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 device s can be constructed by a novel manufacturing technology known as three dim ensional printing(TM) (3Dp(TM)), which fabricates complex structures by ink -jet liquid binder onto loose powder in a laminated fashion. The predominan t 3DP binding mechanism for lactone based absorbable polyester powder is di ssolution-reprecipitation. The objective of this study is to compare the re lative time scales for particle dissolution and solvent evaporation during 3DP processing. An experimental setup was devised to determine the time sca le for particle dissolution. This time scale was found to be particle size independent for small particles, but size dependent for larger particles. T he time scale for chloroform evaporation from typical 3DP powder beds was d etermined to be on the same order as the particle dissolution time scale. D issolution-evaporation (DE) plots were constructed to illustrate the relati onship between evaporation time scale, dissolution time scale, particle siz e, printing conditions, and external mass transfer conditions. The DE plot provides a good estimate of the necessary printing conditions under which t he evaporation time is sufficient for particle dissolution for a given part icle dimension. Microstructural analysis of the printed structures demonstr ated the importance of the relative time scales of particle dissolution and solvent evaporation. Practical implications of these findings in 3DP are d escribed.