**Abstract**

Bioprinting is an emerging field in the areas of tissue engineering and regenerative medicine. It is defined as the printing of structures consisting of living cells, biomaterials and active biomolecules. The ultimate aim is to produce implantable organs and tissues to replace the use of autografts, which cause donor site morbidity and require two invasive surgeries. Not only is bioprinting aimed at the restoration of tissue, it has significant potential for drug delivery and cancer studies. Bioprinting provides control over cell placement and therefore creates a homogenous distribution of cells correlating to a uniform tissue ingrowth. Another attribute of bioprinting is the production of patient-specific spatial geometry, controllable microstructures and a high degree of reproducibility and scalability between designs. This book chapter will discuss the many parameters of bioprinting; manufacturing techniques, precursor materials, types of printed cells and the current research.

**Keywords:** inkjet printing, extrusion, stereolithography, laser-assisted, tissue engineering, hydrogel, bioink, additive manufacture, 3D printing

#### **1. Introduction**

 There are more organ donors and recipients than there have ever been, however, in the UK, up to one in six patients requiring either a liver, heart or lung transplantation becomes too ill or dies while waiting for a donor organ [1]. When a donor organ becomes available, the recipient and clinicians have to make a fast decision whether to accept the organ, which can lead to an improper assessment of the associated risks. Risks associated with the donor organ include the age of the donor, retrieval of the organ after circulatory death and the potential to transmit bloodborne disease or cancer [1].

Bioprinting has the potential to eradicate the problems associated with organ donation and provide implantable organs on-demand. Bioprinting is a subcategory of additive manufacture, a process by which small scale objects are printed from a bottom up approach, through the deposition of successive layers of material. Using this approach enables the production of very precise and accurate designs and shapes to be built using minimal amounts of material. Designs are made on a computer which is then sent to a printer, meaning that designs are highly repeatable. The processes for developing a bioprinted tissue are outlined in **Figure 1**.

Although additive manufacturing uses a variety of materials to fabricate objects with different functions and purposes, bioprinting is specifically the printing of structures consisting of living cells, biomaterials and active biomolecules. First

#### *Biomaterial-supported Tissue Reconstruction or Regeneration*

**Figure 1.** 

*Flow chart depicting the individual process involved with producing a bioprinted tissue.* 

patented attempts of bioprinting started with filling cartridges of table-top inkjet printers with bioinks, consisting mainly of cell-laden hydrogels [2]. Although research using inkjet technology was an early adapter for bioprinting, many other additive manufacturing techniques have also been utilized.

 Common techniques include inkjet printing, stereolithography and extrusion printing, demonstrated in **Figure 2**. Although these techniques are well established, it is only in the last decade that these processes have been properly developed for applications in the field of regenerative medicine and tissue engineering. Compared to the conventional techniques of producing tissue engineering scaffolds, additive manufacture has the ability to consistently produce highly repeatable designs with a precise, well-defined micro and nanoscale structure [3, 4].

The ultimate goal of bioprinting is to produce an entire complex organ capable of being implanted. This will provide an alternative source of organs so that patients will no longer require long waiting periods to receive a donor organ. Additionally, by being able to fabricate organs on demand, the ethical issues surrounding the supply and use of human or animal tissues is removed.

Another possibility for bioprinting is to provide an alternative to animal testing. The potency and dosages of pharmaceuticals can be tested on bioprinted organoids or on an "organ-on-a-chip". This could prove to be a more efficient and effective

**Figure 2.**  *Bioprinting techniques: (a) extrusion-based, (b) inkjet-based, (c) stereolithography and (d) laser-assisted.* 

#### *Bioprinting DOI: http://dx.doi.org/10.5772/intechopen.81135*

method for the testing of pharmaceuticals, as the translation from an animal model in to humans is not without its flaws, as an animal system cannot fully replicate a human system.

Common tissue engineering manufacturing techniques are capable of producing tissue specific scaffolds; however they require to be seeded with cells post-fabrication. Cell seeding post-fabrication can lead to a poor distribution of cells, especially in larger scale 3D scaffolds. Homogeneous distribution of cells is not a problem with bioprinting, as printing can be used to control the positioning of cells during fabrication [5].

Simple tissues have been repaired in a clinical setting using tissue engineering scaffolds, such as the larynx [6], bladder [7] and urinary tract [8], however through bioprinting, the ability to build a more complex tissue scaffold for implantation becomes a greater prospect.
