Comparative chondrogenesis of human cell sources in 3D scaffolds

Covalent Conjugation of Small Molecule Inhibitors and Growth Factors to a Silk Fibroin-Derived Bioink to Develop Phenotypically Stable 3D Bioprinted Cartilage

Implantation of a phenotypically stable cartilage graft could represent a viable approach for repairing osteoarthritic (OA) cartilage lesions. In the present study, we investigated the effects of modulating the bone morphogenetic protein (BMP), transforming growth factor beta (TGFβ), and interleukin-1 (IL-1) signaling cascades in human bone marrow stromal cell (hBMSC)-encapsulated silk fibroin gelatin (SF-G) bioink. The selected small molecules LDN193189, TGFβ3, and IL1 receptor antagonist (IL1Ra) are covalently conjugated to SF-G biomaterial to ensure sustained release, increased bioavailability, and printability, confirmed by ATR-FTIR, release kinetics, and rheological analyses. The 3D bioprinted constructs with chondrogenically differentiated hBMSCs were incubated in an OA-inducing medium for 14 days and assessed through a detailed qPCR, immunofluorescence, and biochemical analyses. Despite substantial heterogeneity in the observations among the donors, the IL1Ra molecule illustrated the maximum efficiency in enhancing the expression of articular cartilage components, reducing the expression of hypertrophic markers (re-validated by the GeneMANIA tool), as well as reducing the production of inflammatory molecules by the hBMSCs. Therefore, this study demonstrated a novel strategy to develop a chemically decorated, printable and biomimetic SF-G bioink to produce hyaline cartilage grafts resistant to acquiring OA traits that can be used for the treatment of degenerated cartilage lesions.

Deep Learning augmented osteoarthritis grading standardization

Manual grading of cartilage histology images for investigating the extent and severity of osteoarthritis (OA) involves critical examination of the cell characteristics, which makes this task tiresome, tedious and error-prone. This results in wide inter-observer variation, causing ambiguities in OA grade prediction. Such drawbacks of manual assessment can be overcome by implementing artificial intelligence (AI) based automated image classification techniques such as deep learning (DL). Hence in this manuscript, we present the feasibility of training a deep neural network with cartilage histology images, which can grade the extent and severity of knee OA based on modified Mankin scoring system. The grading system used here for automating OA grading was simplified and modified based on the microscopic observations from the histology images, where three parameters (Safranin-O staining intensity, chondrocyte distribution & arrangement, and morphology) were considered for evaluating the OA progression. The histology images were tiled, labelled, and grouped together based on the developed grading system (Grade 0-3). Four different DL architectures were tried for image classification and the best performing model was selected by five-fold validation method. With a validation accuracy of about 84%, 0.632 Cohen's kappa score, and an excellent ROC-AUC ranging between 0.89-0.99, DenseNet121 was selected among the four models as the best performing model, and was used for inferencing on new data. Final grades obtained from the models were in accordance with the grades provided by the medical experts. We hereby demonstrate that a DL architecture can be taught to interpret the degree of cartilage degradation, with excellent discriminatory ability across all four classes of OA severity. Unlike other works where radiographic images have been considered for grading of OA, we have considered histology images which is a fundamental approach for grading OA extent and severity. This would bring a paradigm shift in histology-based assessment of OA, making this automated approach to be explored as an option for OA grading standardization.

Small-Molecule Loaded Biomimetic Biphasic Scaffold for Osteochondral Regeneration: An In Vitro and In Vivo Study

Osteoarthritis is a prevalent musculoskeletal disorder in the elderly, which leads to high rates of morbidity. Mesenchymal stem cells (MSCs) are a promising approach to promote tissue regeneration in the absence of effective long-term treatments. Small molecules are relatively inexpensive and can selectively alter stem cell behavior during their differentiation, making them an attractive option for clinical applications. In this study, we developed an extracellular matrix (ECM)-based biphasic scaffold (BPS) loaded with two small-molecule drugs, kartogenin (KGN) and metformin (MET). This cell-free biomimetic biphasic scaffold consists of a bone (gelatin/hydroxyapatite scaffold embedded with metformin [GHSM]) and cartilage (nano-gelatin fiber embedded with kartogenin [NGFK]) layer designed to stimulate osteochondral regeneration. Extracellular matrix (ECM)-based biomimetic scaffolds can promote native cell recruitment, infiltration, and differentiation even in the absence of additional growth factors. The biphasic scaffold (BPS) showed excellent biocompatibility in vitro, with mesenchymal stem cells (MSCs) adhering, proliferating, and differentiated on the biomimetic biphasic scaffolds (GHSM and NGFK layers). The biphasic scaffolds upregulated both osteogenic and chondrogenic gene expression, sulfated glycosaminoglycan (sGAG), osteo- and chondrogenic biomarker, and relative mRNA gene expression. In an in vivo rat model, histo-morphological staining showed effective regeneration of osteochondral defects. This novel BPS has the potential to enhance both subchondral bone repair and cartilage regeneration, demonstrating excellent effects on cell homing and the recruitment of endogenous stem cells.

Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Articular cartilage shows limited self-healing ability owing to its low cellularity and avascularity. Untreated cartilage defects display an increased propensity to degenerate, leading to osteoarthritis (OA). During OA progression, articular chondrocytes are subjected to significant alterations in gene expression and phenotype, including a shift towards a hypertrophic-like state (with the expression of collagen type X, matrix metalloproteinases-13, and alkaline phosphatase) analogous to what eventuates during endochondral ossification. Present OA management strategies focus, however, exclusively on cartilage inflammation and degradation. A better understanding of the hypertrophic chondrocyte phenotype in OA might give new insights into its pathogenesis, suggesting potential disease-modifying therapeutic approaches. Recent developments in the field of cellular/molecular biology and tissue engineering proceeded in the direction of contrasting the onset of this hypertrophic phenotype, but knowledge gaps in the cause-effect of these processes are still present. In this review we will highlight the possible advantages and drawbacks of using this approach as a therapeutic strategy while focusing on the experimental models necessary for a better understanding of the phenomenon. Specifically, we will discuss in brief the cellular signaling pathways associated with the onset of a hypertrophic phenotype in chondrocytes during the progression of OA and will analyze in depth the advantages and disadvantages of various models that have been used to mimic it. Afterwards, we will present the strategies developed and proposed to impede chondrocyte hypertrophy and cartilage matrix mineralization/calcification. Finally, we will examine the future perspectives of OA therapeutic strategies.

