1071
In the Heaviside Projection was employed both on the density and the density gradient to obtain well-defined boundaries and constrain the perimeter length in undercuts and overhangs for 3D cases .
 machanical property: density; machanical property: density gradient; engineering feature: boundaries; engineering feature: undercuts; process parameter: overhangs; concept or principle: 3D
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:
 machanical property: density; machanical property: density gradient; engineering feature: boundaries; engineering feature: undercuts; process parameter: overhangs; concept or principle: 3D