Sequential Biaxial Straining of Semi-Crystalline Polymer Tubes
Solution Overview
Problem
Medical devices made from semi-crystalline polymers often lack sufficient mechanical properties to withstand structural loads in vivo, leading to potential deformation or fracture when placed in the vasculature, and existing straining methods do not effectively improve properties in all directions.
Innovation Solution
A sequential biaxial straining method for semi-crystalline tubes involves longitudinally straining and then radially expanding the tubes in a controlled temperature and pressure environment, allowing for tailored molecular orientation and improved mechanical properties in multiple directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If strain induced crystallinity is applied to improve mechanical properties, then strength in the direction of strain is improved, but mechanical properties in other directions remain insufficient
Solution Approach 1:
The patent applies sequential biaxial straining by transitioning from uniaxial strain in the extrusion direction to biaxial strain by adding radial expansion. This dimensional change allows polymer chains to align in multiple directions (longitudinal and circumferential), creating isotropic mechanical properties throughout the tube rather than just in the direction of initial extrusion.
Solution Approach 2:
The straining process is divided into sequential steps: first longitudinal straining during extrusion, then radial expansion in a second step. This segmentation allows independent control of strain in different directions, enabling tailored molecular orientation and isotropic mechanical properties that cannot be achieved through single-direction straining alone.
2Strength
If polymer chains are aligned in one direction through strain, then mechanical properties improve in that direction, but the device may deform or fracture under multi-directional loads in vivo
Solution Approach 1:
By adding radial expansion to the longitudinal straining process, the patent creates biaxial strain that orients polymer chains in both longitudinal and circumferential directions. This multi-directional alignment enables the tube to withstand structural loads from multiple directions encountered in vivo, preventing deformation and fracture while maintaining reliability.
3Strength
If sequential biaxial straining is applied, then mechanical properties are improved in all directions, but the processing complexity increases
Solution Approach 1:
The complex biaxial straining process is segmented into two manageable sequential steps: longitudinal straining during extrusion followed by radial expansion. Each step can be independently controlled and optimized, making the overall complex process practical for manufacturing while achieving isotropic mechanical properties in the final product.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enhances the elastic modulus and yield stress of the polymer tubes, enabling them to withstand greater structural loads and maintain shape and size in vivo, with specific improvements in the longitudinal and circumferential directions.
Implementation Method 1
The method may include heating the extruded polymer tube to a first temperature before the step of longitudinally straining an extruded polymer tube. The first temperature may be between a glass transition temperature and a cold crystallinity temperature of the polymer material
Implementation Method 2
In order to improve the mechanical properties of semi-crystalline polymers, it is known to cause strain induced crystallinity. Strain induced crystallinity induces alignment of polymer chains in the direction of the strain
Implementation Method 3
The extruded polymer tube may be longitudinally strained in the mold from the initial length to an extended length
Data Source
AI summary
The present disclosure provides a processing method for a polymer material to create a medical device with improved mechanical properties. This method allows better tailoring of the material's mechanical properties, hence a device to withstand greater structural loads in vivo. The method comprises providing an extruded polymer tube having an initial diameter and an initial length along a longitudinal direction, and longitudinally, bi-directionally straining the extruded polymer tube in a mold from the initial length to an expanded or extended length. The mold comprises a plurality of stationary heating elements. After longitudinally straining the tube, it is radially expanding in the mold from the initial diameter to an expanded diameter.