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 (∼100 μm) 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 κappa-carrageenan (κ-CA, 1-4 % w/v), mimicking cartilage extracellular matrix. Poly(ethylene glycol) (PEG) was used to induce β-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 κ-CA/SF ± PBAT formulations showed high print fidelity, mechanical strength, and cell viability, highlighting their potential for cartilage tissue regeneration.