Induction of mesenchymal stem cell chondrogenesis by polyacrylate substrates

Biocompatible Synthetic Polymers for Tissue Engineering Purposes

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

Spidroin striped micropattern promotes chondrogenic differentiation of human Wharton's jelly mesenchymal stem cells

Cartilage tissue engineering, particularly micropattern, can influence the biophysical properties of mesenchymal stem cells (MSCs) leading to chondrogenesis. In this research, human Wharton’s jelly MSCs (hWJ-MSCs) were grown on a striped micropattern containing spider silk protein (spidroin) from Argiope appensa. This research aims to direct hWJ-MSCs chondrogenesis using micropattern made of spidroin bioink as opposed to fibronectin that often used as the gold standard. Cells were cultured on striped micropattern of 500 µm and 1000 µm width sizes without chondrogenic differentiation medium for 21 days. The immunocytochemistry result showed that spidroin contains RGD sequences and facilitates cell adhesion via integrin β1. Chondrogenesis was observed through the expression of glycosaminoglycan, type II collagen, and SOX9. The result on glycosaminoglycan content proved that 1000 µm was the optimal width to support chondrogenesis. Spidroin micropattern induced significantly higher expression of SOX9 mRNA on day-21 and SOX9 protein was located inside the nucleus starting from day-7. COL2A1 mRNA of spidroin micropattern groups was downregulated on day-21 and collagen type II protein was detected starting from day-14. These results showed that spidroin micropattern enhances chondrogenic markers while maintains long-term upregulation of SOX9, and therefore has the potential as a new method for cartilage tissue engineering.

Static Magnetic Fields Enhance the Chondrogenesis of Mandibular Bone Marrow Mesenchymal Stem Cells in Coculture Systems

Objectives

Combining the advantages of static magnetic fields (SMF) and coculture systems, we investigated the effect of moderate-intensity SMF on the chondrogenesis and proliferation of mandibular bone marrow mesenchymal stem cells (MBMSCs) in the MBMSC/mandibular condylar chondrocyte (MCC) coculture system. The main aim of the present study was to provide an experimental basis for obtaining better cartilage tissue engineering seed cells for the effective repair of condylar cartilage defects in clinical practice.

Methods

MBMSCs and MCCs were isolated from SD (Sprague Dawley) rats. Flow cytometry, three-lineage differentiation, colony-forming assays, immunocytochemistry, and toluidine blue staining were used for the identification of MBMSCs and MCCs. MBMSCs and MCCs were seeded into the lower and upper Transwell chambers, respectively, at a ratio of 1 : 2, and exposed to a 280 mT SMF. MBMSCs were harvested after 3, 7, or 14 days for analysis. CCK-8 was used to detect cell proliferation, Alcian blue staining was utilized to evaluate glycosaminoglycan (GAG), and western blotting and real-time quantitative polymerase chain reaction (RT-qPCR) detected protein and gene expression levels of SOX9, Col2A1 (Collagen Type II Alpha 1), and Aggrecan (ACAN).

Results

The proliferation of MBMSCs was significantly enhanced in the experimental group with MBMSCs cocultured with MCCs under SMF stimulation relative to controls (P < 0.05). GAG content was increased, and SOX9, Col2A1, and ACAN were also increased at the mRNA and protein levels (P < 0.05).

Conclusions

Moderate-intensity SMF improved the chondrogenesis and proliferation of MBMSCs in the coculture system, and it might be a promising approach to repair condylar cartilage defects in the clinical setting.

Reprogrammed Synovial Fluid-Derived Mesenchymal Stem/Stromal Cells Acquire Enhanced Therapeutic Potential for Articular Cartilage Repair

OBJECTIVES

Functions of mesenchymal stem/stromal cells (MSCs) are affected by patient-dependent factors such as age and health condition. To tackle this problem, we used the cellular reprogramming technique to epigenetically alter human MSCs derived from the synovial fluid of joints with osteoarthritis (OA) to explore the potential of reprogrammed MSCs for repairing articular cartilage.

