###### Abstract  
Selective laser melting (SLM) is extensively used for fabricating metallic biomedical products. After 3D printing, it is almost always advisable to apply a heat treatment to release the internal tensions or optimize the mechanical properties of the printed parts. The aim of this paper is to investigate the effects of heat treatment of SLM printed Ti-6 Al-4V (Ti64) circular specimens on the areal surface texture parameters and cell attachment. Areal surface texture parameters, including the arithmetic mean height (S\({}_{\text{a}}\)), root-mean-square height (S\({}_{\text{a}}\)), skewness (S\({}_{\text{sk}}\)), and kurtosis (S\({}_{\text{ku}}\)) were characterized. In addition, wavelet-based multi-resolution analysis was applied to investigate the characteristic length scales of untreated and heat-treated Ti64 specimens. In this study, the vertical distance between the highest and lowest position of cell attachment for each sampling area was defined as \(\Delta\)H. Results showed that an increase in the periodic characteristic length scale was primarily due to the formation of large-scale aggregations of Ti64 metal powder particles on the heat-treated surface. In addition, MG-63 cells preferred lying in concave hollows; in heat-treated specimens, values of \(\Delta\)H statistically significantly decreased from 31.6 \(\pm\) 4.2 to 8.8 \(\pm\) 2.8 \(\upmu\)m, while S\({}_{\text{ku}}\) decreased from 3.3 \(\pm\) 1.4 to 2.6 \(\pm\) 0.6, indicating a strong influence of S\({}_{\text{ku}}\) on cell attachment. selective laser melting; heat treatment; surface texture; Ti-6 Al-4V alloy; cell attachment; microstructure +
Footnote †: Correspondence: Correspondence: [EMAIL_ADDRESS]  
stress formation in the printed parts [9; 10]. Therefore, heat treatment in the postprinting phase is of particular importance to release the internal tensions and to optimize the mechanical properties of the printed components [11]. Recent in vitro study has shown that mammalian fibroblast cells do not accumulate in the residual stress zone [12]. It is recognized that subjecting SLM-printed specimens to heat treatment is an important step in improving the cytocompatibility, because it minimizes residual stresses and homogenizes metallic microstructures [10; 13; 14; 15]. In addition, surfaces with high roughness values lead to better interlocking reactions in the implant bone interface zone than do smooth surfaces [16]. Many reports have proven that titanium and its alloys prepared using SLM methods improve osseointegration [17; 18]. Previous studies have indicated that surface characteristics, including surface roughness, surface morphology, and contact angle, are crucial in osseointegration and implant infections [19; 20]. Another important issue that is still not well understood is the effect of surface roughness features on cell proliferation and attachment. A recent in vitro study found that when the average roughness (Ra) was <24.9 \(\upmu\)m, surface roughness promoted the proliferation and differentiation of human osteoblasts [21]. For assessing surface topography, the surfaces' roughness can be quantified using either 2D profile-based or 3D area-based roughness measurements, where the ISO (interational organization for standardization) specification standards ISO 4287 [22] and ISO 25178-2 [23] define profile and areal parameters, respectively. Although the industry still uses mainly profile parameters to characterize the topographies, there is a demand for areal parameters for the characterization of specific features [24; 25]. In metrology, the surface topography is generally classified into form, waviness, and roughness [26]. Both form and waviness measurements measure the large-scale variations in the surface's height, while surface roughness measurement is of the small-scale variations. Besides, the roughness is measured by subtracting the form and waviness components from the surface's actual contour, where this subtraction is achieved through a digital filter, usually a Gaussian filter [26; 27].