A Novel Thermochromic Myocardial Phantom for Radiofrequency Ablation and Cryoablation

A Novel Thermochromic Myocardial Phantom for Radiofrequency Ablation and Cryoablation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A Novel Thermochromic Myocardial Phantom for Radiofrequency Ablation and Cryoablation Carlo Saija, Sukruth Pradeep Kundur, Lisa Leung, Sachin Sabu, and 12 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5483662/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Oct, 2025 Read the published version in Scientific Reports → Version 1 posted 6 You are reading this latest preprint version Abstract In the growing field of electrophysiology, cardiac ablation either via heating or freezing target tissues using catheters, induces localised scarring to block or destroy defective electrical pathways in the heart. To test equipment and ablation settings, studies have resorted to ex-vivo and in-vivo models including pigs, dogs, and chickens. The use of animal tissue presents ethical and logistical complications and introduces variability between samples and between studies. In a scientific community faced with progressively more stringent ethics and regulations on animal testing, a more practical and ethical alternative should be established. To meet this need, multiple studies have proposed tissue-mimicking materials. However, either toxicity or poorly matched physical properties, prevented these materials from reaching widespread application. Furthermore, no material has yet been identified to test both cryoablation and radiofrequency ablation. Here, we present a novel thermochromic alginate hydrogel material that can simulate ablation lesions for both radiofrequency ablation and cryoablation. This material could find direct applications in electrophysiology, but adapted mixtures could also be used to recreate other tissues for different simulations. Health sciences/Cardiology Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Physics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 INTRODUCTION Cardiac ablation (CA) has become a well-established procedure to treat cardiac arrhythmias, which affect a growing number of patients worldwide [ 1 , 2 ]. Radiofrequency cardiac ablation (RCA) uses high temperatures (50–60°C) [ 3 , 4 ] delivered by a catheter to induce localised scarring in the arrhythmogenic regions of the heart. Radiofrequency ablation finds applications across a plethora of medical procedures, e.g. the treatment of liver tumours [ 5 ] and gastroesophageal reflux disease [ 6 ]. An alternative to RCA often utilised in pulmonary vein isolation is cryoablation. Low temperature between − 30°C and − 80°C is applied to freeze cells and create areas of controlled scar [ 7 , 8 , 9 ]. As a minimally invasive procedure yielding effective results in tackling the growing demand for arrythmia treatment, there is great potential in the development of CA technology, and subsequently, a significant need for standardised testing and training. Currently, the majority of clinical studies [ 4 , 10 , 11 , 12 ] tested RCA using ex-vivo tissue models, mainly myocardial and skeletal muscle acquired from swine, dogs, and occasionally chickens. Due to the nature of freezing tissue, ex-vivo muscle does not visibly respond to cryoablation. To analyse the effects of this procedure, in-vivo tests are performed on dogs [ 8 , 9 , 13 ] and the histological effects are analysed post-mortem, days to months after. As well as ethical, financial, and practical difficulties presented by in-vivo and ex-vivo testing, the non-homogeneity of tissue samples poses difficulties in testing [ 14 , 15 ]. In CA, the locus of tissue acquisition (e.g. ventricular wall, cardiac septum, skeletal muscle of the thigh), and the testing apparatus in which the samples are placed, can affect lesion shape and size. Post-operative lesion visualisation, in addition to the plasticity and structural uniformity of the tissue, pose limitations to reliable data acquisition. As a result, numerous studies propose myocardium-mimicking materials for ablation testing. For the myocardium-mimicking material to be suitable, it must display realistic thermal conductivity, realistic electrical resistivity, a realistic mechanical response to the catheter, and must show visibly measurable change post-ablation. Albumin [ 16 ] and thermochromic inks [ 17 , 18 ] have been introduced in conductive polyacrylamide gel to create a conductive medium that could be ablated and would permanently change colour in the areas that reached RCA temperatures (≥ 50°C). This was applied to RCA as well as liver ablation to assess the ablation lesion dimensions. Reversible thermochromic liquid crystals found similar applications in polyacrylamide [ 19 , 20 ], allowing the users to simulate radiofrequency ablation and produce full thermal maps. Despite its repeated appearance in literature, safety concerns regarding the preparation of polyacrylamide complicate the production of all its tissue-mimicking derivates [ 21 ]. The neurotoxicity of the acrylamide monomer [ 22 ] and its correlation with cancer mean that its preparation and handling must be carried out in a controlled environment with appropriate precautions taken. S. Wang et al. [ 4 ] proposed electrically conductive 3D-printed cardiac models coated in 60°C irreversible thermochromic pigment to display ablation lesions. The models raised minimal safety concerns and could be 3D-printed to simulate the shape of the heart, but RCA resulted in superficial lesions on the paint coat. Other alternatives using agar [ 23 ], gelatine [ 24 ], carrageenan [ 25 ], and photopolymerised hydrogel [ 26 ] have been proposed, but often came at the compromise of physical properties when compared to polyacrylamide. Despite the numerous materials proposed to simulate RCA, no similar research could be identified in the field of cryoablation. Calcium alginate, a seaweed-derived hydrogel, has been cited as an ideal tissue-mimicking material due to its tough cross-linked structure and high water-content [ 27 , 28 , 29 ]. Fast preparation and minimal safety concerns [ 30 , 31 ] make moulding calcium alginate an effective and practical material in this context. It presents neither the complications associated with animal tissue, nor the complicated process and safety hazards encountered when making polyacrylamide gel. Calcium alginate commonly finds applications in dentistry as a moulding material and in the food industry [ 32 ] as a vegan ingredient, further emphasising its ethical-compliance and safety. Unlike agar, carrageen, or gelatine, moulding alginate does not melt under 100°C; it can resist higher water temperatures without deterioration and is structurally unaffected by freezing. Similarly to polyacrylamide, the material on its own is not sensitive to radiofrequency or freezing, so ablation-sensitive pigments must be introduced into the mixture to visualise ablation lesions for analysis. In this investigation, conductive alginate hydrogel was prepared with 3 non-hazardous pigments designed to change colour distinctly at the temperatures reached in RCA (50–60°C) and cryoablation (-40°C - -80°C). The resulting non-hazardous tissue-mimicking hydrogel formulations realistically replicate all the previously mentioned physical properties with < 15 minutes preparation time. This gel is the first practical, ethical, and safe alternative to in-vivo and ex-vivo models to simulate both RCA and cryoablation. RESULTS Alginate Formulation Fig. 1 shows the appearance different alginate mixtures: the control mixtures have a similar consistent white colour, while the coloured mixtures acquired the grey, red and yellow tones form their pigments. Preparation time was within 15 minutes for each mixture after having all components measured. All alginate batches cost less than £3.00 to make. A batch of either control mixture cost £0.37, whereas a batch of SFXC, NNC, and Kromagen cost £2.09, £2.15 and £2.09 respectively. Electrical Resistivity Control mixtures C25 and C30 displayed electrical resistivities of respectively 12.1 ± 0.4Ωm and 10.0 ± 0.4Ωm. The SFXC, NNC, and Kromagen mixtures each displayed resistivities of 7.4 ± 0.6Ωm, 7.1 ± 0.2Ωm, and 7.0 ± 0.5Ωm, respectively. Three-day-old ex-vivo porcine myocardium displayed an electrical resistivity of 7.6 ± 0.6Ωm in C. Saija et al. [33]. All the coloured alginates were less resistive than the respective control mixtures. No statistically significant difference was detected at the 5% level between SFXC and heart (p=0.5131), NNC and heart (p=0.0520), or Kromagen and heart (p=0.0548). Hardness The C25 and C30 mixtures respectively showed 23 ± 3 and 23 ± 2 OO Shore hardness. The SFXC mixture displayed 27 ± 2 OO Shore hardness. It was significantly harder than the C30 mixture (p=0.0014) and significantly harder than the literature-based reference (p<0.0001). The NNC mixture displayed 21 ± 2 OO Shore hardness. It was significantly softer than the C30 mixture (p=0.0391) and showed no statistically significant difference against the literature-based reference (p=0.4004). The Kromagen mixture displayed 19 ± 2 OO Shore hardness. It was significantly softer than the C25 mixture (p=0.0391) and showed no statistically significant difference against the literature-based reference (p=0. 4936). Thermal Conductivity The average TC of SFXC alginate was 0.67 ± 0.02W/m.K, which showed no significant difference with the literature overall average TC (p=0.1840). The average TC of NNC alginate was 0.62 ± 0.02W/m.K, which showed no significant difference with the TC of ventricular wall measured at 1.5W (p=0.8686). The average TC of Kromagen alginate was 0.58 ± 0.05W/m.K, which showed no significant difference with the TC of ventricular wall measured at 0.5W (p=0.9439). Electrical conductivity, Shore hardness, and thermal conductivity results are show graphically in Fig. 2. Radiofrequency Ablation System impedance for all three coloured mixtures (shown in Fig. 3) followed the expected inverse relationships with tank salinity and there was no difference in the trend followed by the three alginate mixtures. SFXC ablation lesions measured 3.8± 0.3mm in depth and 7.8 ± 0.8mm in width. SFXC lesions had no statistically significant difference in depth (p=0.0565) and width (p=0.0765) compared to literature values. RGB values for the lesion on SFXC alginate was (245, 246, 243), whilst background was (102, 101, 99). Colour contrast for the lesions against the background was 5.4:1. NNC ablation lesions measured 3.8± +0.4mm in depth and 7.9 ± 0.9mm in width. NNC lesions had no statistically significant difference in depth (p=0.0693) and width (p=0.1929) compared to literature values. RGB values for the lesion on NNC alginate was (240, 237, 235), whilst background was (155, 92, 85). Contrast for the lesions against the background was 4.4:1. Kromagen ablation lesions measured 3.7 ± 0.4mm in depth and 8.0 ± 0.7mm in width. Kromagen lesions had no statistically significant difference in depth (p=0.4422) and width (p=0.1942) compared to literature values. RGB values for the lesion on Kromagen alginate was (214, 137, 104), whilst background was (244, 205, 131). Colour contrast for the lesions against the background was 4.4:1. All lesions had lower variance in the lesion width and lesion depth than the literature values. These results are shown graphically in Fig 4. Cryoablation Only SFXC and NNC responded to