Tissue Engineering: Biomaterials Used in Cartilage Tissue

Tissue engineering (TE) is a rapidly evolving discipline that seeks to repair, replace or regenerate tissues or organs by translating fundamental knowledge in physics, chemistry and biology into practical and effective materials, or devices and clinical strategies.

There are various products for bone tissue regeneration both in our country and abroad. However, the situation is not so simple for cartilage tissue, which is another tissue in the skeletal system. Since there is no vascularization in the cartilage tissue, comprehensive healing is not possible and the difficulty in achieving the right flexibility in the joint areas are among the difficulties faced by tissue engineers working in this field.

In the use of biomaterials, the functioning of living tissues and organs should be preserved while improving the health of the person. Therefore, while developing a biomaterial, attention should be paid to the biological system, biomaterials and their interactions in the body environment. In tissue engineering, natural and synthetic-based biocompatible polymers are used to create the natural cartilage structure.

Basically, there are four types of polymer-based materials used for cartilage joints, these are (i) natural polymers, (ii) synthetic polymers, (iii) hydrogels, and (iv) composites. Biocompatibility polymers known to be found in many living organisms are also actually hydrogels, and some are widely used in combination with other materials as composite scaffolds. These polymers can be used to modify or regenerate native tissue structures and allow positive cell interactions with surrounding tissues. Although hydrogels can be synthesized, they always occur naturally. Composite scaffolds are created by mixing two or more materials to achieve the desired properties and characteristics, making use of each of the materials.

Natural polymers are polymers that are biologically produced and have unique functional properties. Proteins (eg collagen, gelatin, elastin, actin, etc.), polysaccharides (cellulose, starch, dextran, chitin, etc.) and Polynucleotides (DNA and RNA) are the main natural polymers.

Collagen, one of the most widely used natural polymers, occurs naturally in connective tissue, providing mechanical support. Collagen; It is a water-insoluble protein with high mechanical strength. The fibrous and α-helix structure provides collagen with high stretch and resistance. Collagen, which is the main component of connective tissue in the body, constitutes approximately 1/3 of the total body proteins. Collagen is occured in 50% of the cartilage tissue, 68% of the corneal tissue and 74% of the skin.

Gelatin is a biodegradable natural polymer produced by acid or base hydrolysis of collagen. Gelatin, which has a large number of functional side groups, has the property of gelling and can be cross-linked quite easily. These properties give gelatin a significant advantage for its use as a biomaterial. Gelatin is an important biomedical material due to its properties such as being biocompatible, non-toxic, bioactive and biodegradable.

Hyaluronic acid (HA); It is another naturally occurring polysaccharide commonly found in specialized tissues such as synovial fluid, dermis, and cartilage. HA is an important part of cartilage formation in joints. HA surrounds chondrocytes, which are cartilage cells, and gives the joints resistance to pressure with its water retention potential. HA decreases in joints with age.

Since chitosan is soluble in weak acids, a cationic polymer with high charge density is formed. Due to this feature, chitosan can form polyelectrolyte complexes with many anionic polymers. Chitosan is biorenewable; The fact that it is biodegradable, biocompatible, antigenic and non-toxic and has a biofunctional structure has enabled the use of this polymer and the complexes obtained using this polymer in biomedical applications such as wound dressing material and drug delivery systems.

Synthetic polymers are formed by controllable chemical processes to achieve desired material and chemical properties for a wide variety of biomedical applications. The mechanical and proliferation properties of synthetic polymers are relatively more predictive and reproducible. Some synthetic polymers used to mimic the natural cartilage structure are as follows:

Poly (vinyl alcohol) (PVA) is a water-soluble, linear artificial polymer. It has properties such as being non-toxic and non-carcinogenic, mechanically durable, high temperature and pH stability. In addition, it has a high swelling feature in water and biological fluids, its elastic structure; It allows its use as a biomaterial in various applications such as contact lenses, skin, artificial cartilage and drug delivery systems.

Poly(ethylene glycol) (PEG) is an artificial polymer used in many biomedical applications for different purposes and soluble in water and organic solvents. It is a polymer of great interest due to its superior physicochemical and biological properties such as biocompatibility, non-toxicity and hydrophilicity, and it is widely used as a hydrogel.

Polylactic acid or polylactide (PLA) is a biodegradable, bioadsorbable, thermoplastic aliphatic polyester, meaning it is derived from renewable resources. Lactic acid has two optical isomers, L- and D-lactic acid. PLA is used as screws, pins, rods, medical implants in the form of orthopedic devices, and as a mesh. PLA is also used as a biodegradable and biocompatible material in tissue engineering science. In the studies, mineralized hydroxyapatite (HA) was produced on chitosan (CS) coated poly (lactic acid) (PLA) nanofibers for bone regeneration. Their results show that this composite has similar structural, combination and biological functions of natural bone and can be helpful as a good choice for bone.

Polycaprolactone (PCL) is a biocompatible, bioadsorbable and biodegradable polyester. PCL is used in medical implants, dental splints, and targeted drug delivery systems. Recent studies show that PCL scaffolds prepared in combination with other polymers are a biocompatible scaffold to be used in bone and cartilage regeneration.


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