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Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2–3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for the evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. Here, we present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Zphotoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the “feedstock” for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.

Biomineralization in organisms is strictly regulated and therefore chemical compositions as well as crystal structures of the minerals are species specific. During embryonic development sea urchin larvae produce a calcite endoskeleton (spicules) that contains about 5% magnesium. For sea urchins and other organisms, it is assumed that magnesium is important for the process of biomineralization and for the mechanical properties of the resulting biomineral. To study the influence of magnesium on skeletal growth and on biomineral structure and composition, sea urchin larvae spicules were chosen as an in vivotest system. For this purpose the Mg/Ca ratio was modified in the artificial seawater medium wherein sea urchin larvae were growing. It was shown that magnesium deficiency during larval development caused morphology defects of the larvae and of their calcite spicules. The magnesium distribution within the larvae skeleton was analyzed and found to be homogenous. An in vivoreduction of the magnesium content influenced the mechanical performance of larval spicules (Young′s modulus and hardness). Our investigations of larvae exposed to reduced magnesium conditions highlight the important role magnesium plays for sea urchin larvae development, biomineralization process and the resulting biomineral. The sea urchin larvae are presented as an ideal model to study different effects on larval development and morphology and especially on the biomineral properties.Biomineralization in organisms is strictly regulated, and therefore, chemical compositions as well as crystal structures of the minerals are species specific. During the embryonic development, sea urchin larvae produce a calcite endoskeleton (spicules) that contains about 5% of Mg. For sea urchins and other organisms, it is assumed that Mg is important for the process of biomineralization and for the mechanical properties of the resulting biomineral. To study the influence of Mg on skeletal growth and on biomineral structure and composition, sea urchin larvae spicules were chosen as an in vivo test system. For this purpose, the Mg/Ca ratio was modified in the artificial seawater medium wherein sea urchin larvae were growing. It was shown that Mg deficiency during larval development caused morphology defects of the larvae and of their calcite spicules. The Mg distribution within the larvae skeleton was analyzed and found to be homogenous. An in vivoreduction of the Mg content influenced the mechanical performance of larval spicules (Young’s modulus and hardness). The investigations of larvae exposed to reduced Mg conditions highlight the important role Mg plays for sea urchin larvae development, biomineralization process and the resulting biomineral. The sea urchin larvae are presented as an ideal model to study different effects on larval development and morphology, especially on the biomineral properties.

•In situhigh-speed thermal monitoring of melt-pool during laser powder bed fusion.•Probabilistic prediction of pore formation based on in situpyrometry monitoring.•Detection of conduction-to-keyhole transition using high-speed pyrometry.