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6 Challenges and future directions Additive manufacturing provides unprecedented opportunities for producing customized medical implants as this technology can fabricate structures of complex external shapes and intricate internal architectures .
 manufacturing process: Additive manufacturing; application: medical implants; material: as; concept or principle: technology; manufacturing process: fabricate; machanical property: internal architectures
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:
 manufacturing process: Additive manufacturing; application: medical implants; material: as; concept or principle: technology; manufacturing process: fabricate; machanical property: internal architectures