2.5. Three dimensional printing

In a second step, before final 3D printing, a stl-mesh processing (Fig. 3) was performed to ensure a trouble-free and accurate 3D model for printing.

Workflow of the stl-mesh processing with MeshLab (v.1.3.2_64bit) and Open flipper (v. 2.1, http://www.openflipper.org/).

For printing the STL data we used an Ultimaker 2.0 (Ultimaker, Netherlands). The printer works with Fused Filament Fabrication (FFF) print technology and melts plastic and deposits it on a glass plate in an additive process. Speed range from 30 to 300 mm per second, enabling fast prints or slow, high-quality prints. Resolution is about 0.02 mm per print layer. It is also possible to adjust settings during the printing process so that, if a problem is noticed, it can be corrected without restarting the print. The Ultimaker 2 supports the two most popular printing filaments: Acrylnitril-Butadien-Styrol-Copolymerisat (ABS) and polylactic acid (PLA).

In this study we used a resolution of 0.1 mm slice thickness printing the 3D models of the knee cartilage and their defect. The shape accuracy for 3D printing was the same than CT accuracy. The models were created from ABS – thermoplastic filament, as this material is impact resistant, very hard, whilst retaining good flexibility. We created models of the patellar and femoral cartilage layer containing the full sized defect. Also it was feasible of printing a 3D module of the defect zone.