3D-Printed Biomaterial Testing in Response to Cryoablation: Implications for Surgical Ventricular Tachycardia Ablation

Abstract

Background: The lack of thermally and mechanically performant biomaterials represents the major limit for 3D-printed surgical guides, aimed at facilitating complex surgery and ablations. Methods: Cryosurgery is a treatment for cardiac arrhythmias. It consists of obtaining cryolesions, by freezing the target tissue, resulting in selective and irreversible damage. MED625FLX and TPU95A are two biocompatible materials for surgical guides; however, there are no data on their response to cryoenergy delivery. The study purpose is to evaluate the biomaterials' thermal properties, examining the temperature changes on the porcine muscle samples (PMS) when the biomaterials are in place during the cryoablation. Two biomaterials were selected, MED625FLX and TPU95A, with two thicknesses (1.0 and 2.5 mm). To analyze the biomaterials' behavior, the PMS temperatures were measured during cryoablation, firstly without biomaterials (control) and after with the biomaterials in place. To verify the biomaterials' suitability, the temperatures under the biomaterial samples should not exceed a limit of -30.0 °C. Furthermore, the biomaterials' geometry after cryoablation was evaluated using the grid paper test. Results: TPU95A (1.0 and 2.5 mm) successfully passed all tests, making this material suitable for cryoablation treatment. MED625FLX of 1.0 mm did not retain its shape, losing its function according to the grid paper test. Further, MED625FLX of 2.5 mm is also suitable for use with a cryoenergy source. Conclusions: TPU95A (1.0 and 2.5 mm) and MED625FLX of 2.5 mm could be used in the design of surgical guides for cryoablation treatment, because of their mechanical, geometrical, and thermal properties. The positive results from the thermal tests on these materials and their thickness prompt further clinical investigation.

Keywords: 3D surgical guide; arrhythmia treatment; biomaterial tests; cryoablation.

Figure 1

Schematic diagram of experimental tests. The red circle represents the point of cryo-application (with a 60° cryoprobe–tissue angle); instead, the green circle represents the distance of 1.0 mm from the cryo-application (D₁), where the first thermocouple for temperature measurement is located and the blue circle represents a distance of 11.0 mm from cryo-application (D₂), where the second thermocouple for temperature measurement is located.

Figure 2

Experimental tests. Thermal test: upper panel. Biomaterial and thermocouple placement: lower panel. cryoICE catheter in place.

Figure 3

Temperature–time curve of control and biomaterial samples in D₁. The graph represents the temperature–time curve at D₁ from the cryoablation catheter of the control, MED625FLX and TPU95A of 1.0 and 2.5 mm of thickness; the dashed line indicates the threshold set at −30.0 °C. Below the threshold, the freezing causes cell death.

Figure 4

Temperature–time curve of control and biomaterial samples in D₂. The graph represents the temperature–time curve at D₂ from the cryoablation catheter of the control, MED625FLX and TPU95A of 1.0 and 2.5 mm of thickness; the dashed line indicates the threshold set at −30.0 °C. Below the threshold, freezing causes cell death.

Figure 5

Low-temperature DSC of biomaterials. The graph represents the low-temperature DSC behavior of both MED625FLX (with a sample of 8.7200 mg) and TPU95A (with a sample of 8.4700 mg) after VHP sterilization.

Figure 6

Repeatability of temperature measurements and error bars for the control. Repeatability of temperature measurements and error bars for the control.

Figure 7

Repeatability of temperature measurements and error bars for MED625FLX of 2.5 mm. Repeatability of temperature measurements and error bars for MED625FLX of 2.5 mm.

Figure 8

Repeatability of temperature measurements and error bars for MED625FLX of 1.0 mm. Repeatability of temperature measurements and error bars for MED625FLX of 1.0 mm.

Figure 9

Repeatability of temperature measurements and error bars for TPU95A of 2.5 mm. Repeatability of temperature measurements and error bars for TPU95A of 2.5 mm.

Figure 10

Repeatability of temperature measurements and error bars for TPU95A of 1.0 mm. Repeatability of temperature measurements and error bars for TPU95A of 1.0 mm.

Figure 11

The macroscopic biomaterial changes in geometry after the cryoablation catheter. The macroscopic material changes in geometry after the cryo-application are shown in the figure; (A) TPU95A of 1.0 mm of thickness; (B) TPU95A of 2.5 mm of thickness; (C) MED625FLX of 1.0 mm of thickness; (D) MED625FLX of 2.5 mm of thickness; (E) lateral view of MED625FLX of 1.0 mm. The red arrows indicate the material deflection; the blue arrow indicates the break point in correspondence to the cryoablation.