Biodegradable Polyurethane Urea Stent Composition
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Solution Overview
Problem
Current biodegradable polymers used in medical implants often lack the combination of high modulus, high strength, and high elongation required for applications like vascular stents and spinal cages, as they tend to be brittle and lose mechanical properties over time, which can lead to implant failure.
Innovation Solution
A polyurethane or polyurethane/urea composition with specific diisocyanates and chain extenders is developed, achieving a balance of high tensile strength, modulus, and elongation, retaining mechanical properties under physiological conditions until tissue regeneration is complete and degrading biocompatible products afterwards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high modulus and high strength polymers are used, then mechanical strength is improved, but elongation at failure deteriorates (becomes 10% or less)
Solution Approach 1:
The patent changes the chemical composition parameters by incorporating specific soft segments (polyether, polyester, polycarbonate, polyamide, or poly(alpha-hydroxy acid) chains) into the polyurethane structure. This parameter change allows the material to achieve both high modulus (400-2000 MPa) and high elongation (>30%, preferably >50%) by adjusting the molecular structure rather than relying on traditional rubber toughening
Solution Approach 2:
The patent creates a composite-like structure within the polyurethane molecule by combining hard segments (aromatic or aliphatic diisocyanates with chain extenders) and soft segments (flexible polymer chains). This segmented structure provides both the strength from hard segments and the elongation from soft segments, resolving the contradiction between strength and ductility
2Reliability
If biodegradable polymers are used, then biocompatibility is improved, but mechanical strength deteriorates over time due to degradation
Solution Approach 1:
The patent changes the degradation rate parameter by selecting specific biodegradable soft segments (particularly poly(alpha-hydroxy acids) like polyglycolic acid or polylactic acid) and adjusting their molecular weight and composition. This allows control over degradation timing so that mechanical strength is maintained during the critical healing period and then gradually decreases as tissue regeneration completes
Solution Approach 2:
The patent introduces dynamic mechanical properties that change over time - the material maintains high strength initially and then progressively degrades. This dynamic behavior matches the biological healing process, providing strong support when needed and gradually transferring load to regenerated tissue, thus resolving the contradiction between biodegradability and strength retention
3Shape
If rubber particles are incorporated to improve toughness, then elongation is improved, but modulus and strength deteriorate
Solution Approach 1:
The patent extracts the rubber particle reinforcement concept and replaces it with flexible polymer chain segments integrated into the polyurethane backbone. Instead of adding separate rubber particles that compromise strength, the soft segments are chemically bonded into the structure, providing elongation without the negative effects of particle-matrix interface failures
Solution Approach 2:
The patent merges the functions of matrix and reinforcement by integrating soft and hard segments into a single polyurethane molecule. The soft segments provide elongation while the hard segments provide strength, and they work together as a unified material system rather than separate phases, avoiding the strength loss associated with particle reinforcement
4Strength
If inorganic fillers are incorporated to increase modulus, then modulus is improved, but elongation and strength deteriorate
Solution Approach 1:
The patent replaces permanent inorganic fillers with biodegradable organic segments that temporarily provide mechanical support. The soft segments are designed to degrade after serving their purpose of providing initial strength and flexibility, transferring the load to regenerated tissue, thus avoiding the permanent brittleness introduced by inorganic fillers
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 composition provides a biocompatible and biodegradable material with enhanced mechanical properties, maintaining high modulus, strength, and elongation, reducing the risk of brittle failure and ensuring the implant's functionality during tissue repair, while degrading when no longer needed.
Implementation Method 1
The terms 'polyol' and 'chain extender' as used herein refer to the monomers used to make polyesters and polyamides, respectively, by polycondensation
Data Source
AI summary
The present invention provides a polyurethane or polyurethane/urea composition which has a tensile strength greater than 10 MPa, a modulus of elasticity greater than 400 MPa and an elongation at break greater than 30 % at a temperature of between 0°C and 6O °C and at a relative humidity of between 0 % and 100 %. The invention further provides uses of the compositions of the invention in biomedical vascular stents, an orthopaedic implant, a drug delivery coating or in tissue engineering.