Silk Fibroin-Based Hydrogels and Scaffolds for Osteochondral Repair and Regeneration

Mesenchymal stem cells biological and biotechnological advances: Implications for clinical applications

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem cells that are able to differentiate into multiple lineages including bone, cartilage, muscle and fat. They hold immunomodulatory properties and therapeutic ability to treat multiple diseases, including autoimmune and chronic degenerative diseases. In this article, we reviewed the different biological properties, applications and clinical trials of MSCs. Also, we discussed the basics of manufacturing conditions, quality control, and challenges facing MSCs in the clinical setting.

METHODS

Extensive review of the literature was conducted through the databases PubMed, Google Scholar, and Cochrane. Papers published since 2015 and covering the clinical applications and research of MSC therapy were considered. Furthermore, older papers were considered when referring to pioneering studies in the field.

RESULTS

The most widely studied stem cells in cell therapy and tissue repair are bone marrow-derived mesenchymal stem cells. Adipose tissue-derived stem cells became more common and to a lesser extent other stem cell sources e.g., foreskin derived MSCs. MSCs therapy were also studied in the setting of COVID-19 infections, ischemic strokes, autoimmune diseases, tumor development and graft rejection. Multiple obstacles, still face the standardization and optimization of MSC therapy such as the survival and the immunophenotype and the efficiency of transplanted cells. MSCs used in clinical settings displayed heterogeneity in their function despite their extraction from healthy donors and expression of similar surface markers.

CONCLUSION

Mesenchymal stem cells offer a rising therapeutic promise in various diseases. However, their potential use in clinical applications requires further investigation.

Incorporation of kartogenin and silk fibroin scaffolds promotes rat articular cartilage regeneration through enhancement of antioxidant functions

Treating articular cartilage defects in patients remains a challenging task due to the absence of blood vessels within the cartilage tissue. The regenerative potential is further compromised by an imbalance between anabolism and catabolism, induced by elevated levels of reactive oxygen species. However, the advent of tissue engineering introduces a promising strategy for cartilage regeneration, offering viable solutions such as mechanical support and controlled release of chondrogenic molecules or cytokines. In this study, we developed an antioxidant scaffold by incorporating natural silk fibroin (SF) and kartogenin (KGN)-loaded liposomes (SF-Lipo@KGN). The scaffold demonstrated appropriate pore size, connectivity, and water absorption and the sustained release of KGN was achieved through the encapsulation of liposomes. In vitro experiments revealed that the SF-Lipo@KGN scaffolds exhibited excellent biocompatibility, as evidenced by enhanced cell adhesion, migration, and proliferation of chondrocytes. The SF-Lipo@KGN scaffolds were found to stimulate cartilage matrix synthesis through the activation of the nuclear factor erythroid-2-related factor 2/heme oxygenase-1 antioxidant signaling pathway. In vivo experiments demonstrated the effective promotion of articular cartilage regeneration by the SF-Lipo@KGN scaffolds, which enhanced extracellular matrix anabolism and restored the intrinsic redox homeostasis. Overall, this study successfully developed biomimetic KGN-loaded scaffolds that restore cartilage redox homeostasis, indicating promising prospects for cartilage tissue engineering.

Synthesis and Characterization of Photo-Cross-Linkable Silk Fibroin Methacryloyl Hydrogel for Biomedical Applications

Photo-cross-linkable hydrogels have recently gained increased interest in the field of biomedical applications. In this study, silk fibroin was derivatized with methacrylic anhydride (MA) to obtain silk fibroin methacryloyl (SFMA), forming hydrogel under UV light exposure in 1 min. The SFMA sol-gel transition did not involve significant structural change at the early stage. Then, the formation of the irreversible β-sheet was confirmed after 24 h. The resulting SFMA hydrogel showed a homogeneous porous structure with pore sizes ranging from 400 to 700 μm, depending on the content. In addition, these hydrogels demonstrated a lower swelling capacity, higher rheological properties and compressive modulus, and slow degradation behavior at higher content, likely due to the higher degree of cross-linking. An experiment with cells indicated the good cell compatibility of these hydrogels, as revealed by Cell Counting Kit-8 (CCK-8) assays. As a tissue-engineered material, this photo-cross-linkable SFMA is expected to have a wide range of applications in the biomedical field.

