3D-Bioprinting

Published On: 13th February, 2024

Authored By: Iram Aslam

Sharda University, Greater Noida

Introduction

For tissue or organ engineering to be successful, living cells—alone or in conjunction with biomolecules and biomaterials—must be put together in three dimensions. In this study, we define 3D bioprinting as the process of creating complex biological constructs using living cells, proteins, and biomaterials. It is a specific subset of additive manufacturing (AM). Similar to AM binder jetting techniques, 3D bioprinting is created from 2D ink-jet printers by substituting biological substances (bio-ink) for the ink in the cartridge and biodegradable support material for the paper. Few AM methods are currently appropriate for bioprinting applications.

From an economic perspective, 3D bioprinting is a very significant and active research area. The 3D bioprinting industry was estimated by Grand View Research to be worth $1.4 billion in 2020, and between 2021 and 2028, it is projected to expand at a compound annual growth rate of 15.8%. By 2024, the market for 3D bioprinting is expected to account for 10% of the overall 3D printing market. Furthermore, the tissue engineering market is expected to grow from its $2 billion valuation in 2019 to $7 billion by 2027.

The pharmaceutical, cosmetics, and medical industries have been the main drivers of the 3D bioprinting market expansion. One of the primary forces behind the development of 3D bioprinting techniques, which seek to do away with the need for immunosuppression, donor matching, and waiting times, is the high demand for organ transplantation and the scarcity of accessible organs.

Origin

Using a Hewlett-Packard (HP) inkjet printer and two cartridges loaded with a fibronectin solution and a monoclonal antibody solution, Klebe was the first to demonstrate the idea of bioprinting. Afterward, Wilson and Boland printed mammalian cells on an HP660C inkjet printer that had a customized dispensing system, thereby demonstrating the idea of cell printing. Since then, several printing technologies have been invented, each with pros and cons, and the area of bioprinting has grown quickly. Multi-modal printers were created more recently by combining several printing head types and printing processes into a single machine. In addition to outlining the major research issues in this area and the anticipated contributions from the CIRP community, this paper provides a detailed discussion of these various systems.

Bio-Inks

The bio-printable substance is called bio-ink. It is made up of cells combined with biomaterials such as hydrogel, spheroids, or cell aggregates.

With the extraordinary capacity to absorb vast amounts of water without dissolving, hydrogels are 3D hydrophilic polymeric materials generated by chemical (irreversible hydrogels) or physical crosslinks (reversible hydrogels). These materials are pliable and soft, often utilized above the temperature at which glass transitions occur, and they are highly permeable to nutrients, oxygen, and other water-soluble metabolites.

Both synthetic and natural hydrogels can be used to make bio-inks. Collagen, gelatine, hyaluronic acid, alginate, and chitosan are examples of naturally derived polymers that share biochemical characteristics with the extracellular matrix (ECM) but differ in terms of their limited mechanical properties, potential for immunogenicity, batch-to-batch variability, and typically need for intricate purification procedures.

The Basic steps of the 3d bioprinting process

The overall process of 3D bioprinting can be achieved via three different steps; pre-bioprinting, bioprinting, and post-bioprinting.

Pre-bioprinting

Creating a model that the printer will use and selecting the materials to be utilized are the initial steps in the pre-bioprinting process.
The process starts with the biopsy of a tissue sample, which yields a biological model that the 3D bioprinting technique will use to replicate.
In this step, technologies such as magnetic resonance imaging (MRI) scans and computed tomography (CT) are used.
To create 2D images, the images acquired using these techniques are tomographically rebuilt.
Next, the cells required for the procedure are chosen and multiplied. To maintain their viability, the resulting mass of cells is combined with oxygen and other nutrients.

Bioprinting

Placing the bioink in the printer to create a three-dimensional structure is the second step in the printing process.
After the cells, nutrients, and matrix are combined to make bio-ink, the combination is put onto the printer cartridge, which deposits the material according to the predefined digital model.
To create a three-dimensional tissue structure, bioink is deposited onto the scaffold layer by layer during the development of biological constructions.
Because it calls for the development of various cell types according to the kind of tissues and organs to be generated, this step of the bioprinting process is complicated.

Post-bioprinting

The bioprinting process ends with post-bioprinting, which is crucial for giving the printed structure stability.
The bioprinting process ends with post-bioprinting, which is crucial for giving the printed structure stability.
The cells receive signals from these stimulations to restructure and continue the growth of tissues.
The material’s mechanical structure could be damaged in the absence of this phase, which would subsequently impair the material’s ability to function.

3-D bioprinting types

Extrusion based bioprinting

The most popular technique for printing non-biological 3D objects is extrusion-based bioprinting, also known as micro extrusion.
Numerous academic organizations employ this bioprinting technology for their tissue and organ research.
The most popular method for creating pharmaceutical dosage forms in 3D bioprinting is extrusion-based 3D bioprinting because of its process flexibility and material availability.
This method’s printers are equipped with a temperature-controlled material handling and dispensing system that can move along the x, y, and z axes, along with a stage.
In addition, the system includes a fiber optic light source to illuminate the deposit region to activate the photoinitiator (if necessary).
Some micro extrusion bioprinters utilize multiple print heads to allow serial dispensation of numerous materials at once.

Inkjet-based bioprinting

For both biological and non-biological applications, the most widely used method is drop-on-demand bioprinting, also known as inkjet bioprinting.
Originally limited to 2D ink-based printing, this technology was eventually improved to allow for the replacement of paper with an electronically controlled elevator stage for control, and biological material in place of the ink in the cartridge.
At the moment, bioprinters made specifically to handle and print biological materials quickly, accurately, and with high resolution can be used for inkjet bioprinting.
The requirement for liquid biological ingredients to facilitate droplet formation is one of the drawbacks of inkjet bioprinting.

