Poly (e-caprolactone)/SBA-15 composite biomaterials plasticized with greener additives

Abstract

There are several methods for producing foamed materials. These techniques use environmentally hazardous compounds, which contribute to the air pollution and lead to undesirable residues in the final polymeric foam, or high temperatures which can degrade thermosensitive components such as drugs, proteins or other bioactive substances. The main goal of this work was the development, processing and characterization of porous Poly (ε–caprolactone) (PCL)/Silica mesoporous SBA–15 type composite biomaterials by combining greener additives such as ionic liquids, glycofurol and isosorbide dimethyl ether with supercritical fluid process, a clean and environmentally friendly technology. The ionic liquids used were N, N, N–trimethylethanolammonium pentanoate and tetradecyl(trihexyl) phosphonium bistriflamide ([P6,6,6,14][NTf2]). Polymeric foams of pure Poly (ε–caprolactone) and composite biomaterials were prepared via supercritical fluid foaming process by pressure quench method using supercritical carbon dioxide (scCO2) as foaming agent, at constant operating conditions, namely pressure (20 MPa), temperature (40 °C) and soaking time (2 hours). The depressurization rate was 0.37 LCO2·min-1. This technique presented several advantages over the conventional techniques. There is no need the use of organic solvents, which can be harmful to the seeding cells, human and the environment. There is also no need additional step such as drying or other methods to remove the residual solvents that can degrade the thermolabile components. The effect of the various additives on the morphology, thermal and in the mechanical properties of the produced porous materials was assessed by Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA) and compression testing. Furthermore, cytotoxicity tests were performed using LDH assay using redox reactions in SAOS–2 human osteogenic sarcoma cells to assess the biocompatibility of the foams. The results from the cytotoxicity demonstrated that the produced foams present high biocompatibility to the cells. The results from the FTIR and SEM–EDS have confirmed the presence of the two ionic liquids and silica nanoparticles within the polymeric matrix which revealed to be well dispersed. The melting temperature slightly decreased with the addition of the additives. This effect was more substantial for Poly (ε–caprolactone)/Glycofurol and Poly (ε–caprolactone)/Isosorbide dimethyl ether composite, which decreased from 61.73 ± 0.35 °C to 55.37 ± 1.37 °C and 57.20 ± 0.69 °C, respectively. The pore volume increased from 0.65 ± 0.09 10-3 to 0.87 ± 0.24 10-3 cm3·g-1 with the incorporation of small amount of SBA–15 (10 wt. %) and to 4.87 ± 0.31 10-3 with the addition of 30 wt. % of SBA–15. The obtained results from the different techniques have demonstrated that the various additives significantly affected the morphology, the thermal and mechanical properties of the foams which confirmed their strong plasticization effect, especially Glycofurol and Isosorbide dimethyl ether. The supercritical carbon dioxide (scCO2) foaming process revealed to be a feasible technique to produce 3D porous composite accurately with real density ranging from 0.99 to 1.24 g·cm-3 by combining Poly(ε–caprolactone) with SBA–15 and four greener additives and supercritical carbon dioxide technology which present very interesting properties with potential applications in pharmaceutical and biomedical field.