Study on the radiological characteristics of metal infilled filaments for three-dimensional printing according to the infill rate and pattern

Abstract

Three-dimensional (3D) printing technology has been widely used to fabricate customized phantom for patients. High-density structures, such as bone, are not easy to reproduce with regular filaments and require high-density materials. In this study, we use polylactic acid+ (PLA+) filaments and five metal filaments (bronze, copper, aluminum, iron, and tungsten) containing metal powder to investigate variations in the Hounsfield unit (HU) values reflected in computed tomography images under filament and printing output conditions. Samples were produced to verify the element composition using each filament, and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses were performed. The variations of HU values according to the infill patterns were verified using PLA+, and six filaments were used to verify the variation in HU values according to the infill rate. SEM-EDS analysis shows that all filaments contain C and O elements in common and account for the largest proportion. In the case of metal filaments, additional elements were observed: Cu (1.77%) in bronze, Na (0.45%) and Al (4.48%) in aluminum, Ca (0.7%) and Fe (2.54%) in iron, and W (1.61%) in tungsten. Linearity was confirmed according to the infill rates using various infill patterns. The results showed high linearity of 0.99 or higher in the determination coefficient (R-squared; R-2) of most patterns. However, in the case of the full honeycomb (R-2 = 0.8825) and fast honeycomb (R-2 = 0.9606) patterns, HU values increased rapidly or gradually at a certain infill rate, indicating a relatively low determination coefficient. The measurement of the variation in HU value according to the type of filament and the degree of filling showed that the higher the degree of filling, regardless of the type of filament, the higher the HU value. For a 100% fill ratio, the average HU value of the cube output to each filament was measured differently at - 28.7, 526.3, 70.1, - 32.3, and 3061 HU for PLA+, bronze, copper, iron, and tungsten, respectively. This study will help express various HU values using 3D printing. Moreover, metal filaments will positively affect reproducing dense anatomical structures, such as bones, which have been difficult to express in previous studies.