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The samples were prepared by a low-cost open-source FFF 3D printer , and full three-dimensional ( 3D ) geometrical characterizations were performed on them using X-ray micro computed tomography ( micro-CT ) .
 concept or principle: samples; concept or principle: open-source; machine or equipment: FFF 3D printer; concept or principle: three-dimensional; concept or principle: 3D; process characterization: X-ray micro computed tomography; process characterization: micro-CT
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: samples, open-source, FFF 3D printer, three-dimensional, 3D, X-ray micro computed tomography, micro-CT 
Answer:
 concept or principle: samples; concept or principle: open-source; machine or equipment: FFF 3D printer; concept or principle: three-dimensional; concept or principle: 3D; process characterization: X-ray micro computed tomography; process characterization: micro-CT