Degradation and Fatigue Behavior of 3D-Printed Bioresorbable Tracheal Splints

Abstract

Severe infantile tracheobronchomalacia (TBM) is often treated with invasive surgery and fixed-size implants to support the trachea during respiration. A novel 3D-printed extra-luminal splint has been developed as a flexible and bioresorbable alternative. Therefore, the goal of the present study was to use an in vitro breathing simulator model to comprehensively evaluate the structural stiffness and failure modes of two sizes of a novel bioresorbable 3D-printed splint design under a range of physiological degradation conditions. Two thicknesses, 2 mm and 3 mm, of a novel 3D-printed bioresorbable splint were evaluated under two different degradation conditions, phosphate-buffered saline (PBS) and sodium hydroxide (NaOH). The splints were subjected to simulated breathing loading, involving a cyclic opening and closing of the splint by 2 mm, for a targeted duration of 7.5 to 30 million cycles. A separate new set of splints were statically soaked in their respective degradation condition for a comparative analysis of the effects of cyclic loading by the degradation medium. After successfully simulated breathing or static soaking, non-destructive tensile and compressive strengths were evaluated, and overall stiffness was calculated from destructive tensile testing. The present study indicates that the splints were more significantly degraded under simulated breathing conditions than under soaking. Cyclic simulated breathing specimens failed far earlier than the intended duration of loading. Over time, both 2 mm and 3 mm splints became increasingly more flexible when subjected to the static degradation conditions. Interestingly, there was little difference in the compressive and tensile strengths of the 2 mm and 3 mm thickness splints. The bioresorbable nature of PCL offers a valuable advantage as it eliminates the need for splint removal surgery and increases device flexibility over time with degradation. This increased flexibility is crucial because it allows for uninhibited growth and development of the infant's trachea over the intended use period of 2 years. The results of this study confirm that the splints were able to withstand tensile forces to prevent tracheal collapse. This study further supports the successful use of 3D-printed splints in the treatment of infantile TBM.

Keywords: 3D‐printing; Tracheobronchomalacia; degradation; fatigue; splint.

Figure 1.

Tracheal Splints and Testing Apparatus. (a) – (c) Depiction of 3D printed tracheal splints (2mm on left and 3mm on right) (d) Tensile testing apparatus for tracheal splints (e) Compressive testing apparatus for tracheal splints (f) Simulated breathing loading setup (Movement of splints denoted by red arrows)

Figure 2.

Outline of the Six Loading and Degradation Conditions.

Figure 3.

Tension and compression testing results for PBS soak specimens in static, non-destructive testing. Each specimen was tested after degradation and normalized according to the pre-degradation value for that specimen. Specifically, the values shown are obtained by (PBS-Soak Force (N)) – (Original Dry Force (N)). Accordingly, a positive value indicates that the PBS-soaked force was higher than the original dry force. Significance of P < 0.05 is denoted by a *.

Figure 4.

Stiffness results calculated from tensile load-to-failure testing. Specimen stiffness was calculated using the slope of the axial displacement (mm) versus force (N) graph when specimens were distracted in tension until failure. Significance of P < 0.05 is denoted by a *.

Figure 5.

Normalized tension and compression testing results for NaOH soak specimens in static, non-destructive testing. Each specimen was tested after degradation and normalized according to the pre-degradation value for that specimen. Specifically, the values shown are obtained by (PBS-Soak Force (N)) – (Original Dry Force (N)). Accordingly, a positive value indicates that the PBS-soaked force was higher than the original dry force. Significance of P < 0.05 is denoted by a *.

Figure 6.

Cycles before failure. Any crack or separation observed denoted failure. The 3mm specimens with NaOH soak have no standard deviation as failure of all specimens was noted at the same cycle. Significance of P < 0.05 is denoted by a *.

Figure 7.

Cycles before failure. Any crack or separation observed denoted failure. The 3mm specimens with NaOH soak have no standard deviation as failure of all specimens was noted at the same cycle. Significance of P < 0.05 is denoted by a *.

Figure 8.

Tracheal Splint Fracture Types. (a) – (c) common fracture or deformity types that constituted a splint failure (d) complete fracture seen in many of the shorter soak specimens due to the brittleness of the device (e) hairline fracture noted in the longer soaked specimens due to increased flexibility prior to failure.