery system for the anticancer drug doxorubicin based on a biocompatible hydrophilic poly(2-ethyl-2-oxazoline) (PEtOx) carrier with linear architecture and narrow molar mass distribution. The drug is connected to the polymer backbone via an acid-sensitive hydrazone linker, which allows its triggered release in the tumor. The in vitro studies demonstrate successful cellular uptake of conjugates followed by release of the cytostatic cargo. In vivo experiments in EL4 lymphoma bearing mice revealed prolonged blood circulation, increased tumor accumulation and enhanced antitumor efficacy of the PEtOx conjugate having higher molecular weight (40 kDa) compared to the lower molecular weight (20 kDa) polymer. Finally, the in vitro and in vivo anti-cancer properties of the prepared PEtOx conjugates were critically compared with those of the analogous system based on the well-established PHPMA carrier. Despite the relatively slower intracellular uptake of PEtOx conjugates, resulting also in their lower cytotoxicity, there are no substantial differences in in vivo biodistribution and anti-cancer efficacy of both classes of polymer-Dox conjugates. Considering the synthetic advantages of poly(2-alkyl-2-oxazoline)s, the presented study demonstrates their potential as a versatile alternative to well-known PEO- or PHPMA-based materials for construction of drug delivery systems.

Supramolecular structures and self-association processes in polymer systems

Self-organization in a polymer system appears when a balance is achieved between long-range repulsive and short-range attractive forces between the chemically different building blocks. Block copolymers forming supramolecular assemblies in aqueous media represent materials which are extremely useful for the construction of drug delivery systems especially for cancer applications. Such formulations suppress unwanted physicochemical properties of the encapsulated drugs, modify biodistribution of the drugs towards targeted delivery into tissue of interest and allow triggered release of the active cargo. In this review, we focus on general principles of polymer selforganization in solution, phase separation in polymer systems (driven by external stimuli, especially by changes in temperature, pH, solvent change and light) and on effects of copolymer architecture on the self-assembly process.

Biocompatible Soft Nanoparticles with Multiple Morphologies Obtained from Nanoprecipitation of Amphiphilic Graft Copolymers in a Backbone-Selective Solvent

Stealth nanocarriers are a promising technology for the treatment of diseases. However, the preparation and characterization of well-defined soft nanoparticulate systems remain challenging. Here we describe a platform of amphiphilic graft copolymers leading to nanoparticles with multiple morphologies and the role of the hydrophilic backbone in their interaction with a model protein. The amphiphilic graft copolymers platform was composed of hydrophilic backbone poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline) (P(MeOx-co-PentOx)), prepared via cationic ring-opening polymerization. Hydrophobic poly(d,l-lactide) (PLA) chains were grafted on the backbone via Huisgen 1,3-dipolar cycloaddition. The "click" copper-catalyzed cycloaddition reactions of azides with alkynes (CuAAC) were successfully carried out, and a series of amphiphilic copolymers were prepared containing a backbone with a number-average molecular weight of 14.2 × 10³ g mol^-1 and different hydrophobic PLA grafts with various molecular weights (2.8 × 10³-12.4 × 10³ g mol^-1). These original architectures of copolymers, when nanoprecipitated in water, the backbone-selective solvent, allowed us to obtain various structures of nanoparticles with a hydrodynamic diameter in the range of 65-99 nm. More interestingly, a plurality of morphologies going from unilamellar, multilamellar, and large compound vesicles to core-shell nanoparticles and depending on the PLA molecular weights were evidenced by combining cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) studies. A first evaluation of their stealthiness by studying the stability and the interaction of these nano-objects with a model protein revealed the role played by the P(MeOx-co-PentOx) in these interactions, demonstrating the utility of this amphiphilic graft copolymers platform with well-defined architectures for the design of nanocarriers in drug delivery applications.

