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This paper proposes efficient generation strategies for constructing internal porous architectures by using triply periodic minimal surfaces ( TPMSs ) and external freeform shapes through T-spline surfaces .
 porous, triply periodic minimal surfaces, freeform, surfaces
Please list all entity words in the text that fit the category. Output format is "word1, 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:
 porous, triply periodic minimal surfaces, freeform, surfaces