Biglycan and chondroitin sulfate play pivotal roles in bone toughness via retaining bound water in bone mineral matrix

•Glycosaminoglycans (GAGs) and proteoglycans in bone matrix regulate tissue-level hydration status and mechanical behaviors.•Deletion of biglycan (Bgn) decreased the amount of GAGs, chondroitin sulfate (CS) and bound water in mouse bone matrix.•Bgn deficiency is associated with reduction of bone toughness in a bound water dependent way.•Supplementation of CS improved bound water and bone toughness in WT, but not in Bgn KO mice.•Bgn and CS play pivotal roles in retaining bound water in bone matrix, thus imparting the toughness to bone.