7994
Extrusion-based 3D printing of photo-curable hydrogel materials can be used for the generation of complex objects layer by layer without the need for molds .
 3D printing, photo-curable, hydrogel, be, layer by layer, molds
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:
 3D printing, photo-curable, hydrogel, be, layer by layer, molds