Design and evaluation of an air-insulated catheter for intra-arterial selective cooling infusion from numerical simulation and in vitro experiment.

Intra-arterial selective cooling infusion (IA-SCI) is a promising method for neuroprotection of patients with acute ischemic stroke. One shortcoming of IA-SCI is the elevated delivery temperature caused by the cold perfusate warming along the catheter pathway. Therefore, increasing the thermal resistance of the catheter is of significant importance. In this manuscript, an air-insulated catheter was designed and manufactured through extrusion molding technique. The computational fluid dynamics (CFD)-based thermo-/hemo-dynamics models were exploited to evaluate the thermal conductivity of the catheter. Compared with commercially available endovascular catheters, its thermal insulation property was analyzed through an in vitro experiment. The temperature of the 4°C perfusate (20 ml/min) increased to 14.2°C ± 0.2°C after being transferred to the distal tip of the air-insulated catheter, which was significantly lower than that (30°C) of commercially available alternatives. Moreover, the simulated blood (56% glycerin and 44% bi-distilled water, 37°C) in the middle cerebral artery of the artificial circulating system was cooled down to 29.7°C ± 0.1°C by this perfusate. The cooling process of the brain tissue was also estimated by a biological heat-transfer mathematical model, which showed a 2°C decrease within the initial 1 min infusion. This study demonstrated that the air-insulated catheter for IA-SCI was promising in vitro in terms of its high cooling efficiency and could be a competitive intervention catheter for therapeutic hypothermia.

The intra-arterial selective cooling infusion system: A mathematical temperature analysis and in vitro experiments for acute ischemic stroke therapy.

INTRODUCTION: The neuroprotection of acute ischemic stroke patients can be achieved by intra-arterial selective cooling infusion using cold saline, which can decrease brain temperature without influencing the body core temperature. This approach can lead to high burdens on the heart and decreased hematocrit in the scenario of loading a high amount of liquid for longtime usage. Therefore, autologous blood is utilized as perfusate to circumvent those side effects. METHODS: In this study, a prototype instrument with an autologous blood cooling system was developed and further evaluated by a mathematical model for brain temperature estimation. RESULTS: Hypothermia could be achieved due to the adequate cooling capacity of the prototype system, which could provide the lowest cooling temperature into the blood vessel of 10.5°C at 25 rpm (209.7 ± 0.8 ml/min). And, the core body temperature did not alter significantly (-0.7 ~ -0.2°C) after 1-h perfusion. The cooling rate and temperature distributions of the brain were analyzed, which showed a 2°C decrease within the initial 5 min infusion by 44 ml/min and 13.7°C perfusate. CONCLUSION: This prototype instrument system could safely cool simulated blood in vitro and reperfuse it to the target cerebral blood vessel. This technique could promote the clinical application of an autologous blood perfusion system for stroke therapy.

The blood heat exchanger in intra-arterial selective cooling infusion for acute ischemic stroke: A computational fluid-thermodynamics performance, experimental assessment and evaluation on the brain temperature.

Intra-arterial selective cooling infusion with the autologous blood (IA-SCAI) is a promising therapeutic hypothermia induction method for conferring neuroprotection to acute ischemic stroke (AIS) patients. The blood heat exchanger (BHE) plays a crucial role in IA-SCAI's cooling capacity. However, there are no BHEs currently available that are specifically designed for the IA-SCAI, which requires a low blood flow to be compatible with cerebral hemodynamics. In an effort to develop a BHE for AIS patients, a prototype of a commercial BHE, Medtronic MYOtherm XP®, was mathematically modeled; specifically, computational fluid dynamics (CFD) was used to analyze its hemo- and thermo-dynamic characteristics under low blood flow including temperature distribution, velocity field and shear stress. Our numerical model predicted the hemolysis index to be 0.0041%-0.0581% inside the BHE with blood flows rates of 10 ml min-1-50 ml min-1. The in vitro heat transfer experiment showed that the BHE efficiently cooled the simulated blood from the initial 37 °C-5.8 °C within 150 s by using cold water (200 ml·min-1, 0 °C). The cooled simulated blood was able to cool the simulated blood in the middle cerebral artery of an artificial circulating system from 37 °C to 16.8 °C-33.7 °C depending on the blood perfusion rate (10-50 ml/min). A biological heat transfer mathematical model showed that brain tissue could be cooled by 2 °C within the initial 1min of infusion. This study verified the feasibility of using a commercial BHE for IA-SCAI and provided insights into its cooling capacity for therapeutic hypothermia.

Protection of multiple ischemic organs by controlled reperfusion.

Reperfusion injury (RI) is a harmful complication that takes place during recanalization treatment of ischemic organs. Currently, there are no efficacious treatments for protecting the organs against RI. Therefore, it is necessary to discover new strategies to prevent RI. As a novel intervention technique, controlled reperfusion has promising effects on protecting multiple organs from RI, and it is done by adjusting physical parameters of blood flow or chemical compositions of the reperfusion liquid. In this brief review, the status of various controlled reperfusion methods is presented, as well as their application in the protection of ischemic organs.

An overview of graphene-based hydroxyapatite composites for orthopedic applications.

Hydroxyapatite (HA) is an attractive bioceramic for hard tissue repair and regeneration due to its physicochemical similarities to natural apatite. However, its low fracture toughness, poor tensile strength and weak wear resistance become major obstacles for potential clinical applications. One promising method to tackle with these problems is exploiting graphene and its derivatives (graphene oxide and reduced graphene oxide) as nanoscale reinforcement fillers to fabricate graphene-based hydroxyapatite composites in the form of powders, coatings and scaffolds. The last few years witnessed increasing numbers of studies on the preparation, mechanical and biological evaluations of these novel materials. Herein, various preparation techniques, mechanical behaviors and toughen mechanism, the in vitro/in vivo biocompatible analysis, antibacterial properties of the graphene-based HA composites are presented in this review.