Tissue-engineered Bicipital Autologous Tendon Patch Enhances Massive Rotator Cuff Defect Repair in a Rabbit Infraspinatus Tendon Defect Model
Authors: Liao Youguo , Liu Hengzhi , Huang Jiayun , Wang Zetao , Zhang Tao , Hu Xiangjun , He Qiulin , Wang Zichen , Fei Yang , Zhang Yuxiang , Cai Fangyuan , Ruan Dengfeng , Zhang Hong , Jiang Luyong , Yin Zi , Ouyang Hongwei , Chen Xiao , Shen Weiliang 
Published: October 2024

Background
Massive rotator cuff defects represent an important source of shoulder pain and functional debilitation, substantially diminishing patients’ quality of life. The primary treatment of massive rotator cuff defects includes complete or partial repair and patch augmentation. However, because of the tendon’s limited regenerative ability, the tendon retear risk after rotator cuff defect repair is still high. Thus, a new therapy is needed to promote tendon regeneration for repair of massive rotator cuff defects.

Questions/purposes
Using an in vitro analysis, we first asked: (1) What is the biocompatibility and collagen synthesis ability of fibrin glue, and what is the cell growth of tissue-engineered bicipital tendon patches, which is comprised of fibrin glue and biceps tendon tissue particles? Then, using an in vivo animal model of full-thickness defects in the infraspinatus tendon in New Zealand White rabbits, we asked: (2) What is the potential of the tissue-engineered bicipital autologous tendon patch to promote tendon regeneration?

Methods
In vitro experiments were conducted to assess the survival, proliferation, and collagen synthesis ability of tendon stem/progenitor cells cultured in fibrin glue. This was achieved through an assay of live/dead cell viability, cell counting kit-8 (CCK-8) assay, and Sirius red staining, respectively. The in vivo animal study was conducted using 8- to 12-week-old New Zealand White rabbits. The left shoulder of each animal was operated on, with equal numbers of males and females. There were 12 rabbits in the control group and 15 rabbits each in the gel and patch groups. Six rabbits were allocated to each of the three groups at the 1- and 3-month time points and three rabbits each were in the gel and patch groups at 2-month time point. Through an infraspinatus tendon defect model, the effectiveness of tissue-engineered bicipital autologous tendon patches (patch group) in tendon repair was assessed compared with untreated (control group) and fibrin glue (gel group) treatments in vivo. This assessment included histological evaluation of repaired tissue morphology, transmission electron microscopy (TEM) evaluation of regenerated collagen fibrils, and RNA sequencing to explore the potential mechanisms of tissue-engineered bicipital autologous tendon patches in tendon regeneration.

Results
In vitro experiments demonstrated that fibrin glue enhanced the collagen synthesis ability of tendon stem/progenitor cells (0.38 ± 0.02) compared with standard cell culture alone (0.27 ± 0.02, mean difference 0.11 [95% CI 0.07 to 0.14]; p < 0.001). With prolonged cultivation, the cell growth area of tissue-engineered bicipital tendon patches showed a notable increase after culturing for 14 days (78.13% ± 3.68%) compared with 11 days (13.05% ± 8.78%, mean difference -65.08% [95% CI -77.99% to -52.15%]; p󿇀001), 7 days (2.67% ± 2.62%, mean difference -75.46% [95% CI -88.37% to -62.53%]; p󿇀001), and 1 day (0.33% ± 0.30%, mean difference -77.80% [95% CI -90.71% to -64.87%]; p＜0.001). At 3 months after transplantation, in vivo experiments revealed that compared with the control and gel groups, the patch group displayed improved repair outcomes. This was evidenced by better histological scores in the patch group (3.83 ± 2.01) compared with the gel group (10.67 ± 0.58, mean difference 6.84 [95% CI 3.67 to 10.00]; p = 0.001) and control group (10.75 ± 0.66, mean difference 6.92 [95% CI 3.75 to 10.08]; p = 0.001), and by regular alignment and larger diameters of newly formed collagen fibrils in the patch group (77.52 ± 44.41 nm) compared with the control group (53.34 ± 6.64 nm, mean difference 24.18 [95% CI 22.24 to 26.11]; p < 0.001). RNA sequencing analysis revealed that a tissue-engineered bicipital autologous tendon patch facilitated tendon regeneration by modulating the immune response, promoting collagen fibril organization, and alleviating vasoconstriction.

Conclusion
This animal study demonstrates that the tissue-engineered bicipital autologous tendon patch effectively modulates an immune response and collagen fibril organization, leading to the promotion of tendon regeneration.

Clinical Relevance
The tissue-engineered bicipital autologous tendon patch represents a promising strategy for tendon regeneration, offering potential in the repair of massive rotator cuff defects during clinical rotator cuff surgery. Subsequent research could focus on large animal experiments using a tissue-engineered bicipital autologous tendon patch to explore their feasibility for clinical translation.