*4.3. Parameters for the Mimicking of Soft Tissues*

#### *4.3. Parameters for the Mimicking of Soft Tissues*  4.3.1. Dynamic Mechanical Analysis (DMA)

4.3.1. Dynamic Mechanical Analysis (DMA) DMA is a technique that applies an oscillating force to a material/tissue sample and analyzes the response of the sample to that force [47]. The samples were tested using a DMA Q800 equipment of TA Instruments at 37 °C, 1 Hz and a pre-load force of 0.001 N. DMA in compression calculate the storage modulus (E'), which is the elastic part of the DMA is a technique that applies an oscillating force to a material/tissue sample and analyzes the response of the sample to that force [47]. The samples were tested using a DMA Q800 equipment of TA Instruments at 37 ◦C, 1 Hz and a pre-load force of 0.001 N. DMA in compression calculate the storage modulus (E0 ), which is the elastic part of the sample; and the loss modulus (E00), which is the vicious part of the sample.

sample; and the loss modulus (E''), which is the vicious part of the sample.

#### 4.3.2. Shore Hardness Test

4.3.2. Shore Hardness Test Shore hardness is a measurement of the resistance of a sample to indentation. There are different scales based on ASTM D2240 testing standards [48]: A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in having values between 0 and 100, where higher values indicate that a sample is harder. The shore is a key parameter for the mimicking of soft living tissues because it measures the consistency of the samples. This is an Shore hardness is a measurement of the resistance of a sample to indentation. There are different scales based on ASTM D2240 testing standards [48]: A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in having values between 0 and 100, where higher values indicate that a sample is harder. The shore is a key parameter for the mimicking of soft living tissues because it measures the consistency of the samples. This is an important aspect of the perception of surgeons.

important aspect of the perception of surgeons. STM D2240-Durometer Hardness method was used [48]. For that, Shore Durometer Type 00 and 000, supplied by Baxlo, Instrumentos de Medida y Precisión, S.L., Barcelona, Spain, were used for measuring the hardness of the biological tissues (different measurements were done at different parts of the anatomical structure) and material samples. STM D2240-Durometer Hardness method was used [48]. For that, Shore Durometer Type 00 and 000, supplied by Baxlo, Instrumentos de Medida y Precisión, S.L., Barcelona, Spain, were used for measuring the hardness of the biological tissues (different measurements were done at different parts of the anatomical structure) and material samples. Shore Durometer Type A was also used, but only showed values in the heart.

#### Shore Durometer Type A was also used, but only showed values in the heart. 4.3.3. Warner–Bratzler Shear Test

Warner–Bratzler shear test is commonly used in the food industry as a standard characterization method. For example, it has been used to determine the best meat tenderness (toughness) for various types of meat. The Warner–Bratzler consists of a steel frame which is supporting a triangular shear blade (see Figure 6A).

**Figure 6.** (**A**) Liver sample ready for being cut using the Warner–Bratzler. (**B**) Warner–Bratzler shear test method. **Figure 6.** (**A**) Liver sample ready for being cut using the Warner–Bratzler. (**B**) Warner–Bratzler shear test method.

Warner–Bratzler shear test is commonly used in the food industry as a standard characterization method. For example, it has been used to determine the best meat tenderness (toughness) for various types of meat. The Warner–Bratzler consists of a steel frame which

The analysis of the Warner–Bratzler shear test was carried out by focusing on four different parameters: (1) breaking force is the force peak where the cut starts (it is either before the curve is starting to flatten and reaching the maximum force or when there is a change in the curve like a small hole); (2) maximum cutting force is the maximum force of the plot when the sample is being cut; (3) adjustment area is the area under curve until the braking force, and (4) cutting area is the area under the curve from the breaking force

For creating a tissue-mimicking material for surgical training, the Warner–Bratzler shear test was carried out. This technique is related to the surgeon's cut feeling operating. A texturometer Texture Analyser TA.XT.plus (Stable Micro Systems, Surrey, UK) was used with a 50N load cell (Figure 2A). Maximum shear force (N) and area under the curve (J) were measured using the Warner–Bratzler probe. The speed is 1 mm/s during 35 mm of cut. The height of the sample was measured with a digital micrometer. The analysis of the Warner–Bratzler shear test was carried out by focusing on four different parameters: (1) breaking force is the force peak where the cut starts (it is either before the curve is starting to flatten and reaching the maximum force or when there is a change in the curve like a small hole); (2) maximum cutting force is the maximum force of the plot when the sample is being cut; (3) adjustment area is the area under curve until the braking force, and (4) cutting area is the area under the curve from the breaking force until the end.

