Dimensional accuracy of 3D printing navigation templates of chemical-based sterilisation

Accuracy of additively manufactured and steam sterilized surgical guides by means of continuous liquid interface production, stereolithography, digital light processing, and fused filament fabrication

Different printing technologies can be used for prosthetically oriented implant placement, however the influence of different printing orientations and steam sterilization remains unclear. In particular, no data is available for the novel technology Continuous Liquid Interface Production. The objective was to evaluate the dimensional accuracy of surgical guides manufactured with different printing techniques in vertical and horizontal printing orientation before and after steam sterilization. A total of 80 surgical guides were manufactured by means of continuous liquid interface production (CLIP; material: Keyguide, Keyprint), digital light processing (DLP; material: Luxaprint Ortho, DMG), stereolithography (SLA; Surgical guide, Formlabs), and fused filament fabrication (FFF; material: Clear Base Support, Arfona) in vertical and horizontal printing orientation (n = 10 per subgroup). Spheres were included in the design to determine the coordinates of 17 reference points. Each specimen was digitized with a laboratory scanner after additive manufacturing (AM) and after steam sterilization (134 °C). To determine the accuracy, root mean square values (RMS) were calculated and coordinates of the reference points were recorded. Based on the measured coordinates, deviations of the reference points and relevant distances were calculated. Paired t-tests and one-way ANOVA were applied for statistical analysis (significance p < 0.05). After AM, all printing technologies showed comparable high accuracy, with an increased deviation in z-axis when printed horizontally. After sterilization, FFF printed surgical guides showed distinct warpage. The other subgroups showed no significant differences regarding the RMS of the corpus after steam sterilization (p > 0.05). Regarding reference points and distances, CLIP showed larger deviations compared to SLA in both printing orientations after steam sterilization, while DLP manufactured guides were the most dimensionally stable. In conclusion, the different printing technologies and orientations had little effect on the manufacturing accuracy of the surgical guides before sterilization. However, after sterilization, FFF surgical guides exhibited significant deformation making their clinical use impossible. CLIP showed larger deformations due to steam sterilization than the other photopolymerizing techniques, however, discrepancies may be considered within the range of clinical acceptance. The influence on the implant position remains to be evaluated.

Quality Analysis of Micro-Holes Made by Polymer Jetting Additive Manufacturing

Material jetting technology is gaining popularity, especially in polymer science, because of their high accuracy for additive manufacturing (AM) products. This paper aims to investigate the quality of micro-holes that are oriented in three basic directions, and manufactured by the material jetting AM process. This paper proposes a novel methodology to evaluate the accuracy of micro-holes features by using a transparent artifact. A test artifact with horizontal and vertical micro-holes in it, with industrial applications, was designed. Micro-holes were placed on planar and curve surfaces. Samples were manufactured by PolyJet technology from a translucent photopolymer resin which allows a facile investigation (by microscopy) of the inner structure of the micro-holes. The features of ten micro-holes printed in matte and glossy finish type, with diameters in coarse and medium options, according to ISO/ASTM 52902, were analyzed. Quality analysis of the micro-holes features was performed by microscopy investigations. The effects of main factors on the deviation of the micro-hole diameter were investigated by using the statistical design of experiments, and four control factors were considered. The best results were obtained for sample printed in matte finishing with the micro-holes oriented along the x-axis and z-axis. The smallest diameter of the micro-holes obtained by PolyJet technology on an EDEN 350 machine was 0.5 mm, but in industrial applications for a facile post-processing, a higher diameter is recommended to be used. A confirmatory experiment on a wing sample, with a number of micro-holes of the same diameter and a large length to diameter ratio of the micro-holes, was performed, and the repeatability of the results was confirmed.

Sterilization of PLA after Fused Filament Fabrication 3D Printing: Evaluation on Inherent Sterility and the Impossibility of Autoclavation

Three-dimensional printing, especially fused filament fabrication (FFF), offers great possibilities in (bio-)medical applications, but a major downside is the difficulty in sterilizing the produced parts. This study evaluates the questions of whether autoclaving is a possible solution for FFF-printed parts and if the printer itself could be seen as an inherent sterilization method. In a first step, an investigation was performed on the deformation of cylindrically shaped test parts after running them through the autoclaving process. Furthermore, the inherent sterility possibilities of the printing process itself were evaluated using culture medium sterility tests. It could be shown that, depending on the needed accuracy, parts down to a diameter of 5-10 mm can still be sterilized using autoclaving, while finer parts suffer from major deformations. For these, inherent sterilization of the printer itself is an option. During the printing process, over a certain contact time, heat at a higher level than that used in autoclaving is applied to the printed parts. The contact time, depending on the printing parameters, is calculated using the established formula. The results show that for stronger parts, autoclaving offers a cheap and good option for sterilization after FFF-printing. However, the inherent sterility possibilities of the printer itself can be considered, especially when printing with small layer heights for finer parts.