Morphological changes in poly(ɛ-caprolactone) in dense carbon dioxide

Carbon Capture Utilization for Biopolymer Foam Manufacture: Thermal, Mechanical and Acoustic Performance of PCL/PHBV CO2 Foams

Biopolymer foams manufactured using CO₂ enables a novel intersection for economic, environmental, and ecological impact but limited CO₂ solubility remains a challenge. PHBV has low solubility in CO₂ while PCL has high CO₂ solubility. In this paper, PCL is used to blend into PBHV. Both unfoamed and foamed blends are examined. Foaming the binary blends at two depressurization stages with subcritical CO₂ as the blowing agent, produced open-cell and closed-cell foams with varying cellular architecture at different PHBV concentrations. Differential Scanning Calorimetry results showed that PHBV had some solubility in PCL and foams developed a PCL rich, PHBV rich and mixed phase. Scanning Electron Microscopy and pcynometry established cell size and density which reflected benefits of PCL presence. Acoustic performance showed limited benefits from foaming but mechanical performance of foams showed a significant impact from PHBV presence in PCL. Thermal performance reflected that foams were affected by the blend thermal conductivity, but the impact was significantly higher in the foams than in the unfoamed blends. The results provide a pathway to multifunctional performance in foams of high performance biopolymers such as PBHV through harnessing the CO₂ miscibility of PCL.

The role of solvent additive in polymer crystallinity during physical supercritical fluid deposition

The self-assembly of isotactic polypropylene as deposited from supercritical pentane/acetone solutions is studied using a combination of polarized optical microscopy (POM) and grazing incidence wide angle X-ray scattering (GIWAX).

Combining Breath Figures and Supercritical Fluids To Obtain Porous Polymer Scaffolds

Supercritical fluids technology is a clean methodology to foam polymeric materials. However, this technique provides only the formation of inner porosity, whereas the so-called skin layer is commonly observed at the polymer surface. This article describes a new method for the preparation of outer and inner porous poly(ε-caprolactone) (PCL) scaffolds by combination of supercritical CO2 (SCCO2) foaming and the breath figures technique. In the first step, experiments with a SCCO2 reactor were performed at 35-45 °C, 100-250 bar, and 1-20 min depressurization time. The effect of these parameters in the formation of inner porosity was investigated for an adequate optimization. In a late stage, to provide also surface porosity to the polymeric samples and remove the skin layer, the breath figures technique was employed. The evaluation of porosity was determined by scanning electronic microscopy, mercury porosimetry, and micro X-ray computerized tomography scanning processing the images obtained with the ImageJ software. The results of this study using these two complementary techniques showed the existence of interconnectivity between inner and outer porosity of the samples. Furthermore, thermal transitions and crystallinity of the PCL samples have been analyzed by differential scanning calorimetry. Finally, a preliminary biological evaluation of the resulting scaffolds with mouse endothelial cells (C166-GFP) was performed to assess their biocompatibility and cellular viability.

Understanding drug release from PCL/gelatin electrospun blends

Electrospinning is one of the efficient processes to fabricate polymeric fibrous scaffolds for several biomedical applications. Several studies have published to demonstrate drug release from electrospun scaffolds. Blends of natural and synthetic electrospun fibers provide excellent platform to combine mechanical and bioactive properties. Drug release from polymer blends is a complex process. Drug release from polymer can be dominated by one or more of following mechanisms: polymer erosion, relaxation, and degradation. In this study, electrospun polycaprolactone (PCL)–gelatin blends are investigated to understand release mechanism of Rhodamine B dye. Also, this article summarizes the effect of high-pressure carbon dioxide on drug loading and release from PCL–gelatin fibers. Results indicate that release media diffusion is a dominant mechanism for PCL–gelatin electrospun fibers. Thickness of electrospun mat becomes critical for blends with gelatin. As gelatin is highly soluble in water and has tendency of gelation, it affects diffusion of release media in and out of scaffold. This article is a key step forward in understanding release from electrospun blends.

Osteogenic poly(ε-caprolactone)/poloxamine homogeneous blends prepared by supercritical foaming

Homogeneous poly(ε-caprolactone) (PCL) and poloxamines (PLXs) porous blends were prepared using a supercritical carbon dioxide-assisted foaming/mixing (SFM) approach aiming to obtain cytocompatible implantable materials presenting tunable morphologies, bioerosion rates, bioactive molecules release and osteogenic features. Pure PCL, pure PLXs (T908 and T1107 varieties) and three distinct PCL:PLX 75:25, 50:50, 25:75% w/w blends, with and without the osteogenic and angiogenic bioactive molecule simvastatin were processed at constant pressure of 20 MPa and temperature of 40 °C or 43 °C, for T1107 and T908, respectively. Obtained porous blends were characterized applying a wide range of techniques and in vitro methods. Calorimetric analysis showed that hydrophilic T908 and T1107 PLXs are miscible with PCL for all tested compositions. Prepared PCL:PLX porous blends rapidly lost mass when immersed into phosphate buffer pH 7.4 due to PLXs dissolution and then went through slow and almost constant erosion rates for the subsequent weeks due to PCL slow hydrolytic degradation, which explains the rapid initial release of simvastatin and its subsequent sustained release for longer periods of time. PCL and PCL:PLX 75:25% w/w porous blends, containing or not simvastatin, showed a high cytocompatibility with SAOS-2 cells. In addition, prepared biomaterials promoted mesenchymal stem cells proliferation and their differentiation into osteoblasts. Overall, obtained results showed novel possibilities of addressing local treatment of small bone defects/fractures using highly porous PCL:PLX homogeneous blends.