Chondrogenesis of Adipose-Derived Stem Cells Using an Arrayed Spheroid Format

Objective

The chondrogenic response of adipose-derived stem cells (ASCs) is often assessed using 3D micromass protocols that use upwards of hundreds of thousands of cells. Scaling these systems up for high-throughput testing is technically challenging and wasteful given the necessary cell numbers and reagent volumes. However, adopting microscale spheroid cultures for this purpose shows promise. Spheroid systems work with only thousands of cells and microliters of medium.

Methods

Molded agarose microwells were fabricated using 2% w/v molten agarose and then equilibrated in medium prior to introducing cells. ASCs were seeded at 50, 500, 5k cells/microwell; 5k, 50k, cells/well plate; and 50k and 250k cells/15 mL centrifuge tube to compare chondrogenic responses across spheroid and micromass sizes. Cells were cultured in control or chondrogenic induction media. ASCs coalesced into spheroids/pellets and were cultured at 37 °C and 5% CO2 for 21 days with media changes every other day.

Results

All culture conditions supported growth of ASCs and formation of viable cell spheroids/micromasses. More robust growth was observed in chondrogenic conditions. Sulfated glycosaminoglycans and collagen II, molecules characteristics of chondrogenesis, were prevalent in both 5000-cell spheroids and 250,000-cell micromasses. Deposition of collagen I, characteristic of fibrocartilage, was more prevalent in the large micromasses than small spheroids.

Conclusions

Chondrogenic differentiation was consistently induced using high-throughput spheroid formats, particularly when seeding at cell densities of 5000 cells/spheroid. This opens possibilities for highly arrayed experiments investigating tissue repair and remodeling during or after exposure to drugs, toxins, or other chemicals.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00746-8.

Recent advances in bioprinting using silk protein-based bioinks

3D printing has experienced swift growth for biological applications in the field of regenerative medicine and tissue engineering. Essential features of bioprinting include determining the appropriate bioink, printing speed mechanics, and print resolution while also maintaining cytocompatibility. However, the scarcity of bioinks that provide printing and print properties and cell support remains a limitation. Silk Fibroin (SF) displays exceptional features and versatility for inks and shows the potential to print complex structures with tunable mechanical properties, degradation rates, and cytocompatibility. Here we summarize recent advances and needs with the use of SF protein from Bombyx mori silkworm as a bioink, including crosslinking methods for extrusion bioprinting using SF and the maintenance of cell viability during and post bioprinting. Additionally, we discuss how encapsulated cells within these SF-based 3D bioprinted constructs are differentiated into various lineages such as skin, cartilage, and bone to expedite tissue regeneration. We then shift the focus towards SF-based 3D printing applications, including magnetically decorated hydrogels, in situ bioprinting, and a next-generation 4D bioprinting approach. Future perspectives on improvements in printing strategies and the use of multicomponent bioinks to improve print fidelity are also discussed.

Silk Fibroin-Based Biomaterials for Tissue Engineering Applications

Tissue engineering (TE) involves the combination of cells with scaffolding materials and appropriate growth factors in order to regenerate or replace damaged and degenerated tissues and organs. The scaffold materials serve as templates for tissue formation and play a vital role in TE. Among scaffold materials, silk fibroin (SF), a naturally occurring protein, has attracted great attention in TE applications due to its excellent mechanical properties, biodegradability, biocompatibility, and bio-absorbability. SF is usually dissolved in an aqueous solution and can be easily reconstituted into different forms, including films, mats, hydrogels, and sponges, through various fabrication techniques, including spin coating, electrospinning, freeze drying, and supercritical CO₂-assisted drying. Furthermore, to facilitate the fabrication of more complex SF-based scaffolds, high-precision techniques such as micro-patterning and bio-printing have been explored in recent years. These processes contribute to the diversity of surface area, mean pore size, porosity, and mechanical properties of different silk fibroin scaffolds and can be used in various TE applications to provide appropriate morphological and mechanical properties. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have recently been developed. The typical applications of SF-based scaffolds for TE of bone, cartilage, teeth and mandible tissue, cartilage, skeletal muscle, and vascular tissue are highlighted and discussed followed by a discussion of issues to be addressed in future studies.

Silk Hydrogel for Tissue Engineering: A Review

AIM

This review aims to explore the importance of silk hydrogel and its potential in tissue engineering (TE).

BACKGROUND

Tissue engineering is a procedure that incorporates cells into the scaffold materials with suitable growth factors to regenerate injured tissue. For tissue formation in TE, the scaffold material plays a key role. Different forms of silk fibroin (SF), such as films, mats, hydrogels, and sponges, can be easily manufactured when SF is disintegrated into an aqueous solution. High precision procedures such as micropatterning and bioprinting of SF-based scaffolds have been used for enhanced fabrication.

REVIEW RESULTS

In this narrative review, SF physicochemical and mechanical properties have been presented. We have also discussed SF fabrication techniques like electrospinning, spin coating, freeze-drying, and physiochemical cross-linking. The application of SF-based scaffolds for skeletal, tissue, joint, muscle, epidermal, tissue repair, and tympanic membrane regeneration has also been addressed.

CONCLUSION

SF has excellent mechanical properties, tunability, biodegradability, biocompatibility, and bioresorbability.

CLINICAL SIGNIFICANCE

Silk hydrogels are an ideal scaffold matrix material that will significantly impact tissue engineering applications, given the rapid scientific advancements in this field.

Silk Fibroin as a Green Material

Silk fibroin has been explored as a suitable biomaterial due to its biocompatibility, tunable degradability, low toxicity, and mechanical properties. To harness silk fibroin's innate properties, it is purified from native silkworm cocoons by removing proteins and debris that have the potential to cause inflammatory responses. Typically, within the purification and fabrication steps, chemical solvents, energy-intensive equipment, and large quantities of water are used to reverse engineer silk fibroin into an aqueous solution and then process into the final material format. Gentler, green methods for extraction and fabrication have been developed that reduce or remove the need for harmful chemical additives and energy-inefficient equipment while still producing mechanically robust biomaterials. This review will focus on the alternative green processing and fabrication methods that have proven useful in creating silk fibroin materials for a range of applications including consumer and medical materials.