MATERIALS AND METHODS

MSCs isolated from the synovial fluid of three patients' OA knees (Pa-MSCs) were reprogrammed through overexpression of pluripotency factors and then induced for differentiation to establish reprogrammed MSC (Re-MSC) lines. We compared the in vitro growth characteristics, chondrogenesis for articular cartilage chondrocytes, and immunomodulatory capacity. We also evaluated the capability of Re-MSCs to repair articular cartilage damage in an animal model with spontaneous OA.

RESULTS

Our results showed that Re-MSCs increased the in vitro proliferative capacity and improved chondrogenic differentiation toward articular cartilage-like chondrocyte phenotypes with increased THBS4 and SIX1 and decreased ALPL and COL10A1, compared to Pa-MSCs. In addition, Re-MSC-derived chondrocytes expressing elevated COL2A and COL2B were more mature than parental cell-derived ones. The enhancement in chondrogenesis of Re-MSC involves the upregulation of sonic hedgehog signaling. Moreover, Re-MSCs improved the repair of articular cartilage in an animal model of spontaneous OA.

CONCLUSIONS

Epigenetic reprogramming promotes MSCs harvested from OA patients to increase phenotypic characteristics and gain robust functions. In addition, Re-MSCs acquire an enhanced potential for articular cartilage repair. Our study here demonstrates that the reprogramming strategy provides a potential solution to the challenge of variation in MSC quality.

Integrins, cadherins and channels in cartilage mechanotransduction: perspectives for future regeneration strategies

Articular cartilage consists of hyaline cartilage, is a major constituent of the human musculoskeletal system and has critical functions in frictionless joint movement and articular homoeostasis. Osteoarthritis (OA) is an inflammatory disease of articular cartilage, which promotes joint degeneration. Although it affects millions of people, there are no satisfying therapies that address this disease at the molecular level. Therefore, tissue regeneration approaches aim at modifying chondrocyte biology to mitigate the consequences of OA. This requires appropriate biochemical and biophysical stimulation of cells. Regarding the latter, mechanotransduction of chondrocytes and their precursor cells has become increasingly important over the last few decades. Mechanotransduction is the transformation of external biophysical stimuli into intracellular biochemical signals, involving sensor molecules at the cell surface and intracellular signalling molecules, so-called mechano-sensors and -transducers. These signalling events determine cell behaviour. Mechanotransducing ion channels and gap junctions additionally govern chondrocyte physiology. It is of great scientific and medical interest to induce a specific cell behaviour by controlling these mechanotransduction pathways and to translate this knowledge into regenerative clinical therapies. This review therefore focuses on the mechanotransduction properties of integrins, cadherins and ion channels in cartilaginous tissues to provide perspectives for cartilage regeneration.

2D biointerfaces to study stem cell-ligand interactions

Stem cells have great potential in the field of tissue engineering and regenerative medicine due to their inherent regenerative capabilities. However, an ongoing challenge within their clinical translation is to elicit or predict the desired stem cell behavior once transplanted. Stem cell behavior and function are regulated by their interaction with biophysical and biochemical signals present in their natural environment (i.e., stem cell niches). To increase our understanding about the interplay between stem cells and their resident microenvironments, biointerfaces have been developed as tools to study how these substrates can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior. After an introduction on stem cells and their natural environment, static surfaces exhibiting predefined biochemical signals to probe the effect of chemical features on stem cell behaviors are discussed. In the third section, we discuss more complex dynamic platforms able to display biochemical cues with spatiotemporal control using on-off ligand display, reversible ligand display, and ligand mobility. In the last part of the review, we provide the reader with an outlook on future designs of biointerfaces. STATEMENT OF SIGNIFICANCE: Stem cells have great potential as treatments for many degenerative disorders prevalent in our aging societies. However, an ongoing challenge within their clinical translation is to promote stem cell mediated regeneration once they are transplanted in the body. Stem cells reside within our bodies where their behavior and function are regulated by interactions with their natural environment called the stem cell niche. To increase our understanding about the interplay between stem cells and their niche, 2D materials have been developed as tools to study how specific signals can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior.

