Handling electric connections in 3D-printed electrodes and sensors. Part I. Understanding and improving tracks and contacts

Handling electric connections in 3D-printed electrodes and sensors. Part I. 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Part I. Understanding and improving tracks and contacts Ivan Verlangieri, Thawan Gomes de Oliveira, Fernando Silva Lopes, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5968075/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Voltammetric and amperometric sensors typically consist of three sections: an electroactive surface, an electrode substrate, and connection tracks or wires to a potentiostat or other electronic circuit. While the electrical resistance of metal-to-metal connectors can usually be disregarded in such sensors due to their low contact resistance, this is not the case when semiconductor materials, conductive polymers, or composites are involved. This study focuses on the electrical behavior of 3D-printed conductive polymer tracks and connections to metals, aiming to improve and understand their limitations. Carbon black PLA (CB-PLA) was chosen for its favorable electrical properties. Results show that the printed tracks exhibit higher resistivity (17 Ω·cm) than the raw filament (6 Ω·cm). The electrical contact resistance (ECR) found between nickel-plated metals and CB-PLA was considerably high, in the order of 10 2 to 10 3 Ω. The metal-polymer contact promoted solely by pressuring the parts (e.g., with alligator clips) proved to be unstable and, as such, a potential source of noise. Welded metalpolymer contact (WMPC) was developed using induction heating to improve and secure metal-polymer interfaces. Furthermore, it has been demonstrated that the high resistivity of the tracks and connections created by 3D printing actually has no implication on the electrochemical behavior of the sensor, other than the Ohmic drop in these sections that must be considered to ensure the proper functioning of sensors involving current flow. The findings indicate that while 3D-printed conductive polymer sensors show promise for widespread use, careful consideration of ECR and thermal effects is crucial for reliable performance. Electrochemical sensors 3D printing electrical contact resistance cyclic voltammetry welded metal-polymer contact Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Electrochemical sensors, like voltammetric and amperometric ones, can be envisioned as a set of three sections (Fig. 1 ): (1) the electroactive surface, which is responsible for the desired sensing behavior; (2) an electrode substrate, whose surface is the electroactive one or serves as support for deposition of different material or for modifications in order to achieve the desired selectivity and sensitivity; and (3) electric connections and tracks to the potentiostat or other electronic circuit to which counter and/or reference electrodes are separately connected. Actually, the conduction of electric current to and from the electrode is carried out by a combination of wires, cables, printed circuit board traces, and other conductive materials, but they will be collectively referred to as a "track" herein. Usually, this section of connections and tracks is a combination of wires and connectors made of different metals, such as copper or nickel-plated copper wires, gold-plated connectors, tin-lead solder, and so on. Thanks to the high electrical conductivity and typical dimensions, the resistance of these segments is low ( < < 1 Ω). In addition, every time the surfaces of two different conducting bodies are put into contact, another resistance arises: the so-called electrical contact resistance (ECR). It is important to highlight that the term "electric contact resistance" in this context differs from its usage in other papers [ 1 , 2 ]. ECR refers to the resistance encountered when current flows between two conductive surfaces in contact, while any additional resistance is actually considered track resistance. ECR depends on several factors, such as contact area, roughness of the surfaces, formation of oxide layers, moisture, and so on. ECR between two metal segments – both connected by soldering, crimping, or simple pressing contact – is low. As a result, one can assume that, even when a significant current flows, the Ohmic voltage drop (iR potential drop) over this connection track is small enough to be disregarded for most practical purposes, and the potential at the electrode substrate is assumed to be the same as at the potentiostat input. Unfortunately, the same is not true when semiconductor materials, conducting polymers, or composites are used to make these tracks, connectors or even the electrode substrate. In recent years, 3D printing processes – especially fused deposition modeling (FDM) – of pure and composite materials have opened the door to several new possibilities for the production of sensors and analytical devices [ 1 , 3 – 6 ]. In this context, several groups have proposed the use of conductive polymers for the creation of both the electrode substrate and its wiring and connections [ 2 , 7 , 8 ]. Although they recognize the importance of the electrical resistance of these new materials, in general, the studies are focused on the investigation of the devices as electrochemical sensors. The present study shifts the focus from the possibilities and behavior of the electroactive surface to the tracks and connections involving 3D-printed materials in the device construction. It aims to gain a deeper understanding of the behavior of a typical conductive polymer and its necessary connection with metals, as well as how to improve and overcome the imposed limitations. 2. Material and Methods Hexaammineruthenium(III) chloride (Sigma-Aldrich, Burlington, MA) and KCl (Synth, Diadema, Brazil) were used as received. Solutions were prepared using deionized water (resistivity ≥ 18.2 MΩ cm) from a Milli-Q system (Millipore, Billerica, MA). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed in a DSC Q20 and a TGA Q500 (TA Instruments, New Castle, DE), respectively. Resistance and four-point resistance measurements were carried out using a 3458A multimeter (Hewlett-Packard, Palo Alto, CA). The temperature control of the specimens was achieved using an electric oven IPP 500 (Memmert, Schwabach, Germany). All the 3D printed devices were designed in Inventor Professional 2023 (AutoDesk, São Rafael, CA), and printed with an independent dual extruder (IDEx) Tycoon printer (Kywoo3D, Shenzhen, China), after slicing the model using Ultimaker Cura 4.11.0 (Utrecht, Netherlands). The insulating parts were printed in either PLA+ (TopInk, Piracicaba, Brazil) or PLA Easyfill (3DFila, Belo Horizonte, Brazil). ProtoPasta conductive PLA (Vancouver, WA) was used for the electrodes and conducting tracks. The 3D printing conditions and parameters are detailed in the Supplementary Material. Welded metalpolymer contact (WMPC) was achieved either by using a soldering station system (Yaxun 886D, Guangzhou, China) or a mini zero voltage switching (ZVS) module (AliExpress, Hangzhou, China) powered by an adjusted power supply B&K Precision 1550 (Yorba Linda, CA). The electrochemical experiments were carried out with a potentiostat/galvanostat Autolab-PGSTAT302N (Metrohm, Netherlands). Platinum wire and Ag/AgCl, KCl (sat.) (+ 0.197 vs SHE) electrode[ 9 ] were used as auxiliary and reference electrodes, respectively, in a 25 mL electrochemical cell. Cyclic voltammetry (CV) experiments of 0.60 mmol L − 1 of the [Ru(NH 3 ) 6 ] 3+ in KCl 0.10 mol L − 1 were initially performed in a potential range from 0.3 V to -0.5 V. The outer sphere redox probe [Ru(NH 3 ) 6 ] 3+ was used to evaluate the electrochemical performance of the 3D printed electrode [ 10 ]. Data processing was carried out using NOVA software version 2.0 (Metrohm, Netherlands) and Origin 2024 software (OriginLab, Northampton, MA). 3. Results and Discussion Usually, the conductive polymers used for FDM 3D printing are composite materials based on an insulating polymer, such as acrylonitrile butadiene styrene (ABS) or poly(lactic acid) (PLA), and a conductive filler, such as graphite, graphene, or carbon black (CB) [ 4 ]. Some of the materials are prepared in-house [ 11 , 12 ], but there are commercial options available. Protopasta CB-PLA was chosen, because it is a popular option with good electrical characteristics [ 13 ]. The thermogravimetric analyses (Figures S1 and S2) of PLA Easyfill and CB-PLA filaments suggest that the CBPLA has a small amount of mineral filler (ca. 1%) and that the approximate ratio of PLA:CB is 3:1 (w/w). In addition, both materials start to decompose in air above 300°C due to the PLA base. DSC reveals that the glass transition (T g ) for both materials is 54°C (Figures S3 and S4). The thermal behavior will be important in analyzing the results shown in the next sections, as well as in the introduction of WMPC. 3.1 Resistivity and resistance of the CB-PLA filament and printed tracks Scanning electron microscopy images obtained by Dijkshoorn et al. [ 14 ] and Daniel et al. [ 15 ] suggest that the CB particles in the PLA-CB are smaller than 1 µm and they form agglomerates, in which the particles are in contact to each other. The conductive property of the CB-PLA filament can be explained by two basic mechanisms: electron transfer between particles inside the CB agglomerates and by tunneling between particles isolated by small gaps (less than 10 nm) [ 16 ]. For cylindrical or prismatic bodies of a homogenous material, the resistance ( \(\:R\) ) is given by: $$\:R=\rho\:\frac{l}{a}$$ 1 where \(\:\rho\:\) is the resistivity, \(\:l\) and \(\:a\) are the length and sectional area, respectively, of the body. When the ECR is significantly lower than the bulk resistance, a simple ohmmeter can be used; otherwise, a four-point probe method should be employed to measure the material's resistance [ 17 ]. The resistivity of the raw CB-PLA filament obtained by the 4-point approach (Fig. 2 ) was 6.0 Ω·cm at 25°C, which is significantly smaller than stated by the manufacturer 1 (15 Ω·cm), but compatible with the value deduced from the resistance of a 10-cm long segment of filament (2 to 3 k Ω) also informed by the manufacturer. Most probably, the manufacturer has not considered the ECR during the measurements, which is significant as will be shown in the next section. There is a significant variation in the resistivity during a temperature cycling from 10 to 40°C (Fig. 3 ). This feature has been suggested to be used for the implementation of thermal sensors [ 3 , 18 , 19 ]. However, the thermal cycling experiments show drifts alongside the systematic variation of resistance with temperature, a behavior that could be explained not only by a hysteresis effect, but also by a permanent modification of the complex network of particles and aggregates. A possible explanation for this fact is that, even below T g , the polymer suffers structural modification under stress, resulting in a new configuration of the CB agglomerates. Thus, when the filament is removed from the original spool (diameter of 15 cm) and placed in a smaller diameter spool (6.7 cm) for the test, stress arises, which is alleviated under gentle heating. After printing, the CB-PLA filament material does not undergo significant physical or chemical changes, but its apparent resistivity increases. This increase can be explained by two main processes. First, any printed track is formed by combining traces deposited from the 0.4 mm extrusion nozzle, resulting in air pockets that are non-conductive. Second, PLA can absorb moisture when stored. During printing, the vaporization of this accumulated moisture creates microbubbles in the material. Consequently, the printed polymer is not as compact as the original filament, leading to higher apparent resistivity. The apparent resistivities at 25°C for cylindrical tracks with diameter of 0.5 mm and 2.0 mm were (16.6 ± 0.4) Ω·cm and (17.1 ± 0.2) Ω·cm, respectively, in contrast to 6.0 Ω·cm of the raw filament. Therefore, in the forthcoming evaluations of the resistance of 3D-printed objects, an apparent resistivity of 17 Ω·cm will be used, rather than the lower value applicable only to the brand new filament. 