Time-dependent functional maturation of scaffold-free cartilage tissue analogs

Exposure of Tissue-Engineered Cartilage Analogs to Synovial Fluid Hematoma After Ankle Fracture Is Associated With Chondrocyte Death and Altered Cartilage Maintenance Gene Expression

BACKGROUND

The first stage of fracture healing consists of hematoma formation with recruitment of proinflammatory cytokines and matrix metalloproteinases. Unfortunately, when there is an intra-articular fracture, these inflammatory mediators are not retained at the fracture site, but instead, envelop the healthy cartilage of the entire joint via the synovial fluid fracture hematoma (SFFH). These inflammatory cytokines and matrix metalloproteinases are known factors in the progression of osteoarthritis and rheumatoid arthritis. Despite the known inflammatory contents of the SFFH, little research has been done on the effects of the SFFH on healthy cartilage with regard to cell death and alteration in gene expression that could lead to posttraumatic osteoarthritis (PTOA).

METHODS

SFFH was collected from 12 patients with intraarticular ankle fracture at the time of surgery. Separately, C20A4 immortalized human chondrocytes were 3-dimensionally cultured to create scaffold-free cartilage tissue analogs (CTAs) to simulate healthy cartilage. Experimental CTAs (n = 12) were exposed to 100% SFFH for 3 days, washed, and transferred to complete media for 3 days. Control CTAs (n = 12) were simultaneously cultured in complete medium without exposure to SFFH. Subsequently, CTAs were harvested and underwent biochemical, histological, and gene expression analysis.

RESULTS

Exposure of CTAs to ankle SFFH for 3 days significantly decreased chondrocyte viability by 34% (P = .027). Gene expression of both COL2A1 and SOX9 were significantly decreased after exposure to SFFH (P = .012 and P = .0013 respectively), while there was no difference in COL1A1, RUNX2, and MMP13 gene expression. Quantitative analysis of Picrosirius red staining demonstrated increased collagen I deposition with poor ultrastructural organization in SFFH-exposed CTAs.

CONCLUSION

Exposure of an organoid model of healthy cartilage tissue to SFFH after intraarticular ankle fracture resulted in decreased chondrocyte viability, decreased expression of genes regulating normal chondrocyte phenotype, and altered matrix ultrastructure indicating differentiation toward an osteoarthritis phenotype.

CLINICAL RELEVANCE

The majority of ankle fracture open reduction and internal fixation does not occur immediately after fracture. In fact, typically these fractures are treated several days to weeks later in order to let the swelling subside. This means that the healthy innocent bystander cartilage not involved in the fracture is exposed to SFFH during this time. In this study, the SFFH caused decreased chondrocyte viability and specific altered gene expression that might have the potential to induce osteoarthritis. These data suggest that early intervention after intraarticular ankle fracture could possibly mitigate progression toward PTOA.

Self-Assembly Culture Model for Engineering Musculoskeletal Tissues

The goal of a self-assembly tissue engineering is to create functional tissue following a natural cell-driven process that mirrors natural development. This approach to tissue engineering has tremendous potential for the development of reparative strategies to treat musculoskeletal injuries and diseases, especially for articular cartilage which has poor regenerative capacity. Additionally, many bioengineering and culture methods fail to maintain the chondrocyte phenotype and contain the correct matrix composition in the long term. Existing cartilage-engineering approaches have been developed, but many approaches involve complicated culture techniques and require foreign substances and biomaterials as scaffolds. While these scaffold-based approaches have numerous advantages, such as an instant or rapid creation of biomechanical properties, they frequently result in dedifferentiation of cells in part, due to the adherence to foreign scaffold materials. In this chapter, we describe a novel approach of developing a scaffold-less cartilage-like biomaterial, using the simple principle that cells at high density bear a capacity to coalesce when they cannot attach to any culture substrate. We refer to the biomaterial formed as a cartilage tissue equivalent or CTA and have published to describe their characteristics and utility in high-throughput drug screening. The method is described to generate reproducible cartilage analogs using a specialized high-density suspension culture technique using a hydrogel poly-2-hydroxyethyl methacrylate (polyHEMA) coating of a culture dish. We have demonstrated that this approach can rapidly form biomass of chondrocytes that over time becomes very synthetically active producing a cartilage-like extracellular matrix that closely mimics the biochemical and biomechanical characteristics of native articular cartilage. The culture approach can also be used to form CTA from other than articular cartilage-derived chondrocytes as well as mesenchymal stem cells (MSCs) (while differentiating MSCs into chondrocytes). Some of the advantages are phenotype stability, reproducible CTA size, and biomechanical and biochemical characteristics similar to natural cartilage.

