Crosslinker-free silk fibroin/κ-carrageenan bioinks incorporating RGD-functionalized, cell-laden microcarriers for 3D cartilage bioprinting: Formulation and cytocompatibility

One of the key challenges in 3D bioprinting is developing bioinks that ensure both structural integrity and biocompatibility. This study introduces a novel strategy that combines microcarrier technology with 3D bioprinting to improve cell viability and mechanical strength without using toxic crosslinkers, focusing on cartilage tissue engineering. Poly(butylene adipate-co-terephthalate) (PBAT) microcarriers (similar to 100 mu m) were functionalized with RGD peptides to enhance cell attachment and seeded with ATDC5 chondroprogenitor cells. These were incorporated into bioinks composed of silk fibroin (SF, 2-8 % w/v) and kappa appa-carrageenan (kappa-CA, 1-4 % w/v), mimicking cartilage extracellular matrix. Poly(ethylene glycol) (PEG) was used to induce beta-sheet formation in SF, supporting gelation and water-insolubility. The constructs retained structural integrity for up to 4 weeks, especially at 8 % SF, due to increased stiffness. A porous structure was achieved by removing PEG selectively. Printability was optimized using response surface methodology, determining ideal conditions as 10 mg/mL microcarrier concentration, nozzle speed of 4-5 mm/s, and extrusion pressure of 55-60 kPa with a 20G nozzle. The optimized kappa-CA/SF +/- PBAT formulations showed high print fidelity, mechanical strength, and cell viability, highlighting their potential for cartilage tissue regeneration.