Electrically Functional Photopolymer Resins for Vat Photopolymerization

Abstract

Problem. Additive manufacturing of electrically functional parts has progressed from filament-based conductive thermoplastics into vat photopolymerisation (VPP) systems capable of micron-scale resolution, enabling printed electronics, electrostatic-control fixtures, bioelectronics, embedded sensors, sacrificial conductor templates, RF/microwave dielectric components and 4D electro-thermo-responsive actuators. A recurrent interpretive limitation in the literature is the reporting of surface resistivity, volume conductivity and percolation thresholds as single numerical values decoupled from the cured-system configuration. We argue that this reporting convention is the principal cause of the limited cross-study transferability of conductive-AM data: a "conductive resin" is not a stable universal entity but a system-realised conductive structure, and the realised electrical performance of a printed part is a system-level outcome, set jointly by formulation, printer optics, exposure profile, geometry, post-cure protocol and storage history, rather than an intrinsic resin-only property. The SDCF is an author-proposed conceptual framework for organising factors that can contribute to differences between constituent, formulation, printed-part and deployed-system electrical performance. It does not by itself distinguish measurement uncertainty from causal material or process effects. Field fragmentation. The literature on electrically functional VPP photopolymers spans seven distinct conductivity-route chemistries, three operational regimes, an orthogonal dielectric direction, and a wide envelope of application classes from electrostatic fixtures to bioelectronics R&D. The cross-route consolidation needed for engineering-grade material selection is absent from the peer-reviewed body of work, and metrology heterogeneity across studies (different sample geometries, different post-cure histories, different ambient conditions) prevents direct comparison of reported electrical performance across publications. Contribution. This review proposes a unified field synthesis along two complementary axes: a taxonomy of seven electrical-function routes operating across three regimes — Regime A (static-dissipative, evaluated under an application-specific ESD control plan); Regime B (functional conductive, characterised using explicitly stated electrical quantities and methods); Regime C (author-proposed high-conductivity printed-conductor regime, characterised using bulk conductivity) — plus one orthogonal dielectric route (εᵣ > 5, tan δ < 0.05 at GHz frequencies), with two orthogonal design axes (solubility of the cured part, biological-evidence status); and a comparative manufacturing-space positioning of VPP against FDM, DIW, inkjet, aerosol-jet, LMM, Cold Fusion SLS and bulk metallic conductors. The review consolidates 57 numbered literature references and technical monographs (30 in the 2022–2026 window), 6 international standards and 18 publicly available industrial documentation sources. Bulk conductivity, volume resistivity, surface resistance and sheet resistance are distinct quantities. Values and regime boundaries are compared only when the measurement method, specimen thickness, geometry, electrode configuration and conditioning make the comparison technically valid. Framework. We formalise the system-level interpretation as the System-Dependent Conductivity Framework (SDCF) (§1.4, §3.9, Fig. 1, Fig. 7, Table A1), identifying the cure-state and ambient-state governing variables that translate the resin-level chemistry into the part-level realised electrical response, with quantitative anchors including crosslink density envelope 10⁻³–10⁻² mol/cm³, water-driven Fickian diffusion coefficients 10⁻⁸–10⁻⁶ cm²/s, Tg depressions of 5–30 °C at 60–90% RH, silver-nanowire percolation at approximately 5 wt% loading, silver-microparticle percolation at tens of wt%, and a six-stage time-dependent trajectory from as-printed state through long-term ageing to end-of-life. Insight. Peer-reviewed validation is mature in electronics housings and ESD-controlled fixtures, in printed electrodes for bioelectronics R&D (three independent academic anchors documenting the photopolymer-PEDOT:PSS route for DLP-printed conductive hydrogels and ECG/EMG bioelectrodes), in sacrificial PEDOT:PSS templates for multi-material microfluidic devices, in inkjet conductive supports, and in ceramic-loaded high-permittivity photopolymer composites for microwave applications. Industrial deployment runs ahead of peer-reviewed confirmation in 4D electro-thermo-responsive actuators and in photopolymer-printed antennas. Critical limitations include percolation-threshold irreproducibility, conductivity hysteresis and humidity-driven drift in PEDOT:PSS systems, electromigration and sulfur tarnishing of silver-based systems, and the distinction between product-specific material or specimen data that may contribute to a device-level biological evaluation and medical-device approval. Outlook. The principal open directions are standardisation of printed-electronics resistivity metrology, expansion of 4D conductive chemistries beyond single-anchor portfolios, soluble PEDOT:PSS variant development, dielectric photopolymer formulation at higher relative permittivity, and bioprinting integration of electrically functional photopolymers at full VPP resolution.