BMSCs-Seeded Interpenetrating Network GelMA/SF Composite Hydrogel for Articular Cartilage Repair

Because of limited self-healing ability, the treatment of articular cartilage defects is still an important clinical challenge. Hydrogel-based biomaterials have broad application prospects in articular cartilage repair. In this study, gelatin methacrylate (GelMA)and silk fibroin (SF) were combined to form a composite hydrogel with an interpenetrating network (IPN) structure under ultraviolet irradiation and ethanol treatment. Introducing silk fibroin into GelMA hydrogel significantly increased mechanical strength as compressive modulus reached 300 kPa in a GelMA/SF-5 (50 mg/mL silk fibroin) group. Moreover, composite IPN hydrogels demonstrated reduced swelling ratios and favorable biocompatibility and supported chondrogenesis of bone mesenchymal stem cells (BMSCs) at day 7 and day 14. Additionally, significantly higher gene expressions of Col-2, Acan, and Sox-9 (p < 0.01) were found in IPN hydrogel groups when compared with the GelMA group. An in vivo study was performed to confirm that the GelMA-SF IPN hydrogel could promote cartilage regeneration. The results showed partial regeneration of cartilage in groups treated with hydrogels only and satisfactory cartilage repair in groups of cell-seeded hydrogels, indicating the necessity of additional seeding cells in hydro-gel-based cartilage treatment. Therefore, our results suggest that the GelMA/SF IPN hydrogels may be a potential functional material in cartilage repair and regeneration.

An all-silk-derived bilayer hydrogel for osteochondral tissue engineering

Osteochondral repair remains a challenge in clinical practice nowadays despite extensive advances in tissue engineering. The insufficient recruitment of endogenous cells in the early stage and incomplete cell differentiation in the later stage constitute the major difficulty of osteochondral repair. Here, a novel all-silk-derived multifunctional biomaterial platform for osteochondral engineering is reported. The bilayer methacrylated silk fibroin (SilMA) hydrogel was fabricated through stratified photocuring as the basic provisional matrix for tissue regeneration. Platelet-rich plasma (PRP) incorporation promoted the migration and pre-differentiation of the bone marrow mesenchymal stem cells (BMSCs) in the early stage of implantation. The long-term regulation of BMSCs chondrogenesis and osteogenesis was realized by the stratified anchoring of the silk fibroin (SF) microspheres respectively loaded with Kartogenin (KGN) and berberine (BBR) in the hydrogel. The composite hydrogels were further demonstrated to promote BMSCs chondrogenic and osteogenic differentiation under an inflammatory microenvironment and to achieve satisfying cartilage and subchondral bone regeneration with great biocompatibility after 8 weeks of implantation. Since all the components used are readily available and biocompatible and can be efficiently integrated via a simple process, this composite hydrogel scaffold has tremendous potential for clinical use in osteochondral regeneration.

Silk fibroin-based biomaterials for cartilage/osteochondral repair

Osteoarthritis (OA) is a common joint disease with a high disability rate. In addition, OA not only causes great physiological and psychological harm to patients, but also puts great pressure on the social healthcare system. Pathologically, the disintegration of cartilage and the lesions of subchondral bone are related to OA. Currently, tissue engineering, which is expected to overcome the defects of existing treatment methods, had a lot of research in the field of cartilage/osteochondral repair. Silk fibroin (SF), as a natural macromolecular material with good biocompatibility, unique mechanical properties, excellent processability and degradability, holds great potential in the field of tissue engineering. Nowadays, SF had been prepared into various materials to adapt to the demands of cartilage/osteochondral repair. SF-based biomaterials can also be functionally modified to enhance repair performance further. In this review, the preparation methods, types, structures, mechanical properties, and functional modifications of SF-based biomaterials used for cartilage/osteochondral repair are summarized and discussed. We hope that this review will provide a reference for the design and development of SF-based biomaterials in cartilage/osteochondral repair field.

