Bioabsorbable Stent Polymer Coating via Solvent Removal
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Solution Overview
Problem
There is a continuing need for bioabsorbable stents that meet both mechanical requirements and effective methods of manufacturing such stents, particularly those made from biodegradable polymers that can completely erode after their clinical need has ended, while minimizing residual solvent levels and ensuring mechanical integrity.
Innovation Solution
A method of making a stent body involving a polymer solution with a number average molecular weight greater than 250,000 g/mole, where a cylindrical member is immersed or sprayed with the solution, and the solvent is removed to form a tubular layer, with optional repeated processes in various environments to achieve a desired thickness and low residual solvent levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polymer (>250,000 g/mole) is used to ensure mechanical integrity and strength, then the mechanical properties and structural support are improved, but the solvent removal becomes more difficult and residual solvent levels increase
Solution Approach 1:
The patent changes the molecular weight parameter of the polymer to greater than 250,000 g/mole, which fundamentally alters the mechanical properties and solvent interaction characteristics. This parameter change enables the polymer to maintain structural integrity while facilitating solvent removal through the specific processing conditions described in the patent.
Solution Approach 2:
The patent applies preliminary action by forming the polymer coating on the cylindrical member before attempting solvent removal. The coating is applied at controlled concentrations and the solvent removal process is initiated while the polymer is still in a specific state, making subsequent solvent extraction more effective despite the high molecular weight.
2Manufacturing precision
If repeated immersion or spraying cycles are used to achieve desired coating thickness, then the coating uniformity and thickness control are improved, but the manufacturing time and process complexity increase
Solution Approach 1:
The patent employs periodic action through repeated immersion or spraying cycles. Each cycle deposits a controlled amount of polymer solution, and the repeated application builds up the desired coating thickness incrementally. This periodic process allows for better control over coating uniformity compared to single-step application methods.
Solution Approach 2:
The patent applies partial action by using multiple cycles of immersion or spraying rather than attempting to achieve the full desired thickness in a single application. Each cycle deposits a partial layer, and the cumulative effect of multiple partial applications results in the target coating thickness with improved uniformity and control.
3Speed
If solvent removal is performed at higher temperatures to accelerate the process, then the solvent extraction speed is improved, but the polymer degradation and loss of mechanical properties increase
Solution Approach 1:
The patent changes the temperature parameter to specific ranges that optimize both solvent removal rate and polymer stability. By carefully selecting and controlling the temperature parameter within defined boundaries, the patent achieves effective solvent extraction while preventing polymer degradation and maintaining mechanical integrity.
Solution Approach 2:
The patent employs continuous solvent removal processes rather than intermittent heating. The continuous action allows for gradual solvent extraction at controlled temperatures, preventing thermal shock and polymer degradation while maintaining efficient solvent removal rates throughout the process.
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 enables the production of stents with enhanced mechanical properties and low residual solvent levels, ensuring effective support for vascular lumens and complete biodegradability, addressing the challenges of mechanical requirements and solvent removal.
Implementation Method 1
immersing a cylindrical member into the polymer solution and removing the cylindrical member from the polymer solution; wherein a portion of the polymer solution remains on the surface of the cylindrical member upon removal from the polymer solution
Implementation Method 2
removing at least a portion of the solvent from the polymer solution remaining on the cylindrical member to form a tubular layer of the polymer on the cylindrical member
Data Source
Figure 1~2C
Figure 3~4
AI summary
Methods of making polymeric devices, such as stents, using solvent based processes. More particularly, methods of making bioabsorbable stents.