Pressure-assisted bioprinting

The foundation of pressure-assisted bioprinting is the extrusion of biomaterials via the printer’s nozzle to create a three-dimensional biological structure.
Hydrogels, cells, proteins, ceramic material solutions, collagen, chitosan, and other biomaterials are frequently employed in this technique.
The printers continue to operate at a slow speed, offering 40–80% cell viability.
By using pressure-assisted bioprinting, homogeneous cells can be directly incorporated onto the substrate and processed at room temperature.

Laser-assisted bioprinting

The process of depositing biomaterials onto a surface while utilizing a laser as a source of energy is known as “laser-assisted bioprinting.”
This method was originally only used to transfer metals, however, it has now been altered to work with biological materials such as DNA, peptides, and cells.
A ribbon with donor transport support, a focusing mechanism, a layer of biological material produced in a liquid solution, and a receiving substrate facing the projector are the components of a laser-assisted bioprinter.
The hydrogel, culture media, cells, proteins, and ceramic materials are among the biomaterials that will be utilized in laser-assisted bioprinting.
About 95% of the cell viability is retained by the technique, and the bioprinters operate at a medium speed.

Stereolithography

A freeform, nozzle-free process called stereolithography is utilized to create the three-dimensional structures of both biological and non-biological materials.
The most accurate method of fabrication is stereolithography, which also accepts a wide range of materials.
The method forms a three-dimensional structure by layering hydrogels that are responsive to light.
This technique operates at a very high speed (approximately 40,000 mm/s) while maintaining a cell viability of about 90%.

Applications of 3D bioprinting

Tissue engineering

Among the most well-known uses of 3D bioprinting is tissue engineering. It makes it possible to create intricate organs and tissues to replace damaged or missing tissue.
Because it is difficult to integrate the vascular network of arteries and veins and incorporate different cell types to reimagine complicated organ biology, the production of functional tissues and organs at clinically relevant dimensions is a challenge.
However, it has been possible to successfully bio-print a wide range of tissues while preserving their mechanical integrity and functionality.

Drug development

Drug discovery necessitates labor-intensive, expensive, and time-consuming procedures that require a large staff and financial commitment.
Therefore, it is possible to cut down on the amount of time and money needed for drug discovery by developing a technique that improves the ability to forecast the toxicity and efficacy of newly discovered medications earlier in the process.
Bioprinting enables the creation of 3D tissue models with high throughput assay capabilities and resemblance to actual tissue.
Tissue models for drugs are often created mostly from liver and tumor tissues.
Furthermore, tissue models of these cells can be constructed and tested based on the target cells of produced medications.
Rather than taking several tablets throughout the day, 3D-printed composite pills comprising numerous medications with different release rates can be utilized.

Toxicology screening

The process of determining the potentially harmful effects of chemicals on people or the environment is known as toxicology screening or testing.
Chemicals might include substances found in household and industrial products, cosmetics, and pharmaceuticals.
It may seem unethical to use more human participants with different metabolisms for studies assessing the toxicity of possible consistently
While it is possible to conduct some research on animals, it is not always possible to accurately or consistently predict human responses.
Alternatively, highly automated and sophisticated technologies can be obtained through the use of 3D bioprinting, which can create structures that closely resemble the composition and capabilities of human tissues.
High throughput screening of different substances and real-time monitoring is made easier by the usage of such frameworks.

Tissue model for cancer research

Long employed in cancer research, 2D tumor models do not accurately reflect the physiologically relevant environment because they do not include cell-cell interactions.
Nonetheless, 3D bioprinting makes it possible to precisely research cancer development and spread by recapitulating the disease microenvironment.
In a reproducible manner, many cell types can be bio-printed concurrently to construct multicellular structures with controlled cell density and cell-to-cell distance in a spatially mediated microenvironment.
To investigate cell aggregation, HeLa cells can be bio-printed in a gelatin-alginate composite hydrogel.
These tissues can be used to research how cancer progresses and how changes in tissue function and structure occur as a result.

Future challenges of 3-D bioprinting

Appropriate bio inks with high mechanical strength and biocompatibility are the main obstacles in bioprinting.
Current bioprinter technology is somewhat slow and has poor resolution, which presents a hurdle for further advancement. In the same way, a variety of biomaterials should work with the bioprinters.
Since the current speed of bioprinting is slow, it should be accelerated to the point where mass-made biomaterials can be generated at a commercially acceptable level.
Since tissues in 3D bioprinting require constant oxygen and nutrition, the vasculature of the tissue constructs presents a significant difficulty.
Because 3D bioprinting is expensive and may be out of reach for the underprivileged, there are several ethical concerns with this technology.

Conclusion

A new field of transdisciplinary research is 3D bioprinting. The most pertinent resources and cutting-edge technology in the subject were covered in detail in this review. The key needs for bio-ink are covered and the concept is explained in detail. Many difficulties still exist, despite a few encouraging instances involving the use of skin, cartilage, neurons, bone, kidney, and heart tissue. A single substance cannot adequately capture human tissues’ functional and structural properties due to their high complexity. It is essential to combine different materials and create functionally graded materials. New materials with enhanced mechanical, biocompatible, biodegradable, and printability qualities should also be developed. Furthermore, as multi-scale hierarchical structures, biological tissues, and organs undergo physiological changes in reaction to external stimuli.