Critical points for predicting 3D printable filaments behaviour

Abstract

Fractal dimension has been employed for the first time to provide key information about the behaviour of extruded filaments. High drug loaded filaments made of thermoplastic polyurethane and anhydrous theophylline (10–70% w/w of drug content) have been obtained by using a single screw extruder. Fractal analysis was carried out based on the measures of the perimeter of the filaments at different magnification levels, using the box-counting technique approach. The fractal dimension values showed a critical point at 37.8% w/w of drug, which agrees with the behaviour of the printability of the filaments by FDM. The drug percolation threshold derived from drug release results was also in agreement with this critical point. Thus, both approaches concur in the estimation of a critical point around 38% w/w of drug, where printability and dissolution behaviour dramatically change. Therefore, the Fractal Dimension analysis could be considered as a non-destructive, non-expensive and fast method for estimating a crucial parameter for FDM 3D printing as is printability of the filament.