Identifying small molecules for protecting chondrocyte function and matrix integrity after controlled compressive injury

Objective

Articular cartilage injury is central for the development of post-traumatic osteoarthritis (PTOA). With few disease-modifying therapies successful at offsetting progressive osteoarthritis (OA), our goal is to use a high throughput screening platform of cartilage injury to identify novel chondroprotective compounds. Targeting articular cartilage damage immediately after injury remains a promising therapeutic strategy to overcome irreversible tissue damage.

Method

We constructed a single impact-cartilage screening method using a multi-platen system that simultaneously impacts 48 samples and makes use of engineered cartilage tissue analogs (known as CTAs). Drug libraries were screened and assessed for their ability to alter two crucial biological responses to impact injuries, namely matrix degradation and cell stress.

Results

Over 500 small molecules were screened for their ability to alter proteoglycan loss, matrix metalloproteinase activity, and cell stress or death. Fifty-five compounds passed through secondary screening and were from commercial libraries of natural and redox, stem cell related compounds, as well as protease, kinase and phosphatase inhibitors. Through secondary screening, 16 promising candidates exhibited activity on one or more critical function of chondrocytes. While many are mechanistically known compounds, their function in joint diseases is not known.

Conclusion

This platform was validated for screening drug activity against a tissue engineered model of PTOA. Multiple compounds identified in this manner have potential application as early protective therapy for treating PTOA, and require further study. We propose this screening platform can identify novel molecules that act on early chondrocyte responses to injury and provide an invaluable tool for therapeutic development.

Stem Cells and Extrusion 3D Printing for Hyaline Cartilage Engineering

Hyaline cartilage is deficient in self-healing properties. The early treatment of focal cartilage lesions is a public health challenge to prevent long-term degradation and the occurrence of osteoarthritis. Cartilage tissue engineering represents a promising alternative to the current insufficient surgical solutions. 3D printing is a thriving technology and offers new possibilities for personalized regenerative medicine. Extrusion-based processes permit the deposition of cell-seeded bioinks, in a layer-by-layer manner, allowing mimicry of the native zonal organization of hyaline cartilage. Mesenchymal stem cells (MSCs) are a promising cell source for cartilage tissue engineering. Originally isolated from bone marrow, they can now be derived from many different cell sources (e.g., synovium, dental pulp, Wharton’s jelly). Their proliferation and differentiation potential are well characterized, and they possess good chondrogenic potential, making them appropriate candidates for cartilage reconstruction. This review summarizes the different sources, origins, and densities of MSCs used in extrusion-based bioprinting (EBB) processes, as alternatives to chondrocytes. The different bioink constituents and their advantages for producing substitutes mimicking healthy hyaline cartilage is also discussed.

Chondrocyte and mesenchymal stem cell derived engineered cartilage exhibits differential sensitivity to pro-inflammatory cytokines

Tissue engineering is a promising approach for the repair of articular cartilage defects, with engineered constructs emerging that match native tissue properties. However, the inflammatory environment of the damaged joint might compromise outcomes, and this may be impacted by the choice of cell source in terms of their ability to operate anabolically in an inflamed environment. Here, we compared the response of engineered cartilage derived from native chondrocytes and mesenchymal stem cells (MSCs) to challenge by TNFα and IL-1β in order to determine if either cell type possessed an inherent advantage. Compositional (extracellular matrix) and functional (mechanical) characteristics, as well as the release of catabolic mediators (matrix metalloproteinases [MMPs], nitric oxide [NO]) were assessed to determine cell- and tissue-level changes following exposure to IL-1β or TNF-α. Results demonstrated that MSC-derived constructs were more sensitive to inflammatory mediators than chondrocyte-derived constructs, exhibiting a greater loss of proteoglycans and functional properties at lower cytokine concentrations. While MSCs and chondrocytes both have the capacity to form functional engineered cartilage in vitro, this study suggests that the presence of an inflammatory environment is more likely to impair the in vivo success of MSC-derived cartilage repair. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2901-2910, 2018.