Human chondrocyte-conditioned medium promotes chondrogenesis of bone marrow stem cells

Background

Cell-based therapy for osteoarthritis requires culturing of good quality cells, especially with a chondrogenic lineage, for implantation.

Objective

To investigate the ability of chondrocyte-conditioned medium (CCM) to induced chondrogenesis.

Methods

Bone marrow mesenchymal stem cells (BMSCs) were subjected to chondrogenic induction using CCM and chondrocyte induction medium (CIM). The optimal condition for the collection of CCM was evaluated by quantifying the concentration of secreted proteins. The chondrogenic efficiency of BMSCs induced by CCM (iCCM) was evaluated using immunocytochemical analysis, Safranin-O staining, and gene expression.

Results

Protein quantification revealed that CCM obtained from cells at passage 3 at the 72 h collection point had the greatest amount of protein. Supplementation of CCM results in the aggregation of BMSCs; however, no clumping was visible as in iCIM. The expression of collagen type 2 was detected as early as day 7 for all groups except for non-induced BMSCs; however, the level of expression decreased with culture time. Similarly, all tested groups showed positive staining for Safranin-O as early as day 7. The induction of BMSCs by CCM caused the down-regulation of collagen type 1, along with the up-regulation of the collagen type 2, ACP and SOX9 genes.

Conclusion

The optimum CCM to induce BMSC into chondrocytes was collected at passage 3 after 72 h and was used in a 50:50 ratio of CCM to fresh medium.

RGD-Dendrimer-Poly(L-lactic) Acid Nanopatterned Substrates for the Early Chondrogenesis of Human Mesenchymal Stromal Cells Derived from Osteoarthritic and Healthy Donors

Aiming to address a stable chondrogenesis derived from mesenchymal stromal cells (MSCs) to be applied in cartilage repair strategies at the onset of osteoarthritis (OA), we analyzed the effect of arginine–glycine–aspartate (RGD) density on cell condensation that occurs during the initial phase of chondrogenesis. For this, we seeded MSC-derived from OA and healthy (H) donors in RGD-dendrimer-poly(L-lactic) acid (PLLA) nanopatterned substrates (RGD concentrations of 4 × 10⁻⁹, 10⁻⁸, 2.5 × 10⁻⁸, and 10⁻² w/w), during three days and compared to a cell pellet conventional three-dimensional culture system. Molecular gene expression (collagens type-I and II–COL1A1 and COL2A1, tenascin-TNC, sex determining region Y-box9-SOX9, and gap junction protein alpha 1–GJA1) was determined as well as the cell aggregates and pellet size, collagen type-II and connexin 43 proteins synthesis. This study showed that RGD-tailored first generation dendrimer (RGD-Cys-D1) PLLA nanopatterned substrates supported the formation of pre-chondrogenic condensates from OA- and H-derived human bone marrow-MSCs with enhanced chondrogenesis regarding the cell pellet conventional system (presence of collagen type-II and connexin 43, both at the gene and protein level). A RGD-density dependent trend was observed for aggregates size, in concordance with previous studies. Moreover, the nanopatterns’ had a higher effect on OA-derived MSC morphology, leading to the formation of bigger and more compact aggregates with improved expression of early chondrogenic markers.

Study of the polyacrylate interpenetration in a collagen-polyurethane matrix to prepare novel hydrogels for biomedical applications

Currently, the control of the properties of collagen based hydrogels represents a promising area of research to develop novel materials for biomedical applications. The crosslinking of the collagen with trifunctional polyurethane (PU) allows a hybrid matrix to be formed by improving the coupling with exogenous polymeric chains to generate innovative semi-interpenetrated network (semi-IPN) hydrogels. The incorporation of polyacrylate (PA) within a hybrid matrix of collagen-PU allows to regulate the structure and physicochemical properties such as polymerization rate, physicochemical crosslinking, thermal stability, storage module and swelling/degradation behavior of the 3D matrices in the hydrogel state, also exhibiting modulation of their in vitro biocompatibility properties. This work contemplates the study of the effect of PA concentration on the physicochemical properties and the in vitro biological response of these novel semi-IPN hydrogels based on collagen-PU-PA. The results indicate that semi-IPN hydrogels that include 20 wt% of PA exhibit improved swelling with respect to the collagen-PU hydrogel, controlling the degradation rate in acidic, alkaline and proteolytic media; showing E. coli inhibition capacity, high hemocompatibility and not altering the metabolism of monocytes and fibroblasts growing on them. Therefore, these novel hydrogels represent biomaterials with potential application in biomedical strategies such as wound healing dressings.

