Effects of solvent-particle interaction kinetics on microstructure formation during three-dimensional printing

Lactone-based absorbable polyesters, such as polylactide-co-glycolides, are commonly used for the construction of biomedical devices. Many such devices can be constructed by a novel manufacturing technology known as three dimensional printingTM (3DPTM), which fabricates complex structures by ink-jet liquid binder onto loose powder in a laminated fashion. The predominant 3DP binding mechanism for lactone based absorbable polyester powder is dissolution-reprecipitation. The objective of this study is to compare the relative time scales for particle dissolution and solvent evaporation during 3DP processing. An experimental setup was devised to determine the time scale for particle dissolution. This time scale was found to be particle size independent for small particles, but size dependent for larger particles. The time scale for chloroform evaporation from typical 3DP powder beds was determined to be on the same order as the particle dissolution time scale. Dissolution-evaporation (DE) plots were constructed to illustrate the relationship between evaporation time scale, dissolution time scale, particle size, printing conditions, and external mass transfer conditions. The DE plot provides a good estimate of the necessary printing conditions under which the evaporation time is sufficient for particle dissolution for a given particle dimension. Microstructural analysis of the printed structures demonstrated the importance of the relative time scales of particle dissolution and solvent evaporation. Practical implications of these findings in 3DP are described.