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While matrix-assisted autologous chondrocyte implantation has emerged as a promising therapy to treat focal chondral defects, matrices that support regeneration of hyaline cartilage remain challenging. The goal of this work was to investigate the potential of a matrix metalloproteinase (MMP)-sensitive poly(ethylene glycol) (PEG) hydrogel containing the tethered growth factor, transforming growth factor β3 (TGF-β3), and compare cartilage regeneration in vitro and in vivo. The in vitro environment comprised chemically-defined medium while the in vivo environment utilized the subcutaneous implant model in athymic mice. Porcine chondrocytes were isolated and expanded in 2D culture for 10 days prior to encapsulation. The presence of tethered TGF-β3 reduced cell spreading. Chondrocyte-laden hydrogels were analyzed for total sulfated glycosaminoglycan and collagen contents, MMP activity, and spatial deposition of aggrecan, decorin, biglycan, and collagens type II and I. The total amount of extracellular matrix (ECM) deposited in the hydrogel constructs was similar in vitro and in vivo. However, the in vitro environment was not able to support long-term culture up to 64 days of the engineered cartilage leading to the eventual breakdown of aggrecan. The in vivo environment, on the other hand, led to more elaborate ECM, which correlated with higher MMP activity, and an overall higher quality of engineered tissue that was rich in aggrecan, decorin, biglycan and collagen type II with minimal collagen type I. Overall, the MMP-sensitive PEG hydrogel containing tethered TGF-β3 is a promising matrix for hyaline cartilage regeneration in vivo. STATEMENT OF SIGNIFICANCE: Regenerating hyaline cartilage remains a significant clinical challenge. The resultant repair tissue is often fibrocartilage, which long-term cannot be sustained. The goal of this study was to investigate the potential of a synthetic hydrogel matrix containing peptide crosslinks that can be degraded by enzymes secreted by encapsulated cartilage cells (i.e., chondrocytes) and tethered growth factors, specifically TGF-β3, to provide localized chondrogenic cues to the cells. This hydrogel led to hyaline cartilage-like tissue growth in vitro and in vivo, with minimal formation of fibrocartilage. However, the tissue formed in vitro, could not be maintained long-term. In vivo this hydrogel shows great promise as a potential matrix for use in regenerating hyaline cartilage., (Copyright © 2019. Published by Elsevier Ltd.)

Reducing rotator cuff failure after repair remains a challenge due to suboptimal tendon-to-bone healing. In this study we report a novel biomaterial with engineered tendon-fibrocartilage-bone composite (TFBC) and bone marrow-derived mesenchymal stem cell sheet (BMSCS); this construct was tested for augmentation of rotator cuff repair using a canine non-weight-bearing (NWB) model. A total of 42 mixed-breed dogs were randomly allocated to 3 groups (n = 14 each). Unilateral infraspinatus tendon underwent suture repair only (control); augmentation with engineered TFBC alone (TFBC), or augmentation with engineered TFBC and BMSCS (TFBC + BMSCS). Histomorphometric analysis and biomechanical testing were performed at 6 weeks after surgery. The TFBC + BMSCS augmented repairs demonstrated superior histological scores, greater new fibrocartilage formation and collagen fiber organization at the tendon-bone interface compared with the controls. The ultimate failure load and ultimate stress were 286.80 ± 45.02 N and 4.50 ± 1.11 MPa for TFBC + BMSCS group, 163.20 ± 61.21 N and 2.60 ± 0.97 MPa for control group (TFBC + BMSCS vs control, P = 1.12E-04 and 0.003, respectively), 206.10 ± 60.99 N and 3.20 ± 1.31 MPa for TFBC group (TFBC + BMSCS vs TFBC, P = 0.009 and 0.045, respectively). In conclusion, application of an engineered TFBC and BMSCS can enhance rotator cuff healing in terms of anatomic structure, collagen organization and biomechanical strength in a canine NWB model. Combined TFBC and BMSCS augmentation is a promising strategy for rotator cuff tears and has a high potential impact on clinical practice., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Advances in cartilage tissue engineering have led to constructs with mechanical integrity and biochemical composition increasingly resembling that of native tissues. In particular, collagen cross-linking with lysyl oxidase has been used to significantly enhance the mechanical properties of engineered neotissues. In this study, development of collagen cross-links over time, and correlations with tensile properties, were examined in self-assembling neotissues. Additionally, quantitative MRI metrics were examined in relation to construct mechanical properties as well as pyridinoline cross-link content and other engineered tissue components. Scaffold-free meniscus fibrocartilage was cultured in the presence of exogenous lysyl oxidase, and assessed at multiple time points over 8weeks starting from the first week of culture. Engineered constructs demonstrated a 9.9-fold increase in pyridinoline content, reaching 77% of native tissue values, after 8weeks of culture. Additionally, engineered tissues reached 66% of the Young's modulus in the radial direction of native tissues. Further, collagen cross-links were found to correlate with tensile properties, contributing 67% of the tensile strength of engineered neocartilages. Finally, examination of quantitative MRI metrics revealed several correlations with mechanical and biochemical properties of engineered constructs. This study displays the importance of culture duration for collagen cross-link formation, and demonstrates the potential of quantitative MRI in investigating properties of engineered cartilages., Statement of Significance: This is the first study to demonstrate near-native cross-link content in an engineered tissue, and the first study to quantify pyridinoline cross-link development over time in a self-assembling tissue. Additionally, this work shows the relative contributions of collagen and pyridinoline to the tensile properties of collagenous tissue for the first time. Furthermore, this is the first investigation to identify a relationship between qMRI metrics and the pyridinoline cross-link content of an engineered collagenous tissue., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

