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These minimal surfaces are sheet-based designs which are often self-supporting and tend to have zero average curvature at every point on the surface , which makes for a more even distribution of stresses within these structures .
 concept or principle: surfaces; engineering feature: designs; engineering feature: self-supporting; engineering feature: zero average curvature; concept or principle: surface; concept or principle: distribution
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:
 concept or principle: surfaces; engineering feature: designs; engineering feature: self-supporting; engineering feature: zero average curvature; concept or principle: surface; concept or principle: distribution