cryoablation. After preparation, Kromagen progressively reverted back from magenta to yellow over one hour. Kromagen did not retain a permanent colour change after cryoablation. SFXC cryoablation lesions measured 6.9 ± 0.6mm in depth. There was a statistically significant difference between SFXC lesion depth and literature values (p<0.0001 in an unpaired two-tailed t-test). RGB values for the lesion on SFXC alginate was (121, 122, 113), whilst background was (234, 235, 221). Contrast for the lesions against the background was 3.6:1. NNC cryoablation lesions measured 5.2 ± 0.3mm in depth. There was no statistically significant difference between NNC lesion depth and literature values (p= 0.2458 in an unpaired two-tailed t-test). RGB values for the lesion on NNC alginate was (246, 235, 219), whilst background was (208, 248, 121). Contrast for the lesions against the background was 2:1. In all cryoablations, temperature remained between -40°C and -80°C, as expected [8]. These results are shown in Fig. 5. DISCUSSION The method used to create the alginate mixtures was easy, fast, and replicable. It involved the use of non-hazardous materials, and all samples were ready within 15 minutes of having all the components measured. All materials costs were less than £3.00 per batch, which is comparable to the cost of ex-vivo animal tissue. The value of resistivity measured in ex-vivo porcine myocardium for this study (7.6 ± 0.6Ωm) is coherent with the in-vivo electrical resistivity of ventricular myocardium (7.04 ± 2.11Ωm) reported in literature [ 38 ], validating the method adopted in this study. All the coloured alginate samples had no statistically significant difference to porcine myocardium reported in C. Saija et al. [ 33 ]. All pigments were conductive since the addition of these significantly decreased the resistivity of the alginate in all cases. The most electrically conductive pigment was Kromagen 50, which reduced the resistivity of C25 from 12.0 ± 0.4Ωm to 7.0 ± 0.5Ωm. The samples were only directly compared to ventricular myocardium from C. Saija et al. [ 33 ]. To provide a broader comparison, similar readings could have been recorded for different tissues in the heart, such as pericardial fat or connective tissue; however, for the purpose of this study, the electrical resistivities were accurate enough to simulate heart tissue. NNC and Kromagen alginates had realistic Shore hardness on the OO scale and showed no significant difference against the literature-derived hardness of ex-vivo myocardium, whereas SFXC alginate was harder and showed significant difference against the reference. This may stem from SFXC being the only dry pigment used in this study, whilst NNC and Kromagen were pigment slurries. Lower water content makes alginate harder, and water absorption from the pigment may have occurred, ultimately making the sample harder. Future investigations should evaluate if the change in Shore hardness from OO 20 ± 7.5 to 27 ± 2 can be detected by operators at different levels of experience, and if it significantly effects the force response on the catheter during navigation. SFXC (0.67 ± 0.02W/m.K) had the highest TC and showed no statistically significant difference with the overall average TC from ex-vivo myocardium from literature (0.675 ± 0.02 W/m.K). Kromagen (0.58 ± 0.05W/m.K) showed no statistically significant difference with ex-vivo ventricular myocardium measured at 0.5W (0.58 ± 0.02W/m.K). Whereas NNC (0.62 ± 0.02W/m.K) showed no statistically significant difference with ex-vivo ventricular myocardium measured at 1.5W (0.62 ± 0.01W/m.K). Because all results matched literature values of TC from ex-vivo porcine myocardium, all mixtures had appropriately realistic TC for the purpose of a simulation. The method utilised in this test was accurate, however, the standard deviation of TC from the literature values was lower. Future studies should aim to investigate the thermal permittivity as well as the heat capacity of these hydrogels to further simulate heat dissipation post-ablation, insulating the apparatus to improve precision. In the case of radiofrequency ablation, the method directly replicated the one implemented in M. Barkagan et al. [ 11 ], using the same CARTO 3 (Biosense Webster, Irvine, USA) set up and settings. All coloured mixtures showed no statistically significant difference when compared to the lesion dimensions achieved in M. Barkagan et al. [ 11 ] at on ex-vivo myocardium, thus all mixtures could be used to effectively simulate RCA. The pigmented mixtures produced greater precision with comparable means to the literature, emphasising the improvement in results replicability that can be achieved from this hydrogel. Kromagen and NNC are more sensitive, changing colour at 50°C, while SFXC changes colour at 60°C but has higher TC. Consequently, no significant difference in lesion dimensions was identified amongst the three mixtures. SFXC and NNC had the best colour contrasts at 5.4:1 and 4.4:1, making the boundary of the lesions well defined and easy to notice. Kromagen, on the other hand, is a pigment which gradually changes colour and had a colour contrast of 1.8:1, ultimately making the ablation lesion less defined than in SFXC and NNC. This behaviour could be subject of future studies to assess temperature gradients created during RCA. Unexpectedly, Kromagen alginate lesions faded in colour over time, posing a potential limitation to the widespread use of this pigment. Further research would uncover more of the colour behaviour of Kromagen and its potential application in RCA. Though this investigation analysed up to a single pigment per mixture, future developments may combine multiple thermochromic agents of different sensitivities to produce colourful thermal maps indicating the various temperatures reached within the alginate matrix. In the case of cryoablation, our experiment simulated the methods performed on dogs in F. Bessière et al. [ 8 ] using the Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and CryoCath console (Medtronic CryoCath LP, Montreal, Canada) using the same console the same ablation settings. The NNC mixture resulted in ablation lesions comparable to the literature. SFXC responded to freezing, however, the lesions were too large. This discrepancy may be attributed to the difference in TC as well as the pigment’s sensitivity to freezing. Kromagen did not generate any lesion after freezing and did not maintain colour after heating, making it unusable for this simulation. The colour contrast between lesion and background was lower after cryoablation than after RCA, indicating the pigments may be more sensitive to heat. Due to the shape of the catheter, the only measure that could be compared was depth. Future investigations should aim to replicate this test using a range of different catheters to compare to literature while also moulding the material in the shape of atria to test for lesion-transmutability and oesophageal injury. Though only incident in 1% of patients, atrio-oesophageal fistula formation ensuing from CA results in an 80% mortality rate [ 34 ]. This material may therefore find extensive applications in modern research in this field [ 35 , 36 ], allowing operators to study tissue damage and temperature transfer between different layers of tissue. All hydrogels achieved high-fidelity to ex-vivo myocardium and produced realistic results under RCA, but only NNC performed realistically during cryoablation. Assessing the performance across all tests, the NNC mixture obtained the best results overall, having found no statistically significant difference against ex-vivo myocardium on any of the physical tests, while displaying realistic lesions dimensions. Despite its unique colour changing properties, Kromagen had a low colour contrast and underperformed during cryoablation, ultimately making it not a good option. Its properties could be further investigated to produce data on heat propagation in the gel. The SFXC mixture obtained the best electrical properties, thermal properties, and colour contrast, however its hardness was significantly higher than myocardium and it was outperformed by NNC in cryoablation. Ultimately, SFXC performed better than Kromagen but not NNC. In future investigations, users may employ 3D-printing or moulds to shape the alginate mixtures into heart phantoms which could also be perfused with water pumps to emulate blood flow and create a highly-realistic simulation environment without using animal tissue. Though in-vivo tests still remain the most realistic test conditions, the NNC thermochromic hydrogel hereby formulated arguably outperformed ex-vivo porcine myocardium, as it could markedly show the ablation lesion for both cryoablation and RF ablation. This gel is the first synthetic model that allows operators to compare multiple ablation modalities (such as RCA or cryoablation), new ablation equipment (such as catheters), and ablation techniques (such as single shot ablation or point-by-point) without immediately resorting to live animal studies. To conclude, the study assessed the performance of three tissue-mimicking hydrogels for cardiac ablation simulation. The results indicate that the NNC alginate mixture can reliably replicate the thermal, electrical, and mechanical properties of ex-vivo porcine myocardium in order to be used to simulate response to ablation. Unlike previously attempted formulations in the literature, this material is non-hazardous, inexpensive, and ethically compliant, as well as homogeneous and replicable, making it an easy, quick, and ethical tissue-mimicking hydrogel for both RCA and cryoablation tests. METHODS Alginate Formulation White calcium alginate moulding powder (Pebeo, Marseille, France) was utilised as the gelling agent. Saline was prepared at 0.3% and 0.25% mass concentrations using deionised water and NaCl. Kromagen50 (SpotSee, Dallas, Texas), SFXC 60°C Irreversible Thermochromic Pigment (Good Life Innovations Ltd., Seaford, United Kingdom) and NNC TM-SL W50-0 Brown (New Prismatic Enterprise Co., Taipei, Taiwan) were identified as the three thermochromic pigments for these experiments as they retain their new colour after changing. Two control mixtures and three coloured mixtures were prepared following the ratios shown in Table 1 . Liquids and powders were mixed and measured separately before being combined with a hand blender for 30 seconds. The blender was then opened, and the sides were scraped. The mixture was blended for 10 more seconds and poured in moulds to set for 10 minutes. Table 1 Formulations for the mixtures of alginate analysed. Mixture Saline Mass Concentration Pigment Mass (g) Mass Saline (g) Mass Alginate Powder (g) Control Mixtures Control 0.25% (C25) 0.250% 0.00 120 32.0 Control 0.3% (C30) 0.300% 0.00 120 32.0 Coloured Mixtures SFXC 0.300% 2.00 120 32.0 NNC 0.300% 2.50 120 32.0 Kromagen 0.250% 2.50 120 32.0 Electrical Resistivity To evaluate the electrical properties of all mixtures, a volume constrained box 45 x 15 x 15mm was 3D-printed in Anycubic Basic Clear Resin (HongKong Anycubic Technology Co., Hong Kong, China). 