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The external geometry design and manipulation of internal porosity distribution according to the actual application demands are the main challenges of scaffold generation ; moreover , computational efficiency is a key factor that should be considered .
 concept or principle: geometry; engineering feature: design; machanical property: porosity; concept or principle: distribution; engineering feature: scaffold; concept or principle: computational efficiency; material: be
Given options, please tell me the categories of all the listed entity words.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} 
 Entities: geometry, design, porosity, distribution, scaffold, computational efficiency, be 
Answer:
 concept or principle: geometry; engineering feature: design; machanical property: porosity; concept or principle: distribution; engineering feature: scaffold; concept or principle: computational efficiency; material: be