Multiply-Crosslinked Polyisobutylene Polyurethanes for Heart Valves
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Solution Overview
Problem
Current polymeric heart valve materials lack sufficient mechanical properties, durability, and resistance to calcification, necessitating the development of biocompatible, biostable, and long-lasting materials that do not require long-term anticoagulation therapy.
Innovation Solution
The creation of multiply-crosslinked polyisobutylene-based polyurethanes with a co-network of multi-telechelic polyisobutylene segments and urethane segments, utilizing physical and chemical crosslinking methods to achieve enhanced mechanical properties and processability, specifically using a 3-arm star polyisobutylene-based polymer as a crosslinking agent with a number average molecular weight between 3,000-10,000 g/mole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyisobutylene-based polyurethanes are used to achieve biostability and chemical resistance, then biological stability is improved, but mechanical properties deteriorate due to insufficient stress transfer between domains
Solution Approach 1:
The patent creates a composite crosslinked structure combining two different crosslinking mechanisms: physical crosslinking via hydrogen bonding in hard domains and chemical crosslinking via polyfunctional alcohols in soft domains. This composite approach allows the material to simultaneously achieve the biostability of polyisobutylene-based segments and the mechanical strength of a dual-crosslinked network, resolving the contradiction between biological stability and mechanical properties.
2Strength
If conventional polyurethanes are used to achieve good mechanical properties, then strength is improved, but biostability deteriorates due to vulnerability to hydrolytic and oxidative damage
Solution Approach 1:
The patent changes the chemical composition parameters by using polyisobutylene-based segments (with stable -CH2-C(CH3)2- units) instead of conventional polyether/polyester soft segments (with vulnerable -CH2-O- linkages). This parameter change maintains mechanical properties through the dual-crosslinking mechanism while dramatically improving biostability by eliminating hydrolytically and oxidatively vulnerable linkages.
3Strength
If multiply-crosslinked polyisobutylene-based polyurethanes are synthesized to enhance mechanical properties, then strength and creep resistance are improved, but device complexity increases due to multiple crosslinking methodologies
Solution Approach 1:
The patent segments the crosslinking process into two distinct but complementary parts: physical crosslinking of hard domains through hydrogen bonding and chemical crosslinking of soft domains through polyfunctional alcohols. This segmentation allows each crosslinking mechanism to be optimized independently while working together to provide superior creep resistance and mechanical properties, managing the complexity through functional separation.
4Strength
If polyfunctional alcohols are used as crosslinking agents to create permanent chemical bonds, then mechanical properties are improved, but processability may be affected by the crosslinking reaction kinetics
Solution Approach 1:
The patent applies local quality by using polyfunctional alcohols specifically in the soft polyisobutylene domains rather than uniformly throughout the material. This localized chemical crosslinking of soft domains provides mechanical reinforcement without interfering with the physical crosslinking of hard domains, thereby maintaining processability while improving mechanical 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
The resulting material exhibits superior creep resistance, mechanical properties, and biostability, making it suitable for long-term indwelling medical devices like heart valves without the need for anticoagulation therapy.
Implementation Method 1
the soft (polyisobutylene-based) domains are crosslinked by multi-functional alcohols, creating permanent chemical bonds
Implementation Method 2
the hard (diisocyanate-based) domains are crosslinked by physical (crystalline) forces via H-bonding
Data Source
AI summary
A multiply-crosslinked polyisobutylene-based polyurethane includes a plurality of multi-telechelic polyisobutylene-based segments and a plurality of urethane segments having a plurality of chain extender-based segments therein. Each end of one of the plurality of urethane segments is linked either to an end of one of the plurality of multi-telechelic polyisobutylene-based segments, or to an end of one of the plurality of chain extender-based segments. Also, one or more of the plurality of urethane segments are physically crosslinked to one or more other of the plurality of urethane segments. Notably, the plurality of multi-telechelic polyisobutylene-based segments constitute at least 70 weight percent of the polyisobutylene-based polyurethane and the plurality of urethane segments, including the plurality of chain extender-based segments therein, constitute up to 30 weight percent of the polyisobutylene-based polyurethane.