Revolutionizing regenerative medicine through tissue engineering of functional airway tissues
Imagine the sheer biological complexity of the surface that absorbs the oxygen keeping you alive. Every day, you breathe in and out approximately 20,000 times, and with each inhalation, the intricate epithelial lining of your respiratory system performs its vital functions seamlessly.
Tissue engineering of respiratory epithelium represents one of the most promising frontiers in regenerative medicine. Scientists are now developing innovative methods to create bioengineered replacements for damaged airway lining, offering hope to patients with conditions ranging from severe tracheal stenosis to chronic respiratory diseases.
The respiratory epithelium is not a uniform sheet of cells but rather a specialized tissue that changes in composition and function along the respiratory tract. This pseudostratified columnar epithelium is characterized by several key cell types working in concert: ciliated cells that rhythmically beat to move mucus and trapped particles, basal cells that serve as stem/progenitor cells responsible for regeneration, goblet cells that produce protective mucus, and various secretory cells 5 7 .
In tissue engineering, scaffolds serve as the three-dimensional framework that guides cell growth, organization, and development into functional tissue.
The cellular aspect involves selecting and cultivating appropriate cell populations to regenerate functional epithelium.
| Cell Type | Markers | Potential |
|---|---|---|
| Airway Basal Stem Cells | Tp63+, Krt5+ | Basal, ciliated, secretory cells |
| BASCs | CC10+, SPC+ | Bronchiolar and alveolar cells |
| LNEP Cells | Trp63+, Krt5+ | Alveolar regeneration |
| AT2 Cells | Sftpc+ | AT1 cells |
Ovine respiratory epithelial cells were isolated from tracheal mucosa using enzymatic digestion with protease XIV and cultured in specialized Airway Epithelial Cell Growth Medium 1 .
Cells were loaded into 1mL syringes and sprayed through the medical device onto various substrates from a distance of 2 cm 1 .
Researchers systematically tested different air pressures (ranging from 0.4 to 2 bar) and flow velocities (10-95 mL/min, plus manual application) 1 .
Sprayed cells were analyzed using live-dead staining and lactate dehydrogenase (LDH) assays to quantify survival and damage 1 .
Cell Viability at 0.4 bar
Successful Differentiation Period
| Spraying Parameter | Conditions Tested | Impact on Cell Viability |
|---|---|---|
| Air Pressure | 0.4 - 2.0 bar | Optimal at 0.4 bar (88.5% viability for RECs); decreased at higher pressures |
| Flow Velocity | 10-95 mL/min, plus manual | Manual (120-150 mL/min) showed no significant decrease in viability |
| Biomaterial Carrier | With/without fibrin gel | Better ciliary development without fibrin gel at 28 days |
| Reagent/Material | Function | Examples/Specifics |
|---|---|---|
| Cell Culture Media | Support cell growth and differentiation | Airway Epithelial Cell Growth Medium, F-medium for conditional reprogramming |
| Enzymatic Isolation Solutions | Dissociate tissue into individual cells | Protease XIV, trypsin/EDTA solutions |
| Scaffold Materials | Provide 3D structure for tissue development | Decellularized matrix, collagen, PCL, PLGA, fibrin gel |
| Growth Factors | Direct cell differentiation and behavior | EGF, VEGF, FGF, TGF-β, retinoic acid |
| Cell Markers | Identify and characterize cell types | Keratin 5, Keratin 14, CD151, CD49f |
| Rho-kinase Inhibitor | Enhance stem cell survival in culture | Y-27632 |
The ultimate goal of respiratory epithelium engineering is clinical application, particularly for patients with conditions that currently lack satisfactory treatment options. Those with long-segment tracheal defects (involving more than 50% of the trachea in adults or 30% in children) represent a particularly compelling patient population 5 .
Ensuring adequate blood supply to implanted tissue-engineered constructs
Rapid establishment of a functional epithelial layer for mucociliary clearance
Accounting for individual variations in regenerative potential
Seeding and maturing cells on scaffolds in the lab before implantation
Applying cells to scaffolds at the time of implantation, using the body as a bioreactor
Implanting the scaffold alone to recruit the patient's own cells
Tissue engineering of respiratory epithelium represents a remarkable convergence of biology, engineering, and medicine—all directed toward the fundamental human need to breathe. While significant challenges remain, the progress in this field has been substantial, from the development of innovative cell delivery methods like spraying to the creation of increasingly sophisticated biomaterial scaffolds.