Solvent-free 3D printing of silicone elastomers by digital light processing using an oligosiloxanyl substituted bis(acyl)phosphane oxide as photoinitiator

Silicone elastomers possess a wide range of advanced applications, particularly in biomedicine, soft robotics, and wearable electronics. Consequently, the fabrication of sophisticated 3D structures based on poly(dimethylsiloxane) (PDMS) formulations is essential to fully realize these applications. Light-based additive manufacturing methods such as digital light processing (DLP) offer the combination of favourable mechanical performance and high printing precision required for next-generation 3D-printed silicone elastomers. However, despite significant progress in this field, the development of a photoinitiating system compatible with PDMS formulations has been largely overlooked. In this work, we report a new photoinitiator, BAPO-SIL, and demonstrate its application in solvent-free 3D printing of silicone elastomers via DLP. BAPO-SIL exhibits excellent miscibility with a variety of PDMS polymer precursors such as TEGORad 2800 and novel norbornene derivatives, enabling straightforward resin formulation without the need for solvents or mechanical homogenization. Using BAPO-SIL, both commercially available PDMS acrylates and state-of-the-art thiol–norbornene PDMS resins were successfully 3D printed with high spatial resolution, showing good cytocompatibility by preliminary cell tests. Notably, the thiol–norbornene systems enabled the fabrication of ultrasoft silicone elastomers with a Young's modulus as low as 0.06 MPa and elongation at break up to 166%, highlighting the potential of BAPO-SIL for advanced silicone 3D printing applications.