Biodegradable polyester/hydroxyapatite microparticles are widely proposed as microcarriers for drug/cell delivery or scaffolds for bone tissue regeneration. The current research implements the surfactant-free approach for the fabrication of polyester-based microparticles filled with hydroxyapatite nanoparticles (nHA) via the oil/water Pickering emulsion solvent evaporation technique for the first time, to the best of our knowledge. The process of polyester microparticle fabrication using nHA for the oil/water interface stabilization was studied as a function of phase used for nHA addition, which allows the preparation of a range of microparticles either filled with nHA or having it as a shell over the polymeric core. The effect of processing conditions (polymer nature, polymer/nHA ratio, ultrasound treatment) on particles' total yield, size distribution, surface and volume morphology, and chemical structure was analyzed using SEM, EDX, Raman spectroscopy, and mapping. Addition of nHA either within the aqueous or oil phase allowed the effective stabilization of the oil/water interface without additional molecular surfactants, giving rise to hybrid microparticles in which total yield, size distribution, and surface morphology depended on all studied processing conditions. Preliminary ultrasound treatment of any phase before the emulsification process led to a complex effect but did not affect the homogeneity of nHA distribution within the polymeric core of the hybrid microparticles.

Surface-selective laser sintering (SSLS) is a specific version of selective laser sintering, which allows one to fabricate 3D structures with well-defined architectonic via selective melting of microparticle surface without alteration of their core. This mode of laser sintering requires a well-designed surface properties of the microparticles to adsorb laser irradiation. Water was chosen as safer sensitive absorber of laser radiation with a wavelength of 1.9 μm, i.e. one with low absorption coefficient by polymeric core. Biodegradable polylactide microparticles were fabricated via oil/water emulsion solvent evaporation technique using tailored-made chitosan-based macromolecules, which provided the effective interface stabilization during the microparticle fabrication and well balanced microparticle surface hydrophilicity to adsorb water. Especially build SSLS set-up was designed in order to monitor the effectiveness of the 3D scaffold fabrication from the obtained microparticles and to adapt the optimal laser radiation parameters with a wavelength of 1.9 μm (e.g. speed, line density, power).

The paper studies the formation, development and stabilization of the structure of foamed amorphous D,L-polylactide after a slow (quasi-isothermal) and a fast (quasi-adiabatic) relief of the pressure of supercritical carbon dioxide used as a plasticizing/foaming agent. The following regularities have been established: (1) the values of the foam expansion factor in the process of quasi-adiabatic depressurization are significantly lower than in the quasi-isothermal regime because of significant dissipation of the “polymer–foaming agent” system internal energy due to the internal friction in the system; (2) an expansion-collapse effect is observed during the quasi-isothermal foaming; (3) at the intermediate stage between nucleation and intensive foam development, the pore nuclei growth in the plasticized polymer is self-similar. The results obtained are important for selecting foaming regimes that provide the synthesized highly porous matrices with the structural characteristics required for their use in regenerative medicine and tissue engineering.

The influence of mid-IR (1.94 μm) laser radiation on the morphology of polylactide and polycaprolactone nonwoven materials obtained by electrospinning has been revealed. It has been shown that laser irradiation makes it possible to achieve local structuring of the nonwovens at the micrometer level, in particular, to fuse individual fibers, straighten them between fusion points, and prepare monolithic films from the materials or, conversely, create breaks in them. The influence of laser irradiation parameters (power, laser spot speed, scan line density) and additional wetting of the samples on the structure of the nonwovens has been determined.

A laboratory system for the development of new approaches to the experimental study of nucleation and formation of three-dimensional structures in nonequilibrium “polymer-supercritical fluid” heterogeneous systems has been designed and produced. The system is designed to conduct a comprehensive analysis of these processes at various stages starting from supercritical fluid plasticization of the initial polymer, followed by its subsequent nucleation and passage to the glass transition stage of the foamed polymer matrix, providing an opportunity for adequate interpretation.

New results are presented for laser formation—in particular, the “drawing” of microstructures in polymer films using continuous-wave (CW) laser radiation λ = 405 nm with an intensity of 0.8–3.7 kW/cm2. The laser drawing was carried out in the polymer system poly-2,2′-p-oxydiphenylene-5,5′-bis-benzimidazole (OPBI), which consists of two phases: a solid polymer matrix with formic acid (HCOOH) dissolved in it. The formation of microstructures, including the stage of foaming, was carried out in three media: air, water and a supercritical carbon dioxide medium containing dissolved molecules of the silver precursor Ag(hfac)COD. The morphological features of foam-like track structures formed in the near-surface layer of the polymer films by laser “drawing” are considered. A model of processes is presented that explains the appearance of periodic structures. The key point of this model is that it considers the participation of the photoinduced mechanism of explosive boiling of formic acid molecules dissolved in the polymer matrix. Using Raman spectroscopy, spectra were obtained and interpreted, which relate to different stages in the formation of microstructures in OPBI films. The effects associated with the peculiarities of luminescent microstructures on the surfaces of glasses in close contact with polymer films during laser “painting” in the air have been studied.