Plasma Polymer Coatings To Direct the Differentiation of Mouse Kidney-Derived Stem Cells into Podocyte and Proximal Tubule-like Cells

Kidney disease is now recognized as a global health problem and is associated with increased morbidity and mortality, along with high economic costs. To develop new treatments for ameliorating kidney injury and preventing disease progression, there is a need for appropriate renal culture systems for screening novel drugs and investigating the cellular mechanisms underlying renal pathogenesis. There is a need for in vitro culture systems that promote the growth and differentiation of specialized renal cell types. In this work, we have used plasma polymerization technology to generate gradients of chemical functional groups to explore whether specific concentrations of these functional groups can direct the differentiation of mouse kidney-derived stem cells into specialized renal cell types. We found that amine-rich (-NH₂) allylamine-based plasma-polymerized coatings could promote differentiation into podocyte-like cells, whereas methyl-rich (CH₃) 1,7-octadiene-based coatings promoted differentiation into proximal tubule-like cells (PTC). Importantly, the PT-like cells generated on the substrates expressed the marker megalin and were able to endocytose albumin, indicating that the cells were functional.

A soft 3D polyacrylate hydrogel recapitulates the cartilage niche and allows growth-factor free tissue engineering of human articular cartilage

Cartilage degeneration or damage treatment is still a challenge, but, tissue engineering strategies, which combine cell therapy strategies, which combine cell therapy and scaffolds, and have emerged as a promising new approach. In this regard, polyurethanes and polyacrylates polymers have been shown to have clinical potential to treat osteochondral injuries. Here, we have used polymer microarrays technology to screen 380 different polyurethanes and polyacrylates polymers. The top polymers with potential to maintain chondrocyte viability were selected, with scale-up studies performed to evaluate their ability to support chondrocyte proliferation during long-term culture, while maintaining their characteristic phenotype. Among the selected polymers, poly (methylmethacrylate-co-methacrylic acid), showed the highest level of chondrogenic potential and was used to create a 3D hydrogel. Ultrastructural morphology, microstructure and mechanical testing of this novel hydrogel revealed robust characteristics to support chondrocyte growth. Furthermore, in vitro and in vivo biological assays demonstrated that chondrocytes cultured on the hydrogel had the capacity to produce extracellular matrix similar to hyaline cartilage, as shown by increased expression of collagen type II, aggrecan and Sox9, and the reduced expression of the fibrotic marker's collagen type I. In conclusion, hydrogels generated from poly (methylmethacrylate-co-methacrylic acid) created the appropriate niche for chondrocyte growth and phenotype maintenance and might be an optimal candidate for cartilage tissue-engineering applications. SIGNIFICANCE STATEMENT: Articular cartilage has limited self-repair ability due to its avascular nature, therefore tissue engineering strategies have emerged as a promising new approach. Synthetic polymers displaygreat potential and are widely used in the clinical setting. In our study, using the polymer microarray technique a novel type of synthetic polyacrylate was identified, that was converted into hydrogels for articular cartilage regeneration studies. The hydrogel based on poly (methylmethacrylate-co-methacrylic acid-co-PEG-diacrylate) had a controlable ultrastructural morphology, microstructure (porosity) and mechanical properties (stiffness) appropriate for cartilage engineering. Our hydrogel created the optimal niche for chondrocyte growth and phenotype maintenance for long-term culture, producing a hyaline-like cartilage extracellular matrix. We propose that this novel polyacrylate hydrogel could be an appropriate support to help in the treatment efficient cartilage regeneration.

