In Bone Tissue Engineering (BTE), autologous bone-regenerative cells are combined with a scaffold for large bone defect treatment (LBDT). Microporous, polylactic acid (PLA) scaffolds showed good healing results in small animals. However, transfer to large animal models is not easily achieved simply by upscaling the design. Increasing diffusion distances have a negative impact on cell survival and nutrition supply, leading to cell death and ultimately implant failure. Here, a novel scaffold architecture was designed to meet all requirements for an advanced bone substitute. Biofunctional, porous subunits in a load-bearing, compression-resistant frame structure characterize this approach. An open, macro- and microporous internal architecture (100 µm–2 mm pores) optimizes conditions for oxygen and nutrient supply to the implant’s inner areas by diffusion. A prototype was 3D-printed applying Fused Filament Fabrication using PLA. After incubation with Saos-2 (Sarcoma osteogenic) cells for 14 days, cell morphology, cell distribution, cell survival (fluorescence microscopy and LDH-based cytotoxicity assay), metabolic activity (MTT test), and osteogenic gene expression were determined. The adherent cells showed colonization properties, proliferation potential, and osteogenic differentiation. The innovative design, with its porous structure, is a promising matrix for cell settlement and proliferation. The modular design allows easy upscaling and offers a solution for LBDT.
The filament drive is a key part of the extrusion assembly of a Fused Filament Fabrication printer. This investigation examines the maximum feed force and the slip of different driving rollers using a filament made of polylactic-acid (PLA) on a test stand. The test stand systematically varies the main feed process parameters: feed velocity, pinch force between the rollers, and feed force. The maximum feed force has a characteristic dependency on the pinch force combined with a feed-velocity-dependency, which is influenced by the outer diameter of the driving roller. The slip was found to increase linearly with the feed force. The slip decreases with increasing pinch force and is nearly constant for pinch forces above 77 N—172 N, depending on the driving roller tooth geometry and outer diameter. A model derived from contact mechanics was used for phenomenological modeling of the slip in relation to pinch force and feed velocity. An exponential ansatz provided good modeling of the slip at a constant pinch force. The model of the slip combined with the extrusion forces in the liquefier can be used to estimate the material flow in the future, thus leading to increased precision of the parts in a magnitude of systems.
Aim: The aim of this study is the creation of microlattices with spatial distribution via additive extrusion for medical applications, and investigation of the related software tools. Materials & methods: Three approaches for lattice generation are compared and tested on a standard 3D printer. First, the geometry is filled with cubic cells. Second, infills of standard slicer software are used. Last, a custom solution for infill generation is presented. Results: Printability of the cubic cells is limited to three-times the nozzle orifice diameter. The other two approaches create lattices of high quality compromised of one strand at the size of the nozzle orifice diameter, while only the custom solution can create arbitrary spatial distributions. Conclusion: The involved software tools should have to be optimized for every application, but pave the way for customized and functional parts. All 3D-printing methods share the workflow of cutting a virtual model into layers in a slicer software and using proprietary strategies for physical modeling. For medical applications, not only the outer appearance but also the inner microstructure is of major importance. Looking at an extrusion-based printing of porous microstructures, this software piece mainly limits achievable structure sizes and distribution, which is necessary, for example, for improving osseointegration. We compared different approaches for this task. First, the structures were created as geometry data, with limited performance. Next, different slicers were compared and evaluated. Smaller regular structures could be created. In the end, we present a custom slicer solution that is capable of printing microlattices of high quality with a complex spatial distribution. [Formula: see text]
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