*4.4. Statistical Analysis*  Statistics were performed using MATLAB R20. Organs mimicking using different materials was assessed using paired sample *t*-test to compare if the material can mimic the organ by focusing on the parameters of the Warner–Bratzler Shear test (maximum force), DMA, and Shore hardness. Data are represented as mean ± SEM (Standard Error For creating a tissue-mimicking material for surgical training, the Warner–Bratzler shear test was carried out. This technique is related to the surgeon's cut feeling operating. A texturometer Texture Analyser TA.XT.plus (Stable Micro Systems, Surrey, UK) was used with a 50 N load cell (Figure 2A). Maximum shear force (N) and area under the curve (J) were measured using the Warner–Bratzler probe. The speed is 1 mm/s during 35 mm of cut. The height of the sample was measured with a digital micrometer.

of the Mean). *p* ≤ 0.05 (\*), *p* ≤ 0.01(\*\*), and *p* ≤ 0.001 (\*\*\*). The null hypothesis states that an

#### organ and a material are equal. If the *p*-value is lower than 0.05, the hypothesis is rejected; *4.4. Statistical Analysis*

4.3.3. Warner–Bratzler Shear Test

until the end.

is supporting a triangular shear blade (see Figure 6A).

and consequently, it is confirmed that the material cannot mimic the organ. This analysis was only carried out with the most similar materials that can be seen in Figures 1–4. **Author Contributions:** For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used: Conceptualization, A.T.-O. and F.F.-A.; methodology, A.T.-O. and I.A.; software, A.T.-O.; validation, A.T.-O., F.F.-A., I.A. and I.B.-C.; formal analysis, A.T.-O. and I.A.; investigation, A.T.-O. and S.R.-V.; resources, F.F.-A., E.E. and M.Á.M.-T.; data curation, A.T.-O.; writing—original draft preparation, A.T.-O. and F.F.-A.; writing—review and editing, all; supervision, F.F.-A., M.Á.M.-T. and I.B.-C.; Statistics were performed using MATLAB R20. Organs mimicking using different materials was assessed using paired sample *t*-test to compare if the material can mimic the organ by focusing on the parameters of the Warner–Bratzler Shear test (maximum force), DMA, and Shore hardness. Data are represented as mean ± SEM (Standard Error of the Mean). *p* ≤ 0.05 (\*), *p* ≤ 0.01(\*\*), and *p* ≤ 0.001 (\*\*\*). The null hypothesis states that an organ and a material are equal. If the *p*-value is lower than 0.05, the hypothesis is rejected; and consequently, it is confirmed that the material cannot mimic the organ. This analysis was only carried out with the most similar materials that can be seen in Figures 1–4.

project administration, F.F.-A.; funding acquisition, F.F.-A. and E.E. All authors have read and agreed to the published version of the manuscript. **Author Contributions:** Conceptualization, A.T.-O. and F.F.-A.; methodology, A.T.-O. and I.A.; software, A.T.-O.; validation, A.T.-O., F.F.-A., I.A. and I.B.-C.; formal analysis, A.T.-O. and I.A.; investigation, A.T.-O. and S.R.-V.; resources, F.F.-A., E.E. and M.Á.M.-T.; data curation, A.T.-O.; writing original draft preparation, A.T.-O. and F.F.-A.; writing—review and editing, all; supervision, F.F.-A., M.Á.M.-T. and I.B.-C.; project administration, F.F.-A.; funding acquisition, F.F.-A. and E.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research undertaken in this paper has been partially funded by the project named QuirofAM (Exp. COMRDI16-1-0011) funded by ACCIO from the Catalan government and ERDF from the EU.

**Data Availability Statement:** Data can be shared upon request.

**Acknowledgments:** We would like to thank Salvador Borrós and Núria Agulló from IQS for lending the DMA equipment.

**Conflicts of Interest:** The authors declare no conflict of interest.
