How to Bioprint Muscles

Researchers at Harvard Medical School and Sichuan University have developed a novel means of 3D bioprinting live human muscle-tendon tissues. As opposed to normal extrusion bioprinting, which involves depositing cells along X and Y axes, the team’s ‘cryo-bioprinting’ process sees them frozen and stacked vertically, in a way that allows for the creation of freestanding, mixed-cell tissues. According to the scientists, their technique also yields tissues that are more robust and versatile than those produced via conventional bioprinting, particularly when it comes to those anisotropic in nature, thus they say it could now find regenerative medicine, drug discovery, or personalized therapeutic applications.

To overcome the tissue-stacking issues, the researchers have turned to ‘ice-templating,’ a freezing process that causes microchannels to form within cell-laden hydrogel-based structures once they thaw. Naturally, doing so would ordinarily damage the viability of such cells, so to prevent this, the team loaded theirs with the cryoprotective agents (CPAs) melezitose and dimethyl sulfoxide.

Once frozen, the researchers then used ultraviolet (UV) light to vertically cross-link this novel bio-ink, and extrude it into tissues composed of high-resolution, honeycomb-like microchannel networks, capable of supporting various different types of cell, whether they be skeletal muscle myoblasts or human umbilical vein endothelial cells.

Our results indicate that [our] bio-ink, consisting of gelatin methacryloyl and CPAs, could be effectively used in vertical 3D cryo-bioprinting to enable cell encapsulation at high viability,” explained the team in their paper. “With the help of the interconnected, anisotropic, gradient microchannels formed by directional freezing during the process, the desired cellular alignments were also realized.

Given that 3D bioprinting is an emerging technology, it’s hardly surprising that its format is continually subject to change, with researchers constantly bringing innovative new ideas to the field. Just last month, scientists at the UK’s University of Birmingham and University of Huddersfield, revealed that they had developed a novel skin 3D bioprinting technique that enables the treatment of chronic wounds.

Elsewhere, on a more commercial level, Inventia Life Science raised $25 million towards the development of its RASTRUM 3D bioprinting technology in December 2021. In effect, the firm’s approach is designed to enable the layering of cell-loaded droplets onto one another at pace, in a way that allows them to join on contact and doesn’t affect their overall viability.

Looking even further back, researchers at Imperial College London have also experimented with cell-freezing as a means of bioprinting viable human implants.