PLLA/PDLA Stereocomplex Crystallites for Polymeric Stent Toughness

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Solution Overview

Problem

Polymeric stents face challenges with insufficient fracture toughness and radial strength, which can lead to mechanical failure and recoil, and existing nucleating agents may compromise mechanical properties or pose safety concerns.

Innovation Solution

A method involving melt processing a polymer blend of PLLA and PDLA to form stereocomplex crystallites, which increases nucleation density and reduces crystallite size, enhancing fracture toughness by using the stereocomplex as a nucleating agent in the formation of a polymeric stent.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polymeric stents are used to avoid metallic complications, then biocompatibility is improved, but fracture toughness and radial strength are insufficient leading to mechanical failure

Engineering Contradiction:

ImprovebiocompatibilityVSAvoidfracture toughness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent uses a composite material system consisting of PLLA and PDLA stereoisomers that form stereocomplex crystallites. This composite approach combines the biocompatibility of polymeric materials with enhanced mechanical strength through the formation of a heterogeneous crystalline structure where stereocomplex regions provide reinforcement within the polymer matrix.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the physical and chemical parameters of the polymer material by controlling the stereocomplex crystallite formation through specific processing conditions (temperature, cooling rate). This transforms the material properties from typical weak polymeric structure to a reinforced structure with improved fracture toughness while maintaining biocompatibility.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If polymeric stents are used to avoid metallic complications, then biocompatibility is improved, but radial strength is insufficient causing recoil

Engineering Contradiction:

ImprovebiocompatibilityVSAvoidradial strength

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The stereocomplex crystallite composite structure provides enhanced radial strength through the formation of a reinforced network within the polymeric matrix. The interlocking crystallite structure resists radial compressive forces while the polymeric base material maintains biocompatibility and flexibility.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

By controlling the degree of stereocomplex crystallization and crystallite size distribution through processing parameters, the patent optimizes the balance between radial strength and biocompatibility, achieving sufficient force resistance against vessel recoil while maintaining the essential polymeric material properties.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If existing nucleating agents are used to improve crystallization, then processing is enhanced, but mechanical properties are compromised or safety concerns arise

Engineering Contradiction:

Improvecrystallization controlVSAvoidmechanical properties

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs a self-service approach where the PLLA and PDLA polymers themselves serve as the nucleating agents through their inherent stereocomplex formation capability. This eliminates the need for external nucleating agents that could compromise mechanical properties or raise safety concerns, while still achieving controlled crystallization and stereocomplex crystallite formation.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The stereocomplex crystallites act as intermediaries that mediate between the polymer matrix and the desired crystalline structure. These self-formed crystallites provide the necessary nucleation sites for controlled crystallization without requiring external additives, thereby maintaining mechanical integrity and safety.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach significantly improves the fracture toughness and radial strength of polymeric stents, reducing the risk of mechanical failure and allowing for effective crimping, expansion, and cyclic loading while ensuring biocompatibility.

Implementation Method 1

A method involving melt processing a polymer blend of PLLA and PDLA to form stereocomplex crystallites, which increases nucleation density and reduces crystallite size

Methodology Applied

Scientific EffectNucleation: Nucleation

Implementation Method 2

melt processing a polymer blend of PLLA and PDLA to allow formation of PLLA/PDLA stereocomplex crystallites in the blend during the processing

Methodology Applied

Scientific EffectCrystallisation: Crystallisation

Data Source

PatentUS8337739B2Improving fracture toughness of medical devices with a stereocomplex nucleating agent

Publication Date: 2012.12.25 ABBOTT CARDIOVASCULAR SYSTEMS INC

AI summary

Methods of fabricating a polymeric implantable device from a PLLA/PDLA blend such as a stent with improved fracture toughness are disclosed. The blend is melt processed to allow formation of stereocomplex crystallites, which are nucleation sites for crystal growth. A polymer construct is formed from the melt processed blend and device is formed from the polymer construct. The stereocomplex crystallites result in an in increase in nucleation density and reduced crystal size, which increases fracture toughness of the formed device.