Abstract
Arteries with 1-mm thick walls can be successfully vitrified by loading cryoprotective agents (CPAs) such as VS55 (8.4 M) or less concentrated DP6 (6 M) and cooling at or beyond their critical cooling rates of 2.5 and 40 °C/min, respectively. Successful warming from this vitrified state, however, can be challenging. For example, convective warming by simple warm-bath immersion achieves 70 °C/min, which is faster than VS55’s critical warming rate of 55 °C/min, but remains far below that of DP6 (185 °C/min). Here we present a new method that can dramatically increase the warming rates within either a solution or tissue by inductively warming commercially available metal components placed within solutions or in proximity to tissues with non-invasive radiofrequency fields (360 kHz, 20 kA/m). Directly measured warming rates within solutions exceeded 1000 °C/min with specific absorption rates (W/g) of 100, 450 and 1000 for copper foam, aluminum foil, and nitinol mesh, respectively. As proof of principle, a carotid artery diffusively loaded with VS55 and DP6 CPA was successfully warmed with high viability using aluminum foil, while standard convection failed for the DP6 loaded tissue. Modeling suggests this approach can improve warming in tissues up to 4-mm thick where diffusive loading of CPA may be incomplete. Finally, this technology is not dependent on the size of the system and should therefore scale up where convection cannot.
Highlights
cryoprotective agents (CPAs) toxicity can generally be avoided by using lower concentration CPAs, but this means that the critical warming rate (CWR) increases from 55 °C/min for 8.4 M VS55 to 185 °C/min for 6 M DP67,22,34 to avoid devitrification during warming.[7,8,18,22,34]
To assess the warming efficacy, we considered warming rates from 2 140 °C vitrified state to 2 20 °C, where CPA is liquid and the low temperature leads to a reduction in toxicity
This study demonstrates a new approach to increase the warming rates of vitrified biomaterials using inductive heating of thin metal forms
Summary
The use of low temperatures to indefinitely bank and store tissues for eventual transplantation is a main goal of the field of cryobiology.[15,19,24] This approach, often termed cryopreservation, has been successfully used for long-term storage of cells, aggregates, and some smaller tissues.[10,15,19,35] the availability of many tissues and almost all organs is limited due to several important bottlenecks, including the need for faster warming in larger and thicker tissue systems.[11,12,16,18]. There will always be a lower concentration in the center of the loaded tissue which, especially in the case of thicker tissue, will necessitate faster rates of warming to successfully avoid crystallization damage. To address these issues, microwave warming[9,17,23,25,26,36] and nanowarming with nanoparticles[8,18] have been proposed to achieve faster warming of tissues than convection. As a demonstration of use, this approach was used to successfully rewarm DP6 loaded carotid arteries where convection failed
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