Osteoarthritis (OA), one of the most common joint diseases, is characterized by fibrosis, rhagadia, ulcers and attrition of articular cartilage due to a number of factors. The etiology of OA remains unclear, but its occurrence has been associated with age, obesity, inflammation, trauma and genetic factors. Inflammatory cytokines are crucial for the occurrence and progression of OA. The intra‑articular proinflammatory and anti‑inflammatory cytokines jointly maintain a dynamic balance, in accordance with the physiological metabolism of articular cartilage. However, dynamic imbalance between proinflammatory and anti‑inflammatory cytokines can cause abnormal metabolism in knee articular cartilage, which leads to deformation, loss and abnormal regeneration, and ultimately destroys the normal structure of the knee joint. The ability of articular cartilage to self‑repair once damaged is limited, due to its inability to obtain nutrients from blood vessels, nerves and lymphatic vessels, as well as limitations in the extracellular matrix. There are several disadvantages inherent to conventional repair methods, while cartilage tissue engineering (CTE), which combines proinflammatory and anti‑­inflammatory cytokines, offers a new therapeutic approach for OA. The aim of the present review was to examine the proinflammatory factors implicated in OA, including IL‑1β, TNF‑α, IL‑6, IL‑15, IL‑17 and IL‑18, as well as the key anti‑inflammatory factors reducing OA‑related articular damage, including IL‑4, insulin‑like growth factor and TGF‑β. The predominance of proinflammatory over anti‑inflammatory cytokine effects ultimately leads to the development of OA. CTE, which employs mesenchymal stem cells and scaffolding technology, may prevent OA by maintaining the homeostasis of pro‑ and anti‑inflammatory factors.

Acute injury of the articular cartilage can lead to chronic disabling conditions because of the limited self-repair capability of the cartilage. Implantation of stem cells at the injury site is a viable treatment, but requires a scaffold with a precisely controlled geometry and porosity in the 3D space, high biocompatibility, and the capability of promoting chondrogenic differentiation of the implanted stem cells. Here we report the development of gelatin/hydroxyapatite (HAP) hybrid materials by microextrusion 3D bioprinting and enzymatic cross-linking as the scaffold for human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs). The scaffold supports the adhesion, growth, and proliferation of hUCB-MSCs and induces their chondrogenic differentiation in vitro. Doping HAP in the gelatin scaffold increases the fluidity of the hydrogel, improves the gelation kinetics and the rheological properties, and allows better control over 3D printing. Implanting the hUCB-MSC-laden scaffold at the injury site of the articular cartilage effectively repairs the cartilage defects in a pig model. Altogether, this work demonstrates the 3D printing of gelatin-based scaffold materials for hUCB-MSCs to repair cartilage defects as a potential treatment of articular cartilage injury.

Three-dimensional (3D) bioprinting is an emerging technology based on 3D digital imaging technology and multi-level continuous printing. The precise positioning of biological materials, seed cells, and biological factors, known as “additive biomanufacturing”, can provide personalized therapy strategies in regenerative medicine. Over the last two decades, 3D bioprinting hydrogels have significantly advanced the field of cartilage and bone tissue engineering. This article reviews the development of 3D bioprinting and its application in cartilage tissue engineering, followed by a discussion of the current challenges and prospects for 3D bioprinting. This review presents foundational information on the future optimization of the design and manufacturing process of 3D additive biomanufacturing.

Magnetic nanocomposite hydrogels show high potential to improve tissue engineering. In this study, a magnetic nanocomposite hydrogel was prepared from poly(vinyl alcohol), nano-hydroxyapatite (n-HA), and magnetic nanoparticles (Fe₂O₃) using the ultrasonic dispersion method and freeze–thaw cross-linking molding. The water content and crystallinity of the magnetic nanocomposite hydrogel were tested. Microscopic morphology assessment, mechanical testing, and characterization were performed. Additionally, the magnetic nanocomposite hydrogel was co-cultured with bone mesenchymal stem cells (BMSCs) to determine its cell compatibility. We found that the magnetic nanocomposite hydrogel had good mechanical properties and that its mechanical properties were enhanced by the addition of n-HA. The BMSCs showed uniform growth on the surface of the magnetic nanocomposite hydrogel and high rates of proliferation. BMSC growth was also enhanced by the addition of Fe₂O₃ and also significant stimulated chondrocyte-related gene expression. Thus, the magnetic nanocomposite hydrogel scaffold material we describe here could have broad applications in cartilage tissue engineering.

Cartilage tissue engineering is arising as a technique for the repair of cartilage lesions in clinical applications. However, fibrocartilage formation weakened the mechanical functions of the articular, which compromises the clinical outcomes. Due to the low proliferation ability, dedifferentiation property and low production of cartilage-specific extracellular matrix (ECM) of the chondrocytes, the cartilage synthesis in vitro has been one of the major limitations for obtaining high-quality engineered cartilage constructs. This review discusses cells, biomaterial scaffolds and stimulating factors that can facilitate the cartilage-specific ECM production and accumulation in the in vitro culture system. Special emphasis has been put on the factors that affect the production of ECM macromolecules such as collagen type II and proteoglycans in the review, aiming at providing new strategies to improve the quality of tissue-engineered cartilage.

Tissue engineering is becoming an effective strategy for repairing cartilage damage. Synthesized nanocomposite hydrogels mimic the structure of natural cartilage extracellular matrices (ECMs), are biocompatible, and exhibit nano–bio effects in response to external stimuli. These inherent characteristics make nanocomposite hydrogels promising scaffold materials for cartilage tissue engineering. This review summarizes the advances made in the field of nanocomposite hydrogels for artificial cartilage. We discuss, in detail, their preparation methods and scope of application. The challenges involved for the application of hydrogel nanocomposites for cartilage repair are also highlighted.