15mm square copper electrodes were constructed using 0.5mm copper sheets and placed on either side of the box. The electrodes were connected to a switch and a multimeter to measure electrical resistance. Internal resistance of the system was measured at 0.00 ± 0.00kΩ, using the 20kΩ range. Ten 45 x 15 x 15mm slices of each alginate mixture were prepared and moulded to size. Each slice was placed in the box and compressed by the lid, ensuring full contact with the electrodes and consistent volume (Fig. 6 A). The switch was turned on to inspect the initial resistance of the material in kΩ. Resistivity of each material was calculated by multiplying the value of resistance by the cross-sectional area of the sample, divided by its length. Electrical resistivity can otherwise be calculated as the inverse of electrical conductivity. Using the same methods and set up [ 33 ], our previous research measured the electrical resistivity of porcine myocardium to be 7.6 ± 0.6 Ωm. In literature, D. Miklavčič et al. [ 37 ] describes ex-vivo heart tissue to have electrical conductivity of 0.06-0.4S/m (resistivity = 2.5–16.7Ωm); K. Raghavan et al. [ 38 ] reports that in-vivo myocardium has an electrical conductivity of 0.142 ± 0.043S/m (resistivity = 7.04 ± 2.11Ωm). Hardness A HT-6510OO OO-Shore Durometer (Landtek Instruments Co., Guangzhou, China) was mounted on a remote-controlled linear actuator. On the opposite side of the actuator, a 1mm thick cup containing a 20 x 35mm (length x diameter) cylinder of alginate was held in place by two M4 screws, holding it centred with the durometer (Fig. 6 B). The durometer was displaced by 15mm allowing the alginate to come in to contact with the body of the durometer. 10 measurements of hardness were recorded for each mixture, using 10 separate cylinders. A. Tejo-Otero et al. [ 39 ] reported that hydrogels of OO Shore hardness 20 ± 7.5 can be used to recreate ex-vivo cardiac muscle. Based on this, a 10,000-element vector was created following a normal distribution with mean 20 and standard deviation 7.5 using MATLAB function “normrnd” as a literature-derived reference for statistical analysis. Thermal Conductivity Thermal Conductivity (TC) was analysed to compare the thermal behaviour of alginate to ex-vivo myocardium, which would directly affect lesion dimensions via the propagation of heat/cold. The TC of myocardium falls between 0.58 and 0.75 W/m.K [ 15 , 40 ]. The paper by D. Končan et al. [ 15 ] was chosen as a reference for this investigation, as it analysed the TC of the septum and the ventricular wall, two common ablation sites. The study used varying power (0.5W-1.5W) to heat ventricular and septal ex-vivo porcine myocardium and measured their TC. The study reported ventricular TC of 0.58 ± 0.02W/m.K when heating at 0.5W, and 0.62 ± 0.01W/m.K when heating at 1.5W. The overall average TC of myocardium across all methods in D. Končan et al. [ 15 ] is 0.675 ± 0.02 W/m.K. Based on the means and standard deviations of these three TC values, three normally distributed arrays of 10,000 elements were generated using MATLAB function “normrnd” to provide some literature-derived references for statistical analysis. To measure the thermal conductivity of alginate, long cylindrical 110 x 37.5mm samples were cast inside of polylactic acid 3D-printed moulds. The TSL-100 thermal conductivity analyser (Thermtest Instruments, New Brunswick, Canada) was fully inserted into the sample and a value of thermal conductivity was measured (Fig. 6 C). The test was repeated 10 times on different samples for all mixtures. Like all other measured properties, the TC values acquired during this study were compared against the reference using a 5% confidence level in a two-tailed multi-variance t-test. Radiofrequency Ablation To analyse the radiofrequency ablation behaviour of the hydrogel and directly compare the finding to M. Barkagan et al. [ 11 ], the simulator system published in C. Saija et al. [ 33 ] was adapted to replicate the same ablation conditions. To emulate the heart walls 75 x 55 x 10mm slices of coloured alginate were moulded to simulate the thickness of ventricular walls [ 41 ]. The coloured alginate slices were mounted on a perforated base with a 1.5cm sponge using a plastic frame. The base was mounted in the centre of a temperature-controlled 55 x 38 x 27cm acrylic tank filled with saline at different concentrations. The Valleylab Return Patient electrode (Covidien, Dublin, Ireland) was placed on the bottom of the tank facing into the saline in the inferior section of the tank to simulate patch placement on the lower back of the patient (Fig. 7 .A). The saline was kept at 37.0°C and saline mass concentration was progressively increased (0.05%, 0.1%, 0.2%, 0.3%) and the baseline impedance was recorded on 5 separate locations on the slice using a Thermocool SmartTouch Unidirectional Navigation Catheter (NAV ST SF) (Biosense Webster Inc., Irvine, USA) in the CARTO VIZIGO 8.5F (Biosense Webster Inc., Irvine, USA) steerable sheath linked to the SMARTABLATE System (Biosense Webster Inc., Irvine, USA). Based on the idealised electrical model displayed in Fig. 7 B, the relationship between system impedance (R) versus tank salinity (x) can be derived as shown is Eq. 1, where A, B, C, D are constants and α = 1/A and β = 1/B. $$\:R=\frac{1}{\frac{x}{A}+\frac{1}{B}}+\frac{C}{x}+D$$ $$\:\:\:\:\:\:\:\:\:\:\:\:=\frac{1}{\alpha\:x+\beta\:}+\frac{C}{x}+D$$ M. Barkagan et al. [ 11 ] performed ablation lesions in a similar simulator set-up using ex-vivo porcine ventricular wall. Their low impedance (100–130Ω) tests performed lesions at 30W for 20 seconds and averaged a depth of 3.6 ± 0.7 mm and a width of 8.3 ± 1.4 mm using an open-irrigated ablation catheter (Thermocool SmartTouch SF; Biosense Webster, Irvine, USA) and a SmartAblate radiofrequency generator (Stockert GmbH, Freiburg, Germany) linked to the CARTO 3 system (Biosense Webster, Irvine, USA). In order to be comparative to this published study, our tank was filled with 0.075% saline (impedance: 100–130Ω) at 37.0°C and 10 ablation lesions were performed on 10mm slices of the coloured alginate mixtures using the same equipment and settings. The ablation catheter was held perpendicular to the alginate sample using the steerable sheath; ablations were performed at 30W for 20 seconds applying 10g of force and irrigating with 24°C 0.075% saline at 8ml/min as per default. Results of lesion depth and width were measured digitally based on a ruler placed directly next to each sample as shown in Fig. 7 C. Results of width and depth were compared against the findings of M. Barkagan et al. [ 11 ] as previously described using MATLAB. Finally, to evaluate the colour contrast between the lesions and the background alginate, the RGB values of the coloured mixtures were analysed based on pictures acquired under equal light conditions. The RGB values of 125 pixels were acquired from both the background and the lesions and averaged. The colour contrast was then calculated using Colour Contrast Analyser (TPGi, Clearwater, USA). Cryoablation To test the cryoablation properties of the materials, the methods listed in F. Bessière et al. [ 8 ] were replicated using the Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and CryoCath console (Medtronic CryoCath LP, Montreal, Canada) using nitrous oxide (N2O) refrigerant. In their experiment they cryoablated both the atrial and ventricular walls of live dogs using the same settings, resulting in mostly transmural lesions in the atrial walls (3.5 ± 0.4mm), but not in the ventricles. More specifically, only 2.43% of left ventricular lesions were transmural due to wall thickness; the maximum lesion depth reached in this area was on average 5.1 ± 0.3mm with exposure time 2-4min, marking a finite limit of reachable depth. To simulate the same conditions in our experiment, two 10mm ventricle-like alginate slices were prepared for each mixture. For colour change to occur in reverse, each mixture was prepared by adding the pigments in the saline and heating the solutions in plastic containers for 10 minutes at 70°C. Each measured solution was cooled then mixed with alginate powder, as described previously, and cast into 75 x 55 x 10mm slices. Slices were held in a 37.0°C heated water bath; cryoablation was performed replicating the methods of F. Bessière et al. [ 8 ] as closely as possible using a Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and the CryoCath console (Medtronic CryoCath LP, Montreal, Canada) for 3 minutes using nitrous oxide (N2O) refrigerant (Fig. 7 D). As per default settings, temperatures were monitored with a sampling frequency of 10Hz with a 1°C accuracy maintaining temperatures within the range of -40°C to -80°C like in F. Bessière et al. [ 8 ]. Due to the shape of the catheter, the lesions had an annular shape (Fig. 7 E). Two ablations were performed for each material. The annular ablations were sliced, and depth was digitally measured 16 times. Results of lesion dimensions were compared against the findings of F. Bessière et al. [ 8 ] as previously described using MATLAB. Declarations The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. ACKNOWLEDGMENTS We thank Marco Pinto and his colleagues at Biosense Webster for their assistance with operating the CARTO mapping and ablation system. We thank the technical management team in the Surgical and Interventional Engineering Department at King’s College London for their support during our experiments. AUTHOR CONTRIBUTIONS: Mr. Carlo Saija: Establishing the alginate mixtures, all physical tests, all ablation tests, statistical analysis and writing. Mr. Sukruth Pradeep Kundur: physical tests and photography. Dr. Lisa Leung: cryoablation testing and ablation equipment procurement. Dr. Sachin Sabu: ablation equipment procurement and logistics. Mr. Marco Pinto: ablation equipment procurement and consultation for ablation equipment operation. Dr. Mark Herridge: ablation equipment procurement and consultation for ablation equipment operation. Mr. Adharvan Gabbeta: photography and radiofrequency ablation testing. Ms. Rashi Chavan: photography and radiofrequency ablation testing. Ms. Nadia Chowdhury: preliminary testing of electrical resistivity. Dr. Gregory Gibson: ablation equipment procurement, consolation in ablation equipment operation, and logistics. Dr. Calum Byrne: ablation equipment procurement and consolation in ablation equipment operation, and logistics. Dr. Antonia Pontiki: experimental technique and methodology consultation, writing. Dr. Richard James Housden: supervisor, writing. Dr. Jonathan Behar: supervisor, writing. Prof. Kawal Rhode: supervisor, writing. SOURCES OF FUNDING London [WT203148/Z/16/Z]; the British Heart Foundation (BHF) Centre of Excellence at King’s College London; the Department of Health and Social Care (DHSC) through the National Institute for Health and Care Research (NIHR) MedTech; and Vitro Diagnostic Co-operative (MIC) Award for Cardiovascular Diseases to Guy’s & St Thomas’ NHS Foundation Trust in partnership with King’s College London [MIC-2016-019]. This work was supported by funding from Caranx Medical, Nice, France. DISCLOSURES Author Carlo Saija was employed by the company Caranx Medical. Author Pierre Berthet-Ryne was employed by the company Caranx Medical. Author Marco Antonio Coutinho Pinto was employed by the company Biosense Webster. The remaining authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. OPTIONAL EXTENDED DATA: N/a References Morillo, C.A., Banerjee, A., Perel, P., Wood, D. & Jouven, X. Atrial Atrial fibrillation: the current epidemic. Journal of Generic Cardiology 14(3) ,195-203 (2017). Lippi, G., Sanchis-Gomar, F. & Cervellin, G. Global Epidemiology of