Echogenic Gold Nanorod Incorporated Hybrid Poly(2-oxazoline) Nanocapsules for Real-Time Ultrasound/Fluorescent Imaging and Targeted Cancer Theranostics.

In recent years, various nanocarrier systems have been explored to enhance the targeting of cancer cells by improving the ligand-receptor interactions between the nanocarrier and cancer cells for selective cancer cell imaging and targeted delivery of anticancer drugs. Herein, we report multifunctional hydrogen-bonded multilayer nanocapsules functionalized with both folic acid-derived quantum dots (FAQDs) and gold nanorods (AuNRs) for targeted cancer therapy and cancer cell imaging using fluorescence microscopy and medical-range ultrasound imaging systems. The encapsulation efficiency of nanocapsules was found to be 49% for 5-fluorouracil (5-FU). The release percentage reached a plateau at 37% after 1 h at pH 7.4 and increased to 57% after 3 h when the release pH was decreased to pH 5.5 (i.e., the pH of the tumor environment). Under ultrasound irradiation, the release was significantly accelerated, with a total release of 52% and 68% after only 6 min at pH 7.4 and pH 5.5, respectively. While the sonoporation process plays an important role in anticancer activity experiments under ultrasound exposure by generating temporary pores, the targeting ability of FAQDs brings the capsules closer to the cell membrane and improves the cellular uptake of the released drug, thereby increasing local drug concentration. In vitro cytotoxicity experiments with HCT-116 and HEp-2 cells demonstrated anticancer activities of 96% and 98%, respectively. The nanocapsules showed enhanced ultrasound scattering signal intensity and bright spots under ultrasound exposure, most likely caused by high scattering ability and internal reflections of preloaded AuNRs in the interior structure of the nanocapsules. Hence, the demonstrated nanocapsule system not only has the potential to be used as an integrated system for early- stage detection and treatment of cancer cells but also has the ability for live tracking and imaging of cancer cells while undergoing treatment with chemotherapy and radiation therapy.

Stable amorphous solid dispersion of flubendazole with high loading via electrospinning.

In this work, an important step is taken towards the bioavailability improvement of poorly water-soluble drugs, such as flubendazole (Flu), posing a challenge in the current development of many novel oral-administrable therapeutics. Solvent electrospinning of a solution of the drug and poly (2-ethyl-2-oxazoline) (PEtOx) is demonstrated to be a viable strategy to produce stable nanofibrous amorphous solid dispersions (ASDs) with ultrahigh drug-loadings (up to 55 wt% Flu) and long-term stability (at least one year). Importantly, at such high drug loadings, the concentration of the polymer in the electrospinning solution has to be lowered below the concentration where it can be spun in absence of the drug as the interactions between the polymer and the drug result in increased solution viscosity. A combination of experimental analysis and molecular dynamics simulations revealed that this formulation strategy provides strong, dominant and highly stable hydrogen bonds between the polymer and the drug, which is crucial to obtain the high drug-loadings and to preserve the long-term amorphous character of the ASDs upon storage. In vitro drug release studies confirm the remarkable potential of this electrospinning formulation strategy by significantly increased drug solubility values and dissolution rates (respectively tripled and quadrupled compared to the crystalline drug), even after storing the formulation for one year.

Comparative study of the potential of poly(2-ethyl-2-oxazoline) as carrier in the formulation of amorphous solid dispersions of poorly soluble drugs.

Despite the fact that solid dispersions are gaining momentum, the number of polymers that have been used as a carrier during the past 50 years is rather limited. Recently, the poly(2-alkyl-2-oxazoline) (PAOx) polymer class profiled itself as a versatile platform for a wide variety of applications in drug delivery, including their use as amorphous solid dispersion (ASD) carrier. The aim of this study was to investigate the potential of poly(2-ethyl-2-oxazoline) (PEtOx) by applying a benchmark approach with well-known, commercially available carriers (i.e. polyvinylpyrrolidone (PVP) K30, poly(vinylpyrrolidone-co-vinyl acetate) (PVP-VA) 64 and hydroxypropylmethylcellulose (HPMC)). For this purpose, itraconazole (ITC) and fenofibrate (FFB) were selected as poorly water-soluble model drugs. The four polymers were compared by establishing their supersaturation maintaining potential and by investigating their capability as carrier for ASDs with high drug loadings. Spray drying, as well as hot melt extrusion and cryo-milling were implemented as ASD manufacturing technologies for comparative evaluation. For each manufacturing technique, the formulations with the highest possible drug loadings were tested with respect to in vitro drug release kinetics. This study indicates that PEtOx is able to maintain supersaturation of the drugs to a similar extent as the commercially available polymers and that ASDs with comparable drug loadings can be manufactured. The results of the in vitro dissolution tests reveal that high drug release can be obtained for PEtOx formulations. Overall, proof-of-concept is provided for the potential of PEtOx for drug formulation purposes.

