Effect of Gray Scale Binder Levels on Additive Manufacturing of Porous Scaffolds with Heterogeneous Properties

Abstract

An additive manufacturing platform was developed for fabricating constructs with heterogeneous properties. The liquid binder amount was investigated in calcium polyphosphate bone substitutes. Two part categories were produced with 150 and 190 μm layer thickness and 70, 80, 90, 100, and 90/70% gray scale. It was shown that the gray scale level had an effect on samples with 150 μm layer thickness where porosity ranged between 43 ± 1% and 49 ± 2% and the compressive strength varied between 4.8 ± 1.3 MPa and 15.5 ± 1.9 MPa. The results suggest that the binder gray scale level can be used to locally predict porous properties.

Effect of glycerol concentrations on the mechanical properties of additive manufactured porous calcium polyphosphate structures for bone substitute applications

“…Shrinkage analysis of samples before and after sintering did not show any significant difference among the three batches of samples analyzed, and was comparable to shrinkage reported previously for CPP using commercially available binders . Furthermore, according to Figure , in analyzing the SEM results, the shape and size of the sinter necks formed between particles during sintering were similar for all specimens.…”

“…After printing, the green samples were collected from the machine and cleaned to remove the excess powder in preparation for sintering. The heat treatment protocol follows three main steps as previously reported . In first step, liquid binder burns off by air‐annealing the samples at 400°C for 1 h. Next, by increasing the temperature to 630°C and holding for 1 h, the annealing process is initiated.…”

“…Archimedes principle (ASTM C373 Standard) was applied similarly to previous studies to determine the bulk and apparent porosity of parts before and after sintering by selecting a population of samples ( n = 10) from each printed batch. In the first step, the dry mass of each specimen was measured using a precision microscale balance (APX‐203; Denver Instrument, Bohemia, NY) to determine the dry weight ( W dry ).…”

“… where P f represents the failure probability of samples by ranking their compression strength in the ascending order, is the central value representing the Weibull characteristic, and m is the Weibull modulus. This analysis was also performed on CPP specimens in previous studies and will be used as a basis for comparison to this study.…”

“…After the AM process, a postprocessing depowdering step is necessary to remove the excess powder around the part or within the designed cavities . For ceramic materials and metallic alloys, this step is typically followed by a heat treatment to thermally disintegrate the binder and to create sinter necks between the main powder constituents . During the sintering process, the liquid and/or solid binders are typically burned off …”