## 1 Introduction  
According to the reports of the National Ambulatory Medical Care Survey and American Academy of Orthopedic Surgeons, about 6.8 million patients ask for medical therapy due do orthopedic problems every year, and more than two million bone grafting procedures are performed annually [1]. Autografts are considered the gold standard for bone repair because of their excellent properties in osteoconduction, osteoinduction, and osteogenesis [2]; however, autografts have many limitations. These include their limited availability, the requirement for a surgical incision to obtain the graft that carries the extra risks of hematoma, infection, and additional pain [3]. Allografts are another source for orthopedic implants, and nearly one-third of all bone grafts used in North America are allografts [4]. However, allografts are osteoconductive but with reduced osteoinductivity, which increases the risk of nonunion in fracture repair, and there is a risk of infection [5; 6]. In addition, the supply of allografts is limited by the long pretreatment process. For the reasons outlined above, a new method for fabricating a bioengineered bone graft with the proper mechanical properties, osteoconductivity, and osteogenic abilities is highly desired. Bone implants can be produced through a variety of methods including salt leaching [7], chemical/gas foaming [8], freeze-drying [9], and sintering [10]. However, pore size, pore distribution, porosity, and pore interconnectivity cannot be precisely controlled with these approaches [11]. Bone is a porous tissue with numerous interconnected pores that permit cell migration and proliferation, as well as vascularization [12; 13]. Therefore, an osteogenic scaffold should mimic bone morphology, structure, and function in order to ensure its integration with the native tissue. Three-dimensional (3D) printing technology has received considerable attention for tissue regeneration due to its superiority in the fabrication of complicated structures with tailored shapes, internal and external architecture, pre-designed microstructure, mechanical strength, and bioactivity, which can effectively mimic native tissues. With the use of osteogenic biomaterials and computer-aided design, 3D printing technology can generate a customized structure with desired features that can improve bone integration and the restoration of tissue function [14]. Hybrid materials with tunable properties have been explored in 3D printing [14; 15; 16]. Polylactic acid (PLA) is a popular material used for 3D printing medical devices. It is a thermoplastic polymer that is derived from fermented corn starch, cassava starch, or sugarcane [17]. It is an eco-friendly bioplastic as it is entirely biodegradable and consists of renewable raw materials. This material exhibits high tensile strength, low elongation, and high modulus, which enables it to be a suitable candidate for load-bearing applications, such as orthopedic fixation and sutures [17]. In this study, PLA was used to fabricate porous scaffolds through 3D printing. According to previous reports, large pore size and high porosity are key factors in producing an osteogenic response [12; 13; 18]. In addition, a recent study reported that titanium implants with an average pore size of 600 \(\upmu\)m exhibited an earlier and high fixation ability and rapid bone ingrowth comparing with implants with average pore size of 300 and 900 \(\upmu\)m [19]. Therefore, we designed the scaffold with an average pore size of 600 \(\upmu\)m and 60% porosity. PLA is a versatile, biodegradable, and Food and Drug Administration (FDA) proved biomaterial [17], but its surface is hydrophobic and, therefore significantly reduces cell adhesion. Accordingly, surface modification to enhance its cell supportive material properties can be achieved through the addition of micro- and nanoparticles [14], fibers [16], or fabrication of nanocomposites [15].