Bio-ink to replace damaged cartilage

The researchers in the TriggerINK project at DWI – Leibniz Institute for Interactive Materials in Aachen have an ambitious goal: enabling the regeneration of cartilage on a damaged joint. The core feature of the project is a 4-D printed scaffold made of a novel material – bio-ink. The Werner Siemens Foundation is supporting the innovative methodology with a five-year grant.

Joint pain is one of the most common health issues of our time, with cartilage loss (osteoarthritis) or a damaged meniscus in the knee numbering among the most frequent complaints. Cartilage and the menisci have important functions: they absorb shock and distribute the pressure exerted on the knee when we move. In addition, they supply our bones with nutrients and enable bones in a joint to move quickly and smoothly, with minimal friction. However, worn or damaged cartilage tissue can’t regrow on its own. And although modern medicine has developed therapies such as cartilage transplantations and substances that promote tissue regeneration, these procedures frequently cause massive damage to healthy tissue. In addition, there’s no guarantee of success.

Enhanced 3D printing

This could now change, thanks to the TriggerINK project, which starting in 2022, the Werner Siemens Foundation is supporting with a 10-million-euro grant distributed over five years. The interdisciplinary research team at DWI – Leibniz Institute for Interactive Materials in Aachen have designed a visionary method to promote cartilage regeneration. The innovative principle behind TriggerINK is 4D printing, which builds on existing 3D printing technology that prints out a material, layer by layer, to form a three-dimensional structure. Time is the fourth dimension in 4D printing, meaning the 3D structure is designed in such a way that an external trigger – heat, vibration or sound, for example – can move or alter the structure’s form after printing.

Multi-disciplinary expertise

The project is led by Laura De Laporte, member of the scientific board at DWI – Leibniz Institute for Interactive Materials in Aachen and professor of advanced materials and biomedicine at RWTH Aachen University. TriggerINK is a prime example of collaborative modern research that relies on integrating specialist knowledge from various disciplines. In addition to De Laporte, who contributes expertise in the development of biomedical materials, the project includes three other leading scientists: Stefan Hecht (3D printing using light), Andreas Herrmann (ultrasound-induced release of active agents) and Matthias Wessling (technical implementation of the method). “That we’re able to unite this diverse knowledge here in Aachen is unique and, at the same time, also a strength for the project,” Laura De Laporte says. A team of external medical and cell biology specialists work in the project in an advisory capacity.

High-precision control of tissue growth

1. The researchers are planning to realise their project by printing a 4D structure directly into a wound or an affected joint. The targeted treatment and healing process comprises the following six steps:
2. A thin layer of polymer is sprayed onto the existing, sterilised cartilage to ensure good adhesion and enable the body’s own cartilage tissue to grow into the newly applied structure from the 3D-printer.
3. The 3D printer prints the bio-ink directly into the wound, layer by layer. The bio-ink is made up of biodegradable hydrogel, a gelatinous substance. During printing, the layers are repeatedly irradiated with light, thus altering the chemical structure of the bio-ink and reinforcing the bond between the individual printed layers. A porous scaffold is gradually built up, and the cartilage tissue can regrow within this structure.
4. The bio-ink is made up of various materials, including tiny gel sticks containing magnetic particles. When the scaffold is being printed, a weak external magnetic field is activated to align these particles. This procedure ensures that the microstructure conducting the cell growth is set in a specific pattern, allowing the body’s own tissue to regrow in the correct direction.
5. Growth factors and nutrients are some of the other components in the bio-ink. If necessary – as is the case in larger wounds – ultrasound impulses release these substances into the scaffold, where they stimulate the growth of cartilage tissue.
6. To speed up healing after a medical intervention, it’s important that joints and tissues are mobilised as soon as possible. Here, too, the TriggerINK technology works with external impulses: at the right moment, light and heat impulses are emitted to set the growing cartilage into slight motion – a method the researchers have dubbed an “in-vivo gym”.
7. Lastly, once the body’s own cartilage has regenerated, the bio-ink scaffold breaks down on its own. The decomposition process can also be accelerated using external impulses.