3.2 Behavior of electrical contact resistance with time, current, and temperature Despite the thermal behavior discussed in the previous section, CB-PLA printed electrodes and tracks can still be useful. However, when the device is integrated into an actual circuit, ECR comes into play. A great number of factors determine the effective electrical resistance observed when two conducting objects are put into contact [ 20 ]. For metals, this resistance is low enough (< 10 − 2 Ω) to be disregarded when a low current flows through it. However, the contact between a conducting polymer and a metal is expected to be much more resistive [ 17 ]. The simplest way to use 3D-printed electrodes consists in using pressure to create the contact between the polymer and the metal parts, such as a screw or an alligator clip. A stainless steel screw has been used [ 1 ], but such contact may be subject to instabilities that cause variations in ECR, resulting in an increased level of noise or irreproducibility. To evaluate this behavior, 3D printed discs with a diameter of 5 mm and a thickness of 4 mm were pressed at 400 kPa between two nickel-plated steel tapes, which were used as contacts for resistance measurement. Thanks to the ECR, the initial resistance is different for each time that the electrodes are applied. Figure 4 shows the resistance over time for a specific disk and is representative of the various phenomena observed in the several experiments conducted. The initial resistance was 1.0 kΩ, but this value significantly decreases after the first few minutes (plot a in Fig. 4 ). Although it appears stable in terms of relative resistance variation after that, it does not stabilize even after 2.5 hours, as can be observed in the logarithmic graph. This variation can be attributed exclusively to changes in ECR, as the internal resistance of the printed disk is estimated to be only 35 Ω. In other words, the sum of the contact resistances of the two surfaces is at least an order of magnitude greater than the resistance of the body. To emphasize the importance of contact surface quality, both surfaces of the disk were sanded with 500grit sandpaper, removing approximately 5 µm from each one (plot b in Fig. 4 ). Although the macroscopic appearance suggests a reduction in the irregularities from the 3D printing process, the surface now exhibits greater roughness, which hinders contact. This behavior was systematically observed for all the printed disks. It was also observed in all cases that, after the disk was released from the pressurization process, the resistance returned to higher levels (as in plot c in Fig. 4 ). Sometimes, the return is to values close to those observed in the previous run, but the value can be even higher, as shown in Fig. 4 . These results suggest that creep resistance, which is also observed with other materials [ 20 ], does not cause permanent deformation of the surface in the case of CB-PLA, indicating that it is elastic. The roughness obtained after sanding can be reduced by exposing the surface to a temperature higher than the material's T g . For example, exposure for just one minute on a glass surface at 100°C significantly reduces the ECR (plot d in Fig. 4 ). Pure mechanical contact can also exhibit erratic behavior, with significant resistance changes, as shown by the event occurring around 7 h in the last run. That is, even after 7 h of established contact, a subtle mechanical alteration can affect the ECR. Equally surprising is that, even after 24 h, the resistance continued to decrease. The contact between two materials, such as a metallic electrode and a conductive polymer, can also result in the formation of a semiconductor junction, where the current does not vary linearly with the applied voltage; that is, it can exhibit non-Ohmic behavior. To assess this behavior, a current-voltage curve of a CB-PLA filament with a wrapped nickel-plated copper wire was obtained (Fig. 5 ). After compensating the estimated resistance of the bare filament, no evidence of nonlinearity was observed (R 2 = 1.000), which suggests that the junction CB-PLA/nickel is an Ohmic contact. ECR exhibits varying behavior during temperature cycling. Two wire-wrapped metal contacts prepared on the same piece of CB-PLA filament may show different values and trends over temperature changes (Fig. 3 ). This chaotic behavior can be explained by the interplay of the material's intrinsic resistivity with mechanical and thermal modifications at the contact points, affecting the efficiency of charge transport. Any practical usage of a CB-PLA 3D-printed electrochemical sensor involves forming one or more contacts between the polymer and metal wires or rods. Therefore, one cannot ignore ECR in evaluating or using the device, with the possible exception of a potentiometric one due to the low current [ 21 ]. Reducing ECR is not a simple task, but making it at least more stable over time, temperature, and pressure is feasible. This was accomplished by melting the polymer to improve the contact with the metal, as will be discussed in the next section. 3.3 Welded metal-polymer contact (WMPC) A first demonstration of using a WMPC was shown in our previous paper, in which one of the ends of a copper wire was incorporated in the electrode body during the 3D printing process [ 22 ]. The device was designed to have a CB-PLA electrode and a pure PLA body, in which an open channel allows the copper wire be guided to outside the sensor. A special command is inserted in the g-code to pause the printer after printing a specific layer. During the pause, the end of the copper wire is heated using a soldering iron at 220°C allowing the insertion of the wire tip into the CB-PLA electrode. The rest of the wire is fitted into the channel, which is closed while printing resumes. Since this process has been introduced, we have substituted the pure 0.5 mm copper wire by a nickelplated wire wrapping copper wire AWG 28, which is equally appropriate for the electric contact, but more malleable, easing the device manufacturing. Although useful, this strategy has the drawback of requiring the manual insertion of the electrode during a pause of the printing process. Furthermore, one of the most interesting aspects of 3D printing is precisely the possibility of creating more intricate devices produced as automatically as possible. Thus, it is natural to seek the creation of devices that incorporate 3D-printed conductive tracks as well. However, a metal-polymer contact will be inevitable at some point in the setup. Figure 6 exemplifies how WMPC is implemented in a 3D-printed test specimen designed for the evaluation of the resistance of tracks and contacts. The idea for creating the contact involves ending the track with a CB-PLA region that has a hole of appropriate diameter to accommodate the metal terminal. After a few tests, nickel-plated steel nails proved to be a convenient option resulting in a robust and corrosion-resistant contact. Here, a soldering iron at 220°C was initially used to heat the nail head until the polymer was melted by thermal conduction. A later improvement was to introduce electromagnetic induction heating. The 3D-printed device, with the nail positioned in the contact hole, is placed inside the coil of a ZVS module operating at 100 kHz. After a few seconds, the nail, being made of ferromagnetic steel, is heated to a temperature that causes the polymer to melt. This process is faster and more reliable and reproducible than the simple heating with a solder iron. The ZVS module is simple and inexpensive. It operates from 5 to 12 V and the output power is proportional to this voltage. Thus, one can control the energy applied to the metal piece by changing the voltage and/or the time. The pre-manufactured 10-turns coil (30 mm long with i.d. of 17 mm) is appropriate to enclose typical electrodes and sensors for electroanalytical purposes. A thermal camera was used to characterize the profile of delivered power as a small steel washer is inserted in various positions along the inside coil. The result is shown in Fig. 7 . The current consumed in heating can be obtained by the difference between current with and without ferromagnetic material inserted in the coil. From the power and the pulse time, one can estimate and control the total energy, which will determine the maximum temperature reached by the ferromagnetic piece. Of course, the final temperature depends on several parameters, such as the mass, shape, thermal conductivity, and coupling efficiency of the metal and the thermal capacity and conductivity of the surrounding materials. Therefore, the best results are obtained through empirical optimization for each case. However, one general guideline should be observed. As the metal is heated, part of the heat is immediately dissipated into the surroundings, i.e., in locally heating the polymer. As a result, slow heating (low power over a long time) can cause excessive heating not only of the CB-PLA, but also of the device body, potentially leading to permanent deformation. On the other hand, heating too quickly can cause a rise in the local temperature sufficient to start the decomposition of CB-PLA – above 300°C, according to the TGA (Figure S2). Welding by this inductive heating process was used to implement the WMPC of the test specimens and devices shown from now on. Three test specimens as the one shown in Fig. 6 were submitted to successive steps of heating from 25 to 40°C, and all the six contact resistances were monitored (Table S3). Compared to the purely mechanical contacts (as shown in Fig. 3 ), the WMPCs are smaller and more stable. Resistances ranging from 89 to 233 Ω (25°C) and TC smaller than 4.0 Ω/°C were obtained. Moreover, unlike mechanical contacts that tend to exhibit erratic behavior after heating cycles, WMPCs seem to benefit from heating to moderate temperatures. The heating probably helps in relaxing internal stresses generated during the formation of the contact by induction heating. As a result, more reproducible resistances with lower thermal coefficients were observed. Since the induction heating acts only on ferromagnetic metals, an approach has been proposed as an alternative for the incorporation of a copper wire during the 3D printing process. A straight empty channel from the CB-PLA electrode to the end of the device was incorporated in the design. After the printing process is finished, a ferromagnetic wire or strip is inserted into the channel. The portion of the device containing the CB-PLA electrode and the end of the wire is centered in the ZVS coil. When the ZVS module is powered, one can easily feel the polymer melting while the wire is gently pressed. After the insertion of the wire into the electrode, the device is allowed to cool down and the contact is ready. Two ferromagnetic materials have been used in this study: guitar strings and nickel-plated steel strips. Nickel-plated steel strips are used as connections for lithium batteries by using spot welding. Usually, they are available with a width of 4 or 8 mm and different thickness. In turn, guitar strings are designed to have good magnetic coupling, then usually they are made of steel with a thin layer of nickel to prevent oxidation. Any of the six guitar strings can be used. Of course, the thinnest string (1:E) demands more heating time than the thicker one (6:E) due to the smaller energy transfer. These strings were used in the experiments described in the next section. 