{
    "title": "Metallic Wood",
    "inventor_name": "James P. Pikul",
    "publication_year": 2019,
    "device_name": "Nickel Metallic Wood (Nickel Inverse Opal)",
    "goal": "Create a structural material with the strength of titanium but the density of water, enabling lightweight high-strength components.",
    "problem_addressed": "Conventional high-strength metals (e.g., titanium) are relatively heavy; existing lightweight materials lack sufficient mechanical strength for demanding applications.",
    "concept_summary": "A porous nickel cellular material fabricated by self-assembly of polystyrene spheres into an ordered lattice, electroplating nickel into the interstices, and then removing the polymer to leave an inverse-opal structure with nanoscale struts. The resulting \"metallic wood\" combines high strength (size-dependent strengthening of nanostructured struts) with low density.",
    "detailed_description": "The process starts with monodisperse polystyrene beads (~=260-930 nm) that self-assemble in water into a face-centered-cubic lattice as Slow evaporation orders the beads, forming a crystalline scaffold. Nickel is electrodeposited into the voids, filling the spaces between beads. The polymer is dissolved with tetrahydrofuran, leaving an open-cell nickel network (inverse opal). Strut diameters can be as small as ~10 nm, giving yield strengths up to 8 GPa (~=4x bulk nickel). The material's density is ~1 g cm^-^3 (~= water). Variations in bead size, plating thickness, and alloying (e.g., rhenium-nickel) allow tuning of mechanical properties. Samples up to 100 mm^2 have been fabricated; larger-scale production remains a challenge.",
    "category": "Materials Science & Ceramics",
    "principles": [
        "Size-dependent strengthening",
        "Inverse-opal self-assembly",
        "Electroplating infiltration"
    ],
    "scientific_domains": [
        "Materials Science",
        "Mechanical Engineering",
        "Nanotechnology"
    ],
    "mechanisms_of_action": [
        "Nanometer-scale struts increase yield strength",
        "Porosity reduces overall density while maintaining load-bearing pathways"
    ],
    "materials": [
        "Nickel (99.9 %)",
        "Polystyrene (PS) spheres",
        "Rhenium-nickel alloy (optional coating)",
        "Tetrahydrofuran (solvent for polymer removal)"
    ],
    "energy_sources": [],
    "inputs": [
        "Polystyrene beads",
        "Nickel plating solution",
        "Water (for bead suspension)",
        "Tetrahydrofuran"
    ],
    "outputs": [
        "Porous nickel sheet (metallic wood)",
        "Inverse-opal cellular structure"
    ],
    "claimed_performance": "Strength comparable to titanium (yield strength up to 8 GPa), density similar to water (~1 g cm^-^3), specific strength up to 230 MPa*cm^3/kg, and ability to fabricate sheets up to 100 mm^2.",
    "experimental_evidence": "Compression and nano-indentation tests on nanopillars show yield strength increasing from 3.8 GPa to 8.1 GPa as strut diameter decreases from 115 nm to 17 nm. Samples of metallic wood (~=1 cm^2) containing ~1 billion struts have been produced and mechanically characterized.",
    "replication_status": "Laboratory-scale fabrication demonstrated; no commercial scaling reported.",
    "keywords": [
        "metallic wood",
        "inverse opal",
        "nanoporous metal",
        "high strength lightweight material",
        "self-assembly",
        "electroplating"
    ],
    "related_technologies": [
        "Inverse-opal materials",
        "Nanostructured metallic foams",
        "Additive manufacturing of cellular metals"
    ],
    "controversy_level": "low",
    "confidence_score": 0.9,
    "practicability_score": 0.6,
    "fringe_score": 0.2,
    "evidence_strength": 0.7,
    "risk_score": 0.1,
    "trl_estimate": 4,
    "source_urls": [
        "https://www.sciencedaily.com/releases/2019/01/190128125314.htm",
        "https://www.nature.com/articles/s41598-018-36901-3"
    ],
    "organizations": [
        "University of Pennsylvania - School of Engineering and Applied Science",
        "University of Illinois at Urbana-Champaign",
        "University of Cambridge",
        "U.S. Department of Energy - Office of Science"
    ],
    "applications": [
        "Aircraft wing structures",
        "Prosthetic limbs",
        "Energy-storage scaffolds",
        "Lightweight structural panels"
    ],
    "limitations": [
        "Scaling the nanostructured fabrication to industrial sizes is difficult",
        "Requires controlled self-assembly and precise electrodeposition equipment",
        "Mechanical behavior of large-area components not yet fully characterized"
    ],
    "open_questions": [
        "How will the material behave under cyclic loading and impact?",
        "Can the pores be reliably filled with functional materials (e.g., batteries) at scale?",
        "What are the long-term corrosion and fatigue properties of the nickel inverse opal?"
    ],
    "red_flags": [],
    "evidence_quotes": [
        "\"We have built a sheet of nickel with nanoscale pores that make it as strong as titanium but four to five times lighter.\"",
        "\"The struts in the researchers' metallic wood are around 10 nanometers wide, or about 100 nickel atoms across.\"",
        "\"The material's strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X.\"",
        "\"We've made foils of this metallic wood that are on the order of a square centimeter, or about the size of a playing die side.\"",
        "\"The high strength of the metallic wood results from the size-dependent strengthening of the inverse opal struts, which have up to 4X the yield strength of bulk electrodeposited nickel.\""
    ]
}