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well plates. Half of the wells were cultured under normal conditions, while the other half were

supplemented with additional PMs. The plates were then incubated on an orbital shaker. On day 4,

culture supernatants were collected, and the secreted glycosaminoglycan (GAG) content was

measured using an ELISA kit. For C-MTs, at different time points (days 1, 4, and 7) of co-culture,

2 mL aliquots were collected from the co-culture system under mixed conditions. Of these aliquots,

1 mL was used for GAG content detection, and the remaining 1 mL was used for DNA content

assay. GAG content was then normalized to DNA content.

2.4. Preparation and Characterization of MTs/GelMA Composite Bioink

For the modification of gelatin with methacrylic anhydride and subsequent processing, gelatin

was added to Carbonate buffer (0.25 M, pH=9.0) and heated at 50°C to facilitate dissolution. Once

the solution became clear with no visible undissolved gelatin particles, methacrylic anhydride was

slowly added, and the reaction was allowed to proceed under continuous stirring in the dark. During

the reaction, the pH was maintained using 1M NaOH. Following the reaction, the solution was

immediately transferred to a preheated dialysis membrane (molecular weight cutoff: 8000–14000

Da) while still hot for dialysis. Dialysis was performed with water changes three times daily for

one week. After dialysis, the solution was frozen overnight in a -80°C freezer and subsequently

lyophilized for 48 hours, yielding a spongy sample. The sample was then stored dry at -20°C.

1 H NMR spectra were acquired on a Avance III 500 MHz spectrometer (Bruker, Switzerland)

at room temperature. Samples were dissolved in D₂O (10 mg/mL) and measured in a 5 mm NMR

tube. GelMA was dissolved in PBS buffer at 50°C under gentle stirring to prepare a 10% (w/v)

solution. Then, 0.25% (w/v) lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) was

incorporated to form the GelMA bioink. For SEM observation, 1 mL of bioink was crosslinked

under blue light for 30 s in a mold. The resulting hydrogel was frozen in liquid nitrogen, lyophilized

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