Additive Manufacturing (AM), commonly known as “3D printing”, is rapidly integrated into many various fields, from everyday commercial to high-end medical and aerospace. Its production flexibility in small-scale and complex shapes is a significant advantage over conventional methods. However, inferior physical properties of parts manufactured by AM in general, and by material extrusion in particular, compared to traditional fabrication methods, inhibit its full assimilation. Specifically, the mechanical properties of printed parts are not high enough and, more importantly, not consistent enough. Optimization of the many various printing parameters is therefore required. This work reviews the influence of material selection, printing parameters such as path (e.g., layer thickness and raster angle), build (e.g., infill and building orientation) and temperature parameters (e.g., nozzle or platform temperature) on mechanical properties. Moreover, this work focuses on the interactions between the printing parameters, their mechanisms, and the statistical methods required to identify such interactions. Choosing the right parameters can increase mechanical properties by up to 60% (raster angle and orientation build), or render other parameters insignificant (material selection), while specific settings of certain parameters can completely inverse the influence trend of other parameters. Finally, trends for future research are suggested.

Poly(L-lactic acid) (PLLA) is a biocompatible, biodegradable, and semi-crystalline polymer with numerous applications including food packaging, medical implants, stents, tissue engineering scaffolds, etc. Hydroxyapatite (HA) is the major component of natural bone. Conceptually, combining PLLA and HA could produce a bioceramic suitable for implants and bone repair. However, this nanocomposite suffers from poor mechanical behavior under tensile strain. In this study, films of PLLA and HA were prepared with small amounts of nontoxic WS₂ nanotubes (INT-WS₂). The structural aspects of the films were investigated via electron microscopy, X-ray diffraction, Raman microscopy, and infrared absorption spectroscopy. The mechanical properties were evaluated via tensile measurements, micro-hardness tests, and nanoindentation. The thermal properties were investigated via differential scanning calorimetry. The composite films exhibited improved mechanical and thermal properties compared to the films prepared from the PLLA and HA alone, which is advantageous for medical applications.

Advancements in bone tissue engineering have increased interest in 3D-printed scaffolds for bone regeneration. Polylactic acid (PLA), a biocompatible and biodegradable polyester, is a promising candidate for bone scaffold materials. Reinforcing PLA with inorganic nanotubes of tungsten disulfide (INT-WS₂) offers new possibilities for scaffold design. INT-WS₂ is an innovative material known for its chemical stability, non-toxicity, and favorable mechanical properties. Integrating PLA with INT-WS₂ marks a pioneering development in bone scaffold technology, providing a safer, more effective alternative to other nanofillers, such as TiO₂ nanoparticles and carbon nanotubes, which face challenges related to cytotoxicity and dispersion. This study adds an important aspect to the characterization of this material by investigating the cytocompatibility and hydrolytic degradation effects on 3D-printed samples of PLA reinforced with 0.5 wt% INT-WS₂. The samples are proposed as structurally suitable candidate for load-bearing 3D-printed bone scaffolds, with the femur chosen as the upper-limit mechanical benchmark. Controlled hydrolytic degradation of PLA/INT-WS₂ samples was conducted over 12 weeks under human-body simulated conditions. Results demonstrated that the material underwent bulk degradation while maintaining mass and surface hardness. Although the ultimate tensile strength progressively decreased to two-thirds of its initial value, potentially allowing gradual loading of the growing bone, it remained significantly higher than the maximum stress experienced by the human femur during normal walking. Furthermore, the PLA/INT-WS₂ nanocomposite exhibited non-toxic behavior, promoting cell viability and proliferation. Despite the need for a longer experiment to fully assess the degradation rate, these findings support PLA/INT-WS₂ as a promising candidate for tailored 3D-printed bone scaffolds designed for individual patients.