The notion of mimicking natural structures in the synthesis of new structural materials has generated enormous interest but has yielded few practical advances. Natural composites achieve strength and toughness through complex hierarchical designs extremely difficult to replicate synthetically. Here we emulate Nature's toughening mechanisms through the combination of two ordinary compounds, aluminum oxide and polymethylmethacrylate, into ice-templated structures whose toughness can be over 300 times (in energy terms) that of their constituents. The final product is a bulk hybrid ceramic material whose high yield strength and fracture toughness (~200 MPa and ~30 MPa√m) provide specific properties comparable to aluminum alloys. These model materials can be used to identify the key microstructural features that should guide the synthesis of bio-inspired ceramic-based composites with unique strength and toughness.With the quest for more efficient energy-related technologies, there is an imperative to develop lightweight, high-performance structural materials that possess both exceptional strength and toughness. Unfortunately, these two properties tend to be mutually exclusive and the attainment of optimal mechanical performance is invariably a compromise often achieved through the empirical design of microstructures. Nature has long developed the ability to combine brittle minerals and organic molecules into hybrid composites with exceptional fracture resistance and structural capabilities (1-3); indeed, many natural materials like bone, wood and nacre (abalone shell) have highly sophisticated structures with complex hierarchical designs whose properties are far in excess what could be expected from a simple mixture of their components (2,4). Biological mineralized composites, in particular bone, dentin and nacre (5-7), can generate fracture toughness (i.e., resistance to the initiation and growth of a crack) primarily by extrinsic toughening mechanisms (8) that "shield" any crack from the applied loads. These mechanisms, which are quite different to those that toughen metals for

The freezing of concentrated colloidal suspensions is a complex physical process involving a large number of parameters. These parameters provide unique tools to manipulate the architecture of freeze-cast materials at multiple length scales in a single processing step. However, we are still far from developing predictive models to describe the growth of ice crystals in concentrated particle slurries. In order to exert reliable control over the microstructural formation of freeze-cast materials, it is necessary to reach a deeper understanding of the basic relationships between the experimental conditions and the microstructure of the growing solid. In this work, we explore the role of several processing variables (e.g., composition of the suspension, freezing rate, and patterning of the freezing surface) that could affect the formulation strategies for the architectural manipulation of freeze-cast materials. We also demonstrate, using freeze-cast lamellar structures, how reducing the lamellar thickness by less than half increases compressive strength by more than one order of magnitude.

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