A computational theoretical model for radiofrequency ablation of tumor with complex vascularization.

Radiofrequency ablation (RFA) for liver tumors is a minimally invasive procedure that uses electrical energy and heat to destroy cancer cells. One of the critical factors that impedes its successful outcome is the thermal heat sink effects from complex vascular systems that give rise to incomplete destruction of the target tumor tissue, resulting in therapy failure. To better understand the thermal influence of the complex vascular system during RFA, this work proposes the employment of two 3D fractal tree-like branched networks to investigate which key factors of the tree-like vascular system impact heating process. A three-dimensional finite difference analysis is employed to simulate the RFA treatment. Based on the data acquired from the measured experiments, the simulated results derived from combining the Pennes bioheat model and the boundary condition-enforced immersed boundary method (IBM) have demonstrated close agreement with experimental data with a maximum discrepancy of ±8.3%. We employed the orthogonal design approach to analyze 3 factors, namely, the blood vessel's volume, the average distance between probe center and the blood vessel system and the number of the selected part's branches at three different levels. Results have revealed that the distance between RFA probe and blood vessel plays a major role during the heating process compared with the other two factors. In addition, both the ablating rates and the volume of damaged tissue are slightly reduced with increasing number of blood vessel branches.

Nano-assisted radiofrequency ablation of clinically extracted irregularly-shaped liver tumors.

Radiofrequency ablation (RFA) for liver tumors is a minimally invasive procedure that uses electrical energy and heat to destroy cancer cells. One of the critical factors that impedes its successful outcome is the use of inappropriate radiofrequency levels that will not completely destroy the target tumor tissues, resulting in therapy failure. Additionally, the surrounding healthy tissues may suffer from serious damage due to excessive ablation. To address these challenges, this work proposes the employment of injected nanoparticles to thermally promote the ablation efficacy of conventional RFA. A three-dimensional finite difference analysis is employed to simulate the RFA treatment. Based on the data acquired from measured experiments, the simulation results have demonstrated close agreement with experimental data with a maximum discrepancy of within ±8.7%. Several types of nanoparticles were selected to evaluate their influences on liver tissue's thermal and electrical properties. We analysed the effects of nanoparticles on liver RFA via a tumor rending process incorporating several clinically-extracted tumor profiles and vascular systems. Simulations were conducted to explore the temperature difference responses between conventional RFA treatment and one with the inclusion of assisted nanoparticles on several irregularly-shaped tumors. Results have indicated that applying selected nanoparticles with high thermal conductivity and electrical conductivity on the targeted tissue zone promotes heating rate while sustaining a similar ablation zone that experiences lower maximum temperature when compared with the conventional RFA treatment. In sum, incorporating thermally-enhancing nanoparticles promotes heat transfer during the RFA treatment, resulting in improved ablation efficiency.

Current hydrogel solutions for repairing and regeneration of complex tissues.

Hydrogel system, as one of the most important biomaterials, is widely studied because of its tremendous potential in regenerative medicine conferred by its wide range of malleable biochemical and physical characteristics, which include its biocompatibility with the elemental biomolecules in vital tissues, its high water retention capability and adjustable soft-tissue-like physicochemical properties. These properties are modifiable to facilitate the targeted tissue protected from external damaging disturbance and having the encapsulated cells' physiology-functional phenotypes induced or maintained in situ. Recently, hydrogels are increasingly used in the R&D of regenerative medicine to build complex tissue. Most of the insightful work focuses on how to select and fabricate the hydrogel models with desired physicochemical properties, flexibility of auto response to various bio-stimuli, and capability of efficiently forming the complex tissue-mimicking construct at different scales. The present review introduced the major types of hydrogeis, the desirable physicochemical properties, the current fabrication methodologies and special organ-based cases of applications of hydrogels, which are used in complex tissue engineering. In addition, this review also discussed the major hurdles faced by the R&D of hydrogel systems for complex tissue medicine.

Bileaflet aortic valve prosthesis pivot geometry influences platelet secretion and anionic phospholipid exposure.

The clinical histories of the Medtronic Parallel (MP) and St. Jude Medical (SJM) Standard valves suggest pivot geometry influences the thrombogenic characteristics of bileaflet prostheses. This work studied the effects of various pivot geometries on markers of platelet damage in a controlled, in vitro apparatus. The Medtronic Parallel valve, two St. Jude Medical valves, and two demonstration prostheses were used to study the effects of bileaflet pivot design, gap width, and size on platelet secretion and anionic phospholipid expression during leakage flow. A centrifugal pump was used to drive blood through a circuit containing a bileaflet prosthesis. Samples were taken at set time intervals after the start of the pump. These samples were analyzed by cell counting, flow cytometry, and enzyme-linked immunosorbant assay. No significant differences were observed in platelet secretion or anionic phospholipid expression between experiments with the SJM 27 Standard regular leaker, the SJM 20 regular leaker, and the MP 27 valves. Significant differences in platelet secretion and anionic phospholipid expression were observed between a SJM 27 Standard regular leaker and a SJM 27 high leaker valve. These studies suggest that leakage gap width within bileaflet valve pivots has a significant effect on platelet damage initiated by leakage flow.

Performance of enlarged blood pump models with five different impellers.

In earlier studies, a 5:1 enlarged pump model of the Kyoto-NTN Magnetically Suspended Centrifugal Blood Pump had been constructed and the flow characteristics investigated. Although the results obtained were satisfactory, the medium used was air. A 5:1 enlarged pump model using water as the medium thus was designed and constructed. Five different impeller blade profile designs were used in the present study. By varying (1) the blade profile design: forward, radial, and backward, (2) the number of blades used, and (3) the rotating speed, the flow characteristics of the pump were investigated. It was found that the impeller with the higher number of blades, used in the forward and straight blade profiles, have the best performance.

Measurements of enlarged blood pump models using Laser Doppler Anemometer.

In an earlier study (Chua et al., 1998, 1999a), a 5:1 enlarged model of the Kyoto-NTN Magnetically Suspended Centrifugal Blood Pump (Akamatsu et al., 1995) with five different impeller blade profiles was designed and constructed. Their respective flow characteristics with respect to (1) the three different blade profile designs: forward, radial, and backward, (2) the number of blades used, and (3) the rotating speed were investigated. Among the five impeller designs, the results obtained suggested that impellers A and C designs should be adopted if higher head is required. Impellers A and C therefore were selected for the flow in between their blades to be measured using Laser Doppler Anemometer (LDA), so as to have a better understanding of the flow physics with respect to the design parameters.

Recording and measuring the interior features of intracranial aneurysms removed at autopsy: method and initial findings.

Among the factors that determine the behavior of an intracranial aneurysm is the relationship between its volume and the size of the orifice. The investigative method described herein is the means being used to define that relationship in humans. It is a postmortem study that focuses on unruptured aneurysms. Central to the protocol was a synthetic rubber cast of the aneurysm's interior. The cast was made under normal arterial pressure so that unruptured aneurysms were reexpanded to lifelike size and shape. After the cast was removed intact from the specimen, the lumenal features recorded upon it were verified by comparison with the opened aneurysm. Working now only with the cast, the chamber was cut from the artery through its neck. The orifice area was determined by dividing it, mathematically, into many smaller, measurable forms. Chamber volume was ascertained by a fluid displacement technique. Both measurements were made with magnification and engineering instruments. Casts of ruptured or thrombosed aneurysms gave helpful morphological information, but were of limited value for measurement. The techniques are described, and examples of the initial results are presented.