Treating Disease Through Tissue Engineering

In the short time since the initiation of tissue engineering programs,immense progress has been made. In principle, all diseases associated with the failure of tissue functions are currently being addressed. Manyof the tissues, generated in vitro for the replacement of cartilage,articulation, heart, liver and pancreatic islets, have already undergone clinical tests. Cartilage has already reached the stage of clinical application 24 due to the robustness and phenotypic stability of the cells and also the fact that cartilage and bone tissues can be grown in vitro with relative ease. These tissues do not require strong vascularization – still a major challenge in tissue engineering – since there is a sufficient diffusion of nutrients and oxygen through the scaffolds used for this type of cell.
Several tests have been conducted with three-dimensional hyaline cartilage to remedy articular damage or abrasions when other treatments fail (e.g. chondroitin sulfate (Chondrosulf)).Other tissues, such as heart valves and heart-muscle tissues, have also been produced in vitro.However, they have shown poor integration after transplantation into the organ and have not reliably maintained their function. Researchers and medics are working on a cure for liver malfunction (liver cirrhosis and fibrosis), induced by either alcohol abuse or viral infections such as hepatitis. Although the liver can regenerate itself,it can also become so weakened that transplantation is the only solution.
To overcome the perpetual shortage of donor organs, an attempt has been made to propagate hepatocytes in vitro. However, only the culturing of these cells as scaffold-free microtissues or on three-dimensional scaffolds that mimic the natural extracellular matrix of the liver has been successful; growing hepatocytes as monolayers changes their phenotype and results in the loss of their natural function. In addition, research into the generation of pancreatic islet tissues to combat diabetes, the main cause of hormone dysfunction in developed countries, is ongoing.
It is not possible here to list all the organs that are currently being reconstructed in laboratories. We have, therefore, concentrated on the most important diseases, for which a clinical therapy is standard or soon will be. Although researchers have made great advances in the engineering of tissues with simple structures (e.g. cartilage and liver), many tissues do not consist of a single cell type but rather a specific architecture of many cell types that enables them to perform their tasks, as is the case, for example, with the kidney, heart and skin. Hence it is very important to understand the structure and cellular composition of native tissue in order to reconstruct them for therapeutic applications.