Polylactide/TiO₂nanocomposites with different contents of nanoscale TiO₂were prepared by melt blending with a vane extruder in this work.

Using supercritical carbon dioxide (scCO₂) as an alternative to conventional methods in the preparation of porous biodegradable polymer and polymer/nanocomposites for tissue engineering has attracted increasing interest in recent years due to the absence of using organic solvents and the ability to incorporate thermosensitive biologicals without loss of bioactivity. Additionally, scCO₂ can exert a high level of control over porosity and morphology of scaffolds by tuning the processing parameters. This paper describes the newly achievements on the preparation of porous polymer materials using scCO₂ foaming technology with focus on the porous biodegradable materials and its nanocomposites relevant to tissue engineering.

In this study, a typical immiscible system, a poly(lactic acid) (PLA)/polystyrene (PS) bioblend is used to investigate the effect of interface and phase structure on bubble nucleation and porous morphologies using supercritical carbon dioxide as a physical foaming agent. A unique microcellular skin-core structure with a porous core and surface, and a nonporous skin layer which is embedded in a solid PLA phase are observed. The involved possible mechanism of the interfacial nucleation and confined foaming behavior in multi-phase systems has been discussed. Because of the higher gas concentration and lower activation energy barrier, bubble nucleation preferentially occurs at the interface of the PS and PLA phases. Due to the constrained effect of the crystalline PLA phase, smaller space could be provided for the expansion of the PS phase during the foaming process, hence gas bubbles in the interior are restrained from further growth. The porous structures of the PS phases are similar when the blends have comparable phase morphology. The results indicated that the confinement effect on the foam behavior is not only related to the crystalline PLA phase but also the phase structure of the blend.