Peptide-biofunctionalization of biomaterials for osteochondral tissue regeneration in early stage osteoarthritis: challenges and opportunities

Osteoarthritis is a degenerative joint disease characterized by the progressive deterioration of articular cartilage, synovial inflammation and changes in periarticular and subchondral bone, being a leading cause of disability.

Direct Control of Stem Cell Behavior Using Biomaterials and Genetic Factors

Stem cells have recently emerged as an important candidate for cell therapy. However, some major limitations still exist such as a small quantity of cell supply, senescence, and insufficient differentiation efficiency. Therefore, there is an unmet need to control stem cell behavior for better clinical performance. Since native microenvironment factors including stem cell niche, genetic factors, and growth factors direct stem cell fate cooperatively, user-specified in vitro settings are required to understand the regulatory roles and effects of each factor, thereby applying the factors for improved cell therapy. Among others, various types of biomaterials and transfection method have been employed as key tools for development of the in vitro settings. This review focuses on the current strategies to improve stemness maintenance, direct differentiation, and reprogramming using biomaterials and genetic factors without any aids from additional biochemicals and growth factors.

Fabrication of gelatin-micropatterned surface and its effect on osteogenic differentiation of hMSCs

Micropatterned surface with different surface chemistries was fabricated for the direct comparison of their effect on the behaviors of hMSCs and to avoid any batch to batch variations during cell culture.

Expression of miR-145-5p During Chondrogenesis of Mesenchymal Stem Cells

Assessing the quality of tissue engineered (TE) cartilage has historically been performed by endpoint measurements including marker gene expression. Until the adoption of promoter-driven reporter constructs capable of quantitative and real time non-destructive expression analysis, temporal gene expression assessments along a timeline could not be performed on TE constructs. We further exploit this technique to utilize microRNA (miRNA or miR) through the use of firefly luciferase reporter (Luc) containing a 3' UTR perfect complementary target sequence to the mature miR-145-5p. We report the development and testing of a firefly luciferase (Luc) reporter responsive to miR-145-5p for longitudinal tracking of miR-145-5p expression throughout MSC chondrogenic differentiation. Plasmid reporter vectors containing a miR-145-5p responsive reporter (Luc reporter with a perfect complementary target sequence to the mature miR-145-5p sequence in the 3'UTR), a Luc reporter driven by a truncated Sox9 (one of the targets of miR-145-5p) promoter, or the Luc backbone (control) vector without a specific miRNA target were transfected into MSCs by electroporation. Transfected MSCs were mixed with untransfected MSC to generate chondrogenic pellets. Pellets were imaged by bioluminescent imaging (BLI) and harvested along a preset time line. The imaging signals from miR-145-5p responsive reporter and Sox9 promoter-driven reporter showed correlated time-courses (measured by BLI and normalized to Luc-control reporter; Spearman r=0.93, p=0.0002) during MSC chondrogenic differentiation. Expression analysis by qRT-PCR suggests an inverse relationship between miR-145-5p and Sox9 gene expression during MSC chondrogenic differentiation. Non-destructive cell-pellet imaging is capable of supplementing histological analyses to characterize TE cartilage. The miR-145-5p responsive reporter is relatively simple to construct and generates a consistent imaging signal responsive to miR-145-5p during MSC chondrogenesis in parallel to certain molecular and cellular events.

Effects of Functional Groups of Materials on Nonspecific Adhesion and Chondrogenic Induction of Mesenchymal Stem Cells on Free and Micropatterned Surfaces