Silk Fibroin as a Functional Biomaterial for Tissue Engineering

Tissue engineering (TE) is the approach to combine cells with scaffold materials and appropriate growth factors to regenerate or replace damaged or degenerated tissue or organs. The scaffold material as a template for tissue formation plays the most important role in TE. Among scaffold materials, silk fibroin (SF), a natural protein with outstanding mechanical properties, biodegradability, biocompatibility, and bioresorbability has attracted significant attention for TE applications. SF is commonly dissolved into an aqueous solution and can be easily reconstructed into different material formats, including films, mats, hydrogels, and sponges via various fabrication techniques. These include spin coating, electrospinning, freeze drying, physical, and chemical crosslinking techniques. Furthermore, to facilitate fabrication of more complex SF-based scaffolds with high precision techniques including micro-patterning and bio-printing have recently been explored. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have been recently developed. The typical TE applications of SF-based scaffolds including bone, cartilage, ligament, tendon, skin, wound healing, and tympanic membrane, will be highlighted and discussed, followed by future prospects and challenges needing to be addressed.

Kartogenin Enhances Chondrogenic Differentiation of MSCs in 3D Tri-Copolymer Scaffolds and the Self-Designed Bioreactor System

Human cartilage has relatively slow metabolism compared to other normal tissues. Cartilage damage is of great clinical consequence since cartilage has limited intrinsic healing potential. Cartilage tissue engineering is a rapidly emerging field that holds great promise for tissue function repair and artificial/engineered tissue substitutes. However, current clinical therapies for cartilage repair are less than satisfactory and rarely recover full function or return the diseased tissue to its native healthy state. Kartogenin (KGN), a small molecule, can promote chondrocyte differentiation both in vitro and in vivo. The purpose of this research is to optimize the chondrogenic process in mesenchymal stem cell (MSC)-based chondrogenic constructs with KGN for potential use in cartilage tissue engineering. In this study, we demonstrate that KGN treatment can promote MSC condensation and cell cluster formation within a tri-copolymer scaffold. Expression of Acan, Sox9, and Col2a1 was significantly up-regulated in three-dimensional (3D) culture conditions. The lacuna-like structure showed active deposition of type II collagen and aggrecan deposition. We expect these results will open new avenues for the use of small molecules in chondrogenic differentiation protocols in combination with scaffolds, which may yield better strategies for cartilage tissue engineering.

Characterization of Mesenchymal Stem Cell Differentiation within Miniaturized 3D Scaffolds through Advanced Microscopy Techniques

Three-dimensional culture systems and suitable substrates topographies demonstrated to drive stem cell fate in vitro by mechanical conditioning. For example, the Nichoid 3D scaffold remodels stem cells and shapes nuclei, thus promoting stem cell expansion and stemness maintenance. However, the mechanisms involved in force transmission and in biochemical signaling at the basis of fate determination are not yet clear. Among the available investigation systems, confocal fluorescence microscopy using fluorescent dyes enables the observation of cell function and shape at the subcellular scale in vital and fixed conditions. Contrarily, nonlinear optical microscopy techniques, which exploit multi-photon processes, allow to study cell behavior in vital and unlabeled conditions. We apply confocal fluorescence microscopy, coherent anti-Stokes Raman scattering (CARS), and second harmonic generation (SHG) microscopy to characterize the phenotypic expression of mesenchymal stem cells (MSCs) towards adipogenic and chondrogenic differentiation inside Nichoid scaffolds, in terms of nuclear morphology and specific phenotypic products, by comparing these techniques. We demonstrate that the Nichoid maintains a rounded nuclei during expansion and differentiation, promoting MSCs adipogenic differentiation while inhibiting chondrogenesis. We show that CARS and SHG techniques are suitable for specific estimation of the lipid and collagenous content, thus overcoming the limitations of using unspecific fluorescent probes.

Influence of hydrogel network microstructures on mesenchymal stem cell chondrogenesis in vitro and in vivo

Hydrogels, which provide three-dimensional (3D) niches for encapsulating bone marrow mesenchymal stem cells (BMSCs), are becoming a promising tissue engineering solution for chondrogenic differentiation of BMSCs. However, it remains a challenge to design a hydrogel material for effective chondrogenesis of BMSCs because of the complexity of cartilage ECM and cell-matrix interactions. Thus far, various studies have shown the physical-chemical cues of hydrogel materials to impact BMSCs chondrogenesis, but the design of the 3D network microstructure of the hydrogel to induce BMSCs chondrogenesis is still far from optimized. In this study, we successfully prepared two types of collagen hydrogels, namely, the fibrous network and porous network, with the same chemical composition and similar mechanical strength but with two distinct network microstructures. The two different network microstructures significantly influenced mass transfer, protein adsorption, degradability, and contraction of the collagen hydrogels. Moreover, the cells presented distinct proliferation and morphology in the two hydrogels, which consequently modulated chondrogenic differentiation of BMSCs derived from rat. Collagen hydrogels with a fibrous network promoted more chondrogenic differentiation of BMSCs without additional growth factors in vitro and subcutaneous implantation in vivo than those with a porous network. Moreover, fibrous network resulted in less ECM calcification than porous network. However, the fibrous network could not prevent hypertrophy of the chondrogenic cells induced by BMSCs. Overall, these results revealed that the 3D network microstructure of a hydrogel was a key design parameter for the chondrogenic differentiation of BMSCs. STATEMENT OF SIGNIFICANCE: Hydrogels had been used to induce the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in cartilage tissue engineering, but the key design parameters remain unoptimized. This was mainly due to the different material properties including composition, strength, and microstructure, which would interplay with each other and result in difficulties to investigate the effects for one factor. In this study, we fabricated two collagen hydrogels with the same chemical composition and mechanical strength, but two distinct network microstructures. The effects of the two network microstructures on the chondrogenic differentiation of BMSCs were investigated by in vitro and in vivo assays. The results highlight the effects of network microstructures and provide important information about optimizing the design of future hydrogels in cartilage tissue engineering.

