Evaluation of a co-culture of rapidly isolated chondrocytes and stem cells seeded on tri-layered collagen-based scaffolds in a caprine osteochondral defect model

Cartilage has poor regenerative capacity and thus damage to the joint surfaces presents a major clinical challenge. Recent research has focussed on the development of tissue-engineered and cell-based approaches for the treatment of cartilage and osteochondral injuries, with current clinically available cell-based approaches including autologous chondrocyte implantation and matrix-assisted autologous chondrocyte implantation. However, these approaches have significant disadvantages due to the requirement for a two-stage surgical procedure and an in vitro chondrocyte expansion phase which increases logistical challenges, hospital times and costs. In this study, we hypothesized that seeding biomimetic tri-layered scaffolds, with proven regenerative potential, with chondrocyte/infrapatellar fat pad stromal cell co-cultures would improve their regenerative capacity compared to scaffolds implanted cell-free. Rapid cell isolation techniques, without the requirement for long term in vitro culture, were utilised to achieve co-cultures of chondrocytes and stromal cells and thus overcome the limitations of existing cell-based techniques. Cell-free and cell-seeded scaffolds were implanted in osteochondral defects, created within the femoral condyle and trochlear ridge, in a translational large animal goat model. While analysis showed trends towards delayed subchondral bone healing in the cell-seeded scaffold group, by the 12 month timepoint the cell-free and cell-seeded groups yield cartilage and bone tissue with comparable quality and quantity. The results of the study reinforce the potential of the biomimetic tri-layered scaffold to repair joint defects but failed to demonstrate a clear benefit from the addition of the CC/FPMSC co-culture to this scaffold. Taking into consideration the additional cost and complexity associated with the cell-seeded scaffold approach, this study demonstrates that the treatment of osteochondral defects using cell-free tri-layered scaffolds may represent a more prudent clinical approach.

Layer-specific stem cell differentiation in tri-layered tissue engineering biomaterials: Towards development of a single-stage cell-based approach for osteochondral defect repair

Successful repair of osteochondral defects is challenging, due in part to their complex gradient nature. Tissue engineering approaches have shown promise with the development of layered scaffolds that aim to promote cartilage and bone regeneration within the defect. The clinical potential of implanting these scaffolds cell-free has been demonstrated, whereby cells from the host bone marrow MSCs infiltrate the scaffolds and promote cartilage and bone regeneration within the required regions of the defect. However, seeding the cartilage layer of the scaffold with a chondrogenic cell population prior to implantation may enhance cartilage tissue regeneration, thus enabling the treatment of larger defects. Here the development of a cell seeding approach capable of enhancing articular cartilage repair without the requirement for in vitro expansion of the cell population is explored. The intrinsic ability of a tri-layered scaffold previously developed in our group to direct stem cell differentiation in each layer of the scaffold was first demonstrated. Following this, the optimal chondrogenic cell seeding approach capable of enhancing the regenerative capacity of the tri-layered scaffold was demonstrated with the highest levels of chondrogenesis achieved with a co-culture of rapidly isolated infrapatellar fat pad MSCs (FPMSCs) and chondrocytes (CCs). The addition of FPMSCs to a relatively small number of CCs led to a 7.8-fold increase in the sGAG production over chondrocytes in mono-culture. This cell seeding approach has the potential to be delivered within a single-stage approach, without the requirement for costly in vitro expansion of harvested cells, to achieve rapid repair of osteochondral defects.

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Tri-layered scaffold capable of directing layer specific stem cell differentiation.

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Potential of cell seeding regimes to enhance chondrogenic repair explored.

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Optimal cell seeding regime was an infrapatellar fat pad MSC:chondrocyte coculture.

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Adding infrapatellar fat pad MSCs to chondrocytes led to >7-fold increase in sGAG.

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This cell-seeded scaffold has potential for rapid repair of osteochondral defects.

