## 1 Introduction
Finally, smart bone implant materials with piezoelectric properties have been developed during the last decades [14]. Piezoelectricity is a property of certain materials to convert mechanical vibration into an electric signal or inversely. The first observation on the piezoelectric properties of natural bone was reported by [PERSON] [15]. Next studies confirmed the generation of electrical potentials in bone and other hard tissues due to mechanical stresses and underlined the role of organic matrix on this behavior [16; 17]. According to [PERSON] et al., piezoelectric biomaterials can be classified as follows: (i) naturally occurring piezocrystals, (ii) piezoceramics like barium titanate, zinc oxide, hydroxyapatite, etc. (iii) piezopolymers like collagen, silk, poly(l-lactic acid) (PLLA), poly(vinylidene fluoride) (PVDF), etc., and (iv) piezocomposites [18]. The most commonly used piezoelectric materials for bone tissue applications include natural or synthetic polymers such as collagen, PVDF, etc., as well as inorganic materials like barium titanate, boron nitride, and zinc oxide [14; 19]. For example, it has been shown that scaffolds composed of polylactic acid and exfoliated boron nitride (EBN) as filler are non-toxic with osteoblastic cells and also displayed osteogenic potential [20]. In another work, implants with ferroelectric BiFeO\({}_{3}\) nanofilms significantly enhanced the in vivo osseointegration in a rat femur [21]. In addition, exposure of human adipose stem cells on electroactive membranes of b-PVDF promoted osteogenic differentiation [22]. Barium titanate (BT) has high dielectric permittivity and undergoes a phase transition from the tetragonal (ferroelectric) to a cubic (paraelectric) structure at Curie Temperature which is around 120 \({}^{\circ}\)C [23; 24]. Due to its superior properties and biocompatibility, BT is the most common piezoelectric material used for biological applications. When BT is used in the form of nanoparticles wrapping with bioactive macromolecules or coating with polymers is needed to prevent barium migration from its surface. For example, glycol-chitosan stabilized BT nanoparticles showed good biocompatibility against rat mesenchymal stem cells [25]. Barium titanate can play an important role during new bone formation. It has been found that BT nanoparticles enhanced the osteogenesis of mesenchymal stem cells [26]. In another study, collagen/HAp/BT composites that were prepared by freeze-drying showed excellent osteoinductive properties on amniotic fluid cell cultures [27]. Furthermore, the addition of BT in titania ceramics increased their bioactivity [28]. Many studies have been performed to prepare multifunctional composites or ceramics based on BT. These materials combine the piezoelectric properties of BT with the bioactive properties of calcium phosphates, mainly of HAp, and are considered very promising materials for bone tissue engineering applications. HAp coating of porous BT scaffolds enhanced the in vitro bioactivity [29], while BT has been incorporated in injectable calcium phosphate bone cements and the materials showed good mechanical properties and high bioactivity and biocompatibility [30]. The methods used to produce composite bioscaffolds include cast molding, electrospinning, freeze-drying, etc. The main drawback of the above methods is that the control of pore size and shape, together with pore interconnectivity, is not adequate. Three-dimensional printing is a newly emerged technology able to fabricate bioscaffolds with controlled pore size and porosity and with complex architectures. Fabrication of 3D scaffolds can be achieved using different techniques. The most common techniques are fused deposition modeling (FDM), stereolithography (SLA), selective laser sintering (SLS), direct light processing (DLP), and binder jetting [31; 32]. Today, 3D fabricated smart or multifunctional biomaterials are considered the next generation of biomaterials with a plethora of biomedical applications [18].