Silk fibroin/cholinium gallate-based architectures as therapeutic tools

The combination of natural resources with biologically active biocompatible ionic liquids (Bio-IL) is presented as a combinatorial approach for developing tools to manage inflammatory diseases. Innovative biomedical solutions were constructed combining silk fibroin (SF) and Ch[Gallate], a Bio-IL with antioxidant and anti-inflammatory features, as freeze-dried 3D-based sponges. An evaluation of the effect of the Ch[Gallate] concentration (≤3% w/v) on the SF/Ch[Gallate] sponges was studied. Structural changes observed on the sponges revealed that the Ch[Gallate] presence positively affected the β-sheet formation while not influencing the silk native structure, which was suggested by the FTIR and solid-state NMR results, respectively. Also, it was possible to modulate their mechanical properties, antioxidant activity and stability/degradation in an aqueous environment, by changing the Ch[Gallate] concentration. The architectures showed high water uptake ability and a weight loss that follows the controlled Ch[Gallate] release rate studied for 7 days. Furthermore, the sponges supported human adipose stem cells growth and proliferation, up to 7 days. TNF-α, IL-6 (pro-inflammatory) and IL-10 (anti-inflammatory) release quantification from a human monocyte cell line revealed a decrease in the pro-inflammatory cytokines concentrations in samples containing Ch[Gallate]. These outcomes encourage the use of the developed architectures as tissue engineering solutions, potentially targeting inflammation processes. STATEMENT OF SIGNIFICANCE: Combining natural resources with active biocompatible ionic liquids (Bio-IL) is herein presented as a combinatorial approach for the development of tools to manage inflammatory diseases. We propose using silk fibroin (SF), a natural protein, with cholinium gallate, a Bio-IL, with antioxidant and anti-inflammatory properties, to construct 3D-porous sponges through a sustainable methodology. The morphological features, swelling, and stability of the architectures were controlled by Bio-IL content in the matrices. The sponges were able to support human adipose stem cells growth and proliferation, and their therapeutic effect was proved by the blockage of TNF-α from activated and differentiated THP-1 monocytes. We believe that these bio-friendly and bioactive SF/Bio-IL-based sponges are effective for targeting pathologies with associated inflammatory processes.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

A Review on Antibacterial Silk Fibroin-based Biomaterials: Current State and Prospects

Bacterial contamination of biomaterials is a common problem and a serious threat to human health worldwide. Therefore, the development of multifunctional biomaterials that possess antibacterial properties and can resist infection is a continual goal for biomedical applications. Silk fibroin (SF), approved by U.S. Food and Drug Administration (FDA) as a biomaterial, is one of the most widely studied natural polymers for biomedical applications due to its unique mechanical properties, biocompatibility, tunable biodegradation, and versatile material formats. In the last decade, many methods have been employed for the development of antibacterial SF-based biomaterials (SFBs) such as physical loading or chemical functionalization of SFBs with different antibacterial agents and bio-inspired surface modifications. In this review, we first describe the current understanding of the composition and structure-properties relationship of SF as a leading-edge biomaterial. Then we demonstrate the different antibacterial agents and methods implemented for the development of bactericidal SFBs, their mechanisms of action, and different applications. We briefly address their fabrication methods, advantages, and limitations, and finally discuss the emerging technologies and future trends in this research area.

3D printed porous sulfonated polyetheretherketone scaffold for cartilage repair: Potential and limitation

Objective

The treatment of cartilage lesions has always been a difficult problem. Although cartilage tissue engineering provides alternative treatment options for cartilage lesions, biodegradable tissue engineering scaffolds have limitations.

Methods

In this study, we constructed a porous PEEK scaffold via 3D printing, surface-engineered with concentrated sulfuric acid for 15 s (SPK-15), 30 s (SPK-30), and 60 s (SPK-60). We systematically evaluated the physical and chemical characteristics and biofunctionalities of the scaffolds, and then evaluated the macrophage polarization modulating ability and anti-inflammatory effects of the sulfonated PEEK, and observed the cartilage-protective effect of SPK using a co-culture study. We further evaluated the repair effect of PEEK and SPK by implanting the prosthetic scaffold into a cartilage defect in a rabbit model.

Results

Compared to the PEEK, SPK-15 and SPK-60 scaffolds, SPK-30 has a good micro/nanostructure, appropriate biomechanical properties (compressive modulus, 43 ± 5 MPa; Shaw hardness, 20.6 ± 1.3 HD; close to native cartilage, 30 ± 8 MPa, 17.8 ± 0.8 HD), and superior biofunctionalities. Compared to PEEK, sulfonated PEEK can favor macrophage polarization to the M2 phenotype, which increases anti-inflammatory cytokine secretion. Furthermore, SPK can also prevent macrophage-induced cartilage degeneration. The in-vivo animal experiment demonstrates that SPK can favor new tissue ingrowth and integration, prevent peri-scaffold cartilage degeneration and patellar cartilage degeneration, inhibit inflammatory cytokine secretion, and promote cartilage function restoration.

