Differential maturation and structure-function relationships in mesenchymal stem cell- and chondrocyte-seeded hydrogels

3D printed hybrid scaffolds do not induce adverse inflammation in mice and direct human BM-MSC chondrogenesis in vitro

Biomaterials that can improve the healing of articular cartilage lesions are needed. To address this unmet need, we developed novel 3D printed silica/poly(tetrahydrofuran)/poly(ε-caprolactone) (SiO2/PTHF/PCL-diCOOH) hybrid scaffolds. Our aim was to carry out essential studies to advance this medical device towards functional validation in pre-clinical trials. First, we show that the chemical composition, microarchitecture and mechanical properties of these scaffolds were not affected by sterilisation with gamma irradiation. To evaluate the systemic and local immunogenic reactivity of the sterilised 3D printed hybrid scaffolds, they were implanted subcutaneously into Balb/c mice. The scaffolds did not trigger a systemic inflammatory response over one week of implantation. The interaction between the host immune system and the implanted scaffold elicited a local physiological reaction with infiltration of mononuclear cells without any signs of a chronic inflammatory response. Then, we investigated how these 3D printed hybrid scaffolds direct chondrogenesis in vitro. Human bone marrow-derived mesenchymal stem/stromal cells (hBM-MSCs) seeded within the 3D printed hybrid scaffolds were cultured under normoxic or hypoxic conditions, with or without chondrogenic supplements. Chondrogenic differentiation assessed by both gene expression and protein production analyses showed that 3D printed hybrid scaffolds support hBM-MSC chondrogenesis. Articular cartilage-specific extracellular matrix deposition within these scaffolds was enhanced under hypoxic conditions (1.7 or 3.7 fold increase in the median of aggrecan production in basal or chondrogenic differentiation media). Our findings show that 3D printed SiO2/PTHF/PCL-diCOOH hybrid scaffolds have the potential to support the regeneration of cartilage tissue.

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.

Agarose Gel: An Overview of the Dermal Filler and a Clinical Experience With 700 Patients

Background

Dermal fillers currently in the market have several advantages and disadvantages over each other. Agarose gel (AG) is a unique material due to its special rheological characteristics and gel-forming capability.

Objectives

The authors aimed to share their clinical experience on AG for a variety of facial augmentation procedures and its long-term results.

Methods

The study population consisted of 700 patients (532 females; 168 males) aged 18 to 52 years. Follow-up visits were at 1, 3, 6, 12, and 24 months after the injections. Patient satisfaction was evaluated on a scale from 0 to 10 using a survey and clinical improvement was evaluated using the Global Aesthetic Improvement Scale (GAIS) by 2 independent plastic surgeons before the injection and at 1-year follow-up.

Results

Eighty-two percent of the patients scored 1 or 2 (exceptional or great improvement) on GAIS. Eighty-five percent of the patients scored 8 or above (very satisfied). Most patients experienced at least 80% persistence of effect at 1-year follow-up.

Conclusions

AG appears to be suitable for a variety of facial augmentation and contouring applications, as it is safe and has long-lasting favorable cosmetic efficacy.

Level of Evidence 3

Applied Compressive Strain Governs Hyaline-like Cartilage versus Fibrocartilage-like ECM Produced within Hydrogel Constructs

The goal of cartilage tissue engineering (CTE) is to regenerate new hyaline cartilage in joints and treat osteoarthritis (OA) using cell-impregnated hydrogel constructs. However, the production of an extracellular matrix (ECM) made of fibrocartilage is a potential outcome within hydrogel constructs when in vivo. Unfortunately, this fibrocartilage ECM has inferior biological and mechanical properties when compared to native hyaline cartilage. It was hypothesized that compressive forces stimulate fibrocartilage development by increasing production of collagen type 1 (Col1), an ECM protein found in fibrocartilage. To test the hypothesis, 3-dimensional (3D)-bioprinted hydrogel constructs were fabricated from alginate hydrogel impregnated with ATDC5 cells (a chondrogenic cell line). A bioreactor was used to simulate different in vivo joint movements by varying the magnitude of compressive strains and compare them with a control group that was not loaded. Chondrogenic differentiation of the cells in loaded and unloaded conditions was confirmed by deposition of cartilage specific molecules including glycosaminoglycans (GAGs) and collagen type 2 (Col2). By performing biochemical assays, the production of GAGs and total collagen was also confirmed, and their contents were quantitated in unloaded and loaded conditions. Furthermore, Col1 vs. Col2 depositions were assessed at different compressive strains, and hyaline-like cartilage vs. fibrocartilage-like ECM production was analyzed to investigate how applied compressive strain affects the type of cartilage formed. These assessments showed that fibrocartilage-like ECM production tended to reduce with increasing compressive strain, though its production peaked at a higher compressive strain. According to these results, the magnitude of applied compressive strain governs the production of hyaline-like cartilage vs. fibrocartilage-like ECM and a high compressive strain stimulates fibrocartilage-like ECM formation rather than hyaline cartilage, which needs to be addressed by CTE approaches.

