**4.1 Bioprinting of tissues and organs**

One of the critical medical issues is the failure of organs and tissues as a result of accident, congenital defects, aging etc (**Figure 1**) and the current resolution for this problem is organ transplant from dead or living donors. However, only few

**Figure 1.** *Different medical applications of 3D printing technology.*

fortunate people receive organs and the rest die due to donor shortage. Moreover, the procedures for organ transplants are so expensive that it is out of reach of common people. Another problem with transplant surgery is that donors with tissue match are difficult to find [7, 53].

The solution to this problem lies in the fact that the required tissue or organ should be fabricated using the patient's own body cells, which would decrease the risk of tissue or organ rejection; moreover, the requirement for immunosuppressant will also be greatly reduced [7, 54].

In the conventional method of tissue engineering from a small tissue sample, stem cells are isolated, amalgamated with growth factor, and then multiplied in the laboratory. Then the cells are seeded onto scaffolds that direct cell proliferation and differentiation into a functioning tissue.

Placement of cell with accuracy, digitally controlled speed, drop volume, resolution, concentration of cells and diameter of printed cell are some of the additional advantages that 3D bioprinting offers over traditional tissue engineering [2, 54].

Depending upon the porosity, the type of tissue, and required strength, various materials are present to make the scaffolds. Among all materials, hydrogels are said to be the most suitable for building soft tissues [2, 55].

No doubt that organ printing is still in the phase of development but several researches have demonstrated its concept with proof. Scientists have built an artificial ear, cartilage and bone, and heart valve by the help of 3D printers [2, 47, 55]. Wang et al. used 3D bioprinting technology to deposit different cells within various biocompatible hydrogels to produce an artificial liver [54].

As with the increasing interest of researcher and academician and with vast potential of this technology it can possibly unfold new potential therapeutic drugs thereby greatly cutting research cost and time [7].
