THREE-DIMENSIONAL PRINTING OF SCAFFOLDS FOR TISSUE ENGINEERING

For biomedical applications, 3-D printing has established its appreciable potential in the production of functional scaffolds. Day by day increase in advancement in the techniques of 3D printing gave rise to hope for enhancements in regenerative medication. The aim of this field of research is the use of stem cells and different techniques to replace and repair the injured organs, cells, or tissues.

Basic concept of Tissue Engineering:
In 1993, tissue engineering concept was formalized in a paper by two scientist Langer and Vacanti, applications and characteristics of biodegradable 3-D scaffolds were described in detailed (An, J. et al., 2015). Tissue engineering is a developing branch, in which tissue scaffolds are used for the development of new tissues and these tissues used for various medical purposes. After many years of continuous efforts, a group of tissue culture, implantation replacement technologies have been established, which allows artificial extracellular fabricating matrices, i.e. scaffold, to bring growth factors, stem cells, and biological materials aiming at the reparation of damaged tissue functions (Liu, J. and Yan, C. 2018).

Components of Tissue Engineering:

• Cells- Stem cells
• Scaffolds- metals, ceramics, or polymers
• Signaling molecules- growth factors, morphogenetic proteins, or hormones

What are 3-D Scaffolds?
Scaffolds are the structures of either natural or artificial materials on which novel tissue could be grown that helps to replace or repair injured tissue. It can be seeded with progenitor cells, adult or embryonic stem cells, co-cultures of cells, mature differentiated cells to induce the formation of tissue in vivo and in vitro (Luo, Y. et al., 2014). To ease tissue regeneration, scaffolds should be designed in such a way to provide an appropriate atmosphere for cell growth. A design of scaffold comprises physicochemical, mechanical, or biological (Maria P. et al., 2019).

• Physicochemical (Pore size, surface chemistry, biodegradation, etc.)
• Mechanical (elastic modulus, stiffness, etc.)
• Biological (vascularization, biocompatibility, cell adhesion, etc.) 

3D printing methods for tissue engineering:
In the last few years a wide range of 3D printing technologies have been developed. On the basis of their technique features, printing methods are categorized into four groups, which are:

• Powder-based 3D printing
• Ink-based 3D printing
• Polymerization-based 3D printing
• Four-dimensional (4D) printing 

1. Powder-based 3D printing:
After a few years of development, the original powder-based 3D printing technique, binder jetting, and selective laser sintering (SLS), are all built on primary concept. Selective laser sintering usually used in scaffold fabrication, a high-power laser is used for ceramic or metal powder sintering to the formation of the scaffold. Throughout the printing process powders are exposed with lasers, then they can be bonded into huge parts, a layer-by-layer scaffold is made (Du, X. et al., 2018).
Advantages:

• No any support required
• In a single bed multiple materials can be process

2. Ink-based 3Dprinting:
Ink-based 3D printing is a method in which small amount of individual droplet of fluidic materials deposit from a nozzle on a 3D printing platform with an objective of making structures through post-printing solidification. It is a best suitable way for tissue materials processing because it can print bioinks directly (Du, X. et al., 2018 and Liu, J. and Yan, C. 2018).
Advantages:

•  Mechanical strength is very high
•  Multifunctional

3. Polymerization-based 3D printing:
The polymerization-based method starts with a process that exposing liquid photopolymer to a laser beam, then this specific exposing area would be solidified through polymer chain reaction. After repeating this process layer by layer, the final complex 3D structure can be constructed. SLA employs a single beam laser to polymerize or crosslink a photosensitive polymer to get thin layers of the polymer and then stacks the struts layer-by-layer (Du, X. et al., 2018 and Liu, J. and Yan, C. 2018).
Advantages:

•  High resolution
•  large molding products 

4. Four-dimensional (4D) printing:
Four-Dimensional printing is the process that allows 3-D printed materials to self transform into a new structure over the effect of external energy such as light, temperature, or other stimuli. 4-D printing utilizes the same manufacturing methods, or devices as used in 3-D printing (Tamay, D. et al., 2019).
Advantages:

• Overcomes weaknesses of 3D printing
• Dynamic and animate structures are produces. 

REFERENCES:
1. Luo, Y., Engelmayr, G., Auguste, D. T., da Silva Ferreira, L., Karp, J. M., Saigal, R., & Langer, R. (2014). 3D Scaffolds. Principles of Tissue Engineering, 475–494.

2. Maria P. Nikolovaa, Murthy S. Chavalib. (2019). Recent advances in biomaterials for 3D scaffolds: A review. Bioactive Materials 4 271–292

3. An, J., Teoh, J. E. M., Suntornnond, R., & Chua, C. K. (2015). Design and 3D Printing of Scaffolds and Tissues. Engineering, 1(2), 261–268.

4. Jingyu Liu and Cheng Yan. (2018). 3D Printing of Scaffolds for Tissue Engineering

5. Du, X., Fu, S., & Zhu, Y. (2018). 3D printing of ceramic-based scaffolds for bone tissue engineering: an overview. Journal of Materials Chemistry B, 6(27), 4397–4412.

6. Tamay, D. G., Dursun Usal, T., Alagoz, A. S., Yucel, D., Hasirci, N., & Hasirci, V. (2019). 3D and 4D Printing of Polymers for Tissue Engineering Applications. Frontiers in Bioengineering and Biotechnology, 7.

By: Sadia Israr