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In metal additive manufacturing , microstructural inhomogeneities , like anisotropic mechanical strength and geometric limitations in directed energy deposition , electron beam melting , or selective laser sintering , have led to the exploration of alternative techniques in recent years .
 metal additive manufacturing, microstructural, anisotropic, strength, directed energy deposition, electron beam melting, selective laser sintering, led
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:
 metal additive manufacturing, microstructural, anisotropic, strength, directed energy deposition, electron beam melting, selective laser sintering, led