3.4 The impact of the resistances on an electrochemical sensor The shape and dimensions of the devices designed for the present test were inspired by our previous work [ 22 ]. However, once again, the objective of the present study was not to explore analytical applications or electrochemical studies, but to evaluate the impact of the electrical resistance of the internal components of the devices. The electrodes were designed with a diameter of 5 mm and a thickness of 4 mm, being completely embedded in the body of the device, exposing only the circular surface. During the slicing step before 3D printing, the wall thickness and the infill percentages indicated in Fig. 8 were selected. As shown in the previous section, experimentally evaluating the resistance of this electrode is challenging due to significant contact resistance. However, it can be estimated using the dimensions and apparent resistivity of the CB-PLA. The resistance between the faces of a 100% infill body is expected to be 35 Ω, increasing to 52 Ω for a 0% infill. Naturally, intermediate infills would result in intermediate resistances. At first glance, a 100% infill should always be adopted to reduce resistance. However, it should be considered that if the incorporation of metallic contact is desired, partial infill is more appropriate, as the melting of the polymer creates space for its accommodation. It is worth noting that, regardless of the infill percentage, this resistance is generally much lower than that of the tracks or polymer-metal contacts. For test purposes, three different tracks and connections were created for the same electrode. Two of them were made of CB-PLA with different diameters: 0.5 and 2.0 mm. The first lies almost in the limit of the printer resolution in the XY plan (0.4 mm) and presents high resistance (44 kΩ calculated), while the second with generous diameter has smaller resistance (2.7 kΩ calculated). The third connection was created with a metallic conductor – guitar string segment – and, thus, with a resistance smaller than 1 Ω. Of course, all the three CBPLA/metal connections contribute an additional ECR around 10 2 Ω. These three options, therefore, can be used to evaluate the behavior of the same electrode – which has a resistance on the order of 10 1 Ω – using connections with resistance varying by three orders of magnitude: 10 2 Ω, 10 3 Ω, and 10 4 Ω for guitar string, 2.0 mm, and 0.5 mm CB-PLA tracks, respectively. Figure 9 shows cyclic voltammograms obtained for the same electrode but using the different tracks. Since the guitar string has a much smaller resistance than the 0.5 and 2.0 mm CB-PLA tracks, it was used as a reference for the experiment. These connections with three different orders of resistance magnitude help us to demonstrate a misconception about the impact of the connection resistivity on the electrochemical process. As shown in Fig. 1 , the characteristic behavior of a sensor is determined by its electroactive surface. The substrate layer (b), along with any cabling or connectors (c), does not affect the electrochemical behavior. However, depending on the magnitude of the current flowing through the circuit, there can be a significant iR voltage drop if the resistance is high. The operational amplifier’s feedback ensures that its input remains at zero volts (GND), regardless of the current flowing through the electrode and the feedback loop. However, due to the Ohmic drop, the electroactive surface will experience an offset voltage. Consequently, the electrochemical process that occurs will correspond to the actual potential difference at the electrode/electrolyte interface, rather than the one applied by the instrument on the assumption that the working electrode is settled at zero volts. This behavior can be clearly explained by the experiments shown in Fig. 9 . The same electrode, when connected through the 0.5 mm track, exhibits a shape that appears entirely different compared to when using the guitar string (D). However, when the offset voltage is subtracted from the applied potential value, the peak potentials align closely with the expected values (E). Even so, the voltammograms are significantly different because the scanned potential range is smaller. For example, in Fig. 9 D, when the scan supposedly reaches − 500 mV, considering the iR drop, the electrode interface is actually exposed to -360 mV. Therefore, a possible strategy would be to anticipate the Ohmic drop and compensate for it in the choice of potential range. However, since the actual profile involved in a new CV is not known in advance, it would be necessary to repeat the experiments. It should also be noted that, with the expansion of the potential range (from 800 mV to 931 mV in this case), it becomes necessary to adjust the scan rate accordingly, ensuring that the 931 mV are scanned within the same period as the original 800 mV, i.e., 116 mV/s instead of 100 mV/s. Table 1 shows the parameters obtained from the analysis of the voltammograms presented in Fig. 9 , allowing for a comparison of the electrode connected with the guitar string and with the 0.5 mm and 0.2 mm tracks, using both the original and modified potential range and scan rate. In addition to the variation in peak potential, the transfer coefficient was also calculated [ 23 ]: $$\:{\alpha\:}_{c}=\frac{RT}{F}\frac{dln\left|{j}_{c}\right|}{dE}$$ 2 where R , T , F , and j c are the gas constant, thermodynamic temperature, the Faraday constant, and the density of cathodic current, respectively. When the 0.5 mm track is used, α becomes significantly different from 1.0, leading to the false assumption that the electron transfer might not be efficient. However, when the same track is used with proper iR drop compensation, α c becomes closer to 1.0, similar to the other connections with lower electrical resistance. Table 1 Distortion of voltammetric parameters obtained for the CVs of [Ru(NH 3 ) 6 ] 3+/2+ due to the resistance of the connection between the potentiostat and the working electrode (sensor) Condition a E p,a / mV E p,c / mV ∆E p / mV I p,a / µA I p,c / µA α c guitar string (400 Ω) -122 -229 107 2.61 5.58 1.05 0.5 mm (35.6 kΩ) -24.3 -432 408 2.16 4.68 0.67 0.5 mm compensated b -105 -267 162 2.48 5.00 1.00 2.0 mm (2.59 kΩ) -114 -238 124 2.57 5.16 1.04 2.0 mm compensated c -113 -238 125 2.57 5.16 1.03 a The default condition was 300 to -500 mV at 100 mV/s b 318 to -613 mV at 116 mV/s c 301 to -508 mV at 101 mV/s Even after the use of a compensated potential range and scan rate, there is still some discrepancy in the voltammograms using 0.5 and 2.0 mm tracks (Fig. 9 ), but this cannot be easily overcome because the new scan rate, calculated based on the new potential range, is kept constant. Ideally, the scan rate applied by the instrument should be variable so that the effective scan rate perceived by the electrode remains constant after compensating for the Ohmic drop. Obviously, this task is not simple and would require dynamic control of the scan rate, which becomes unfeasible. This type of issue, which is not a deficiency of the electrode itself but rather the way the measurements are conducted, can be better addressed by choosing the appropriate instrument, which will be the subject of the second part of this work. 4. Concluding Remarks The conductive polymer used in the 3D printing of sensors and other electrochemical devices escalates the electrical resistance of the electrode substrate, the tracks, and the connector junction, compared with metallic counterparts. Obviously, there may be resistance to electron transfer at the electroactive surface in contact with the solution, which is resistive by itself, but these issues are beyond the scope of the present study. While the resistance of the tracks may primarily contribute to the total resistance, we have shown that the polymer-metal ECR can be the most significant factor affecting stability, reproducibility, and noise in the measurements. In this context, utilizing WMPC is an appealing strategy, because it enhances stability, reduces ECR and it is easy to implement. Overall conductive polymer resistance can become a crucial factor in the use of 3D-printed working electrodes and the interpretation of voltammetric results, as uncompensated Ohmic drop causes an alteration of the true potential applied to the electroactive surface/solution interface. Some researchers have attributed these alterations to anomalies or poor performance of the conductive polymer as an electrode. However, we have demonstrated that the electrochemical behavior is independent of the significant electrical connection’s resistance. This resistance can, in fact, be compensated for by using the appropriate instrumentation, and this specific topic will be covered in detail in the second part of this study. Declarations Competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This work was supported by FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo (2017/13137-5). The authors thank for the fellowships granted by CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico (307259/2021-8, 180838/2024-5, 308996/2023-2 and 141495/2023-5). Author Contribution I.V., T.G.O., and F.S.L.: data curation, investigation, and writing–review and editing. I.G.R.G.: methodology, supervision, and writing–review and editing. L.A.: funding acquisition, methodology, project administration, supervision, and writing–review and editing. C.L.L.: conceptualization, formal analysis, funding acquisition, methodology, project administration, supervision, writing–original draft, and writing–review and editing. Acknowledgments This work was supported by FAPESP (2017/13137-5). The authors thank for the fellowships granted by CNPq (307259/2021-8, 180838/2024-5, 308996/2023-2 and 141495/2023-5). Data Availability The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request. References Veloso WB, Paixão TRLC, Meloni GN (2023) 3D printed electrodes design and voltammetric response. Electrochim Acta. 449:142166.https://doi.org/10.1016/j.electacta.2023.142166 Veloso WB, Paixão TRLC, Meloni GN (2024) The Current Shortcomings and Future Possibilities of 3D Printed Electrodes. 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Analytical Chemistry 94:6417 – 29.10.1021/acs.analchem.1c05523 Crapnell RD, Ferrari AGM, Whittingham MJ, Sigley E, Hurst NJ, Keefe EM, Banks CE (2022) Adjusting the Connection Length of Additively Manufactured Electrodes Changes the Electrochemical and Electroanalytical Performance. Sensors 22.10.3390/s22239521 Selemani MA, Cenhrang K, Azibere S, Singhateh M, Martin RS (2024) 3D printed microfluidic devices with electrodes for electrochemical analysis. Anal Methods 16:6941 – 53.10.1039/D4AY01701C Pedrotti JJ, Angnes L, Gutz IGR (1996) Miniaturized reference electrodes with microporous polymer junctions. Electroanalysis 8:673–675. https://doi.org/10.1002/elan.1140080713 Guidelli R, Compton RG, Feliu JM, Gileadi E, Lipkowski J, Schmickler W, Trasatti S (2014) Defining the transfer coefficient in electrochemistry: An assessment (IUPAC Technical Report). Pure and Applied Chemistry 86:245 – 58. 