Cross-linked Biodegradable Polymer for Vascular Stents
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Solution Overview
Problem
Conventional biodegradable polymers used in vascular stents suffer from insufficient mechanical strength, stress relaxation behavior, and complex synthesis processes, making them unsuitable for medical applications due to issues like low elastic moduli, instability, and challenging mass production.
Innovation Solution
Development of cross-linked biodegradable polymers with elastic moduli ranging from 10 MPa to 4,500 MPa and biodegradation rates from 3 months to 36 months, achieved by bonding crosslinkable reactive groups to terminal groups of biodegradable prepolymers and subjecting them to thermal polymerization or light irradiation, allowing for improved mechanical properties and controlled biodegradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cross-linked polymers are used to improve mechanical strength and reduce stress relaxation, then elastic modulus and structural stability are improved, but device complexity and manufacturing difficulty increase due to requiring special equipment for molding
Solution Approach 1:
The patent applies preliminary action by performing cross-linking after the molding process rather than before. The polymer is first molded in a conventional thermoplastic state using standard injection molding equipment, then cross-linked in a separate post-processing step using steam or chemical treatment. This sequence allows the use of conventional molding equipment while still achieving the mechanical benefits of cross-linked structures.
Solution Approach 2:
The patent replaces the need for specialized cross-linking molding equipment with a two-step process: conventional mechanical injection molding followed by thermal/chemical cross-linking. This substitution allows standard thermoplastic molding machines to be used, eliminating the need for complex integrated cross-linking molding systems while achieving similar or superior mechanical properties.
2Stability of the object's composition
If conventional cross-linked polymer synthesis is used to achieve cross-linked structure, then structural stability is improved, but manufacturing complexity increases due to complicated multi-step synthesis processes
Solution Approach 1:
The patent uses pre-synthesized linear or branched poly(lactic acid) or poly(glycolic acid) polymers as starting materials, which are commercially available or easily produced. These pre-polymers are then molded and cross-linked in a simple post-processing step. This approach eliminates the need for complex multi-step cross-linking synthesis processes while maintaining structural stability.
Solution Approach 2:
The patent changes the approach from chemical synthesis complexity to physical/thermal process simplicity. By using ready-made polymers and applying cross-linking through steam treatment or chemical immersion after molding, the process complexity is dramatically reduced while achieving the desired cross-linked structure and structural stability.
3Ease of manufacture
If thermoplastic biodegradable polymers are used for easy molding and processing, then ease of manufacture is improved, but reliability deteriorates due to stress relaxation behavior
Solution Approach 1:
The patent performs molding first while the polymer is in its thermoplastic state, taking advantage of the ease of processing. After molding is complete, a cross-linking step is applied to eliminate stress relaxation. This sequence allows the polymer to exhibit thermoplastic behavior during manufacturing while achieving cross-linked stability in the final product.
Solution Approach 2:
The patent utilizes phase transitions by molding the polymer in its thermoplastic phase (above glass transition temperature) where it is easy to process, then cross-linking in the solid state or through steam treatment to create the cross-linked network. This phase transition approach allows easy manufacturing followed by stress relaxation prevention.
4Reliability
If cross-linking is performed before molding to achieve structural stability, then stress relaxation is reduced, but device complexity increases due to requiring special equipment for cross-linking molding
Solution Approach 1:
The patent inverts the conventional sequence by molding first and cross-linking afterward, rather than cross-linking before molding. This reversal eliminates the need for specialized cross-linking molding equipment while achieving the same or better stress relaxation resistance. The molding is done with conventional equipment, then cross-linking is applied as a separate post-processing step.
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 biodegradable vascular stents exhibit enhanced mechanical strength, stability, and adjustable biodegradation rates, ensuring compatibility with vascular healing durations and effective radial support, while simplifying the synthesis process to enable mass production without solvents.
Implementation Method 1
bonding crosslinkable reactive groups to terminal groups of biodegradable prepolymer having two or more arms and then subjecting the prepolymer to thermal polymerization or light irradiation
Implementation Method 2
biodegradable cross-linked polymer... biodegradation rates from 3 months to 36 months
Data Source
AI summary
A biodegradable cross-linked polymer and methods of preparing same are provided. The biodegradable cross-linked polymer is formed from a biodegradable polymeric material having two or more arms, which is a random copolymer formed of a first monomer and a second monomer different from the first monomer. The first monomer is selected from the group consisting of L-lactide, DL-lactide, glycolid, ε-caprolactone, trimethylene carbonate, p-dioxanone, amino acid-derived polycarbonates and polyorthoesters. The second monomer is one or two selected from the group consisting of D-lactide, DL-lactide, glycolide, ε-caprolactone, trimethyl carbonate, salicylic acid, carbonates, amino acids and derivatives thereof. The biodegradable polymeric material has a molecular weight of from 5,000 to 1,200,000 and an intrinsic viscosity of from 0.1 to 9.0 dl/g. Each of the terminal groups on the arms of the biodegradable polymeric material is selected from the group consisting of hydroxyl amino and carboxyl groups.