Tethered TGF-β1 in a Hyaluronic Acid-Based Bioink for Bioprinting Cartilaginous Tissues

In 3D bioprinting for cartilage regeneration, bioinks that support chondrogenic development are of key importance. Growth factors covalently bound in non-printable hydrogels have been shown to effectively promote chondrogenesis. However, studies that investigate the functionality of tethered growth factors within 3D printable bioinks are still lacking. Therefore, in this study, we established a dual-stage crosslinked hyaluronic acid-based bioink that enabled covalent tethering of transforming growth factor-beta 1 (TGF‑β1). Bone marrow-derived mesenchymal stromal cells (MSCs) were cultured over three weeks in vitro, and chondrogenic differentiation of MSCs within bioink constructs with tethered TGF‑β1 was markedly enhanced, as compared to constructs with non-covalently incorporated TGF‑β1. This was substantiated with regard to early TGF‑β1 signaling, chondrogenic gene expression, qualitative and quantitative ECM deposition and distribution, and resulting construct stiffness. Furthermore, it was successfully demonstrated, in a comparative analysis of cast and printed bioinks, that covalently tethered TGF‑β1 maintained its functionality after 3D printing. Taken together, the presented ink composition enabled the generation of high-quality cartilaginous tissues without the need for continuous exogenous growth factor supply and, thus, bears great potential for future investigation towards cartilage regeneration. Furthermore, growth factor tethering within bioinks, potentially leading to superior tissue development, may also be explored for other biofabrication applications.

Adipose Stem Cells in Regenerative Medicine: Looking Forward

Over the last decade, stem cell-based regenerative medicine has progressed to clinical testing and therapeutic applications. The applications range from infusions of autologous and allogeneic stem cells to stem cell-derived products. Adult stem cells from adipose tissue (ASCs) show significant promise in treating autoimmune and neurodegenerative diseases, vascular and metabolic diseases, bone and cartilage regeneration and wound defects. The regenerative capabilities of ASCs in vivo are primarily orchestrated by their secretome of paracrine factors and cell-matrix interactions. More recent developments are focused on creating more complex structures such as 3D organoids, tissue elements and eventually fully functional tissues and organs to replace or repair diseased or damaged tissues. The current and future applications for ASCs in regenerative medicine are discussed here.

Exercise-induced piezoelectric stimulation for cartilage regeneration in rabbits

A biodegradable piezoelectric scaffold excited by exercise promotes chondrogenesis and cartilage regeneration in rabbit osteochondral defects.

Cartilage Tissue Engineering Approaches Need to Assess Fibrocartilage When Hydrogel Constructs Are Mechanically Loaded

Chondrocytes that are impregnated within hydrogel constructs sense applied mechanical force and can respond by expressing collagens, which are deposited into the extracellular matrix (ECM). The intention of most cartilage tissue engineering is to form hyaline cartilage, but if mechanical stimulation pushes the ratio of collagen type I (Col1) to collagen type II (Col2) in the ECM too high, then fibrocartilage can form instead. With a focus on Col1 and Col2 expression, the first part of this article reviews the latest studies on hyaline cartilage regeneration within hydrogel constructs that are subjected to compression forces (one of the major types of the forces within joints) in vitro. Since the mechanical loading conditions involving compression and other forces in joints are difficult to reproduce in vitro, implantation of hydrogel constructs in vivo is also reviewed, again with a focus on Col1 and Col2 production within the newly formed cartilage. Furthermore, mechanotransduction pathways that may be related to the expression of Col1 and Col2 within chondrocytes are reviewed and examined. Also, two recently-emerged, novel approaches of load-shielding and synchrotron radiation (SR)–based imaging techniques are discussed and highlighted for future applications to the regeneration of hyaline cartilage. Going forward, all cartilage tissue engineering experiments should assess thoroughly whether fibrocartilage or hyaline cartilage is formed.

