Control of the Crystalline Properties of 2‑Isopropyl-2-oxazoline Copolymers in Condensed State and in Solution Depending on the Composition

Copolymers of 2-isopropyl- (<i>i</i>PrOx) and 2-<i>n</i>-propyl-2-oxazoline (<i>n</i>PrOx) were obtained, and attempts to control their crystallization both in condensed state and in solution were made. The homopolymer of <i>n</i>PrOx showed a weaker crystallization tendency than P<i>i</i>PrOx; nevertheless, the frequently encountered assumption that it is completely amorphous and is not able to crystallize was found to be unjustified. By increasing the amount of <i>n</i>PrOx in copolymers, their crystallization ability decreased both in the condensed state and in solution. The highest degree of crystallization was achieved for copolymer <i>i</i>PrOx/<i>n</i>PrOx of the composition 85:15 mol %, and χ_c values of ∼60% in condensed state and ∼45% in water were obtained. On the other hand, for the copolymer with 50 mol % of <i>n</i>PrOx no crystalline fraction was observed, even when it was subjected to mild thermal treatment, both in the condensed state and in solution. However, when copolymers were subjected to more rigorous external conditions, such as exposure to high, predefined temperature for a significantly extended time, the crystallization of seemingly amorphous copolymer could be forced

Smart Polymeric Nanocarriers of Met-enkephalin

This study describes a novel approach to polymeric nanocarriers of the therapeutic peptide met-enkephalin based on the aggregation of thermoresponsive polymers. Thermoresponsive bioconjugate poly­((di­(ethylene glycol) monomethyl ether methacrylate)-<i>ran</i>-(oligo­(ethylene glycol) monomethyl ether methacrylate) is synthesized by AGET ATRP using modified met-enkephalin as a macroinitiator. The abrupt heating of bioconjugate water solution leads to the self-assembly of bioconjugate chains and the formation of mesoglobules of controlled sizes. Mesoglobules formed by bioconjugates are stabilized by coating with cross-linked two-layer shell via nucleated radical polymerization of <i>N</i>-isopropylacrylamide using a degradable cross-linker. The targeting peptide RGD, containing the fluorescence marker carboxyfluorescein, is linked to a nanocarrier during the formation of the outer shell layer. In the presence of glutathione, the whole shell is completely degradable and the met-enkephalin conjugate is released. It is anticipated that precisely engineered nanoparticles protecting their cargo will emerge as the next-generation platform for cancer therapy and many other biomedical applications

Crystallization of Poly(2-isopropyl-2-oxazoline) in Organic Solutions

The crystallization of polymers from organic solvents is a common phenomenon. Poly­(2-isopropyl-2-oxazoline) (PIPOx) is known to crystallize in aqueous or aqueous/organic solvent solutions. This process is associated with the dehydration of polymer chains above the polymer’s lower critical solution temperature (LCST). In this work, the ability of PIPOx to crystallize in nonaqueous media is presented. The annealing of a solution of PIPOx in organic solvents, such as acetonitrile, dimethyl sulfoxide, or propylene carbonate, leads to the precipitation of insoluble material. DSC and WAXS studies confirm the formation of a crystalline phase in the solution, with the degree of crystallinity dependent on the solvent and the polymer concentration. SEM analysis reveals micron-sized fibril structures of the PIPOx crystalline fraction. The glass transition temperature (<i>T</i>_g) and the melting temperature (<i>T</i>_m) of PIPOx crystallized in organic solutions are equal to those of the polymer crystallized in bulk. The enthalpy of melting (Δ<i>H</i>) of the PIPOx crystalline fraction versus its degree of crystallinity (χ_c) is shown. The value of the enthalpy of melting for hypothetical, fully crystalline PIPOx (Δ<i>H</i>_100%) is determined

Relevance of the Poly(ethylene glycol) Linkers in Peptide Surfaces for Proteases Assays

Poly­(ethylene glycol)­s (PEGs) with different lengths were used as linkers during the preparation of peptide surfaces for protease detection. In the first approach, the PEG monolayers were prepared using a “grafting to” method on 3-aminopropyltrietoxysilane (APTES)-modified silicon wafers. Protected peptides with a fluorescent marker were synthesized by Fmoc solid phase synthesis. The protected peptide structures enabled their site-specific immobilization onto the PEG surfaces. Alternatively, the PEG-peptide surface was obtained by immobilizing a PEG-peptide conjugate directly onto the modified silicon wafer. The surfaces (composition, grafting density, hydrophilicity, and roughness) were characterized by time-of-flight-secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and atomic force microscopy (AFM). Introducing the PEG linker between the peptide and surface increased their resistance toward nonspecific protein adsorption. The peptide surfaces were examined as analytical platforms to study the action of trypsin as a representative protease. The products of the enzymatic hydrolysis were analyzed by fluorescence spectroscopy, electrospray ionization–mass spectrometry (ESI-MS), and ToF-SIMS. Conclusions about the optimal length of the PEG linker for the analytical application of PEG-peptide surfaces were drawn. This work demonstrates an effective synthetic procedure to obtain PEG-peptide surfaces as attractive platforms for the development of peptide microarrays

