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 Animals Organic phase is biopolymers Nacre Plants phytolith Argonite (CaCO3) plates as inorganic with protein (polyamide) as organic Teeth, spines in echinderms Mussel shells, sponges, diatoms and corals are utilize hybrid organic-inorganic materials Carbohydrates are the template and organic phase

Silica (SiO2) & protein radiolaria diatoms Proteins act as templates for building silica architectures

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

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

More Bio-Hybrids based on CaCO3: Nacre Argonite (CaCO3) plates as inorganic phase with protein (polyamide) as organic phase Fracture strength is 3000 times higher than its mineral constituent CaCO3. Mother-of-pearl Opalescence from light diffraction in nacre (argonite blocks height ≈ λ light)

The hierarchical structure of nacre Macromolecular Growth rings (mesolayers) Phase morphology The shell itself Inner surface of shell (mother or pearl) Long range order: stacked crystals argonite crystal structure Barthelat F Phil. Trans. R. Soc. A 2007;365:2907-2919

Lobster exoskelton CaCO3 & Carbohydrate & protein

Teeth: Enamel, dentin, and cementum Apatite – hydrated CaPO4 Protein– collagen & others

Bones Apatite – hydrated CaPO4 Protein– collagen 200 MPa yield strength 30 MPaM0.5 toughness

Echinoderm spine CaCO3 Protein templating

Phytoliths SiO2 silica 2-3% silicon by weight Horsetail, banana leaves

Silica in Sponges hierarchical structures Templated by proteins

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

Bio Hybrid Organic-Inorganic Materials Sophisticated, highly evolved hybrids -nominally weak, but bio-accessible minerals (eg. CaCO3) -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