Microwave-assisted cationic ring-opening polymerization of 2-oxazolines

Clickable polyethyleneimine incorporated into triblock copolymeric micelles as an efficient platform in the delivery of siRNA to NSCLC cells

The efficacy of transfection vectors to cross the endosomal membrane into the cytosol is a central aspect in the development of nucleic acid-based therapeutics. The challenge remains the same: Delivery, Delivery, Delivery. Despite a rational and appropriate construct of triblock polymeric micelles, which could serve as an ideal platform for the co-delivery of siRNAs and hydrophobic anticancer drugs, we show here its inability to properly convey oligonucleotides to their final destination. In order to overcome biological barriers, a linear PEI comprising two orthogonal groups was synthesized, holding an appropriate balance between safety and efficacy. Micellar carriers were then formulated with this polymer to enhance endosomal siRNA release. This chemical technology also addresses the two major challenges to consider when developing novel micellar products for siRNA delivery, namely cytotoxicity of polycations and endosomal escape. Herein, we demonstrate successful release of siRNA using a polymer tailoring strategy combined with a relevant in vitro approach, considering STAT3 as a promising target in the treatment of non-small cell lung cancer (NSCLC).

Influence of Hydrophobic Side-Chain Length in Amphiphilic Gradient Copoly(2-oxazoline)s on the Therapeutics Loading, Stability, Cellular Uptake and Pharmacokinetics of Nano-Formulation with Curcumin

Due to the simple one-step preparation method and a promising application in biomedical research, amphiphilic gradient copoly(2-oxazoline)s are gaining more and more interest compared to their analogous block copolymers. In this work, the curcumin solubilization ability was tested for a series of amphiphilic gradient copoly(2-oxazoline)s with different lengths of hydrophobic side-chains, consisting of 2-ethyl-2-oxazoline as a hydrophilic monomer and 2-(4-alkyloxyphenyl)-2-oxazoline as a hydrophobic monomer. It is shown that the length of the hydrophobic side-chain in the copolymers plays a crucial role in the loading of curcumin onto the self-assembled nanoparticles. The kinetic stability of self-assembled nanoparticles studied using FRET shows a link between their integrity and cellular uptake in human glioblastoma cells. The present study demonstrates how minor changes in the molecular structure of gradient copoly(2-oxazoline)s can lead to significant differences in the loading, stability, cytotoxicity, cellular uptake, and pharmacokinetics of nano-formulations containing curcumin. The obtained results on the behavior of the complex of gradient copoly(2-oxazoline)s and curcumin may contribute to the development of effective next-generation polymeric nanostructures for biomedical applications.

Synthesis and Structure-Property Relationship of Amphiphilic Poly(2-ethyl-co-2-(alkyl/aryl)-2-oxazoline) Copolymers

Poly(2-oxazoline)s (POZs) are widely investigated for their applications in various fields due to their unique properties. To exploit and combine different characteristics of the POZ family, 2-oxazoline monomers can be copolymerized to prepare tailor-made copolymers with the desired glass transition temperature (T g), melting temperature (T m), amphiphilicity, and functionality. Here, we report the synthesis and characterization of 2-oxazoline monomers and a range of POZ copolymers produced, thereof. 2-Propyl-2-oxazoline (PrOZ) and 2-pentyl-2-oxazoline (PeOZ) monomers were synthesized by two different methods starting from nitriles or carboxylic acids. A number of POZ copolymers were synthesized by copolymerization of 2-ethyl-2-oxazoline (EOZ) with either one of PrOZ, PeOZ, or 2-phenyl-2-oxazoline (PhOZ) at three different compositions (25:75, 50:50, and 75:25) and three molecular weights (1000, 2000, and 5000 Da). The successful synthesis of the monomers and copolymers was demonstrated through their structural analysis by 1H NMR and FTIR. SEC results confirmed the targeted molar masses of the copolymers and living nature of the polymerization by showing low dispersity values. Thermal properties of the copolymers were studied using DSC and TGA. DSC studies revealed the amorph and random state of the copolymers with obtained T g values for the copolymers in the range of -3 to 84 °C depending on their molecular weight and type of the side chain. While the presence of longer aliphatic side chains resulted in lower T g values, the presence of 2-phenyl substituents on the polymer led to higher T g values. The decomposition temperatures determined by TGA were in the range of 328 to 383 °C depending on the molecular weight, composition, and side chain of the copolymers. It was observed that higher molecular weights led to higher T g values and decomposition temperatures. While copolymers with aliphatic side chains exhibited a single-step decomposition profile, the decomposition of copolymers having aromatic side chains occurred in multiple steps. The variations in the molecular weight, composition, and side chains of the copolymers resulted in a library of tailorable amphiphilic copolymers suitable for multiple applications ranging from biomedical applications to composite manufacturing.

