The thermoresponsive surfaces of brush structure (linear polymer chains tethered on the surface) based on poly(2-isopropyl-2-oxazoline)s and copolymers of 2-ethyl-2-oxazoline and 2-nonyl-2-oxazoline were obtained using the grafting-to method. The living oxazoline (co)polymers have been synthesized by cationic ring-opening polymerization and subsequently terminated by the reactive amine groups present on the surface. The changes in the surface morphology, philicity and thickness occurring during surface modification were monitored via atomic force microscopy, contact angle and ellipsometry. The thickness of the (co)poly(2-substituted-2-oxazoline) layers ranged from 4 to 11 nm depending on the molar mass of immobilized polymer and reversibly varied with the temperature changes. This confirmed thermoresponsive properties of obtained surfaces. The obtained polymer surfaces were used as a support for dermal fibroblast culture and detachment. The fibroblasts' adhesion and proliferation on the polymer surfaces were observed when the culture temperature was above the cloud point temperature of the immobilized polymer. Lowering the temperature resulted in the detachment of the dermal fibroblast sheets from the polymer layers, which makes these surfaces suitable for the treatment of wounds and in skin tissue engineering.

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 (T g) and the melting temperature (T m) of PIPOx crystallized in organic solutions are equal to those of the polymer crystallized in bulk. The enthalpy of melting (ΔH) of the PIPOx crystalline fraction versus its degree of crystallinity (χc) is shown. The value of the enthalpy of melting for hypothetical, fully crystalline PIPOx (ΔH 100%) is determined.

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.