2.1. Materials

CH was procured from Aladdin Inc (Shanghai, China). Viscosity average molecular weight and deacetylation degree of CH were determined as 1.19 (±0.15) × 10⁵ and 92.6 (±1.8)% using reported methods [11,12]. Human recombinant BMP-2 and BMP-2 ELISA Kit were purchased from PeproTech Inc (Rocky Hill, NJ, USA) and Abcan Inc (Shanghai, China), respectively. HA (sodium salt, Mw: 90–110 kDa), GP and sodium tripolyphosphate (TPP) were purchased from Sigma-Aldrich (Shanghai, China). All other reagents and chemicals were of analytical grade and purchased from Sinopharm (Shanghai, China).

CH-PDO copolymers were synthesized by grafting PDO side chains onto the C-6 sites of CH backbone using a group-protection method described elsewhere [13], and the optimized CH-PDO with a PDO weight percentage of about 30 wt% was used for the preparation of nanoparticles.