One of the most difficult complications in traumatological and orthopedic surgery is the non-union of bones, the frequency of which depends on many factors, averaging 1.9% per fracture, but can reach 26% in open tibial fractures. Large diaphyseal defects of long bones of critical size are by definition considered incapable of spontaneous healing and require a surgical intervention. Bone grafts are considered to be the gold standard in the treatment of large defects and disorders of bone regeneration, but the limitation of their volume and the violation of the donor site necessitated the development of alternative methods.A promising method of treating bone defects is the use of bioceramic frames made of synthetic polymers and biologically active elements of natural polymers or minerals. The use of 3D printing in bone grafts allows the treatment of bone defects thanks to the creation of a porous framework with sufficient mechanical strength and a favorable macro- and microstructure. A new stage in the development of a bioengineering approach to healing bone tissue is the use of mesenchymal stem cells in combination with biomaterials.The purpose of the study was to experimentally substantiate the possibility of enhancing the reparative regeneration of bone defects of critical size using transcortical 3D implants based on polylactide and tricalcium phosphate with the addition of allogeneic mesenchymal stem cells.The experimental studies were carried out on the basis of the laboratory of experimental modeling and the department of transplantology of the State University "IPHS named after Prof. E. Sitenko of the National Academy of Sciences of Ukraine" with the fulfillment of the requirements of humane treatment of experimental animals in accordance with the Laws of Ukraine, the European Convention, the directives of the European Parliament and the Council of Europe.^UOne of the most difficult complications in traumatological and orthopedic surgery is the non-union of bones, the frequency of which depends on many factors, averaging 1.9% per fracture, but can reach 26% in open tibial fractures. Large diaphyseal defects of long bones of critical size are by definition considered incapable of spontaneous healing and require a surgical intervention. Bone grafts are considered to be the gold standard in the treatment of large defects and disorders of bone regeneration, but the limitation of their volume and the violation of the donor site necessitated the development of alternative methods.A promising method of treating bone defects is the use of bioceramic frames made of synthetic polymers and biologically active elements of natural polymers or minerals. The use of 3D printing in bone grafts allows the treatment of bone defects thanks to the creation of a porous framework with sufficient mechanical strength and a favorable macro- and microstructure. A new stage in the development of a bioengineering approach to healing bone tissue is the use of mesenchymal stem cells in combination with biomaterials.The purpose of the study was to experimentally substantiate the possibility of enhancing the reparative regeneration of bone defects of critical size using transcortical 3D implants based on polylactide and tricalcium phosphate with the addition of allogeneic mesenchymal stem cells.The experimental studies were carried out on the basis of the laboratory of experimental modeling and the department of transplantology of the State University "IPHS named after Prof. E. Sitenko of the National Academy of Sciences of Ukraine" with the fulfillment of the requirements of humane treatment of experimental animals in accordance with the Laws of Ukraine, the European Convention, the directives of the European Parliament and the Council of Europe.