3D printing collagen/chitosan scaffold ameliorated axon regeneration and neurological recovery after spinal cord injury

Spinal cord injury (SCI) is a disaster that can cause severe motor, sensory, and functional disorders. Implanting biomaterials have been regarded as hopeful strategies to restore neurological function. However, no optimized scaffold has been available. In this study, a novel 3D printing technology was used to fabricate the scaffold with designed structure. The composite biomaterials of collagen and chitosan were also adopted to balance both compatibility and strength. Female Sprague-Dawley rats were subjected to a T8 complete-transection SCI model. Scaffolds of C/C (collagen/chitosan scaffold with freeze-drying technology) or 3D-C/C (collagen/chitosan scaffold with 3D printing technology) were implanted into the lesion. Compared with SCI or C/C group, 3D-C/C implants significantly promoted locomotor function with the elevation in Basso-Beattie-Bresnahan (BBB) score and angle of inclined plane. Decreased latency and increased amplitude were observed both in motor-evoked potential and somatosensory-evoked potential in 3D-C/C group compared with SCI or C/C group, which further demonstrated the improvement of neurological recovery. Fiber tracking of diffusion tensor imaging (DTI) showed the most fibers traversing the lesion in 3D-C/C group. Meanwhile, we observed that the correlations between the locomotor (BBB score or angle of inclined plane) and the DTI parameters (fractional anisotropy values) were positive. Although C/C implants markedly enhanced biotin dextran amine (BDA)-positive neural profiles compared with SCI group, rats implanted with 3D-C/C scaffold displayed the largest degree of BDA profiles regeneration. Collectively, our 3D-C/C scaffolds demonstrated significant therapeutic effects on rat complete-transected spinal cord model, which provides a promising and innovative therapeutic approach for SCI. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1898-1908, 2019.

Decellularization of rat adipose tissue, diaphragm, and heart: a comparison of two decellularization methods

Decellularization is a process that involves the removal of cellular material from the tissues and organs while maintaining the structural, functional, and mechanical properties of extracellular matrix. The purpose of this study was to carry out decellularization of rat adipose tissue, diaphragm, and heart by using two different methods in order to compare their efficiency and investigate proliferation profiles of rat adipose-tissue-derived mesenchymal stem cells (AdMSCs) on these scaffolds. Tissues were treated with an optimized detergent-based decellularization (Method A) and a freeze-and-thaw-based decellularization (Method B). AdMSCs were then seeded on scaffolds having a density of 2 × 10⁵ cells/scaffold and AO/PI double-staining and MTT assays were performed in order to determine cell viability. In this study, which is the first research comparing two methods of decellularization of an adipose tissue, diaphragm, and heart scaffolds with AdMSCs, Method A provided efficient decellularization in these three tissues and it was shown that these porous scaffolds were cyto-compatible for the cells. Method B caused severe tissue damage in diaphragm and insufficient decellularization in heart whereas it also resulted in cyto-compatible adipose tissue scaffolds.

Characterization of the Proliferating Layer Chondrocytes of Growth Plate for Cartilage Regeneration

IMPACT STATEMENT

In recent years, cell-based therapy is a promising strategy for repairing defect cartilage. However, in vitro expansion of articular chondrocytes (ACs) for collecting enough cell numbers eventually develops cell de-differentiation. In the present study, we choose the proliferative layer chondroctytes (PLCs) of growth plate as new candidate. The novel findings include (1) the higher proliferation potential of PLCs in comparison with the ACs, (2) PLCs produced more GAG than ACs, (3) the increased in GAG matrix production, (4) and lower senescence in PLCs. From these results, we found PLCs might be suitable as cell source for cartilage regeneration.

Interplay between stiffness and degradation of architectured gelatin hydrogels leads to differential modulation of chondrogenesis in vitro and in vivo

The limited capacity of cartilage to heal large lesions through endogenous mechanisms has led to extensive effort to develop materials to facilitate chondrogenesis. Although physical-chemical properties of biomaterials have been shown to impact in vitro chondrogenesis, whether these findings are translatable in vivo is subject of debate. Herein, architectured 3D hydrogel scaffolds (ArcGel) (produced by crosslinking gelatin with ethyl lysine diisocyanate (LDI)) were used as a model system to investigate the interplay between scaffold mechanical properties and degradation on matrix deposition by human articular chondrocytes (HAC) from healthy donors in vitro and in vivo. Using ArcGel scaffolds of different tensile and shear modulus, and degradation behavior; in this study, we compared the fate of ex vivo engineered ArcGels-chondrocytes constructs, i.e. the traditional tissue engineering approach, with thede novoformation of cartilaginous tissue in HAC laden ArcGels in an ectopic nude mouse model. While the softer and fast degrading ArcGel (LNCO3) was more efficient at promoting chondrogenic differentiation in vitro, upon ectopic implantation, the stiffer and slow degrading ArcGel (LNCO8) was superior in maintaining chondrogenic phenotype in HAC and retention of cartilaginous matrix. Furthermore, surprisingly the de novo formation of cartilage tissue was promoted only in LNCO8. Since HAC cultured for only three days in the LNCO8 environment showed upregulation of hypoxia-associated genes, this suggests a potential role for hypoxia in the observed in vivo outcomes. In summary, this study sheds light on how immediate environment (in vivo versus in vitro) can significantly impact the outcomes of cell-laden biomaterials.

STATEMENT OF SIGNIFICANCE

In this study, 3D architectured hydrogels (ArcGels) with different mechanical and biodegradation properties were investigated for their potential to promote formation of cartilaginous matrix by human articular chondrocytes in vitro and in vivo. Two paradigms were explored (i) ex vivo engineering followed by in vivo implantation in ectopic site of nude mice and (ii) short in vitro culture (3 days) followed by implantation to induce de novo cartilage formation. Softer and fast degrading ArcGel were better at promoting chondrogenesis in vitro, while stiffer and slow degrading ArcGel were strikingly superior in both maintaining chondrogenesis in vivo and inducing de novo formation of cartilage. Our findings highlight the importance of the interplay between scaffold mechanics and degradation in chondrogenesis.

