Overview of Tissue Engineering

This process uses cells to replace biological tissue

In This Article

The human body's ability to regenerate tissues and organs is extremely inefficient, and losing human tissue and organs can happen easily due to things like congenital defects, diseases, and sudden trauma. When tissue dies (called necrosis), it can't be brought back to life—if it's not removed or repaired it can affect other areas of the body, such as surrounding tissue, organs, bone, and skin.

This is where tissue engineering is useful. By using biomaterial (matter that interacts with the body’s biological systems such as cells and active molecules), functional tissues can be created to help restore, repair, or replace damaged human tissue and organs.

A Brief History

Tissue engineering is a relatively new field of medicine, with research only starting in the 1980s. An American bioengineer and scientist named Yuan-Cheng Fung submitted a proposal to the National Science Foundation (NSF) for a research center to be dedicated to living tissues. Fung took the concept of human tissue and expanded it to apply to any living organism between cells and organs.

Based on this proposal, the NSF labeled the term “tissue engineering” in an effort to form a new field of scientific research. This led to the formation of The Tissue Engineering Society (TES), which later became the Tissue Engineering and Regenerative Medicine International Society (TERMIS).

TERMIS promotes both education and research in the field of tissue engineering and regenerative medicine. Regenerative medicine refers to a broader field that focuses on both tissue engineering as well as the ability of the human body to self-heal itself in order to restore normal function to tissue, organs, and human cells.

Purpose of Tissue Engineering

Tissue engineering has a few main functions in medicine and research: helping with tissue or organ repair including bone repair (calcified tissue), cartilage tissue, cardiac tissue, pancreas tissue, and vascular tissue. The field also conducts research on stem cell behavior. Stem cells can develop into many different types of cells and may help repair areas of the body.

The field of tissue engineering allows researchers to create models to study various diseases, such as cancer and heart disease.

The 3D nature of tissue engineering allows tumor architecture to be studied in a more accurate environment. Tissue engineering also provides an environment to test potential new drugs on these diseases.

How It Works

The process of tissue engineering is a complicated one. It involves forming a 3D functional tissue to help repair, replace, and regenerate a tissue or an organ in the body. To do this, cells and biomolecules are combined with scaffolds.

Scaffolds are artificial or natural structures that mimic real organs (such as the kidney or liver). The tissue grows on these scaffolds to mimic the biological process or structure that needs to be replaced. When these are constructed together, new tissue is engineered to replicate the old tissue's state when it wasn't damaged or diseased.

Scaffolds, Cells, and Biomolecules

Scaffolds, which are normally created by cells in the body, can be built from sources such as proteins in the body, man-made plastics, or from an existing scaffold, such as one from a donor organ. In the case of a donor organ, the scaffold would be combined with cells from the patient to make customizable organs or tissue that is actually likely to be rejected by the patient’s immune system.

Regardless of how it’s formed, it is this scaffold structure that sends messages to the cells that help support and optimize cell functions in the body.

Picking the right cells is an important part of tissue engineering. There are two main types of stem cells.

Two Main Types of Stem Cells

  • Embryonic Stem Cells: originate from embryos, usually in eggs that have been fertilized in vitro (outside of the body).
  • Adult Stem Cells: found inside the body among regular cells—they can multiply by cell division to replenish dying cells and tissue.

There is currently a lot of research being conducted on pluripotent stem cells as well (adult stem cells that are induced to behave like embryonic stem cells). In theory, there is an unlimited supply of pluripotent stem cells, and the use of them does not involve the issue of destroying human embryos (which causes an ethical problem as well). In fact, Nobel Prize-winning researchers released their findings on pluripotent stem cells and their uses.

Overall, biomolecules include four major classes (though there are secondary classes as well): carbohydrates, lipids, proteins, and nucleic acids. These biomolecules help make up cell structure and function. Carbohydrates help organs like the brain and heart function as well as systems run like the digestive and immune systems.

Proteins provide antibodies against germs as well as structural support and body movement. Nucleic acids contain DNA and RNA, giving genetic information to cells.

Medical Use

Tissue engineering is not widely used for patient care or treatment. There have been a few cases which have used tissue engineering in skin grafts, cartilage repair, small arteries, and bladders in patients. However, tissue-engineered larger organs like the heart, lungs, and liver have not been used in patients yet (although they have been created in labs).

Aside from the risk-factor of using tissue engineering in patients, the procedures are extremely costly. Though tissue engineering is helpful when it comes to medical research, particularly when testing new drug formulations.

Using live, functioning tissue in an environment outside of the body helps researchers make gains in personalized medicine.

Personalized medicine helps to determine if some drugs work better for certain patients based on their genetic makeup, as well as reduces costs of development and testing on animals.

Examples of Tissue Engineering

A recent example of tissue engineering conducted by the National Institute of Biomedical Imaging and Bioengineering includes the engineering of a human liver tissue which is then implanted in a mouse. Since the mouse uses its own liver, the human liver tissue metabolizes drugs, mimicking how humans would respond to certain medications inside the mouse. This helps researchers see what possible drug interactions there may be with a certain medication.

In an effort to have engineered tissue with a built-in network, researchers are testing a printer which would make a vascular-like network from a sugar solution. The solution would form and harden in the engineered tissue until blood is added to the process, traveling through the man-made channels.

Finally, the regenerating of a patient’s kidneys using the patient’s own cells is another project of the Institute. Researchers used cells from donor organs to combine with biomolecules and a collagen scaffold (from the donor organ) to grow new kidney tissue.

This organ tissue was then tested for functioning (such as absorbing nutrients and producing urine) both outside and then inside rats. Progress in this area of tissue engineering (which can also work similarly for organs like the heart, liver, and lungs) could help with donor shortages as well reduce any diseases associated with immunosuppression in organ transplant patients.

How It Relates to Cancer

Metastatic tumor growth is one of the reasons that cancer is a leading cause of death. Before tissue engineering, tumor environments were only able to be created outside of the body in 2D form. Now, 3D environments, as well as the development and utilization of certain biomaterials (like collagen), allow researchers to look at a tumor’s environment down to the microenvironment of certain cells to see what happens to the disease when certain chemical compositions in cells are altered.

In this way, tissue engineering helps researchers understand both cancer progression as well as what the effects of certain therapeutic approaches might be on patients with the same type of cancer.

While progress has been made studying cancer through tissue engineering, tumor growth can often cause new blood vessels to form. This means that even with the advancements tissue engineering has made with cancer research, there may be limitations that can only be eliminated by implanting the engineered tissue into a live organism.

With cancer, however, tissue engineering can help establish how these tumors are forming, what normal cell interactions should look like, as well as how cancer cells grow and metastasize. This helps researchers test drugs that will only affect cancer cells, as opposed to the whole organ or body.

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