Researchers have developed a novel bioink that uses a sustained-release hormone to promote the growth and regeneration of 3D-printed muscle tissues. Their approach opens the door to developing new therapies to help people who’ve suffered muscle loss or damage due to trauma, disease, or surgery.
Generating native-like muscle tissue can be a tricky business. The tissue consists of many different cell types, and the environment around muscles is regulated by complex biochemical and biomechanical pathways, including inflammatory cytokines and growth factors that maintain internal stability and support tissue repair.
Currently, repairing muscles injured or lost because of trauma, disease, or surgery involves transferring healthy muscle to the affected site, a technique called autologous transfer. This isn’t ideal as it negatively impacts the area from which the healthy tissue is taken, and complications such as poor innervation can impede functional muscle recovery.
Now, researchers from the Terasaki Institute for Biomedical Innovation (TIBI) in Los Angeles have come up with a novel, improved bioink to enhance 3D-printed skeletal muscle constructs and overcome the limitations of autologous transfer.
Normal skeletal muscle development is a gradual process that relies on myoblasts, committed muscle cell precursors, fusing together to form myotubes, which eventually become muscle fibers. This process is called myogenesis. So, in engineering muscles, it’s crucial that functionality is maintained by ensuring maturing muscle cells are structurally aligned and their survivability is enhanced.
To mimic myogenesis, the researchers relied on a key ingredient in their specially formulated bioink: insulin-like growth factor-1 (IGF-1), a hormone with a molecular structure similar to insulin that, along with growth hormone, is vital for normal bone and tissue growth and development.
The bioink is composed of a biocompatible gelatin-based hydrogel called gelatin methacryloyl (GeIMA), myoblast cells, and PLGA microparticles coated with IGF-1 designed to slowly release the hormone as the particles degraded. Poly(lactic-co-glycolic acid) or PLGA is one of the most effective biodegradable polymeric nanoparticles due to its sustained-release properties, low toxicity and biocompatibility. A control version of the bioink was created without IGF-1.
The researchers found that three days after bioprinting muscle constructs, the myoblasts were viable, confirming that the printing process had not damaged the cells. They observed enhanced myoblast alignment and the fusion of myoblasts to form myotubes, which were significantly longer and wider in the constructs containing IGF-1. Myotubes covered 25% of the area in the PLGA/IGF-1 condition, compared to less than 16% in the control condition.
At around 10 days after bioprinting, the formed tissue started to contract spontaneously with enough force that it shook the hydrogel substrate, as seen in the video below. The amplitude of the contractions was significantly higher in areas incorporating the sustained release of IGF-1.
3D-printed muscle cells spontaneously contracting
The researchers then implanted 3D-printed muscle constructs into mice. After six weeks, the mice that received the constructs with sustained-release IGF-1 showed the most muscle tissue regeneration. They concluded that the study’s findings strongly suggested that their novel bioink allowed the development of a contractile 3D structure closely resembling native muscle tissue.
“The sustained release of IGF-1 facilitates the maturation and alignment of muscle cells, which is a crucial step in muscle tissue repair and regeneration,” said Ali Khademhosseini, corresponding author of the study. “There is great potential for using this strategy for the therapeutic creation of functional, contractile muscle tissue.”
The study was published in the journal Macromolecular Bioscience.
Source: Terasaki Institute