Scaffold-free tissue engineering for injured joint surface restoration

Articular cartilage does not heal spontaneously due to its limited healing capacity, and thus effective treatments for cartilage injuries has remained challenging. Since the first report by Brittberg et al. in 1994, autologous chondrocyte implantation (ACI) has been introduced into the clinic. Recently, as an alternative for chondrocyte-based therapy, mesenchymal stem cell (MSC)-based therapy has received considerable research attention because of the relative ease in handling for tissue harvest, and subsequent cell expansion and differentiation. In this review, we discuss the latest developments regarding stem cell-based therapies for cartilage repair, with special focus on recent scaffold-free approaches.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.

Fast fabrication of stable cartilage-like tissue using collagen hydrogel microsphere culture

Mesenchymal stem cells (MSCs) had been increasingly regarded as a potent cell source for cartilage repair. However, due to the instability of MSC-derived chondrocyte phenotype and ossification of the synthesised cartilage matrix, regenerating a stable cartilage tissue by MSCs is still challenging. The fate of chondrogenesis from MSCs is regulated by their local microenvironment, which is of vital importance to the cell behaviours, chondrogenic phenotype and matrix synthesis. In this study, we fabricated cartilage-like tissues by the chondrogenesis of MSC in three different microenvironments, including cell pellets, collagen hydrogel bulk (CHB) and collagen hydrogel microspheres (CHMs) in vitro. After 15 days in culture, the cell number was increased to 472.6% in CHMs, compared to a 58.6% decrease in CHB and a 46.6% decrease in pellets; resulting in a 230% increase in CHM size, but a 36.8% decrease in CHB and only a 20.1% increase in pellets. Histological staining demonstrated a more intensive but less homogeneous glycosaminoglycan (GAG) pattern in pellets than in CHMs. The outer area of CHB showed a stronger GAG staining than its inner area from day 5 to day 15, but the staining was weaker than that in both pellets and CHMs. The PCR results showed that CHMs achieved a significantly higher chondrogenic gene (AGG, COL2A1, SOX9) expression and a lower hypertrophic gene (COL10A1) expression than pellets and CHB, suggesting a better chondrogenic differentiation potential with a more stable phenotype in CHMs. In summary, this study highlights the advantages of CHM microenvironments over those of CHB and pellets by a better mimicking of the natural MSC proliferation process and enhancing mass exchange in vitro. The CHM culture demonstrated potential to fabricate stable cartilage-like tissue in MSC based cartilage tissue regeneration.

The Self-Assembling Process and Applications in Tissue Engineering

Tissue engineering strives to create neotissues capable of restoring function. Scaffold-free technologies have emerged that can recapitulate native tissue function without the use of an exogenous scaffold. This review will survey, in particular, the self-assembling and self-organization processes as scaffold-free techniques. Characteristics and benefits of each process are described, and key examples of tissues created using these scaffold-free processes are examined to provide guidance for future tissue-engineering developments. We aim to explore the potential of self-assembly and self-organization scaffold-free approaches, detailing the recent progress in the in vitro tissue engineering of biomimetic tissues with these methods toward generating functional tissue replacements.

Physioxia Promotes the Articular Chondrocyte-Like Phenotype in Human Chondroprogenitor-Derived Self-Organized Tissue

INTRODUCTION

Biomaterial-based tissue engineering has not successfully reproduced the structural architecture or functional mechanical properties of native articular cartilage. In scaffold-free tissue engineering systems, cells secrete and organize the entire extracellular matrix over time in response to environmental signals such as oxygen level. In this study, we investigated the effect of oxygen on the formation of neocartilage from human-derived chondrogenic cells.

MATERIALS AND METHODS

Articular chondrocytes (ACs) and articular cartilage progenitor cells (ACPs) derived from healthy human adults were guided toward cell condensation by centrifugation onto plate inserts that were uncoated or coated with either agarose or fibronectin. Neocartilage discs were cultured at hyperoxic (20%) or physioxic (5%) oxygen levels, and biochemical, biomechanical, and molecular analyses were used to compare the cartilage produced by ACs versus ACPs.

