## 1 Introduction  
Articular hyaline cartilage is composed of chondrocytes included within an extracellular matrix (ECM) set as a framework of macromolecules like collagens, glycosaminoglycans (GAGs), proteoglycans, glycoproteins and water. It shows a typical stratified organization of fibrils, mainly collagen type II, which supply tensile strengthening to a highly hydrated proteoglycans gel, resulting in a structure able to support the compressive load and protect the bone surface. During life, articular cartilage is subjected to a physiological inner remodeling through neo-synthesis and replacing ECM components with chondrocytes. Nevertheless, chondral tissue possesses low self-repair potential [1]. Moreover, aging reduces the capability of chondrocytes to maintain such turnover rate and to re-establish functional tissue, increasing the risk of progressive degeneration and damage to the joints' cartilage surface. Age-related and traumatic lesions of articular cartilage, if left untreated, lead to joint pain and impairment, which is clinically defined as osteoarthritis (OA). Carttilage depletion represents a truly disabling condition, and over 200 million people worldwide suffer from OA [2]. The surgical treatment of these pathological manifestations presents limitations, as mature cell- and tissue-based transplants, such as autologous ex vivo cultured chondrocytes implantation or osteochondral grafts, often fail to restore hyaline cartilage structure and functionality [3, 4]. The latter is due to chondrocyte poor in vitro proliferation and de-differentiation susceptibility. In this scenario, adult stem cells rapidly emerged as a valuable cell source for articular cartilage tissue engineering [5]. In particular, Mesenchymal Stem (and/or Stromal) Cells (MSCs), which are adult mesoderm-derived undifferentiated cells, showed the capability to self-renew together with a multilineage differentiation potential (e.g., chondrogenic, osteogenic, and adipogenic) and have been already employed including cartilage regenerative medicine for a variety of clinical applications [6]. Among MSCs populations, Adipose-Derived Stem Cells (ADSCs) have shown promising potential for chondrogenesis and the advantage of being easily obtainable from liposome waste [7; 8; 9; 10]. Moreover, most in vivo animal studies have reported good results using pre-differentiated or undifferentiated, autologous or allogeneic ASCs to regenerate cartilage in osteochondral defects or surgically induced osteoarthritis. The application of electromagnetic fields (EMFs) has already shown a positive impact in vitro on enhancing chondrogenesis [11; 12; 13]. In particular, recent studies highlighted the high biological activity of some extremely low-frequency magnetoelectric fields (ELF-EMFs) [14]. It has been shown that low-frequency pulsed electromagnetic fields improve patients' recovery both in the short (90 days) and in the long term (3 years), as demonstrated in the results of two level-I clinical studies. The long-term benefit results from biophysical chondoprotection of articular cartilage and prevention of the fibrotic stimuli exerted by pro-inflammatory cytokines on wounded tissue. Regenerative medicine also relies on biophysical stimulation, exerting a protective effect on the repair of tissue from catabolic effects of the inflammatory reaction elicited by the surgical implantation procedure. The microenvironment regulating stem cell differentiation can be cell-matrix adhesions or cell-cell interactions. The microenvironment is certainly helpful for maintaining MSC survival, commitment, and differentiation. It has already been reported that a hyaluron-enriched microenvironment can both initiate and promote the chondrogenic differentiation of human adipose-derived stem cells (ADSCs) and that single-pulse electromagnetic field (SPEMF) stimulation may promote chondrogenic differentiation and cartilaginous matrix formation thus being applied for articular cartilage tissue engineering.