Additive manufacturing (AM) has emerged as a transformative technology in the fabrication of intricate structures, offering unparalleled adaptability in crafting complex geometries. Particularly noteworthy is its burgeoning significance within the realm of medical prosthetics, owing to its capacity to seamlessly replicate anatomical forms utilizing biocompatible materials. Notably, the fabrication of porous architectures stands as a cornerstone in orthopaedic prosthetic development and bone tissue engineering. Porous constructs crafted via AM exhibit meticulously adjustable pore dimensions, shapes, and porosity levels, thus rendering AM indispensable in their production. This systematic review ventures to furnish a comprehensive examination of extant research endeavours centred on the generation of porous scaffolds through additive manufacturing modalities. Its primary aim is to delineate variances among distinct techniques, materials, and structural typologies employed, with the overarching objective of scrutinizing the cutting-edge methodologies in engineering self-supported stochastic printable porous frameworks via AM, specifically for bone scaffold fabrication. Findings show that most of the structures analysed correspond to lattice structures. However, there is a strong tendency to use organic structures generated by mathematical models and printed using powder bed fusion techniques. However, no work has been found that proposes a self-supporting design for organic structures.

In-orbit additive manufacturing (AM) is a promising approach for fabrication of large structures. It allows to expand and accelerate human space exploration possibilities. Extrusion-based AM was demonstrated in zero gravity, while the realization of such a process in orbit-like vacuum conditions is currently under exploration. Still, a solution for protection of the UV and IR radiation sensitive polymers is needed in order to prevent their early mechanical failure under space conditions. Vacuum arc plasma based process is widely applied on earth for thin protective coating deposition. Its major advantage is its scalability—from tiny size used in electric propulsion to large scale coating devices. The usability of the vacuum arc process in space conditions was shown in electric propulsion applications in nano-satellites. In this work we discuss and demonstrate the integration of vacuum arc process as a post processing step after Fused Filament Fabrication (FFF) for additive manufacturing and functionalization of long polymer structures. Here we address the concept for technical realization, which integrates the vacuum arc into additive manufacturing process chain. More over we present a laboratory prototype, which implements this concept together with a use case, where a previously printed PEEK structure is coated with aluminum based coating suitable for UV radiation protection.

A simple and time efficient model for atmospheric arc plasmas is presented in this work. It uses experimentally recorded emission spectra in order to estimate radial temperature and electron density profiles in welding arc plasmas. The plasma parameters are calculated using the Elenbaas–Heller and Saha equations, together with welding current, gas composition and simplified cylindrical arc geometry with a particular radius as input parameters. From these parameters an emission spectrum is calculated under the assumption, that the individual lines are mainly broadened due to the Stark effect. Here only second order perturbation theory for the Stark effect without any further influences of ion collision or other additional effects is considered. The comparison of measured and calculated spectra leads to a cost function. Its minimisation is used to find the radius of the arc model. This model was successfully applied for the estimation of plasma parameters in gas tungsten arc welding processes with argon and argon–helium as shielding gases. The calculated gas temperature and electron density profiles were compared with experimental data obtained by Thomson scattering. Further extension of the model for dynamic processes containing metal vapours and its application in feedback control are planned in the future.

The application of material extrusion in vacuum and its combination with physical vapor deposition techniques such as vacuum arc coating technology opens new possibilities of functionalization of polymers during additive manufacturing. This allows to modify polymer surface properties such as thermal and electrical conductivity or radiation resistance. This is in particular interesting for in-space manufacturing and medical applications. In this work, the applicability of surface functionalization for UV protection of polymers was investigated. Therefore, an aluminum-based coating was chosen as a protective coating. The UV resistivity was assessed by testing the tensile properties of the specimens before and after radiation in dependence of coating parameters. The experimental results indicate that specimens coated with an $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 layer of $$\ge {200}\,\hbox {nm}$$ ≥ 200 nm retain their tensile strength when compared to untreated specimens, even after exposure to UV radiation. Hence, a $${200}\,\hbox {nm}$$ 200 nm thick coating is suitable to protect polymers from UV-C-induced degradation. This demonstrates the applicability of enhanced extrusion-based additive manufacturing as a promising method for in-space manufacturing, servicing and coating repair.