Fig. 2

The 29-mer/alginate gel promotes Achilles tendon healing. a Representative H&E-stained longitudinal tendon sections 2 days after surgery. Rat Achilles tendon rupture was created by inserting an 18-G needle (the injured region is marked by a dashed line). The sections at higher magnification show normal tendon with a relative scarcity of cells among the collagen fibers. The injured region shows inflammation, marked by numerous blue-stained nuclei. b, c Representative H&E-stained sections 3 weeks after surgery. The 29-mer hydrogel treatment led to a dense, regular tendon tissue at the healing region (HR) compared to the disorganized tissue in tendons treated with vehicle hydrogel. Asterisk (*)—uninjured region. Arrowhead (red)—inflammatory matrix formed by high inflammatory cell invasion. Black arrow—neovessel. d Representative Masson’s trichrome-stained longitudinal tendon sections 3 weeks after surgery. The 29-mer-induced dense alignment of collagen fibers. e Histology scores of tendon healing 3 weeks after treatment. The histological scoring was performed double-blind. Fiber arrangement—scale of 0–3, 0 represents compacted and parallel, and 3 represents no identifiable pattern. Fiber structure—scale of 0–3, 0 represents continuous, long fibers, and 3 represents severely fragmented. Rounding of nuclei—scale of 0–3, 0 represents long spindle shape, and 3 represents severe rounding. Cell density—scale of 0–3, 0 represents normal pattern, and 3 represents severely increased. Fibroblasts/PMN/monocytes—1 (< 50 per field), 2 (51–100 per field), and 3 (101–150 per field). Vascularity—1 (< 5 per field), 2 (6–10 per field), and 3 (> 10 per field). High powered field (× 20). Results are expressed as mean ± SE of three independent experiments. *P < 0.001 versus vehicle-treated group. NS, not significant, P = 0.08