The manner of studying of the fracture modes could be done through fractography. Fractography is the study of fracture surface morphologies and it gives an insight into damage and failure mechanisms, underpinning the development of physically-based failure criteria. In composites research it provides a crucial link between predictive models and experimental observations. Fractographic methods are routinely used to determine the cause of failure in all engineering structures, especially in product failure and the practice of forensic engineering or failure analysis. In material science research, fractography is used to develop and evaluate theoretical models of crack growth behavior. One of the aims of fractographic examination is to determine the cause of failure by studying the characteristics of a fracture surface. Different types of crack growth produce characteristic features on the surface, which can be used to help identify the failure mode. The overall pattern of cracking can be more important than a single crack, however, especially in the case of brittle behavior materials. Initial fractographic examination is commonly carried out on a macro scale utilizing low power optical microscopy and oblique lighting techniques to identify the extent of cracking, possible modes and likely origins. When it is needed to identify the nature of failure, an analysis at high magnification is required and scanning electron microscopy (SEM) seems to be the best choice. The problem of fracture behavior of biometallic materials is a real one, being well and repeatedly presented in literature. Variations in alloy compositions can lead to subtle differences in mechanical, physical, or electrochemical properties. However, these differences are minor compared with the potential variability caused by differences in fabrication methodology, heat treatment, cold working, and surface finishing, where surface treatments are particularly important for corrosion and wear properties. The aim of this paper, therefore, is to summarize the different types of metals and alloys used as biomaterials, the corrosion of metals in the human body, and different failure damages of metallic implants.
Metallosis is an adverse event developed in relation with an orthopedic implant. It was brought into attention by metal on metal total hip arthroplasty. Lately, cases were diagnosed in total knee, total elbow, and spinal surgery. Metallic debris - released because of wear or corrosion - start an inflammatory response in a chronic condition. Beside local effects, systemic effects are also described; among them toxic effects, neurological and psychiatric, alteration in thyroid and heart function, skin rushes and discoloration. Diagnosis is helped by x-ray examination but is based on fluid aspiration with ions level determination and histological examination. Osteolysis phenomena induced by metallosis may compromise bone ingrowth and promote implant loosening; as result bone stock may be compromised. The cases we present have a particular development pattern; each of them was initiated as a result of atypical behavior of the implants. Two of them necessitated bone grafting in order to replace the reduced bone stock and all three required revision surgery. The cases emphasize the diagnosis methodology and the possible complications encountered during orthopedic implant surgery.
Biodegradable magnesium-based alloys shows good prospects in their use as biodegradable orthopedic materials. The aim of this study is to demonstrate good biocompatibility and lack of local and systemic toxicity of some experimental implants made by magnesium alloy type Mg-Ca 0,8 [%wt]. The study was conducted by implanting some experimental pins made by magnesium alloy type Mg-Ca 0,8 [%wt] in bone, proximal femur and intramedullary tibia, and in thigh muscle of the rabbits. Also, we follow the evolution of blood levels of Mg, Ca, blood counts, liver and kidney function. The evolution of the experience animals was followed for 6 weeks by radiologic imaging, and taking blood samples. After 6 weeks, we obtain after euthanasia of animal experience the harvest blood samples, and musculoskeletal tissue samples for histopathological examination. The histopathology results have not demonstrated peri-implant cytotoxicity, bone and muscle cells being viable. Fibrosis at tissue implant border was minimal showing a good integration. There were no pathological increases in blood levels of Mg and Ca, or changes in blood counts, as well as no change in renal or hepatic function. All this experimental results demonstrates that the magnesium alloy type Mg-Ca 0,8 [%wt] represent a promising solution in orthopedic surgery, proving to be safe, with a high degree of biocompatibility, and without toxic effects.
