ACTA PHYSICA POLONICA A No. 2 Vol. 142 (2022) Biological and Morphological Effects of Apatite Kinds (Sheep/Synthetic) on MgO Reinforced Bone Tissue with Hydroxyapatite Matrix A. Akilli Ari a,* , H. Evlen b and N. Demirkol c a Mechanical Engineering, Amasya University, 05300, Amasya, Turkey b Industrial Design Engineering, Karabuk University, 78050, Karabuk, Turkey c Department of Ceramic, Kocaeli University, Kocaeli, 41140, Turkey Received: 30.12.2021 & Accepted: 20.04.2022 Doi: 10.12693/APhysPolA.142.201 * e-mail: aysu.akilli@amasya.edu.tr In this study, the biological and morphological structure of the bone tissue of hydroxyapatite produced from synthetic and natural bone was investigated. For this purpose, a three-dimensional bioprinter was designed and manufactured. For the production of bone tissue scaffolds, 10 wt% magnesium oxide added to synthetic hydroxyapatite and sheep hydroxyapatite bioink composites were prepared. The rheologi- cal analysis of the prepared bioinks was carried out. With the produced three-dimensional bioprinter, 10 × 10 × 2 mm 3 bone tissue scaffolds were bioprinted. Calcium chloride was used to form connective tissue between layers. 4 weeks of in-vitro bioactivity tests were applied in order to observe the behavior of the produced bone scaffolds and the formation of apatite in the body. After the bioactivity tests, scanning electron microscope and energy dispersive spectrometry analyzes were performed. In addition, a 3-4,5-dimethyl-thiazolyl-2,5-diphenyltetrazolium bromide test was performed in the laboratory envi- ronment of the bone tissue scaffolds. In this test, cytotoxicity analyses and cell counts were performed by fibroblast and osteoblast cell loading. Viability and cell proliferation were observed using the phal- loidin staining method, and comparisons were made between the mixtures. As a result of the study, the printing ability of both bioinks on the three-dimensional bioprinter was successful. Thus, the bone tissue scaffold of the printed bioink was produced in the desired porous structure. Apatite formations were observed in the scanning electron microscope images of the bone tissue scaffolds that were kept in artificial body fluid for 4 weeks. In the cell culture analysis performed at the last stage with cell viability analysis, the continuation of cell viability was promising. topics: magnesium oxide, bioink, bone scaffold, cell culture 1. Introduction The three-dimensional (3D) bioprinting tech- nique is the process of producing functional tissue structures and organs from digital 3D models using bioinks. In this process, cell-loaded bioinks or scaf- folds with subsequent cell cultivation are used [1,2]. Also, the 3D bioprinting method has the poten- tial to produce automation, high precision, sophis- ticated, biomimetic tissue structures [3]. Whether or not an artificial scaffold shows the expected performance is evaluated according to cri- teria such as the compatibility of the scaffold with the body without causing toxic effects, the number of viable cells and its gradual increase. Obtaining a successful cell scaffold with all these features de- pends on the biomaterial from which the scaffold is produced and the correct production parameters. Many studies are carried out to achieve the desired accuracy of parameter in the artificial bone scaffold- ing studies with bioprinters. Studies aimed at de- termining the optimum printing parameters require a variety of printing parameters defined for a bio- printer. In designed and manufactured bioprinters, the scaffold pore in microns should be created for bone tissue printing. These pores affect the abil- ity of the scaffold to retain cells during cell cul- ture. In addition, features such as syringe print- ing pressure, speed and movements of the printer head, the needle (printer tip) inner diameter [4–6], ensuring air circulation of the environment, disin- fection of the environment and the scaffold with UV, and a mechanism spraying the cross-link so- lution to the scaffolds are used in scaffold printing. These are the most important features to look for in a printer. Therefore, it is necessary to determine the optimum printing parameters to ensure success- ful printing when printing bioink. Different printing parameters bring different results and enable the de- sired result to be achieved [7]. Tapered needles are the most suitable needle structure to obtain differ- ent cylindrical shapes and to achieve high printing speeds [8]. While the syringe causes the bioink to spread on the tissue scaffold tip when too close to 201