## 1 Introduction  
Articular cartilage is hyaline cartilage covering the articular surface of bones. Because of its avascular characteristic, once injured, articular cartilage has poor self-repair abilities. The management of injured cartilage involves conservative and surgical approaches, but there is currently no effective treatment. Bone marrow stimulation (microfracture surgery) could induce cartilage formation, but the newly formed cartilage is fibrocartilage instead of hyaline cartilage [1; 2; 3]. Several methods of chondrocyte implantation have been used to treat cartilage defects in humans, but implanted grafts do not provide mechanical stability, and various side effects lead to procedure failure [4; 5]. Osteochondral plug transplantation (mosaicplasty) has been developed, but the limitations of this technique include donor site morbidity and the limited availability of grafts that can be harvested [6; 7]. The long-term outcome is constrained by the age and gender of the patient and the size of the wound [6]. Recently, mesenchymal stem cells (MSCs) have received much attention as a cell source for cartilage cell therapy [8; 9; 10]. MSCs isolated from bone marrow and adipose tissue have the ability to differentiate into various types of cells in mesodermal lineages, such as osteoblasts, chondrocytes, adipocytes, myocytes, and cardiomyocytes [11; 12; 13]. For efficient cartilage tissue formation of MSCs, a variety of scaffolds providing structural support to MSCs and facilitating their chondrogenic differentiation to form three-dimensional (3D) cartilage-like tissue are needed. MSC-seeded scaffolds for cartilage tissue regeneration should be biocompatible and biodegradable. Biopolymers and polymers used as these scaffolds have been reviewed in terms of state of the art and future trends. Furthermore, to fabricate a uniform cellular matrix, scaffold porosity should be high to provide sufficient space for extracellular matrix (ECM) regeneration, and the pore structure should be interconnected so that spatially homogeneous tissue formation can occur [14]. Approaches using 3D scaffolds and MSCs to remodel cartilage have resulted in the development of strategic natural biomaterials such as scaffolds based on agarose, chitosan, hyaluronic acid, and collagen [14; 15]. Collagen has recently been explored in numerous applications in tissue engineering and regenerative medicine. Atelocollagen has been investigated largely because of its antigenic determination on the peptide chains and its ability to manipulate the backbone of amino residues [16]. Atelocollagen is clinically used as an artificial substitute in plastic surgery and dermatology, but its shrinking property, lower elasticity, and inflammatory response are major concerns for the formation of ECM-like structures at defect sites [17]. Moreover, since highly rigid scaffolds compatible with native cartilage tissue (10-20 MPa) are desirable in cartilage tissue regeneration using MSCs [18], atelocollagen gels are not suitable for this application. Thus, the development of scaffold-like silica nonwoven fabrics that replace atelocollagen gels has been demanded. Furthermore, 3D cell culture systems mimicking in vivo environments have been developed to control MSC differentiation. In tissue engineering for regenerative medicine and in vitro assay technology, 3D cell culture systems provide higher cellular functionality than traditional two-dimensional (2D) cell culture. There are various 3D cell culture methods, including spheroid formation [19; 20] and cell seeding in scaffolds, such as polymer hydrogels [21; 22], porous materials [23; 24], and fibrous fabrics [25]. Recently, 3D printing of cell constructs has received much attention as a low-cost technique to fabricate cellular scaffolds that possess high mechanical strength and enable enhanced cellular performance [26]. This technique has the potential to create implant matrix substitutes to articular tissue. However, the fabrication of scaffolds with microscopic structures and low porosity (<50%) is challenging [26].