Poly(e-caprolactone) is used for biomedical applications due to its biocompatibility and biodegradability. Its processing with supercritical carbon dioxide represents a sustainable alternative to the classical methods involving toxic and environmentally hazardous organic solvents. In the presentwork, the behavior of poly(e-caprolactone) in the presence of supercritical CO2 has been studied. The influence of CO2 on the melting point and crystallinity content of the polymer was analyzed, the solubility and diffusivity of gas into poly(e-caprolactone) was measured, and the experimental data were correlated using Sanchez-Lacombe equation of state and PC SAFT model. Supercritical CO2 was then used for foaming poly(e-caprolactone) to obtain tissue engineering scaffolds, and the connection between process parameters (temperature, pressure), gas solubility in the polymer, and foam morphology was studied.
The presented research was oriented towards the preparation of dry biodegradable alginate aerogels with multi-membranes using a multi-step sol-gel process with potential applications as carriers during oral drug delivery. First alginate spherical hydrogels were formed in CaCl2 or BaCl2 solutions by ionic cross-linking. These cores were further immersed into alginate sodium solution, filtered through a sieve, and dropped into the salt solution again. Multi-membrane hydrogels were obtained by repeating the above process. They were further converted into aerogels by supercritical drying. The effect of the number of membranes was investigated regarding the loading and release of the model drugs nicotinic acid and theophylline. Moreover, the efficiencies of Ba(2+) and Ca(2+) metal ions for forming tridimensional networks that retain and extend drug release were also investigated. Nicotinicacid release was prolonged by adding membranes around the core and using Ca(2+) for cross-linking. However, retarded theophylline release was only obtained by using Ba(2+) for cross-linking. Namely, by increasing the number of membranes and BaCl2 concentration drug release became linear versus time in all studied cases. In the case of nicotinic acid loading increased by adding membranes around the core, however, for theophylline the opposite results were obtained due to the different nature of the model drugs.
The aim of this work was to investigate the properties of polyethylenes (PE) of various densities (low-density and high-density) under pressure of CO2 and propane. The phase equilibria of PE of different density in presence of CO2 and in presence of propane in dependence of pressure and temperature were investigated. The phase transitions of PE at atmospheric pressure were determined by differential scanning calorimetry (DSC). Furthermore, phase transitions of polymers under pressure of gases were measured by using an optical high pressure cell. Measurements of phase transition were performed in range of pressure of 1–90 MPa. The results show that melting points of LDPE decreased in presence of CO2 and in presence of propane. For high-density polyethylene (HDPE) the melting point decrease was observed only in presence of propane, while in presence of CO2 melting point increases with increasing pressure. The melting points of LDPE and HDPE decrease in average for 10–20 K in presence of propane, while in presence of CO2 the melting point decrease for both LDPE was lower (5–10 K). Solubility and diffusivity of supercritical CO2 in two low-density polyethylenes (LDPE) and in high-density polyethylene (HDPE) were measured at temperature 373 K and pressures up to 30 MPa using a magnetic suspension balance (MSB). The solubility data were used for estimating the binary diffusion coefficients. The solubilities increased with increasing density. The diffusion coefficient shows strong CO2 density and CO2 solubility dependence. Diffusion coefficient starts to decrease with increasing density and solubility of CO2.