Atrial Fibrillation: An increasing epidemic and Public Health Challenge. International Journal of Stroke 16, 217–221 (2020). Iwasawa, J. et al. Temperature-controlled radiofrequency ablation for pulmonary vein isolation in patients with atrial fibrillation. Journal of the American College of Cardiology 70, 542–553 (2017). Wang, S. et al. Cardiac radiofrequency ablation simulation using a 3D-printed bi-atrial thermochromic model. Applied Sciences 12, 6553 (2022). Gervais, D. & McDermott, S. Radiofrequency ablation of liver tumors. Seminars in Interventional Radiology 30, 049–055 (2013). Nandini, V. V., Venkatesh, K. Y. & Nair, K. C. Alginate impressions: A practical perspective. Journal of Conservative Dentistry 11, 37 (2008). Friedman, P. L. Catheter cryoablation of cardiac arrhythmias. US Cardiology Review 1, 126–128 (2004). Bessière, F. et al. Focal Transcatheter Cryoablation: Is a Four-Minute Application Still Required? Journal of Cardiovascular Electrophysiology 28 , 559–563 (2017). Khairy, P. et al. Lower incidence of thrombus formation with Cryoenergy versus radiofrequency catheter ablation. Circulation 107 , 2045–2050 (2003). Thiagalingam, A. et al. Importance of Catheter Contact Force during Irrigated Radiofrequency Ablation: Evaluation in a Porcine Ex Vivo Model using a Force‐Sensing Catheter. Journal of Cardiovascular Electrophysiology 21 , 806–811 (2010). Barkagan, M., Rottmann, M., Leshem, E., Shen, C., Buxton, A.E., & Anter, E. Effect of baseline impedance on ablation lesion dimensions. Circulation: Arrhythmia and Electrophysiology 11 , 10 (2018). Kongsgaard, E., Foerster, A., Aass, H., Madsen, S. & Amlie, J.P. Power and temperature guided radiofrequency catheter ablation of the right atrium in Pigs. Pacing and Clinical Electrophysiology 17 , 1610–1620 (1994). Feld, G. K. Journal of Interventional Cardiac Electrophysiology 8, 135–140 (2003). Yuan, D.Y., Valvano, J.W., & Anderson, G.T. Measurement of thermal conductivity, thermal diffusivity, and perfusion. Biomedical Sciences Instrumentation 29 , 435-442 (1993). Končan, D. et al. Thermal conductivity of the porcine heart tissue. Pflügers Archiv - European Journal of Physiology 440, S1 (2000). Bu-Lin, Z. et al. polyacrylamide Gel Phantom for radiofrequency ablation. International Journal of Hyperthermia 24, 568–576 (2008). Zhong, X., Cao, Y. & Zhou, P. Thermochromic tissue-mimicking phantoms for thermal ablation based on polyacrylamide gel. Ultrasound in Medicine & Biology 48, 1361–1372 (2022). Mikhail, A.S. et al. Evaluation of a tissue‐mimicking thermochromic phantom for radiofrequency ablation. Medical Physics 43, 4304–4311 (2016). Chik, W.W. et al. High spatial resolution thermal mapping of radiofrequency ablation lesions using a novel thermochromic liquid crystal myocardial Phantom. Journal of Cardiovascular Electrophysiology 24, 1278–1286 (2013). Qian, P.C. et al. Irrigated microwave catheter ablation can create deep ventricular lesions through epicardial fat with relative sparing of adjacent coronary arteries. Circulation: Arrhythmia and Electrophysiology 13, (2020). Zhong, X., Cao, Y. & Zhou, P. Thermochromic tissue-mimicking phantoms for thermal ablation based on polyacrylamide gel. Ultrasound in Medicine & Biology 48, 1361–1372 (2022). Smith, E. A. & Oehme, F. W. Acrylamide and polyacrylamide: A review of production, use, environmental fate and neurotoxicity. Reviews on Environmental Health 9, (1991). Lobo, S.M. et al. Radiofrequency ablation: Modeling the enhanced temperature response to adjuvant NaCl Pretreatment. Radiology 230, 175–182 (2004). Lazebnik, M., Madsen, E. L., Frank, G. R. & Hagness, S. C. Tissue-mimicking phantom materials for narrowband and ultrawideband microwave applications. Physics in Medicine and Biology 50, 4245–4258 (2005). Kuroda, M. et al. Development of a new hybrid gel phantom using Carrageenan and gellan gum for visualizing three-dimensional temperature distribution during hyperthermia and radiofrequency ablation. International Journal of Oncology (2005). doi:10.3892/ijo.27.1.175 Maruyama, H., Yokota, Y., Hosono, K. & Arai, F. Hydrogel heart model with temperature memory properties for surgical simulation. Sensors 19, 1102 (2019). Ji, D. et al. Superstrong, superstiff, and conductive alginate hydrogels. Nature Communications 13, (2022). Lee, K. Y. & Mooney, D. J. Alginate: Properties and biomedical applications. Progress in Polymer Science 37, 106–126 (2012). Chen, W. J., Wang, Q. & Kim, C. Y. Gel Phantom models for radiofrequency and microwave ablation of the liver. Digestive Disease Interventions 04, 303–310 (2020). Cervino, G. et al. Alginate materials and dental impression technique: A current state of the art and application to dental practice. Marine Drugs 17, 18 (2018). Rambe, A. O., Eriwati, Y. K. & Santosa, A. S. Preparation of experimental dental alginate impression material from Sargassum spp. seaweed extract based on its setting time. Journal of Physics: Conference Series 1073, 052013 (2018). Zhao, W. et al. Morphology and thermal properties of calcium alginate/reduced graphene oxide composites. Polymers 10, 990 (2018). Saija, C. et al. Evaluation of a Three-Dimensional Printed Interventional Simulator for Cardiac Ablation Therapy Training. Applied Sciences 14 , 8423–8423 (2024). He, F., Zhang, W., Xu, B., Huang, G.-P. & Chen, H.-D. Atrioesophageal fistula after atrial fibrillation catheter ablation. Medicine 100 , e24226–e24226 (2021). Sanchez, J. et al. Atrioesophageal Fistula Rates Before and After Adoption of Active Esophageal Cooling During Atrial Fibrillation Ablation. JACC: Clinical Electrophysiology 9 , 2558–2570 (2023). Leung, L. W. M. et al. Preventing esophageal complications from atrial fibrillation ablation: A review. Heart Rhythm O2 2 , 651–664 (2021). Miklavčič, D., Pavšelj, N. & Hart, F. X. Electric properties of tissues. Wiley Encyclopedia of Biomedical Engineering (2006). doi:10.1002/9780471740360.ebs0403 Raghavan, K. et al. Electrical conductivity and permittivity of murine myocardium. IEEE Transactions on Biomedical Engineering 56, 2044–2053 (2009). Tejo-Otero, A. et al. Soft-tissue-mimicking using hydrogels for the development of phantoms. Gels 8, 40 (2022). Bowman, H. F., Cravalho, E. G. & Woods, M. Theory, measurement, and application of thermal properties of biomaterials. Annual Review of Biophysics and Bioengineering 4, 43–80 (1975). Yalçin, F., Abraham, T. P. & Gottdiener, J. S. Letter by Yalçin et al regarding article, “left ventricular wall thickness and the presence of asymmetric hypertrophy in healthy young army recruits: Data from the large heart study”. Circulation: Cardiovascular Imaging 6, (2013). Additional Declarations Competing interest reported. Author Carlo Saija was employed by the company Caranx Medical. Author Pierre Berthet-Ryne was employed by the company Caranx Medical. Author Marco Antonio Coutinho Pinto was employed by the company Biosense Webster. The remaining authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest. Cite Share Download PDF Status: Published Journal Publication published 07 Oct, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Accepted 03 Sep, 2025 Reviews received at journal 09 May, 2025 Reviewers agreed at journal 23 Apr, 2025 Reviewers invited by journal 21 Apr, 2025 Submission checks completed at journal 20 Apr, 2025 First submitted to journal 08 Apr, 2025 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. 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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-5483662","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":445758477,"identity":"ac35d47c-5c12-4475-a4a7-bdcd42c3b6ea","order_by":0,"name":"Carlo 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London","correspondingAuthor":false,"prefix":"","firstName":"Jonathan","middleName":"M","lastName":"Behar","suffix":""},{"id":445758492,"identity":"3a5baddb-710f-46db-99dc-a0c1c870e540","order_by":15,"name":"Kawal Rhode","email":"","orcid":"","institution":"King's College London","correspondingAuthor":false,"prefix":"","firstName":"Kawal","middleName":"","lastName":"Rhode","suffix":""}],"badges":[],"createdAt":"2024-11-19 12:53:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5483662/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5483662/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-18732-1","type":"published","date":"2025-10-07T15:57:14+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81116087,"identity":"69f43c7c-642f-4fce-87c4-6018c14855d9","added_by":"auto","created_at":"2025-04-22 11:40:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":643141,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA: C25 Alginate Mixture. B: C30 Alginate Mixture. C: SFXC Alginate Mixture. D: NNC Alginate Mixture. E: Kromagen Alginate Mixture.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/9c852648ab1bdf15e0b01a1a.png"},{"id":81116395,"identity":"a0ad0b3c-2895-474e-92d8-09232d51e3de","added_by":"auto","created_at":"2025-04-22 11:48:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":164339,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003ePhysical properties of alginate mixtures compared to literature-derived references. A: Electrical resistivity of alginate compared to ex-vivo porcine myocardium in the same experimental set-up [33]. B: OO Shore hardness of alginate compared to myocardium as reported in A. Tejo-Otero et al. [39]. \u0026nbsp;C: Thermal conductivity of alginate compared to ex-vivo porcine myocardium thermal conductivity values derived from D. Končan et al. [15]. Red crosses show outliers.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/f32f671539e9ec55c11861f2.png"},{"id":81116088,"identity":"13f4e619-c729-4b61-bec3-5d20c5e8d012","added_by":"auto","created_at":"2025-04-22 11:40:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":160089,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSystem impedance measured on 10mm SFXC (A), NNC (B), and Kromagen (C) alginate slices in different saline concentrations in the 55x38x27cm tank. The dotted red line represents Equation 1 plotted as the line of best fit to represent the relationship between Impedance and Tank Salinity.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/f5c84ff5f67fe7e2088ed44d.png"},{"id":81116089,"identity":"8d7a2c52-a0ff-4642-a418-93ac735e076f","added_by":"auto","created_at":"2025-04-22 11:40:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":925680,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA, B, C: RCA lesions shape and colour contrast for Kromagen (A) SFXC (B), NNC (C). D: Radiofrequency Ablation Lesion Width in Coloured Alginate Mixtures compared to Ex-Vivo Porcine Myocardium from M. Barkagan et al. [11]. E: Radiofrequency Ablation Lesion Depth in Coloured Alginate Mixtures compared to Ex-Vivo Porcine Myocardium from M. Barkagan et al. [11].\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/af87e42d6759bc8ae7eb2edc.png"},{"id":81116393,"identity":"08ca61a4-54aa-4567-8b3c-768da147c8c7","added_by":"auto","created_at":"2025-04-22 11:48:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":961392,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA, B, C: Cryoablation Lesions Shape and Colour Contrast for Kromagen (A) SFXC (B), NNC (C). D: Cryoablation Lesion Depth for Coloured Alginates (marked as NNC and SFXC) after Cryoablation compared to in-vivo dogs from F. Bessière et al. [8].