10.1515/pac-2014-5026 Augusto KKL, Crapnell RD, Bernalte E, Zighed S, Ehamparanathan A, Pimlott JL, Andrews HG, Whittingham MJ, Rowley-Neale SJ, Fatibello O, Banks CE (2024) Optimised graphite/carbon black loading of recycled PLA for the production of low-cost conductive filament and its application to the detection of β-estradiol in environmental samples. Microchimica Acta 191.10.1007/s00604-024-06445-7 Lisboa TP, de Faria LV, de Oliveira WB, Oliveira RS, Matos MA, Dornellas RM, Matos RC (2023) Cost-effective protocol to produce 3D-printed electrochemical devices using a 3D pen and lab-made filaments to ciprofloxacin sensing. Microchimica Acta 190.10.1007/s00604-023-05892-y Hernández-Rodríguez JF, Trachioti MG, Hrbac J, Rojas D, Escarpa A, Prodromidis MI (2024) Spark-Discharge-Activated 3D-Printed Electrochemical Sensors. Analytical Chemistry 96:10127 – 33.10.1021/acs.analchem.4c01249 Dijkshoorn A, Schouten M, Stramigioli S, Krijnen G (2021) Modelling of Anisotropic Electrical Conduction in Layered Structures 3D-Printed with Fused Deposition Modelling. Sensors 21.10.3390/s21113710 Daniel F, Patoary NH, Moore AL, Weiss L, Radadia AD (2018) Temperature-dependent electrical resistance of conductive polylactic acid filament for fused deposition modeling. International Journal of Advanced Manufacturing Technology 99:1215 – 24.10.1007/s00170-018-2490-z Schwartz G, Cerveny S, Marzocca AJ (2000) A numerical simulation of the electrical resistivity of carbon black filled rubber. Polymer 41:6589 – 95.10.1016/s0032-3861(99)00894-0 Lange U, Mirsky VM (2008) Separated analysis of bulk and contact resistance of conducting polymers: Comparison of simultaneous two- and four-point measurements with impedance measurements. Journal of Electroanalytical Chemistry 622:246 – 51.10.1016/j.jelechem.2008.06.013 Sajid M, Gul JZ, Kim SW, Kim HB, Na KH, Choi KH (2018) Development of 3D-Printed Embedded Temperature Sensor for Both Terrestrial and Aquatic Environmental Monitoring Robots. 3d Printing and Additive Manufacturing 5:160 – 9.10.1089/3dp.2017.0092 Stopforth R (2021) Conductive polylactic acid filaments for 3D printed sensors: Experimental electrical and thermal characterization. Scientific African 14.10.1016/j.sciaf.2021.e01040 Zhai CP, Hanaor D, Proust G, Gan YX (2017) Stress-Dependent Electrical Contact Resistance at Fractal Rough Surfaces. J Eng Mech 143:8.10.1061/(asce)em.1943-7889.0000967 Rojas D, Torricelli D, Cuartero M, Crespo GA (2024) 3D-Printed Transducers for Solid Contact Potentiometric Ion Sensors: Improving Reproducibility by Fabrication Automation. Analytical Chemistry.10.1021/acs.analchem.4c02098 Negahdary M, do Lago CL, Gutz IGR, Buoro RM, Durazzo M, Angnes Lú (2024) Developing a nanomaterial-based 3D-printed platform: Application as a cancer aptasensor via detection of heat shock protein 90 (HSP90). Sens Actuators B 409:135592. https://doi.org/10.1016/j.snb.2024.135592 Guidelli R, Compton RG, Feliu JM, Gileadi E, Lipkowski J, Schmickler W, Trasatti S (2014) Definition of the transfer coefficient in electrochemistry (IUPAC Recommendations 2014). Pure Appl Chem 86:259–262. 10.1515/pac-2014-5025 Footnotes https://proto-pasta.com/pages/conductive-pla#CCmade in June 6, 2024 Additional Declarations No competing interests reported. Supplementary Files PartI.graphicalabstract.svg Handlingelectricconnections.PartI.SI.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5968075","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":413019113,"identity":"067d5f6a-dcb8-41f6-909f-3472b965bd31","order_by":0,"name":"Ivan Verlangieri","email":"","orcid":"","institution":"University of São Paulo","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"","lastName":"Verlangieri","suffix":""},{"id":413019116,"identity":"c21a3798-3398-47f4-8a1b-3c61dc621124","order_by":1,"name":"Thawan Gomes de Oliveira","email":"","orcid":"","institution":"University of São Paulo","correspondingAuthor":false,"prefix":"","firstName":"Thawan","middleName":"Gomes","lastName":"de Oliveira","suffix":""},{"id":413019119,"identity":"aac2cc15-b589-4cd9-a1d8-48fd29263868","order_by":2,"name":"Fernando Silva Lopes","email":"","orcid":"","institution":"University of São Paulo","correspondingAuthor":false,"prefix":"","firstName":"Fernando","middleName":"Silva","lastName":"Lopes","suffix":""},{"id":413019121,"identity":"bc9d8106-4f1d-4b1a-90fc-1af20ba3b3d0","order_by":3,"name":"Ivano Gebhardt Rolf Gutz","email":"","orcid":"","institution":"University of São Paulo","correspondingAuthor":false,"prefix":"","firstName":"Ivano","middleName":"Gebhardt Rolf","lastName":"Gutz","suffix":""},{"id":413019122,"identity":"0c456aef-dda0-4ee3-ab7a-104f28e70a8d","order_by":4,"name":"Lúcio Angnes","email":"","orcid":"","institution":"University of São Paulo","correspondingAuthor":false,"prefix":"","firstName":"Lúcio","middleName":"","lastName":"Angnes","suffix":""},{"id":413019123,"identity":"faf7bc29-a7e7-43a9-9fa9-40cd612e782b","order_by":5,"name":"Claudimir Lucio do Lago","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0UlEQVRIiWNgGAWjYDACdiDmASJ+ZqiAAUEtzFAtks2kamEwOECsFv5m5mcSbyq2yRgfZ97AzPPnDoO59AH8WiQOs5lJzjlzm8fsMFsBM2/bMwbLvgT8WgyYGcykedtAWngMmHkbDjMYnCHgMANm9m/SvP9u8xg3A7Xw/CFKCw/QlobbIPVAxEaEFonDPMWWc47d5gF6quDg3LZnPJY9BLTwt7dvvPGm5rY9f//hjQ/e/LkjZ85DQAuKIw8wMBwgRQMkEg+QpGMUjIJRMApGBgAAF7A57WATOYgAAAAASUVORK5CYII=","orcid":"","institution":"University of São Paulo","correspondingAuthor":true,"prefix":"","firstName":"Claudimir","middleName":"Lucio do","lastName":"Lago","suffix":""}],"badges":[],"createdAt":"2025-02-05 18:38:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5968075/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5968075/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":76178486,"identity":"4dbb525f-c948-4720-badd-75618d6a35b6","added_by":"auto","created_at":"2025-02-13 06:59:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":20593,"visible":true,"origin":"","legend":"\u003cp\u003eA model for a voltammetric or amperometric sensor (A) consisting of an electroactive surface (a), an electrode substrate (b), and tracks and connections (c) to the current-to-voltage converter circuit of the potentiostat, and an insulating body (d) allowing only the electroactive surface to be exposed to the environment to be monitored. From an electrical perspective, the conducting regions behave as resistors in series (B), including the region responsible for electron transfer (R\u003csub\u003eet\u003c/sub\u003e) in the redox process, the electrode substrate (R\u003csub\u003ebe\u003c/sub\u003e), and all other conductive materials (R\u003csub\u003et\u003c/sub\u003e) used to connect the sensor to the potentiostat input. The interface between two different conductive materials also contributes an additional resistance (not shown), which is the so-called electric contact resistance (ECR). For metal-to-metal connections, this resistance is low and can often be ignored. However, when, for example, a conductive polymer electrode substrate is connected to a copper wire, the contact resistance becomes significant and must be considered. In the same way, any additional polymer-metal junction along the path to the potentiostat input also contributes a significant ECR, which is implicitly included in R\u003csub\u003et\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/a82b146296c8e0a82885c53f.png"},{"id":76178489,"identity":"5d2c2b32-68ce-4f51-be9f-600bbf28db6e","added_by":"auto","created_at":"2025-02-13 06:59:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":149840,"visible":true,"origin":"","legend":"\u003cp\u003eSetup for 4-point resistance measurement. A CB-PLA filament (approximately 1.1 m long) was coiled around a 3D-printed purpose-made PETG support (A), and nickel-plated AWG 28 wire was used to create the wire-wrapped contacts (B) at intervals of 210 mm along the filament. The equivalent circuit (C) is, thus, composed of 6 contact resistances (R\u003csub\u003ec0\u003c/sub\u003e to R\u003csub\u003ec5\u003c/sub\u003e) and 5 resistances corresponding to the 210\u0026nbsp;mm segments of filament (R\u003csub\u003es1\u003c/sub\u003e to R\u003csub\u003es5\u003c/sub\u003e). When the current flows through R\u003csub\u003ec0\u003c/sub\u003e, the CB-PLA filament, and R\u003csub\u003ec5\u003c/sub\u003e, the resistances R\u003csub\u003es2\u003c/sub\u003e to R\u003csub\u003es4\u003c/sub\u003e can be obtained without the contributions of the contact resistances R\u003csub\u003ec1\u003c/sub\u003e to R\u003csub\u003ec4\u003c/sub\u003e, by measuring the voltage over any pair with a high impedance instrument. The voltage between terminals 0 and 1 allows obtaining R\u003csub\u003ec0\u003c/sub\u003e + R\u003csub\u003es1\u003c/sub\u003e. The average of R\u003csub\u003es2\u003c/sub\u003e to R\u003csub\u003es4\u003c/sub\u003e is used in replacement of R\u003csub\u003es1\u003c/sub\u003e, and, thus, R\u003csub\u003ec0\u003c/sub\u003e is obtained. The same can be done to obtain R\u003csub\u003ec5\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/bc2578b0797a487a57e12fcd.png"},{"id":76178906,"identity":"6062b3e7-437a-4205-ab00-75989c0d846a","added_by":"auto","created_at":"2025-02-13 07:07:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":15970,"visible":true,"origin":"","legend":"\u003cp\u003eResistance of three 21-cm long segments of CB-PLA filament (a) and two contact resistances (b and c) under temperature cycling from 10 to 40 °C. The resistance of the filament exhibits reproducible behavior, showing a hysteretic non-linear positive thermal coefficient, with a minor final shift towards higher resistance. In contrast, ECR changes unsystematically. For example, one contact (b) shows a small thermal coefficient and hysteresis, while the other contact (c) experiences a significant shift towards higher resistance while cooling (even though the thermal expansion coefficient of the wire surrounding the polymer is higher).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/168dbcba21149e6a664e71ad.png"},{"id":76178493,"identity":"af4c0b46-7982-4053-948f-d36f82068d4a","added_by":"auto","created_at":"2025-02-13 06:59:20","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":22839,"visible":true,"origin":"","legend":"\u003cp\u003eResistance over time of a 3D printed disc with a diameter of 5 mm and a thickness of 4 mm pressed at 400 kPa between two nickel-plated steel tapes. The resistance exhibited by the assembly was 1.0 kΩ, and although it appears stable, it is possible to observe in the logarithmic graph (a) that the resistance continuously decreased over the hours. After sanding both surfaces of the disk with 500-grit sandpaper, the resistance increases to 20 kΩ and, once again, systematically decreases over time (b). After 6.5 hours, the experiment was interrupted, and the disk was left to rest for 5 min. Upon reestablishing contact, the resistance returned to high levels (c) – in this case, even higher than at the beginning of the experiment b – and a new decrease was observed over time. Once again, the disk was removed from the setup, but this time it was left to rest on a glass surface heated to 100°C for 1 minute on each side. The result was a significant reduction in ECR, but the systematic downward trend persisted (d). During the experiments, some mechanical accommodation may occur, such as the one observed around 7 hours, which alters the resistance of the assembly. In any case, the resistance continues to decrease even after 24 hours of the experiment.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/abbde11d9d196d3d0ed81abb.png"},{"id":76178907,"identity":"faab5de1-0765-42ed-8748-e25e361b6f5b","added_by":"auto","created_at":"2025-02-13 07:07:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":29392,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent-voltage curve in the range -3 to 3 mA. Three wire-wrapped electrodes were placed on a segment of 1.75\u0026nbsp;mm CB-PLA filament (A) and connected to a galvanostat as auxiliary (a), reference (r), and working (w) electrodes. Because the current through the reference electrode is minimal, the filament current can be accurately controlled without ECR interference from the central electrode. The Ohmic drop on the 15-mm long CB-PLA filament (R\u003csub\u003es\u003c/sub\u003e) was subtracted. Linear regression (B) resulted in a virtually perfect fit, which suggests Ohmic behavior of the CB-PLA/nickel-plated copper junction with a resistance (R\u003csub\u003ec\u003c/sub\u003e) of 162\u0026nbsp;Ω.