What Is Tissue Engineering in Orthopedics?
Using a combination of cells, materials, methods, engineering, and appropriate physicochemical and biochemical factors to repair or replace biological tissues is described as tissue engineering. It also uses scaffolds to form new biologically viable tissues for clinical purposes. Tissue engineering is often used synonymously with the term regenerative medicine. It is important to select the accurate combination of signals, scaffolds, and cells while designing tissue engineering in orthopedic surgeries. Tissue engineering is used in musculoskeletal problems, including osteonecrosis, fracture nonunion, and osteochondral defects.
What Are the Principles of Tissue Engineering in Orthopedics?
The pattern of tissue engineering consists of scaffolds, signals, and cell types. These three factors can be used independently or in combination to generate new viable tissues in a limitless number of ways. They are also said to be elements of tissue engineering.
1. Scaffold
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The scaffolds used in tissue engineering are cytocompatibility biomaterials, meaning the cells can adhere to the scaffold or be replaced with an extracellular matrix to form its native tissues.
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Scaffolds can be available as morselized autologous bone or as injectable, synthetic, and thermally responsive hydrogels capable of mineralizing inside it.
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The simple morselized autologous bone can be divided into small portions, and the complex hydrogel contains water as its liquid component.
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Scaffolds are divided into metals, ceramics, and polymers, which can be further divided into naturally derived and synthetically manufactured products. The materials can also be available as resorbable and non-resorbable products.
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Even though these scaffolds are stable, their delivery system and non-resorbable scaffolds cannot repair the damaged tissues and replace the native tissues, which may cause a chronic foreign body reaction during tissue healing.
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The naturally derived scaffolds are resorbable and form ligands to improve cell adhesion. These also have physical properties like degradation, osteoinductive or osteoconductive, and mechanical strength.
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Only a few synthetic scaffolds are biodegradable; thus, additional components are required to adhere to the cells.
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Another important property needed for the scaffold is compatibility. If it absorbs too fast, it may not support the formation of new tissues; if it resorbs too slowly, it may not fully attach to the surrounding tissues and cause infections.
2. Signals
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The signals used in tissue engineering are environmental factors that can be derived internally or externally to improve tissue regeneration. It can be classified as chemical, mechanical, biological, and electrical signals.
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The most commonly used orthopedics signals are biological ones that include rhBMP-2 (osteogenic growth factor). The adverse effect of this signal is that it may cause osteosarcoma.
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The other commonly used signal is platelet-rich plasma (PRP). It remains uncertain in the regeneration of tissues because of the ease of autologous bone.
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An example of chemical signals is antibiotics. In persons with infected orthopedic problems, the antibiotics encapsulated in the scaffolds may stimulate healing.
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Mechanical signals have been used to accelerate bone formation, like distraction osteogenesis.
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Electrical signals are also important in regenerating tissues.
3.Cells
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Cells are essential to form native tissues in tissue engineering. The cells can be sent to the implanted scaffolds by some methods, which include osteoconduction or osteoinduction, releasing chemokines, attaching cell ligands to the scaffold, or implanting scaffolds that contain cells.
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The cell types used in tissue engineering are adipose tissue-derived cells and bone marrow-derived cells.
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The most commonly used cells are mesenchymal stem cells. These cells can differentiate into osteoblasts, chondroblasts, tenocytes, and myeloblast.
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From this, the adipose-derived mesenchymal stem cells are used more commonly as they are available more, can be harvested at low cost, and have ease of expansion.
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Amniotic fluid-derived mesenchymal cells are also used. The other sources for deriving mesenchymal stem cells are the periosteum, skin, and umbilical cord blood.
4. Platelet-Derived Growth Factor
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Platelet-derived growth factors play a vital role in tissue engineering in orthopedics by promoting angiogenesis, cell proliferation, and tissue regeneration. Platelet-derived growth factors stimulate the migration and division of mesenchymal cells, which are important for bone and connective tissue formation.
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In orthopedics, platelet-derived growth factors are often incorporated into scaffolds to enhance healing. It aids in the recruitment of cells involved in bone repair, such as osteoblasts and endothelial cells, contributing to the development of functional and structurally sound tissues.
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Controlled release of platelet-derived growth factors mimics the natural healing process. This allows an improved outcome in orthopedic applications.
5. Stem Cells
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Stem cells play a pivotal role in orthopedic tissue engineering by their ability to differentiate into various cell types, including osteoblasts (bone-forming cells) and chondrocytes (cartilage-forming cells). These cells are essential for regenerating and repairing damaged or injured musculoskeletal tissues.
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In orthopedic tissue engineering, stem cells are often combined with scaffolds and growth factors to create constructs that mimic the natural tissue environment. These constructs provide a supportive framework for stem cell proliferation, differentiation, and tissue-specific matrix production.
How Does Tissue Engineering in Orthopedics Apply Clinically?
Studies have shown that tissue engineering in orthopedics is successfully done for conditions like osteonecrosis, fracture nonunion, and osteochondral defects.
1. Fracture Nonunion
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Fracture nonunion is said when there is incomplete healing of fractured bone beyond nine months after injury or when there is the absence of progression of healing.
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It has been studied that vascularity is the major reason for nonunion.
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It is observed that atelocollagen gives positive results in tissue regeneration in fracture nonunion.
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Studies have shown that a combination of scaffolds, signals, and cells heals the injured bone in fracture nonunion cases.
2. Osteonecrosis
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It is reported that patients with osteonecrosis have poor regenerative capacity of their bones. It is also said that corticosteroid-induced osteonecrosis has decreased mesenchymal stem cells.
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Studies have shown that combining scaffolds and cells like bone marrow-derived mesenchymal stem cells implanted with morselized allograft results in healing osteonecrosis.
3. Osteochondral Defects
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Usually, cell monotherapy is used for treating cartilage in orthopedic problems.
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The autologous adipose-derived mesenchymal stem cells and acellular collagen-hydroxyapatite scaffold have successfully treated chondral and osteochondral defects.
Conclusion:
Tissue engineering in orthopedics has a lot of scope in the future. A lot of work needed to be done in tissue engineering. New techniques like high-resolution bioprinting for forming scaffolds and coating the implants with antimicrobial coating may help to reduce foreign body infections on the scaffold surfaces. In addition, products such as Medtronic and Cortical give hope to tissue engineering. In the early days, the successful treatment of osteoporosis may lack the disease progression, but with tissue engineering during treatments, there may be the absence of disease. Tissue engineering in orthopedics is under much study. It kept evolving with new techniques to repair the damaged tissues, replace the biological tissue in place, and promote the healing of the injury.