At the tendon-to-bone insertion, there is a unique transitional structure: tendon, non-calcified fibrocartilage, calcified fibrocartilage, and bone. The reconstruction of this special graded structure after defects or damage is an important but challenging task in orthopedics. In particular, reconstruction of the fibrocartilage zone has yet to be successfully achieved. In this study, the development of a novel book-shape scaffold derived from the extracellular matrix of fibrocartilage was reported. Specifically, fibrocartilage from the pubic symphysis was obtained from rabbits and sliced into the shape of a book (dimensions: 10 mm × 3 mm × 1 mm) with 10 layers, each layer (akin to a page of a book) with a thickness of 100-μm. These fibrocartilage "book" scaffolds were decellularized using sequentially 3 freeze-thaw cycles, 0.1% Triton X-100 with 1.5 M KCl, 0.25% trypsin, and a nuclease. Histology and DNA quantification analysis confirmed substantial removal of cells from the fibrocartilage scaffolds. Furthermore, the quantities of DNA, collagen, and glycosaminoglycan in the fibrocartilage were markedly reduced following decellularization. Scanning electron microscopy confirmed that the intrinsic ultrastructure of the fibrocartilage tissue was well preserved. Therefore, the results of this study suggest that the novel "book" fibrocartilage scaffold could have potential applications in tissue engineering.

Damaged cartilage has poor self-healing ability and usually progresses to scar or fibrocartilaginous tissue, and finally degenerates to osteoarthritis (OA). Here we demonstrated that one of alternative isoforms of IGF-1, mechano growth factor (MGF) acted synergistically with transforming growth factor β3 (TGF-β3) embedded in silk fibroin scaffolds to induce chemotactic homing and chondrogenic differentiation of mesenchymal stem cells (MSCs). Combination of MGF and TGF-β3 significantly increased cell recruitment up to 1.8 times and 2 times higher than TGF-β3 did in vitro and in vivo. Moreover, MGF increased Collagen II and aggrecan secretion of TGF-β3 induced hMSCs chondrogenesis, but decreased Collagen I in vitro. Silk fibroin (SF) scaffolds have been widely used for tissue engineering, and we showed that methanol treated pured SF scaffolds were porous, similar to compressive module of native cartilage, slow degradation rate and excellent drug released curves. At 7 days after subcutaneous implantation, TGF-β3 and MGF functionalized silk fibroin scaffolds (STM) recruited more CD29+/CD44+cells (P<0.05). Similarly, more cartilage-like extracellular matrix and less fibrillar collagen were detected in STM scaffolds than that in TGF-β3 modified scaffolds (ST) at 2 months after subcutaneous implantation. When implanted into articular joints in a rabbit osteochondral defect model, STM scaffolds showed the best integration into host tissues, similar architecture and collagen organization to native hyaline cartilage, as evidenced by immunostaining of aggrecan, collagen II and collagen I, as well as Safranin O and Masson's trichrome staining, and histological evalution based on the modified O'Driscoll histological scoring system (P<0.05), indicating that MGF and TGF-β3 might be a better candidate for cartilage regeneration. This study demonstrated that TGF-β3 and MGF functionalized silk fibroin scaffolds enhanced endogenous stem cell recruitment and facilitated in situ articular cartilage regeneration, thus providing a novel strategy for cartilage repair., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Disc degeneration is the loss of the normal nucleus pulposus disc matrix to a more fibrotic and less cartilaginous structure. This change in disc micro-anatomy can be associated with pain and deformity, however, prevention and treatment options of disc degeneration are currently limited. Much research is going on to understand intervertebral discs at a molecular/ cellular level in hopes of creating clinically applicable options for treating disc degeneration. This review article will give insight into the current and developing status of treating intervertebral disc degeneration from a molecular standpoint.