RESULTS

Fibronectin-coated inserts proved optimal for growing cartilaginous discs from both cell types. In comparison with culture in hyperoxia, AC neocartilage cultured at physioxia exhibited a significant increase in chondrogenic gene expression, proteoglycan production, and mechanical properties with a concomitant decrease in collagen content. At both oxygen levels, ACP-derived neocartilage produced tissue with significantly enhanced mechanical properties and collagen content relative to AC-derived neocartilage. Both ACs and ACPs produced substantial collagen II and reduced levels of collagens I and X in physioxia relative to hyperoxia. Neocartilage from ACPs exhibited anisotropic organization characteristic of native cartilage with respect to collagen VI of the pericellular matrix when compared with AC-derived neocartilage; however, only ACs produced abundant surface-localized lubricin.

DISCUSSION AND CONCLUSIONS

Guiding human-derived cells toward condensation and subsequent culture in physioxia promoted the articular cartilage tissue phenotype for ACs and ACPs. Unlike ACs, ACPs are clonable and highly expandable while retaining chondrogenicity. The ability to generate large tissues utilizing a scaffold-free approach from a single autologous progenitor cell may represent a promising source of neocartilage destined for cartilage repair.

* Optimization of Preculture Conditions to Maximize the In Vivo Performance of Cell-Seeded Engineered Intervertebral Discs

The development of engineered tissues has progressed over the past 20 years from in vitro characterization to in vivo implementation. For musculoskeletal tissue engineering in particular, the emphasis of many of these studies was to select conditions that maximized functional and compositional gains in vitro. However, the transition from the favorable in vitro culture environment to a less favorable in vivo environment has proven difficult, and, in many cases, engineered tissues do not retain their preimplantation phenotype after even short periods in vivo. Our laboratory recently developed disc-like angle-ply structures (DAPS), an engineered intervertebral disc for total disc replacement. In this study, we tested six different preculture media formulations (three serum-containing and three chemically defined, with varying doses of transforming growth factor β3 [TGF-β3] and varying strategies to introduce serum) for their ability to preserve DAPS composition and metabolic activity during the transition from in vitro culture to in vivo implantation in a subcutaneous athymic rat model. We assayed implants before and after implantation to determine collagen content, glycosaminoglycan (GAG) content, metabolic activity, and magnetic resonance imaging (MRI) characteristics. A chemically defined media condition that incorporated TGF-β3 promoted the deposition of GAG and collagen in DAPS in vitro, the maintenance of accumulated matrix in vivo, and minimal changes in the metabolic activity of cells within the construct. Preculture in serum-containing media (with or without TGF-β3) was not compatible with DAPS maturation, particularly in the nucleus pulposus (NP) region. All groups showed increased collagen production after implantation. These findings define a favorable preculture strategy for the translation of engineered discs seeded with disc cells.

Transplantation of a Scaffold-Free Cartilage Tissue Analogue for the Treatment of Physeal Cartilage Injury of the Proximal Tibia in Rabbits

PURPOSE

The purpose of this study was to investigate the effects of transplantation of an in vitro-generated, scaffold-free, tissue-engineered cartilage tissue analogue (CTA) using a suspension chondrocyte culture in a rabbit growth-arrest model.

MATERIALS AND METHODS

We harvested cartilage cells from the articular cartilage of the joints of white rabbits and made a CTA using a suspension culture of 2×10⁷ cells/mL. An animal growth plate defect model was made on the medial side of the proximal tibial growth plate of both tibias of 6-week-old New Zealand white rabbits (n=10). The allogenic CTA was then transplanted onto the right proximal tibial defect. As a control, no implantation was performed on the left-side defect. Plain radiographs and the medial proximal tibial angle were obtained at 1-week intervals for evaluation of bone bridge formation and the degree of angular deformity until postoperative week 6. We performed a histological evaluation using hematoxylin-eosin and Alcian blue staining at postoperative weeks 4 and 6.

