library_construction_protocol: We created 2-mm calvarial bone defects on the parietal bones and implanted CGG hydrogels or CGG-Cit hydrogels. At 2 weeks post-surgery, the defect regions were carefully trimmed, and tissues were digested in 0.3% collagenase in α-MEM. Cell suspensions were filtered through 70 μm strainers, and single cells were subjected to RNA sequencing. The 10x libraries were constructed using Chromium Controller and Chromium Single Cell 3'Reagent Kits. In brief, single-cell suspensions in each channel of the chip were loaded on a Chromium Controller (10x Genomics, Pleasanton, CA) to generate single-cell GEMs (gel beads in emulsion).  Then the 10x libraries of each channel were prepared using the Chromium Single Cell 3'Gel Bead and Library Kit v2 (PN-120236, 120267, 120262;  10x Genomics)或者 v3 (PN-1000153， 1000075, 120262; 10x Genomics). Libraries were sequenced by the Illumina NovaSeq sequencer with 150-bp  paired-end reads in Novogene Bioinformatics Technology Co., Ltd (Tianjing, China)