Smart Bioinks for Printing Human Tissue Models
By Alia Nichol
3D printing is a manufacturing technique that involves the creation of physical objects by adding layers upon layers of material based on a predefined computer model. Since its creation, this technology has been used to develop innovative applications because it is allows for rapid prototyping and mass-customization. 3D printing enables the creation of complex geometries that are not achievable by other manufacturing methods. Recently, 3D printing has become financially more affordable for smaller companies, allowing this manufacturing method to transform industries, such as the medical sector. Now, plastics and metals are not the only materials involved in the creation of three-dimensional objects, human cells have revolutionized this technology, and now the medical field is leveraging what is now known as bioprinting. 3D bioprinting has attracted many scientists, researchers, and engineers in recent years due to its potential to advance the field of engineering.
The goal of 3D bioprinting is to reproduce the three-dimensional organization of cells to replicate the natural human body. This technology has the potential to fabricate custom tissues and organs using cells from patients, thereby reducing the risk of rejection when finally implemented into the body. 3D bioprinted constructs consist of an assembly of cells produced in a layer-by-layer fashion based on a predefined digital model. 3D printing has already been used for the fabrication of several types of tissues including multi-layer skin, bones, brain tissue, and heart tissue.
Compared to traditional 3D printing, 3D bioprinting requires careful consideration in terms of the type of cells, how to grow the cells, and where to grow the cells. To create a bioprinted structure, one must follow a three-step process. This consists of (i) selecting materials, (ii) designing and formulating a printable bioink, and (iii) generating enough printable bioink. A bioink is a gel-like substance that made of a mixture of material and human molecules or cells that can be used for bioprinting. Most bioinks are characterized as hydrogels which means they are a highly hydrated network of cells that mimic the natural structure of a human cell.
Hydrogels must meet specific characteristics so they can support cell growth and function. These characteristics include:
1. Viscosity – the bioink’s thickness and flow influences the fabrication process and determines if the constructs can be printed consistently.
2. Mechanical – controlling the stiffness of a hydrogel bioink determines its strength, stability, and its ability to be extruded from a printer in a layer-by-layer manner.
3. Biocompatibility – biocompatibility is a term used to describe a substance’s ability to perform its desired function in living tissue without causing any adverse responses. A biocompatible bioink helps to promote the growth of cells and preserves the health of the cell population.
Creating a hydrogel-based bioink involves combining the ink with the desired biomaterial. The bioprinted structure must then be cultured or grown under controlled conditions and then enriched with special nutrients that enhance cell growth and function. Lots of care must be taken when choosing a suitable bioink for a given tissue application because it greatly influences the biocompatibility and the mechanical behaviour of the printed structure. After the bioprinted structures are created, they undergo several cellular and mechanical tests to further characterize their behaviour and function.
The use of bioinks in tissue engineering has led to many achievements in the health care industry. For instance:
Skin substitutes for patients who have lost skin tissue has been an active subject of research for almost 15 years, but recently, 3D bioprinting has shown potential for wound repair and skin regeneration.
The development of 3D bioprinted bone and cartilage has opened doors to potential treatments for patients with arthritis, bone fractures, and dental infections.
The combination of hydrogels and nanoparticles to create nanocomposite bioinks with enhanced mechanical properties and the ability to work as drug delivery systems.
Many studies highlight the broad range of bioinks made from different chemical compositions that can be used for applications in the healthcare industry. This article discusses the relatively recent concept of “smart” bioinks, a type of composite bioink that is capable of releasing drugs in a controlled manner following a specific stimulus. These special kind of bioinks take advantage of drug-releasing particles to promote the desired behaviour of the printed cells. Micro and nanotechnologies play a vital role in enhancing medicine/drug formulas, controlled drug release, and drug delivery. In this piece, literature in this area has been reviewed and used to bring forward recommendations for future work.