3D printing of fibre-reinforced cartilaginous templates for the regeneration of osteochondral defects

Successful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage that is resistant to vascularization and endochondral ossification. During skeletal development articular cartilage also functions as a surface growth plate, which postnatally is replaced by a more spatially complex bone-cartilage interface. Motivated by this developmental process, the hypothesis of this study is that bi-phasic, fibre-reinforced cartilaginous templates can regenerate both the articular cartilage and subchondral bone within osteochondral defects created in caprine joints. To engineer mechanically competent implants, we first compared a range of 3D printed fibre networks (PCL, PLA and PLGA) for their capacity to mechanically reinforce alginate hydrogels whilst simultaneously supporting mesenchymal stem cell (MSC) chondrogenesis in vitro. These mechanically reinforced, MSC-laden alginate hydrogels were then used to engineer the endochondral bone forming phase of bi-phasic osteochondral constructs, with the overlying chondral phase consisting of cartilage tissue engineered using a co-culture of infrapatellar fat pad derived stem/stromal cells (FPSCs) and chondrocytes. Following chondrogenic priming and subcutaneous implantation in nude mice, these bi-phasic cartilaginous constructs were found to support the development of vascularised endochondral bone overlaid by phenotypically stable cartilage. These fibre-reinforced, bi-phasic cartilaginous templates were then evaluated in clinically relevant, large animal (caprine) model of osteochondral defect repair. Although the quality of repair was variable from animal-to-animal, in general more hyaline-like cartilage repair was observed after 6 months in animals treated with bi-phasic constructs compared to animals treated with commercial control scaffolds. This variability in the quality of repair points to the need for further improvements in the design of 3D bioprinted implants for joint regeneration. STATEMENT OF SIGNIFICANCE: Successful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage. In this study, we hypothesised that bi-phasic, fibre-reinforced cartilaginous templates could be leveraged to regenerate both the articular cartilage and subchondral bone within osteochondral defects. To this end we used 3D printed fibre networks to mechanically reinforce engineered transient cartilage, which also contained an overlying layer of phenotypically stable cartilage engineered using a co-culture of chondrocytes and stem cells. When chondrogenically primed and implanted into caprine osteochondral defects, these fibre-reinforced bi-phasic cartilaginous grafts were shown to spatially direct tissue development during joint repair. Such developmentally inspired tissue engineering strategies, enabled by advances in biofabrication and 3D printing, could form the basis of new classes of regenerative implants in orthopaedic medicine.

Effects of dynamic radial tensile stress on fibrocartilage differentiation of bone marrow mesenchymal stem cells

BACKGROUND

Uniaxial/biaxial tensile stress has been employed to induce chondrocyte differentiation of mesenchymal stem cells. However, the effects of radial tensile stimuli on differentiation of MSCs into fibrocartilage remain unclear.

RESULTS

It was found that induced bone marrow mesenchymal stem cells (BMSCs) were not only similar to TMJ disc cells in morphology, but also could synthesize type I collagen (Col I), a small amount of type II collagen (Col II) and glycosaminoglycans (GAGs). The synthesis of Col I significantly increased while that of Col II gradually decreased with increasing tensile strength. The ratio of Col I to Col II was 1.8 to 1 and 2 to 1 in the 10% and 15% stretching groups, respectively. The gene expression of Col I and GAGs was significantly upregulated, whereas that of Col II was downregulated. However, the higher tensile stimulation (15%) promoted the synthesis of α-smooth muscle actin (α-SMA). Too much α-SMA is not conducive to constructing engineered tissue.

CONCLUSION

Therefore, the 10% radial tensile stimulus was the optimal strength for inducing the BMSCs to differentiate into fibrochondrocytes of the temporomandibular joint (TMJ) disc. This work provided a novel approach for inducing BMSCs to differentiate into fibrochondrocytes.

Hydrogels for Cartilage Regeneration, from Polysaccharides to Hybrids

The aims of this paper are: (1) to review the current state of the art in the field of cartilage substitution and regeneration; (2) to examine the patented biomaterials being used in preclinical and clinical stages; (3) to explore the potential of polymeric hydrogels for these applications and the reasons that hinder their clinical success. The studies about hydrogels used as potential biomaterials selected for this review are divided into the two major trends in tissue engineering: (1) the use of cell-free biomaterials; and (2) the use of cell seeded biomaterials. Preparation techniques and resulting hydrogel properties are also reviewed. More recent proposals, based on the combination of different polymers and the hybridization process to improve the properties of these materials, are also reviewed. The combination of elements such as scaffolds (cellular solids), matrices (hydrogel-based), growth factors and mechanical stimuli is needed to optimize properties of the required materials in order to facilitate tissue formation, cartilage regeneration and final clinical application. Polymer combinations and hybrids are the most promising materials for this application. Hybrid scaffolds may maximize cell growth and local tissue integration by forming cartilage-like tissue with biomimetic features.

