###### Abstract  
Mechanical and resorbable scaffolds are in high demand for stem cell-based regenerative medicine, to treat refractory bone defects in craniofacial abnormalities and injuries. Multipotent progenitor cells, such as dedifferentiated fat (DFAT) cells, are prospective sources for regenerative therapies. Herein, we aimed to demonstrate that a composite gelatin sponge (\(\alpha\)-TCP/CS) of alfa-tricalcium phosphate (\(\alpha\)-TCP) mixed with gelatin scaffolds (GS), with/without DFATs, induced bone regeneration in a rat calvarial defect model in vivo. \(\alpha\)-TCP/GS was prepared by mixing \(\alpha\)-TCP and 2% GS using vacuum-heated methods. \(\alpha\)-TCP/GS samples with/without DFATs were transplanted into the model. After 4 weeks of implantation, the samples were subjected to micro-computed tomography (\(\mu\)-CT) and histological analysis. \(\alpha\)-TCP/GS possessed adequate mechanical strength; \(\alpha\)-TCP did not convert to hydroxyapatite upon contact with water, as determined by X-ray diffraction. Moreover, stable \(\alpha\)-TCP/GS was formed by electrostatic interactions, and verified based on the infrared peak shifts. \(\mu\)-CT analyses showed that bone formation was higher in the \(\alpha\)-TCP/GS+ DFAT group than in the \(\alpha\)-TCP/GS group. Therefore, the implantation of \(\alpha\)-TCP/GS comprising DFAT cells enhanced bone regeneration and vascularization, demonstrating the potential for healing critical-sized bone defects.  
b 2021 13 December 2  
composition as collagen, which accounts for approximately 95% of the organic phase of bone [7; 8]. In addition, unlike collagen, gelatin is a modified biopolymer; the choice of gelatin as a scaffold material therefore precludes the immunogenicity and pathogen infection concerns associated with collagen [8]. However, the application of biopolymers to hard tissue regeneration scaffolds is limited because of the low mechanical strength of the latter. Researchers have developed hybrid scaffolds with combined biopolymers and bioceramics to enhance their mechanical properties [2; 4; 5; 9; 10]. Previous studies have demonstrated the role of alfa-tricalcium phosphate (\(\alpha\)-TCP) particles in bone rebuilding by the gradual biodegradation and formation of adjacent bone [11; 12]. Our previous studies [2; 5] reported that transplantation of scaffolding material, made using porous \(\alpha\)-TCP particles and chemically synthesized collagen model polypeptides, resulted in bone regeneration in beagle and mini pig bone defect models.  
Although tissue engineering involves several types of cells, mesenchymal stem cells (MSCs), in particular, display therapeutic properties. MSCs from adipose tissue, also known as adipose-derived stem cells (ASCs), are extensively used for bone tissue engineering [13; 14]. However, they are a heterogeneous cell population, particularly in the early passages; this may be attributed to their development from the non-adipocyte fraction of adipose tissue, such as the stromal vascular fraction [15]. Mature adipocytes isolated from fat tissue can be dedifferentiated into fibroblast-like cells by ceiling culture, and are referred to as dedifferentiated fat (DFAT) cells [16]. Our previous study [17] demonstrated that human DFAT cells have a higher ability to differentiate osteoblasts than ASC's DFAT cells from the human buccal fat pad.  
The technical details regarding the use of DFAT cells for bone defect regeneration are unknown. The success rate of bone regeneration depends on the interaction between DFAT cells and the scaffold that holds and supports them. Gelatin and \(\alpha\)-TCP are novel choices for preparing these scaffolds; whereas gelatin has natural pores to hold cells, \(\alpha\)-TCP can provide suitable ions for stem cell growth. Therefore, we aimed to prepare allogeneic DFAT cells combined with \(\alpha\)-TCP/gelatin scaffolds (GS) and implant them into rat calvarial defects, to examine their osteogenesis ability in vivo.