Matching mechanical heterogeneity of the native spinal cord augments axon infiltration in 3D-printed scaffolds

Scaffolds delivered to injured spinal cords to stimulate axon connectivity often match the anisotropy of native tissue using guidance cues along the rostral-caudal axis, but current approaches do not mimic the heterogeneity of host tissue mechanics. Although white and gray matter have different mechanical properties, it remains unclear whether tissue mechanics also vary along the length of the cord. Mechanical testing performed in this study indicates that bulk spinal cord mechanics do differ along anatomical level and that these differences are caused by variations in the ratio of white and gray matter. These results suggest that scaffolds recreating the heterogeneity of spinal cord tissue mechanics must account for the disparity between gray and white matter. Digital light processing (DLP) provides a means to mimic spinal cord topology, but has previously been limited to printing homogeneous mechanical properties. We describe a means to modify DLP to print scaffolds that mimic spinal cord mechanical heterogeneity caused by variation in the ratio of white and gray matter, which improves axon infiltration compared to controls exhibiting homogeneous mechanical properties. These results demonstrate that scaffolds matching the mechanical heterogeneity of white and gray matter improve the effectiveness of biomaterials transplanted within the injured spinal cord.

Protein-engineered biomaterials for cartilage therapeutics and repair

Cartilage degeneration and injury are major causes of pain and disability that effect millions, and yet treatment options for conditions like osteoarthritis (OA) continue to be mainly palliative or involve complete replacement of injured joints. Several biomaterial strategies have been explored to address cartilage repair either by the delivery of therapeutics or as support for tissue repair, however the complex structure of cartilage tissue, its mechanical needs, and lack of regenerative capacity have hindered this goal. Recent advances in synthetic biology have opened new possibilities for engineered proteins to address these unique needs. Engineered protein and peptide-based materials benefit from inherent biocompatibility and nearly unlimited tunability as they utilize the body's natural building blocks to fabricate a variety of supramolecular structures. The pathophysiology and needs of OA cartilage are presented here, along with an overview of the current state of the art and next steps for protein-engineered repair strategies for cartilage.

Non-hypertrophic chondrogenesis of mesenchymal stem cells through mechano-hypoxia programing

Cartilage tissue engineering aims to generate functional replacements to treat cartilage defects from damage and osteoarthritis. Human bone marrow-derived mesenchymal stem cells (hBM-MSC) are a promising cell source for making cartilage, but current differentiation protocols require the supplementation of growth factors like TGF-β1 or -β3. This can lead to undesirable hypertrophic differentiation of hBM-MSC that progress to bone. We have found previously that exposing engineered human meniscus tissues to physiologically relevant conditions of the knee (mechanical loading and hypoxia; hence, mechano-hypoxia conditioning) increased the gene expression of hyaline cartilage markers, SOX9 and COL2A1, inhibited hypertrophic marker COL10A1, and promoted bulk mechanical property development. Adding further to this protocol, we hypothesize that combined mechano-hypoxia conditioning with TGF-β3 growth factor withdrawal will promote stable, non-hypertrophic chondrogenesis of hBM-MSC embedded in an HA-hydrogel. We found that the combined treatment upregulated many cartilage matrix- and development-related markers while suppressing many hypertrophic- and bone development-related markers. Tissue level assessments with biochemical assays, immunofluorescence, and histochemical staining confirmed the gene expression data. Further, mechanical property development in the dynamic compression treatment shows promise toward generating functional engineered cartilage through more optimized and longer culture conditions. In summary, this study introduced a novel protocol to differentiate hBM-MSC into stable, cartilage-forming cells.

Physioxic Culture of Chondrogenic Cells

Cartilage resides under a low oxygen tension within articulating joints. The oxygen tension within cartilage of the knee joint has been measured to be between 2% and 5% oxygen. Although the literature has historically termed this level of oxygen as hypoxia, particularly when doing experiments in vitro in this range, this is actually the physiological oxygen tension experienced in vivo and is more accurately termed physioxia. In general, culture of chondrogenic cells under physioxia has demonstrated a donor-dependent beneficial effect on chondrogenesis, with an upregulation in cartilage genes (SOX9, COL2A1, ACAN) and matrix deposition (sulfated glycosaminoglycans (sGAGs), collagen II). Physioxia also reduces the expression of hypertrophic markers (COL10A1, MMP13). This chapter will outline the methods for the expansion and differentiation of chondrogenic cells under physioxia using oxygen-controlled incubators and glove box environments, with the typical assays used for qualitative and quantitative assessment of chondrogenesis.

