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3 Topological design of porous metallic structures for orthopaedic implants 3.1 Porous metallic implants and topology optimization techniques As mentioned previously , bone is a 3D inhomogeneous structure with elaborate features from macro-to nano-scales .
 engineering feature: Topological design; engineering feature: porous metallic structures; application: orthopaedic implants; application: Porous metallic implants; engineering feature: topology optimization; material: As; biomedical: bone; engineering feature: 3D inhomogeneous structure; engineering feature: nano-scales
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 engineering feature: Topological design; engineering feature: porous metallic structures; application: orthopaedic implants; application: Porous metallic implants; engineering feature: topology optimization; material: As; biomedical: bone; engineering feature: 3D inhomogeneous structure; engineering feature: nano-scales