Functional groups of materials are known to affect cell behaviors, yet the corresponding effect on stem cell differentiation is always coupled with that of cell spreading; it is thus unclear whether the chemical groups influence cell differentiation directly or via cell spreading indirectly. Herein we used a unique surface patterning technique to decouple the corresponding effects. Mesenchymal stem cells (MSCs) derived from bone marrow were seeded on surfaces coated with alkanethiols with one of four functional end groups (-CH₃, -OH, -COOH, and -NH₂) and underwent 9 days of chondrogenic induction. The measurements of quartz crystal microbalance with dissipation confirmed less proteins adsorbed from the cell culture media on the neutral -CH₃ and -OH surfaces than on the charged -COOH and -NH₂ surfaces. The neutral surfaces exhibited less cell spreading and higher extents of chondrogenic differentiation than the charged surfaces, according to the characterizations of immunofluorescence staining and quantitative real-time polymerase chain reaction. We further used a transfer lithography technique to prepare patterned surfaces on nonfouling poly(ethylene glycol) hydrogels to localize single MSCs on microislands with self-assembly monolayers of different alkanethiols, under given microisland areas and thus well-defined spreading areas of cells. While small microislands were always beneficial for chondrogenic induction, we found that the type of functional groups had no significant effect on chondrogenic induction under the given cell spreading areas, implying that the chemical groups influence cell differentiation only indirectly. Our results hence illustrate that functional groups regulate stem cell differentiation via tuning protein adsorption and then nonspecific cell adhesion and thus cell spreading.

A comparative evaluation of the effect of polymer chemistry and fiber orientation on mesenchymal stem cell differentiation

Bioengineered tissue scaffolds in combination with cells hold great promise for tissue regeneration. The aim of this study was to determine how the chemistry and fiber orientation of engineered scaffolds affect the differentiation of mesenchymal stem cells (MSCs). Adipogenic, chondrogenic, and osteogenic differentiation on aligned and randomly orientated electrospun scaffolds of Poly (lactic‐co‐glycolic) acid (PLGA) and Polydioxanone (PDO) were compared. MSCs were seeded onto scaffolds and cultured for 14 days under adipogenic‐, chondrogenic‐, or osteogenic‐inducing conditions. Cell viability was assessed by alamarBlue metabolic activity assays and gene expression was determined by qRT‐PCR. Cell‐scaffold interactions were visualized using fluorescence and scanning electron microscopy. Cells grew in response to scaffold fiber orientation and cell viability, cell coverage, and gene expression analysis showed that PDO supports greater multilineage differentiation of MSCs. An aligned PDO scaffold supports highest adipogenic and osteogenic differentiation whereas fiber orientation did not have a consistent effect on chondrogenesis. Electrospun scaffolds, selected on the basis of fiber chemistry and alignment parameters could provide great therapeutic potential for restoration of fat, cartilage, and bone tissue. This study supports the continued investigation of an electrospun PDO scaffold for tissue repair and regeneration and highlights the potential of optimizing fiber orientation for improved utility. © 2016 The Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2843–2853, 2016.

Stem Cells in Skeletal Tissue Engineering: Technologies and Models

This review surveys the use of pluripotent and multipotent stem cells in skeletal tissue engineering. Specific emphasis is focused on evaluating the function and activities of these cells in the context of development in vivo, and how technologies and methods of stem cell-based tissue engineering for stem cells must draw inspiration from developmental biology. Information on the embryonic origin and in vivo differentiation of skeletal tissues is first reviewed, to shed light on the persistence and activities of adult stem cells that remain in skeletal tissues after embryogenesis. Next, the development and differentiation of pluripotent stem cells is discussed, and some of their advantages and disadvantages in the context of tissue engineering are presented. The final section highlights current use of multipotent adult mesenchymal stem cells, reviewing their origin, differentiation capacity, and potential applications to tissue engineering.

Steric Interference of Adhesion Supports In-Vitro Chondrogenesis of Mesenchymal Stem Cells on Hydrogels for Cartilage Repair

Recent studies suggest the presence of cell adhesion motifs found in structural proteins can inhibit chondrogenesis. In this context, the current study aims to determine if a polyethylene glycol (PEG)-modified fibrinogen matrix could support better chondrogenesis of human bone marrow mesenchymal stem cells (BM-MSC) based on steric interference of adhesion, when compared to a natural fibrin matrix. Hydrogels used as substrates for two-dimensional (2D) BM-MSC cultures under chondrogenic conditions were made from cross-linked PEG-fibrinogen (PF) and compared to thrombin-activated fibrin. Cell morphology, protein expression, DNA and sulfated proteoglycan (GAG) content were correlated to substrate properties such as stiffness and adhesiveness. Cell aggregation and chondrogenic markers, including collagen II and aggrecan, were observed on all PF substrates but not on fibrin. Shielding fibrinogen's adhesion domains and increasing stiffness of the material are likely contributing factors that cause the BM-MSCs to display a more chondrogenic phenotype. One composition of PF corresponding to GelrinC™--a product cleared in the EU for cartilage repair--was found to be optimal for supporting chondrogenic differentiation of BM-MSC while minimizing hypertrophy (collagen X). These findings suggest that semi-synthetic biomaterials based on ECM proteins can be designed to favourably affect BM-MSC towards repair processes involving chondrogenesis.

