Fig. 6: Design and physical limits of joule heating as the external heat source for rewarming.
From: Rapid joule heating improves vitrification based cryopreservation
a To achieve rapid and sufficiently uniform rewarming (area in red), the pulse width (tp) can be selected based on biosystem heat diffusion length (h). When the pulse width is much smaller than heat diffusion time (td = h2/2α, α is the thermal diffusivity of the biosystem: 10−6 m2/s was used for the calculation), non-uniform warming occurs. For longer pulse widths (i.e., > 10 td), the achieved rewarming rate is slow. We assume sufficiently uniform rewarming can be achieved using tp = 1 ~ 10 td. b Achievable warming rate inside the biosystems as a function of biosystem heat diffusion length. The black and red lines represent the warming rates (calculated as 200 °C / tp) when tp = td and tp = 10 td, respectively. The achieved warming rate decreases with increasing pulse width. c Within the rapid and uniform warming region defined in a, selection of cryoprotective agent (CPA) concentration for optimal cryopreservation of different biosystems using external joule heating source. The upper bound of CPA concentration (green line) is estimated using the longer pulse width (i.e., tp = 10 td) and glycerol as the CPA (i.e., relatively high critical warming rate). The lower bound of CPA concentration (blue line) is estimated using the shorter pulse width (i.e., tp = td) and propylene glycol (PG) as the CPA (i.e., relatively low critical warming rate). The CPA toxicity is the major failure mode of cryopreservation in the upper corner region (i.e., orange color). The devitrification is the major failure mode of cryopreservation in the lower corner region (i.e., blue color).