RESULTS

Radiologic study revealed a median medial proximal tibial angle of 59.0° in the control group and 80.0° in the CTA group at 6 weeks. In the control group, statistically significant angular deformities were seen 3 weeks after transplantation (p<0.05). On histological examination, the transplanted CTA was maintained in the CTA group at 4 and 6 weeks postoperative. Bone bridge formation was observed in the control group.

CONCLUSION

In this study, CTA transplantation minimized deformity in the rabbit growth plate injury model, probably via the attenuation of bone bridge formation.

Self-assembly of tissue spheroids on polymeric membranes

In this study, multicellular tissue spheroids were fabricated on polymeric membranes in order to accelerate the fusion process and tissue formation. To this purpose, tissue spheroids composed of three different cell types, myoblasts, fibroblasts and neural cells, were formed and cultured on agarose and membranes of polycaprolactone (PCL) and chitosan (CHT). Membranes prepared by a phase-inversion technique display different physicochemical, mechanical and transport properties, which can affect the fusion process. The membranes accelerated the fusion process of a pair of spheroids with respect to the inert substrate. In this process, a critical role is played by the membrane properties, especially by their mechanical characteristics and oxygen and carbon dioxide mass transfer. The rate of fusion was quantified and found to be similar for fibroblast, myoblast and neural tissue spheroids on membranes, which completed the fusion within 3 days. These spheroids underwent faster fusion and maturation on PCL membrane than on agarose, the rate of fusion being proportional to the value of oxygen and carbon dioxide permeances and elastic characteristics. Consequently, tissue spheroids on the membranes expressed high biological activity in terms of oxygen uptake, making them more suitable as building blocks in the fabrication of tissues and organs. Copyright © 2015 John Wiley & Sons, Ltd.

Cartilage Tissue Engineering: What Have We Learned in Practice?

Many technologies that underpin tissue engineering as a research field were developed with the aim of producing functional human cartilage in vitro. Much of our practical experience with three-dimensional cultures, tissue bioreactors, scaffold materials, stem cells, and differentiation protocols was gained using cartilage as a model system. Despite these advances, however, generation of engineered cartilage matrix with the composition, structure, and mechanical properties of mature articular cartilage has not yet been achieved. Currently, the major obstacles to synthesis of clinically useful cartilage constructs are our inability to control differentiation to the extent needed, and the failure of engineered and host tissues to integrate after construct implantation. The aim of this chapter is to distil from the large available body of literature the seminal approaches and experimental techniques developed for cartilage tissue engineering and to identify those specific areas requiring further research effort.

A high-throughput model of post-traumatic osteoarthritis using engineered cartilage tissue analogs

OBJECTIVE

A number of in vitro models of post-traumatic osteoarthritis (PTOA) have been developed to study the effect of mechanical overload on the processes that regulate cartilage degeneration. While such frameworks are critical for the identification therapeutic targets, existing technologies are limited in their throughput capacity. Here, we validate a test platform for high-throughput mechanical injury incorporating engineered cartilage.

METHOD

We utilized a high-throughput mechanical testing platform to apply injurious compression to engineered cartilage and determined their strain and strain rate dependent responses to injury. Next, we validated this response by applying the same injury conditions to cartilage explants. Finally, we conducted a pilot screen of putative PTOA therapeutic compounds.

RESULTS

Engineered cartilage response to injury was strain dependent, with a 2-fold increase in glycosaminoglycan (GAG) loss at 75% compared to 50% strain. Extensive cell death was observed adjacent to fissures, with membrane rupture corroborated by marked increases in lactate dehydrogenase (LDH) release. Testing of established PTOA therapeutics showed that pan-caspase inhibitor [Z-VAD-FMK (ZVF)] was effective at reducing cell death, while the amphiphilic polymer [Poloxamer 188 (P188)] and the free-radical scavenger [N-Acetyl-L-cysteine (NAC)] reduced GAG loss as compared to injury alone.

CONCLUSIONS

The injury response in this engineered cartilage model replicated key features of the response of cartilage explants, validating this system for application of physiologically relevant injurious compression. This study establishes a novel tool for the discovery of mechanisms governing cartilage injury, as well as a screening platform for the identification of new molecules for the treatment of PTOA.