## 1 Introduction  
One of the utmost purposes of research in tissue engineering and regenerative medicine is to create tissue/organ mimicking the natural structure of the human body for utilization in organ transplantation therapies [1; 2; 3]. Recently, three-dimensional (3D) bioprinting has emerged as a key approach in designing and constructing artificial tissue/organ [4; 5; 6; 7]. This technology incorporates various cells, growth factors, and biomaterials to generate biomedical constructs in which the cell aggregates are deposited layer-by-layer with a supportive matrix bioink [8; 9; 10]. In the frame of biological field, hydrogel has been suggested as an ideal material for bioink due to its high biocompatibility, low cytotoxicity, and structural resemblance to the extracellular matrix [11; 12; 13]. However, applying hydrogels in bioprinting technology may be troublesome since it requires suitable mechanical properties and gelation characteristics to support a steady deposition from the printer [14]. Besides, the fact that not every hydrogel is repeatable to proceed by the printer leads to the quantification of hydrogel printability, which is sometimes rough and resulting in lack of hydrogel bioink [6; 8]. Furthermore, a major obstacle to achieve a better encapsulation of cells and maintain cell viability after 3D printing procedure still present as challenging issues to be resolved [6; 10; 15]. Due to these facts, the improvement of a printable hydrogel that can maintain a stable structure and facilitate the growth and function of the cell is demanded to escalate the existing approach in tissue engineering [7; 12; 16]. The 3D printed construct and cell viability are known to be directly influenced by materials used for bioink and bioprinting parameters [13; 16]. Recently, a thermo-sensitive polymer, so-called Pluronic-F127 (F127), has been known to possess promising properties for 3D bioprinting and tissue engineering applications [7; 17]. This material can be moved and shifted simply due to its micellar-packing gelation characteristic [18]. The F127 has a broad range of sol-gel transition temperature (10-40 \({}^{\circ}\)C), resulting in a stable viscosity at room temperature and human body temperature [13; 18; 19]. The reversible properties of F127 can be useful in producing complex and stable 3D cell-laden with high resolution of the printed constructs [4]. It can be easily printed without excessive stress for the encapsulated cells and can be simply washed away from the target structure after printing [20; 21]. Most importantly, this material is regarded as one of the best types of printable hydrogels for cell printing applications owing to its inert properties towards various cell types [19; 20]. In addition to the F127, Arg-Gly-Asp (RGD) peptide has also attracted particular interest in 3D cell culture for promoting cell growth and proliferation [22; 23; 24]. RGD is an integrin binding site, which belongs to the class of adhesive proteins [25]. RGD region is found in various proteins, and is crucial for facilitating cell-adhesive activity. Moreover, it has been demonstrated that the Gly-Arg-Gly-Asp (GRGD) peptide sequence is identical to the cell-binding region of fibronectin protein [26]. Accordingly, it would be beneficial if F127 could be developed as bioink by the modification of GRGD peptide to enhance cell growth and proliferation activity. Not only materials used for bioink, but also ideal printing parameters, particularly positioning and printing resolution, are important aspects for successful bioprinting results [16]. Previously, the increase of polymer concentration was a primary approach to enhance the printability of hydrogels. Unfortunately, this method entails precise control over the deposition process [18; 27]. Sometime there will be a fine balance between printing parameters such as printing speed, nozzle diameter, and temperature, which can affect the result of bioprinting, especially when printing the cell-laden with hydrogels.