D lactide

PLLA (M_w = 2.0 × 10⁵ g mol⁻¹) was purchased from Nature Works Company. d-Lactide (optical purity > 99%) was obtained from Jinan Daigang Biomaterial Co., Ltd (Shandong, China). δ-Valerolactone (VL, 98%), ε-caprolactone (CL, 99%), diethylene glycol (DEG, >98%), 2-amino-4-hydroxyl-6-methylpyrimidine and 1,6-hexyldiisocyanate (HDI) were purchased from J&K Chemical (Beijing, China). Dibutyltin dilaurate and stannous octoate (Sn(Oct)₂) were acquired from Sinopharm Group Chemical Reagent (China). 2(6-Isocyanatohexylaminocarbonyl-amino)-6-methyl-4[1H]pyrimidinone (UPy-NCO) was synthesized according to a previously reported method^{35 (link)} using 2-amino-4-hydroxyl-6-methylpyrimidine and 1,6-hexyldiisocyanate as raw materials. Toluene was further dried by distillation from sodium prior to use. Other reagents were of analytical grade and used without further purification.

PLA 4032D (M_w = 2.1×10⁵ g/mol, PDI = 1.7, 98% _L-isomer content) was obtained from NatureWorks. Tetracalcium phosphate (TTCP) was provided by Ensail Beijing Co., Ltd. (China). D-Lactide was purchased from Jinan Daigang Biomaterial Co., Ltd (China). Methylbenzene, dichloromethane (DCM) and petroleum ether were purchased from Chengdu Kelong Chemical Co., Ltd. (Chengdu, China). Stannous octanoate (Sn(Oct)₂), and 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) were purchased from Aladdin Chemistry Co., Ltd (Shanghai, China). The mouse fibroblast cell (L929) was purchased from American Type Culture Collection (ATCC, USA.) Male Sprague-Dawley (SD) rats (1 week) were purchased from Chengdu Dossy Experimental Animals Co., Ltd (Chengdu, China). The Animal Ethics Committee of West China Hospital of Sichuan University granted permission for the experiments. All the animal procedures in the current study were performed in accordance with the Guidelines for Care and Use of Laboratory Animals of Sichuan University.