# Role of Autologous Platelet Gel (APG) in Bone Healing: A Rabbit Study
## 4 Discussion
reported increased bone mineral density and bone volume in calvaria bone defects of rabbits treated with PRF already after six weeks, with similar results to two other platelets concentrates tested: PRP and Concentrated Growth Factor [29]. So in the present study we have observed similar results to that of PRF. While [PERSON] et al. observed that L-PRF did not provide any additional effect on the quantity and quality of bone during guided bone healing over a period of 12 weeks [30]. Frequently, platelet concentrates have been used mixed with bone graft to promote bone regeneration [31]. The growth factors present in APG have been shown to induce bone formation and enhance fibroblast proliferation when mixed with hydroxyapatite [32]. Furthermore, fibrin matrix increases the rate of collagen formation, tissue vascularity, and mitosis of mesenchymal stem cells, endothelial cells, and osteoblasts [17]. APG promotes adhesiveness and tensile strength for clot stabilization, especially in bone defects. Our results showed that the treatment of bone defects by APG application significantly increases the healing dynamics, at least in terms of new bone formation. However, the role of fibrin matrix in bone defect is controversial, [PERSON] et al. reported that the L-PRF did not influence bone formation when it was used in non-critical bone defects in rabbit tibia at 28 days [33]. [PERSON] et al. found in a rat model that L-PRF reduced inflammatory response and enhanced bone neoformation [34]. Many studies showed that L-PRF mixed with scaffold improved bone repair [35; 36; 37]. In conclusion, there is a clear positive effect of APG on bone healing with enhanced bone tissue repair restricted to the cortical bone of critical size defects in rabbit tibia during our four week experiment, while it did not enhance bone tissue repair in the medullary space. The present study has a major limitation: The treated and control defects were on the same tibia, therefore there was a possibility of the growth factors generating from the APG site migrating to the empty site. While migration of the fibrin matrix is not possible, it is probable that the fibrin matrix plays an important role in bone healing. Another limit is that the present study has investigated the role of APG on bone healing by a histomorphometry approach without an evaluation of mechanical strength and the localized or systemic concentration of the growth factors, which ones, and the duration of their increases. Conceptualization, A.S.; methodology, A.S.; software, A.S.; validation, A.S.; formal analysis, A.S.; investigation, E.Q., A.S., F.L. ; resources, A.S.; data curation, A.S., F.L. ; writing--original draft preparation, A.S.; writing--review and editing, A.S., F.L. ; visualization, A.S., B.R., A.G.L., F.L; supervision, A.S., B.R., A.G.L., F.L., E.Q. ; project administration, A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The study has been approved by the local Ethics Committee of Albania University, Tirana, Albania. Informed Consent Statement: Not applicable. Data Availability Statement: All experimental data to support the findings of this study are available contacting the corresponding author upon request. The authors have annotated the entire data building process and empirical techniques presented in the paper. The authors declare no acknowledgement for the present research. Conflicts of Interest: The authors declare no conflict of interest.