Parametric study of a bubble removing device for hemodialysis.

BACKGROUND: This paper sets out to design a device for removing bubbles during the process of hemodialysis. The concept is to guide the bubbles while traveling through the device and eventually the bubbles can be collected. The design focuses on the analysis of various parameters i.e. inlet diameter, inlet velocity and size of the pitch. The initial diameters of Models 1 and 2 have thread regions of 6 and 10 mm, respectively. PARAMETERS: Swirl number, Taylor number, Lift coefficient along with pressure field are also implemented. RESULTS: Based on computational fluid dynamics analysis, the bubbles' average maximum equilibrium position for Model 1 reached 1.995 mm, being greater than that of Model 2, which attained 1.833 mm. Then, 16,000 bubbles were released into Model 1 to validate the performance of the model. This number of bubbles is typically found in the dialysis. Thus, it was found that 81.53% of bubbles passed through the radial region of 2.20 ± 0.30 mm. The appropriate collecting plane was at 100 mm, as measured from the inlet position along the axial axis. The Taylor number, Lift coefficient, and Swirl number proved to be significant parameters for describing the movement of the bubbles. Results were based on multiple inlet velocities. It is seen that Model 3, the improved model with unequal pitch, reached a maximum equilibrium position of 2.24 mm. CONCLUSION: Overall, results demonstrated that Model 1 was the best design compared to Models 2 and 3. Model 1 was found capable of guiding the bubbles to the edge location and did not generate extra bubbles. Thus, the parametric study, herein, can be used as a prototype for removing bubbles during the process of hemodialysis.

Effect of intermittent hydrostatic pressure on aging human chondrocyte cells.

In this study, a hydrostatic pressure chamber (HPC) is designed and developed to host chondrocyte cell culture. External stimuli such as forces, pressure, vibration etc. are found to be significant factors on upregulating the relevant proteins for constructing the extracellular matrix (ECM) during culturing. The aim of this paper is to design a system which provides external stimuli during chondrocyte cell culture as well as to discover the relevant gene which can generate the repair and regeneration of aging cells. The system consists of a controllable HPC that provides intermittent hydrostatic pressure (HP) on the cultured cells. The chamber is capable of applying intermittent HP in the range: 0 to1 MPa, at a frequency of 0.5-1Hz. An investigation was undertaken to determine the improvement of human chondrocyte cells viz. of 3 sub-jects whose ages are 60 and above. The effect of HP on the aging cells is observed through the extracted ribonucleic acid (RNA) after the cell is treated with HP for two hours, each day, over four days. The experiments were conducted to observe the effect of HP on the level of collagen type I, collagen type II, and aggrecan. Results show that HP did little to help in upregulating the aggrecan and collagen type II in aged-chondrocyte cells. Further, it was found that the application of HP depended on the number of days applied. The results presented the possibility of ap-plying HP in regeneration of damaged cartilage in elderly.

Evaluation of Stress Distribution on Implant-Retained Auricular Prostheses: The Finite Element Method.

PURPOSE: The purpose of this study was to evaluate stress distribution around two craniofacial implants in an auricular prosthesis according to the removal forces. Three attachment combinations were used to evaluate the stress distribution under removal forces of 45 and 90 degrees. MATERIALS AND METHODS: Three attachment designs were examined: (1) a Hader bar with three clips; (2) a Hader bar with one clip and two extracoronal resilient attachments (ERAs); and (3) a Hader bar with one clip and two Locators. The removal force was determined by means of an Instron universal testing machine with a crosshead speed of 10 mm/minute. All three designs were created in three dimensions using SolidWorks. The applied removal force and the models were then introduced to finite element software to analyze the stress distribution. RESULTS: The angle of removal force greatly affected the magnitude and direction of stress distribution on the implants. The magnitude of stress under the 45-degree removal force was higher than the stress at 90 degrees. The combination of the 1,000-g retention clip and 2,268-g retention Locator exhibited the highest stress on the implant flange when the removal force was applied at 45 degrees. CONCLUSION: The removal angle greatly influences the amount of force and stress on the implants. Prosthodontists are encouraged to inform patients to remove the prosthesis at 90 degrees and, if possible, use a low-retentive attachment to reduce stress.

Stress analysis of two craniofacial implants in implant retained auricular prostheses.

Implant-retained auricular prostheses require attachments to connect the implants and prostheses. Different attachments have different retention forces and hence different stress is transmitted to the implants. Splinting the implants together with a Hader bar allows the combination of different attachments with the Hader bar and allows changes in the amount and pattern of stress on the implants. However, the amount of removal force is also influenced by the retention components and the direction of removal of the prosthesis. In this paper, we studied the stress distribution around two craniofacial implants, in an auricular prosthesis, according to the removal forces, among three different attachment combinations and evaluated the stress distribution around two craniofacial implants in an auricular prosthesis with removal force at normal direction. The mean removal force was experimentally determined and the models were created using finite element software to analyze the distribution of von-Mises stress. Within the limitations of this study, the prosthodontist should place an emphasis on encouraging patients to remove the prosthesis at 90 degrees and if possible use a low retentive attachment to reduce the stress.

