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.

A numerical study on the effect of geometrical parameters and loading profile on the expansion of stent.

BACKGROUND: Stenting has been proposed as an effective treatment to restore blood flow in obstructed arteries by plaques. Although several modified designs for stents have been suggested, most designs have the risk of disturbing blood flow. OBJECTIVE: The main objective is to propose a stent design to attain a uniform lumen section after stent deployment. METHODS: Mechanical response of five different designs of J & J Palmaz-Schatz stent with the presence of plaque and artery are investigated; four stents have variable strut thickness of different magnitudes and the rest one is a uniform-strut-thickness stent. Nonlinear finite element is employed to simulate the expansion procedure of the intended designs using ABAQUS explicit. RESULTS: The stent design whose first cell thickness linearly increases by 35 percent, exhibits the best performance, that is it has the lowest recoiling and stress induced in the intima for a given lumen gain. It also enjoys the minimal discrepancy between the final at the distal and proximal ends. CONCLUSIONS: A uniform widened artery can be achieved by using the stent design with 35 percent increase in its first cell, which provides the possibility to prevent from disturbing blood flow and consequently post-operation complications.