Conclusion

The present study confirmed that the 3D printed porous sulfonated PEEK scaffold could promote cartilage functional repair, and suggests a new promising strategy for treating cartilage defects with a functional prosthesis that spontaneously inhibits nearby cartilage degeneration.

Translational potential of this article

In the present study, we propose a new cartilage repair strategy based on a porous, non-biodegradable polyetheretherketone (PEEK) scaffold, which may bring up a new treatment route for elderly patients with cartilage lesions in the future.

Biomedical applications of silkworm (Bombyx Mori) proteins in regenerative medicine (a narrative review)

Silk worm (Bombyx Mori) protein, have been considered as potential materials for a variety of advanced engineering and biomedical applications for decades. Recently, silkworm silk has gained significant importance in research attention mainly because of its remarkable and exceptional mechanical properties. Silk has already been shown to have unique interactions with cells in tissues through bio-recognition units. The natural silk contains fibroin and sericin and has been used in various tissues of the human body (skin, bone, nerve, and so on). Besides, silk also still has anti-cancer, anti-tyrosinase, anti-coagulant, anti-oxidant, anti-bacterial, and anti-diabetic properties. This article is supposed to describe the diverse biomedical capabilities of B. Mori silk as the appropriate biomaterial among the assorted natural and artificial polymers that are presently accessible, and ideal for usage in regenerative medicine fields.

Chitosan/β-TCP composites scaffolds coated with silk fibroin: a bone tissue engineering approach

Bone regeneration and natural repair are long-standing processes that can lead to uneven new tissue growth. By introducing scaffolds that can be autografts and/or allografts, tissue engineering provides new approaches to manage the major burdens involved in this process. Polymeric scaffolds allow the incorporation of bioactive agents that improve their biological and mechanical performance, making them suitable materials for bone regeneration solutions. The present work aimed to create chitosan/beta-tricalcium phosphate-based scaffolds coated with silk fibroin and evaluate their potential for bone tissue engineering. Results showed that the obtained scaffolds have porosities up to 86%, interconnectivity up to 96%, pore sizes in the range of 60-170 μm, and a stiffness ranging from 1 to 2 MPa. Furthermore, when cultured with MC3T3 cells, the scaffolds were able to form apatite crystals after 21 d; and they were able to support cell growth and proliferation up to 14 d of culture. Besides, cellular proliferation was higher on the scaffolds coated with silk. These outcomes further demonstrate that the developed structures are suitable candidates to enhance bone tissue engineering.

Strontium mineralized silk fibroin porous microcarriers with enhanced osteogenesis as injectable bone tissue engineering vehicles

In this paper, silk fibroin (SF) porous microcarriers containing strontium were constructed as injectable bone tissue engineering vehicles. The effects of SF concentration and strontium content on micromorphology, element distribution, strontium ion release and cellular behavior of the constructed microcarriers were investigated. The microcarriers with an open interconnected pore can be fabricated by controlling the concentration of SF. The strontium functionalized SF microcarriers showed the sustained release of strontium ion and allowed bone mesenchymal stem cells (BMSCs) to attach, proliferate and secrete extracellular matrix. Furthermore, the strontium functionalized SF microcarriers improved the osteogenic capability of BMSCs in vitro compared with those microcarriers without sustained release of strontium ion. This study presents a valuable approach to fabricate polymeric microcarriers with the capability of sustained release of strontium ion that show potential in bone tissue engineering applications.

Designed protein- and peptide-based hydrogels for biomedical sciences

Proteins are fundamentally the most important macromolecules for biochemical, mechanical, and structural functions in living organisms. Therefore, they provide us with diverse structural building blocks for constructing various types of biomaterials, including an important class of such materials, hydrogels. Since natural peptides and proteins are biocompatible and biodegradable, they have features advantageous for their use as the building blocks of hydrogels for biomedical applications. They display constitutional and mechanical similarities with the native extracellular matrix (ECM), and can be easily bio-functionalized via genetic and chemical engineering with features such as bio-recognition, specific stimulus-reactivity, and controlled degradation. This review aims to give an overview of hydrogels made up of recombinant proteins or synthetic peptides as the structural elements building the polymer network. A wide variety of hydrogels composed of protein or peptide building blocks with different origins and compositions - including β-hairpin peptides, α-helical coiled coil peptides, elastin-like peptides, silk fibroin, and resilin - have been designed to date. In this review, the structures and characteristics of these natural proteins and peptides, with each of their gelation mechanisms, and the physical, chemical, and mechanical properties as well as biocompatibility of the resulting hydrogels are described. In addition, this review discusses the potential of using protein- or peptide-based hydrogels in the field of biomedical sciences, especially tissue engineering.

