Vat photopolymerization additive manufacturing: A critical review of materials, processes, applications, and sustainability

Vat photopolymerization (VPP) has advanced from a laser-scanned prototyping into a multi-material additive manufacturing platform whose chemistry, process variants, application reach warrant critical appraisal. This review synthesizes 355 peer-reviewed articles indexed in Scopus between 2018 and 2026, retrieved through a structured query within article title, abstract, and keyword fields and filtered for English-language journal articles. A reproducible search strategy, a validated thematic classification protocol (inter-rater Cohen’s κ = 0.87 on a 20% double-coded subsample), and uncertainty intervals for every reported corpus share accompany the synthesis. The corpus is dissected across five analytical layers: photopolymer chemistry (initiators, monomers, oligomers, bio-derived feedstocks, fillers, and high-solid slurries); process variants spanning stereolithography, digital light processing, masked liquid-crystal-display printing, continuous liquid interface production, two-photon polymerization, and emerging volumetric and tomographic routes; ceramic VPP from slurry rheology through debinding and sintering of alumina, zirconia, bioactive ceramics, and polymer-derived SiC/SiOC; biomedical translation across bone, dental, drug delivery, hydrogel, and device subdomains; and the functional, smart, and sustainable frontiers. Two domains receive dedicated depth: biocompatibility-driven formulation design, covering cytocompatible photoinitiators, monomers and additives for biomedical VPP, and light-based 3D bioprinting of cell-laden hydrogels, analysed as a distinct biomedical frontier. Each process variant is discussed through governing parameters rather than publication chronology, and each application section closes with quantitative critical comparison. Quantitative trends show biomedical use, ceramic structural parts, and functional composites collectively account for more than half of recent output, whereas life-cycle assessment, fracture mechanics, and closed-loop recycling remain conspicuously underdeveloped. Twelve research gaps and ten actionable future directions are articulated, prioritized by technological maturity, evidence base, industrial relevance and feasibility, each paired with measurable targets, supported by fifteen schematic figures and comparative tables. The review positions VPP as a chemistry-led, process-flexible technology whose next decade will be defined by sustainability accounting, multi-material control, and clinically qualified translation.