Application-Driven Analysis of MEX Parameters for Deformation Control in Annealed HTPLA Patient-Specific Instruments

Computer-Aided Design (CAD) and Additive Manufacturing (AM), particularly Material Extrusion (MEX) with PLA, are increasingly used in medicine for cost-effective production of sterilizable Patient-Specific Instruments (PSIs). However, dimensional stability remains challenging when large geometries undergo post-processing such as annealing prior to sterilization. This study investigates the influence of selected MEX parameters on deformation in a clinically relevant large-scale PSI. A replicated 24 factorial design was used to evaluate the effect of raft thickness, infill orientation, first-layer pattern, and cooling fan speed through overall 3D and cross-sectional deformation. Infill orientation affected all deformation responses, while fan speed mainly influenced overall 3D and longitudinal deformation. Raft thickness affected the cross-section parallel to the build plane. Interactions involving fan speed were also significant for the overall 3D response. A 25% fan speed, 90° infill orientation, and 6-layer raft were associated with the lowest predicted overall deformation. These findings demonstrate that dimensional stability in large MEX-printed High-Temperature Polylactic Acid (HTPLA) PSIs depends on both individual process parameters and their interactions, with local deformation behaviour differing from the overall response. The results provide a basis for controlling deformation in large PSIs and support further investigations incorporating additional process levels, different PSIs geometries, and sterilization effects.