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/b1e70f713e40b8e0b8d4cbfc.png"},{"id":76178917,"identity":"90a5325f-be35-45ea-ac6d-6d931da6b256","added_by":"auto","created_at":"2025-02-13 07:07:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":73226,"visible":true,"origin":"","legend":"\u003cp\u003e3D printed test specimen with conductive tracks and connections. The body was designed to be printed in an insulating polymer, such as PLA+, containing holes (\u003cstrong\u003ea\u003c/strong\u003e – \u003cstrong\u003ed\u003c/strong\u003e) to insert metal contacts (\u003cstrong\u003ef\u003c/strong\u003e) and a conducting track (\u003cstrong\u003ee\u003c/strong\u003e) in CB‑PLA. The 4‑point resistance measurements were carried out with the current being applied at electrodes \u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003ec\u003c/strong\u003e, while voltage is measured at electrodes \u003cstrong\u003eb\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/be23bfa0e71024242a6abb31.png"},{"id":76178502,"identity":"d8bd4797-6726-4dd1-bb87-a31a6de0bf3b","added_by":"auto","created_at":"2025-02-13 06:59:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":380868,"visible":true,"origin":"","legend":"\u003cp\u003eInduction heating using a ZVS module (A). When 8 V is applied to the module, the coil couples with the 10‑mm steel washer inserted in a PLA support and transfers energy (B), which results in an increasing temperature depending on the washer position along the coils axes (C). Position 0 mm is at the center of the coil, which extends to ± 15 mm (the vertical dotted lines in C). The energy – and, thus, temperature – at the center is approximately three times higher than at the ends of the coil. However, some heating is promoted in ferromagnetic parts even at a few millimeters away from the coil.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/f41e1656930b9adabf784d9f.png"},{"id":76179845,"identity":"258c032d-1b48-4580-9982-18886cf9b0b5","added_by":"auto","created_at":"2025-02-13 07:15:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":94850,"visible":true,"origin":"","legend":"\u003cp\u003eTest specimen for electrochemical evaluation. During the slicing step, the electrode (A) was set to be created with wall (lines red and green) thickness of 1.0 mm and top and bottom (yellow lines) thickness of 0.8 mm. The infill was set to 0% (B), 50% (C), or 100% (D). The device (E) was designed to be printed in PLA+ with electrode (d) and tracks with CB-PLA. Two alternate tracks were created with different diameters: 2.0 mm (a) and 0.5 mm (c). An empty channel (b) was also included allowing a steel wire (guitar string) to be inserted to access the same electrode.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/6ea3ef50f1b7a4ce36cb4db2.png"},{"id":76180233,"identity":"a9653587-bc9a-42f6-82dc-9723d2bc6881","added_by":"auto","created_at":"2025-02-13 07:23:32","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":37116,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammetry of a 0.6\u0026nbsp;mmol\u0026nbsp;L\u003csup\u003e-1\u003c/sup\u003e hexaammineruthenium(III) chloride solution in 0.1 mol\u0026nbsp;L\u003csup\u003e-1\u003c/sup\u003e supporting electrolyte using the same electrode (d) and three different tracks (a, b, and c). The resistances in the equivalent circuit of the device shown in Figure 8 were experimentally determined (A) and used in the correction of the voltammograms. The voltammogram using the guitar string connection (b) (300 to -500\u0026nbsp;mV and 100\u0026nbsp;mV/s) is repeated in dashed line in all the figures from B to F, for reference. At the same voltage range and scan rate, deformed CVs were obtained with the 2.0 mm track (B), of intermediate resistance (a), and markedly with the 0.5 mm track (D), of higher resistance (c). Point-by-point correction of the abscissa values for the calculated iR voltage drop resulted in peak potentials closer to the reference CV (E). By anticipating the voltage drop based on the currents at the switching potentials of the reference CV – i.e., 318 to -613\u0026nbsp;mV and 116\u0026nbsp;mV/s for the 0.5 mm track (F), and 301 to -508\u0026nbsp;mV at 101\u0026nbsp;mV/s for the 2.0 mm track (C) –, the pronounced deformation of the CV with the more resistive track was minimized.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/40f51a636ee315b1c3f837a3.png"},{"id":76201161,"identity":"34899054-dff3-4f51-9103-99d2bc9804e7","added_by":"auto","created_at":"2025-02-13 11:24:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1563345,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/9690b8f4-053e-4128-8153-10d325a1ccb8.pdf"},{"id":76178487,"identity":"7bcc03e0-940a-42ee-ac12-f5de3c9e81f0","added_by":"auto","created_at":"2025-02-13 06:59:20","extension":"svg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":100420,"visible":true,"origin":"","legend":"","description":"","filename":"PartI.graphicalabstract.svg","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/628ad945e4621f93ddc262f9.svg"},{"id":76179850,"identity":"9962b3e3-e190-406b-8618-ac2875b6b549","added_by":"auto","created_at":"2025-02-13 07:15:21","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1086713,"visible":true,"origin":"","legend":"","description":"","filename":"Handlingelectricconnections.PartI.SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-5968075/v1/42d0c65babd554699f824572.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Handling electric connections in 3D-printed electrodes and sensors. Part I. Understanding and improving tracks and contacts","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eElectrochemical sensors, like voltammetric and amperometric ones, can be envisioned as a set of three sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): (1) the electroactive surface, which is responsible for the desired sensing behavior; (2) an electrode substrate, whose surface is the electroactive one or serves as support for deposition of different material or for modifications in order to achieve the desired selectivity and sensitivity; and (3) electric connections and tracks to the potentiostat or other electronic circuit to which counter and/or reference electrodes are separately connected. Actually, the conduction of electric current to and from the electrode is carried out by a combination of wires, cables, printed circuit board traces, and other conductive materials, but they will be collectively referred to as a \"track\" herein. Usually, this section of connections and tracks is a combination of wires and connectors made of different metals, such as copper or nickel-plated copper wires, gold-plated connectors, tin-lead solder, and so on. Thanks to the high electrical conductivity and typical dimensions, the resistance of these segments is low (\u0026thinsp;\u0026lt;\u0026thinsp;\u0026lt;\u0026thinsp;1 Ω). In addition, every time the surfaces of two different conducting bodies are put into contact, another resistance arises: the so-called electrical contact resistance (ECR).\u003c/p\u003e \u003cp\u003eIt is important to highlight that the term \"electric contact resistance\" in this context differs from its usage in other papers [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. ECR refers to the resistance encountered when current flows between two conductive surfaces in contact, while any additional resistance is actually considered track resistance.\u003c/p\u003e \u003cp\u003eECR depends on several factors, such as contact area, roughness of the surfaces, formation of oxide layers, moisture, and so on. ECR between two metal segments \u0026ndash; both connected by soldering, crimping, or simple pressing contact \u0026ndash; is low. As a result, one can assume that, even when a significant current flows, the Ohmic voltage drop (iR potential drop) over this connection track is small enough to be disregarded for most practical purposes, and the potential at the electrode substrate is assumed to be the same as at the potentiostat input. Unfortunately, the same is not true when semiconductor materials, conducting polymers, or composites are used to make these tracks, connectors or even the electrode substrate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn recent years, 3D printing processes \u0026ndash; especially fused deposition modeling (FDM) \u0026ndash; of pure and composite materials have opened the door to several new possibilities for the production of sensors and analytical devices [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In this context, several groups have proposed the use of conductive polymers for the creation of both the electrode substrate and its wiring and connections [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Although they recognize the importance of the electrical resistance of these new materials, in general, the studies are focused on the investigation of the devices as electrochemical sensors.\u003c/p\u003e \u003cp\u003eThe present study shifts the focus from the possibilities and behavior of the electroactive surface to the tracks and connections involving 3D-printed materials in the device construction. It aims to gain a deeper understanding of the behavior of a typical conductive polymer and its necessary connection with metals, as well as how to improve and overcome the imposed limitations.\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cp\u003eHexaammineruthenium(III) chloride (Sigma-Aldrich, Burlington, MA) and KCl (Synth, Diadema, Brazil) were used as received. Solutions were prepared using deionized water (resistivity\u0026thinsp;\u0026ge;\u0026thinsp;18.2 MΩ cm) from a Milli-Q system (Millipore, Billerica, MA).\u003c/p\u003e \u003cp\u003eDifferential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed in a DSC Q20 and a TGA Q500 (TA Instruments, New Castle, DE), respectively. Resistance and four-point resistance measurements were carried out using a 3458A multimeter (Hewlett-Packard, Palo Alto, CA). The temperature control of the specimens was achieved using an electric oven IPP 500 (Memmert, Schwabach, Germany).\u003c/p\u003e \u003cp\u003eAll the 3D printed devices were designed in Inventor Professional 2023 (AutoDesk, S\u0026atilde;o Rafael, CA), and printed with an independent dual extruder (IDEx) Tycoon printer (Kywoo3D, Shenzhen, China), after slicing the model using Ultimaker Cura 4.11.0 (Utrecht, Netherlands). The insulating parts were printed in either PLA+ (TopInk, Piracicaba, Brazil) or PLA Easyfill (3DFila, Belo Horizonte, Brazil). ProtoPasta conductive PLA (Vancouver, WA) was used for the electrodes and conducting tracks. The 3D printing conditions and parameters are detailed in the Supplementary Material. Welded metalpolymer contact (WMPC) was achieved either by using a soldering station system (Yaxun 886D, Guangzhou, China) or a mini zero voltage switching (ZVS) module (AliExpress, Hangzhou, China) powered by an adjusted power supply B\u0026amp;K Precision 1550 (Yorba Linda, CA).\u003c/p\u003e \u003cp\u003eThe electrochemical experiments were carried out with a potentiostat/galvanostat Autolab-PGSTAT302N (Metrohm, Netherlands). Platinum wire and Ag/AgCl, KCl\u003csub\u003e(sat.)\u003c/sub\u003e (+\u0026thinsp;0.197 vs SHE) electrode[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] were used as auxiliary and reference electrodes, respectively, in a 25 mL electrochemical cell. Cyclic voltammetry (CV) experiments of 0.60 mmol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of the [Ru(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3+\u003c/sup\u003e in KCl 0.10 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were initially performed in a potential range from 0.3 V to -0.5 V. The outer sphere redox probe [Ru(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3+\u003c/sup\u003e was used to evaluate the electrochemical performance of the 3D printed electrode [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Data processing was carried out using NOVA software version 2.0 (Metrohm, Netherlands) and Origin 2024 software (OriginLab, Northampton, MA).