Regional-specific meniscal extracellular matrix hydrogels and their effects on cell-matrix interactions of fibrochondrocytes

Decellularized meniscal extracellular matrix (ECM) material holds great potential for meniscus repair and regeneration. Particularly, injectable ECM hydrogel is highly desirable for the minimally invasive treatment of irregularly shaped defects. Although regional-specific variations of the meniscus are well documented, no ECM hydrogel has been reported to simulate zonally specific microenvironments of the native meniscus. To fill the gap, different (outer, middle, and inner) zones of porcine menisci were separately decellularized. Then the regionally decellularized meniscal ECMs were solubilized by pepsin digestion, neutralized, and then form injectable hydrogels. The hydrogels were characterized in gelation behaviors and mechanical properties and seeded with bovine fibrochondrocytes to evaluate the regionally biochemical effects on the cell-matrix interactions. Our results showed that the decellularized inner meniscal ECM (IM) contained the greatest glycosaminoglycan (GAG) content and the least collagen content compared with the decellularized outer meniscal ECM (OM) and middle meniscal ECM (MM). The IM hydrogel showed lower compressive strength than the OM hydrogel. When encapsulated with fibrochondrocytes, the IM hydrogel accumulated more GAG, contracted to a greater extent and reached higher compressive strength than that of the OM hydrogel at 28 days. Our findings demonstrate that the regionally specific meniscal ECMs present biochemical variation and show various effects on the cell behaviors, thus providing information on how meniscal ECM hydrogels may be utilized to reconstruct the microenvironments of the native meniscus.

Biomaterial-mediated presentation of wnt5a mimetic ligands enhances chondrogenesis and metabolism of stem cells by activating non-canonical Wnt signaling

The presentation of development-relevant bioactive cues by biomaterial scaffolds is essential to the guided differentiation of seeded human mesenchymal stem cells (hMSCs) and subsequent tissue regeneration. Wnt5a is a critical non-canonical Wnt signaling ligand and plays a key role in the development of musculoskeletal tissues including cartilage. Herein we investigate the efficacy of biofunctionalizing the hyaluronic acid hydrogel with a synthetic Wnt5a mimetic ligand (Foxy5 peptide) to promote the chondrogenesis of hMSCs and the potential underlying molecular mechanism. Our findings show that the conjugation of Foxy5 peptide in the hydrogels activates non-canonical Wnt signaling of encapsulated hMSCs via the upregulation expression of PLCE1, CaMKII-β, and downstream NFATc1, leading to enhanced expression of chondrogenic markers such as SOX9. The decoration of Foxy5 peptide also promotes the metabolic activities of encapsulated hMSCs as evidenced by upregulated gene expression of mitochondrial complex components and glucose metabolism biomarkers, leading to enhanced ATP biosynthesis. Furthermore, the conjugation of Foxy5 peptide activates the non-canonical Wnt, PI3K-PDK-AKT and IKK/NF-κB signaling pathways, thereby inhibiting the hypertrophy of the chondrogenically induced hMSCs in the hydrogels under both in vitro and in vivo conditions. This enhanced chondrogenesis and attenuated hypertrophy of hMSCs by the biomaterial-mediated bioactive cue presentation facilitates the potential clinical translation of hMSCs for cartilage regeneration. Our work provides valuable guidance to the rational design of bio-inductive scaffolds for various applications in regenerative medicine.

Metabolic Labeling to Probe the Spatiotemporal Accumulation of Matrix at the Chondrocyte-Hydrogel Interface

Hydrogels are engineered with biochemical and biophysical signals to recreate aspects of the native microenvironment and to control cellular functions such as differentiation and matrix deposition. This deposited matrix accumulates within the pericellular space and likely affects the interactions between encapsulated cells and the engineered hydrogel; however, there has been little work to study the spatiotemporal evolution of matrix at this interface. To address this, metabolic labeling is employed to visualize the temporal and spatial positioning of nascent proteins and proteoglycans deposited by chondrocytes. Within covalently crosslinked hyaluronic acid hydrogels, chondrocytes deposit nascent proteins and proteoglycans in the pericellular space within 1 d after encapsulation. The accumulation of this matrix, as measured by an increase in matrix thickness during culture, depends on the initial hydrogel crosslink density with decreased thicknesses for more crosslinked hydrogels. Encapsulated fluorescent beads are used to monitor the hydrogel location and indicate that the emerging nascent matrix physically displaces the hydrogel from the cell membrane with extended culture. These findings suggest that secreted matrix increasingly masks the presentation of engineered hydrogel cues and may have implications for the design of hydrogels in tissue engineering and regenerative medicine.

In situ ornamenting poly(ε-caprolactone) electrospun fibers with different fiber diameters using chondrocyte-derived extracellular matrix for chondrogenesis of mesenchymal stem cells

Biomimetic instructive tissue engineering scaffolds are critical for achieving successful tissue regeneration. In the present study, we developed a novel scaffold via ornamenting poly(ε-caprolactone) (PCL) electrospun fibers with a chondrocyte-derived extracellular matrix (ECM)-coating, which was applied for chondrogenesis of mesenchymal stem cells (MSCs). PCL fibrous films with different fiber diameters (1282±121 nm, 549±61 nm and 285±38 nm) were first prepared via electrospinning. Rabbit articular chondrocytes (rACs) were cultured on PCL fibrous scaffolds, followed by a decellularization treatment to generate decellularized ECM (dECM)-coated PCL scaffolds (dECM/PCL). Rabbit bone marrow-derived MSCs (rMSCs) were then seeded onto these scaffolds and adhesion, proliferation and chondrogenic differentiation were evaluated. dECM/PCL scaffolds displayed distinct surface microstructural features with varying fiber diameters and fibrous mesh-like ECM with more developed collagen fibers was observed on nanofibers. On dECM/PCL scaffolds, rMSCs tended to spread more at 24 h post-seeding and proliferated better within 7 d compared to those on uncoated PCL scaffolds. Based on analysis of gene expression, rMSCs underwent the best chondrogenic differentiation on dECM/PCL scaffolds of 549-nm fibers. Collectively, such dECM/PCL composite scaffolds are very promising for cartilage tissue regeneration.

