Soluble polymeric carriers for drug delivery. Part 2. Preparation and in vivo behaviour of N-acylethylenimine copolymers

Synthesis of Double Hydrophilic Block Copolymers Poly(2-isopropyl-2-oxazoline-b-ethylenimine) and their DNA Transfection Efficiency

Gene delivery is now a part of the therapeutic arsenal for vaccination and treatments of inherited or acquired diseases. Polymers represent an opportunity to develop new synthetic vectors for gene transfer, with a prerequisite of improved delivery and reduced toxicity compared to existing polymers. Here, the synthesis in a two-step's procedure of linear poly(ethylenimine-b-2-isopropyl-2-oxazoline) block copolymers with the linear polyethylenimine (lPEI) block of various molar masses is reported; the molar mass of the poly(2-isopropyl-2-oxazoline) (PiPrOx) block has been set to 7 kg mol^-1 . Plasmid DNA condensation is successfully achieved, and in vitro transfection efficiency of the copolymers is at least comparable to that obtained with the lPEI of same molar mass. lPEI-b-PiPrOx block copolymers are however less cytotoxic than their linear counterparts. PiPrOx can be a good alternative to PEG which is often used in drug delivery systems. The grafting of histidine moieties on the lPEI block of lPEI-b-PiPrOx does not provide any real improvement of the transfection efficiency. A weak DNA condensation is observed, due to increased steric hindrance along the lPEI backbone. The low cytotoxicity of lPEI-b-PiPrOx makes this family a good candidate for future gene delivery developments.

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.

Linear and Branched Lactide Polymers for Targeted Drug Delivery Systems

Abstract

The review presents modern advances in the synthesis of biodegradable polymers based on lactide of various topologies and also analyzes the main methods for preparation of nanoparticles that show promise for the creation of targeted drug delivery systems.

The role of poly(2-alkyl-2-oxazoline)s in hydrogels and biofabrication

Poly(2-alkyl-2-oxazoline)s (PAOXAs) have been rapidly emerging as starting materials in the design of tissue engineering supports and for the generation of platforms for cell cultures, especially in the form of hydrogels. Thanks to their biocompatibility, chemical versatility and robustness, PAOXAs now represent a valid alternative to poly(ethylene glycol)s (PEGs) and their derivatives in these applications, and in the formulation of bioinks for three-dimensional (3D) bioprinting. In this review, we summarize the recent literature where PAOXAs have been used as main components for hydrogels and biofabrication mixtures, especially highlighting how their easily tunable composition could be exploited to fabricate multifunctional biomaterials with an extremely broad spectrum of properties.

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.

Atmospheric Pressure Plasma Polymerized 2-Ethyl-2-oxazoline Based Thin Films for Biomedical Purposes

Polyoxazoline thin coatings were deposited on glass substrates using atmospheric pressure plasma polymerization from 2-ethyl-2-oxazoline vapours. The plasma polymerization was performed in dielectric barrier discharge burning in nitrogen at atmospheric pressure. The thin films stable in aqueous environments were obtained at the deposition with increased substrate temperature, which was changed from 20 ∘C to 150 ∘C. The thin film deposited samples were highly active against both S. aureus and E. coli strains in general. The chemical composition of polyoxazoline films was studied by FTIR and XPS, the mechanical properties of films were studied by depth sensing indentation technique and by scratch tests. The film surface properties were studied by AFM and by surface energy measurement. After tuning the deposition parameters (i.e., monomer flow rate and substrate temperature), stable films, which resist bacterial biofilm formation and have cell-repellent properties, were achieved. Such antibiofouling polyoxazoline thin films can have many potential biomedical applications.

Thermal and crystalline properties of poly(2-oxazoline)s

The review gathers together data concerning the influence of poly(2-substituted-2-oxazoline)s structure on their thermal and crystalline properties, and how this relationship can be adjusted in controlled manner.

Atmospheric Pressure Plasma Polymerized Oxazoline-Based Thin Films-Antibacterial Properties and Cytocompatibility Performance

Polyoxazolines are a new promising class of polymers for biomedical applications. Antibiofouling polyoxazoline coatings can suppress bacterial colonization of medical devices, which can cause infections to patients. However, the creation of oxazoline-based films using conventional methods is difficult. This study presents a new way to produce plasma polymerized oxazoline-based films with antibiofouling properties and good biocompatibility. The films were created via plasma deposition from 2-methyl-2-oxazoline vapors in nitrogen atmospheric pressure dielectric barrier discharge. Diverse film properties were achieved by increasing the substrate temperature at the deposition. The physical and chemical properties of plasma polymerized polyoxazoline films were studied by SEM, EDX, FTIR, AFM, depth-sensing indentation technique, and surface energy measurement. After tuning of the deposition parameters, films with a capacity to resist bacterial biofilm formation were achieved. Deposited films also promote cell viability.

