Biodegradable Stent Plasticizer Tg Control
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Solution Overview
Problem
There is a need for biodegradable stents that meet mechanical requirements and methods for their fabrication, particularly to address the issue of late stent thrombosis associated with drug-eluting stents, which require materials that can erode or disintegrate after the clinical need has ended.
Innovation Solution
A method involving the use of biodegradable polymers, where a polymer is processed with a plasticizer at a temperature above its melting or glass transition point, followed by additional processing operations such as expansion and pattern formation, to create a stent that can erode completely after treatment, ensuring mechanical integrity and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If biodegradable polymers are used to make stents that erode after treatment, then the risk of late stent thrombosis is reduced and vessel healing is promoted, but the mechanical strength and structural integrity during the erosion period may be compromised
Solution Approach 1:
The patent applies parameter changes by modifying the glass transition temperature (Tg) of the biodegradable polymer through plasticizer addition. By controlling the Tg to be below body temperature (37°C), the polymer maintains a rubbery, flexible state that provides adequate mechanical strength while allowing controlled erosion. The specific parameter changed is the Tg, which is adjusted from typically higher values (above 37°C) to below 37°C through plasticizer incorporation, enabling the polymer to remain mechanically competent during the erosion period while facilitating controlled degradation.
Solution Approach 2:
The patent employs composite materials by combining biodegradable polymer with plasticizer to create a modified polymer system. The plasticizer acts as a secondary component that modifies the physical properties of the primary polymer matrix, creating a composite material system where the plasticized polymer maintains both mechanical integrity and controlled erodibility. This composite approach allows the stent to exhibit both strength during deployment and controlled erosion over time.
2Strength
If the polymer is processed at high temperature to ensure proper forming, then the mechanical integrity is maintained, but the plasticizer may degrade or evaporate, affecting the desired erosion properties
Solution Approach 1:
The patent applies parameter changes by carefully controlling the processing temperature to remain below the degradation temperature of the plasticizer while still achieving proper stent formation. The processing temperature parameter is optimized to be sufficient for forming (above polymer Tg) but constrained to prevent plasticizer degradation. This temperature parameter control ensures both mechanical integrity of the formed stent and preservation of the plasticizer content necessary for controlled erosion.
Solution Approach 2:
The patent applies preliminary action by incorporating the plasticizer into the polymer matrix before the forming process. This pre-mixing ensures uniform distribution of the plasticizer throughout the polymer, which protects it during subsequent processing and ensures consistent erosion behavior. The plasticizer is integrated into the material structure in advance, preventing loss or degradation during the forming operation.
3Reliability
If the stent is designed to erode completely after treatment, then late stent thrombosis is prevented, but the time required to provide adequate mechanical support must be carefully controlled
Solution Approach 1:
The patent applies parameter changes by controlling the glass transition temperature of the polymer to directly influence the erosion rate. By setting Tg below 37°C, the polymer maintains a rubbery state at body temperature that facilitates controlled hydrolysis and erosion. The Tg parameter serves as a key control variable that simultaneously affects both the mechanical properties (flexibility, strength) and the erosion kinetics, enabling the stent to provide mechanical support for the required duration while ensuring complete erosion to prevent late thrombosis.
Solution Approach 2:
The patent applies the principle of disposable/short-living objects by designing the stent as a temporary implant that is intended to erode and disappear after fulfilling its mechanical support function. The biodegradable polymer with controlled Tg enables the stent to serve its purpose temporarily and then safely degrade, eliminating the need for permanent foreign body implantation. This approach trades permanent durability for temporary functionality followed by complete biodegradation, preventing long-term complications.
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 biodegradable stents that provide adequate mechanical support and erode safely, reducing the risk of late stent thrombosis and other complications by ensuring the stent disappears after its clinical need has ended, thus promoting vessel healing.
Implementation Method 1
adding a plasticizer to the polymer prior to, during, or both prior to and during the processing of the polymer at the above temperature
Implementation Method 2
processing the polymer, optionally with another material, at a temperature above the melting temperature of the polymer, if the polymer exhibits a melting temperature above 35° C.
Implementation Method 3
processing the polymer, optionally with another material, at a temperature higher than (where 'higher than' is at least 20° C., preferably at least 35° C., more preferably at least 50° C., and even more preferably at least 100° C.) the glass transition temperature (Tg)
Data Source
AI summary
Methods of making polymeric devices, such as stents, with one or more modifications such as addition of plasticizers, to improve processing, and the devices made by these methods.