3D printing is well understood and ubiquitous by now but not many may know of 4D printing.
To put it simply, 4D printing is the process by which a 3D-printed object transforms itself into another structure, under the influence of external stimuli such as light, temperature, water, a magnetic field or chemicals.
You can, for example, print a flat object with some smart material and program it to fold into a 3D shape when, say, exposed to water. This process has been used by a team of scientists at the Department of Materials Engineering and Bioengineering, Indian Institute of Science, Bengaluru, to make artificial blood vessels.
The team, led by Dr Kaushik Chatterjee and Dr Amit Nain, developed a nanoengineered hydrogel ink and printed it on sheets. (Hydrogels are gel material from which liquid has been sucked out.) These sheets self-fold into tubular structures when immersed in a calcium chloride solution.
The team coated the surface of the vessels with gelatin so that cells may stick to it, says an article in IISc’s in-house publication Kernel.
It says the gel formulation was “chemically modified prior to 3D printing” to give the printed structures anti-oxidative and anti-inflammatory properties. It will also help deal with clotting.
“Current grafts require additional surgeries, carry risks of rejection and disease transmission, and are prone to clotting and other complications. These artificial blood vessels are a step forward in solving these challenges,” the article says.
Building organs
4D-printed blood vessels are crucial for tissue engineering, which, in turn, is a vital part of regenerating organs.
These blood vessels act as a scaffold for seed cells to grow on; they also supply blood to the growing tissue.
While there are synthetic blood vessels made of materials such as polytetrafluoroethylene and polyurethane, they are not “dynamic”, namely they cannot adapt to the changing environment.
But 4D-printed blood vessels can expand, contract or grow in response to biological cues such as changes in blood pressure. This adaptability enables engineered tissues to grow and function better.
Further, tissue engineering essentially involves culturing harvested cells, for which they need a scaffold — the framework for cells to adhere to and grow into the desired organ.
4D-printed blood vessels can self-assemble into complex, interconnected vascular networks after being implanted, which enhances the efficiency of tissue vascularisation. And, of course, the blood vessels also perform their primary job of keeping the tissue cells well supplied with blood.
“The artificial development of a vascular system, specifically the blood vessel network, is considered the holy grail of tissue engineering,” write Daphene Marques Solis and Aleksander Czekanski of York University, Canada, in a 2022 scientific paper.
Though tissue engineering has advanced, the production of blood vessels “remains a challenge that inhibits the production of organs and tissues thicker than 200 m,” they say, adding that “ascularization is a bottleneck in the evolution of tissue engineering”.
4D-printed blood vessels promise to remove this bottleneck.