3-dimensionally (3D) printing has risen in the biomedical field by overcoming the problems found in subtractive manufacturing, such as high material waste, non-customization of the clinical case, non-production of complex devices, and difficulties in machining [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Although additive manufacturing also has limitations, its benefits outweigh the limitations of subtractive manufacturing, which is why it has become a current target of research to optimize the devices produced [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12].

In the manufacturing of metallic biomedical devices, titanium (Ti) has a wide application because it has high resistance to corrosion, biocompatibility, and fatigue resistance [12], [13], [14], [15], [16], [17]. Ti-6Al-4V is the most used Ti alloy because it presents an excellent combination of physical and mechanical properties, it is reiterated that it has become the subject of discussion in recent years due to its modulus of elasticity (110 GPa) being superior to that of alveolar bone (10-30 GPa) that can induce atrophy and low bone remodeling, a phenomenon known as stress shielding, and its chemical elements aluminum (Al) and vanadium (V) be considered potentially cytotoxic, so in recent years the Ti alloys free of these elements composed of tantalum (Ta), zirconium (Zr), and molybdenum (Mb), considered modulus reducers of elasticity and cytocompatible, have risen in the biomedical field [5], [15], [18], [19], [20].

The most consolidated technique for the additive manufacturing of metal structures is Powder Bed Fusion (PBF), which is divided depending on the energy source used in Laser Powder Bed Fusion (L-PBF) and Electron Beam Melting (EBM) [21], [22], [23], [24], [25], [26], [27], [28], [29]. The first emits a high-power laser beam, while the second uses a tungsten filament to produce an electron beam, both fuse the metal powder for a layered construction of the desired part [21], [22], [23], [24], [25], [26], [27], [28], [29]. When performed in a vacuum or inert atmosphere, they allow greater purity and do not compromise the mechanical properties of the final structure [21], [22], [23], [24], [25], [26], [27], [28], [29].

Other processes such as Direct Metal Laser Sintering (DMLS) and Selective Laser Sintering (SLS) are also effective, each with its own particularities and processing characteristics [10], [30], [31], [32], [33], [34], [35], [36]. The advantages of additive manufacturing include the precise construction of devices in complex geometries, reducing the need for material removal and device finishing [21], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46].

The improvement of techniques for the production of metal parts is the subject of studies to reduce the possible problems found such as warping due to the presence of residual stresses and incomplete solidification of the particles, factors that significantly interfere in the physicochemical and mechanical properties of the device obtained [47], [48], [49], [50], [51]. Therefore, the modification of the printing parameters is an alternative that makes it possible to change from the laser power, laser spot size, laser rotated angle, scanning speed, layer thickness, and printing angle to the type of alloy and morphology of the metallic powder [5], [10], [52], [53], [54], [55], [56], [57], [58], [59], [60]. So, the variation of those implies products with different microstructures, roughness, density, cooling rate, and mechanical performance [5], [10], [52], [53], [54], [55], [56], [57], [58], [59], [60].

The printing angle is defined as the inclination at which objects are produced with respect to the build plate (XY). The most studied orientations, “0°–45°–90°,” also referred to as “horizontal–diagonal–vertical”, have become a focus of research due to the structural anisotropies they cause [61], [62], [63], [64]. These anisotropies arise from the layer-by-layer construction process and can lead to significant mechanical failures depending on the direction of the applied force. Therefore, this parameter requires special consideration in comparison to others [61], [62], [63], [64].

Another fundamental concept in additive manufacturing that must be clearly distinguished from the printing angle is the build direction (BD). This refers to the general orientation in which the object is built on the platform, which is consistently vertical (along the Z-axis) [61], [62], [63], [64], [65]. Fig. 1 illustrates these concepts.

The additive manufacturing process of angled samples induces a staircase effect (layer stratification) that interferes with thermal conductivity and consequent micro/macrostructural and mechanical quality of the devices produced [61], [65]. Therefore, heat treatments are suggested to relieve stress and homogenize the microstructure, however, these are disadvantageous on an industrial scale because they require additional processing that increases the cost and production time [66], [67], [68], [69]. Thus, to fill this gap, this systematic review aimed to answer the question “What is the state-of-the-art in the effect of the printing angle of titanium devices printed by additive manufacturing on the material properties?” to identify the best angle of as-built samples for biomedical application through the correlation of microstructural, mechanical properties, and roughness.