Multiscale mechanics of tissue-engineered cartilage grown from human chondrocytes and human-induced pluripotent stem cells

Tissue-engineered cartilage has shown promising results in the repair of focal cartilage defects. However, current clinical techniques rely on an extra surgical procedure to biopsy healthy cartilage to obtain human chondrocytes. Alternatively, induced pluripotent stem cells (iPSCs) have the ability to differentiate into chondrocytes and produce cartilaginous matrix without the need to biopsy healthy cartilage. However, the mechanical properties of tissue-engineered cartilage with iPSCs are unknown and might be critical to long-term tissue function and health. This study used confined compression, cartilage on glass tribology, and shear testing on a confocal microscope to assess the macroscale and microscale mechanical properties of two constructs seeded with either chondrocyte-derived iPSCs (Ch-iPSCs) or native human chondrocytes. Macroscale properties of Ch-iPSC constructs provided similar or better mechanical properties than chondrocyte constructs. Under compression, Ch-iPSC constructs had an aggregate modulus that was two times larger than chondrocyte constructs and was closer to native tissue. No differences in the shear modulus and friction coefficients were observed between Ch-iPSC and chondrocyte constructs. On the microscale, Ch-iPSC and chondrocyte constructs had different depth-dependent mechanical properties, neither of which matches native tissue. These observed depth-dependent differences may be important to the function of the implant. Overall, this comparison of multiple mechanical properties of Ch-iPSC and chondrocyte constructs shows that using Ch-iPSCs can produce equivalent or better global mechanical properties to chondrocytes. Therefore, iPSC-seeded cartilage constructs could be a promising solution to repair focal cartilage defects. The chondrocyte constructs used in this study have been implanted into humans for clinical trials. Therefore, Ch-iPSC constructs could also be used clinically in place of the current chondrocyte construct.

Restoration of cartilage defects using a superparamagnetic iron oxide-labeled adipose-derived mesenchymal stem cell and TGF-β3-loaded bilayer PLGA construct

Aim: We aimed to evaluate the capacity of the bilayer polylactic-co-glycolic acid (PLGA)/TGF-β3/adipose-derived mesenchymal stem cell (ADSC) construct used to repair cartilage defects and the role of ADSCs in the repair process in vivo. Materials & methods: Defects were created surgically on the femoropatellar groove of knee joints in 64 rabbits. All the rabbits were randomly divided into four groups: defect group, PLGA group, PLGA/TGF-β3 group and PLGA/TGF-β3/ADSC group. In vivo MRI and Prussian blue staining were applied. Quantitative real-time PCR and western blot methods were used to analyze the gene and protein expression. Results & conclusion: The result showed that TGF-β3 could effectively stimulate the expressions of aggrecan, collagen type II and SRY-related HMG box 9 (SOX9). The bilayer PLGA/TGF-β3/ADSC construct showed a promising repair effect.

Biomimetic Cell-Laden MeHA Hydrogels for the Regeneration of Cartilage Tissue

Methacrylated hyaluronic acid (MeHA) and chondroitin sulfate (CS)-biofunctionalized MeHA (CS-MeHA), were crosslinked in the presence of a matrix metalloproteinase 7 (MMP7)-sensitive peptide. The synthesized hydrogels were embedded with either human mesenchymal stem cells (hMSCs) or chondrocytes, at low concentrations, and subsequently cultured in a stem cell medium (SCM) or chondrogenic induction medium (CiM). The pivotal role of the synthesized hydrogels in promoting the expression of cartilage-related genes and the formation of neocartilage tissue despite the low concentration of encapsulated cells was assessed. It was found that hMSC-laden MeHA hydrogels cultured in an expansion medium exhibited a significant increase in the expression of chondrogenic markers compared to hMSCs cultured on a tissue culture polystyrene plate (TCPS). This favorable outcome was further enhanced for hMSC-laden CS-MeHA hydrogels, indicating the positive effect of the glycosaminoglycan binding peptide on the differentiation of hMSCs towards a chondrogenic phenotype. However, it was shown that an induction medium is necessary to achieve full span chondrogenesis. Finally, the histological analysis of chondrocyte-laden MeHA hydrogels cultured on an ex vivo osteochondral platform revealed the deposition of glycosaminoglycans (GAGs) and the arrangement of chondrocyte clusters in isogenous groups, which is characteristic of hyaline cartilage morphology.