\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/c27a087c67403393505a7fa1.png"},{"id":81116113,"identity":"7d8908fc-4889-4c94-b2db-bce9768697e4","added_by":"auto","created_at":"2025-04-22 11:40:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":866003,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA:Volume-constrained box (1) connected to a multimeter (3) using wires and a switch (2) to measure electrical resistivity. B:HT-6510OO OO-Shore Durometer (4) mounted on the linear actuator (5). C: TSL-100 Thermal Conductivity Analyser (6) setup.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/7b2dbb35aa83f67fc8c07087.png"},{"id":81116097,"identity":"7f28dbf9-3b4b-48d7-b12b-927bf91ada8f","added_by":"auto","created_at":"2025-04-22 11:40:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2394727,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA: The RCA simulator system. The thermostat system (1), Grounding patch (2), and RCA catheter (3) \u0026nbsp;B: Electrical path followed by the radiofrequency starting at the tip of the catheter on the left and terminating with the grounding patch on the right, derived from M. Barkagan et al. [11]. C: Digital lesion dimensions measurements. D,E: The Cryoablation simulation system using a cryoballoon catheter (4).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/10fc166d272a8453a171209a.png"},{"id":93420056,"identity":"65de77f9-0aea-4655-a586-80ecaa61580d","added_by":"auto","created_at":"2025-10-13 16:09:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7924914,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5483662/v1/f4c8392d-ae34-4c2b-b9d0-b433c3bc907e.pdf"}],"financialInterests":"Competing interest reported. Author Carlo Saija was employed by the company Caranx Medical. Author Pierre Berthet-Ryne was employed by the company Caranx Medical. Author Marco Antonio Coutinho Pinto was employed by the company Biosense Webster. The remaining authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.","formattedTitle":"A Novel Thermochromic Myocardial Phantom for Radiofrequency Ablation and Cryoablation","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eCardiac ablation (CA) has become a well-established procedure to treat cardiac arrhythmias, which affect a growing number of patients worldwide [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Radiofrequency cardiac ablation (RCA) uses high temperatures (50\u0026ndash;60\u0026deg;C) [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] delivered by a catheter to induce localised scarring in the arrhythmogenic regions of the heart. Radiofrequency ablation finds applications across a plethora of medical procedures, e.g. the treatment of liver tumours [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] and gastroesophageal reflux disease [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. An alternative to RCA often utilised in pulmonary vein isolation is cryoablation. Low temperature between \u0026minus;\u0026thinsp;30\u0026deg;C and \u0026minus;\u0026thinsp;80\u0026deg;C is applied to freeze cells and create areas of controlled scar [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs a minimally invasive procedure yielding effective results in tackling the growing demand for arrythmia treatment, there is great potential in the development of CA technology, and subsequently, a significant need for standardised testing and training. Currently, the majority of clinical studies [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] tested RCA using ex-vivo tissue models, mainly myocardial and skeletal muscle acquired from swine, dogs, and occasionally chickens. Due to the nature of freezing tissue, ex-vivo muscle does not visibly respond to cryoablation. To analyse the effects of this procedure, in-vivo tests are performed on dogs [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and the histological effects are analysed post-mortem, days to months after. As well as ethical, financial, and practical difficulties presented by in-vivo and ex-vivo testing, the non-homogeneity of tissue samples poses difficulties in testing [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In CA, the locus of tissue acquisition (e.g. ventricular wall, cardiac septum, skeletal muscle of the thigh), and the testing apparatus in which the samples are placed, can affect lesion shape and size. Post-operative lesion visualisation, in addition to the plasticity and structural uniformity of the tissue, pose limitations to reliable data acquisition. As a result, numerous studies propose myocardium-mimicking materials for ablation testing.\u003c/p\u003e \u003cp\u003eFor the myocardium-mimicking material to be suitable, it must display realistic thermal conductivity, realistic electrical resistivity, a realistic mechanical response to the catheter, and must show visibly measurable change post-ablation. Albumin [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and thermochromic inks [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] have been introduced in conductive polyacrylamide gel to create a conductive medium that could be ablated and would permanently change colour in the areas that reached RCA temperatures (\u0026ge;\u0026thinsp;50\u0026deg;C). This was applied to RCA as well as liver ablation to assess the ablation lesion dimensions. Reversible thermochromic liquid crystals found similar applications in polyacrylamide [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], allowing the users to simulate radiofrequency ablation and produce full thermal maps. Despite its repeated appearance in literature, safety concerns regarding the preparation of polyacrylamide complicate the production of all its tissue-mimicking derivates [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The neurotoxicity of the acrylamide monomer [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] and its correlation with cancer mean that its preparation and handling must be carried out in a controlled environment with appropriate precautions taken. S. Wang \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] proposed electrically conductive 3D-printed cardiac models coated in 60\u0026deg;C irreversible thermochromic pigment to display ablation lesions. The models raised minimal safety concerns and could be 3D-printed to simulate the shape of the heart, but RCA resulted in superficial lesions on the paint coat. Other alternatives using agar [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], gelatine [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], carrageenan [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], and photopolymerised hydrogel [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] have been proposed, but often came at the compromise of physical properties when compared to polyacrylamide. Despite the numerous materials proposed to simulate RCA, no similar research could be identified in the field of cryoablation.\u003c/p\u003e \u003cp\u003eCalcium alginate, a seaweed-derived hydrogel, has been cited as an ideal tissue-mimicking material due to its tough cross-linked structure and high water-content [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Fast preparation and minimal safety concerns [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] make moulding calcium alginate an effective and practical material in this context. It presents neither the complications associated with animal tissue, nor the complicated process and safety hazards encountered when making polyacrylamide gel. Calcium alginate commonly finds applications in dentistry as a moulding material and in the food industry [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] as a vegan ingredient, further emphasising its ethical-compliance and safety. Unlike agar, carrageen, or gelatine, moulding alginate does not melt under 100\u0026deg;C; it can resist higher water temperatures without deterioration and is structurally unaffected by freezing. Similarly to polyacrylamide, the material on its own is not sensitive to radiofrequency or freezing, so ablation-sensitive pigments must be introduced into the mixture to visualise ablation lesions for analysis.\u003c/p\u003e \u003cp\u003eIn this investigation, conductive alginate hydrogel was prepared with 3 non-hazardous pigments designed to change colour distinctly at the temperatures reached in RCA (50\u0026ndash;60\u0026deg;C) and cryoablation (-40\u0026deg;C - -80\u0026deg;C). The resulting non-hazardous tissue-mimicking hydrogel formulations realistically replicate all the previously mentioned physical properties with \u0026lt;\u0026thinsp;15 minutes preparation time. This gel is the first practical, ethical, and safe alternative to in-vivo and ex-vivo models to simulate both RCA and cryoablation.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003e\u003cstrong\u003eAlginate Formulation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig. 1 shows the appearance different alginate mixtures: the control mixtures have a similar consistent white colour, while the coloured mixtures acquired the grey, red and yellow tones form their pigments. Preparation time was within 15 minutes for each mixture after having all components measured. All alginate batches cost less than \u0026pound;3.00 to make. A batch of either control mixture cost \u0026pound;0.37, whereas a batch of SFXC, NNC, and Kromagen cost \u0026pound;2.09, \u0026pound;2.15 and \u0026pound;2.09 respectively.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrical Resistivity\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eControl mixtures C25 and C30 displayed electrical resistivities of respectively 12.1 \u0026plusmn; 0.4\u0026Omega;m and 10.0 \u0026plusmn; 0.4\u0026Omega;m. The SFXC, NNC, and Kromagen mixtures each displayed resistivities of 7.4 \u0026plusmn; 0.6\u0026Omega;m, 7.1 \u0026plusmn; 0.2\u0026Omega;m, and 7.0 \u0026plusmn; 0.5\u0026Omega;m, respectively. Three-day-old ex-vivo porcine myocardium displayed an electrical resistivity of 7.6 \u0026plusmn; 0.6\u0026Omega;m in C. Saija \u003cem\u003eet al.\u003c/em\u003e [33]. All the coloured alginates were less resistive than the respective control mixtures. No statistically significant difference was detected at the 5% level between SFXC and heart (p=0.5131), NNC and heart (p=0.0520), or Kromagen and heart (p=0.0548).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHardness\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe C25 and C30 mixtures respectively showed 23 \u0026plusmn; 3 and 23 \u0026plusmn; 2 OO Shore hardness. The SFXC mixture displayed 27 \u0026plusmn; 2 OO Shore hardness. It was significantly harder than the C30 mixture (p=0.0014) and significantly harder than the literature-based reference (p\u0026lt;0.0001). The NNC mixture displayed 21 \u0026plusmn; 2 OO Shore hardness. It was significantly softer than the C30 mixture (p=0.0391) and showed no statistically significant difference against the literature-based reference (p=0.4004). The Kromagen mixture displayed 19 \u0026plusmn; 2 OO Shore hardness. It was significantly softer than the C25 mixture (p=0.0391) and showed no statistically significant difference against the literature-based reference (p=0. 4936).