\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eUsually, the conductive polymers used for FDM 3D printing are composite materials based on an insulating polymer, such as acrylonitrile butadiene styrene (ABS) or poly(lactic acid) (PLA), and a conductive filler, such as graphite, graphene, or carbon black (CB) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Some of the materials are prepared in-house [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], but there are commercial options available. Protopasta CB-PLA was chosen, because it is a popular option with good electrical characteristics [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe thermogravimetric analyses (Figures \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and S2) of PLA Easyfill and CB-PLA filaments suggest that the CBPLA has a small amount of mineral filler (ca. 1%) and that the approximate ratio of PLA:CB is 3:1 (w/w). In addition, both materials start to decompose in air above 300\u0026deg;C due to the PLA base. DSC reveals that the glass transition (T\u003csub\u003eg\u003c/sub\u003e) for both materials is 54\u0026deg;C (Figures S3 and S4). The thermal behavior will be important in analyzing the results shown in the next sections, as well as in the introduction of WMPC.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Resistivity and resistance of the CB-PLA filament and printed tracks\u003c/h2\u003e \u003cp\u003eScanning electron microscopy images obtained by Dijkshoorn et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] and Daniel et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] suggest that the CB particles in the PLA-CB are smaller than 1 \u0026micro;m and they form agglomerates, in which the particles are in contact to each other. The conductive property of the CB-PLA filament can be explained by two basic mechanisms: electron transfer between particles inside the CB agglomerates and by tunneling between particles isolated by small gaps (less than 10 nm) [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. For cylindrical or prismatic bodies of a homogenous material, the resistance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:R\\)\u003c/span\u003e\u003c/span\u003e) is given by:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:R=\\rho\\:\\frac{l}{a}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e is the resistivity, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:l\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:a\\)\u003c/span\u003e\u003c/span\u003e are the length and sectional area, respectively, of the body. When the ECR is significantly lower than the bulk resistance, a simple ohmmeter can be used; otherwise, a four-point probe method should be employed to measure the material's resistance [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe resistivity of the raw CB-PLA filament obtained by the 4-point approach (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) was 6.0 Ω\u0026middot;cm at 25\u0026deg;C, which is significantly smaller than stated by the manufacturer\u003csup\u003e1\u003c/sup\u003e (15 Ω\u0026middot;cm), but compatible with the value deduced from the resistance of a 10-cm long segment of filament (2 to 3 k Ω) also informed by the manufacturer. Most probably, the manufacturer has not considered the ECR during the measurements, which is significant as will be shown in the next section.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThere is a significant variation in the resistivity during a temperature cycling from 10 to 40\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This feature has been suggested to be used for the implementation of thermal sensors [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. However, the thermal cycling experiments show drifts alongside the systematic variation of resistance with temperature, a behavior that could be explained not only by a hysteresis effect, but also by a permanent modification of the complex network of particles and aggregates. A possible explanation for this fact is that, even below T\u003csub\u003eg\u003c/sub\u003e, the polymer suffers structural modification under stress, resulting in a new configuration of the CB agglomerates. Thus, when the filament is removed from the original spool (diameter of 15 cm) and placed in a smaller diameter spool (6.7 cm) for the test, stress arises, which is alleviated under gentle heating.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfter printing, the CB-PLA filament material does not undergo significant physical or chemical changes, but its apparent resistivity increases. This increase can be explained by two main processes. First, any printed track is formed by combining traces deposited from the 0.4 mm extrusion nozzle, resulting in air pockets that are non-conductive. Second, PLA can absorb moisture when stored. During printing, the vaporization of this accumulated moisture creates microbubbles in the material. Consequently, the printed polymer is not as compact as the original filament, leading to higher apparent resistivity.\u003c/p\u003e \u003cp\u003eThe apparent resistivities at 25\u0026deg;C for cylindrical tracks with diameter of 0.5 mm and 2.0 mm were (16.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4) Ω\u0026middot;cm and (17.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2) Ω\u0026middot;cm, respectively, in contrast to 6.0 Ω\u0026middot;cm of the raw filament. Therefore, in the forthcoming evaluations of the resistance of 3D-printed objects, an apparent resistivity of 17 Ω\u0026middot;cm will be used, rather than the lower value applicable only to the brand new filament.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Behavior of electrical contact resistance with time, current, and temperature\u003c/h2\u003e \u003cp\u003eDespite the thermal behavior discussed in the previous section, CB-PLA printed electrodes and tracks can still be useful. However, when the device is integrated into an actual circuit, ECR comes into play. A great number of factors determine the effective electrical resistance observed when two conducting objects are put into contact [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. For metals, this resistance is low enough (\u0026lt;\u0026thinsp;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Ω) to be disregarded when a low current flows through it. However, the contact between a conducting polymer and a metal is expected to be much more resistive [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe simplest way to use 3D-printed electrodes consists in using pressure to create the contact between the polymer and the metal parts, such as a screw or an alligator clip. A stainless steel screw has been used [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], but such contact may be subject to instabilities that cause variations in ECR, resulting in an increased level of noise or irreproducibility.\u003c/p\u003e \u003cp\u003eTo evaluate this behavior, 3D printed discs with a diameter of 5 mm and a thickness of 4 mm were pressed at 400 kPa between two nickel-plated steel tapes, which were used as contacts for resistance measurement. Thanks to the ECR, the initial resistance is different for each time that the electrodes are applied. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the resistance over time for a specific disk and is representative of the various phenomena observed in the several experiments conducted. The initial resistance was 1.0 kΩ, but this value significantly decreases after the first few minutes (plot a in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Although it appears stable in terms of relative resistance variation after that, it does not stabilize even after 2.5 hours, as can be observed in the logarithmic graph. This variation can be attributed exclusively to changes in ECR, as the internal resistance of the printed disk is estimated to be only 35 Ω. In other words, the sum of the contact resistances of the two surfaces is at least an order of magnitude greater than the resistance of the body.\u003c/p\u003e \u003cp\u003eTo emphasize the importance of contact surface quality, both surfaces of the disk were sanded with 500grit sandpaper, removing approximately 5 \u0026micro;m from each one (plot b in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Although the macroscopic appearance suggests a reduction in the irregularities from the 3D printing process, the surface now exhibits greater roughness, which hinders contact. This behavior was systematically observed for all the printed disks. It was also observed in all cases that, after the disk was released from the pressurization process, the resistance returned to higher levels (as in plot c in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Sometimes, the return is to values close to those observed in the previous run, but the value can be even higher, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. These results suggest that creep resistance, which is also observed with other materials [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], does not cause permanent deformation of the surface in the case of CB-PLA, indicating that it is elastic. The roughness obtained after sanding can be reduced by exposing the surface to a temperature higher than the material's T\u003csub\u003eg\u003c/sub\u003e. For example, exposure for just one minute on a glass surface at 100\u0026deg;C significantly reduces the ECR (plot d in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePure mechanical contact can also exhibit erratic behavior, with significant resistance changes, as shown by the event occurring around 7 h in the last run. That is, even after 7 h of established contact, a subtle mechanical alteration can affect the ECR. Equally surprising is that, even after 24 h, the resistance continued to decrease.\u003c/p\u003e \u003cp\u003eThe contact between two materials, such as a metallic electrode and a conductive polymer, can also result in the formation of a semiconductor junction, where the current does not vary linearly with the applied voltage; that is, it can exhibit non-Ohmic behavior. To assess this behavior, a current-voltage curve of a CB-PLA filament with a wrapped nickel-plated copper wire was obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). After compensating the estimated resistance of the bare filament, no evidence of nonlinearity was observed (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;1.000), which suggests that the junction CB-PLA/nickel is an Ohmic contact.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eECR exhibits varying behavior during temperature cycling. Two wire-wrapped metal contacts prepared on the same piece of CB-PLA filament may show different values and trends over temperature changes (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This chaotic behavior can be explained by the interplay of the material's intrinsic resistivity with mechanical and thermal modifications at the contact points, affecting the efficiency of charge transport.\u003c/p\u003e \u003cp\u003eAny practical usage of a CB-PLA 3D-printed electrochemical sensor involves forming one or more contacts between the polymer and metal wires or rods. Therefore, one cannot ignore ECR in evaluating or using the device, with the possible exception of a potentiometric one due to the low current [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Reducing ECR is not a simple task, but making it at least more stable over time, temperature, and pressure is feasible. This was accomplished by melting the polymer to improve the contact with the metal, as will be discussed in the next section.