TCP/PLGA composite scaffold loaded rapamycin in situ enhances lumbar fusion by regulating osteoblast and osteoclast activity

The purpose of this study was to develop a novel β-tricalcium phosphate (TCP)/poly (D,L-lactic-co-glycolic acid) (PLGA) composite scaffold loaded with rapamycin that can regulate the activity of osteoblasts and osteoclasts for lumbar fusion. The TCP/PLGA composite scaffold was fabricated by cryogenic three-dimensional printing techniques and then loaded with rapamycin in situ. The structural surface morphology of the composite scaffold was tested with scanning electron microscope. To evaluate the biocompatibility of the composite scaffold in vitro, bone marrow mesenchymal stem cells (BMSCs) were cultured on the TCP/PLGA composite scaffold slide and tested with Live/Dead Viability Kit. The effect of rapamycin on osteoclast and osteoblast was studied with staining and Western blotting. The in vitro results showed that the rapamycin-loaded TCP/PLGA composite scaffold showed good biocompatibility with BMSC and released rapamycin obviously promoted the osteoblast differentiation and mineralization. In vivo study, the TCP/PLGA composite scaffold loaded with rapamycin were implanted in lumbar fusion model and study with micro-computed tomography scanning, hematoxylin-eosin, Masson, and immune-histological staining, to evaluate the effect of rapamycin on bone fusion. The in vivo results demonstrated that rapamycin-loaded TCP/PLGA composite scaffold could enhance bone formation by regulating osteoblast and osteoclast activity, respectively. In this study, the TCP/PLGA composite scaffold loaded with rapamycin was confirmed to provide great compatibility and improved performance in lumbar fusion by regulating osteoblastic and osteoclastic activity and would be a promising composite biomaterial for bone tissue engineering.

Chitosan hydrogel/silk fibroin/Mg(OH)2 nanobiocomposite as a novel scaffold with antimicrobial activity and improved mechanical properties

Herein, a novel nanobiocomposite scaffold based on modifying synthesized cross-linked terephthaloyl thiourea-chitosan hydrogel (CTT-CS hydrogel) substrate using the extracted silk fibroin (SF) biopolymer and prepared Mg(OH)2 nanoparticles was designed and synthesized. The biological capacity of this nanobiocomposite scaffold was evaluated by cell viability method, red blood cells hemolytic and anti-biofilm assays. According to the obtained results from 3 and 7 days, the cell viability of CTT-CS/SF/Mg(OH)2 nanobiocomposite scaffold was accompanied by a considerable increment from 62.5 to 89.6% respectively. Furthermore, its low hemolytic effect (4.5%), and as well, the high anti-biofilm activity and prevention of the P. aeruginosa biofilm formation confirmed its promising hemocompatibility and antibacterial activity. Apart from the cell viability, blood biocompatibility, and antibacterial activity of CTT-CS/SF/Mg(OH)2 nanobiocomposite scaffold, its structural features were characterized using spectral and analytical techniques (FT-IR, EDX, FE-SEM and TG). As well as, given the mechanical tests, it was indicated that the addition of SF and Mg(OH)2 nanoparticles to the CTT-CS hydrogel could improve its compressive strength from 65.42 to 649.56 kPa.

Recent Progress in 3D Printing of Elastic and High-Strength Hydrogels for the Treatment of Osteochondral and Cartilage Diseases

Despite considerable progress for the regenerative medicine, repair of full-thickness articular cartilage defects and osteochondral interface remains challenging. This low efficiency is largely due to the difficulties in recapitulating the stratified zonal architecture of articular cartilage and engineering complex gradients for bone-soft tissue interface. This has led to increased interest in three-dimensional (3D) printing technologies in the field of musculoskeletal tissue engineering. Printable and biocompatible hydrogels are attractive materials for 3D printing applications because they not only own high tunability and complexity, but also offer favorable biomimetic environments for live cells, such as porous structure, high water content, and bioactive molecule incorporation. However, conventional hydrogels are usually mechanically weak and brittle, which cannot reach the mechanical requirements for repair of articular cartilage defects and osteochondral interface. Therefore, the development of elastic and high-strength hydrogels for 3D printing in the repairment of cartilage defects and osteochondral interface is crucial. In this review, we summarized the recent progress in elastic and high-strength hydrogels for 3D printing and categorized them into six groups, namely ion bonds interactions, nanocomposites integrated in hydrogels, supramolecular guest-host interactions, hydrogen bonds interactions, dynamic covalent bonds interactions, and hydrophobic interactions. These 3D printed elastic and high-strength hydrogels may provide new insights for the treatment of osteochondral and cartilage diseases.

