Multilayer Bioabsorbable Stent Scaffold Design
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Solution Overview
Problem
Developing a fully bioabsorbable polymeric stent that balances radial strength, stiffness, toughness, and suitable degradation rate to address the challenges of restenosis and long-term complications in vascular treatments, while ensuring safe and complete resorption without fragment release.
Innovation Solution
A radially expandable stent scaffold is fabricated using a multilayer structure composed of alternating bioresorbable polymer layers, achieved through a layer multiplying co-extrusion process, which enhances fracture toughness by arresting crack propagation and combining rigid and flexible polymer materials, ensuring adequate mechanical support and controlled degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single-layer polymeric stent is used, then the degradation rate can be controlled, but the fracture toughness and radial strength are insufficient
Solution Approach 1:
The patent applies composite materials by combining multiple polymeric layers with different mechanical and degradation properties. The multilayer structure integrates a first polymer material providing radial strength and a second polymer material providing fracture toughness, creating a composite stent that overcomes the limitations of single-layer designs while maintaining controlled degradation.
Solution Approach 2:
The stent is segmented into multiple functional layers, each with specific thickness and material composition. The first polymer layers and second polymer layers are alternately arranged, with each layer serving distinct mechanical functions. This segmentation allows independent optimization of radial strength, fracture toughness, and degradation rate for each layer.
2Strength
If the stent wall thickness is increased to improve radial strength, then the radial compressive resistance improves, but the flexibility for crimping and expansion deteriorates
Solution Approach 1:
Different regions of the stent wall are assigned different material properties through the multilayer structure. The first polymer material provides radial strength in regions requiring compressive resistance, while the second polymer material provides flexibility and fracture toughness in regions requiring deformation during crimping and expansion. This local differentiation resolves the contradiction between strength and flexibility.
3Reliability
If a bioabsorbable polymer is used to enable complete resorption, then the long-term complications are reduced, but the radial strength and stiffness are insufficient compared to metallic stents
Solution Approach 1:
The patent uses composite polymeric materials where the first polymer material (e.g., PLLA, PDLA, or their stereocomplex) provides high radial strength and stiffness comparable to metallic stents, while the second polymer material ensures complete bioabsorbability and controlled degradation without fragment release. This composite approach achieves both strength and reliability.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the polymeric materials, including molecular weight, crystallinity, and layer thickness, to optimize the balance between radial strength and degradation rate. By controlling these parameters, the stent achieves metallic-level strength while maintaining complete bioabsorbability.
4Strength
If the layer thickness is decreased to improve fracture toughness, then the crack propagation is arrested more effectively, but the manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the layer thickness parameter within a specific range (1-10 micrometers) to balance fracture toughness improvement with manufacturing feasibility. This parameter optimization ensures that the thin layers effectively arrest crack propagation while remaining producible using conventional extrusion and lamination techniques.
Data Source
AI summary
A bioabsorbable scaffold composed of a multilayer structure of alternating layers of different polymers is disclosed. The multilayer structure can have 20 to 1000 layers and the individual thickness of the layers can be 0.2 to 5 microns. A method of making the scaffold including a layer multiplying extrusion process is disclosed.