Biomedical implants should have low density for patient comfort and high porosity and surface area to facilitate vascularization and the ingrowth of new bone. Ideally, the implant will allow sufficiently easy fluid flow for cell nutrition and osteoblast multiplication as well as migration for cellular colonization of the implant to become uniform. The pores contained within the foam's cellular matrix mimic the extracellular matrix of bone, allowing the body to fixate with the implant. The porosity of the implant also promotes apposition and facilitates vascularization−as cells are able to attach, reproduce and form basic functions. It has been shown that a macropore size of 200–500 µm is preferred for ingrowths of new bone tissues and transportation of body fluids. The lower bound is controlled by the size of cells (~20 µm), and the upper bound is related to the specific surface area through the availability of binding sites. Finer pores further help in tissue growth and biofluid movement. Anisotropic, elongated pores (such as those attainable via the freeze-casting technique) may be beneficial in bone implants in that they can further mimic the structure of bone.
The porous surface geometry of the foam promotes bone in-growth, provides anchorage for fixation, and ensures stresses are transferred from the implant to the bone. Surface roughness in the pore can enhance bone in-growth, and coarser cell size facilitates faster tissue growth.
To optimize the implants functionality and ability to successfully fuse with bone, it may be necessary to manipulate the materials manufacturing methods in order to modify the foam's pore structure. Changes in pore structure can directly influence implant strength as well as other key properties.