Modeling, design and tailoring of a tough, strong and stiff multilayered bone graft material.

Damage tolerance, stiffness, and strength are critical mechanical properties that are difficult to achieve concurrently in synthetic monolithic materials. This limits the range of certain applications, including in bone graft materials where bone-like mechanical reliance is desired. For example, calcium sulfate (CS) is a biologically compatible ceramic that possesses several properties of an ideal bone graft material, but its applications in medicine is limited by its brittleness. Brittleness may be alleviated by the addition of stronger and more ductile reinforcements, with the best mechanical improvements obtained when the layered architecture and the interfaces for these reinforcements are tailored. Here we propose a systematic modeling and design approach to tailor the architecture and properties of a multilayered bone graft material composed of a brittle ceramic and a more ductile material such as metals. More specifically, the volume fraction, moduli, number of layers, and the toughness of the interfaces between the different phases are tailored to maximize overall stiffness, strength, and energy absorption capacity. Our model predicts that when the stiffness of the reinforcement is higher (lower) than the ceramic, the beams with lower (higher) number of layers and higher (lower) volume fraction of metal are stronger. However, while the higher number of layers is always desired in terms of energy dissipation, the effects of other variables is more complex to understand and should thus be studied in conjunction with each other.