Bone Marrow Aspirate Concentrate: Its Uses in Osteoarthritis

Human bone marrow (BM) is a kind of source of mesenchymal stem cells (MSCs) as well as growth factors and cytokines that may aid anti-inflammation and regeneration for various tissues, including cartilage and bone. However, since MSCs in BM usually occupy only a small fraction (0.001%) of nucleated cells, bone marrow aspirate concentrate (BMAC) for cartilage pathologies, such as cartilage degeneration, defect, and osteoarthritis, have gained considerable recognition in the last few years due to its potential benefits including disease modifying and regenerative capacity. Although further research with well-designed, randomized, controlled clinical trials is needed to elucidate the exact mechanism of BMAC, this may have the most noteworthy effect in patients with osteoarthritis. The purpose of this article is to review the general characteristics of BMAC, including its constituent, action mechanisms, and related issues. Moreover, this article aims to summarize the clinical outcomes of BMAC reported to date.

Heterogeneous matrix deposition in human tissue engineered cartilage changes the local shear modulus and resistance to local construct buckling

Human tissue engineered cartilage is a promising solution for focal cartilage defects, but these constructs do not have the same local mechanical properties as native tissue. Most clinically relevant engineered cartilage constructs seed human chondrocytes onto a collagen scaffold, which buckles at low loads and strains. This buckling creates local regions of high strain that could cause cell death and damage the engineered tissue. Since human tissue engineered cartilage is commonly grown in-vivo prior to implantation, new matrix deposition could improve the local implant mechanics and prevent local tissue buckling. However, the relationship between local biochemical composition and the local mechanics or local buckling probability has never been quantified. Therefore, this study correlated the local biochemical composition of human tissue engineered cartilage constructs using Fourier transform infrared spectroscopy (FTIR) with the local shear modulus and local buckling probability. The local shear modulus and local buckling probability were obtained using a confocal elastography technique. The local shear modulus increased with increases in local aggrecan content in the interior region (inside the scaffold). A minimum amount of aggrecan was required to prevent local construct buckling at physiologic strains. Since the original scaffold was primarily composed of collagen, increases in collagen content due to new matrix deposition was minimal and had little effect on the mechanical properties. Thus, we concluded that aggrecan deposition inside the scaffold pores is the most effective way to improve the mechanical function and prevent local tissue damage in human tissue engineered cartilage constructs.

The Use of Nanomaterials in Tissue Engineering for Cartilage Regeneration; Current Approaches and Future Perspectives

The repair and regeneration of articular cartilage represent important challenges for orthopedic investigators and surgeons worldwide due to its avascular, aneural structure, cellular arrangement, and dense extracellular structure. Although abundant efforts have been paid to provide tissue-engineered grafts, the use of therapeutically cell-based options for repairing cartilage remains unsolved in the clinic. Merging a clinical perspective with recent progress in nanotechnology can be helpful for developing efficient cartilage replacements. Nanomaterials, < 100 nm structural elements, can control different properties of materials by collecting them at nanometric sizes. The integration of nanomaterials holds promise in developing scaffolds that better simulate the extracellular matrix (ECM) environment of cartilage to enhance the interaction of scaffold with the cells and improve the functionality of the engineered-tissue construct. This technology not only can be used for the healing of focal defects but can also be used for extensive osteoarthritic degenerative alterations in the joint. In this review paper, we will emphasize the recent investigations of articular cartilage repair/regeneration via biomaterials. Also, the application of novel technologies and materials is discussed.

Microribbon-hydrogel composite scaffold accelerates cartilage regeneration in vivo with enhanced mechanical properties using mixed stem cells and chondrocytes

Juvenile chondrocytes are robust in regenerating articular cartilage, but their clinical application is hindered by donor scarcity. Stem cells offer an abundant autologous cell source but are limited by slow cartilage deposition with poor mechanical properties. Using 3D co-culture models, mixing stem cells and chondrocytes can induce synergistic cartilage regeneration. However, the resulting cartilage tissue still suffers from poor mechanical properties after prolonged culture. Here we report a microribbon/hydrogel composite scaffold that supports synergistic interactions using co-culture of adipose-derived stem cells (ADSCs) and neonatal chondrocytes (NChons). The composite scaffold is comprised of a macroporous, gelatin microribbon (μRB) scaffolds filled with degradable nanoporous chondroitin sulfate (CS) hydrogel. We identified an optimal CS concentration (6%) that best supported co-culture synergy in vitro. Furthermore, 7 days of TGF-β3 exposure was sufficient to induce catalyzed cartilage formation. When implanted in vivo, μRB/CS composite scaffold supported over a 40-fold increase in compressive moduli of cartilage produced by mixed ADSCs/NChons to ~330 kPa, which surpassed even the quality of cartilage produced by 100% NChons. Together, these results validate μRB/CS composite as a promising scaffold for cartilage regeneration using mixed populations of stem cells and chondrocytes.

