**6.2 Kidney**

Long-term hemodialysis and peritoneal dialysis have been widely used in the treatment of end-stage renal failure patients**.** These treatment modalities have bridged thousands of patients to transplantation. The kidney is the first solid organ whose function could be replaced by an external device. Portable and wearable dialysis devices for the treatment of patients with end-stage kidney failure are being developed.

The evolution of devices designed to treat renal impaired patients has followed the sequence of portable artificial kidney [PAK], second- generation PAK, a wearable artificial kidney [WAK], and implantable bioartificial kidney [BAK]. All of these devices are to be smaller, lighter and intended for use outside the clinic. BAK can partially replace tubular function and it provides an extension to conventional dialysis systems and artificial kidneys by incorporating elements of living cellular and tissue function. The key features for the development of a bioengineered kidney require three main components. These are, cellular components, material engineering, and emerging technologies. Hollow membranes, extracellular matrix proteins, porous structures, and novel chemistries are included in material engineering. Organoids, 3D printing, decellularized kidney and induced pluripotent stem cells compose the emerging technologies. Specialized kidney cells and stem cells constitute the cellular component. A bioartificial kidney is expected to be able to reproduce the metabolic, endocrine, immunomodulatory, and secretory functions of a normal kidney [42].

Bioengineering and regenerative medicine also play a role in the efforts to construct an artificial kidney as a final target. New branches of engineering like artificial intelligence and machine learning for the real-time analysis of equipment alarm, dialysis parameters and patient-related data contribute to developments in this field. The problems encountered in the transplantation of recellularized whole kidney scaffolds are needed to efficiently repopulate the endothelium of the vascular network of the engineered kidney before implantation and optimal source of cells to repopulate an acellular kidney scaffold [43].

Generation of human- induced pluripotent stem cells derived kidney organoids has been an important step in regenerative medicine and kidney organoids are expected to be used for disease modeling, drug discovery and ultimately be applicable for transplant [44].
