In situ additive manufacturing of embedded multifunctional laser-induced graphene in PEEK.

While additive manufacturing is widely recognized for enabling geometric complexity, its transformative potential lies in direct fabrication of functional devices with integrated sensing, actuation, and electronic capabilities. Although fused filament fabrication (FFF) is one of the most widely used additive manufacturing technologies, it remains largely limited to producing structural components. Direct laser scribing (DLS) on polyether ether ketone (PEEK) to produce laser-induced graphene (LIG) offers a promising route to overcome this limitation. PEEK is a high-performance, carbon-rich precursor for laser-induced graphitization, while LIG provides direct-written conductivity, piezoresistivity, and electrothermal functionality. In this study, we present an integrated FFF-DLS platform with a self-developed G-code post-processor that enables in situ, layer-by-layer alternating PEEK deposition and LIG graphitization within a single manufacturing process, providing an automated route to fabricating multifunctional PEEK devices with spatially registered, programmable LIG networks. Building on this platform, a series of fabrication characterizations were conducted. Using the optimized fabrication parameters, we further demonstrated the versatility of the platform in directly fabricating functional devices for multiple applications, including Joule heating, temperature sensing, and strain sensing, used in aerospace and biomedical areas.