Chitosan composite scaffolds for articular cartilage defect repair: a review

Articular cartilage (AC) defects lack the ability to self-repair due to their avascular nature and the declined mitotic ability of mature chondrocytes. To date, cartilage tissue engineering using implanted scaffolds containing cells or growth factors is the most promising defect repair method. Scaffolds for cartilage tissue engineering have been comprehensively researched. As a promising scaffold biomaterial for AC defect repair, the properties of chitosan are summarized in this review. Strategies to composite chitosan with other materials, such as polymers (including collagen, gelatin, alginate, silk fibroin, poly-caprolactone, and poly-lactic acid) and bioceramics (including calcium phosphate, calcium polyphosphate, and hydroxyapatite) are presented. Methods to manufacture three-dimensional porous structures to support cell attachment and nutriment exchange have also been included.

Properties of chitosan/polymer and chitosan/bioceramic composite scaffolds for articular cartilage defect repair are reviewed.

3D printing PLGA: a quantitative examination of the effects of polymer composition and printing parameters on print resolution

In the past few decades, 3D printing has played a significant role in fabricating scaffolds with consistent, complex structure that meet patient-specific needs in future clinical applications. Although many studies have contributed to this emerging field of additive manufacturing, which includes material development and computer-aided scaffold design, current quantitative analyses do not correlate material properties, printing parameters, and printing outcomes to a great extent. A model that correlates these properties has tremendous potential to standardize 3D printing for tissue engineering and biomaterial science. In this study, we printed poly(lactic-co-glycolic acid) (PLGA) utilizing a direct melt extrusion technique without additional ingredients. We investigated PLGA with various lactic acid:glycolic acid (LA:GA) molecular weight ratios and end caps to demonstrate the dependence of the extrusion process on the polymer composition. Micro-computed tomography was then used to evaluate printed scaffolds containing different LA:GA ratios, composed of different fiber patterns, and processed under different printing conditions. We built a statistical model to reveal the correlation and predominant factors that determine printing precision. Our model showed a strong linear relationship between the actual and predicted precision under different combinations of printing conditions and material compositions. This quantitative examination establishes a significant foreground to 3D print biomaterials following a systematic fabrication procedure. Additionally, our proposed statistical models can be applied to couple specific biomaterials and 3D printing applications for patient implants with particular requirements.

Isolation and characterization of human articular chondrocytes from surgical waste after total knee arthroplasty (TKA)

BACKGROUND

Cartilage tissue engineering is a fast-evolving field of biomedical engineering, in which the chondrocytes represent the most commonly used cell type. Since research in tissue engineering always consumes a lot of cells, simple and cheap isolation methods could form a powerful basis to boost such studies and enable their faster progress to the clinics. Isolated chondrocytes can be used for autologous chondrocyte implantation in cartilage repair, and are the base for valuable models to investigate cartilage phenotype preservation, as well as enable studies of molecular features, nature and scales of cellular responses to alterations in the cartilage tissue.

METHODS

Isolation and consequent cultivation of primary human adult articular chondrocytes from the surgical waste obtained during total knee arthroplasty (TKA) was performed. To evaluate the chondrogenic potential of the isolated cells, gene expression of collagen type 2 (COL2), collagen 1 (COL1) and aggrecan (ACAN) was evaluated. Immunocytochemical staining of all mentioned proteins was performed to evaluate chondrocyte specific production.

RESULTS

Cartilage specific gene expression of COL2 and ACAN has been shown that the proposed protocol leads to isolation of cells with a high chondrogenic potential, possibly even specific phenotype preservation up to the second passage. COL1 expression has confirmed the tendency of the isolated cells dedifferentiation into a fibroblast-like phenotype already in the second passage, which confirms previous findings that higher passages should be used with care in cartilage tissue engineering. To evaluate the effectiveness of our approach, immunocytochemical staining of the evaluated chondrocyte specific products was performed as well.

DISCUSSION

In this study, we developed a protocol for isolation and consequent cultivation of primary human adult articular chondrocytes with the desired phenotype from the surgical waste obtained during TKA. TKA is a common and very frequently performed orthopaedic surgery during which both femoral condyles are removed. The latter present the ideal source for a simple and relatively cheap isolation of chondrocytes as was confirmed in our study.

The use of mesenchymal stem cells for cartilage repair and regeneration: a systematic review

BACKGROUND

The management of articular cartilage defects presents many clinical challenges due to its avascular, aneural and alymphatic nature. Bone marrow stimulation techniques, such as microfracture, are the most frequently used method in clinical practice however the resulting mixed fibrocartilage tissue which is inferior to native hyaline cartilage. Other methods have shown promise but are far from perfect. There is an unmet need and growing interest in regenerative medicine and tissue engineering to improve the outcome for patients requiring cartilage repair. Many published reviews on cartilage repair only list human clinical trials, underestimating the wealth of basic sciences and animal studies that are precursors to future research. We therefore set out to perform a systematic review of the literature to assess the translation of stem cell therapy to explore what research had been carried out at each of the stages of translation from bench-top (in vitro), animal (pre-clinical) and human studies (clinical) and assemble an evidence-based cascade for the responsible introduction of stem cell therapy for cartilage defects. This review was conducted in accordance to PRISMA guidelines using CINHAL, MEDLINE, EMBASE, Scopus and Web of Knowledge databases from 1st January 1900 to 30th June 2015. In total, there were 2880 studies identified of which 252 studies were included for analysis (100 articles for in vitro studies, 111 studies for animal studies; and 31 studies for human studies). There was a huge variance in cell source in pre-clinical studies both of terms of animal used, location of harvest (fat, marrow, blood or synovium) and allogeneicity. The use of scaffolds, growth factors, number of cell passages and number of cells used was hugely heterogeneous.

SHORT CONCLUSIONS

This review offers a comprehensive assessment of the evidence behind the translation of basic science to the clinical practice of cartilage repair. It has revealed a lack of connectivity between the in vitro, pre-clinical and human data and a patchwork quilt of synergistic evidence. Drivers for progress in this space are largely driven by patient demand, surgeon inquisition and a regulatory framework that is learning at the same pace as new developments take place.

