Water‐in‐oil emulsion templating of isocyanates: end‐capping, foaming, porous structures and cell growth

Abstract PolyHIPEs are porous polymer monoliths synthesized within high internal phase emulsions (HIPEs) with >74% dispersed phase. Biodegradable polyester‐based poly(urethane urea) (PUU) monoliths have been synthesized within water‐in‐oil emulsions via simultaneous diisocyanate–polyol urethane reactions (predominant) and diisocyanate–water urea reactions (CO 2 byproduct) and then used for cell culture and soft tissue engineering. Here, in contrast, an innovative sequential reaction route was used. The polycaprolactone and polylactide polyols were end‐capped with diisocyanates, generating urethane groups, prior to emulsion formation. The novel monolith‐forming reaction used here was the isocyanate–water urea reaction. Different diisocyanates, from relatively flexible to relatively stiff, highlighted the effects of diisocyanate stiffness on macromolecular stiffness, crystallinity and modulus. Similarly, different polyesters highlighted the effects of polyester stiffness. In addition, the novel isocyanate–water monolith formation reaction was investigated using a lysine‐derived diisocyanate. The hierarchical porosity of the resulting CO 2 ‐foamed polyHIPEs contained millimeter‐scale bubbles and micrometer‐scale emulsion‐templated porous structures. The crystalline polycaprolactone‐based PUUs exhibited melting points between 50 and 80 °C, reflecting the unique macromolecular uniformity generated by the sequential urethane–urea reactions compared to the simultaneous urethane–urea reactions that produced amorphous PUUs. Cell growth within the resulting elastomeric polyHIPEs demonstrated potential for soft tissue engineering, with mouse skeletal muscle cells adhering, spreading, proliferating, organizing and filling the entire space. © 2025 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.