biodegradable implants

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Here is a comprehensive overview of biodegradable implants drawn from authoritative surgical and medical textbooks:

Biodegradable Implants

Biodegradable (resorbable) implants are devices designed to provide temporary mechanical or pharmacological function and then degrade in the body, eliminating the need for surgical removal.

Key Materials

Synthetic Polymers

The most widely used class in orthopaedic and craniofacial surgery:

Polyglycolic acid (PGA) and polylactic acid (PLA) — first-generation synthetic polymers. Now largely superseded due to suboptimal release profiles.
Poly(DL-lactide) (PDLLA) and PLGA (copolymers of PLA and PGA) — preferred because of better bulk-erosion-based release kinetics. Degradation produces acidic byproducts, so use is best limited to small-volume applications such as implant coatings.
Polytrimethylene carbonate (PTMC) — fully biocompatible, degrades without acidic products, yielding a constant and controlled antibiotic release over time. Currently the preferred synthetic polymer.

— Rockwood and Green's Fractures in Adults, 10th ed.

Natural Polymers

Collagen — most extensively studied; biocompatible, low-cost, derived from connective tissue. Releases antibiotics mainly by diffusion rather than degradation (rapid bolus release). Limited by donor-site issues.
Chitosan — polysaccharide with innate broad-spectrum antimicrobial properties due to its polycationic structure.
Others: thrombin, autologous blood clot, gelatin.

Bone Graft Substitutes

Calcium sulfate — natural bioceramic; fills dead space and releases antibiotics locally, but drainage/seroma formation and uncontrolled drug release are downsides.
Hydroxyapatite — stimulates osteoid formation, enhances bone remodelling.
Bioactive glass — combines angiogenic, osteoconductive, and antimicrobial properties; integrates into bone and soft tissue without requiring removal.

Clinical Applications

1. Orthopaedic Fixation (Fractures)

Biodegradable plates and screws are used in fracture fixation, particularly in the paediatric craniofacial skeleton, where permanent titanium plates risk growth restriction and transcranial migration.

Advantages:

Poly-alpha-hydroxy acid systems provide initial fracture stability during healing, then gradually resorb — avoiding the need for plate removal surgery.
Faster paediatric bone remodelling makes this approach especially feasible in children.

Limitations:

Bulkier profile than titanium (risk of visibility/palpability).
More technically demanding (require thermal contouring, pre-tapping).
Inflammatory reactions during hydrolysis phase (6–18 months): infection, fluid collection, granulation tissue, hardware extrusion.
Inferior strength vs. titanium — not FDA-approved for load-bearing areas (e.g., the mandible).
Reports of fracture nonunion and malunion, especially with polyglycolide screws (osteolysis and sterile wound sinuses in ~26% in some ankle fracture series).

— Cummings Otolaryngology Head and Neck Surgery; Rockwood and Green's Fractures in Adults, 10th ed.

2. Antibiotic-Delivery Devices (Osteomyelitis)

Biodegradable carriers replace non-degradable PMMA (polymethylmethacrylate) beads in the local treatment of chronic osteomyelitis:

Obliterate dead space after surgical debridement.
Release the majority of their antibiotic load after degradation.
No residual substratum for bacterial colonisation (unlike PMMA).
Compatible with a wider range of antibiotics (unlike PMMA, which is incompatible with tetracyclines and rifampicin).
Require fewer subsequent surgeries than PMMA.

Future directions include combining osteoinductive, osteoconductive, and antimicrobial properties in a single biodegradable carrier, and antimicrobial implant coatings to prevent biofilm formation.

— Rockwood and Green's Fractures in Adults, 10th ed.

3. Drug-Eluting Stents (ENT)

The Propel corticosteroid-releasing implant (Intersect ENT) — the only FDA-approved biodegradable drug-eluting sinus stent — delivers sustained local mometasone release over 30 days post-endoscopic sinus surgery. Acts simultaneously as a mechanical spacer and anti-inflammatory agent, reducing polyposis and adhesion formation.

— K.J. Lee's Essential Otolaryngology

4. Intravitreal Implants (Ophthalmology)

Ozurdex (dexamethasone 700 µg, Allergan) — biodegradable PLGA intravitreal implant for macular oedema associated with retinal vein occlusion. The GENEVA trial demonstrated significant visual and anatomical improvement. Also used off-label for diabetic macular oedema and uveitis.

— Kanski's Clinical Ophthalmology, 10th ed.

5. Tissue Engineering Scaffolds (Regenerative Medicine)

Biodegradable scaffolds seeded with autologous cells have been clinically implanted for:

Bladder augmentation (spina bifida patients, normal pressures at 5+ years)
Urethra replacement (5-cm tubularized scaffolds; normal flow and architecture at 6 years)
Vaginal reconstruction (4 patients; normal structure at 8 years)

These represent the most advanced clinical translations of tissue engineering, where the scaffold biodegrades as the native tissue grows in.

— Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice

Summary Table

Application	Material	Key Advantage	Key Limitation
Paediatric facial fracture fixation	PLA/PGA plates	No plate removal needed	Weaker than titanium; inflammatory reactions
Osteomyelitis treatment	PLGA, PTMC, collagen, calcium sulfate	Local antibiotic delivery, dead-space fill	Limited commercial products
Sinus stents (ESS)	Biodegradable polymer	Sustained steroid release + spacer function	Patient-specific indications
Intravitreal implant	PLGA (Ozurdex)	Sustained dexamethasone; no removal	Limited duration (~3–4 months)
Tissue engineering	Various biodegradable scaffolds	Replaced by native tissue over time	Long-term durability data still accumulating

Biodegradable implants offer the compelling advantage of eliminating second surgeries for removal, while providing temporary structural or pharmacological support. However, their mechanical inferiority compared to permanent metals, inflammatory degradation reactions, and limited load-bearing capacity remain areas of active development.

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