Well-Defined Linear and Grafted Poly(2-isopropenyl-2-oxazoline)s Prepared via Copper-Mediated Reversible-Deactivation Radical Polymerization Methods

Redesigning Ibuprofen for Improved Oral Delivery and Reduced Side Effects

Ibuprofen (IBP) is one of the most widely used nonsteroidal anti-inflammatory drugs (NSAIDs). Being well-known for its efficacy, long history of use, and reduced adverse events compared to other NSAIDs, IBP is authorized as an analgesic and antipyretic drug. IBP's mechanism of action consists of inhibiting cyclooxygenases, which are crucial oxidoreductases in prostaglandin synthesis and generation of inflammation and pain. However, despite being effective and relatively safe, IBP can still induce a dose-dependent toxicity which manifests mainly in the gastrointestinal system as ulcerations and altered mucosal blood flow and cytotoxicity characterized by mitochondrial dysfunction and increased membrane permeability in enterocytes and hepatocytes. Therefore, ongoing research is performed to improve the IBP's activity and treatment outcome, and one way to achieve such improvements is through reducing IBP's toxicity by designing less harmful but still effective novel IBP conjugates. The aim of this review is to summarize the latest achievements with IBP conjugation techniques that created such valuable IBP formulations less toxic than but as effective as the parent drug.

Metal-Free Curing of 3D Printable Silicone Elastomers via Thermally Triggered 2-Oxazoline Cross-Linkers

Silicone elastomers are commonly cured by hydrosilylation or condensation reactions, both of which require metal-based catalysts. Due to environmental, toxicological, and cost concerns, there is considerable interest in developing metal-free alternatives. Herein, we present a novel solution via an atom-efficient, catalyst-free ring-opening of poly(2-isopropenyl-2-oxazoline) (PiPOx) as a curing agent. PiPOx are macromolecules bearing pendant reactive 2-oxazoline groups capable of undergoing a ring-opening reaction in the presence of carboxylic acids to give covalent amide-ester bonds. Polydimethylsiloxane (PDMS) chains with COOH moieties at the chain ends could be effectively cured with PiPOx as a latent curing agent. The reaction does not proceed at room temperature but cures in less than 5 min at elevated temperatures (>80 °C) in the absence of catalysts or solvents and without the evolution of volatiles. The PDMS diacids are easily accessible via a simple thiolene addition to divinyl siloxanes in a single step, thus extending the utility of this approach to all divinyl siloxanes, which are widely commercially available in a broad range of chain lengths. The cured elastomers contain up to 98 wt % of the PDMS constituent (including the end-groups), hence mirroring the chemical structure of traditional metal-cured commercial PDMS elastomers. Solvent-free, thermally triggered curing in a practical temperature range facilitates processing using standard extrusion-based processing and additive manufacturing techniques.

Poly(2-isopropenyl-2-oxazoline) as a Versatile Functional Polymer for Biomedical Applications

Functional polymers play an important role in various biomedical applications. From many choices, poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a promising reactive polymer with great potential in various biomedical applications. PIPOx, with pendant reactive 2-oxazoline groups, can be readily prepared in a controllable manner via several controlled/living polymerization methods, such as living anionic polymerization, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) or rare earth metal-mediated group transfer polymerization. The reactivity of pendant 2-oxazoline allows selective reactions with thiol and carboxylic group-containing compounds without the presence of any catalyst. Moreover, PIPOx has been demonstrated to be a non-cytotoxic polymer with immunomodulative properties. Post-polymerization functionalization of PIPOx has been used for the preparation of thermosensitive or cationic polymers, drug conjugates, hydrogels, brush-like materials, and polymer coatings available for drug and gene delivery, tissue engineering, blood-like materials, antimicrobial materials, and many others. This mini-review covers new achievements in PIPOx synthesis, reactivity, and use in biomedical applications.