A novel culture system for modulating single cell geometry in 3D

Dedifferentiation of chondrocytes during in vitro expansion remains an unsolved challenge for repairing serious articular cartilage defects. In this study, a novel culture system was developed to modulate single cell geometry in 3D and investigate its effects on the chondrocyte phenotype. The approach uses 2D micropatterns followed by in situ hydrogel formation to constrain single cell shape and spreading. This enables independent control of cell geometry and extracellular matrix. Using collagen I matrix, we demonstrated the formation of a biomimetic collagenous "basket" enveloping individual chondrocytes cells. By quantitatively monitoring the production by single cells of chondrogenic matrix (e.g. collagen II and aggrecan) during 21-day cultures, we found that if the cell's volume decreases, then so does its cell resistance to dedifferentiation (even if the cells remain spherical). Conversely, if the volume of spherical cells remains constant (after an initial decrease), then not only do the cells retain their differentiated status, but previously de-differentiated redifferentiate and regain a chondrocyte phenotype. The approach described here can be readily applied to pluripotent cells, offering a versatile platform in the search for niches toward either self-renewal or targeted differentiation.

Growth factor and ultrasound-assisted bioreactor synergism for human mesenchymal stem cell chondrogenesis

Ultrasound at 5.0 MHz was noted to be chondro-inductive, with improved SOX-9 gene and COL2A1 protein expression in constructs that allowed for cell-to-cell contact. To achieve tissue-engineered cartilage using macroporous scaffolds, it is hypothesized that a combination of ultrasound at 5.0 MHz and transforming growth factor-β3 induces human mesenchymal stem cell differentiation to chondrocytes. Expression of miR-145 was used as a metric to qualitatively assess the efficacy of human mesenchymal stem cell conversion. Our results suggest that in group 1 (no transforming growth factor-β3, no ultrasound), as anticipated, human mesenchymal stem cells were not efficiently differentiated into chondrocytes, judging by the lack of decrease in the level of miR-145 expression. Human mesenchymal stem cells differentiated into chondrocytes in group 2 (transforming growth factor-β3, no ultrasound) and group 3 (transforming growth factor-β3, ultrasound) with group 3 having a 2-fold lower miR-145 when compared to group 2 at day 7, indicating a higher conversion to chondrocytes. Transforming growth factor-β3-induced chondrogenesis with and without ultrasound stimulation for 14 days in the ultrasound-assisted bioreactor was compared and followed by additional culture in the absence of growth factors. The combination of growth factor and ultrasound stimulation (group 3) resulted in enhanced COL2A1, SOX-9, and ACAN protein expression when compared to growth factor alone (group 2). No COL10A1 protein expression was noted. Enhanced cell proliferation and glycosaminoglycan deposition was noted with the combination of growth factor and ultrasound stimulation. These results suggest that ultrasound at 5.0 MHz could be used to induce chondrogenic differentiation of mesenchymal stem cells for cartilage tissue engineering.

Controlled chondrogenesis from adipose-derived stem cells by recombinant transforming growth factor-β3 fusion protein in peptide scaffolds

