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The Importance of Porosity

Bone is a porous structure. It has a hierarchical structure that should be mimicked to ensure that the maximum regrowth can occur. Macropores are required to enable the complete infiltration of bodily substances such as cells, nutrients and metabolites. Although there is no specific size that can guarantee the optimal tissue response, macroporosity should be in the range of 200-500μm. Although macroporosity is required, it has a detrimental effect on the strength of the implant, resulting in structures that are unsuitable for the high loads placed upon structures used as scaffolds for structural augmentation. Micropores are much smaller, and are approximately 2-50μm in most cases. As such, cells can not infiltrate microporous structures, however they can adhere to the surface. Once attached, they proliferate and, in the case of bone cells, differentiate along osteoblastic lineages. From this, it is therefore suitable to state that porosity is an incredibly important parameter in producing structures that instigate regrowth.

Porous nature of bone

Scaffolds can be produced out of a number of materials using a range of techniques that can be broadly classified as conventional or rapid prototyping. Rapid prototyping techniques involve the design of a scaffold using CAD software and the associated production using CAM. Although such techniques can be used to generate highly controllable structures, the resolution of the machinery generally hinders the solution and microporosity is not obtainable. Conventional techniques on the other hand are less controllable but under the right conditions can yield structures with macroporosity, microporosity and even both.

Scaffolds

One of the most promising techniques if the Adaptive Foam Reticulation technique, a combination of two conventional techniques, the freeze casting and foam reticulation methods. This has been developed at the University of Warwick and the work of this PhD is to further the initial work that has been undertaken.