The group led by Prof. Aleksandra Ovsianikov at TU Wien, together with PhD student Oliver Kopinski-Grünwald and in collaboration with Vienna-based trauma and medical centers within the Austrian Cluster for Tissue Regeneration, filled a cartilage defect in a rabbit’s knee with a mesh made from a material designed to gradually disappear. They printed spherical scaffolds approximately 0.3 mm in diameter, about the size of a grain of sand, seeded them with cartilage cells grown from stem cells, assembled them into a larger implant, and implanted it into the damaged area. After twelve weeks, new tissue had formed in the defect, covering a significantly larger portion of it and reaching approximately 91% of the thickness of natural cartilage. Histological analysis assessed it as “nearly normal cartilage.”

The word “printed” itself carries little weight here, because these days virtually everything is printed, including dental bridges. The real hero is the material. The scaffold was made from DEGRAD INX resin developed by Belgian company BIO INX and cured using multiphoton lithography, a laser-based printing technique capable of resolutions below one micrometer. For this method, the result represents a first, because it has moved for the first time from the laboratory dish into a living organism.

Why cartilage cannot repair itself

Cartilage is one of the tissues with exceptionally poor regenerative capacity. A defect that might gradually heal elsewhere in the body remains a defect in a joint because the tissue lacks the ability to rebuild itself. The study focused on critical-sized osteochondral defects, meaning defects that affect both the cartilage and the underlying bone and are large enough that they cannot heal on their own. This is one of the more challenging targets in regenerative medicine, so if the method was going to be tested, this was precisely the kind of injury to target.

Multiphoton lithography is one of the most precise printing techniques currently available. A laser builds the structure point by point, reaching the micrometer scale and even below it, allowing researchers to create a dense, highly organized microenvironment for cells that previously could not be produced. The rest is essentially an exercise in assembling building blocks. Cartilage cell spheroids were placed onto printed scaffolds approximately 0.3 mm in diameter, where they were allowed to mature. The individual building blocks were then combined into a larger implant. The scaffold serves a temporary function: it supports and organizes the cells, and as new tissue develops, it gradually breaks down until it disappears. To achieve this, the team needed a material that was simultaneously printable at such a high resolution, biodegradable, and biocompatible. That material is DEGRAD INX.

The number that carries the weight of the result is 91%. After twelve weeks, the regenerated tissue reached roughly 91% of the thickness of natural cartilage and integrated well with the surrounding tissue, while the untreated group showed a clearly weaker result. Histologically, the regenerated tissue was assessed as “nearly normal cartilage.” Those remaining few percentage points represent the gap still left to close.

This is the kind of progress that happens slowly, in a narrow, highly specialized corner of 3D printing where certification and validation are measured in years.

The study shows that the resin performed successfully as a cell carrier in a specific in vivo experiment. Ovsianikov says explicitly that his group has been working on the micro-scaffold strategy for 10 years.

What does this result really change?

Until now, the micro-scaffold strategy for minimally invasive tissue engineering had primarily been an idea demonstrated in laboratory dishes. The publication in the European Polymer Journal provides the first confirmation that the approach can work in a living organism.

The potential clinical significance of all this precision can be summed up in one sentence from the study description: such scaffolds could potentially be injected to fill irregular cartilage defects without opening the joint. Cell-loaded building blocks would be delivered into the damaged area, where they could adapt to the shape of the defect and gradually transform into cartilage, while the scaffold itself disappears.