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Background and Objectives: Minimally invasive surgeries for acetabulum fracture fixation are gaining popularity due to their known advantages versus open reduction and internal fixation. Antegrade or retrograde screw fixation along the long axis of the posterior column of the acetabulum is increasingly applied in surgical practice. While there is sufficient justification in the literature for the application of the anterior approach, there is a deficit of reports related to the posterior approach. The aim of this study was to evaluate the biomechanical competence of posterior column acetabulum fracture fixation through antegrade screw placement using either a standard cannulated screw or a cannulated compression headless screw (CCHS) via posterior approach. Materials and Methods: Eight composite pelvises were used, and a posterior column acetabulum fracture according to the Letournel Classification was simulated on both their left and right sides via an osteotomy. The sixteen hemi-pelvic specimens were assigned to two groups (n = 8) for either posterior column standard screw (group PCSS) or posterior column CCHS (group PCCH) fixation. Biomechanical testing was performed by applying steadily increased cyclic load until failure. Interfragmentary movements were investigated by means of motion tracking. Results: Initial stiffness demonstrated significantly higher values in PCCH (163.1 ± 14.9 N/mm) versus PCSS (133.1 ± 27.5 N/mm), p = 0.024. Similarly, cycles and load at failure were significantly higher in PCCH (7176.7 ± 2057.0 and 917.7 ± 205.7 N) versus PCSS (3661.8 ± 1664.5 and 566.2 ± 166.5 N), p = 0.002. Conclusion: From a biomechanical perspective, CCHS fixation demonstrates superior stability and could be a valuable alternative option to the standard cannulated screw fixation of posterior column acetabulum fractures, thus increasing the confidence in postoperative full weight bearing for both the patient and treating surgeon. Whether uneventful immediate postoperative full weight bearing can be achieved with CCHS fixation should primarily be investigated in further human cadaveric studies with a larger sample size.

In the thesis is examined the process of electrochemical anodizing of titanium alloy Ti-6Al-7Nb. The analysis in chapter 1 is concentrated in titanium, titanium alloys, methods for surface treatment and anodizing titanium alloys in general. The methods for conducting scientific studies are present in Chapter 2. Chapter 3 contains notes, comments and observations acquired during the preliminary experiments. A method for monitoring the electrical parameters - current and charge is developed in Chapter 4. There is a computer simulation model for the oxide growth during electrochemical anodizing of Ti-6Al-7Nb as well. Chapter 5 consists of study on the influence of thechnological parameters in the process of electrochemical anodizing of titanium alloy Ti-6Al-7Nb. В дисертационния труд е разгледан процесът на електрохимично анодиране на титанова сплав Ti-6Al-7Nb. Анализът в глава 1 се концентрира върху титан, титанови сплави, методи за повърхностна обработка и анодиране на титан и титанови сплави. Методите за провеждане на научни изследвания присъстват в глава 2. Глава 3 съдържа бележки, коментари и наблюдения, получени по време на предварителните експерименти. Метод за наблюдение на електрическите параметри - ток и заряд е разработен в глава 4, освен това е описан модел за компютърна симулация за растежа на оксидите по време на електрохимично анодиране на Ti-6Al-7Nb. Глава 5 се състои в проучване на влиянието на технологичните параметри в процеса на електрохимично анодизиране на титанoва сплав Ti-6Al-7Nb.

The dissertation examines and analyzes the application of process "Brush-plating" in repair process of details from ship machines and mechanisms. The analysis in Chapter 1 focuses on different types of metals involved in marine industry, the possibilities for surface modification and reconditioning of worn out parts. Main tasks and objectives have been set. In Chapter 2 has been made an overview of the most common methods for examining structural and mechanical properties of selective coatings. In Chapter 3 focuses on examination the influence of technological parameters upon the properties of selective coatings, applied by means of "Brush-plating" technologie, on stainless steel 316L and titanium alloy Ti-6Al-4V. Chapter 4 represents a proposal for mathematical analysis, by means of regression analysis for the process "Brush-plating" for application cobalt coating. Chapter 5 focuses on effective practical implementation of "Brush-plating" process, for reconditioning details from ship pump systems., Дисертационния труд изследва и анализира приложението на процеса „Brush-plating” при ремонтния процес на детайли от корабните машини и механизми. Анализа в Глава 1 се фокусира върху различните типове материали използвани в морската индустрия, възможностите за повърхностно модифициране и възстановяване на износените части. Поставени са основната цел и задачи на дисертационния труд. В Глава 2 беше направен преглед на основните методики за изследване структурата и механичните качества на селективните покрития. В Глава 3 се разглежда влиянието на технологичните параметри върху качествата на селективните покрития нанесени по технологията „Brush-plating”, върху стомана 316L и титаниева сплав Ti-6Al-4V. Глава 4 представя, предложение за математически анализ, чрез регресионен анализ на процеса „Brush-plating”, за нанасяне на покритие кобалт. Глава 5 се фокусира върху ефективното практическо приложение на процеса „Brush-plating”, при възстановяване на детайли от корабните помпени системи.