# Investigating the Reliability and Dynamic Response of Fully 3D-Printed Thermistors
## 2 Materials and Methods  
The multi-material thermistor was designed with three core components: a polymer substrate, a pair of conductive electrodes, and a thin sensing layer. The overall device dimensions were adjusted based on the sensing area, which was determined from values reported in the literature [22,33,37]. During the thermistor design process, fabrication flexibility and printing resolution limits of the equipment used such as deposition width and layer thickness were also taken into account to ensure manufacturability and performance. The dimensions of the thermistor are depicted in Figure 1a. Two distinct designs featuring different sensing areas, referred to as D1 and D2, were developed using SolidWorks(r) (Dassault Systemes, Waltham, MA, USA). Figure 1b,c demonstrate the designed structure and a manufactured thermistor. The thermistors were constructed using three distinct materials: Ultimaker's PC filament for the substrate, an Ag paste (C2180423D2, Sun Chemical, Parsippany, NJ, USA) for the contact electrodes, and a PEDOT:PSS (Sigma-Aldrich, Burlington, MA, USA, 768650) for the sensing layer. Both the Ag paste and PEDOT:PSS were used in their original form as supplied by the manufacturers, without further synthesis or purification. Although primarily formulated for screen printing, based on the information gained from the literature, Ag and PEDOT:PSS materials can also be suitable for the dispensing method. Further technical details on the thermistor materials are provided in Table 1.  
Print parameters were set using Ultimaker Cura software (version 4.9) for the substrate layer made from PC, while Slic3r software (version 1.2.9) and FullControl GCode Designer [38] were used to generate the gcodes for the Ag and PEDOT:PSS layers. PC substrates were fabricated using an Ultimaker(r) 3D printer (Ultimaker B.V., Utrecht, The Netherlands) based on FDM technology. The substrates were c  
Figure 1: (**a**) Dimensions of thermistors, (**b**) design of the thermistor showing the layers, and (**c**) manufactured D1 thermistor. prior to further processing. The contact electrodes were then dispensed and cured inside a temperature incubator (GenBank-INC/50/DIG, Wolfabs, York, UK) at 100 \({}^{\circ}\)C for 2 h. Subsequently, the PEDOT:PSS sensing layer was dispensed onto the structure and cured at 80 \({}^{\circ}\)C for 1 h, as per the manufacturer's recommendation. Both the Ag and PEDOT:PSS layers were dispensed using a syringe-based micro-dispenser printer, Hyperl System 30M (Hyrel3D, Norcross, Atlanta, GA, USA). For each design, a set of five thermistors was fabricated. All printing parameters utilized for the thermistor layers are given in Table 2.  
The thermistors were characterized by exposing them to a temperature range of 25-45 \({}^{\circ}\)C while measuring their corresponding resistance. This process was conducted within an environmental control chamber, HygroGen (Rotornic Instrument Ltd., Crawley, West Sussex, UK), which was used to acclimatize the thermistors. The chamber's temperature and humidity were precisely controlled using the integrated HygroClip S control probe. The 3D-printed thermistor operates based on the temperature-dependent resistance behavior of its PEDOT:PSS sensing layer. As temperature changes, the electrical resistance of PEDOT:PSS alters. In other words, the resistance varies as a function of temperature. This variation is detected through the silver contact electrodes, which capture the corresponding electrical response. Therefore, resistance measurements, used to evaluate thermal measurement capability, were performed using the two-wire resistance measurement method with a Fluke 179 True RMS multimeter. After an initial stabilization period of 1 h at 25 \({}^{\circ}\)C, the temperature was adjusted in 2 \({}^{\circ}\)C increments up to 45 \({}^{\circ}\)C and then gradually reduced back to 25 \({}^{\circ}\)C for each measurement cycle. The thermal index (\(\beta\)), a critical parameter for evaluating the temperature sensor's measurement capability, was considered to evaluate