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Welded metal-polymer contact (WMPC)\u003c/h2\u003e \u003cp\u003eA first demonstration of using a WMPC was shown in our previous paper, in which one of the ends of a copper wire was incorporated in the electrode body during the 3D printing process [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The device was designed to have a CB-PLA electrode and a pure PLA body, in which an open channel allows the copper wire be guided to outside the sensor. A special command is inserted in the g-code to pause the printer after printing a specific layer. During the pause, the end of the copper wire is heated using a soldering iron at 220\u0026deg;C allowing the insertion of the wire tip into the CB-PLA electrode. The rest of the wire is fitted into the channel, which is closed while printing resumes.\u003c/p\u003e \u003cp\u003eSince this process has been introduced, we have substituted the pure 0.5 mm copper wire by a nickelplated wire wrapping copper wire AWG 28, which is equally appropriate for the electric contact, but more malleable, easing the device manufacturing. Although useful, this strategy has the drawback of requiring the manual insertion of the electrode during a pause of the printing process. Furthermore, one of the most interesting aspects of 3D printing is precisely the possibility of creating more intricate devices produced as automatically as possible. Thus, it is natural to seek the creation of devices that incorporate 3D-printed conductive tracks as well. However, a metal-polymer contact will be inevitable at some point in the setup.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e exemplifies how WMPC is implemented in a 3D-printed test specimen designed for the evaluation of the resistance of tracks and contacts. The idea for creating the contact involves ending the track with a CB-PLA region that has a hole of appropriate diameter to accommodate the metal terminal. After a few tests, nickel-plated steel nails proved to be a convenient option resulting in a robust and corrosion-resistant contact. Here, a soldering iron at 220\u0026deg;C was initially used to heat the nail head until the polymer was melted by thermal conduction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA later improvement was to introduce electromagnetic induction heating. The 3D-printed device, with the nail positioned in the contact hole, is placed inside the coil of a ZVS module operating at 100 kHz. After a few seconds, the nail, being made of ferromagnetic steel, is heated to a temperature that causes the polymer to melt. This process is faster and more reliable and reproducible than the simple heating with a solder iron.\u003c/p\u003e \u003cp\u003eThe ZVS module is simple and inexpensive. It operates from 5 to 12 V and the output power is proportional to this voltage. Thus, one can control the energy applied to the metal piece by changing the voltage and/or the time. The pre-manufactured 10-turns coil (30 mm long with i.d. of 17 mm) is appropriate to enclose typical electrodes and sensors for electroanalytical purposes.\u003c/p\u003e \u003cp\u003eA thermal camera was used to characterize the profile of delivered power as a small steel washer is inserted in various positions along the inside coil. The result is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The current consumed in heating can be obtained by the difference between current with and without ferromagnetic material inserted in the coil. From the power and the pulse time, one can estimate and control the total energy, which will determine the maximum temperature reached by the ferromagnetic piece.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOf course, the final temperature depends on several parameters, such as the mass, shape, thermal conductivity, and coupling efficiency of the metal and the thermal capacity and conductivity of the surrounding materials. Therefore, the best results are obtained through empirical optimization for each case. However, one general guideline should be observed. As the metal is heated, part of the heat is immediately dissipated into the surroundings, i.e., in locally heating the polymer. As a result, slow heating (low power over a long time) can cause excessive heating not only of the CB-PLA, but also of the device body, potentially leading to permanent deformation. On the other hand, heating too quickly can cause a rise in the local temperature sufficient to start the decomposition of CB-PLA \u0026ndash; above 300\u0026deg;C, according to the TGA (Figure S2).\u003c/p\u003e \u003cp\u003eWelding by this inductive heating process was used to implement the WMPC of the test specimens and devices shown from now on. Three test specimens as the one shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e were submitted to successive steps of heating from 25 to 40\u0026deg;C, and all the six contact resistances were monitored (Table S3). Compared to the purely mechanical contacts (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), the WMPCs are smaller and more stable. Resistances ranging from 89 to 233 Ω (25\u0026deg;C) and TC smaller than 4.0 Ω/\u0026deg;C were obtained. Moreover, unlike mechanical contacts that tend to exhibit erratic behavior after heating cycles, WMPCs seem to benefit from heating to moderate temperatures. The heating probably helps in relaxing internal stresses generated during the formation of the contact by induction heating. As a result, more reproducible resistances with lower thermal coefficients were observed.\u003c/p\u003e \u003cp\u003eSince the induction heating acts only on ferromagnetic metals, an approach has been proposed as an alternative for the incorporation of a copper wire during the 3D printing process. A straight empty channel from the CB-PLA electrode to the end of the device was incorporated in the design. After the printing process is finished, a ferromagnetic wire or strip is inserted into the channel. The portion of the device containing the CB-PLA electrode and the end of the wire is centered in the ZVS coil. When the ZVS module is powered, one can easily feel the polymer melting while the wire is gently pressed. After the insertion of the wire into the electrode, the device is allowed to cool down and the contact is ready. Two ferromagnetic materials have been used in this study: guitar strings and nickel-plated steel strips.\u003c/p\u003e \u003cp\u003eNickel-plated steel strips are used as connections for lithium batteries by using spot welding. Usually, they are available with a width of 4 or 8 mm and different thickness. In turn, guitar strings are designed to have good magnetic coupling, then usually they are made of steel with a thin layer of nickel to prevent oxidation. Any of the six guitar strings can be used. Of course, the thinnest string (1:E) demands more heating time than the thicker one (6:E) due to the smaller energy transfer. These strings were used in the experiments described in the next section.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.4 The impact of the resistances on an electrochemical sensor\u003c/h2\u003e \u003cp\u003eThe shape and dimensions of the devices designed for the present test were inspired by our previous work [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. However, once again, the objective of the present study was not to explore analytical applications or electrochemical studies, but to evaluate the impact of the electrical resistance of the internal components of the devices.\u003c/p\u003e \u003cp\u003eThe electrodes were designed with a diameter of 5 mm and a thickness of 4 mm, being completely embedded in the body of the device, exposing only the circular surface. During the slicing step before 3D printing, the wall thickness and the infill percentages indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e were selected. As shown in the previous section, experimentally evaluating the resistance of this electrode is challenging due to significant contact resistance. However, it can be estimated using the dimensions and apparent resistivity of the CB-PLA. The resistance between the faces of a 100% infill body is expected to be 35 Ω, increasing to 52 Ω for a 0% infill. Naturally, intermediate infills would result in intermediate resistances. At first glance, a 100% infill should always be adopted to reduce resistance. However, it should be considered that if the incorporation of metallic contact is desired, partial infill is more appropriate, as the melting of the polymer creates space for its accommodation. It is worth noting that, regardless of the infill percentage, this resistance is generally much lower than that of the tracks or polymer-metal contacts.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor test purposes, three different tracks and connections were created for the same electrode. Two of them were made of CB-PLA with different diameters: 0.5 and 2.0 mm. The first lies almost in the limit of the printer resolution in the XY plan (0.4 mm) and presents high resistance (44 kΩ calculated), while the second with generous diameter has smaller resistance (2.7 kΩ calculated). The third connection was created with a metallic conductor \u0026ndash; guitar string segment \u0026ndash; and, thus, with a resistance smaller than 1 Ω. Of course, all the three CBPLA/metal connections contribute an additional ECR around 10\u003csup\u003e2\u003c/sup\u003e Ω. These three options, therefore, can be used to evaluate the behavior of the same electrode \u0026ndash; which has a resistance on the order of 10\u003csup\u003e1\u003c/sup\u003e Ω \u0026ndash; using connections with resistance varying by three orders of magnitude: 10\u003csup\u003e2\u003c/sup\u003e Ω, 10\u003csup\u003e3\u003c/sup\u003e Ω, and 10\u003csup\u003e4\u003c/sup\u003e Ω for guitar string, 2.0 mm, and 0.5 mm CB-PLA tracks, respectively.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows cyclic voltammograms obtained for the same electrode but using the different tracks. Since the guitar string has a much smaller resistance than the 0.5 and 2.0 mm CB-PLA tracks, it was used as a reference for the experiment. These connections with three different orders of resistance magnitude help us to demonstrate a misconception about the impact of the connection resistivity on the electrochemical process.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the characteristic behavior of a sensor is determined by its electroactive surface. The substrate layer (b), along with any cabling or connectors (c), does not affect the electrochemical behavior. However, depending on the magnitude of the current flowing through the circuit, there can be a significant iR voltage drop if the resistance is high. The operational amplifier\u0026rsquo;s feedback ensures that its input remains at zero volts (GND), regardless of the current flowing through the electrode and the feedback loop. However, due to the Ohmic drop, the electroactive surface will experience an offset voltage. Consequently, the electrochemical process that occurs will correspond to the actual potential difference at the electrode/electrolyte interface, rather than the one applied by the instrument on the assumption that the working electrode is settled at zero volts.\u003c/p\u003e \u003cp\u003eThis behavior can be clearly explained by the experiments shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The same electrode, when connected through the 0.5 mm track, exhibits a shape that appears entirely different compared to when using the guitar string (D). However, when the offset voltage is subtracted from the applied potential value, the peak potentials align closely with the expected values (E).