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThermal Conductivity\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe average TC of SFXC alginate was 0.67 \u0026plusmn; 0.02W/m.K, which showed no significant difference with the literature overall average TC (p=0.1840). The average TC of NNC alginate was 0.62 \u0026plusmn; 0.02W/m.K, which showed no significant difference with the TC of ventricular wall measured at 1.5W (p=0.8686). The average TC of Kromagen alginate was 0.58 \u0026plusmn; 0.05W/m.K, which showed no significant difference with the TC of ventricular wall measured at 0.5W (p=0.9439).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eElectrical conductivity, Shore hardness, and thermal conductivity results are show graphically in Fig. 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRadiofrequency Ablation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSystem impedance for all three coloured mixtures (shown in Fig. 3) followed the expected inverse relationships with tank salinity and there was no difference in the trend followed by the three alginate mixtures. SFXC ablation lesions measured 3.8\u0026plusmn; 0.3mm in depth and 7.8 \u0026plusmn; 0.8mm in width. SFXC lesions had no statistically significant difference in depth (p=0.0565) and width (p=0.0765) compared to literature values. RGB values for the lesion on SFXC alginate was (245, 246, 243), whilst background was (102, 101, 99). Colour contrast for the lesions against the background was 5.4:1. NNC ablation lesions measured 3.8\u0026plusmn; +0.4mm in depth and 7.9 \u0026plusmn; 0.9mm in width. NNC lesions had no statistically significant difference in depth (p=0.0693) and width (p=0.1929) compared to literature values. RGB values for the lesion on NNC alginate was (240, 237, 235), whilst background was (155, 92, 85). Contrast for the lesions against the background was 4.4:1. Kromagen ablation lesions measured 3.7 \u0026plusmn; 0.4mm in depth and 8.0 \u0026plusmn; 0.7mm in width. Kromagen lesions had no statistically significant difference in depth (p=0.4422) and width (p=0.1942) compared to literature values. RGB values for the lesion on Kromagen alginate was (214, 137, 104), whilst background was (244, 205, 131). Colour contrast for the lesions against the background was 4.4:1. All lesions had lower variance in the lesion width and lesion depth than the literature values. These results are shown graphically in Fig 4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCryoablation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOnly SFXC and NNC responded to cryoablation. After preparation, Kromagen progressively reverted back from magenta to yellow over one hour. Kromagen did not retain a permanent colour change after cryoablation. SFXC cryoablation lesions measured 6.9 \u0026plusmn; 0.6mm in depth. \u0026nbsp;There was a statistically significant difference between SFXC lesion depth and literature values (p\u0026lt;0.0001 in an unpaired two-tailed t-test). RGB values for the lesion on SFXC alginate was (121, 122, 113), whilst background was (234, 235, 221). Contrast for the lesions against the background was 3.6:1. NNC cryoablation lesions measured 5.2 \u0026plusmn; 0.3mm in depth. \u0026nbsp;There was no statistically significant difference between NNC lesion depth and literature values (p= 0.2458 in an unpaired two-tailed t-test). RGB values for the lesion on NNC alginate was (246, 235, 219), whilst background was (208, 248, 121). Contrast for the lesions against the background was 2:1. In all cryoablations, temperature remained between -40\u0026deg;C and -80\u0026deg;C, as expected [8]. These results are shown in Fig. 5.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe method used to create the alginate mixtures was easy, fast, and replicable. It involved the use of non-hazardous materials, and all samples were ready within 15 minutes of having all the components measured. All materials costs were less than \u0026pound;3.00 per batch, which is comparable to the cost of ex-vivo animal tissue.\u003c/p\u003e \u003cp\u003eThe value of resistivity measured in ex-vivo porcine myocardium for this study (7.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6Ωm) is coherent with the in-vivo electrical resistivity of ventricular myocardium (7.04\u0026thinsp;\u0026plusmn;\u0026thinsp;2.11Ωm) reported in literature [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], validating the method adopted in this study. All the coloured alginate samples had no statistically significant difference to porcine myocardium reported in C. Saija \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. All pigments were conductive since the addition of these significantly decreased the resistivity of the alginate in all cases. The most electrically conductive pigment was Kromagen 50, which reduced the resistivity of C25 from 12.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4Ωm to 7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5Ωm. The samples were only directly compared to ventricular myocardium from C. Saija \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. To provide a broader comparison, similar readings could have been recorded for different tissues in the heart, such as pericardial fat or connective tissue; however, for the purpose of this study, the electrical resistivities were accurate enough to simulate heart tissue.\u003c/p\u003e \u003cp\u003eNNC and Kromagen alginates had realistic Shore hardness on the OO scale and showed no significant difference against the literature-derived hardness of ex-vivo myocardium, whereas SFXC alginate was harder and showed significant difference against the reference. This may stem from SFXC being the only dry pigment used in this study, whilst NNC and Kromagen were pigment slurries. Lower water content makes alginate harder, and water absorption from the pigment may have occurred, ultimately making the sample harder. Future investigations should evaluate if the change in Shore hardness from OO 20\u0026thinsp;\u0026plusmn;\u0026thinsp;7.5 to 27\u0026thinsp;\u0026plusmn;\u0026thinsp;2 can be detected by operators at different levels of experience, and if it significantly effects the force response on the catheter during navigation.\u003c/p\u003e \u003cp\u003eSFXC (0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02W/m.K) had the highest TC and showed no statistically significant difference with the overall average TC from ex-vivo myocardium from literature (0.675\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 W/m.K). Kromagen (0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05W/m.K) showed no statistically significant difference with ex-vivo ventricular myocardium measured at 0.5W (0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02W/m.K). Whereas NNC (0.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02W/m.K) showed no statistically significant difference with ex-vivo ventricular myocardium measured at 1.5W (0.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01W/m.K). Because all results matched literature values of TC from ex-vivo porcine myocardium, all mixtures had appropriately realistic TC for the purpose of a simulation. The method utilised in this test was accurate, however, the standard deviation of TC from the literature values was lower. Future studies should aim to investigate the thermal permittivity as well as the heat capacity of these hydrogels to further simulate heat dissipation post-ablation, insulating the apparatus to improve precision.\u003c/p\u003e \u003cp\u003eIn the case of radiofrequency ablation, the method directly replicated the one implemented in M. Barkagan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], using the same CARTO 3 (Biosense Webster, Irvine, USA) set up and settings. All coloured mixtures showed no statistically significant difference when compared to the lesion dimensions achieved in M. Barkagan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] at on ex-vivo myocardium, thus all mixtures could be used to effectively simulate RCA. The pigmented mixtures produced greater precision with comparable means to the literature, emphasising the improvement in results replicability that can be achieved from this hydrogel. Kromagen and NNC are more sensitive, changing colour at 50\u0026deg;C, while SFXC changes colour at 60\u0026deg;C but has higher TC. Consequently, no significant difference in lesion dimensions was identified amongst the three mixtures. SFXC and NNC had the best colour contrasts at 5.4:1 and 4.4:1, making the boundary of the lesions well defined and easy to notice. Kromagen, on the other hand, is a pigment which gradually changes colour and had a colour contrast of 1.8:1, ultimately making the ablation lesion less defined than in SFXC and NNC. This behaviour could be subject of future studies to assess temperature gradients created during RCA. Unexpectedly, Kromagen alginate lesions faded in colour over time, posing a potential limitation to the widespread use of this pigment. Further research would uncover more of the colour behaviour of Kromagen and its potential application in RCA. Though this investigation analysed up to a single pigment per mixture, future developments may combine multiple thermochromic agents of different sensitivities to produce colourful thermal maps indicating the various temperatures reached within the alginate matrix.\u003c/p\u003e \u003cp\u003eIn the case of cryoablation, our experiment simulated the methods performed on dogs in F. Bessi\u0026egrave;re \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] using the Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and CryoCath console (Medtronic CryoCath LP, Montreal, Canada) using the same console the same ablation settings. The NNC mixture resulted in ablation lesions comparable to the literature. SFXC responded to freezing, however, the lesions were too large. This discrepancy may be attributed to the difference in TC as well as the pigment\u0026rsquo;s sensitivity to freezing. Kromagen did not generate any lesion after freezing and did not maintain colour after heating, making it unusable for this simulation. The colour contrast between lesion and background was lower after cryoablation than after RCA, indicating the pigments may be more sensitive to heat. Due to the shape of the catheter, the only measure that could be compared was depth. Future investigations should aim to replicate this test using a range of different catheters to compare to literature while also moulding the material in the shape of atria to test for lesion-transmutability and oesophageal injury. Though only incident in 1% of patients, atrio-oesophageal fistula formation ensuing from CA results in an 80% mortality rate [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. This material may therefore find extensive applications in modern research in this field [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], allowing operators to study tissue damage and temperature transfer between different layers of tissue.\u003c/p\u003e \u003cp\u003eAll hydrogels achieved high-fidelity to ex-vivo myocardium and produced realistic results under RCA, but only NNC performed realistically during cryoablation. Assessing the performance across all tests, the NNC mixture obtained the best results overall, having found no statistically significant difference against ex-vivo myocardium on any of the physical tests, while displaying realistic lesions dimensions. Despite its unique colour changing properties, Kromagen had a low colour contrast and underperformed during cryoablation, ultimately making it not a good option. Its properties could be further investigated to produce data on heat propagation in the gel. The SFXC mixture obtained the best electrical properties, thermal properties, and colour contrast, however its hardness was significantly higher than myocardium and it was outperformed by NNC in cryoablation. Ultimately, SFXC performed better than Kromagen but not NNC. In future investigations, users may employ 3D-printing or moulds to shape the alginate mixtures into heart phantoms which could also be perfused with water pumps to emulate blood flow and create a highly-realistic simulation environment without using animal tissue.