Degradable Stent Partition Layer pH Isolation
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Solution Overview
Problem
Current degradable stents face issues with side effects such as restenosis and thrombosis due to pH shifts caused by degradation products, which can be harmful to pH-unstable agents like rapamycin and paclitaxel, and slow endothelialization, especially when coated with antiproliferative agents.
Innovation Solution
A degradable metal stent design featuring a partition layer on the luminal side and an agent-containing layer on the abluminal side, which spatially separates degradation products from agents, preventing pH-related damage and promoting rapid endothelialization by ensuring the stent struts only contact the partition layer, not the agent layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stent is coated with agent-containing polymer on both luminal and abluminal surfaces, then the support structure is protected and agents are delivered, but the pH shifts from degradation products harm the stability of pH-unstable agents
Solution Approach 1:
The coating is segmented into two distinct layers: a partition layer in contact with degradation products and an agent-containing layer protected from pH shifts. This segmentation isolates the agents from harmful pH environments while maintaining controlled delivery functionality.
Solution Approach 2:
The partition layer acts as an intermediary barrier between the degradation products (source of pH shifts) and the agent-containing layer. This intermediary structure protects the pH-unstable agents from direct exposure to harmful pH conditions while still allowing the system to function.
2Reliability
If the stent is coated with growth-inhibiting antiproliferative agents on luminal surface, then restenosis is prevented, but endothelialization is slowed and thrombosis risk is increased
Solution Approach 1:
The coating configuration provides local quality differentiation: the abluminal surface receives antiproliferative agents for restenosis prevention, while the luminal surface remains agent-free to promote endothelialization and reduce thrombosis risk. This localized application strategy addresses different functional requirements at different locations.
3Reliability
If degradable polymer matrix is used for agent coating, then the coating is biocompatible and degradable, but the pH sinks due to hydrolysis and negatively influences stent degradation speed
Solution Approach 1:
The coating system is segmented into a partition layer that faces the pH-sinking polymer degradation and an agent-containing layer that remains protected. This segmentation allows the use of biocompatible degradable polymers while isolating the agents from the harmful acidic environment generated during polymer hydrolysis.
Solution Approach 2:
The partition layer serves as an intermediary that buffers the pH sink effect generated by polymer hydrolysis. It protects the agent-containing layer from the acidic conditions while allowing the biocompatible degradable polymer to maintain its beneficial properties.
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
This design enhances the stability of agents, prevents adverse pH effects, and accelerates endothelialization, reducing the risk of thrombosis and ensuring effective delivery of agents to the vascular wall with higher and more reproducible concentrations.
Implementation Method 1
a partition layer which is applied to the surface of the stent main body so that at least parts of the surface of the luminal side are not covered
Implementation Method 2
If polymer material (e.g., polyester) degradable by hydrolysis is used as the matrix for the agent coating, the pH value of a stent implanted in a vessel sinks as a result of the hydrolysis of the degradable polymer
Implementation Method 3
The release of the agents from the polymer matrix typically results via diffusion processes and/or erosion processes of the polymer matrix
Implementation Method 4
an agent-containing layer which is applied to the surface of the partition layer at least partially on the abluminal side of the stent main body
Data Source
AI summary
A stent comprising a degradable metal stent main body; a partition layer which is applied to the surface of the stent main body so that at least parts of the surface of the luminal side are not covered; and an agent-containing layer which is applied to the surface of the partition layer at least partially on the abluminal side of the stent main body and comprises one or more agents and possibly one or more polymers.