Molecularly imprinted polymers as selective adsorbents for ambient plasma mass spectrometry

The application of molecularly imprinted polymers (MIPs) as molecular scavengers for ambient plasma ionization mass spectrometry has been reported for the first time. MIPs were synthesized using methacrylic acid as functional monomer; nicotine, propyphenazone, or methylparaben as templates; ethylene glycol dimethacrylate as a cross-linker; and 2,2′-azobisisobutyronitrile as polymerization initiator. To perform ambient plasma ionization experiments, a setup consisting of the heated crucible, a flowing atmospheric-pressure afterglow (FAPA) plasma ion source, and a quadrupole ion trap mass spectrometer has been used. The heated crucible with programmable temperature allows for desorption of the analytes from MIPs structure which results in their direct introduction into the ion stream. Limits of detection, linearity of the proposed analytical procedure, and selectivities have been determined for three analytes: nicotine, propyphenazone, and methylparaben. The analytes used were chosen from various classes of organic compounds to show the feasibility of the analytical procedure. The limits of detections (LODs) were 10 nM, 10, and 0.5 μM for nicotine, propyphenazone, and methylparaben, respectively. In comparison with the measurements performed for the non-imprinted polymers, the values of LODs were improved for at least one order of magnitude due to preconcentration of the sample and reduction of background noise, contributing to signal suppression. The described procedure has shown linearity in a broad range of concentrations. The overall time of single analysis is short and requires ca. 5 min. The developed technique was applied for the determination of nicotine, propyphenazone, and methylparaben in spiked real-life samples, with recovery of 94.6–98.4%. The proposed method is rapid, sensitive, and accurate which provides a new option for the detection of small organic compounds in various samples.

Graphical abstract

Engineered Hydrogen-Bonded Glycopolymer Capsules and Their Interactions with Antigen Presenting Cells

Hollow glycopolymer microcapsules were fabricated by hydrogen-bonded layer-by-layer (LbL) assembly, and their interactions with a set of antigen presenting cells (APCs), including dendritic cells (DCs), macrophages (MACs), and myeloid derived suppressor cells (MDSCs), were investigated. The glycopolymers were obtained by cascade postpolymerization modifications of poly(oligo(2-ethyl-2-oxazoline methacrylate)-stat-glycidyl methacrylate) involving the modification of the glycidyl groups with propargylamine and the subsequent attachment of mannose azide by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Multilayer assembly of the hydrogen-bonding pair (glycopolymer/poly(methacrylic acid) (PMA)) onto planar and particulate supports (SiO₂ particles, d = 1.16 μm) yielded stable glycopolymer films upon cross-linking by CuAAC. The silica (SiO₂) particle templates were removed yielding hollow monodisperse capsules, as demonstrated by fluorescence and scanning electron microscopy. Cellular uptake studies using flow cytometry revealed the preferential uptake of the capsules by DCs when compared to MACs or MDSCs. Mannosylated capsules showed a cytokine independent cis-upregulation of CD80 specifically on DCs and a trans-downregulation of PDL-1 on MDSCs. Thus, the glycopolymer capsules may have potential as vaccine carriers, as they are able to upregulate costimulatory molecules for immune cell stimulation on DCs and at the same time downregulate immune inhibitory receptors on suppressor APC such as MDSCs.

Supramolecular Amphiphilic Polymer-Based Micelles with Seven-Armed Polyoxazoline Coating for Drug Delivery

Supramolecular polymer micelles composed of seven-armed poly(2-methy-2-oxazoline) as the coating and linear poly(dl-lactide) as the core were prepared through synthesizing β-cyclodextrin-terminated poly(2-methy-2-oxazoline) and adamantine-terminated linear poly(dl-lactide), followed by host-guest interaction between β-cyclodextrin and adamantine groups in two polymers and self-assembly in aqueous solution. Dynamic light-scattering measurement showed that the micelles based on supramolecular amphiphilic polymers have the size of 119 nm and were highly stable in salt solution. When the micelles were used as the carrier of cabazitaxel, an antitumor agent for drug-resistant cancers, satisfactory drug loading content and encapsulation efficacy were obtained. In vitro cellular cytotoxicity assays found that cabazitaxel-loaded micelles presented obvious cytotoxicity against taxane-sensitive and -resistant cancer cells. Further in vivo antitumor activity evaluation showed that cabazitaxel-loaded micelles have significantly superior efficacy in inhibiting tumor growth and prolonging survival in tumor-bearing mice compared to that of free paclitaxel and free cabazitaxel.

Uracil-bearing poly(2-isopropyl-2-oxazoline): Hg(ii)-selective control of its thermoresponsiveness

A poly(2-isopropyl-2-oxazoline)-containing mercury ion (Hg²⁺)-responsive uracil moiety (U-PiPOx-U) was synthesized and it exhibited thermoresponsiveness in its aqueous solution.

Thermo-responsive polymers and their application as smart biomaterials

This review summarises smart thermo-responsive polymeric materials with reversible and ‘on–off’ remotely switchable properties for a wide range of biomedical and biomaterials applications.