\u003c/p\u003e \u003cp\u003eEven so, the voltammograms are significantly different because the scanned potential range is smaller. For example, in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eD, when the scan supposedly reaches \u0026minus;\u0026thinsp;500 mV, considering the iR drop, the electrode interface is actually exposed to -360 mV. Therefore, a possible strategy would be to anticipate the Ohmic drop and compensate for it in the choice of potential range. However, since the actual profile involved in a new CV is not known in advance, it would be necessary to repeat the experiments. It should also be noted that, with the expansion of the potential range (from 800 mV to 931 mV in this case), it becomes necessary to adjust the scan rate accordingly, ensuring that the 931 mV are scanned within the same period as the original 800 mV, i.e., 116 mV/s instead of 100 mV/s.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the parameters obtained from the analysis of the voltammograms presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, allowing for a comparison of the electrode connected with the guitar string and with the 0.5 mm and 0.2 mm tracks, using both the original and modified potential range and scan rate. In addition to the variation in peak potential, the transfer coefficient was also calculated [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{\\alpha\\:}_{c}=\\frac{RT}{F}\\frac{dln\\left|{j}_{c}\\right|}{dE}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eR\u003c/em\u003e, \u003cem\u003eT\u003c/em\u003e, \u003cem\u003eF\u003c/em\u003e, and \u003cem\u003ej\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e are the gas constant, thermodynamic temperature, the Faraday constant, and the density of cathodic current, respectively. When the 0.5 mm track is used, α becomes significantly different from 1.0, leading to the false assumption that the electron transfer might not be efficient. However, when the same track is used with proper iR drop compensation, \u003cem\u003eα\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e becomes closer to 1.0, similar to the other connections with lower electrical resistance.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDistortion of voltammetric parameters obtained for the CVs of [Ru(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3+/2+\u003c/sup\u003e due to the resistance of the connection between the potentiostat and the working electrode (sensor)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCondition \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eE\u003csub\u003ep,a\u003c/sub\u003e / mV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eE\u003csub\u003ep,c\u003c/sub\u003e / mV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e∆E\u003csub\u003ep\u003c/sub\u003e / mV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eI\u003csub\u003ep,a\u003c/sub\u003e / \u0026micro;A\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eI\u003csub\u003ep,c\u003c/sub\u003e / \u0026micro;A\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003eα\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eguitar string (400\u0026nbsp;Ω)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-122\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-229\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5 mm (35.6\u0026nbsp;kΩ)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-24.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-432\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e408\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5 mm compensated \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-267\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e162\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.0 mm (2.59\u0026nbsp;kΩ)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-238\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e124\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.0 mm compensated \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-238\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003csup\u003ea\u003c/sup\u003e The default condition was 300 to -500 mV at 100 mV/s\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003csup\u003eb\u003c/sup\u003e 318 to -613 mV at 116 mV/s\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003csup\u003ec\u003c/sup\u003e 301 to -508 mV at 101 mV/s\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eEven after the use of a compensated potential range and scan rate, there is still some discrepancy in the voltammograms using 0.5 and 2.0 mm tracks (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e), but this cannot be easily overcome because the new scan rate, calculated based on the new potential range, is kept constant. Ideally, the scan rate applied by the instrument should be variable so that the effective scan rate perceived by the electrode remains constant after compensating for the Ohmic drop. Obviously, this task is not simple and would require dynamic control of the scan rate, which becomes unfeasible. This type of issue, which is not a deficiency of the electrode itself but rather the way the measurements are conducted, can be better addressed by choosing the appropriate instrument, which will be the subject of the second part of this work.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Concluding Remarks","content":"\u003cp\u003eThe conductive polymer used in the 3D printing of sensors and other electrochemical devices escalates the electrical resistance of the electrode substrate, the tracks, and the connector junction, compared with metallic counterparts. Obviously, there may be resistance to electron transfer at the electroactive surface in contact with the solution, which is resistive by itself, but these issues are beyond the scope of the present study.\u003c/p\u003e \u003cp\u003eWhile the resistance of the tracks may primarily contribute to the total resistance, we have shown that the polymer-metal ECR can be the most significant factor affecting stability, reproducibility, and noise in the measurements. In this context, utilizing WMPC is an appealing strategy, because it enhances stability, reduces ECR and it is easy to implement.\u003c/p\u003e \u003cp\u003eOverall conductive polymer resistance can become a crucial factor in the use of 3D-printed working electrodes and the interpretation of voltammetric results, as uncompensated Ohmic drop causes an alteration of the true potential applied to the electroactive surface/solution interface. Some researchers have attributed these alterations to anomalies or poor performance of the conductive polymer as an electrode. However, we have demonstrated that the electrochemical behavior is independent of the significant electrical connection\u0026rsquo;s resistance. This resistance can, in fact, be compensated for by using the appropriate instrumentation, and this specific topic will be covered in detail in the second part of this study.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eCompeting interest\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by FAPESP - Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de S\u0026atilde;o Paulo (2017/13137-5). The authors thank for the fellowships granted by CNPq - Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico (307259/2021-8, 180838/2024-5, 308996/2023-2 and 141495/2023-5).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eI.V., T.G.O., and F.S.L.: data curation, investigation, and writing\u0026ndash;review and editing. I.G.R.G.: methodology, supervision, and writing\u0026ndash;review and editing. L.A.: funding acquisition, methodology, project administration, supervision, and writing\u0026ndash;review and editing. C.L.L.: conceptualization, formal analysis, funding acquisition, methodology, project administration, supervision, writing\u0026ndash;original draft, and writing\u0026ndash;review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was supported by FAPESP (2017/13137-5). The authors thank for the fellowships granted by CNPq (307259/2021-8, 180838/2024-5, 308996/2023-2 and 141495/2023-5).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eVeloso WB, Paix\u0026atilde;o TRLC, Meloni GN (2023) 3D printed electrodes design and voltammetric response. 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Pure Appl Chem 86:259\u0026ndash;262. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1515/pac-2014-5025\u003c/span\u003e\u003cspan address=\"10.1515/pac-2014-5025\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://proto-pasta.com/pages/conductive-pla#CCmade\u003c/span\u003e\u003cspan address=\"https://proto-pasta.com/pages/conductive-pla#CCmade\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e in June 6, 2024\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Electrochemical sensors, 3D printing, electrical contact resistance, cyclic voltammetry, welded metal-polymer contact","lastPublishedDoi":"10.21203/rs.3.rs-5968075/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5968075/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eVoltammetric and amperometric sensors typically consist of three sections: an electroactive surface, an electrode substrate, and connection tracks or wires to a potentiostat or other electronic circuit. While the electrical resistance of metal-to-metal connectors can usually be disregarded in such sensors due to their low contact resistance, this is not the case when semiconductor materials, conductive polymers, or composites are involved. This study focuses on the electrical behavior of 3D-printed conductive polymer tracks and connections to metals, aiming to improve and understand their limitations. Carbon black PLA (CB-PLA) was chosen for its favorable electrical properties. Results show that the printed tracks exhibit higher resistivity (17 Ω\u0026middot;cm) than the raw filament (6 Ω\u0026middot;cm). The electrical contact resistance (ECR) found between nickel-plated metals and CB-PLA was considerably high, in the order of 10\u003csup\u003e2\u003c/sup\u003e to 10\u003csup\u003e3\u003c/sup\u003e Ω. The metal-polymer contact promoted solely by pressuring the parts (e.g., with alligator clips) proved to be unstable and, as such, a potential source of noise. Welded metalpolymer contact (WMPC) was developed using induction heating to improve and secure metal-polymer interfaces. Furthermore, it has been demonstrated that the high resistivity of the tracks and connections created by 3D printing actually has no implication on the electrochemical behavior of the sensor, other than the Ohmic drop in these sections that must be considered to ensure the proper functioning of sensors involving current flow. The findings indicate that while 3D-printed conductive polymer sensors show promise for widespread use, careful consideration of ECR and thermal effects is crucial for reliable performance.\u003c/p\u003e","manuscriptTitle":"Handling electric connections in 3D-printed electrodes and sensors. Part I. Understanding and improving tracks and contacts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-13 06:59:15","doi":"10.21203/rs.3.rs-5968075/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"614bbe73-5466-4185-9def-d3411614c054","owner":[],"postedDate":"February 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-02-13T11:24:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-13 06:59:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5968075","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5968075","identity":"rs-5968075","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}