Three-Dimensional Printing Articular Cartilage: Recapitulating the Complexity of Native Tissue<sup/>

In the past few decades, the field of tissue engineering combined with rapid prototyping (RP) techniques has been successful in creating biological substitutes that mimic tissues. Its applications in regenerative medicine have drawn efforts in research from various scientific fields, diagnostics, and clinical translation to therapies. While some areas of therapeutics are well developed, such as skin replacement, many others such as cartilage repair can still greatly benefit from tissue engineering and RP due to the low success and/or inefficiency of current existing, often surgical treatments. Through fabrication of complex scaffolds and development of advanced materials, RP provides a new avenue for cartilage repair. Computer-aided design and three-dimensional (3D) printing allow the fabrication of modeled cartilage scaffolds for repair and regeneration of damaged cartilage tissues. Specifically, the various processes of 3D printing will be discussed in details, both cellular and acellular techniques, covering the different materials, geometries, and operational printing conditions for the development of tissue-engineered articular cartilage. Finally, we conclude with some insights on future applications and challenges related to this technology, especially using 3D printing techniques to recapitulate the complexity of native structure for advanced cartilage regeneration.

Changes in expression of cartilaginous genes during chondrogenesis of Wharton's jelly mesenchymal stem cells on three-dimensional biodegradable poly(L-lactide-co-glycolide) scaffolds

Background

In cartilage tissue regeneration, it is important to develop biodegradable scaffolds that provide a structural and logistic template for three-dimensional cultures of chondrocytes. In this study, we evaluated changes in expression of cartilaginous genes during in vitro chondrogenic differentiation of WJ-MSCs on PLGA scaffolds.

Methods

The biocompatibility of the PLGA material was investigated using WJ-MSCs by direct and indirect contact methods according to the ISO 10993–5 standard. PLGA scaffolds were fabricated by the solvent casting/salt-leaching technique. We analyzed expression of chondrogenic genes of WJ-MSCs after a 21-day culture.

Results

The results showed the biocompatibility of PLGA and confirmed the usefulness of PLGA as material for fabrication of 3D scaffolds that can be applied for WJ-MSC culture. The in vitro penetration and colonization of the scaffolds by WJ-MSCs were assessed by confocal microscopy. The increase in cell number demonstrated that scaffolds made of PLGA copolymers enabled WJ-MSC proliferation. The obtained data showed that as a result of chondrogenesis of WJ-MSCs on the PLGA scaffold the expression of the key markers collagen type II and aggrecan was increased.

Conclusions

The observed changes in transcriptional activity of cartilaginous genes suggest that the PLGA scaffolds may be applied for WJ-MSC differentiation. This primary study suggests that chondrogenic capacity of WJ-MSCs cultured on the PLGA scaffolds can be useful for cell therapy of cartilage.

Engineering DN hydrogels from regenerated silk fibroin and poly(N-vinylcaprolactam)

The development of novel hydrogels that possess adequate elasticity and toughness to withstand mechanically active environments, along with being biocompatible, remains a significant challenge in the design of materials for tissue engineering applications. In this study, a family of regenerated silk fibroin (RSF) based double network (DN) hydrogels were fabricated for the first time using a rapid one-pot method. The DN hydrogels combine the rigid covalently crosslinked RSF with the softer poly(N-vinylcaprolactam) (PVCL) through strong physical interactions. The formation of these DN hydrogels resulted in an improvement of the water uptake capacity, elasticity and toughness compared to the individual RSF hydrogel. The elasticity of the RSF/PVCL DN hydrogels was closer to that of native cartilage, which makes them promising materials for cartilage regeneration applications. An in vitro study on adhesion, proliferation and differentiation of a mouse pre-chondrocyte cell line (ATDC5) conducted using microscopic analysis, a cell proliferation assay and RT-PCR confirmed the cells cultured on the less stiff hydrogels demonstrated the most favourable chondrogenic response. Thus, this study demonstrates the potential of RSF-based hybrid hydrogels for cartilage tissue engineering applications.

Poly(ε-caprolactone)-based substrates bearing pendant small chemical groups as a platform for systemic investigation of chondrogenesis

OBJECTIVES

Physiochemical properties of biomaterials play critical roles in dictating types of cell behaviour. In this study, a series of poly(ε-caprolactone) (PCL)-derived polymers bearing different small chemical groups was employed as a platform to evaluate chondrogenesis of different cell types.

MATERIALS AND METHODS

Thin films were prepared by spin-coating PCL derivatives. Rabbit articular chondrocytes (rACs) and rabbit bone marrow-derived mesenchymal stem cells (rMSCs) were seeded on to the films, and cell adhesion, proliferation, extracellular matrix production and gene expression were evaluated.

RESULTS

The presence of hydrophilic groups (-NH2 , -COOH, -OH and -C=O) promoted adhesion and proliferation of primary rACs and rMSCs. On these polymeric films, chondrogenesis of primary rACs depended on culture time. For passaged cells, re-differentiation was induced on these films by chondrogenic induction, but less for cells of passage 5 compared to passage 3. While films with hydrophilic groups favoured chondrocytic gene expression of both types of passaged cells, production of glycosaminoglycans (GAG) was similar for those of passage 3 on all films, and PCL-CH3 film better supported GAG production for cells of passage 5. Under chondrogenic conditions, rMSCs were more efficient at GAG production on PCL and PCL-NH2 films.

CONCLUSIONS

This study demonstrates that different cells displayed distinct responses to substrate surface chemistry, implying that cell-biomaterial interactions can be developmental stage dependent. This provides a novel perspective for developing biomaterials for cartilage regeneration.

Polyester type polyHIPE scaffolds with an interconnected porous structure for cartilage regeneration

Development of artificial materials for the facilitation of cartilage regeneration remains an important challenge in orthopedic practice. Our study investigates the potential for neocartilage formation within a synthetic polyester scaffold based on the polymerization of high internal phase emulsions. The fabrication of polyHIPE polymer (PHP) was specifically tailored to produce a highly porous (85%) structure with the primary pore size in the range of 50–170 μm for cartilage tissue engineering. The resulting PHP scaffold was proven biocompatible with human articular chondrocytes and viable cells were observed within the materials as evaluated using the Live/Dead assay and histological analysis. Chondrocytes with round nuclei were organized into multicellular layers on the PHP surface and were observed to grow approximately 300 μm into the scaffold interior. The accumulation of collagen type 2 was detected using immunohistochemistry and chondrogenic specific genes were expressed with favorable collagen type 2 to 1 ratio. In addition, PHP samples are biodegradable and their baseline mechanical properties are similar to those of native cartilage, which enhance chondrocyte cell growth and proliferation.