Poly(2-oxazoline)s as Stimuli-Responsive Materials for Biomedical Applications: Recent Developments of Polish Scientists

Poly(2-oxazoline)s are the synthetic polymers that are the products of the cationic ring-opening polymerization (CROP) of 2-oxazoline monomers. Due to their beneficial properties, from which biocompatibility, stealth behavior, high functionalization possibilities, low dispersity, stability, nonionic character, and solubility in water and organic solvents should be noted, they have found many applications and gained enormous interest from scientists. Additionally, with high versatility attainable through copolymerization or through post-polymerization modifications, this class of polymeric systems has been widely used as a polymeric platform for novel biomedical applications. The chemistry of polymers significant expanded into biomedical applications, in which polymeric networks can be successfully used in pharmaceutical development for tissue engineering, gene therapies, and also drug delivery systems. On the other hand, there is also a need to create ‘smart’ polymer biomaterials, responsive to the specified factor, that will be sensitive to various environmental stimuli. The commonly used stimuli-responsive biomedical materials are based mostly on temperature-, light-, magnetic-, electric-, and pH-responsive systems. Thus, creating selective and responsive materials that allow personalized treatment is in the interest of the scientific world. This review article focuses on recent discoveries by Polish scientists working in the field of stimuli-responsive poly(2-oxazoline)s, and their work is compared and contrasted with results reported by other world-renowned specialists.

Polymer Processing under Microwaves

Over the last decades, microwave heating has experienced a great development and reached various domains of application, especially in material processing. In the field of polymers, this unusual source of energy showed important advantages arising from the direct microwave/matter interaction. Indeed, microwave heating allows regio-, chemio-, and stereo-selectivity, faster chemical reactions, and higher yields even in solvent-free processes. Thus, this heating mode provides a good alternative to the conventional heating by reducing time and energy consumption, hence reducing the costs and ecological impact of polymer chemistry and processing. This review states some achievements in the use of microwaves as energy source during the synthesis and transformation of polymers. Both in-solution and free-solvent processes are described at different scales, with comparison between microwave and conventional heating.

Strategies for the design of nanoparticles: starting with long-circulating nanoparticles, from lab to clinic

Short half-life is one of the main causes of drug attrition in clinical development, which also leads to the failure of many leading compounds and hits to become drug candidates. Nowadays, nanomaterials have been applied to drug development to address this problem. In fact, the clinical application of nanoparticles (NPs) is severely limited due to their rapid elimination by the reticuloendothelial system (RES) in vivo. In this paper, we aim to summarize representative strategies on prolonging the circulation time for bridging the gap between excellent pharmaceutics and proper half-life and encourage clinical translation.

Poly(2-ethyl-2-oxazoline-co-ethyleneimine)-block-poly(ε-caprolactone) based micelles: synthesis, characterization, peptide conjugation and cytotoxic activity

Here we present self-assembled polymeric micelles as potential delivery systems for therapeutic agents with highly tunable properties.