\u003c/p\u003e \u003cp\u003eThough in-vivo tests still remain the most realistic test conditions, the NNC thermochromic hydrogel hereby formulated arguably outperformed ex-vivo porcine myocardium, as it could markedly show the ablation lesion for both cryoablation and RF ablation. This gel is the first synthetic model that allows operators to compare multiple ablation modalities (such as RCA or cryoablation), new ablation equipment (such as catheters), and ablation techniques (such as single shot ablation or point-by-point) without immediately resorting to live animal studies.\u003c/p\u003e \u003cp\u003eTo conclude, the study assessed the performance of three tissue-mimicking hydrogels for cardiac ablation simulation. The results indicate that the NNC alginate mixture can reliably replicate the thermal, electrical, and mechanical properties of ex-vivo porcine myocardium in order to be used to simulate response to ablation. Unlike previously attempted formulations in the literature, this material is non-hazardous, inexpensive, and ethically compliant, as well as homogeneous and replicable, making it an easy, quick, and ethical tissue-mimicking hydrogel for both RCA and cryoablation tests.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eAlginate Formulation\u003c/h2\u003e \u003cp\u003eWhite calcium alginate moulding powder (Pebeo, Marseille, France) was utilised as the gelling agent. Saline was prepared at 0.3% and 0.25% mass concentrations using deionised water and NaCl. Kromagen50 (SpotSee, Dallas, Texas), SFXC 60\u0026deg;C Irreversible Thermochromic Pigment (Good Life Innovations Ltd., Seaford, United Kingdom) and NNC TM-SL W50-0 Brown (New Prismatic Enterprise Co., Taipei, Taiwan) were identified as the three thermochromic pigments for these experiments as they retain their new colour after changing. Two control mixtures and three coloured mixtures were prepared following the ratios shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Liquids and powders were mixed and measured separately before being combined with a hand blender for 30 seconds. The blender was then opened, and the sides were scraped. The mixture was blended for 10 more seconds and poured in moulds to set for 10 minutes.\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\u003eFormulations for the mixtures of alginate analysed.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\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=\"char\" char=\".\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e Mixture\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSaline Mass Concentration\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePigment Mass (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMass Saline (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMass Alginate Powder (g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eControl Mixtures\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 0.25% (C25)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.250%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e32.0\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControl 0.3% (C30)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.300%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e32.0\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003eColoured Mixtures\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eSFXC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.300%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2.00\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e32.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eNNC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.300%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2.50\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e32.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eKromagen\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.250%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2.50\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e120\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e32.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eElectrical Resistivity\u003c/h2\u003e \u003cp\u003eTo evaluate the electrical properties of all mixtures, a volume constrained box 45 x 15 x 15mm was 3D-printed in Anycubic Basic Clear Resin (HongKong Anycubic Technology Co., Hong Kong, China). 15mm square copper electrodes were constructed using 0.5mm copper sheets and placed on either side of the box. The electrodes were connected to a switch and a multimeter to measure electrical resistance. Internal resistance of the system was measured at 0.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00kΩ, using the 20kΩ range. Ten 45 x 15 x 15mm slices of each alginate mixture were prepared and moulded to size. Each slice was placed in the box and compressed by the lid, ensuring full contact with the electrodes and consistent volume (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). The switch was turned on to inspect the initial resistance of the material in kΩ. Resistivity of each material was calculated by multiplying the value of resistance by the cross-sectional area of the sample, divided by its length. Electrical resistivity can otherwise be calculated as the inverse of electrical conductivity. Using the same methods and set up [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], our previous research measured the electrical resistivity of porcine myocardium to be 7.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 Ωm. In literature, D. Miklavčič \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] describes ex-vivo heart tissue to have electrical conductivity of 0.06-0.4S/m (resistivity\u0026thinsp;=\u0026thinsp;2.5\u0026ndash;16.7Ωm); K. Raghavan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] reports that in-vivo myocardium has an electrical conductivity of 0.142\u0026thinsp;\u0026plusmn;\u0026thinsp;0.043S/m (resistivity\u0026thinsp;=\u0026thinsp;7.04\u0026thinsp;\u0026plusmn;\u0026thinsp;2.11Ωm).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eHardness\u003c/h2\u003e \u003cp\u003eA HT-6510OO OO-Shore Durometer (Landtek Instruments Co., Guangzhou, China) was mounted on a remote-controlled linear actuator. On the opposite side of the actuator, a 1mm thick cup containing a 20 x 35mm (length x diameter) cylinder of alginate was held in place by two M4 screws, holding it centred with the durometer (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003eB). The durometer was displaced by 15mm allowing the alginate to come in to contact with the body of the durometer. 10 measurements of hardness were recorded for each mixture, using 10 separate cylinders. A. Tejo-Otero \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] reported that hydrogels of OO Shore hardness 20\u0026thinsp;\u0026plusmn;\u0026thinsp;7.5 can be used to recreate ex-vivo cardiac muscle. Based on this, a 10,000-element vector was created following a normal distribution with mean 20 and standard deviation 7.5 using MATLAB function \u0026ldquo;normrnd\u0026rdquo; as a literature-derived reference for statistical analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eThermal Conductivity\u003c/h2\u003e \u003cp\u003eThermal Conductivity (TC) was analysed to compare the thermal behaviour of alginate to ex-vivo myocardium, which would directly affect lesion dimensions via the propagation of heat/cold. The TC of myocardium falls between 0.58 and 0.75 W/m.K [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The paper by D. Končan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] was chosen as a reference for this investigation, as it analysed the TC of the septum and the ventricular wall, two common ablation sites. The study used varying power (0.5W-1.5W) to heat ventricular and septal ex-vivo porcine myocardium and measured their TC. The study reported ventricular TC of 0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02W/m.K when heating at 0.5W, and 0.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01W/m.K when heating at 1.5W. The overall average TC of myocardium across all methods in D. Končan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] is 0.675\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 W/m.K. Based on the means and standard deviations of these three TC values, three normally distributed arrays of 10,000 elements were generated using MATLAB function \u0026ldquo;normrnd\u0026rdquo; to provide some literature-derived references for statistical analysis.\u003c/p\u003e \u003cp\u003eTo measure the thermal conductivity of alginate, long cylindrical 110 x 37.5mm samples were cast inside of polylactic acid 3D-printed moulds. The TSL-100 thermal conductivity analyser (Thermtest Instruments, New Brunswick, Canada) was fully inserted into the sample and a value of thermal conductivity was measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003eC). The test was repeated 10 times on different samples for all mixtures. Like all other measured properties, the TC values acquired during this study were compared against the reference using a 5% confidence level in a two-tailed multi-variance t-test.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eRadiofrequency Ablation\u003c/h2\u003e \u003cp\u003eTo analyse the radiofrequency ablation behaviour of the hydrogel and directly compare the finding to M. Barkagan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], the simulator system published in C. Saija \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] was adapted to replicate the same ablation conditions. To emulate the heart walls 75 x 55 x 10mm slices of coloured alginate were moulded to simulate the thickness of ventricular walls [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The coloured alginate slices were mounted on a perforated base with a 1.5cm sponge using a plastic frame. The base was mounted in the centre of a temperature-controlled 55 x 38 x 27cm acrylic tank filled with saline at different concentrations. The Valleylab Return Patient electrode (Covidien, Dublin, Ireland) was placed on the bottom of the tank facing into the saline in the inferior section of the tank to simulate patch placement on the lower back of the patient (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e.A). The saline was kept at 37.0\u0026deg;C and saline mass concentration was progressively increased (0.05%, 0.1%, 0.2%, 0.3%) and the baseline impedance was recorded on 5 separate locations on the slice using a Thermocool SmartTouch Unidirectional Navigation Catheter (NAV ST SF) (Biosense Webster Inc., Irvine, USA) in the CARTO VIZIGO 8.5F (Biosense Webster Inc., Irvine, USA) steerable sheath linked to the SMARTABLATE System (Biosense Webster Inc., Irvine, USA). Based on the idealised electrical model displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003eB, the relationship between system impedance (R) versus tank salinity (x) can be derived as shown is Eq.