Polyester

Poly+ester

PET

PLA

PGA (Polyglycolic Acid)

PLA (Polylactic Acid)

PLGA (Poly(lactic-co-glycolic acid))

PCL (Polycaprolactone)

PLA (Polylactic Acid)

Derived from renewable resources (corn starch, sugarcane).

Biodegradable through hydrolysis of ester bonds.

Used in sutures, stents, orthopedic fixation devices, and drug delivery systems.

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PGA (Polyglycolic Acid)

Strong but brittle, degrades faster than PLA.

Common in absorbable sutures and tissue scaffolds.

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PLGA (Poly(lactic-co-glycolic acid))

Copolymer of PLA and PGA; degradation rate can be tuned by composition.

Widely used in controlled drug delivery (microspheres, nanoparticles, implants).

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PCL (Polycaprolactone)

Slow-degrading, flexible polyester.

Applications in long-term implants, drug delivery, bone regeneration scaffolds.

Degradation rate

Zoladex® (Goserelin Acetate Implant)

• Polymer: PLA or PLA-based copolymer (with PGA).
• Drug: Goserelin acetate (a luteinizing hormone–releasing hormone analog).
• Formulation: A small biodegradable subcutaneous implant rod.
• Mechanism:
• PLA slowly degrades by hydrolysis of ester bonds, producing lactic acid.
• This erosion allows controlled diffusion and release of the peptide over time.
• Release profile: Provides sustained release over 1 or 3 months, depending on dosage.
• Indications: Used for prostate cancer, breast cancer, and endometriosis.

1. Chemical Structure

• PET is an aromatic polyester made from terephthalic acid (benzene ring) and ethylene glycol.
• The benzene ring in terephthalate is very stable and hydrophobic, shielding the ester linkage from hydrolysis.
• In contrast, aliphatic polyesters like PLA, PGA, or PCL have no aromatic rings, so water molecules and enzymes can more easily access and hydrolyze their ester bonds.

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2. Crystallinity and Physical Barrier

• PET often has high crystallinity (30–40% in fibers/films, up to ~60% in engineered grades).
• Crystalline domains pack tightly, leaving little free volume for water or enzymes to diffuse in.
• Hydrolysis happens mostly in the amorphous regions, but the crystalline parts are highly resistant.

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3. Hydrophobicity

• PET is relatively hydrophobic compared to aliphatic polyesters.
• This reduces water penetration, which is necessary for hydrolytic degradation.

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4. Enzymatic Resistance

• Most naturally occurring enzymes (esterases, lipases) have low activity toward PET’s rigid aromatic ester bonds.
• Special engineered enzymes (e.g., PETase from Ideonella sakaiensis, discovered in 2016) can break PET down, but natural biodegradation in the human body is negligible.�

5. Thermal and Mechanical Stability

• PET has a high glass transition temperature (Tg ≈ 70–80 °C) and melting temperature (Tm ≈ 250–260 °C).
• These high transition temperatures reflect strong intermolecular interactions, making chain mobility low at body temperature (~37 °C), which further hinders degradation.

1. Tissue Engineering and Regenerative Medicine

• Vascular grafts and stents

PET (often under the trade name Dacron) has been widely used for artificial blood vessels.

Its woven/knitted textile form provides porosity for tissue ingrowth and mechanical stability.

Common in aortic and large-diameter vascular grafts.

• Soft tissue repair

PET meshes are used in hernia repair, pelvic floor reconstruction, and tendon/ligament repair.

Provides structural support while integrating with surrounding tissues.

2. Medical Textiles

• PET fibers are used in sutures, wound dressings, and surgical meshes.
• Non-absorbable sutures made of PET offer long-term strength and are used when prolonged mechanical support is needed.
• Surface modification (plasma treatment, coatings) improves hydrophilicity, cell adhesion, and bioactivity.

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3. Biomedical Devices and Implants

• Heart valve sewing rings: PET fabrics are used to secure prosthetic heart valves.
• Orthopedic implants: PET composites (reinforced with fibers) have been explored for bone fixation and joint replacements.
• Dental applications: PET films and fibers are investigated in periodontal membranes and scaffolds.

Dacron