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Biodegradable Polymers (Applications (Stents, Sutures, Drug Delivery, TE…
Biodegradable Polymers
Applications
Stents
Sutures
Drug Delivery
TE Scaffolds
Biodegradable Implants
Pros
Short-Term Use
No need for secondary surgery
Cons
Degradation Products Toxicity
Biodegradable vs Bioerodible
Biodegradable
Definition
Degradation + Biological Agent
Enzymes
Cells
Organisms
Degradation
Definition
Chemical Process
Cleavage Covalent Bonds
Bioerodible/Bioresorbable
Definiton
Hydrolytic Degradation
Water-insoluble polymer => Water-soluble polymer
Dissolution (Physical) + Backbone Cleavage (Chem)
Physiological Conditions
Erosion
Definition
Physical Process
Physical Changes
Size
Mass
Shape
Requirements
Biocompatibility
Inflammatory
Allergic
Toxic
Suitable Mechanical Properties
Controlled Degradation Rate
Safe Release of Degradation Products
Processability into final product form
Acceptable Shelf Life
Ability to be sterilized
Classes
Synthetic Polymers
Degradation Rate
Highest
Few Days
Poly-Anhydrides (COOCOR)
Most Reactive
Most Hydrolytically Unstable
Sensitive to Water
Medium
PLA
PGA
Surface Erosion
Lowest
Poly ortho-esters (COOCH3)
Surface Erosion-Controlled Release
Controlled Drug Delivery
Degradation Method
Hydrolysis
Pros
Availability
Few Complications
No harvest surgery
No Immunogenic Rejection
Property Variations
Polymer Types
Homopolymer
PGA
Absorbable Suture
Simple Linear Aliphatic Polyester
Properties
Highly Crystalline
Insoluble in Organic Solvents
Stiff
High Strength & Modulus
Degradation Mode
Cleavage of Polymer Backbone
Hydrolytic Degradation
Ester Bond prone to hydrolysis
PLA
Isomer Type
D-lactide
CH3-H
L-lactide
H-CH3
Degradation Rate
Long
Years
Reason
Steric Hindrance
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Properties
High Tensile Strength
High Modulus
Low Elongation
Applications
Load-Bearing
Sutures
Orthopaedic Fixtures
Polymerisation Mechanism
Ring-Opening
PLA vs PGA
Degradation Rate
PGA > PLA
Compare by side groups
Copolymer
PLGA
Characteristics
Non-Crystalline/Amorphous
Non-Uniform
Degradation Rate
More Empty Spaces for H2O to enter
Degrade faster
Compare by crystallinity
Crystallinity
Amorphous
LA/GA ratio: 75/25
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Degrades faster
Natural Polymers
Types
Chitosan
Shape & Form
Collagen
Connective Tissue
Mechanical Support
Protein
Cartilage, Skin
Keratin
Hair
Elastin
Neck, Skin
Degradation Method
Enzymolysis
Degradation Modes
Types
Chemical
Mode 1
Degradable Cross-links Cleavage btwn water soluble polymer chains
Mode 2
Transformation /Cleavage Polymer Side Chains (X) => Polar/Charged Groups (Y)
Mode 3
Cleavage of Polymer Backbone
Hydrolytic Degradation of Linear Aliphatic Polyesters
Physical
Hydrolysis of Ester Bonds (COOR)