PDMS-PMOXA-Nanoparticles Featuring a Cathepsin B-Triggered Release Mechanism

Background: It was our intention to develop cathepsin B-sensitive nanoparticles for tumor-site-directed release. These nanoparticles should be able to release their payload as close to the tumor site with a decrease of off-target effects in mind. Cathepsin B, a lysosomal cysteine protease, is associated with premalignant lesions and invasive stages of cancer. Previous studies have shown cathepsin B in lysosomes and in the extracellular matrix. Therefore, this enzyme qualifies as a trigger for such an approach. Methods: Poly(dimethylsiloxane)-b-poly(methyloxazoline) (PDMS-PMOXA) nanoparticles loaded with paclitaxel were formed by a thin-film technique and standard coupling reactions were used for surface modifications. Despite the controlled release mechanism, the physical properties of the herein created nanoparticles were described. To characterize potential in vitro model systems, quantitative polymerase chain reaction and common bioanalytical methods were employed. Conclusions: Stable paclitaxel-loaded nanoparticles with cathepsin B digestible peptide were formed and tested on the ovarian cancer cell line OVCAR-3. These nanoparticles exerted a pharmacological effect on the tumor cells suggesting a release of the payload.

Polyoxazolines based mixed micelles as PEG free formulations for an effective quercetin antioxidant topical delivery

This study aims to prove the value of the polyoxazolines polymer family as surfactant in formulations for topical application and as an alternative to PEG overuse. The amphiphilic polyoxazolines (POx) were demonstrated to have less impact on cell viability of mice fibroblasts (NIH3T3) than their PEG counterparts. Mixed micelles, made of POx and phosphatidylcholine, were manufactured using thin film and high pressure homogenizer process. The mixed micelles were optimized to produce nanosized vesicles of about 20 nm with a spherical shape and stable over 28 days. The natural lipophilic antioxidant, quercetin, was successfully encapsulated (encapsulation efficiency 94 ± 4% and drug loading 3.6 ± 0.2%) in the mixed micelles with no morphological variation. Once loaded in the formulation, the quercetin impact on cell viability of NIH3T3 was decreased while its antioxidant activity remained unchanged. This work highlights the capacity of amphiphilic POx to create, in association with phospholipids, stable nanoformulations which show promise for topical delivery of antioxidant and ensure skin protection against oxidative stress.

Influence of charged groups on the cross-linking efficiency and release of guest molecules from thiol-ene cross-linked poly(2-oxazoline) hydrogels

We describe the preparation of hydrogels using highly functionalized poly(oxazoline) based polymeric precursors and cross-linking via UV mediated radical thiol-ene chemistry. Random copolymers were synthesized based on the combination of the more hydrophilic 2-methyl-2-oxazoline or the less hydrophilic monomer 2-ethyl-2-oxazoline with 2-(3-butenyl)-2-oxazoline. These copolymers were functionalized via a post-polymerization technique with thiol or cysteine functionality at the side chain. Hence, hydrogels were obtained, for which the thermo-responsive behavior, network density and correlated properties such as swelling and mechanics, as well as the possibility of electrostatic interaction, can be tuned. Cell culture tests demonstrated good cytocompatibility of the synthesized copolymers and hydrogels. A study with two low molecular weight substances, methylene blue and fluorescein sodium, was performed to investigate how the thermo-responsive behavior or the positive charge incorporated by cysteine could influence the interaction with the compounds. It was found that the interaction with the hydrogel network was strongly influenced by the chemical properties of the dye. A hydrophilic and positively charged hydrogel network was shown to be a promising candidate for the uptake and prolonged release of negatively charged low molecular weight substances.

Mission ImPOxable – or the unknown utilization of non-toxic poly(2-oxazoline)s as cryoprotectants and surfactants at the same time

Polymeric nanoparticles are produced using hydrophilic poly(2-oxazoline)s (P(Ox)s) as particle stabilizers during preparation, purification and lyophilization as an all-in-one system.