\u0026nbsp;1, where A, B, C, D are constants and α\u0026thinsp;=\u0026thinsp;1/A and β\u0026thinsp;=\u0026thinsp;1/B.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:R=\\frac{1}{\\frac{x}{A}+\\frac{1}{B}}+\\frac{C}{x}+D$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:=\\frac{1}{\\alpha\\:x+\\beta\\:}+\\frac{C}{x}+D$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eM. Barkagan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] performed ablation lesions in a similar simulator set-up using ex-vivo porcine ventricular wall. Their low impedance (100\u0026ndash;130Ω) tests performed lesions at 30W for 20 seconds and averaged a depth of 3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 mm and a width of 8.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4 mm using an open-irrigated ablation catheter (Thermocool SmartTouch SF; Biosense Webster, Irvine, USA) and a SmartAblate radiofrequency generator (Stockert GmbH, Freiburg, Germany) linked to the CARTO 3 system (Biosense Webster, Irvine, USA). In order to be comparative to this published study, our tank was filled with 0.075% saline (impedance: 100\u0026ndash;130Ω) at 37.0\u0026deg;C and 10 ablation lesions were performed on 10mm slices of the coloured alginate mixtures using the same equipment and settings. The ablation catheter was held perpendicular to the alginate sample using the steerable sheath; ablations were performed at 30W for 20 seconds applying 10g of force and irrigating with 24\u0026deg;C 0.075% saline at 8ml/min as per default. Results of lesion depth and width were measured digitally based on a ruler placed directly next to each sample as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003eC. Results of width and depth were compared against the findings of M. Barkagan \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] as previously described using MATLAB.\u003c/p\u003e \u003cp\u003eFinally, to evaluate the colour contrast between the lesions and the background alginate, the RGB values of the coloured mixtures were analysed based on pictures acquired under equal light conditions. The RGB values of 125 pixels were acquired from both the background and the lesions and averaged. The colour contrast was then calculated using Colour Contrast Analyser (TPGi, Clearwater, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eCryoablation\u003c/h2\u003e \u003cp\u003eTo test the cryoablation properties of the materials, the methods listed in F. Bessi\u0026egrave;re et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] were replicated using the Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and CryoCath console (Medtronic CryoCath LP, Montreal, Canada) using nitrous oxide (N2O) refrigerant. In their experiment they cryoablated both the atrial and ventricular walls of live dogs using the same settings, resulting in mostly transmural lesions in the atrial walls (3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4mm), but not in the ventricles. More specifically, only 2.43% of left ventricular lesions were transmural due to wall thickness; the maximum lesion depth reached in this area was on average 5.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3mm with exposure time 2-4min, marking a finite limit of reachable depth. To simulate the same conditions in our experiment, two 10mm ventricle-like alginate slices were prepared for each mixture. For colour change to occur in reverse, each mixture was prepared by adding the pigments in the saline and heating the solutions in plastic containers for 10 minutes at 70\u0026deg;C. Each measured solution was cooled then mixed with alginate powder, as described previously, and cast into 75 x 55 x 10mm slices. Slices were held in a 37.0\u0026deg;C heated water bath; cryoablation was performed replicating the methods of F. Bessi\u0026egrave;re et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] as closely as possible using a Medtronic Artic Front Advance (Medtronic CryoCath LP, Montreal, Canada) and the CryoCath console (Medtronic CryoCath LP, Montreal, Canada) for 3 minutes using nitrous oxide (N2O) refrigerant (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003eD). As per default settings, temperatures were monitored with a sampling frequency of 10Hz with a 1\u0026deg;C accuracy maintaining temperatures within the range of -40\u0026deg;C to -80\u0026deg;C like in F. Bessi\u0026egrave;re et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Due to the shape of the catheter, the lesions had an annular shape (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003eE). Two ablations were performed for each material. The annular ablations were sliced, and depth was digitally measured 16 times. Results of lesion dimensions were compared against the findings of F. Bessi\u0026egrave;re et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] as previously described using MATLAB.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eACKNOWLEDGMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Marco Pinto and his colleagues at Biosense Webster for their assistance with operating the CARTO mapping and ablation system. We thank the technical management team in the Surgical and Interventional Engineering Department at King\u0026rsquo;s College London for their support during our experiments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAUTHOR CONTRIBUTIONS:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMr. Carlo Saija: Establishing the alginate mixtures, all physical tests, all ablation tests, statistical analysis and writing.\u003c/p\u003e\n\u003cp\u003eMr. Sukruth Pradeep Kundur: physical tests and photography.\u003c/p\u003e\n\u003cp\u003eDr. Lisa Leung: cryoablation testing and ablation equipment procurement.\u003c/p\u003e\n\u003cp\u003eDr. Sachin Sabu: ablation equipment procurement and logistics.\u003c/p\u003e\n\u003cp\u003eMr. Marco Pinto: ablation equipment procurement and consultation for ablation equipment operation.\u003c/p\u003e\n\u003cp\u003eDr. Mark Herridge: ablation equipment procurement and consultation for ablation equipment operation.\u003c/p\u003e\n\u003cp\u003eMr. Adharvan Gabbeta: photography and radiofrequency ablation testing.\u003c/p\u003e\n\u003cp\u003eMs. Rashi Chavan: photography and radiofrequency ablation testing.\u003c/p\u003e\n\u003cp\u003eMs. Nadia Chowdhury: preliminary testing of electrical resistivity.\u003c/p\u003e\n\u003cp\u003eDr. Gregory Gibson: ablation equipment procurement, consolation in ablation equipment operation, and logistics.\u003c/p\u003e\n\u003cp\u003eDr. Calum Byrne: ablation equipment procurement and consolation in ablation equipment operation, and logistics.\u003c/p\u003e\n\u003cp\u003eDr. Antonia Pontiki: experimental technique and methodology consultation, writing.\u003c/p\u003e\n\u003cp\u003eDr. Richard James Housden: supervisor, writing.\u003c/p\u003e\n\u003cp\u003eDr. Jonathan Behar: supervisor, writing.\u003c/p\u003e\n\u003cp\u003eProf. Kawal Rhode: supervisor, writing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSOURCES OF FUNDING\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLondon [WT203148/Z/16/Z]; the British Heart Foundation (BHF) Centre of Excellence at King\u0026rsquo;s College London; the Department of Health and Social Care (DHSC) through the National Institute for Health and Care Research (NIHR) MedTech; and Vitro Diagnostic Co-operative (MIC) Award for Cardiovascular Diseases to Guy\u0026rsquo;s \u0026amp; St Thomas\u0026rsquo; NHS Foundation Trust in partnership with King\u0026rsquo;s College London [MIC-2016-019]. This work was supported by funding from Caranx Medical, Nice, France.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDISCLOSURES\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthor Carlo Saija was employed by the company Caranx Medical. Author Pierre Berthet-Ryne was employed by the company Caranx Medical. Author Marco Antonio Coutinho Pinto was employed by the company Biosense Webster. The remaining authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOPTIONAL EXTENDED DATA:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eN/a\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eMorillo, C.A., Banerjee, A., Perel, P., Wood, D. \u0026amp; Jouven, X. Atrial Atrial fibrillation: the current epidemic. \u003cem\u003eJournal of Generic Cardiology\u003c/em\u003e\u003cstrong\u003e14(3)\u003c/strong\u003e,195-203 (2017).\u003c/li\u003e\n \u003cli\u003eLippi, G., Sanchis-Gomar, F. \u0026amp; Cervellin, G. 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To test equipment and ablation settings, studies have resorted to ex-vivo and in-vivo models including pigs, dogs, and chickens. The use of animal tissue presents ethical and logistical complications and introduces variability between samples and between studies. In a scientific community faced with progressively more stringent ethics and regulations on animal testing, a more practical and ethical alternative should be established. To meet this need, multiple studies have proposed tissue-mimicking materials. However, either toxicity or poorly matched physical properties, prevented these materials from reaching widespread application. Furthermore, no material has yet been identified to test both cryoablation and radiofrequency ablation.\u003c/p\u003e \u003cp\u003eHere, we present a novel thermochromic alginate hydrogel material that can simulate ablation lesions for both radiofrequency ablation and cryoablation. This material could find direct applications in electrophysiology, but adapted mixtures could also be used to recreate other tissues for different simulations.\u003c/p\u003e","manuscriptTitle":"A Novel Thermochromic Myocardial Phantom for Radiofrequency Ablation and Cryoablation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-22 11:40:11","doi":"10.21203/rs.3.rs-5483662/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Accepted","date":"2025-09-03T08:16:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-09T21:20:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"160329382779156348076692147784360390720","date":"2025-04-23T12:40:02+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-21T12:33:56+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-21T03:04:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-04-08T13:27:24+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8e55bd99-5ee6-4e6a-a039-35007731a32d","owner":[],"postedDate":"April 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47449588,"name":"Health sciences/Cardiology"},{"id":47449589,"name":"Physical sciences/Engineering"},{"id":47449590,"name":"Physical sciences/Materials science"},{"id":47449591,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2025-10-13T16:07:13+00:00","versionOfRecord":{"articleIdentity":"rs-5483662","link":"https://doi.org/10.1038/s41598-025-18732-1","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-10-07 15:57:14","publishedOnDateReadable":"October 7th, 2025"},"versionCreatedAt":"2025-04-22 11:40:11","video":"","vorDoi":"10.1038/s41598-025-18732-1","vorDoiUrl":"https://doi.org/10.1038/s41598-025-18732-1","workflowStages":[]},"version":"v1","identity":"rs-5483662","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5483662","identity":"rs-5483662","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}