Light-based additive manufacturing of PolyHIPEs: controlling the surface porosity for 3D cell culture applications

Using stereolithography (vat photopolymerisation) to polymerise High Internal Phase Emulsions (PolyHIPEs) is apotent additive manufacturing route to produce materials with a hierarchical porosity. These multiscale porousmaterials have a microporosity (1–50 μm) dictated by emulsion templating and a macroporosity (100 μmup-wards) controlled by additive manufacturing. The interconnected, hierarchical porosity of these structures is par-ticularly desirable in the field of bone tissue engineering as it promotes tissue formation and allows efficient masstransport. However, due to the high light-scattering nature of the HIPEs, the achievable feature resolution is poorin comparison to other photocurable polymers, and they are prone to the formation of a closed porosity ‘skinlayer’ at the surface. This study focuses on different methods of both improving the resolution of structures fab-ricated from HIPEs via stereolithography and minimising skin formation. The inclusion of 2-(2H-Benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (commercially UV-234 or Tinuvin®234), a UV light-absorber, wasfound to significantly improve the achievable resolution of PolyHIPE structures fabricated via stereolithographywith no cytotoxic effe cts and reduce the skin formation. Furthermore, in direct comparison with a non-microporous scaffold of the same architecture, the inclusion of a microporosity significantly promoted the prolif-eration of MLO-A5 murine osteoblasts and permitted superior bone-matrix deposition.