Soluble Polymeric Carriers for Drug Delivery—Part 4: Tissue Autoradiography, and Whole-Body Tissue Distribution in Mice, of N-(2-Hydroxypropyl)Methacrylamide Copolymers Following Intravenous Administration

The tissue distribution of water-soluble, non-biodegradable co polymers prepared from N-(2-hydroxypropyl)methacrylamide (HPMA) and N-[2-(4-hydroxyphenyl)ethyl]acrylamide (HPEA) is described, and their poten tial for use as carriers in drug delivery is discussed. Copolymers with weight- average molecular weights (Mw) of 4, 18, 75, and 90 x 103 Daltons, of low poly dispersity ( ≅Mw/Mn ≤ 1.40), were radiolabelled with 125I and administered intravenously to mice. The biodistribution of the radioiodinated copolymers was determined at 10 min, 0.5, 2, 6, 12, 24, 48, 72, and 168 h. All the copoly mers exhibited a molecular weight related clearance from the blood compart ment. Over the time course of our experiments the copolymers were found to access and be retained within different tissues of the body, in particular the skin and muscle, their rate of access and retention being governed by their molecular size (indicated here by molecular weight). No fractionation of molec ular weight occurred in vivo, as determined by Gel Permeation Chromatog raphy of extracted radioiodinated material from the mice. Comparatively little poly(HPMA/HPEA) was found associated with the liver and spleen, (organs of the mononuclear phagocyte system). Autoradiography of animal tissue sug gested that the copolymers appeared to be located in vivo in the muscle, dermis, at the interface of fat deposits (but not over the fat), hair follicles, and epider mis. The copolymers appeared not to be located intracellularly. For drug- delivery applications it is unlikely that these nonbiodegradable polymers will be of clinical use in chronic situations unless it can be categorically demon strated that the polymers are able to be completely removed from the body.

Soluble Polymeric Carriers for Drug Delivery - Part 6: Preparation and Biodistribution of N5-Hydroxyethyl-L-Glutamine-co-L-Glutamic Acid Copolymers in Rats

The purpose of this work was to examine the biodistribution of poly( N5-hydroxyethyl-L-glutamine- co-L-glutamic acid) [poly(HEG- co-GA)] after intravenous administration to rats. Poly(γ-methyl-L-glutamate- co-γ-benzyl-L- glutamate) was prepared by ring-opening polymerization of the amino acid N-carboxyanhydride (NCA) derivatives. Sequential removal of the copolymer benzyl groups followed by reaction of the methyl ester groups with 2-amino ethanol gave poly(HEG- co-GA). Three samples of poly(HEG-co-GA) were pre pared with nominal HEG:GA compositions of 50:50, 95:5 and 90:10 mole %, and with weight average molecular weights ( Mw) of 37,000, 50,000 and 110,000 respectively. Following reaction with N-2[4-hydroxyphenyl]ethylamine (tyra mine), the copolymers were radioiodinated with 125 I and administered intra venously to male Wistar rats. 125 I-copolymer tissue distribution was assessed after 10, 15, 30 and 120 min and 8 h. It was found that the copolymer was removed rapidly from the blood compartment and excreted from the body via the kidneys. Only very low amounts of radioactivity were found in the liver and in other organs of the mononuclear phagocyte system. Degradation of the co polymer in vitro, as assessed by size exclusion chromatography (SEC), in plasma and urine over the time scale of the biodistribution experiment ap peared to be minimal.

Soluble Polymeric Carriers for Drug Delivery: Part 5: Solution Properties and Biodistribution Behaviour of N-(2-Hydroxypropyl)Methacrylamide-co-N-(2-[4-Hydroxyphenyl]Ethyl) Acrylamide Copolymer Substituted with Cholesterol

A copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-(2-[4-hydroxyphenyl]ethyl)acrylamide (HPEA) was derivatized with 2-4 mole% of N-(2-[(cholest-5-en-3-yl(3β)oxycarbonyl)oxypropyl]methacrylamide residues (cholesteryl residues). The effect of polymer modification on some of its solution properties, and on its behaviour in vivo in experimental animals, has been examined.

Amphiphilic gels of solvatochromic fluorescent poly(2-oxazoline)s containing D–π–A pyrenes

We report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) (POZO-py) and poly(2-ethyl-2-oxazoline) (PEtOZO-py), which contain D–π–A pyrene dye units in their side chains.

Plasma polymerised polyoxazoline thin films for biomedical applications

Poly(2-oxazoline)s are emerging revolutionary biomaterials, exhibiting comparable and even superior properties to well-established counterparts. Overcoming current tedious wet synthesis methods, we report solvent-free and substrate independent, plasma polymerised nanoscale biocompatible polyoxazoline coatings capable of controlling protein and cell adhesion, and significantly reducing biofilm build up.