Engineering cartilaginous grafts using chondrocyte-laden hydrogels supported by a superficial layer of stem cells

During postnatal joint development, progenitor cells that reside in the superficial region of articular cartilage first drive the rapid growth of the tissue and later help direct the formation of mature hyaline cartilage. These developmental processes may provide directions for the optimal structuring of co-cultured chondrocytes (CCs) and multipotent stromal/stem cells (MSCs) required for engineering cartilaginous tissues. The objective of this study was to engineer cartilage grafts by recapitulating aspects of joint development where a population of superficial progenitor cells drives the development of the tissue. To this end, MSCs were either self-assembled on top of CC-laden agarose gels (structured co-culture) or were mixed with CCs before being embedded in an agarose hydrogel (mixed co-culture). Porcine infrapatellar fat pad-derived stem cells (FPSCs) and bone marrow-derived MSCs (BMSCs) were used as sources of progenitor cells. The DNA, sGAG and collagen content of a mixed co-culture of FPSCs and CCs was found to be lower than the combined content of two control hydrogels seeded with CCs and FPSCs only. In contrast, a mixed co-culture of BMSCs and CCs led to increased proliferation and sGAG and collagen accumulation. Of note was the finding that a structured co-culture, at the appropriate cell density, led to greater sGAG accumulation than a mixed co-culture for both MSC sources. In conclusion, assembling MSCs onto CC-laden hydrogels dramatically enhances the development of the engineered tissue, with the superficial layer of progenitor cells driving CC proliferation and cartilage ECM production, mimicking certain aspects of developing cartilage. Copyright © 2015 John Wiley & Sons, Ltd.

Coupling Freshly Isolated CD44(+) Infrapatellar Fat Pad-Derived Stromal Cells with a TGF-β3 Eluting Cartilage ECM-Derived Scaffold as a Single-Stage Strategy for Promoting Chondrogenesis

An alternative strategy to the use of in vitro expanded cells in regenerative medicine is the use of freshly isolated stromal cells, where a bioactive scaffold is used to provide an environment conducive to proliferation and tissue-specific differentiation in vivo. The objective of this study is to develop a cartilage extracellular matrix (ECM)-derived scaffold that could facilitate the rapid proliferation and chondrogenic differentiation of freshly isolated stromal cells. By freeze-drying cryomilled cartilage ECM of differing concentrations, it is possible to produce scaffolds with a range of pore sizes. The migration, proliferation, and chondrogenic differentiation of infrapatellar fat pad-derived stem cells (FPSCs) depend on the concentration/porosity of these scaffolds, with greater sulphated glycosaminoglycan (sGAG) accumulation observed in scaffolds with larger-sized pores. It is then sought to determine if freshly isolated fat pad-derived stromal cells, seeded onto a transforming growth factor (TGF)-β3 eluting ECM-derived scaffold, could promote chondrogenesis in vivo. While a more cartilage-like tissue could be generated using culture expanded FPSCs compared to nonenriched freshly isolated cells, fresh CD44(+) stromal cells are capable of producing a tissue in vivo that stained strongly for sGAGs and type II collagen. These findings open up new possibilities for in-theatre cell-based therapies for joint regeneration.

Tissue Engineering Whole Bones Through Endochondral Ossification: Regenerating the Distal Phalanx

Novel strategies are urgently required to facilitate regeneration of entire bones lost due to trauma or disease. In this study, we present a novel framework for the regeneration of whole bones by tissue engineering anatomically shaped hypertrophic cartilaginous grafts in vitro that subsequently drive endochondral bone formation in vivo. To realize this, we first fabricated molds from digitized images to generate mesenchymal stem cell-laden alginate hydrogels in the shape of different bones (the temporomandibular joint [TMJ] condyle and the distal phalanx). These constructs could be stimulated in vitro to generate anatomically shaped hypertrophic cartilaginous tissues that had begun to calcify around their periphery. Constructs were then formed into the shape of the distal phalanx to create the hypertrophic precursor of the osseous component of an engineered long bone. A layer of cartilage engineered through self-assembly of chondrocytes served as the articular surface of these constructs. Following chondrogenic priming and subcutaneous implantation, the hypertrophic phase of the engineered phalanx underwent endochondral ossification, leading to the generation of a vascularized bone integrated with a covering layer of stable articular cartilage. Furthermore, spatial bone deposition within the construct could be modulated by altering the architecture of the osseous component before implantation. These findings open up new horizons to whole limb regeneration by recapitulating key aspects of normal bone development.