Poly-l-lactic acid: Pellets to fiber to fused filament fabricated scaffolds, and scaffold weight loss study

Poly-l-lactic acid (PLLA) is a bioresorbable polymer used in a variety of biomedical applications. Many 3D printers employ the fused filament fabrication (FFF) approach with the ubiquitous low-cost poly-lactic acid (PLA) fiber. However, use of the FFF approach to fabricate scaffolds with medical grade PLLA polymer remains largely unexplored. In this study, high molecular weight PL-32 pellets were extruded into ∼1.7 mm diameter PLLA fiber. Melt rheometric data of the PLLA polymer was analyzed and demonstrated pseudo-plastic behavior with a flow index of n = 0.465 (<1). Differential scanning calorimetry (DSC) was conducted using samples from the extruded fiber to obtain thermal properties. DSC of the 3D printed struts was also analyzed to assess changes in thermal properties due to FFF. The DSC and rheometric analysis results were subsequently used to define appropriate FFF process parameters. Constant porosity scaffolds were FFF 3D printed with 4 distinct laydown patterns; 0/90° rectilinear (control), 45/135° rectilinear, Archimedean chords, and honeycomb using the in-house developed custom multi-modality 3D bioprinter (CMMB). The effect of laydown pattern on scaffold bulk erosion (weight loss) was studied by immersion in phosphate-buffered saline (PBS) over a 6-month period and measured monthly. A repeated measures analysis of variance (ANOVA) was performed to identify statistically significant differences between mean percent weight loss of the four laydown patterns at each time point (1-6 months). The resulting data follows distinct temporal trends, but no statistically significant differences between means at individual time points were found. Cross-sectional scanning electron microscope (SEM) images of the 6-month degraded scaffolds showed noticeable structural deterioration. The study demonstrates successful processing of PLLA fiber from PL-32 pellets and FFF-based 3D printing of bioresorbable scaffolds with pre-defined laydown patterns using medical grade PLLA polymer which could prove beneficial in biomedical applications.