Utilization of 4-(trifluoromethyl)benzenesulfonates as Counter Ions Tunes the Initiator Efficiency of Sophisticated Initiators for the Preparation of Well-Defined poly(2-oxazoline)s

During the last decades, poly(2-oxazoline)s (POx) have gained increased interest due to their versatility. In particular, cationic ring-opening polymerization (CROP) enables the synthesis of well-defined polymers bearing quantitative α- and ω-functionalities. In contrast to small initiating groups, the introduction of more sophisticated, respectively demanding groups remains challenging. To fulfill this challenge, the initiator should comply with one major requirement in order to yield well-defined polymers: a fast and complete initiation. The straight forward two-step synthesis of a novel initiator containing a 4-(trifluoromethyl)benzenesulfonate (fluorylate, TosCF₃ ) counter-ion is herein presented to accomplish the introduction of a sophisticated functional 3-(2-(2-ethoxy)ethoxy)ethoxy)prop-1-ene (TEG) initiating group. Kinetic studies are conducted in acetonitrile and chlorobenzene using the hydrophilic 2-ethyl-2-oxazoline (EtOx) as well as the hydrophobic 2-octyl-2-oxazoline (OctOx) as monomers to examine the influences of the solvent as well as the different monomers. In particular, the initiator efficiency is determined by ¹ H and ¹⁹ F nuclear magnetic resonance spectroscopy and compared to the corresponding tosylate (TEGTos) and triflate (TEGTf). It is shown that the fluorylate combines the stability of the tosylate and an enhanced propagation rate comparable to the triflate.

UV-mediated thiol-ene click reactions for the synthesis of drug-loadable and degradable gels based on copoly(2-oxazoline)s

An 80-membered library of gels composed of monofunctional 2-ethyl-2-oxazoline and 2-nonyl-2-oxazoline and one of four selected difunctional 2-oxazolines (containing either ether or ester bonds) were synthesized by microwave-assisted ring-opening polymerizations. The difunctional 2-oxazolines were prepared from the thiol-ene reaction of glycol dimercaptoacetate or 2,2'-(ethylenedioxy)diethanethiol and 2-but-3'-enyl-2-oxazoline or 2-dec-9'-enyl-2-oxazoline. 53 of the gels exhibited glass-transition temperatures, which ranged from -5.9 to 45.3 °C. 13 Derivatives exhibited glass-transition temperatures in the range from 20 to 30 °C, which renders them stiff at room temperature and flexible at body temperature. The gels that did not contain any 2-ethyl-2-oxazoline acted as lipogels, whereas the gels that did not contain any 2-nonyl-2-oxazoline acted as hydrogels; all other gels may be classified as amphigels. The swelling degrees were measured by gravimetry and maximum swelling degrees of 6 (in water) were observed for the gels with the lowest degrees of crosslinking. In a second approach, the synthesis of crosslinked networks had been achieved by performing the polymeranalogous thiol-ene reaction of copoly(2-oxazoline)s containing olefinic side-chains and glycol dimercaptoacetate. This soft strategy enabled the straightforward loading of such gels with active pharmaceutical ingredients without altering them. This method delivered gels with selected composition exhibiting a targeted disc-shape and loaded with active pharmaceutical ingredients from one-step syntheses. The maximum swelling degrees of these specimens were found to be in accordance with the ones from the first route investigated. Preliminary degradation studies were performed at 25 °C; these types of gels were found to be degraded in alkaline media as well as by esterases.

Enhanced cytocompatibility and functional group content of poly(l-lysine) dendrimers by grafting with poly(oxazolines)

We report the use of polyoxazolines as materials for modifying the surface of a generation 5 l-lysine dendrimer resulting in a significant improvement in the biocompatibility properties compared to the unmodified dendrimer. The polyoxazoline coatings represent interesting alternatives to polyethylene glycol and can also offer an opportunity for increasing drug loading.

Crosslinked Poly(2-oxazoline)s as "Green" Materials for Electronic Applications

Poly(2-nonyl-2-oxazoline)₈₀-stat-poly(2-dec-9'-enyl-2-oxazoline)₂₀ and poly(2-dec-9'-enyl-2-oxazoline)₁₀₀ can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10^-2 to 10⁶ Hz and at temperatures ranging from -20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10^-12 to 8 × 10^-9 S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as "green" alternatives for polyamides as insulators in electronic applications.