From (18)F‑MC225 to Conformationally Free Derivatives.

Among the various currently available additive manufacturing (AM) methods, fused deposition modelling (FDM) dominates both desktop and industrial-scale polymer printing, primarily due to its low capital cost, high material utilisation, and direct conversion of digital models into physical objects [,,]. Originally developed as a rapid prototyping method, FDM has evolved into a production-grade technology capable of manufacturing functional end-use parts—including jigs, fixtures and structural components—for the aerospace, automotive, biomedical and consumer electronics sectors [,]. This process deposits thermoplastic filament in a layer-by-layer manner through a heated nozzle. Compared with subtractive or other shaping methods, this additive mechanism offers two inherent manufacturing advantages: the ability to achieve virtually unlimited geometric complexity without dedicated tooling and a substantially reduced time to market. However, this layerwise construction inevitably introduces characteristic defects such as the “staircase effect” [], interlayer voids and porosity [], all of which affect surface integrity, dimensional accuracy and mechanical properties of printed parts. Consequently, process parameter optimisation has become a central theme in FDM research. Among the various thermoplastics suitable for FDM, acrylonitrile butadiene styrene (ABS) is one of the most widely used engineering materials due to its excellent mechanical properties, and it is primarily employed in the manufacture of structural parts, housing, automotive interior components, consumer electronic casings and functional elements []. However, the thermal and rheological characteristics of ABS also render it highly sensitive to operating conditions; inappropriate parameter selection can lead to poor interlayer bonding, excessive warpage and pronounced surface defects, thereby affecting the reliability of ABS parts and composite ABS filament parts in demanding applications [,]. For ABS parts intended for functional applications, two surface-related performance indicators are critical: surface roughness (Ra) and coefficient of friction (COF). Ra, typically quantified as the arithmetic mean deviation of the surface profile, directly affects the appearance, fatigue resistance, wettability, coating adhesion and local stress of printed parts. In assemblies where parts must fit precisely or withstand cyclic loading, even moderate changes in roughness can induce premature failure []. Therefore, Ra in FDM ABS is not merely an aesthetic attribute but a key determinant of mechanical reliability. COF is a physical quantity describing the frictional resistance between objects, and it determines frictional performance, energy dissipation, noise generation and overall service life, particularly in sliding or contacting applications such as gears, bearings, snap-fit assemblies and sliding guides [,]. The frictional performance of additively manufactured polymers has been identified as one of the greatest challenges for functional deployment, especially in load-bearing applications where frictional performance is a critical concern []. Studies have begun to explore the complex relationship between surface topography and frictional performance. Recent work by Mahmood et al. [] conducted experiments on FDM-printed polylactic acid (PLA) and found that skewness (Ssk) and maximum valley depth (Sv) exhibited stronger positive correlations with COF than average surface roughness (Ra), indicating that extreme topographical features, rather than average roughness, dominated the frictional response. Portoacă et al. [] analysed the effects of process parameters on the coefficient of friction, surface roughness parameters and cumulative linear wear of 3D-printed PLA and ABS parts. Their results showed that, under the same layer thickness and infill density, the surface roughness of ABS parts was consistently higher than that of PLA parts; however, the comparison of COF and cumulative linear wear between the two materials depended on the specific process parameters: under some parameter sets ABS parts exhibited lower values, while under others PLA parts were lower. Taken together, these findings indicate that the unique layerwise structure of FDM produces a complex, anisotropic surface texture, resulting in a relationship between Ra and COF that is neither monotonic nor independent, and there is no simple one-to-one correspondence between the two. However, the simultaneous collaborative optimisation of Ra and COF within a unified modelling and optimisation framework remains insufficiently explored in existing research.