Advanced hydrogels for the repair of cartilage defects and regeneration

Cartilage defects are one of the most common symptoms of osteoarthritis (OA), a degenerative disease that affects millions of people world-wide and places a significant socio-economic burden on society. Hydrogels, which are a class of biomaterials that are elastic, and display smooth surfaces while exhibiting high water content, are promising candidates for cartilage regeneration. In recent years, various kinds of hydrogels have been developed and applied for the repair of cartilage defects in vitro or in vivo, some of which are hopeful to enter clinical trials. In this review, recent research findings and developments of hydrogels for cartilage defects repair are summarized. We discuss the principle of cartilage regeneration, and outline the requirements that have to be fulfilled for the deployment of hydrogels for medical applications. We also highlight the development of advanced hydrogels with tailored properties for different kinds of cartilage defects to meet the requirements of cartilage tissue engineering and precision medicine.

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The biotechnology of developing hydrogels for cartilage defects repair is promising.

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The principle for cartilage regeneration using hydrogels and requirements for clinical transformation are summarized.

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Advanced hydrogels with tailored properties for different kinds of cartilage defects are discussed.

Scaffold-Mediated Gene Delivery for Osteochondral Repair

Osteochondral defects involve both the articular cartilage and the underlying subchondral bone. If left untreated, they may lead to osteoarthritis. Advanced biomaterial-guided delivery of gene vectors has recently emerged as an attractive therapeutic concept for osteochondral repair. The goal of this review is to provide an overview of the variety of biomaterials employed as nonviral or viral gene carriers for osteochondral repair approaches both in vitro and in vivo, including hydrogels, solid scaffolds, and hybrid materials. The data show that a site-specific delivery of therapeutic gene vectors in the context of acellular or cellular strategies allows for a spatial and temporal control of osteochondral neotissue composition in vitro. In vivo, implantation of acellular hydrogels loaded with nonviral or viral vectors has been reported to significantly improve osteochondral repair in translational defect models. These advances support the concept of scaffold-mediated gene delivery for osteochondral repair.

An Off-the-Shelf Tissue Engineered Cartilage Composed of Optimally Sized Pellets of Cartilage Progenitor/Stem Cells

Articular cartilage focal lesion remains an intractable challenge in sports medicine, and autologous chondrocytes' implantation (ACI) is one of the most commonly utilized treatment modality for this ailment. However, the current ACI technique requires two surgical steps which increases patients' morbidity and incurs additional medical costs. In the present study, we developed a one-step cryopreserved off-the-shelf ACI tissue-engineered (TE) cartilage by seeding pellets of spheroidal cartilage stem/progenitor cells (CSPCs) on a silk scaffold. The pellets were developed through a hanging-drop method, and the incubation time of 1 day could efficiently produce spheroidal pellets without any adverse influence on the cell activity. The pellet size was also optimized. Under chondrogenic induction, pellets consisting of 40 000 CSPCs were found to exhibit the most abundant cartilage matrix deposition and the highest mRNA expression levels of SOX9, aggrecan, and COL2A1, as compared with pellets consisting of 10 000, 100 000, or 200 000 CSPCs. Scaffolds seeded with CSPCs pellets containing 40 000 cells could be preserved in liquid nitrogen with the viability, migration, and chondrogenic ability remaining unaffected for as long as 3 months. When implanted in a rat trochlear cartilage defect model for 3 months, the ready-to-use, cryopreserved TE cartilage yielded fully cartilage reconstruction, which was comparable with the uncryopreserved control. Hence, our study provided preliminary data that our off-the-shell TE cartilage with optimally sized CSPCs pellets seeded within silk scaffolds exhibited strong cartilage repair capacity, which provided a convenient and promising one-step surgical approach to ACI.