Scientists demonstrate bioprinting technique in organoids

The research team consisted of scientists from the University of Padova in Italy and NIHR Great Ormond Street Hospital Biomedical Research Centre (a collaboration between GOSH and UCL) in London.

Hydrogel-in-hydrogel live bioprinting

Typically when researchers work with organoids – small 3D structures that mimic the structure and function of real organs – the composition, mechanical properties, and geometric constraints of the hydrogel are typically fixed at the initial time of fabrication. This limits the modification of the hydrogel characteristics as the cultures evolve.

This is where the hydrogel-in-hydrogel live bioprinting approach is a game-changer. The team achieved this by creating a photosensitive hydrogel material, meaning its physical properties will change when exposed to light.

Following this, scientists carefully introduced the photosensitive hydrogel in the existing culture in a specific location depending upon their desired outcome. Then they used a high-resolution microscope to direct light onto the hydrogel. 

The photosensitive hydrogel can now be selectively solidified in real-time, allowing them to shape the hydrogel material and create precise structures within the organoids. This process of cross-linking photosensitive hydrogels via two-photon absorption allows them to solidify and shape the hydrogel material, giving them complete control over the growth and behavior of the organoids.

Another advantage this process offers is the ability to introduce new elements into existing hydrogel-based organoid cultures at any time during their growth.

Printing applications of hydrogel-in-hydrogel live bioprinting

The research team additionally demonstrated the hydrogel-hydrogel live bioprinting method via four examples:

• Ordered cells: The team used the technique to create hardened gel rails to guide the growth of neurons or brain cells, which are impossible to isolate. This method enables the creation of organized and isolated bundles of neurons, which can be studied and observed.
• Defined shapes: They created complicated hydrogel molds to direct organoid growth to mimic the intricate architecture of growing intestines. This involved the creation of structures, such as villi and crypts.
• Creating branches: The team successfully patterned a hydrogel to encourage lung cells to form bronchi, similar to an actual lung. This allows for the study of branching patterns and exploration of lung development. 
• Cancer spread: Lastly, they use their bioprinting technique to create hardened gel cages around cancer cells to monitor how they move depending on the density of their surrounding. This helps in understanding how cancer spreads in different tissue densities. 

In a press release, the lead author Dr. Anna Urciuolo from the University of Padova and lead of the Neuromuscular Engineering Lab at the Institute of Pediatric Research, said, "This work is an exemplar of the advancements of the multidisciplinary approach that is exploding in biomedical research. The ability to reproduce models of organs in the lab and the development of technologies that help scientists recapitulate healthy and diseased tissues and organ complexity on the bench is the outset of how translational medicine will change in the future."

The hydrogel-hydrogel live bioprinting technique is successful in mimicking organ complexity, providing a controlled microenvironment for study, disease modeling, and drug testing and screening. It is a powerful tool that has the potential to revolutionize the medical industry and perhaps even remove the need for animal testing.

The findings of the study are published in the journal Nature Communications.

Study abstract:

Three-dimensional hydrogel-based organ-like cultures can be applied to study development, regeneration, and disease in vitro. However, the control of engineered hydrogel composition, mechanical properties and geometrical constraints tends to be restricted to the initial time of fabrication. Modulation of hydrogel characteristics over time and according to culture evolution is often not possible. Here, we overcome these limitations by developing a hydrogel-in-hydrogel live bioprinting approach that enables the dynamic fabrication of instructive hydrogel elements within pre-existing hydrogel-based organ-like cultures. This can be achieved by crosslinking photosensitive hydrogels via two-photon absorption at any time during culture. We show that instructive hydrogels guide neural axon directionality in growing organotypic spinal cords, and that hydrogel geometry and mechanical properties control differential cell migration in developing cancer organoids. Finally, we show that hydrogel constraints promote cell polarity in liver organoids, guide small intestinal organoid morphogenesis and control lung tip bifurcation according to the hydrogel composition and shape.