Adipose-derived stem cells (ADSCs) are promising for cartilage repair due to their easy accessibility and chondrogenic potential. Although chondrogenesis of transforming growth factor-β (TGF-β) mediated mesenchymal stem cells (MSCs) is well established in vitro, clinical tissue engineering requires effective and controlled delivery of TGF-β in vivo. In this work, a self-assembled peptide scaffold was employed to construct cartilages in vivo through the chondrogenesis from ADSCs controlled by recombinant fusion protein LAP-MMP-mTGF-β3 that was transfected by lentiviral vectors. During this course, the addition of matrix metalloproteinases (MMPs) can trigger the release of mTGF-β3 from the recombinant fusion protein of LAP-MMP-mTGF-β3 in the combined scaffolds, thus stimulating the differentiation of ADSCs into chondrogenesis. The specific expression of cartilage genes was analyzed by real-time polymerase chain reaction and Western blot. The expression of chondrocytic markers was obviously upregulated to a higher level compared to the one by commonly used TGF-β3 alone. After 3 weeks of in vitro culturing, the hybrids with differentiated chondrogenesis were then injected subcutaneously into nude mice and retrieved after 4 weeks of culturing in vivo. Histological analysis also confirmed that the recombinant fusion protein was more effective for the formation of cartilage matrix than the cases either with TGF-β3 alone or without LAP-MMP-mTGF-β3 (P<0.05). This study demonstrates that controlled local delivery of the LAP-MMP-mTGF-β3 constructs can accelerate differentiation of ADSCs into the cartilage in vivo, which indicates the great potential of this hybrid in rapid therapy of osteoarthritis.

Icariin promotes directed chondrogenic differentiation of bone marrow mesenchymal stem cells but not hypertrophy in vitro

Icariin (ICA), a Traditional Chinese Medicine, has been demonstrated to be a promoting compound for extracellular matrix synthesis and gene expression of chondrocytes. However, whether ICA can act as a substitute for or cooperate with growth factors to directly promote stable chondrogenesis of bone marrow mesenchymal stem cells (BMSCs) remains unknown. In the present study, rat BMSCs were cultivated in monolayer cultures with a chondrogenic medium containing transforming growth factor-β3 for 14 days; ICA was added to the same chondrogenic medium throughout the culture period at a concentration of 1×10⁻⁶ M. Cell morphology was observed using an inverted microscope, and chondrogenic differentiation markers, including collagen II, aggrecan and SRY (sex determining region Y)-box 9 (SOX9), were detected by immunofluorescence, reverse transcription-quantitative polymerase chain reaction and western blot analysis. Hypertrophic differentiation was also analyzed using collagen I gene expression and alkaline phosphatase (ALP) activity. The results revealed that ICA was effective at forming an increased number of and larger aggregates, and significantly upregulated the mRNA expression levels and protein synthesis of collagen II, aggrecan and SOX9. Furthermore, the chondrogenic medium alone caused hypertrophic differentiation through the upregulation of collagen I gene expression and ALP activity, which was not potentiated by the presence of ICA. Thus, ICA promoted directed chondrogenic differentiation of BMSCs, but had no effect on hypertrophic differentiation. The present results also suggested that ICA may be an effective accelerant of growth factors for cartilage tissue engineering by promoting their chondrogenic differentiating effects but reducing the effect of hypertrophic differentiation.

Three-dimensional hydrogel scaffolds facilitate in vitro self-renewal of human skin-derived precursors

Skin-derived precursors (SKPs) are multipotent cells with dermal stem cell properties. These easily available cells possess the capacity to reconstitute the skin in vivo, as well as a broader differentiation potential in vitro, which endows them with great prospects in regenerative medicine. However, the present authors' group and others previously found that adult human SKPs (hSKPs) expanded deficiently in vitro, which largely counteracted their research and practical values. Taking the physiological micro-environment of hSKPs into consideration, the authors sought to establish a hydrogel scaffold-based three-dimensional (3-D) culture system for hSKPs in the present study. After comparing their morphology, growth characteristics, signature gene expression and differentiation potential in different hydrogels, the present authors found that a chemically defined hyaluronic acid and denatured collagen-based hydrogel system that mimicked the natural niche of hSKPs in the dermis could alleviate hSKP senescence, support hSKP proliferation as spheres, while largely retaining their properties and potential. This study suggested that recapitulating the in vivo stem cell niche by providing them with 3-D extracellular matrix environments could help them achieve better self-renewal in vitro. In addition, the animal-origin-free and biocompatible 3-D hydrogel system will certainly benefit fundamental research and clinical applications of hSKPs in the near future.