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Composite poly-L-lactide acid-based scaffolds with hydroxyapatite (HAp) content up to 75 wt.% were fabricated via solution blow spinning. The influence of HAp concentration on structure, wettability, mechanical properties and chemical and phase composition of the produced materials was examined. It was found that with an increase of HAp content the average fiber diameter was increased, the uniaxial strength and relative elongation were reduced, while the phase composition and surface wettability did not change. The performance of the scaffolds during implantation in the parietal bone of a rat skull for a period from 15 to 90 days was studied. The materials have shown high ability to integrate with both soft and hard tissues. It was found that scaffolds with 25 wt.% HAp content significantly enhance osteogenesis during scarification (damage) of the periosteum. Overall, the fabricated scaffolds proved to be highly efficient for replacing bone defects in long tubular bones.

Early treatment of bone fractures was performed using implants, which are often used in the form of plates of various types, which are fixed on the bone surface (extra-

A comparative study of flexible intramedullary nails (FIN) used for lengthening of long tubular bones in children is presented. It has been found that the presence of calcium phosphate coating obtained by micro-arc oxidation or a composite coating based on a copolymer of vinylidene fluoride with tetrafluoroethylene and hydroxyapatite on the surface of FIN significantly enhances the formation of bone regenerate in the area of osteotomy during limb lengthening by combined osteosynthesis. The investigation of physico-chemical properties of FIN with calcium phosphate coating obtained by micro-arc oxidation demonstrated that improved bone tissue formation is due to favourable conditions for adhesion, proliferation, and differentiation of MMSCs into osteoblasts on the coating surface. Composite coatings stimulated the formation of bone tissue only in vivo, mainly due to the piezoelectric properties of the copolymer of vinylidene fluoride with tetrafluoroethylene. Keywords: flexible intramedullary nails, calcium phosphate coating, vinylidene fluoride -tetrafluoroethylene, piezoelectric, combined limb lengthening 1. Introduction Deterioration of the environmental situation, primarily in industrialized countries, and rising frequency of genetic diseases provoke an increase in the number of patients and the severity of orthopaedic pathologies associated with congenital shortening and deformities of the limbs. The limb shortening, progressing as a person develops, leads to pathological changes in the entire biomechanical system. For example, overloading a healthy limb and skewing of the pelvis cause the development of pathologies associated with deformations and dislocation of the healthy hip, leading to a decrease in the quality of life. Thus, the restoration of the limb length allows solving not only the problems of orthopaedic and biomechanical recovery, but also the problem of social rehabilitation and patient's integration into society. For congenital limb length discrepancy the correction of pathology in the affected segment and functionally related elements of the biomechanical system could be done only through surgical interventions. A major contribution for solving this problem was made by outstanding orthopaedic surgeon G.A. Ilizarov, who developed the methods of surgical treatment based on distraction osteogenesis [1,2]. The recent development of G.A Ilizarov method resulted in development of combined osteosynthesis. In this approach, the external fixation devices and thin (up to 2.5 mm) flexible intramedullary nails (FIN) implanted into medullary canal of the tubular bone are used [3,4]. The circular external fixator allows to achieve the high stability of the bone fragments positioning. FIN located in the anatomical zone with multipotent cells depot and a good blood supply, allows to control the histogenesis aimed at bone tissue production. The unique anatomical location of FIN makes it one of the key elements of the combined osteosynthesis. FIN properties largely determine the clinical success of the limb leng...