Adhesive Bonding and Structural Joining of Printed Photopolymers

A bonded joint on a printed photopolymer is usually described by a single number in megapascals, and that number is usually a property of the wrong thing. This review treats the joining of vat-photopolymerised components as a problem in which the adherend, not the adhesive, is most often the limiting element, and in which the adherend arrives at the bond line in a state that the printing workflow has determined and that almost nobody records. The controlling variables are the post-cure state, the oxygen-inhibited free surface, the wash-solvent history and the layer geometry — every one of which is set upstream of the joining operation and none of which appears in a conventional adhesive specification. The literature supports this framing convergently: across processes and laboratories, printed adherends tend to fail before the bond line does. It also fails to support the quantitative claims most often made from it. This review located no verified structural lap-shear study of a vat-photopolymer-to-vat-photopolymer adhesively bonded joint, no study connecting the oxygen-inhibited surface layer to joint strength, and no study connecting wash-solvent residue to joint strength, although both are known to change the substrate. The usable quantitative evidence is dental shear-bond-strength data whose test geometry makes it non-comparable with engineering lap-shear values. This review therefore separates what is established, what is bounded by analogy from other additive processes, and what must be generated locally, and specifies a joining qualification architecture built around determining the failure locus rather than reporting a strength.