The results of the experimental and theoretical studies of the behavior of the amorphous D,L-polylacide foam are reported. D,L-polylacide is preliminarily plasticized using sub- or supercritical carbon dioxide at a constant temperature of 313.3 K under various pressures in the range from 4 to 20 MPa; after plasticizing, it is foamed by quasi-isothermal depressurization with low depressurization rates (from 0.005 to 0.05 MPa/s). It is found that the transition from the expansion of the polylactide foam to its collapse occurs during depressurization when polylactide is plasticized under supercritical conditions (with the carbon dioxide pressure above 8 MPa). Using the equation of state first proposed by S. Ross for a thermodynamically equilibrated foam, the criterion for such a transition is established. It is shown that this phenomenon is caused by a substantial increase in the surface tension of the polymer when slowly reducing the carbon dioxide pressure.

Abstract—An apparatus for selective laser sintering of micron and submicron fraction powders is described. The apparatus allows studies with small volumes of polymer powders, as well as aqueous and alcoholic suspensions to refine the sintering process in order to achieve high spatial resolution (on the order of 10 μm). Thin (approximately 20 μm) layers of spherical microparticles of polymethylmethacrylate (PMMA) with an average diameter of 0.5 to 3 μm were formed. Optimization of the parameters of selective laser sintering and stepwise formation of single layers of PMMA allowed us to obtain 3D structures with a resolution of less than 100 μm.

Supercritical fluid encapsulation of doxycycline into aliphatic polyesters was used to fabricate bioresorbable antibacterial polylactoglycolide scaffolds. The distributions of doxycycline concentration on the surface and in the bulk of polymer structures were analyzed using high (≈1 μm) spatial resolution Raman spectroscopy. The release kinetics of doxycycline from these scaffolds into saline solution was studied. It is shown that, with the exception of the first 3 h, when about 15% of its total amount goes into the solution, the release of doxycycline occurs almost linearly. During the first day, the total yield of the antibiotic was about 22%. In 15 days (maximum observation time), the total amount of doxycycline released from polylactoglycolide scaffolds was about 70%. Thus, bioresorbable polymer scaffolds fabricated with supercritical carbon dioxide can be used for local sustained release of antibiotics, as well as for biologically active scaffolds for tissue engineering.

The use of surface-selective laser sintering is considered for creating and modifying the architecture of three-dimensional structures from biocompatible and bioresorbable polylactide materials. The approach allows to eliminate the thermal degradation of sintered materials by localizing heating processes on their surfaces. This is achieved via the selective absorption of mid-infrared laser radiation (1.9 μm) by a thin layer of water droplets deposited on the surfaces of polymer particles (polymer fibers) or the use of hygroscopic coatings that absorb the energy of laser radiation better than the polymer material.

The dynamics of polymer particle heating by laser irradiation during surface-selective laser sintering (SSLS) has been studied both experimentally and theoretically. Water aerosol wetting of the polymer particle surface was applied to increase the absorbance of thulium fiber laser radiation at 1.96 mu m. Theoretical modeling of the laser-induced thermal processes was performed in thermolabile polylactic-co-glycolic acid powder coated with a thin water layer. Temperature gradients on the surface and inside the sintered particle volume were evaluated and analyzed. It was shown that for certain optimized SSLS parameters an effective sintering process can be achieved by delicate melting of the particle surface only, without noticeable changes in the chemical and phase compositions of the internal domains.

A new approach for high-resolution three-dimensional printing using selective laser sintering is proposed. Novel ultrafine powder is synthesized and modified to face the requirements of the laser sintering process. The effect of the powder particle size and shape on the characteristics of the sintered structures is studied.

An apparatus is described that allows studying various physical and chemical processes in the atmosphere of supercritical carbon dioxide at pressures of up to 25 MPa and temperatures of up to 100°C. The apparatus is based on a compact modular cylindrical high-pressure reactor with a diameter of 90 mm and a height of 100 mm with an internal volume of 14 cm3. It is equipped with eight optical ports, a system for measuring and adjusting the pressure and temperature, as well as a system for letting in and gradually reducing the pressure of the test medium. In addition, the reactor is equipped with two video cameras with a resolution of 1920 × 1080 pixels, which allow video recording of processes occurring in the reactor volume, which is synchronized with the pressure and temperature data recording system. The efficiency of the described apparatus is demonstrated by studying the processes of plasticization and foaming of polymer materials in the medium of supercritical carbon dioxide.

Gallstones with a zonal morphological structure have been studied using X-ray microtomography, X-ray diffraction analysis, Raman spectroscopy, and elemental analysis. Concrements have been investigated in vitro in the dried state; phases of cholesterol, bilirubin, calcium carbonate, and sodium and potassium chlorides are found in their composition. The analysis is performed within the development of tomographic methods, which can be used in future for intravital diagnostics of cholesterol cholelithiasis. The possibility of determining the phase composition of heterogeneous gallstones, based on the analysis of linear-absorption-coefficient distributions derived from X-ray monochromatic microtomography data, is demonstrated. The results of the tomographic analysis are in agreement with the data obtained using conventional direct methods for determining the phase and elemental composition of the objects under study.

The study is directed to the development of the complex machining of hard transparent materials such as quartz, sapphire, and diamond using pulsed laser light (5 ns pulse duration, 532 nm wavelength, 1 kHz repetition rate). The deepening rate of the laser-induced backside etching of sapphire in a water solution of silver nitrate was studied as a function of liquid pressure in the range of 0.1-25 MPa. Its linear increase of about 1.5-2 times with pressure was demonstrated, which associated with the stronger microbubbles cavitation impact on hard material and chemical etching by sub- and super-critical water. The increase in the etching efficiency of sapphire at a higher pressure for this particular case can be generalized to other types of laser-induced backside wet etching and other materials.