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

Fabrication and characterization of spongy denuded amniotic membrane based scaffold for tissue engineering

Objective

As a biological tissue material, amniotic membrane (AM) has low immunogenicity and to date has been widely adopted in clinical practice. However, some features such as low biomechanical consistency and rapid biodegradation is limited the application of AM. Therefore, in this study, we fabricated a novel three-dimensional (3D) spongy scaffold made of the extracellular matrix (ECM) of denuded AM. Due to their unique characteristics which are similar to the skin, these scaffolds can be considered as an alternative option in skin tissue engineering.

Materials and Methods

In this experimental study, cellular components of human amniotic membrane (HAM) were removed with 0.03% (w/v) sodium dodecyl sulphate (SDS). Quantitative analysis was performed to determine levels of Glycosaminoglycans (GAGs), collagen, and deoxyribonucleic acid (DNA). To increase the low efficiency and purity of the ECM component, especially collagen and GAG, we applied an acid solubilization procedure hydrochloridric acid (HCl 0.1 M) with pepsin (1 mg/ml). In the present experiment 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross linker agent was used to improve the mechanical properties of 3D lyophilized AM scaffold. The spongy 3D AM scaffolds were specified, by scanning electron microscopy, hematoxylin and eosin (H&E) staining, a swelling test, and mechanical strength and in vitro biodegradation tests. Human fetal fibroblast culture systems were used to establish that the scaffolds were cytocompatible.

Results

Histological analysis of treated human AM showed impressive removal of cellular components. DNA content was diminished after treatment (39 ± 4.06 μg/ml vs. 341 ± 29.60 μg/ml). Differences were observed between cellular and denude AM in matrix collagen (478 ± 18.06 μg/mg vs. 361 ± 27.47 μg/mg).With the optimum concentration of 1 mM NHS/EDC ratio1:4, chemical cross-linker agent could significantly increase the mechanical property, and resistance to collagenase digestion. The results of 2, 4, 6-Trinitrobenzenesulfonic acid (TNBS) test showed that cross-linking efficiency of AM derived ECM scaffolds was about 65% ± 10.53. Scaffolds treated with NHS/EDC cross-linker agent by 100 μg/ml collagenase, lost 75% of their dry weight after 14 days. The average pore size of 3D spongy scaffold was 160 µm measured from scanning electron microscope (SEM) images that it is suitable for cell penetration, nutrients and gas change. In addition, the NHS/ EDC cross-linked AM scaffolds were able to support human fetal fibroblast cell proliferation in vitro. Extracts and contact prepared from the 3D spongy scaffold of AM showed a significant increase in the attachment and proliferation of the human fetal fibroblasts cells.

Conclusion

The extra-cellular matrix of denuded AM-based scaffold displays the main properties required for substitute skin including natural in vitro biodegradation, similar physical and mechanical characterization, nontoxic biomaterial and no toxic effect on cell attachment and cell proliferation.

The role of growth factors in stem cell-directed chondrogenesis: a real hope for damaged cartilage regeneration

PURPOSE

The use of stem cells in regenerative medicine offers hope to treat numerous orthopaedic disorders, including articular cartilage defects. Although much research has been carried out on chondrogenesis, this complicated process is still not well understood and much more research is needed. The present review provides an overview of the stages of chondrogenesis and describes the effects of various growth factors, which act during the multiple steps involved in stem cell-directed differentiation towards chondrocytes.

METHODS

The current literature on stem cell-directed chondrogenesis, in particular the role of members of the transforming growth factor-β (TGF-β) superfamily-TGF-βs, bone morphogenetic proteins (BMPs) and fibroblast growth factors (FGFs)-is reviewed and discussed.

RESULTS

Numerous studies have reported the chondrogenic potential of both adult- and embryonic-like stem cells and the role of growth factors in programming differentiation of these cells towards chondrocytes. Mesenchymal stem cells (MSCs) are adult multipotent stem cells, whereas induced pluripotent stem cells (iPSC) are reprogrammed pluripotent cells. Although better understanding of the processes involved in the development of cartilage tissues is necessary, both cell types may be of value in the clinical treatment of cartilage injuries or osteoarthritic cartilage lesions.

CONCLUSIONS

MSCs and iPSCs both present unique characteristics. However, at present, it is still unclear which cell type is most suitable in the treatment of cartilage injuries.

Tissue-engineered cartilage: the crossroads of biomaterials, cells and stimulating factors

Damage to cartilage represents one of the most challenging tasks of musculoskeletal therapeutics due to its limited propensity for healing and regenerative capabilities. Lack of current treatments to restore cartilage tissue function has prompted research in this rapidly emerging field of tissue regeneration of functional cartilage tissue substitutes. The development of cartilaginous tissue largely depends on the combination of appropriate biomaterials, cell source, and stimulating factors. Over the years, various biomaterials have been utilized for cartilage repair, but outcomes are far from achieving native cartilage architecture and function. This highlights the need for exploration of suitable biomaterials and stimulating factors for cartilage regeneration. With these perspectives, we aim to present an overview of cartilage tissue engineering with recent progress, development, and major steps taken toward the generation of functional cartilage tissue. In this review, we have discussed the advances and problems in tissue engineering of cartilage with strong emphasis on the utilization of natural polymeric biomaterials, various cell sources, and stimulating factors such as biophysical stimuli, mechanical stimuli, dynamic culture, and growth factors used so far in cartilage regeneration. Finally, we have focused on clinical trials, recent innovations, and future prospects related to cartilage engineering.

Directed differentiation of induced pluripotent stem cells into chondrogenic lineages for articular cartilage treatment

In recent years, increases in the number of articular cartilage injuries caused by environmental factors or pathological conditions have led to a notable rise in the incidence of premature osteoarthritis. Osteoarthritis, considered a disease of civilization, is the leading cause of disability. At present, standard methods for treating damaged articular cartilage, including autologous chondrocyte implantation or microfracture, are short-term solutions with important side effects. Emerging treatments include the use of induced pluripotent stem cells, a technique that could provide a new tool for treatment of joint damage. However, research in this area is still early, and no optimal protocol for transforming induced pluripotent stem cells into chondrocytes has yet been established. Developments in our understanding of cartilage developmental biology, together with the use of modern technologies in the field of tissue engineering, provide an opportunity to create a complete functional model of articular cartilage.

