Cells rely on collagen to attach to extracellular matrix (a complex mixture of non-living materials) to organize themselves into tissues. In turn, each tissue depends on collagen for attachment to form organs. Finally, collagen allows organs to unite to form a complex multi-organ organism. Collagen is like a biological adhesive for its role in tissue and organ formations. Without this biological adhesive, all tissues and organs would break down into a disorganized mass of cells. Conversely, if cells are removed from tissues and organs, the resulting structural network is consisted mainly of collagen.

When tissues and organs are injured, collagen-based structural supports are damaged as well. In the absence of an immediate and effective repair to the damaged collagen support, the injured tissues or organs would have difficulty recovering from injuries. Therefore, the timely use of exogenous collagen scaffolds can facilitate injury repairs.

At present, major sources of medical-grade tissue and organ scaffolds include:

1. Autografts:These are tissues and organs surgically moved from uninjured site of the body to the injured site of the same individual. For example, in coronary artery bypass surgery, a vein from the thigh is transferred to the heart to replace the obstructed coronary artery of the same individual. The greatest drawback of autografts is the unavoidable injury created to obtain normal healthy tissues and organs.

2. Allografts:Tissues and organs can also be obtained from another individual to repair the injured site. Their availability depends heavily on donation. Attitude towards donation of body parts is generally positive in the West; therefore, some patients are able to take advantage of them. However, attitude is different in Asia, thus, allografts are not widely available.

3. Xenografts:These are tissues and organs obtained from common farm animals such as cattle, sheep, pigs, horses, and etc. Processing xenografts is the same as allografts, requiring the complete elimination of cells, lipids, and free proteins in order to prevent allergic reaction and rejection by the patient.

4. Chemically synthesized biological materials:Many of the commonly used biomedical materials, such as collagen, hyaluronic acid, polylactic acid, alginate, and other biological or composite materials, are chemically synthesized. A purification process is required to purify them into medical-grade raw materials. These raw materials are then synthetically reconstituted into a variety of medical-grade repair materials. Although they are widely available, they have two major drawbacks. First, material strength and porosity are not the same as naturally occurring materials. Second, the addition of chemical crosslinkers in the synthesis process often leads to adverse allergic reaction by the patient.