Enhancement of the chondrogenic differentiation of mesenchymal stem cells and cartilage repair by ghrelin

Transforming growth factor beta (TGF-β) is commonly utilized in chondrogenic differentiation protocols, but this often results in incomplete maturation of the derived chondrocytes. Gene expression analysis, quantitation of sulfated glycosaminoglycan and collagen, and histological staining were performed to assess the effects of ghrelin. The signaling pathways involved were investigated with inhibitors or targeted by shRNAs. Joint cavity delivery of TGF-β with or without ghrelin, within a rat cartilage defect model was performed to evaluate the in vivo effects of ghrelin. Ghrelin dramatically enhanced gene expression levels of SOX9, ACAN, and COL II and resulted in increased synthesis of sulfated glycosaminoglycan (sGAG) and collagen in vitro. Combined treatment with TGF-β and ghrelin synergistically enhanced the phosphorylation of ERK1/2 and DMNT3A, which accounted for increased expression of chondrogenic genes. Delivery of ghrelin in combination with TGF-β after MSC implantation within a rat osteochondral defect model significantly enhanced de novo cartilage regeneration, as compared to delivery with TGF-β alone. In conclusion, ghrelin could significantly enhance MSC chondrogenic differentiation in vitro and can also enhance cartilage regeneration in vivo when used in combination with TGF-β. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1387-1397, 2019.

Bone Tissue Engineering in a Perfusion Bioreactor Using Dexamethasone-Loaded Peptide Hydrogel

The main goal of this study was the formation of bone tissue using dexamethasone (DEX)-loaded [COCH₃]-RADARADARADARADA-[CONH₂] (RADA 16-I) scaffold that has the ability to release optimal DEX concentration under perfusion force. Bone-marrow samples were collected from three patients during a hip arthroplasty. Human mesenchymal stem cells (hMSCs) were isolated and propagated in vitro in order to be seeded on scaffolds made of DEX-loaded RADA 16-I hydrogel in a perfusion bioreactor. DEX concentrations were as follows: 4 × 10^-3, 4 × 10^-4 and 4 × 10^-5 M. After 21 days in a perfusion bioreactor, tissue was analyzed by scanning electron microscopy (SEM) and histology. Markers of osteogenic differentiation were quantified by real-time polymerase chain reaction (RT-PCR) and immunocytochemistry. Minerals were quantified and detected by the von Kossa method. In addition, DEX release from the scaffold in a perfusion bioreactor was assessed. The osteoblast differentiation was confirmed by the expression analysis of osteoblast-related genes (alkaline phosphatase (ALP), collagen I (COL1A1) and osteocalcin (OC). The hematoxylin/eosin staining confirmed the presence of cells and connective tissue, while SEM revealed morphological characteristics of cells, extracellular matrix and minerals-three main components of mature bone tissue. Immunocytochemical detection of collagen I is in concordance with given results, supporting the conclusion that scaffold with DEX concentration of 4 × 10^-4 M has the optimal engineered tissue morphology. The best-engineered bone tissue is produced on scaffold loaded with 4 × 10^-4 M DEX with a perfusion rate of 0.1 mL/min for 21 days. Differentiation of hMSCs on DEX-loaded RADA 16-I scaffold under perfusion force has a high potential for application in regenerative orthopedics.

FADD-deficient mouse embryonic fibroblasts undergo RIPK1-dependent apoptosis and autophagy after NB-UVB irradiation

Sun or therapy-related ultraviolet B (UVB) irradiation induces different cell death modalities such as apoptosis, necrosis/necroptosis and autophagy. Understanding of mechanisms implicated in regulation and execution of cell death program is imperative for prevention and treatment of skin diseases. An essential component of death-inducing complex is Fas-associated protein with death domain (FADD), involved in conduction of death signals of different death modalities. The purpose of this study was to enlighten the role of FADD in the selection of cell death mode after narrow-band UVB (NB-UVB) irradiation using specific cell death inhibitors (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]- fluoromethylketone (zVAD-fmk), Necrostatin-1 and 3-Methyladenine) and FADD-deficient (FADD^-/-) mouse embryonic fibroblasts (MEFs) and their wild type (wt) counterparts. The results imply that lack of FADD sensitized MEFs to induction of receptor-interacting protein 1 (RIPK1)-dependent apoptosis by the generation of reactive oxygen species (ROS), but without activation of the proteins p53, Bax and Bcl-2 as well as without the enrolment of calpain-2. Autophagy was established as a contributing factor to NB-UVB-induced death execution. By contrast, wt cells triggered intrinsic apoptotic pathway that was resistant to the inhibition by zVAD-fmk and Necrostatin-1 pointing to the mechanism overcoming the cell survival. These findings support the role of FADD in prevention of autophagy-dependent apoptosis.

