Tissue Engineering in ENT

1. Introduction and Scope

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery - Vol 1, p. 119

2. Core Concepts

The Tissue Engineering Triad

1. Scaffolds - provide the 3D structural framework for cell growth
2. Cells - seeded onto or recruited into the scaffold (stem cells, chondrocytes, osteoblasts)
3. Signalling molecules / growth factors - drive cell differentiation and tissue formation

Bone Graft Properties (Relevant to Head & Neck TE)

• Osteogenesis - live donor cells (e.g., mesenchymal stem cell-derived osteoblasts) survive and synthesize new bone at the recipient site
• Osteoinduction - cytokines such as bone morphogenetic proteins (BMPs) recruit host mesenchymal stem cells and induce their differentiation into osteoblasts
• Osteoconduction - a supporting scaffold matrix allows ingrowth of new bone

• Scott-Brown's Vol 1, p. 119-120

3. Scaffold Materials

Natural Scaffolds

Synthetic Scaffolds

• Scott-Brown's Vol 1, p. 167-168

4. Bioreactors

• Scott-Brown's Vol 1, p. 122

5. Cytokines and Growth Factors

• Scott-Brown's Vol 1, p. 122; Scott-Brown's Vol 3, p. 1074-1076

6. Clinical Applications in ENT

6.1 Auricular Reconstruction (Microtia)

• 3D printing has been applied to whole auricular reconstruction. Patient-specific scaffolds with defined micro-architecture (e.g., polycaprolactone/PCL) can be printed and seeded with chondrocyte/hyaluronic acid hydrogel
• Preclinical success: A 3D-printed PCL scaffold seeded with chondrocyte/hyaluronic acid hydrogel, implanted subcutaneously in athymic rodents for 2 months, preserved auricular features
• Human trial in China: Tissue-engineered cartilage for human ear reconstruction has been described, but several obstacles remain for implementation elsewhere
• Current barriers to clinical translation:
  • Regulatory challenges (no feasible pathway in many jurisdictions)
  • Cost and resources
  • Determining optimal cell numbers and cell types for seeding
  • Achieving confluent cartilage growth reliably
  • Co-culturing chondrocytes with pluripotent cell populations may reduce chondrocyte numbers needed
  • Scaffold design affects "chondrogenicity"
  • A bioprinting solution that alternates scaffold material and chondrocytes is in preclinical testing
  • Growth factor components are prohibitively expensive to manufacture
• Cummings Otolaryngology, p. 3717

6.2 Craniomaxillofacial / Bone Reconstruction

• rhBMP-7 in type I collagen carrier for bilateral alveolar cleft defects - 6.5 year follow-up showed very good radiographic bone regeneration
• Bone marrow cells in β-TCP/hydroxyapatite for osteoradionecrosis, pathological fractures, and large maxillary defects - showed osteogenesis, nerve reinnervation, and skin regeneration
• Cranial/frontal sinus hard-tissue defects: 13 consecutive cases treated with TE constructs showing clinical utility
• Scott-Brown's Vol 1, p. 123

6.3 Tympanic Membrane Repair

• FGFs have been successfully applied for repair of tympanic membrane perforations, likely via effects on key ECM components in the lamina propria
• Scott-Brown's Vol 1, p. 123

6.4 Vocal Fold Regeneration

• bFGF for presbyphonia (vocal fold atrophy): clinical improvement in aerodynamic and acoustic parameters maintained up to 3 months
• TGF-β3: Suppresses granulation-tissue formation and scarring; experimental (beagle dogs) - collagen better organized and less dense, significantly better vibratory function at 6 months
• GM-CSF: Reduces collagen type I and fibronectin deposition, improves mucosal waves; increases hyaluronan synthase-2, tropoelastin, MMP-1, HGF, c-Met mRNA expression in vitro

• MSCs can be harvested from blood, migrate to injury sites, stimulate resident stem cell proliferation, secrete growth factors, and differentiate into myofibroblasts and fibroblasts
• GFP-labelled MSC study in rats: MSCs distributed throughout vocal fold from day 1 after injury; upregulation of HGF compared with controls
• Terudermis scaffold (atelocollagen sponge from calf dermis, large pores): MSCs adhere well; positive for vimentin, desmin, fibronectin, fsp1; in vivo beagle dog study showed greater regeneration with MSCs + atelocollagen vs. atelocollagen alone
• HA/ALG hydrogel containing human adipose-derived MSCs (hAdMSCs): prevented excessive collagen type I deposition, increased HGF activity, improved viscoelastic properties

• Concerns about neoplastic potential
• Complexity of laryngeal anatomy/physiology limits application to vocal fold scarring rather than framework injuries
• Scott-Brown's Vol 3, p. 1074-1076

6.5 Tracheal Reconstruction

• Involves a biodegradable scaffold seeded with host cells that differentiate and replace the scaffold after ECM production
• Seeded cells may produce chemoattractants that facilitate ingrowth of circulating host cells
• Early successes reported in pediatric populations
• "In vivo tissue engineering" technique: cryopreserved aortic homografts supported by Nitinol stents and external muscle flap; host cell migration and cartilage regeneration demonstrated
• Jungebluth et al.: Successful bioengineered tracheal transplantation using autologous bone marrow-derived MSCs on a bioartificial nanocomposite
• Much progress has been clouded by controversy; widespread benefit for adult malignancy is yet to be demonstrated
• MSCs are more suited to tracheal TE than laryngeal TE due to simpler anatomy
• Cummings Otolaryngology, p. 2184; Scott-Brown's Vol 3, p. 1076

6.6 Laryngotracheal Transplantation (Related to TE)

• First human attempt (partial laryngectomy): 1969
• First successful total laryngeal transplant: 1998 - survived at least 12 years despite chronic rejection
• 13 further cases reported from Colombia
• Farwell et al.: Successful modified transplant of larynx with long tracheal segment; revascularized and selectively reinnervated; no rejection at 3 months
• Porcine laryngeal transplantation: patent airways and restored swallowing at 1 week
• Challenges: patient selection, reinnervation, lifelong immunosuppression, cost-benefit
• Scott-Brown's Vol 3, p. 1076-1077

7. Key Points Summary

• Cummings Otolaryngology, p. 3718
• "Laryngeal tissue engineering is an expanding field which has provided a foundation for transplantation in animal models and humans." - Scott-Brown's Vol 3, p. 1077

8. Barriers to Clinical Translation

1. Regulatory hurdles (especially in the US/Europe for cell-based products)
2. Manufacturing cost of cell and growth factor components
3. Achieving reliable vascularization of large engineered constructs (VEGF critical but insufficient alone)
4. Optimal cell sourcing, numbers, and seeding methodology
5. Risk of neoplastic transformation with stem cells
6. Immune rejection for allogeneic constructs
7. Mechanical property mismatches with native tissue
8. Limited long-term clinical outcome data

• Cummings Otolaryngology Head and Neck Surgery - Chapters on Microtia Reconstruction and Tracheal Surgery
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery - Vol 1, Chapter 12 (Biomaterials and Tissue Engineering); Vol 3, Chapter on Laryngotracheal Trauma and Reconstruction