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In this article , we report the synthesis of a series of multi-branched benzylidene ( BI ) ketone-based photo-initiators for two-photon polymerisation based 3D printing/additive manufacturing .
 BI, two-photon polymerisation, 3D, manufacturing
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:
 BI, two-photon polymerisation, 3D, manufacturing