Combination of bioactive factors and IEIK13 self-assembling peptide hydrogel promotes cartilage matrix production by human nasal chondrocytes

Nasal reconstruction remains a challenge for every reconstructive surgeon. Alloplastic implants are proposed to repair nasal cartilaginous defects but they are often associated with high rates of extrusion and infection and poor biocompatibility. In this context, a porous polymeric scaffold filled with an autologous cartilage gel would be advantageous. In this study, we evaluated the capacity of IEIK13 self-assembling peptide (SAP) to serve as support to form such cartilage gel. Human nasal chondrocytes (HNC) were first amplified with FGF-2 and insulin, and then redifferentiated in IEIK13 with BMP-2, insulin, and T3 (BIT). Our results demonstrate that IEIK13 fosters HNC growth and survival. HNC phenotype was assessed by RT-PCR analysis and neo-synthesized extracellular matrix was characterized by western blotting and immunohistochemistry analysis. BIT-treated cells embedded in IEIK13 displayed round morphology and expressed cartilage-specific markers such as type II and type IX collagens and aggrecan. In addition, we did not detect significant production of type I and type X collagens and gene products of dedifferentiated and hypertrophic chondrocytes that are unwanted in hyaline cartilage. The whole of these results indicates that the SAP IEIK13 represents a suitable support for hydrogel-based tissue engineering of nasal cartilage. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 893-903, 2019.

Long-term mechanical function and integration of an implanted tissue-engineered intervertebral disc

Tissue engineering holds great promise for the treatment of advanced intervertebral disc degeneration. However, assessment of in vivo integration and mechanical function of tissue-engineered disc replacements over the long term, in large animal models, will be necessary to advance clinical translation. To that end, we developed tissue-engineered, endplate-modified disc-like angle ply structures (eDAPS) sized for the rat caudal and goat cervical spines that recapitulate the hierarchical structure of the native disc. Here, we demonstrate functional maturation and integration of these eDAPS in a rat caudal disc replacement model, with compressive mechanical properties reaching native values after 20 weeks in vivo and evidence of functional integration under physiological loads. To further this therapy toward clinical translation, we implanted eDAPS sized for the human cervical disc space in a goat cervical disc replacement model. Our results demonstrate maintenance of eDAPS composition and structure up to 8 weeks in vivo in the goat cervical disc space and maturation of compressive mechanical properties to match native levels. These results demonstrate the translational feasibility of disc replacement with a tissue-engineered construct for the treatment of advanced disc degeneration.

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.

Increased recruitment of endogenous stem cells and chondrogenic differentiation by a composite scaffold containing bone marrow homing peptide for cartilage regeneration

Even small cartilage defects could finally degenerate to osteoarthritis if left untreated, owing to the poor self-healing ability of articular cartilage. Stem cell transplantation has been well implemented as a common approach in cartilage tissue engineering but has technical complexity and safety concerns. The stem cell homing-based technique emerged as an alternative promising therapy for cartilage repair to overcome traditional limitations. In this study, we constructed a composite hydrogel scaffold by combining an oriented acellular cartilage matrix (ACM) with a bone marrow homing peptide (BMHP)-functionalized self-assembling peptide (SAP). We hypothesized that increased recruitment of endogenous stem cells by the composite scaffold could enhance cartilage regeneration. Methods: To test our hypothesis, in vitro proliferation, attachment and chondrogenic differentiation of rabbit mesenchymal stem cells (MSCs) were tested to confirm the bioactivities of the functionalized peptide hydrogel. The composite scaffold was then implanted into full-thickness cartilage defects on rabbit knee joints for cartilage repair, in comparison with microfracture or other sample groups. Stem cell recruitment was monitored by dual labeling with CD29 and CD90 under confocal microcopy at 1 week after implantation, followed by chondrogenic differentiation examined by qRT-PCR. Repaired tissue of the cartilage defects was evaluated by histological and immunohistochemistry staining, microcomputed tomography (micro-CT) and magnetic resonance imaging (MRI) at 3 and 6 months post-surgery. Macroscopic and histological scoring was done to evaluate the optimal in vivo repair outcomes of this composite scaffold. Results: The functionalized SAP hydrogels could stimulate rabbit MSC proliferation, attachment and chondrogenic differentiation during in vitro culture. At 7 days after implantation, increased recruitment of MSCs based on CD29+ /CD90+ double-positive cells was found in vivo in the composite hydrogel scaffold, as well as upregulation of cartilage-associated genes (aggrecan, Sox9 and type II collagen). After 3 and 6 months post-surgery, the articular cartilage defect in the composite scaffold-treated group was fully covered with cartilage-like tissue with a smooth surface, which was similar to the surrounding native cartilage, according to the results of histological and immunohistochemistry staining, micro-CT and MRI analysis. Macroscopic and histological scoring confirmed that the quality of cartilage repair was significantly improved with implantation of the composite scaffold at each timepoint, in comparison with microfracture or other sample groups. Conclusion: Our findings demonstrated that the composite scaffold could enhance endogenous stem cell homing and chondrogenic differentiation and significantly improve the therapeutic outcome of chondral defects. The present study provides a promising approach for in vivo cartilage repair without cell transplantation. Optimization of this strategy may offer great potential and benefits for clinical application in the future.