Cell-Free Fat Extract Attenuate Osteoarthritis via Chondrocytes Regeneration and Macrophages Immunomodulation

Background: The prevalence of osteoarthritis (OA) is increasing, yet clinically effective and economical treatments are unavailable. We have previously proposed a cell-free fat extract (CEFFE) containing multiple cytokines, which possessed anti-apoptotic, anti-oxidative, and proliferation promotion functions, as a “cell-free” strategy. In this study, we aimed to evaluate the therapeutic effect of CEFFE in vivo and in vitro . Methods: In vivo study, sodium iodoacetate-induced OA rats were treated with CEFFE by intra-articular injections for 8 weeks. Behavioral experiments were performed every two weeks. Histological analyses, anti-type II collagen, and toluidine staining provided structural evaluation. Macrophage infiltration was assessed by anti-CD68 and anti-CD206 staining. In vitro study, the effect of CEFFE on macrophage polarization and secretory factors was evaluated by flow cytometry, immunofluorescence, and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The effect of CEFFE on cartilage regeneration was accessed by cell counting kit-8 assay and qRT-PCR. The generation of reactive oxygen species (ROS) and levels of ROS-related enzymes were investigated by qRT-PCR and western blotting. Results: In rat models with sodium iodoacetate (MIA)-induced OA, CEFFE increased claw retraction pressure while decreasing bipedal pressure in a dose-depend manner. Moreover, CEFFE promoted cartilage structure restoration and increased the proportion of CD206 + macrophages in the synovium. In vitro , CEFFE decreased the proportion of CD86 + cells and reduced the expression of pro-inflammatory factors in LPS + IFN-γ induced Raw 264.7. In addition, CEFFE decreased the expression of interleukin-6 and ADAMTs-5 and promoted the expression of SOX-9 in mouse primary chondrocytes. Besides, CEFFE reduced the intracellular levels of reactive oxygen species in both in vitro models through regulating ROS-related enzymes. Conclusions: CEFFE inhibits the progression of OA by promoting cartilage regeneration and limiting low-grade joint inflammation.

Mesenchymal stromal cell-based therapy for cartilage regeneration in knee osteoarthritis

Osteoarthritis, as a degenerative disease, is a common problem and results in high socioeconomic costs and rates of disability. The most commonly affected joint is the knee and characterized by progressive destruction of articular cartilage, loss of extracellular matrix, and progressive inflammation. Mesenchymal stromal cell (MSC)-based therapy has been explored as a new regenerative treatment for knee osteoarthritis in recent years. However, the detailed functions of MSC-based therapy and related mechanism, especially of cartilage regeneration, have not been explained. Hence, this review summarized how to choose, authenticate, and culture different origins of MSCs and derived exosomes. Moreover, clinical application and the latest mechanistical findings of MSC-based therapy in cartilage regeneration were also demonstrated.

Effect of passage number of genetically modified TGF-β3 expressing primary chondrocytes on the chondrogenesis of ATDC5 cells in a 3D coculture system

Due to the lack of blood vessels, nerves and lymphatics, articular cartilage is difficult to repair once damaged. Tissue engineering is considered to be a potential strategy for cartilage regeneration. Successful tissue engineering strategies depend on the effective combination of biomaterials, seed cells and biological factors. In our previous study, a genetically modified coculture system with chondrocytes and ATDC5 cells in an alginate hydrogel has exhibited a superior ability to enhance chondrogenesis. In this study, we further evaluated the influence of chondrocytes at various passages on chondrogenesis in the coculture system. The results demonstrated that transfection efficiency was hardly influenced by the passage of chondrocytes. The coculture system with passage 5 (P5) chondrocytes had a better effect on chondrogenesis of ATDC 5 cells, while chondrocytes in this coculture system presented higher levels of dedifferentiation than other groups with P1 or P3 chondrocytes. Therefore, P5 chondrocytes were shown to be more suitable for the coculture system, as they accumulated in sufficient cell numbers with more passages and had a higher level of dedifferentiation, which was prone to form a favorable niche for chondrogenesis of ATDC5 cells. This study may provide fresh insights for future cartilage tissue engineering strategies with a combination of a coculture system and advanced biomaterials.