Cytotoxicity and Bioimmunological Activity of Poly(2-Isopropenyl-2-oxazoline) Conjugates with Ibuprofen Using 3D Reconstructed Tissue Models

Poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a universal polymer platform with pendant 2-oxazoline groups, allowing the preparation of biomaterials for various biomedical applications. However, there is a lack of information on PIPOx concerning the effect of molar mass (Mn) on cytotoxicity and bioimmunological properties. Here, aqueous copper(0)-mediated reversible-deactivation radical polymerization (Cu0-RDPR) was used for the preparation of PIPOx with defined Mn and low dispersity. PIPOx of different Mn are used for the synthesis of conjugates with ibuprofen (5 mol %), the nonsteroidal anti-inflammatory drug. The release of ibuprofen at 37 °C and different pH values is monitored using high-performance liquid chromatography, where the rate of drug release increases with increasing pH and lower Mn. In vitro cytotoxicity and bioimmunological properties of PIPOx and drug conjugates are studied using 3D reconstructed tissue models of the human epidermis and intestinal epithelium. We demonstrate low cytotoxicity of PIPOx and conjugates with different Mn values on both 3D tissue models.

Covalent segmented polymer networks composed of poly(2-isopropenyl-2-oxazoline) and selected aliphatic polyesters: designing biocompatible amphiphilic materials containing degradable blocks

To promote facile and efficient synthesis of segmented covalent networks, we developed a cross-linking process with reactive polymeric components in a system without catalysts or side products. To achieve the direct formation of amphiphilic networks, an addition reaction was performed between the polyesters containing carboxyl terminal groups with pendant groups distributed along poly(2-isopropenyl-2-oxazoline) chains. Covalent cross-linking was achieved from predetermined amounts of components dissolved in DMSO at 140 °C. To tune the properties of the resulting networks, the composition and length of the polyester segments and the degree of cross-linking were changed in the feed. The chemical structure of the networks was characterized using Fourier transform infrared-attenuated total reflection spectroscopy and 13C magic-angle spinning NMR. The swelling ability of the formed networks was investigated in aqueous and organic media. Moreover, mechanical properties were tested during uniaxial compression. The cytocompatibility of the scaffolds was confirmed by MTT assay. Through the results obtained, the first report describing the cross-linking of polyesters on hydrophilic PiPOx was provided to prepare new, biocompatible materials with tuneable properties that are promising for potential biomedical applications.

Poly(2-isopropenyl-2-oxazoline) as a reactive polymer for materials development

Poly(2-isopropenyl-2-oxazoline) has attracted growing interest as a reactive polymer that can be used as a starting material for the construction of more complex structures.

Synthesis of discrete bottlebrush polymers via the iterative convergent growth technique and post-functionalization

The formation of discrete bottlebrush polymers (Step 1: Iterative convergent growth. Step 2: Post-functionalization using thiol–ene click chemistry.)

In Vitro Assessment of the Hydrolytic Stability of Poly(2-isopropenyl-2-oxazoline)

Poly(2-isopropenyl-2-oxazoline) (PiPOx) is emerging as a promising, versatile polymer platform to design functional materials and particularly biomaterials that rely on the hydrophilic character of the 2-oxazoline side units. To be able to assess the applicability of PiPOx in a biomedical context, it is essential to understand its stability and degradation behavior in physiological conditions. In the present work, the hydrolytic stability of PiPOx was systematically investigated as a function of pH during incubation in various buffers. PiPOx was found to be stable in deionized water (pH 6.9), to have good stability in basic conditions (pH 8 and 9), to be satisfactorily stable in neutral conditions (pH 7.4), and to have moderate to low stability in acidic conditions (decreases drastically from pH 6 to pH 1.2). At pH 4, PiPOx formed a crosslinked network in a timeframe of hours, while at pH 1.2, PiPOx was transformed to a water-soluble poly(N-(2-hydroxyethyl)methacrylamide) type of structure over the course of 2 weeks. In vitro stability assays were performed in phosphate-buffered saline (pH 7.4), simulated body fluid (SBF) (pH 7.4), simulated saliva (pH 6.4), simulated intestinal fluid (pH 6.8), and plasma (pH 7.4) revealing that PiPOx is stable in these SBFs up to 1 week of incubation. When incubated in simulated gastric fluid (pH 1.2), PiPOx exhibited a similar degradation behavior to that observed in the buffer at pH 1.2, rendering a water-soluble structure. The presented results on the stability of PiPOx will be important for future use of PiPOx for the development of drug-delivery systems and biomedical applications, such as hydrogels.

