**4. Regenerative medicine**

Regenerative medicine is a new branch of medicine that tries to change the course of chronic diseases, and in many cases, regenerates organ systems that fail due to age, disease, damage, or genetic defects. The area has quickly become one of the promising treatment options for patients with tissue failure. It also includes tissue engineering, but also involves the search for self-healing—the body uses its own systems, sometimes with the help of foreign biological materials to reconstitute cells and rebuild tissues and organs. The terms "*tissue engineering*" and "*regenerative medicine*" have become highly interchangeable, with the field hoping to focus on treatments rather than complex and often chronic disease treatments.

Tissue engineering is an emerging biomedical field aimed at helping to restore physical tissue defects to the point of self-repair as well as replacing the biological functions of damaged and injured members using cells with reproductive and differential abilities. In addition to basic research on these cells, there is no doubt that successful tissue engineering is indispensable for creating an artificial environment that enables cells to stimulate tissue regeneration. Such an environment can be achieved using scaffolds for cell proliferation, differentiation, and growth factors, as well as combining them. Growth factors are often required to promote tissue regeneration, as they can stimulate the formation of blood vessels, which supply oxygen and nutrients to the transplanted cells to replace the organ to maintain its biological functions.

It requires functional platforms or scaffolds with specific properties concerning the morphology, chemistry of the surface, and interconnectivity to promote cell adhesion and proliferation. These requisites are not only important for cellular migration but also to supply nutrients and expulsion of waste molecules. Cell type must be considered when designing of using a specific cellular grown system as scaffold; for instance, if they are autologous, allogeneic, or xenogeneic. The challenge in tissue engineering is to develop an organized three-dimensional architecture with functional characteristics that mimic the extracellular matrix. In this regard, with the advent of nanotechnology, scaffolds are now being developed that meet most of the requisites.

The technology of tissue engineering has evolved from the development of biological materials (biomaterials) and refers to the practice of combining scaffolds, cells, and biologically active molecules of functional tissues. The aim of tissue engineering is to gather functional structures that restore, maintain, or improve damaged tissues or full organs. Artificial engineered skin and cartilage tissues are examples that have been recently authorized by the FDA [2].

The operation is usually initiated by building a scaffold from a wide range of potential sources, from proteins to plastics. When scaffolds are created, cells with or without a "mix" of growth factors can be introduced. Assuming that the environment is appropriate, the tissue grows. Sometimes, cells, scaffolds, and growth factors are mixed together simultaneously, giving the tissue the opportunity to "self-assemble" [2].

Different ways to create a new fabric or tissue is using the present scaffold. The donor tissue or organ cells are stripped and the maintained collagen scaffold is used to form a new tissue. A new tissue has been created in the biological engineering of the heart, liver, lungs, and kidney tissues in rat. This approach holds great promise for the use of scaffolds from human tissues that are discarded during surgery and integrated with the patient's own cells for the work of dedicated members that cannot be rejected by the immune system.

The tissue needs a good "draining and plumbing system" (veins or arteries), a way to feed nutrients into cells and carry waste. Without blood supply or any similar mechanism, cells die quickly. Ideally, scientists would like to be able to create engineered tissue using a plumbing system that has already been built (lattices). New hope for the bum knee: cartilage has been very difficult, if it is not impossible to repair since cartilage lacks a blood supply to promote regeneration. The gel/adhesive combo was successful in regenerating cartilage tissue following surgery in a recent clinical trial of patients.
