Polyurethane Microparticles for Controlled Drug Release
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Solution Overview
Problem
Bioresorbable polymers based on caprolactone and polyethylene glycol suffer from slow degradation rates, limited structure-property variations, and unpredictable drug release profiles, making them unsuitable for efficient medical applications.
Innovation Solution
Development of bioresorbable polyurethane microparticles formed from structural units of caprolactone, poly(alkylene oxide), and diisocyanates, with controlled particle size and dispersivity for sustained release of pharmaceutically active agents, utilizing a two-step polymerization process to tailor degradation rates and release profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional bioresorbable polymers like PCL and PEG are used, then the material provides good biocompatibility and processability, but the degradation rate is too slow (∼24 months for PCL)
Solution Approach 1:
The patent modifies the chemical structure parameters of the polymer by incorporating different PEG molecular weights (200-8000 Da) and varying the PEG-to-caprolactone ratio in the copolymer structure. This changes the hydrophilicity and molecular weight of the resulting polyurethane, thereby controlling the degradation rate from weeks to months while maintaining biocompatibility
Solution Approach 2:
The invention creates a composite polymer structure combining caprolactone segments (providing mechanical strength and controlled degradation) with PEG segments (providing hydrophilicity and influencing degradation rate). The segmented polyurethane architecture integrates hard segments (caprolactone-diisocyanate) and soft segments (PEG) to achieve balanced properties
2Ease of manufacture
If simple polymer structures are used, then the manufacturing process is simple, but the structure-property variations are limited
Solution Approach 1:
The patent employs a segmented polyurethane structure where the polymer consists of alternating hard segments (from caprolactone and diisocyanate) and soft segments (from PEG). This segmentation allows independent optimization of each segment's properties and enables systematic variation of overall polymer properties by changing segment lengths and ratios
Solution Approach 2:
The invention introduces local quality variations by using PEG of different molecular weights (200, 400, 600, 800, 2000, 4000, 6000, 8000 Da) at specific positions in the copolymer chain. This allows tailoring of local hydrophilicity and chain flexibility to achieve desired bulk properties while maintaining a relatively simple overall manufacturing process
3Reliability
If conventional polymers are used, then the material is well-studied and reliable, but the drug release profile shows initial burst delivery which is unpredictable
Solution Approach 1:
The patent systematically varies key parameters including PEG molecular weight (200-8000 Da), PEG-to-caprolactone molar ratio (1:4 to 4:1), and diisocyanate-to-prepolymer ratio (1:1 to 2:1) to control the drug release profile. These parameter changes enable transition from burst release to sustained release patterns with predictable kinetics
Solution Approach 2:
The segmented polyurethane structure creates microphase-separated domains with different drug loading and release characteristics. The hydrophilic PEG segments and hydrophobic caprolactone segments create a composite structure that controls drug diffusion and release rates, eliminating unpredictable burst delivery
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 microparticles provide a controlled and sustained release of active agents, avoiding initial burst delivery and ensuring a prolonged therapeutic effect, with tailored degradation and release profiles suitable for various medical applications.
Implementation Method 1
The degradation rate and mechanism appear to depend on a number of factors, such as the chemical structure of the polymer and on the surrounding environmental conditions, such as the degradation media. Two stages have been indentified in the degradation process of aliphatic polyesters. Initially, the degradation proceeds by random hydrolytic chain scission of the ester bonds
Data Source
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AI summary
Polyurethane microparticles are derived from structural units comprising poly(alkylene oxide) moieties, caprolactone moieties and urethane moieties. The microparticles may include an active agent and have a particle size from 0,1 to 100 microns. Microparticles for injection have a particle size of 15 to 80 microns; for use as a aerosol 1 to 3 microns; and for intraocular use 0.02 to 2 microns. Dispersivity is in the range 1 to 3.