RESEARCH SUMMARY
This study developed flexible, 3D-printed, piezoelectric hydrogel platforms designed to provide multiple bioinstructive cues for skeletal muscle development and volumetric muscle loss repair. The platform used an interpenetrating GelMA-PAA hydrogel network incorporating barium titanate nanoparticles to combine skeletal-muscle-like stiffness, microchannel-guided alignment, self-adhesion, flexibility, and ultrasound-responsive electroactivity. Rheological testing showed gel-like viscoelasticity and shear-thinning behaviour suitable for extrusion 3D printing, while stereomicroscopy and SEM confirmed high print fidelity, defined microchannels, and porous internal architecture. Mechanical testing showed that BTO incorporation improved compressive robustness and increased platform stiffness to approximately 50 kPa, remaining close to skeletal muscle-relevant stiffness. The platforms generated surface potentials of about 90 mV under ultrasound-induced deformation, supporting their ability to provide wireless bioelectrical cues. C2C12 myoblast studies showed strong biocompatibility, sustained proliferation, aligned myotube formation along microchannels, and enhanced myotube thickness, cytoskeletal organization, myogenic marker expression, and maturation on GelMA-PAA/BTO platforms, especially with ultrasound activation. Temporal analysis suggested that the most beneficial stimulation window occurred by day 7, while prolonged daily ultrasound to day 14 reduced myotube integrity. Western blotting showed increased FAK and ERK phosphorylation at day 7, suggesting mechanotransductive signalling involvement. Overall, the work presents a multifunctional acellular platform that integrates mechanical, topographical, biochemical, and ultrasound-triggered bioelectrical cues to support organized skeletal muscle tissue development.
A CellScale UniVert universal testing machine was used for uniaxial compression testing of hydrogel platform cylinders to quantify their mechanical properties. Cylindrical platforms measuring 9 mm in diameter and 4 mm in height were placed between 25 mm diameter compression platens at room temperature and compressed using a 10 N load cell at a crosshead speed of 1 mm/min. Load-displacement and stress-strain curves were generated using CellScale Biomaterial Testing software version 12.58, and Young’s modulus was calculated from the slope of the stress-strain curves. The UniVert results showed that GelMA-PAA/1.0%BTO platforms had the highest compressive strength, 92.6 ± 8.7 kPa, compared with 83.1 ± 5.4 kPa for pure GelMA, although differences among formulations were not statistically significant. The stress-strain curves also showed a steeper response for GelMA-PAA/1.0%BTO, indicating greater resistance to compressive strain. Incorporating PAA and BTO progressively increased Young’s modulus, with GelMA-PAA/1.0%BTO reaching approximately 50 kPa, which the authors describe as close to native skeletal muscle stiffness. These UniVert measurements were important because they verified that the 3D-printed platforms had mechanically relevant stiffness and compressive durability for skeletal muscle tissue engineering.
