# Water Jacket Systems for Temperature Control of Petri Dish Cell Culture Chambers
## 4 Conclusions  
In this study, we investigated the thermal characteristics of a water jacket system used for temperature control of Petri dish cell culture chambers. In particular, we studied the temperature distribution across samples under stable conditions and the transition period of samples under dynamic conditions. Under stable reference conditions, the temperature gradient along the radial axis of a  
Figure 8: Comparison of the “transition period” for heating (37 to 45 \({}^{\circ}\)C) and cooling (37 to 29 \({}^{\circ}\)C) modes of the sample using different strategies, obtained by numerical simulations: (**a**) reference conditions. (**b**) Increased flow rate of water recirculating through the water jacket. (**c**) Decreased diameter of Petri dish. (**d**) Reduced sample volume stored in the Petri dish. (**e**) Increased thermal conductivity of the Petri dish by replacing polystyrene with glass. (**f**) Placing a heating element underneath the Petri dish. (**g**) Increasing the localized convection coefficient below the Petri dish. 35 mm diameter Petri dish was 3.28 \({}^{\circ}\)C. Under dynamic conditions, the transition period of a 35 mm Petri dish, which is the amount of time required to increase the sample temperature from 37 to 45 \({}^{\circ}\)C, was 27.5 min. These results indicate the limited capability of a conventional water jacket system for creating uniform temperature profiles and rapid temperature changes across a sample. We studied the role of various operational, geometric, and environmental conditions on the temperature distribution and transition period of the sample. Our results suggest that reducing the diameter of the Petri dish and incorporating a heater underneath the Petri dish were the two most effective solutions for reducing the temperature gradient across the sample under stable conditions. For example, reducing Petri dish diameter to 25 and 15 mm decreased the temperature gradient to 1.8 and 0.6 \({}^{\circ}\)C, respectively, whereas integrating a heater with an input power of 187 mW decreased the temperature gradient to 0.2 \({}^{\circ}\)C. Our results also suggest that reducing the diameter of the Petri dish, reducing sample volume, and using glass Petri dish chambers were the three most effective solutions for reducing the transition period of the sample under dynamic conditions. For example, reducing the Petri dish diameter to 25 and 15 mm decreased the transition period to 18 and 9.5 min, respectively, in comparison reducing the sample volume to 25% and using a glass Petri dish both decreased the transition period to 21 min. These results were obtained when heating the sample from 37 to 45 \({}^{\circ}\)C with almost similar transition periods obtained when cooling from 37 to 29 \({}^{\circ}\)C.  
Future work includes developing more accurate numerical models to consider (i) sample evaporation in long-term experiments, (ii) convective instabilities driven by Marangoni and buoyancy-driven flows caused by the inhomogeneous concentrations of species [28], (iii) presence of high-density cultured cells and (iv) presence of miniaturized self-sufficient devices for passive/active release of chemicals [29] or encapsulation of cells inside droplets [30]. **Supplementary Materials:** The followings are available online at [[http://www.mdpi.com/2076-3417/9/4/621/s1](http://www.mdpi.com/2076-3417/9/4/621/s1)]([http://www.mdpi.com/2076-3417/9/4/621/s1](http://www.mdpi.com/2076-3417/9/4/621/s1)). Figure S1: Prototype water jacket used for measuring the temperature profile across the top free surface of the Petri dish using an infrared camera. Figure S2: Characterizing the thermal performance of the water jacket system with respect to the flow rate of the water recirculating through the water jacket (\(Q_{water}\)). Figure S3: Characterizing the thermal performance of the water jacket system with respect to the temperature of the water entering the water jacket (\(T_{water}\)).