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Implicit surface modelling uses single mathematical equations to freely introduce pore shapes such as triply periodic minimal surfaces , which is highly flexible in designing scaffolds .
 engineering feature: Implicit surface; concept or principle: mathematical equations; machanical property: pore; material: as; concept or principle: surfaces; engineering feature: scaffolds
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: Implicit surface; concept or principle: mathematical equations; machanical property: pore; material: as; concept or principle: surfaces; engineering feature: scaffolds