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of PMs at different predetermined time intervals were observed by SEM. Furthermore, the protein

adsorption efficacy of PMs was investigated by the standard Bradford assay kit. Briefly, PMs were

placed in 96-well plates, and then 200 µL of 10% FBS-containing DMEM was added into each

well, and the medium was replaced at predetermined time intervals. After washes with PBS, the

PMs were immersed with 200 µL of protein eluent for 30 min, and the protein content was

determined by the Bradford assay kit.

2.3. Preparation and Characterization of Cartilaginous and Endothelium-Osteoblastic

Microtissues

MC3T3-E1, C518 and MAEC (Beina Biotechnology Research Institute, Beijing, China)

were cultured in a medium supplemented with 10% (v/v) FBS, 1% (v/v) penicillin-streptomycin at

37ºC in 5% CO2 and 95% relative humidity. Firstly, PMs suspension with different concentrations

(0.25, 0.5, 1 mg/mL) was prepared in DMEM and added to the cells for different incubation times.

The cell viability was detected by CCK-8 assay. Cartilaginous and endothelium-osteoblastic

microtissues were built by encapsulating the cells in PMs separately 32,46 . For the construction of C-

MTs, briefly, microspheres were placed in each well after sterilization in a 96-well plate. Then, 200

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μL of C518 cells suspension at a concentration of 1.6 × 10 cells/mL was added for culturing modes,

respectively. Firstly, the PMs was placed in an incubator for static culture, and in addition, the PMs

was placed at 37℃ and 110 rpm for dynamic culture under the condition of ensuring nutrition and

oxygen supply. Similarly, EO-MTs were constructed by co-culturing MAEC and MC3T3-E1 cells

together with PMs. After 3, 9, and 24 h of culture, non-adherent cells were removed by washing

three times with PBS after removing the medium, and PMs were collected and digested with trypsin

and counted. Adhesion and proliferation assays were performed using triplicate cultures and data

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