Screening of the Supercritical Impregnation of Olea europaea Leaves Extract into Filaments of Thermoplastic Polyurethane (TPU) and Polylactic Acid (PLA) Intended for Biomedical Applications

Abstract

The leaves of Olea europaea as agricultural waste represent a convenient source of antioxidants. In combination with supercritical CO2 (scCO2), assisted impregnation is an interesting strategy for the preparation of biomedical devices with specific bioactivity. For this purpose, 3D-printable filaments of thermoplastic polyurethane (TPU) and polylactic acid (PLA) were employed for the supercritical impregnation of ethanolic olive leaves extract (OLE) for biomedical application. The extraction of OLE was performed using pressurized liquids. The effect of pressure (100–400 bar), temperature (35–55 °C), and the polymer type on the OLE impregnation and the swelling degree were studied including a morphological analysis and the measurement of the final antioxidant activity. All the studied variables as well as their interactions showed significant effects on the OLE loading. Higher temperatures favored the OLE loading while the pressure presented opposite effects at values higher than 250 bar. Thus, the highest OLE loadings were achieved at 250 bar and 55 °C for both polymers. However, TPU showed c.a. 4 times higher OLE loading and antioxidant activity in comparison with PLA at the optimal conditions. To the best of our knowledge, this is the first report using TPU for the supercritical impregnation of a natural extract with bioactivity.

Green Processing of Neat Poly(lactic acid) Using Carbon Dioxide under Elevated Pressure for Preparation of Advanced Materials: A Review (2012–2022)

“…Kuska et al [ 15 ] reported an increase in thymol loading into PLA beads from 11.0 to 19.8% at 20 MPa and 120 °C by prolongation of the process from 2 to 24 h. This BC acted as a molecular lubricant, which resulted in the increased free volume of the PLA matrix and consequently in the higher sorption of a supercritical solution. The prolonged exposure of PLA to sc-CO 2 with thymol led to a 40–90% greater swelling extent in comparison to the first 2 h. A similar result was reported for the SSI of olive leaves extract into PLA filaments, where the prolongation in soaking time from 0.5 to 1 h increased both the swelling and loading [ 125 ]. However, an increase in the soaking time can also lead to a decrease in the loading of BC during the SSI process.…”

“…This process requires good solubility of the substance in question in sc-CO 2 , which facilitates its mass transport within the polymeric matrix [ 18 ]. If the solubility of a BC in sc-CO 2 is low for the PLA impregnation process, it could be improved by the addition of a polar co-solvent such as ethanol [ 124 , 125 ]. After contact between a polymeric material and a BC for a certain soaking time, sc-CO 2 can be completely removed from the obtained material by a pressure decrease, while BC will remain within the polymer matrix due to precipitation or chemical bonding [ 86 , 126 ].…”

“…Usually, an increase in pressure increases BC loading, while an increase in temperature decreases BC loading [ 75 , 134 ]. However, it was also reported that BC loading into PLA can be increased both with pressure and temperature [ 20 , 125 , 129 , 135 , 136 ]. Considering that the pressure and temperature determine CO 2 density and its solvation power, this result can be obtained when the crossover pressure for BC dissolution in sc-CO 2 is reached/overcome [ 136 ].…”

“…Usually, an increase in soaking time increases the BC loading into the PLA matrix [ 15 , 75 , 125 , 139 ]. Kuska et al [ 15 ] reported an increase in thymol loading into PLA beads from 11.0 to 19.8% at 20 MPa and 120 °C by prolongation of the process from 2 to 24 h. This BC acted as a molecular lubricant, which resulted in the increased free volume of the PLA matrix and consequently in the higher sorption of a supercritical solution.…”

“…This local delivery of drugs can limit drug side effects, provide bioactivity at site-specific places, and increase patient adherence [ 20 ]. Three-dimensional-printed filaments of PLA were impregnated with ethanolic olive leaves extracted for biomedical application [ 125 ]. These filaments demonstrated a 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition of 6–15% for the antioxidant loading of 0.2–0.5 mg/g, which can be used for a decrease in free radicals that induce oxidative damage in biomolecules (e.g., lipids and proteins).…”