Figure 2. Temperature-triggered changes in gel behavior.

(a) Relative decrease of the NiPAAm:AAm gel diameter as a function of different NiPAAm:AAM ratios (left), and as a function of different MBAAM percentages (right). Experiments were performed in water. (b) Relative decrease of the gel diameter (for 85:15 w/v NiPAAm:AAm, 5% MBAAM) in water (○) and in PBS buffer (■) when the temperature is changed from room temperature to 50 °C using a water bath. The diameter of the gel at 24 °C (Do) was 7.3 ± 0.08 mm in water and 7.2 ± 0.11 mm in PBS. All data points correspond to the average of at least 3 different experiments and the error bars are calculated using the standard deviation. (c) Change of the NiPAAm:AAm gel diameter in water when the temperature is cycled between 37 °C and 45 °C, showing that NiPAAm gels can be thermally actuated for several cycles between 37–45 °C. (d) Percentage of TRITC-dextran (20 kDa) released from a device immersed in water when thermally actuated (◻) at 45 °C for 15 minutes once per day for four consecutive days, or not actuated (■). All devices were kept at 37 °C prior to and between actuations. Fluorescence (λ_ex = 540 nm, λ_em = 580 nm) was measured using a plate reader as a function of time. All data points correspond to the average of at least 3 different experiments and the error bars are calculated using the standard deviation. (E) Release of different MW fluorescent dextran from capsule over time.