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

Abstract

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.

Keywords: Aligned channels; Polycaprolactone; Porous scaffolds; Supercritical CO(2) foaming.