Innovative Strategies for Tissue Engineering - Advances in Biomaterials Science and Biomedical Applications - page 308

suspensions may also come about from the high shear stresses observed during ejection and
impact of a fluid drop [50, 51, 52].
In many cases, the bioprinting process requires that before and during printing, cells and
molecules must be carried in a fluid vehicle that shortly after printing requires consolidation
and should consequently behave as a viscoelastic solid. This phase change must occur without
damage to the biochemical, cells, or more complex units within the fluid, which presents a
considerable challenge. Concurrently, tissue printed mustn't be too solid, or cell spheroids
won`t interact and form a continued tissue.
Organ printing is a technology that promises to transform tissue engineering into a
commercially successful biomedical industry. Unlike other tissue engineered approaches,
organ printing involves the high throughput generation of organs, relying on automated cell
sorters, cell and organ bioreactors and robotic bioprinters, most of them which are already
commercially available [46]. However, much research is necessary to turn this technology into
reality of clinical application.
4. Conclusion: Tissue engineering — From the bench to the bedside
It is known that any technology takes about 20 years to reach the market, and despite progress
in many fields, this timeframe has yet to shorten [20]. Accordingly, tissue engineering, which
has officially given its first steps during the late eighties, hasn`t brought many products to the
bedside [20].
In contrast to biomaterials - which are readily available as hip implants, contact lenses, silicon
breast prosthesis, among others -, and cell therapy - which is also available for bone marrow
transplants, as well as its first allogeneic stem cell therapy products [21] -, constructs have been
successfully produced for only few applications, largely limited to non-modular organs such
as skin epidermis, corneal epithelium and cartilage [40]. Indeed, Apligraf - a bilayered skin
substitute - was the first allogeneic cell based therapy to be approved by the US Food and Drug
Administration (FDA), receiving permission for sale as a treatment for venous leg ulcers13.
Apligraf is constructed by culturing human foreskin-derived neonatal fibroblasts in a bovine
type I collagen matrix over which human foreskin-derived neonatal epidermal keratinocytes
are then cultured and allowed to stratify [68]. Even though it is considered one of the first tissue
engineering products ever approved for commercialization, Apligraf doesn`t directly restore
skin, but transiently protects and provides injured skin with scaffold and signaling molecules
(produced by the cells within the construct) which fosters and accelerate skin regeneration.
Engineered bladders and airways have also been built and implanted in vivo , but as they
require highly customized and complex approaches, they are available to a small number of
patients, and are not considered products to be sold, such as Apligraf and other similar
products.
Therefore, it is clear that, in spite of recent advances, tissue engineering has much to deliver.
Innovative strategies, such as the presented in this chapter, present out of the box solutions