Chitosan feasibility to retain retinal stem cell phenotype and slow proliferation for retinal transplantation

Retinal stem cells (RSCs) are promising in cell replacement strategies for retinal diseases. RSCs can migrate, differentiate, and integrate into retina. However, RSCs transplantation needs an adequate support; chitosan membrane (ChM) could be one, which can carry RSCs with high feasibility to support their integration into retina. RSCs were isolated, evaluated for phenotype, and subsequently grown on sterilized ChM and polystyrene surface for 8 hours, 1, 4, and 11 days for analysing cell adhesion, proliferation, viability, and phenotype. Isolated RSCs expressed GFAP, PKC, isolectin, recoverin, RPE65, PAX-6, cytokeratin 8/18, and nestin proteins. They adhered (28 ± 16%, 8 hours) and proliferated (40 ± 20 cells/field, day 1 and 244 ± 100 cells/field, day 4) significantly low (P < 0.05) on ChM. However, they maintained similar viability (>95%) and phenotype (cytokeratin 8/18, PAX6, and nestin proteins expression, day 11) on both surfaces (ChM and polystyrene). RSCs did not express alpha-SMA protein on both surfaces. RSCs express proteins belonging to epithelial, glial, and neural cells, confirming that they need further stimulus to reach a final destination of differentiation that could be provided in in vivo condition. ChM does not alternate RSCs behaviour and therefore can be used as a cell carrier so that slow proliferating RSCs can migrate and integrate into retina.

Neocartilage formation from mesenchymal stem cells grown in type II collagen-hyaluronan composite scaffolds

Three-dimensional (3D) collagen type II-hyaluronan (HA) composite scaffolds (CII-HA) which mimics the extracellular environment of natural cartilage were fabricated in this study. Rheological measurements demonstrated that the incorporation of HA increased the compression modulus of the scaffolds. An initial in vitro evaluation showed that scaffolds seeded with porcine chondrocytes formed cartilaginous-like tissue after 8 weeks, and HA functioned to promote the growth of chondrocytes into scaffolds. Placenta-derived multipotent cells (PDMC) and gingival fibroblasts (GF) were seeded on tissue culture polystyrene (TCPS), CII-HA films, and small intestinal submucosa (SIS) sheets for comparing their chondrogenesis differentiation potentials with those of adipose-derived adult stem cells (ADAS) and bone marrow-derived mesenchymal stem cells (BMSC). Among different cells, PDMC showed the greatest chondrogenic differentiation potential on both CII-HA films and SIS sheets upon TGF-β3 induction, followed by GF. This was evidenced by the up-regulation of chondrogenic genes (Sox9, aggrecan, and collagen type II), which was not observed for cells grown on TCPS. This finding suggested the essential role of substrate materials in the chondrogenic differentiation of PDMC and GF. Neocartilage formation was more obvious in both PDMC and GF cells plated on CII-HA composite scaffolds vs. 8-layer SIS at 28 days in vitro. Finally, implantation of PDMC/CII-HA constructs into NOD-SCID mice confirmed the formation of tissue-engineered cartilage in vivo.

Chondrogenic Differentiation of Human Umbilical Cord Blood-Derived Unrestricted Somatic Stem Cells on A 3D Beta-Tricalcium Phosphate-Alginate-Gelatin Scaffold

OBJECTIVE

Finding cell sources for cartilage tissue engineering is a critical procedure. The purpose of the present experimental study was to test the in vitro efficacy of the beta-tricalcium phosphate-alginate-gelatin (BTAG) scaffold to induce chondrogenic differentiation of human umbilical cord blood-derived unrestricted somatic stem cells (USSCs).

MATERIALS AND METHODS

In this experimental study, USSCs were encapsulated in BTAG scaffold and cultured for 3 weeks in chondrogenic medium as chondrogenic group and in Dulbecco's Modified Eagle's Medium (DMEM) as control group. Chondrogenic differentiation was evaluated by histology, immunofluorescence and RNA analyses for the expression of cartilage extracellular matrix components. The obtain data were analyzed using SPSS version 15.

RESULTS

Histological and immunohistochemical staining revealed that collagen II was markedly expressed in the extracellular matrix of the seeded cells on scaffold in presence of chondrogenic media after 21 days. Reverse transcription-polymerase chain reaction (RT-PCR) showed a significant increase in expression levels of genes encoded the cartilage-specific markers, aggrecan, type I and II collagen, and bone morphogenetic protein (BMP)-6 in chondrogenic group.

CONCLUSION

This study demonstrates that BTAG can be considered as a suitable scaffold for encapsulation and chondrogenesis of USSCs.

Osteochondral tissue engineering in vivo: a comparative study using layered silk fibroin scaffolds from mulberry and nonmulberry silkworms

The ability to treat osteochondral defects is a major clinical need. Existing polymer systems cannot address the simultaneous requirements of regenerating bone and cartilage tissues together. The challenge still lies on how to improve the integration of newly formed tissue with the surrounding tissues and the cartilage-bone interface. This study investigated the potential use of different silk fibroin scaffolds: mulberry (Bombyx mori) and non-mulberry (Antheraea mylitta) for osteochondral regeneration in vitro and in vivo. After 4 to 8 weeks of in vitro culture in chondro- or osteo-inductive media, non-mulberry constructs pre-seeded with human bone marrow stromal cells exhibited prominent areas of the neo tissue containing chondrocyte-like cells, whereas mulberry constructs pre-seeded with human bone marrow stromal cells formed bone-like nodules. In vivo investigation demonstrated neo-osteochondral tissue formed on cell-free multi-layer silk scaffolds absorbed with transforming growth factor beta 3 or recombinant human bone morphogenetic protein-2. Good bio-integration was observed between native and neo-tissue within the osteochondrol defect in patellar grooves of Wistar rats. The in vivo neo-matrix formed comprised of a mixture of collagen and glycosaminoglycans except in mulberry silk without growth factors, where a predominantly collagenous matrix was observed. Immunohistochemical assay showed stronger staining of type I and type II collagen in the constructs of mulberry and non-mulberry scaffolds with growth factors. The study opens up a new avenue of using inter-species silk fibroin blended or multi-layered scaffolds of a combination of mulberry and non-mulberry origin for the regeneration of osteochondral defects.