Tissue engineering combines cells, engineering and material methods, and suitable biochemical and physicochemical factors to improve or replace biological tissues. One of the major components required for tissue engineering is scaffolds. These scaffolds provide a structural support for cells to grow and exchange nutrients. Traditionally, non-biodegradable scaffolds made of titanium, plastics or ceramics were used. However, recently researchers have focused on developing biodegradable scaffolds that can degrade over time as the new tissue forms.

What are Biodegradable Scaffolds?
The main goal of tissue engineering is to regenerate natural tissues and organs. For this to happen, scaffolds play a key role by acting as a template for new cell growth. Biodegradable scaffolds are 3D porous structures made of polymers or natural materials that degrade over time and get replaced by the new tissues. Some commonly used materials for biodegradable scaffolds include collagen, hyaluronic acid, fibrin, chitosan, alginate and synthetic polymers like polyglycolic acid (PGA), polylactic acid (PLA) and their co-polymers.

Advantages of Biodegradable Scaffolds
Biodegradable scaffolds offer several advantages over non-biodegradable ones:

- Degradation and Replacement: As the scaffolds degrade, they get replaced by the new tissues formed. This avoids the need for secondary surgery to remove non-biodegradable scaffolds.

- Host Compatibility: Biodegradable scaffolds made of natural polymers pose very little toxicity issues and show excellent host compatibility. They mimic the natural extracellular matrix.

- Mechano-regulation: As the scaffolds degrade, they transfer load to the new forming tissues, allowing mechano-regulation and stimulating tissue development.

- Porosity and Pore Size: Appropriate porosity and pore size in biodegradable scaffolds facilitates cell infiltration, diffusion of nutrients and integration with host tissues.

- Cost-Effective: Certain biodegradable materials like collagen are cheaper than metals or ceramics, making tissue engineering more affordable.

Applications of Biodegradable Scaffolds
Some major clinical applications where biodegradable scaffolds are proving effective include:

Bone Tissue Engineering
- Scaffolds made of calcium phosphate, hydroxyapatite or PLA/PGA are extensively used for bone grafts to treat fractures, non-union breaks, and bone defects.

Cartilage Tissue Engineering
- Collagen, chitosan or synthetic polymer scaffolds seeded with chondrocytes are a promising approach for cartilage repair in cases of osteoarthritis and worn-out joints.

Blood Vessel Grafts
- Biodegradable fiber-based PLA or PLGA tubular scaffolds resembling blood vessels show potential for replacing diseased arteries.

Skin Tissue Engineering
- Bilayered collagen-chitosan or hyaluronic acid scaffolds along with keratinocytes and fibroblasts demonstrate efficacy for burn injuries and chronic ulcer treatment.

Nerve Tissue Engineering
- Co-polymers of PLA/PCL or laminin-coated chitosan/silk fibroin scaffolds with Schwann cells aid peripheral nerve regeneration after injuries.

Challenges in Biodegradable Scaffolds
While biodegradable scaffolds hold immense potential, certain design challenges remain:

- Controlled Degradation: The degradation rate needs to match the tissue formation rate. Faster degradation may cause mechanical instability, while slower degradation leads to inflammation.

- Scaffold Mechanical Properties: Biodegradable Scaffolds  should mimic the modulus, strength and viscoelastic behavior of the target tissues to prevent structural failure on load bearing.

- Scaffold Porosity and Pore Size: Optimal porosity and pore size aid cell invasion and vascularization but are difficult to control during fabrication.

- Stimulating Cell Differentiation: Developing strategies to actively stimulate stem cell differentiation according to the target tissue remains challenging.

- Clinical Translation: Large-scale production and quality control as per regulatory protocols need standardization for clinical translation of scaffold-based therapies.

Biodegradable scaffolds have revolutionized the field of tissue engineering. By addressing various design challenges, they can support tissue regeneration and emerge as effective alternatives to organ transplants. With continual material and process innovations, the commercialization of scaffold products will make regenerative therapies widely accessible. Significant progress in the next decade is expected to translate scaffold technology from research to routine clinical practice for improving health worldwide.
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