Thin PTFE Layers with Closed-Cell Microstructure
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Solution Overview
Problem
Conventional polytetrafluoroethylene (PTFE) layers used in intracorporeal devices are unsatisfactory due to their porosity and high permeability, which is not suitable for applications requiring thin, non-fluid-permeable layers with controlled permeability and mechanical suppleness.
Innovation Solution
A method involving the extrusion and processing of PTFE layers with controlled lubricant content and stretching agents to create thin, low or non-fluid-permeable PTFE layers with a closed cell microstructure, maintaining suppleness and limpness without significant recoil, achieved through specific processing conditions such as calendering and tentering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional expansion process is used to increase porosity and permeability, then fluid permeability is improved, but thickness control deteriorates and the layer becomes too thick
Solution Approach 1:
The patent changes the fundamental processing parameters from conventional expansion (which increases porosity) to controlled stretching and calendering processes that maintain low porosity (10-40%) while achieving thin thickness (0.002-0.050 inches). This parameter transformation resolves the contradiction by decoupling thickness control from porosity control.
Solution Approach 2:
The patent creates a composite structure with specific microarchitecture - a closed-cell or foam-like structure with controlled cell sizes (0.001-0.010 inches) that provides both thinness and controlled permeability. The composite nature of the microstructure allows simultaneous optimization of thickness and fluid permeability properties.
2Length of stationary object
If PTFE layer is made thin to reduce profile, then thickness is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent successfully creates thin PTFE films (0.002-0.050 inches) that maintain adequate mechanical strength through controlled microstructure development. The stretching and calendering processes create a microarchitecture that provides structural integrity to thin films, enabling them to function without excessive thickness.
Solution Approach 2:
The controlled composite microstructure with interconnected cells and specific density (0.90-1.10 g/cm³) provides mechanical reinforcement to thin PTFE layers, allowing them to maintain strength despite reduced thickness.
3Reliability
If conventional expansion process is used, then porosity is increased, but recoil and spring back increase reducing limpness
Solution Approach 1:
The patent inverts the conventional approach by using controlled stretching and calendering to create a microstructure with lower porosity (10-40%) compared to conventional expanded PTFE. This parameter change reduces the elastic recoil and spring-back effects, improving limpness and ease of mechanical manipulation.
Solution Approach 2:
Instead of expanding PTFE to increase porosity as in conventional processes, the patent uses stretching and calendering to create a denser microstructure with controlled cell sizes. This inverted approach to microstructure development eliminates the excessive recoil associated with highly porous expanded PTFE.
4Length of stationary object
If PTFE layer is made thin with low porosity, then thickness and fluid impermeability are improved, but manufacturing complexity increases
Solution Approach 1:
The patent incorporates lubricant into the PTFE compound before extrusion, and uses stretching agents during the stretching process. These preliminary actions facilitate the complex stretching and calendering operations, enabling thin film production while managing the inherent manufacturing complexity through pre-prepared material conditions.
Solution Approach 2:
The patent uses specific parameter ranges (temperature, stretch ratios, calendering pressures) to streamline the manufacturing process. By optimizing these parameters, the complex multi-step process of extrusion, stretching, and calendering becomes more controllable and manufacturable despite the inherent complexity of producing thin, low-porosity PTFE layers.
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 resulting PTFE layers exhibit low or no fluid permeability, high suppleness, and controlled thickness, suitable for applications like endovascular grafts, with properties optimized for specific medical device requirements.
Implementation Method 1
The PTFE compound is extruded through a die to form a PTFE layer
Implementation Method 2
The PTFE layer is stretched in the machine direction to reduce the thickness of the PTFE layer to a desired thickness
Implementation Method 3
The stretched PTFE layer is calendered to reduce the thickness of the stretched PTFE layer to a desired thickness
Data Source
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AI summary
Thin PTFE layers are described having little or no node and fibril microstructure and methods of manufacturing PTFE layers are disclosed that allow for controllable permeability and porosity of the layers. In some embodiments, the PTFE layers may act as a barrier layer in an endovascular graft or other medical device.