Modeling soft-tissue deformation prior to cutting for surgical simulation: finite element analysis and study of cutting parameters.

This paper presents an experimental study to understand the localized soft-tissue deformation phase immediately preceding crack growth as observed during the cutting of soft tissue. Such understanding serves as a building block to enable realistic haptic display in simulation of soft tissue cutting for surgical training. Experiments were conducted for soft tissue cutting with a scalpel blade while monitoring the cutting forces and blade displacement for various cutting speeds and cutting angles. The measured force-displacement curves in all the experiments of scalpel cutting of pig liver sample having a natural bulge in thickness exhibited a characteristic pattern: repeating units formed by a segment of linear loading (deformation) followed by a segment of sudden unloading (localized crack extension in the tissue). During the deformation phase immediately preceding crack extension in the tissue, the deformation resistance of the soft tissue was characterized with the local effective modulus (LEM). By iteratively solving an inverse problem formulated with the experimental data and finite element models, this measure of effective deformation resistance was determined. Then computational experiments of model order reduction were conducted to seek the most computationally efficient model that still retained fidelity. Starting with a 3-D finite element model of the liver specimen, three levels of model order reduction were carried out with computational effort in the ratio of 1.000:0.103:0.038. We also conducted parametric studies to understand the effect of cutting speed and cutting angle on LEM. Results showed that for a given cutting speed, the deformation resistance decreased as the cutting angle was varied from 90 degrees to 45 degrees. For a given cutting angle, the deformation resistance decreased with increase in cutting speed.

Study of soft tissue cutting forces and cutting speeds.

A versatile equipment to study the cutting of soft tissue with surgery scalpel was designed and constructed. Experiments were performed with pig liver (ex-vivo) to measure the blade-tissue interaction forces at cutting speeds ranging from 0.1 cm/sec-2.54 cm/sec. The experimentally measured force-displacement curves reveal that the liver cutting process was made up of a sequence of repeating local units with similar features. Each local unit was comprised of a linear deformation phase followed by a crack growth phase. A method was developed to quantify the deformation resistance of the tissue during each local deformation phase in cutting. This deformation resistance was presented in the form of a self-consistent local effective Young's modulus (LEYM), and was determined by post-processing force-displacement data with finite element models. Values for LEYM were determined from plane-stress finite element model and plane-strain finite element model. The plane-stress LEYM values were within a close bound of the plane-strain values. Results of the self-consistent LEYM at different cutting speeds show that the tissue's resistance to deformation decreased as the cutting speed increased.

Determining deformation resistance in cutting soft tissue with nonuniform thickness.

Understanding soft tissue response during tool tissue interaction is important for developing a reality based haptic interaction model for surgical training and simulation. In this work, experiments were conducted to cut liver specimens with nonuniform thickness. Three cutting speeds ranging from 0.1 cm/sec-2.54 cm/sec were used. The cutting forces, cutting tool displacement, and tool/tissue imaging via stereo camera system were collected. The time varying depth-of-cut in the thickness-varying specimen was then determined using image analysis. The force-displacement data revealed that the cutting process consisted of a sequence of repeating units each comprising of a localized deformation phase followed by localized crack extension phase in the tissue. Based on depth-of-cut normalized cutting force, the deformation resistance of the tissue during the localized deformation phases was determined. The deformation resistance was characterized via the local effective modulus (LEM) of the soft tissue. The effect of cutting speed on the deformation resistance of the soft tissue was determined.

Measuring forces in liver cutting: new equipment and experimental results.

We are interested in modeling the liver cutting process as accurately as possible by determining the mechanical properties experimentally and developing a predictive model that is self-consistent with the experimentally determined properties. In this paper, we present the newly developed hardware and software to characterize the mechanical response of pig liver during (ex vivo) cutting. We describe the custom-made cutting apparatus, the data acquisition system, and the characteristics of the cutting force versus displacement plot. The force-displacement behavior appears to reveal that the cutting process consists of a sequence of intermittent localized crack extension in the tissue on the macroscopic scale. The macroscopic cutting force-displacement curve shows repeating self-similar units of localized linear loading followed by sudden unloading. The sudden unloading coincides with observed onset of localized crack growth. This experimental data were used to determine the self-consistent local effective Young's modulus for the specimens, to be used in finite element models. Results from finite element analyses models reveal that the magnitude of the self-consistent local effective Young's modulus determined by plane-stress and plane-strain varies within close bounds. Finally, we have also observed that the local effective Young's modulus determined by plane stress and plane strain analysis decreases with increasing cutting speed.