Temperature-dependent tensile properties of polyamide 12 for the use in percutaneous transluminal coronary angioplasty balloon catheters

Abstract

Background Percutaneous transluminal coronary angioplasty (PTCA) balloon catheters must withstand high pressures required for the lesion treatment, pushing loads during insertion, and pulling loads during withdrawal. These loads pose a challenge especially for polymeric tubular shafts with small cross sections. In order to enable new design innovations and to better understand the mechanics of current catheter technologies, the tensile properties of polyamide (PA) 12 were investigated. PA 12 dog bone specimens and medical PA 12 tubes were either stored at ambient temperature and humidity or conditioned in water, and subjected to tensile loads at different temperatures. In addition, the effect on the tensile properties of the necking process, a forming process to reduce the wall thickness of the tubes, was determined. Results The tested tubes showed a reduction in both Young’s Modulus (− 41.5%) and yield stress (− 29.2%) compared to standardized specimens. Furthermore, an increase in temperature and water absorption softens the material and reduces the mechanical properties like the Young’s Modulus and the yield stress. It was found that the material strengthens during the necking process. Likely due to the orientation of the polymers chain molecules in load direction (Rösler et al., 2007), the Young’s Modulus of the material could be increased by 43.5%. Furthermore, the absence of a yield point after necking allows for a greater loading capacity of the material without unstable neck growth. Besides the strengthening, the ultimate strain is reduced by 50%. This indicates that the necking process induces plastic deformation. Conclusion The investigation showed that the environmental conditions like temperature and humidity can influence mechanical properties. It could also be shown that pre-forming processes such as necking can enhance the mechanical properties, such as the Young’s Modulus, while reducing the wall thickness. These findings suggest possible further development of catheters with a small cross section and higher mechanical strength and highlight the importance to account for the targeted operating temperature during the design process.

Inverse Finite Element Approach to Identify the Post-Necking Hardening Behavior of Polyamide 12 under Uniaxial Tension

“…In [18], uniaxial tensile tests were performed on ambient (stored at 23 • C and 50% r. H.) and conditioned (stored in water at 23 • C for 40 days) injection molded Grilamid®L25 PA12 dog bone specimens (ISO 527-2, Type 1A, EMS-CHEMIE AG, Domat/Ems, Switzerland). The specimens had a cross-section of 10 × 4 mm 2 and a total length of 170 mm and were subjected to a tensile load with a constant cross-head velocity of 50 mm/min until fracture.…”

“…The force-displacement curves, the identified Young's modulus (E) and the Poisson's ratio (ν) were used from [18] for the present work.…”

“…The present work inversely identifies the hardening curves post-necking for the semi-crystalline polymer PA12 in a temperature range from 23 • C to 100 • C. The used experimental data are based on uniaxial tensile tests on dog bone specimens published by Amstutz et al [18].…”

Construction of Helically Oriented Syndiotactic Polypropylene/Isotactic Polypropylene Composites for Medical Interventional Tubes via Rotation Extrusion

“…With the continuous development of the medical industry, requirements for medical devices are becoming stricter to ensure personal security and satisfy public concern. − Polymer tubes are one of the most widely used medical devices in the medical industry. − Nevertheless, medical polymer tubes still face fatal problems, such as poor kink resistance and biocompatibility. Medical tubes will be subjected to various complex stresses, such as stretching, bending, and torsion, when inserted into the human body to reach the target point. , If a kink or rupture occurs, it can easily lead to bleeding and infection of the patient, and may even lead to death. , Therefore, the hoop mechanical strength is the most important property for medical tubes as they undergo bending and torsion during intervention …”

“…Medical tubes will be subjected to various complex stresses, such as stretching, bending, and torsion, when inserted into the human body to reach the target point. 7,8 If a kink or rupture occurs, it can easily lead to bleeding and infection of the patient, and may even lead to death. 9,10 Therefore, the hoop mechanical strength is the most important property for medical tubes as they undergo bending and torsion during intervention.…”