Cell-Mediated Immunoreactivity of Poly(2-isopropenyl-2-oxazoline) as Promising Formulation for Immunomodulation

Poly(2-isopropenyl-2-oxazoline) (PIPOx) represents a functional polymer with high potential for drug delivery, tissue engineering, and immunomodulation. The immunomodulatory efficiency of the PIPOx formulation has been studied in vitro following splenic cells and RAW 264.7 macrophages exposition. The cell-specific immunomodulative effect on production of Th1, Th2, Th17, and Treg signature cytokines has been demonstrated. The impact on the functionality of PIPOx-sensitized RAW 264.7 macrophages was assessed by cell phagocytosis. Time- and concentration-dependent cell internalization and intracellular organelles colocalization of fluorescently labeled PIPOx has been examined. The in vitro results demonstrated the PIPOx bioavailability and the capability of triggering immune cell responses resulting in the induced production of cell-specific signature interleukins, important prerequisite properties for future potential biomedical applications.

Poly(2-oxazoline)- and Poly(2-oxazine)-Based Self-Assemblies, Polyplexes, and Drug Nanoformulations-An Update

For many decades, poly(2-oxazoline)s and poly(2-oxazine)s, two closely related families of polymers, have led the life of a rather obscure research topic with only a few research groups world-wide working with them. This has changed in the last five to ten years, presumably triggered significantly by very promising clinical trials of the first poly(2-oxazoline)-based drug conjugate. The huge chemical and structural toolbox poly(2-oxazoline)s and poly(2-oxazine)s has been extended very significantly in the last few years, but their potential still remains largely untapped. Here, specifically, the developments in macromolecular self-assemblies and non-covalent drug delivery systems such as polyplexes and drug nanoformulations based on poly(2-oxazoline)s and poly(2-oxazine)s are reviewed. This highly dynamic field benefits particularly from the extensive synthetic toolbox poly(2-oxazoline)s and poly(2-oxazine)s offer and also may have the largest potential for a further development. It is expected that the research dynamics will remain high in the next few years, particularly as more about the safety and therapeutic potential of poly(2-oxazoline)s and poly(2-oxazine)s is learned.

Reduction-Responsive Molecularly Imprinted Poly(2-isopropenyl-2-oxazoline) for Controlled Release of Anticancer Agents

Trigger-responsive materials are capable of controlled drug release in the presence of a specific trigger. Reduction induced drug release is especially interesting as the reductive stress is higher inside cells than in the bloodstream, providing a conceptual controlled release mechanism after cellular uptake. In this work, we report the synthesis of 5-fluorouracil (5-FU) molecularly imprinted polymers (MIPs) based on poly(2-isopropenyl-2-oxazoline) (PiPOx) using 3,3'-dithiodipropionic acid (DTDPA) as a reduction-responsive functional cross-linker. The disulfide bond of DTDPA can be cleaved by the addition of tris(2-carboxyethyl)phosphine (TCEP), leading to a reduction-induced 5-FU release. Adsorption isotherms and kinetics for 5-FU indicate that the adsorption kinetics process for imprinted and non-imprinted adsorbents follows two different kinetic models, thus suggesting that different mechanisms are responsible for adsorption. The release kinetics revealed that the addition of TCEP significantly influenced the release of 5-FU from PiPOx-MIP, whereas for non-imprinted PiPOx, no statistically relevant differences were observed. This work provides a conceptual basis for reduction-induced 5-FU release from molecularly imprinted PiPOx, which in future work may be further developed into MIP nanoparticles for the controlled release of therapeutic agents.

Poly(2-isopropenyl-2-oxazoline) – a structural analogue to poly(vinyl azlactone) with Orthogonal Reactivity

A modular copolymer platform based on two oxazole derivatives is presented. Post-polymerisation modifications revealed the potential to selectively modify the individual side groups, providing access to functional copolymer libraries in the future.