Rapid manufacturing techniques in the development of an axial blood pump impeller
Abstract This paper presents a comparison of manufacturing techniques used in the development of an axial blood pump impeller. In this development process the impeller was designed and its performance was evaluated with the aid of computational fluid dynamics (CFD). Prototypes of those designs where the CFD results show promise were needed in sufficient quantities at a low cost for experimental validation of the CFD results. As the impeller is less than 16 mm in diameter with a maximum blade thickness of about 1.5 mm, innovative manufacturing techniques are explored in this paper to determine the best process for quick fabrication of prototypes that are dimensionally accurate, structurally robust and low in cost. Four rapid prototyping techniques were explored. The completed parts were compared on the basis of manufacturing time, quality and strength of parts obtained, manufacturing cost and also in vitro performances. Based on these studies, it was concluded that selective laser sintering (SLS) is the most appropriate method for the quick production of prototype parts for evaluation of pump performance.
Model for a general mechanical blood damage prediction.
Knowledge of the correlation between mechanical loading of formed blood elements and the amount of their destruction is important for the prediction of blood trauma in artificial circulatory devices as well as in natural circulation. A hemodynamic assessment and optimization of artificial organs to minimize trauma could be undertaken in the design phase given a comprehensive mechanical blood damage model. A theory to determine blood trauma theoretically as a combination of a mechanical loading analysis and a phenomenological blood damage resistance hypothesis is presented. Arbitrary stress-time functions of blood particles predicted by flow analysis are reduced to a set of simple time functions for which the damage behavior may, in principle, be obtained from mechanical blood damage tests. A classification of those stress functions into damaging and nondamaging parts is followed by an overall trauma prediction considering cumulative effects by means of a damage accumulation hypothesis. Theoretical determination of blood destruction caused by mechanical stresses in a centrifugal pump is one possible application of the proposed theory. The strategy of hemolysis prediction is demonstrated for the Aries Medical Isoflow Pump. Irregular stress-time loading functions of particles passing the pump domain obtained by three-dimensional numerical flow simulations were reduced and classified into harmonic components. To relate these functions to their hemolytic response can only be done in a qualitative manner since blood damage behavior under transient stress loading has not been sufficiently investigated. Accurate prediction of blood trauma using the proposed theory will require detailed study of the influence of frequency and amplitude of harmonic stress loading on formed blood elements.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.