The Role of Mechanical Engineering in Regenerative Medicine

When biological tissues or organs lose their function due to illness or accidents, if the damage is extensive, the organism's self-repair capabilities cannot achieve a complete recovery. Conventional medicine has reconstructed lost functions using organ transplants or artificial organs made from artificial materials (such as artificial blood vessels and artificial joints), but it has faced challenges such as a shortage of donors and limitations in the functional regeneration of biological tissues by artificial materials. As a new form of medicine to overcome these problems, "regenerative medicine," which reconstructs human body tissues and organs using cells, is gaining attention. Especially since the establishment of iPS cells by Professor Yamanaka of Kyoto University, expectations for regenerative medicine have been steadily increasing.

Now, given what has been described so far, you might wonder why I, a researcher belonging to the Department of Mechanical Engineering, am conducting research related to "regenerative medicine." The Department of Mechanical Engineering is likely strongly associated with the development of things like automobiles, rockets, and engines. However, if we consider living organisms as "machines" composed of structures, although primarily made of organic materials like proteins, I believe you can understand that there are approaches to regenerative medicine from a mechanical engineering perspective. In particular, mechanical engineering approaches are very useful in the regeneration of articular cartilage, which I have been involved with.

Let me briefly introduce the regeneration of articular cartilage. Articular cartilage is a biological tissue found on the lubricating surfaces where bones meet in the body's joints. It is an excellent tissue with a very low coefficient of friction and the ability to withstand forces several times body weight. In automobiles or robots, the equivalent would be the bearings that support rotating parts. Because articular cartilage has no blood vessels or nerves, unlike other biological tissues, it does not heal easily once damaged, often leading to joint diseases such as osteoarthritis. You may know people around you who have difficulty walking due to pain in their knees or hips. In many cases, this is caused by the cartilage in the affected area wearing away due to osteoarthritis, resulting in bone rubbing directly against bone with a "grinding" sensation.

Now, for the treatment of such articular cartilage, an approach using regenerative medicine to create cartilage tissue outside the body (ex vivo) using cells is very effective. In this method, a small number of cartilage cells are harvested from a healthy area, mixed into a highly water-retentive gel (hydrogel), and cultured to regenerate cartilage tissue (Fig. 1). This method of three-dimensional culture using a gel or sponge-like material as a scaffold is extremely effective for regenerating biological tissue and is a commonly used technique. However, the strength of the regenerated cartilage is only one-tenth or less compared to the strength of native articular cartilage in the body. Therefore, we devised a new method of culturing cells while applying stimulation. The cells within articular cartilage are subjected to repeated compressive forces daily as humans walk. Therefore, we developed a device that can culture cartilage cells embedded in a jelly (hydrogel) while applying compressive deformation at the frequency of the human walking cycle (approximately 0.5 to 1 Hz) (Fig. 2). In fact, as a preliminary step before experiments using human cells, we cultured calf articular cartilage cells, whose loading patterns are similar to humans, while applying stimulation that mimics walking. We succeeded in increasing the strength of the resulting regenerated cartilage by two to three times (Fig. 3). The ability to develop such a device is arguably a unique approach to regenerative medicine that can only come from a laboratory with a background in mechanical engineering, combined with an understanding of the structure and function of cells and biological tissues.