Tissue Engineering in ENT

Definition

1. Scaffolds (structural framework)
2. Cells (stem cells, chondrocytes, epithelial cells)
3. Bioactive molecules (growth factors, cytokines)

Core Components

1. Scaffolds

• Collagen (gels, nanofibers, porous scaffolds)
• Fibrin (injectable adhesive gels)
• Alginate (hydrogels)
• Hyaluronic acid (gels, sponges)
• Silk, chitosan, agarose

• Ceramics: Hydroxyapatite (HA), beta-tricalcium phosphate (TCP), bioactive glasses
• Polymers: Poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL)
• Decellularized donor tissue (biological scaffold with cellular material removed)

2. Cells

• Chondrocytes - for cartilage regeneration (ear, nose, larynx)
• Mesenchymal stem cells (MSCs) - derived from bone marrow, adipose tissue, spleen, thymus; can differentiate into osteogenic, chondrogenic, and adipogenic lineages
• Epithelial stem cells - for luminal surface reconstruction (trachea)
• Human induced pluripotent stem cells (iPSCs) - for mucosal and epithelial replacement
• Human vocal fold fibroblasts (hVFFs) - for lamina propria repair

3. Growth Factors / Cytokines

• bFGF (basic Fibroblast Growth Factor) - tympanic membrane perforation repair, vocal fold atrophy (presbyphonia)
• TGF-beta3 (Transforming Growth Factor) - reduces collagen synthesis and scar formation in vocal fold injury
• VEGF (Vascular Endothelial Growth Factor) - promotes angiogenesis, essential for vascularizing large scaffolds
• BMP-2, BMP-7 (Bone Morphogenetic Proteins) - osteoinductive; used for craniomaxillofacial defects and alveolar cleft repair
• GM-CSF - promotes epithelial wound healing in vocal folds; reduces TGF-beta1-induced collagen synthesis
• HGF (Hepatocyte Growth Factor) - upregulated by MSCs; promotes vocal fold regeneration

Applications in ENT

1. Auricular (Ear) Reconstruction

• Used for microtia and anotia reconstruction as an alternative to autologous rib cartilage.
• 3D bioprinting of patient-specific polycaprolactone (PCL) scaffolds seeded with a chondrocyte/hyaluronic acid hydrogel has been developed.
• Tissue-engineered cartilage in the shape of a human ear was first described in China clinically (Zhou et al.).
• In preclinical models: 3D-printed PCL scaffolds seeded with chondrocytes in hyaluronic acid hydrogel were subcutaneously implanted in athymic rodents with preservation of auricular features.
• Challenges: Regulatory barriers, high cost of cell manufacturing, determining optimal cell numbers and types, achieving confluent cartilage growth.
• Co-culturing chondrocytes with pluripotent cell populations may reduce the number of chondrocytes needed.

2. Tracheal Reconstruction

• Used for long-segment tracheal stenosis, tracheal malignancy, and congenital tracheal agenesis.
• Decellularized cadaveric trachea repopulated with autologous epithelial stem cells (luminal surface) and MSC-derived chondrocytes (cartilaginous rings), grown in a bioreactor, then transplanted. Five-year clinical success has been reported.
• Bioartificial polymeric scaffold modelling tracheobronchial morphology, seeded ex vivo with autologous bone marrow mononuclear cells, combined with growth factor-induced mobilization of endogenous stem cells.
• In children, the scaffold must have the potential to grow with the child.
• Mucociliary clearance is the key functional challenge - luminal ciliated respiratory epithelium must be established.
• Seeded host cells also produce chemoattractants that facilitate ingrowth of circulating host cells.

3. Larynx and Vocal Fold Reconstruction

• Used for scarred vocal folds following trauma, vocal fold atrophy (presbyphonia), and vocal fold paralysis.
• bFGF injections improve vocal fold atrophy at 1 week, with aerodynamic and acoustic improvements maintained up to 3 months.
• TGF-beta3 suppresses granulation tissue formation and scarring; produces well-organized collagen distribution with better vibratory function (demonstrated in beagle dog model).
• GM-CSF reduces collagen type I and fibronectin deposition; improves mucosal wave function.
• MSC therapy: MSCs directly injected into vocal folds (alone or as cell-scaffold composite) support remodelling and reduce scarring.
• Scaffolds used for MSCs:
  • Terudermis (atelocollagen sponge from calf dermis) - enables MSC adhesion
  • Hyaluronic acid/alginate (HA/ALG) hydrogel with human adipose-derived MSCs - prevents excessive collagen I deposition, increases HGF activity
• Cell-free scaffolds of collagen, hyaluronic acid, or fibrin can enhance laryngeal wound healing even without cells.

4. Nasal Reconstruction

• Autologous chondrocytes can be grown in vitro and used to generate cartilage implants for nasal defects.
• Tissue-engineered cartilage well tolerated as replacement for native cartilage in rhinoplasty.

5. Craniomaxillofacial / Bone Reconstruction

• Tissue-engineered bone using:
  • rhBMP-7 in type I collagen carrier for alveolar cleft repair (followed up 6.5 years, good radiographic bone regeneration)
  • Cultured bone marrow cells in beta-tricalcium phosphate and hydroxyapatite for osteoradionecrosis and non-healing fractures
• Angiogenesis via VEGF is the key challenge for large head and neck defects.

6. Tympanic Membrane

• bFGF has been successfully applied for repair of tympanic membrane perforations in clinical trials.

7. Peripheral Nerve (RLN, Facial Nerve)

• Muscle-derived MSCs improve outcomes in recurrent laryngeal nerve (RLN) injuries.
• Neural-induced MSCs combined with platelet-rich plasma (PRP) enhance facial nerve regeneration following axonotomy.

8. Olfactory Epithelium

• The nasal mucosa provides autologous olfactory ensheathing cells which assist neural and other regenerative procedures.

Challenges and Future Directions

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