Poly[tri(ethylene glycol) ethyl ether methacrylate]-Coated Surfaces for Controlled Fibroblasts Culturing

Well-defined thermosensitive poly­[tri­(ethylene glycol) monoethyl ether methacrylate] (P­(TEGMA-EE)) brushes were synthesized on a solid substrate by the surface-initiated atom transfer radical polymerization of TEGMA-EE. The polymerization reaction was initiated by 2-bromo-2-methylpropionate groups immobilized on the surface of the wafers. The changes in the surface composition, morphology, philicity, and thickness that occurred at each step of wafer functionalization confirmed that all surface modification procedures were successful. Both the successful modification of the surface and bonding of the P­(TEGMA-EE) layer were confirmed by X-ray photoelectron spectroscopy (XPS) measurements. The thickness of the obtained P­(TEGMA-EE) layers increased with increasing polymerization time. The increase of environmental temperature above the cloud point temperature of P­(TEGMA-EE) caused the changes of surface philicity. A simultaneous decrease in the polymer layer thickness confirmed the thermosensitive properties of these P­(TEGMA-EE) layers. The thermosensitive polymer surfaces obtained were evaluated for the growth and harvesting of human fibroblasts (basic skin cells). At 37 °C, seeded cells adhered to and spread well onto the P­(TEGMA-EE)-coated surfaces. A confluent cell sheet was formed within 24 h of cell culture. Lowering the temperature to an optimal value of 17.5 °C (below the cloud point temperature of the polymer, <i>T</i>_CP, in cell culture medium) led to the separation of the fibroblast sheet from the polymer layer. These promising results indicate that the surfaces produced may successfully be used as substrate for engineering of skin tissue, especially for delivering cell sheets in the treatment of burns and slow-healing wounds

Nonviral Plasmid DNA Carriers Based on <i>N</i>,<i>N</i>′‑Dimethylaminoethyl Methacrylate and Di(ethylene glycol) Methyl Ether Methacrylate Star Copolymers

Star polymers with random and block copolymer arms made of cationic <i>N</i>,<i>N</i>′-dimethylaminoethyl methacrylate (DMAEMA) and nonionic di­(ethylene glycol) methyl ether methacrylate (DEGMA) were synthesized via atom transfer radical polymerization (ATRP) and used for the delivery of plasmid DNA in gene therapy. All stars were able to form polyplexes with plasmid DNA. The structure and size of the polyplexes were precisely determined using light scattering and cryo-TEM microscopy. The hydrodynamic radius of a complex of DNA with star was dependent on the architecture of the star arms, the DEGMA content and the number of amino groups in the star compared to the number of phosphate groups of the nucleic acid (N/P ratio). The smallest polyplexes (<i>R</i>_h^90° ∼ 50 nm) with positive zeta potentials (∼15 mV) were formed of stars with N/P = 6. The introduction of DEGMA into the star structure caused a decrease of polyplex cytotoxicity in comparison to DMAEMA homopolymer stars. The overall transfection efficiency using HT-1080 cells showed that the studied systems are prospective gene delivery agents. The most promising results were obtained for stars with random copolymer arms of high DEGMA content

Controlling the Crystallinity of Thermoresponsive Poly(2-oxazoline)-Based Nanolayers to Cell Adhesion and Detachment

Semicrystalline, thermoresponsive poly­(2-isopropyl-2-oxazoline) (PIPOx) layers covalently bonded to glass or silica wafers were obtained via the surface-termination of the living polymer chains. Polymer solutions in acetonitrile were exposed to 50 °C for various time periods and were poured onto the functionalized solid wafers. Fibrillar crystallites formed in polymerization solutions settled down onto the wafers next to the amorphous polymer. The amount of crystallites adsorbed on thermoresponsive polymer layers depended on the annealing time of the PIPOx solution. The wettability of PIPOx layers decreased with the increasing amount of crystallites. The higher content of crystallites weakened the temperature response of the layer, as evidenced by the philicity and thickness measurements. Semicrystalline thermoresponsive PIPOx layers were used as biomaterials for human dermal fibroblasts (HDFs) culture and detachment. The presence of crystallites on the PIPOx layers promoted the proliferation of HDFs. Changes in the physicochemical properties of the layer, caused by the temperature response of the polymer, led to the change in the cells shape from a spindle-like to an ellipsoidal shape, which resulted in their detachment. A supporting membrane was used to assist the detachment of the cells from PIPOx biosurfaces and to prevent the rolling of the sheet