Table 1.

Comparison among natural enthesis, regenerative enthesis and scar tissues

	Compositions and structure	Mechanical properties	Ref.
Natural enthesis	Natural gradient tissue be divided into five parts: pure dense fibrous tissues (collagen I), uncalcified fibrocartilage (collagen II), tidemark, calcified fibrocartilage and bone tissue. The content of calcium rises from 0% (unmineralized region) to 60% (gradient region), then declines from 70% to 60% in the mineralized region.	Transfer loads effectively. Strain about 7% in the compliant region under 50 GPa.	[10–14]
Regenerative enthesis	Form gradient mineralization site in the middle with high cell viability. Achieve graded tenogenic and osteogenic differentiation along the mineral gradient.	Have better mechanical properties when they overcome the difficulty of layer-to-layer integration.	[15]
Scar tissues	Disorganized fibrovascular scar tissue consists of collagen III and gets gradually replaced with collagen I without collagen II. Lack of gradient mineral and collagen fiber distribution. Lack of undifferentiated cells. Reduction of cellularity and synthetic activity.	Excessive mechanical loading on the healing tendon. The mechanical strength is much lower, resulting in the high failure rate.	[10, 16, 17]