Pavlov A. Rationale for the use of a composite based on polylactide and calcium-phosphate ceramics for surgical treatment of periarticular fractures (experimental study).

The dissertation is devoted to the urgent problem of creating a biodegradable composite biomaterial, substantiating its properties and developing individual implants for osteosynthesis using 3D printing. The high frequency of musculoskeletal injuries and the increase in their complexity due to the war in Ukraine necessitates the introduction into clinical practice of new technological developments for the manufacture of implants for osteosynthesis. This will have significant clinical effectiveness, economic feasibility and will contribute to improving the quality of life of patients. Implants that biodegrade after implantation into the human body and made of polylactide and copolymers based on it occupy a significant place in orthopedics and traumatology. The peculiarity of these polymers is biocompatibility, osteoconductivity and the ability to biodegrade with subsequent replacement of the implantation site with bone tissue. However, an unresolved problem is their low mechanical strength, which limits their use in areas of the skeleton under load. The solution may be the development of polylactide-based composites with improved mechanical properties due to the addition of calcium phosphate ceramics, carbon-based materials and polymers. Since tricalcium phosphate and hydroxylapatite are structurally similar to the mineral components of human bone tissue, in our work we focused on composites created on the basis of polylactide/tricalcium phosphate/hydroxyapatite. The manufacturing technology is important for the quality of the retainers, especially if it will allow the manufacture of implants of different shapes and sizes, individual for each patient. Such a technology is 3D printing, and many implants printed on a 3D printer are based on polylactides. As a result of the research, a composite biomaterial based on polylactide (PLA), hydroxylapatite (HA) and tricalcium phosphate (TCF) was created and experimental studies of its properties were conducted. Based on calculations of the modulus of elasticity of a polylactide composite with different percentages of calcium phosphate ceramics from 10 to 50%, it was proven that the optimal composition is 70% polylactide, 20% tricalcium phosphate and 10% hydroxylapatite, which was used in further research for 3D printing using FDM technology (layer deposition). A study of the biocompatibility and toxicity of a new composite of polylactide and calcium phosphate ceramics in vivo in rats for 180 days was conducted. Based on histological analysis of tissues (capsule thickness around implants; cell density and their phenotype; absence of inflammatory cells; condition of capillaries) around the implanted composite discs in subcutaneous fat, its biocompatibility and gradual degradation from day 90 after implantation were confirmed. The absence of toxic effects on kidney and liver function of the new composite was shown based on biochemical analysis of such indicators in rat blood serum as alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, bilirubin, creatinine, and urea. The osseointegration properties of the developed composite were evaluated after implantation of 3D-printed pins into a perforated defect of the femoral metaphysis of rats for 180 days. A higher osseointegration index was established in pins made of the composite compared to pure polylactide starting from day 30 (47.9± 2.13% versus 27.8± 2.25%) and this difference was maintained until the end of the experiment on day 180 (82.0 ± 2.07% versus 66.1 ± 3.4%), when this indicator was 1.7 times and 1.2 times higher, respectively. On day 180, the implants in the bone defect retained their shape, which indicates the possibility of their long-term use. As in the case of disc implantation, the presence of pins in the rat body during bone regeneration and remodeling for a year did not have a toxic effect according to the analysis of biochemical markers of the liver and kidneys. Under the conditions of fixation with a bone plate made of a PLA-based composite material for 180 days, the absence of destructive changes in the periosteum (periosteum) and cortex of the femoral diaphysis of rabbits was shown. The mechanical properties of 3D-printed plates for bone osteosynthesis and implants made of the developed polylactide-based composite were studied. As a result of calculations, it was found that the plates made of polylactide are too soft and must be three times thicker than titanium to ensure similar fixation stiffness.