Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 5: Naturally occurring hybrids

Biological hybrids: key points Hybrids made by plants or animals Strong composites from very weak components – Wet protein and carbohydrates are very soft – calcium carbonate is also weak and soft Multiple phases, hierarchical structures

Hybrid Organic-Inorganic materials are common in nature: composites Nacre Argonite (CaCO 3 ) plates as inorganic with protein (polyamide) as organic Animals Plants phytolith Teeth, spines in echinderms Mussel shells, sponges, diatoms and corals are utilize hybrid organic-inorganic materials Organic phase is biopolymers Carbohydrates are the template and organic phase

What is a hierarchical structure? In materials, a structure with different structures at different length scales: like in tendons (above)

The Building Plan Fabrication Conditions in Living Organisms only few elements: C, H, O, N, P, S, Ca, Si, Mg mild pH ambient pressure and temperature Calcite Crystals Extracted from the Prismatic Layer of Pinna Nobilis Shells Marin et al., J. Biol. Chem., 2005, 40, 33895

The Building Plan Hierarchical Design – Morhpology Control on Several Levels Interaction of an Organic and an Inorganic Component Fabrication Conditions in Living Organisms only few elements: C, H, O, N, P, S, Ca, Si, Mg mild pH ambient pressure and temperature Incorporation of biopolymers  increased fracture resistence & aspartate residue in peptide bond chitin network Nudelman et al., Faraday Discuss. 2007, 136, 9

Colloidal silica in diatoms: Hierarchical structure Silica walls are build up from ca. 5nm particles to give ca. 40nm diameter particles that are organized within the frustule. pH ≈ 5

Silica (SiO 2 ) & protein radiolariadiatoms Proteins act as templates for building silica architectures

Bio-Hybrids based on CaCO 3 : Nacre Argonite (CaCO 3 ) plates as inorganic phase with protein (polyamide) as organic phase Mother-of-pearl Opalescence from light diffraction in nacre (argonite blocks height ≈ λ light) Fracture strength is 3000 times higher than its mineral constituent CaCO 3.

The hierarchical structure of nacre Barthelat F Phil. Trans. R. Soc. A 2007;365: argonite crystal structure Phase morphology Long range order: stacked crystals Growth rings (mesolayers) Macromolecular Inner surface of shell (mother or pearl) The shell itself

Lobster exoskelton CaCO 3 & Carbohydrate & protein

Teeth: Enamel, dentin, & cementum Apatite – hydrated CaPO 4 Protein– collagen & others

The layered, rod structure of hydroxyapatite (a calcium phopshate) in dental enamel. Very tough for a ceramic.

Hierarchical structure of alligator gar, a primitive fish, scales. Ganoine is mostly mineral, like enamel, with tougher bone beneath.

Enamel and collagen Regular Fish Scales

Fish scale puncture resistance fish scales are better than polycarbonate. note how they give, and then reload. This is just one scale.

200 MPa yield strength30 MPaM 0.5 toughness Apatite – hydrated CaPO 4 Protein– collagen Bones

The Building Plan Hierarchical Design – Morhpology Control on Several Levels Interaction of an Organic and an Inorganic Component structural optimization from the atomic to the macroscopic scale Fabrication Conditions in Living Organisms only few elements: C, H, O, N, P, S, Ca, Si, Mg mild pH ambient pressure and temperature & Bone Fratzl et al., Progr. Mat. Science, 2007 Peterlik et al., Nat. Mat., 2006 Gupta et al., PNAS, 2006

Echinoderm spine CaCO 3 Protein templating

Phytoliths Horsetail, banana leaves 2-3% silicon by weight SiO 2 silica

Silica in Sponges Templated by proteins hierarchical structures

Euplectella sp.  7 hierarchical levels Stress-deflection responses of synthetic silica rod and sponge spicule in flexuretesting. (Courtesy of M. Sarikaya and G. Mayer.)

conch shell Almost no protein 3 hierarchical levels of layers made from layers of calcite.

Chiton Teeth the tips of the teeth are hard magnetite (Fe 3 O 4 ) with a tough fibrous calcite interior

Metal in Spider Fangs carbohydrate fibers in a protein matrix with zinc and magnesium ions Politi, Y., Priewasser, M., Pippel, E., Zaslansky, P., Hartmann, J., Siegel, S., Li, C., Barth, F. G. and Fratzl, P. (2012), A Spider's Fang: How to Design an Injection Needle Using Chitin-Based Composite Material. Adv. Funct. Mater., 22: 2519–2528

Biomaterial: Toucan Beak (a) Toucan beak; (b) external shell made of keratin scales. Cellular materials: (a) synthetic aluminium foam; (b) foam found in the inside of toucan beak.(Courtesy of M. S. Schneider andK. S. Vecchio.)

Bio Hybrid Organic-Inorganic Materials Sophisticated, highly evolved hybrids -nominally weak, but bio-accessible minerals (eg. CaCO 3 ) -hydrophilic, water plasticized biopolymers (eg. protein) -Integrated at nano-length scales -Phase separation templating of hierarchical structures -All water based chemistry!! The ultimate green chemistry Optimized to give non-additive property (synergistic effects) Models for many research programs in hybrid materials