Today, the synthesis of biocompatible and bioresorbable composite materials such as “polymer matrix-mineral constituent,” which stimulate the natural growth of living tissues and the restoration of damaged parts of the body, is one of the challenging problems in regenerative medicine. In this study, composite films of bioresorbable polymers of polyvinylpyrrolidone (PVP) and sodium alginate (SA) with hydroxyapatite (HA) were obtained. HA was introduced by two different methods. In one of them, it was synthesized in situ in a solution of polymer mixture, and in another one, it was added ex situ. Phase composition, microstructure, swelling properties and biocompatibility of films were investigated. The crosslinked composite PVP-SA-HA films exhibit hydrogel swelling characteristics, increasing three times in mass after immersion in a saline solution. It was found that composite PVP-SA-HA hydrogel films containing HA synthesized in situ exhibited acute cytotoxicity, associated with the presence of HA synthesis reaction byproducts—ammonia and ammonium nitrate. On the other hand, the films with HA added ex situ promoted the viability of dental pulp stem cells compared to the films containing only a polymer PVP-SA blend. The developed composite hydrogel films are recommended for such applications, such as membranes in osteoplastic surgery and wound dressing.

The process of open-porous structure development in highdensity polyethylene (HDPE) films during uniaxial deformation in supercritical carbon dioxide (SC-CO 2 ) fluid at 35 °C and 10 MPa has been studied and visualized by means of atomic force microscopy. We suggest that the supercritical fluid act as adsorption-active medium, and the porous structure is developed via the crazing mechanism due to the increasing the distance between of lamellae and the formation of oriented separate fibrils in the intercrystallite space. Effective bulk porosity of the films has been up to 40%. Small-angle X-ray scattering studies and ethanol permeability measurements have revealed that the pores and fibrils are about 10 nm in diameter. The prepared nanoporous materials exhibit good vapor permeability. Structural and mechanical behavior of the prepared porous films has been investigated. Large reversible deformation (up to 80%) of HDPE in the SC-CO 2 has been observed. Repeated drawing of the shrunk films in air under ambient conditions has led to the open-porous structure recovery.

Uniaxial tensile drawing of films based on semicrystalline isotactic PP in the medium of supercrit ical carbon dioxide at a pressure of 10 MPa and a temperature of 35°C is studied. The tensile drawing of PP is shown to proceed in the homogeneous mode without necking and is accompanied by intense cavitation. The maximum level of porosity is 60 vol %. The porous structure that develops owing to the tensile drawing of the polymer in supercritical CO 2 is provided by formation of a set of crazes that are primarily localized in interlamellar regions. According to small angle X ray scattering data, the average diameter of fibrils that bridge craze walls changes slightly with an increase in tensile strain and is ~10 nm; the specific surface of the craze fibrils is 100-150 m 2 /cm 3 .

During this study the formation and growth of silver chloride crystals in crazed porous polymeric matrixes of poly(ethylene terephthalate) (PET) and polypropylene (PP) were under investigation. The rate of formation and dispersity and the way AgCl particles aggregate in porous polymers were shown to be dependent on the effective volume porosity, pore dimension, and physical state of the polymer. Methods of the determination of diffusion and distribution constants for low-molecular substances in porous polymers were suggested, and a mechanism of silver chloride crystallization in porous medium was proposed.

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