Properties and reactivity of polyoxazoline plasma polymer films

Polyoxazolines arise as a promising new class of polymers for biomedical applications, but creating oxzoline-based coatings via conventional methods is challenging. Herein, nanoscale polyoxazoline coatings were generated via a single step plasma deposition process. The effects of plasma deposition conditions on the film stability, structure and chemical group density were investigated. Detailed examination of the physical and chemical properties of plasma deposited polyoxazoline via XPS, FTIR, contact angle and ellipsometry unravels the complex functionality of the films. Partial retention of the oxazoline ring facilitates a covalent reaction with the carboxylic acid groups present on nanoparticles and biomolecules. Surface bound proteins effectively retain their bioactivity, therefore a vast range of potential applications unlocks for plasma deposited polyoxazoline coatings in the field of biosensing, medical arrays and diagnosis.

Biocompatibility of poly(2-alkyl-2-oxazoline) brush surfaces for adherent lung cell lines

Development of synthetic surfaces that are highly reproducible and biocompatible for in vitro cell culture offers potential for development of improved models for studies of cellular physiology and pathology. They may also be useful in tissue engineering by removal of the need for biologically-derived components such as extracellular matrix proteins. We synthesised four types of 2-alkyl-2-oxazoline polymers ranging from the hydrophilic poly(2-methyl-2-oxazoline) to the hydrophobic poly(2-n-butyl-2-oxazoline). The polymers were terminated using amine-functionalised glass coverslips, enabling the synthetic procedure to be reproducible and scaleable. The polymer-coated glass slides were tested for biocompatibility using human epithelial (16HBE14o-) and fibroblastic (MRC5) cell lines. Differences in adhesion and motility of the two cell types was observed, with the poly(2-isopropyl-2-oxazoline) polymer equally supporting the growth of both cell types, whereas poly(2-n-butyl-2-oxazoline) showed selectivity for fibroblast growth. In summary, 2-alkyl-2-oxazoline polymers may be a useful tool for building in vitro model cell culture models with preferential adhesion of specific cell types.

Side-chain cysteine-functionalized poly(2-oxazoline)s for multiple peptide conjugation by native chemical ligation

We prepared statistical copolymers composed of 2-methyl-2-oxazoline (MeOx) in combination with 2-butenyl-2-oxazoline (BuOx) or 2-decenyl-2-oxazoline (DecOx) as a basis for polymer analogous introduction of 1,2-aminothiol moieties at the side chain. MeOx provides hydrophilicity as well as cyto- and hemocompatibility, whereas the alkene groups of BuOx and DecOx serve for functionalization with a thiofunctional thiazolidine by UV-mediated thiol-ene reaction. After deprotection the cysteine content in functionalized poly(2-oxazoline) (POx) is quantified by NMR and a modified trinitrobenzenesulfonic acid assay. The luminescent cell viability assay shows no negative influence of cysteine-functionalized POx (cys-POx) concerning cell viability and cell number. cys-POx was used for multiple chemically orthogonal couplings with thioester-terminated peptides through native chemical ligation (NCL), which was performed and confirmed by NMR and MALDI-ToF measurements.

Poly(2-oxazoline)s as materials for biomedical applications

The conjunction of polymers and medicine enables the development of new materials that display novel features, opening new ways to administrate drugs, design implants and biosensors, to deliver pharmaceuticals impacting cancer treatment, regenerative medicine or gene therapy. Poly(2-oxazoline)s (POx) constitute a polymer class with exceptional properties for their use in a plethora of different biomedical applications and are proposed as a versatile platform for the development of new medicine. Herein, a global vision of POx as a platform for novel biomaterials is offered, by highlighting the recent advances and breakthroughs in this fascinating field.

Poly(2-oxazoline)s as polymer therapeutics

Poly(2-oxazoline)s (POx) are currently discussed as an upcoming polymer platform for biomaterials design and especially for polymer therapeutics. POx meet specific requirements needed for the development of next-generation polymer therapeutics such as biocompatibility, high modulation of solubility, variation of size, architecture as well as chemical functionality. Although in the early 1990s first and promising POx-based systems were presented, the field lay dormant for almost two decades. Only very recently, POx-based polymer therapeutics came back into the focus of very intensive research. In this review, we give an overview on the chemistry and physicochemical properties of POx and summarize the research of POx-protein conjugates, POx-drug conjugates, POx-based polyplexes and POx micelles for drug delivery.