The formation of fibrocartilage at the healing site following a rotator cuff tear repair is a major problem in the field of tendon-bone healing. The present study aimed to enhance the healing of the tendon-bone interface following rotator-cuff tear repair by the interposition of hydroxyapatite (HA) encapsulated with transforming growth factor β1 (TGFβ1). Using an acute rotator cuff repair model, rats were divided into three groups: i) Repair only (control); ii) HA group; and iii) HA-TGFβ1 group. Animals were sacrificed at 2, 4 and 8 weeks following surgery. Micro-computed tomography (CT), histomorphometric analyses and biomechanical tests were used to evaluate the supraspinatus tendon-bone complex. The micro-CT images revealed notable novel bone formation in the groups treated with HA-TGFβ1. The histomorphometric analyses demonstrated improved fibrocartilage formation and collagen organization at the tendon-bone interface. The HA-TGFβ1 combination significantly improved the area of fibrocartilage, particularly at early time points (2 and 4 weeks). There was a significantly greater load-to-failure force achieved in the HA and HA-TGFβ1 groups compared with the control group at 4 and 8 weeks. Augmentation of the ceramic powder with HA-TGFβ1 at the tendon-bone interface was demonstrated to strengthen the healing entheses, increase bone and fibrocartilage formation and improve collagen organization compared with surgical repair alone. Local application of HA-TGFβ1 demonstrates potential in improving tendon-bone healing following rotator cuff repair.

Articular cartilage plays an important role in human body. How to repair articular cartilage defects when they appear due to various factors has always been a major clinical challenge. Recently, studies have shown that slowing the degradation of cartilage extracellular matrix (ECM) and modulating the inflammatory response of the host thereby promoting cartilage tissue regeneration are important in the cartilage repair process. In this study, a drug-loaded injectable hydrogel was constructed for repairing articular cartilage. This hydrogel could not only maintain the phenotype of chondrocytes but also regulate the inflammatory response of the host. The injectable sodium alginate (SA)/bioglass (BG) hydrogel was mixed with the injectable thermal-responsive SA/agarose (AG)/quercetin (Que) hydrogel to obtain an injectable hydrogel containing both Que and BG (Que-BG hydrogel) for articular cartilage regeneration. The Que-BG hydrogel has a proper swelling ratio that can promote integration between the formed tissue and host tissue, and it allows Que to release slowly in situ to improve its bioavailability. The Que-BG hydrogel could upregulate SRY-box 9 (SOX9), aggrecan (ACAN), and collagen type II alpha 1 chain (COL2A1) of normal chondrocytes to maintain the normal chondrocyte phenotype. In addition, it could promote macrophage M2 polarization, reduce inflammation, and inhibit ECM degradation by downregulating the expression of inducible nitric oxide synthase (iNOS), matrix metalloproteinase-13 (MMP13), and matrix metalloproteinase-1 (MMP1) in degenerative chondrocytes. After injecting the Que-BG hydrogel into a rat cartilage defect model, the formed tissue was observed to be similar to the normal tissue and was highly integrated with the surrounding tissue. Therefore, the injectable Que-BG hydrogel improves Que bioavailability, maintains chondrocyte phenotype, inhibits ECM degradation, and reduces inflammatory response.