Influence of the Aliphatic Side Chain on the Near Atmospheric Pressure Plasma Polymerization of 2-Alkyl-2-oxazolines for Biomedical Applications.

Plasma polymerization is gaining popularity as a technique for coating surfaces due to the low cost, ease of operation, and substrate-independent nature. Recently, the plasma polymerization (or deposition) of 2-oxazoline monomers was reported resulting in coatings that have potential applications in regenerative medicine. Despite the structural versatility of 2-oxazolines, only a few monomers have been subjected to plasma polymerization. Within this study, however, we explore the near atmospheric pressure plasma polymerization of a range of 2-oxazoline monomers, focusing on the influence of the aliphatic side-chain length (methyl to butyl) on the plasma polymerization process conditions as well as the properties of the obtained coatings. While side-chain length had only a minor influence on the chemical composition, clear effects on the plasma polymerization conditions were observed, thus gaining valuable insights in the plasma polymerization process as a function of monomer structure. Additionally, cytocompatibility and cell attachment on the coatings obtained by 2-oxazoline plasma polymerization was assessed. The coatings displayed strong cell interactive properties, whereby cytocompatibility increased with increasing aliphatic side-chain length of the monomer, reaching up to 93% cell viability after 1 day of cell culture compared to tissue culture plates. As this is in stark contrast to the antifouling behavior of the parent polymers, we compared the properties and composition of the plasma-polymerized coatings to the parent polymers revealing that a significantly different coating structure was obtained by plasma polymerization.

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.

Ultra-high performance size-exclusion chromatography in polar solvents.

Size-exclusion chromatography (SEC) is amongst the most widely used polymer characterization methods in both academic and industrial polymer research allowing the determination of molecular weight and distribution parameters, i.e. the dispersity (Ɖ), of unknown polymers. The many advantages, including accuracy, reproducibility and low sample consumption, have contributed to the worldwide success of this analytical technique. The current generation of SEC systems have a stationary phase mostly containing highly porous, styrene-divinylbenzene particles allowing for a size-based separation of various polymers in solution but limiting the flow rate and solvent compatibility. Recently, sub-2µm ethylene-bridged hybrid (BEH) packing materials have become available for SEC analysis. These packing materials can not only withstand much higher pressures up to 15000psi but also show high spatial stability towards different solvents. Combining these BEH columns with the ultra-high performance LC (UHPLC) technology opens up UHP-SEC analysis, showing strongly reduced runtimes and unprecedented solvent compatibility. In this work, this novel characterization technique was compared to conventional SEC using both highly viscous and highly polar solvents as eluent, namely N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and methanol, focusing on the suitability of the BEH-columns for analysis of highly functional polymers. The results show a high functional group compatibility comparable with conventional SEC with remarkably short runtimes and enhanced resolution in methanol.

Hydrogen bonded multilayer films based on poly(2-oxazoline)s and tannic acid.

In recent years, the layer-by-layer (LbL) assembly based on hydrogen bonding interactions is gaining popularity for the preparation of thin film coatings, especially for biomedical purposes, based on the use of neutral, non-toxic building blocks. The use of tannic acid (TA) as hydrogen bonding donor is especially interesting as it results in LbL films that are stable under physiological conditions. In this work, investigations on the LbL thin film preparation of TA with poly(2-oxazoline)s with varying hydrophilicity, namely poly(2-methyl-2-oxazoline) (PMeOx), poly(2-ethyl-2-oxazoline) (PEtOx) and poly(2-n-propyl-2-oxazoline) (PnPropOx), are reported. The LbL assembly process is investigated by quartz crystal microbalance and UV-vis spectroscopy revealing linear growth of the film thickness. Furthermore, isothermal titration calorimetry demonstrates the LbL assembly of TA, and PMeOx is found to be mostly enthalpy driven while the LbL assembly of TA with PEtOx and PnPropOx is mostly entropy driven. Finally, scanning electron microscopy and ellipsometry demonstrate the formation of smooth thin films for LbL assembly of TA with all three polymers. Such poly(2-oxazoline) coatings have high potential for use as anti-biofouling coatings.