Tuning the three-dimensional architecture of supercritical CO2 foamed PCL scaffolds by a novel mould patterning approach.

In tissue engineering, the use of supercritical CO2 foaming is a valuable and widespread choice to design and fabricate porous bioactive scaffolds for cells culture and new tissue formation in three dimensions. Nevertheless, the control of scaffold pores size, shape and spatial distribution with foaming technique remains, to date, a critical limiting step. To mimic the biomimetic structure of tissues like bone, blood vessels and nerve tissues, we developed a novel supercritical CO2-foaming approach for the preparation of dual-scale, dual-shape porous polymeric scaffolds with pre-defined arrays of micro-channels within a foamed porosity. The scaffolds were prepared by foaming the polymer inside polytetrafluoroethylene moulds having precisely designed arrays of pillars and obtained by computer-aided micromachining technique. Polycaprolactone was chosen as model polymer for scaffolds fabrication and the effect of mould patterning and scCO2 foaming conditions on scaffolds morphology, structural properties and biocompatibility was addressed and discussed. The results reported in this study demonstrated that the proposed approach enabled the preparation of polycaprolactone scaffolds with dual-scale, dual-shape porosity. In particular, by saturating the polymer with CO2 at 38 °C, 10 MPa and 1 h and by selecting 2 s as the venting time, scaffolds with ordered arrays of aligned channels, diameters ranging from 500 to 1000 µm, were obtained. Furthermore, the channels spatial distribution was controlled by defining mould patterning while the size of foamed pores was modulated by saturation and foaming temperatures and venting time control. The prepared scaffolds evidenced overall porosity up to 95%, with 100% interconnectivity and compression moduli in the 4 to 5 MPa range. Finally, preliminary in vitro cell culture tests evidenced that the scaffolds were biocompatible and that the micro-channels promoted and guided cells adhesion and colonization into the scaffolds core.

Reprint of: self-assembly of nanoparticles employing polymerization-induced phase separation.

Nanoparticles (NPs) may be homogeneously dispersed in the precursors of a polymer (reactive solvent) by an adequate selection of their stabilizing ligands. However, the dispersion can become metastable or unstable in the course of polymerization. If this happens, NP-rich domains can be segregated by a process called polymerization-induced phase separation (PIPS). This occurs mainly due to the decrease in the entropic contribution of the reactive solvent to the free energy of mixing (increase in its average size) and, for a reactive solvent generating a cross-linked polymer, the additional contribution of the elastic energy in the post-gel stage. The extent of PIPS will depend on the competition between phase separation and polymerization rates. It can be completely avoided, limited to a local scale or conveyed to generate different types of NPs' aggregates such as crystalline platelets, self-assembled structures with a hierarchical order and partitioning at the interface, and bidimensional patterns of NPs at the film surface. The use of a third component in the initial formulation such as a linear polymer or a block copolymer, provides the possibility of generating an internal template for the preferential location and self-assembly of phase-separated NPs. Some illustrative examples of morphologies generated by PIPS in solutions of NPs in reactive solvents, are analyzed in this feature article.

Self-assembly of nanoparticles employing polymerization-induced phase separation.

Nanoparticles (NPs) may be homogeneously dispersed in the precursors of a polymer (reactive solvent) by an adequate selection of their stabilizing ligands. However, the dispersion can become metastable or unstable in the course of polymerization. If this happens, NP-rich domains can be segregated by a process called polymerization-induced phase separation (PIPS). This occurs mainly due to the decrease in the entropic contribution of the reactive solvent to the free energy of mixing (increase in its average size) and, for a reactive solvent generating a cross-linked polymer, the additional contribution of the elastic energy in the post-gel stage. The extent of PIPS will depend on the competition between phase separation and polymerization rates. It can be completely avoided, limited to a local scale or conveyed to generate different types of NPs' aggregates such as crystalline platelets, self-assembled structures with a hierarchical order and partitioning at the interface, and bidimensional patterns of NPs at the film surface. The use of a third component in the initial formulation such as a linear polymer or a block copolymer, provides the possibility of generating an internal template for the preferential location and self-assembly of phase-separated NPs. Some illustrative examples of morphologies generated by PIPS in solutions of NPs in reactive solvents, are analyzed in this feature article.