Icariin promotes stable chondrogenic differentiation of bone marrow mesenchymal stem cells in self‑assembling peptide nanofiber hydrogel scaffolds

Icariin, a traditional Chinese medicine, has previously been demonstrated to promote chondrogenesis of bone marrow mesenchymal stem cells (BMSCs) in traditional 2D cell culture. The present study investigated whether icariin has the potential to promote stable chondrogenic differentiation of BMSCs without hypertrophy in a 3D microenvironment. BMSCs were cultivated in a self-assembling peptide nanofiber hydrogel scaffold in chondrogenic medium for 3 weeks. Icariin was added to the medium throughout the culture period at concentrations of 1×10⁻⁶ M. Chondrogenic differentiation markers, including collagen II and SRY-type high mobility group box 9 (SOX9) were detected by immunofluorescence, reverse transcription-quantitative polymerase chain reaction and toluidine blue staining. Hypertrophic differentiation was further assessed by detecting collagen X and collagen I gene expression levels and alkaline phosphatase activity. The results demonstrated that icariin significantly enhanced cartilage extracellular matrix synthesis and gene expression levels of collagen II and SOX9, and additionally promoted more chondrocyte-like rounded morphology in BMSCs. Furthermore, chondrogenic medium led to hypertrophic differentiation via upregulation of collagen X and collagen I gene expression levels and alkaline phosphatase activity, which was not potentiated by icariin. In conclusion, these results suggested that icariin treatment may promote chondrogenic differentiation of BMSCs, and inhibit the side effect of growth factor activity, thus preventing further hypertrophic differentiation. Therefore, icariin may be a potential compound for cartilage tissue engineering.

Engineering large cartilage tissues using dynamic bioreactor culture at defined oxygen conditions

Mesenchymal stem cells maintained in appropriate culture conditions are capable of producing robust cartilage tissue. However, gradients in nutrient availability that arise during three-dimensional culture can result in the development of spatially inhomogeneous cartilage tissues with core regions devoid of matrix. Previous attempts at developing dynamic culture systems to overcome these limitations have reported suppression of mesenchymal stem cell chondrogenesis compared to static conditions. We hypothesize that by modulating oxygen availability during bioreactor culture, it is possible to engineer cartilage tissues of scale. The objective of this study was to determine whether dynamic bioreactor culture, at defined oxygen conditions, could facilitate the development of large, spatially homogeneous cartilage tissues using mesenchymal stem cell laden hydrogels. A dynamic culture regime was directly compared to static conditions for its capacity to support chondrogenesis of mesenchymal stem cells in both small and large alginate hydrogels. The influence of external oxygen tension on the response to the dynamic culture conditions was explored by performing the experiment at 20% O₂ and 3% O₂. At 20% O₂, dynamic culture significantly suppressed chondrogenesis in engineered tissues of all sizes. In contrast, at 3% O₂ dynamic culture significantly enhanced the distribution and amount of cartilage matrix components (sulphated glycosaminoglycan and collagen II) in larger constructs compared to static conditions. Taken together, these results demonstrate that dynamic culture regimes that provide adequate nutrient availability and a low oxygen environment can be employed to engineer large homogeneous cartilage tissues. Such culture systems could facilitate the scaling up of cartilage tissue engineering strategies towards clinically relevant dimensions.

Mimetic Hierarchical Approaches for Osteochondral Tissue Engineering

In order to engineer biomimetic osteochondral (OC) construct, it is necessary to address both the cartilage and bone phase of the construct, as well as the interface between them, in effect mimicking the developmental processes when generating hierarchical scaffolds that show gradual changes of physical and mechanical properties, ideally complemented with the biochemical gradients. There are several components whose characteristics need to be taken into account in such biomimetic approach, including cells, scaffolds, bioreactors as well as various developmental processes such as mesenchymal condensation and vascularization, that need to be stimulated through the use of growth factors, mechanical stimulation, purinergic signaling, low oxygen conditioning, and immunomodulation. This chapter gives overview of these biomimetic OC system components, including the OC interface, as well as various methods of fabrication utilized in OC biomimetic tissue engineering (TE) of gradient scaffolds. Special attention is given to addressing the issue of achieving clinical size, anatomically shaped constructs. Besides such neotissue engineering for potential clinical use, other applications of biomimetic OC TE including formation of the OC tissues to be used as high-fidelity disease/healing models and as in vitro models for drug toxicity/efficacy evaluation are covered.

HIGHLIGHTS

Biomimetic OC TE uses "smart" scaffolds able to locally regulate cell phenotypes and dual-flow bioreactors for two sets of conditions for cartilage/bone Protocols for hierarchical OC grafts engineering should entail mesenchymal condensation for cartilage and vascular component for bone Immunomodulation, low oxygen tension, purinergic signaling, time dependence of stimuli application are important aspects to consider in biomimetic OC TE.

Near-Infrared Spectroscopy Predicts Compositional and Mechanical Properties of Hyaluronic Acid-Based Engineered Cartilage Constructs

Hyaluronic acid (HA) has been widely used for cartilage tissue engineering applications. However, the optimal time point to harvest HA-based engineered constructs for cartilage repair is still under investigation. In this study, we investigated the ability of a nondestructive modality, near-infrared spectroscopic (NIR) analysis, to predict compositional and mechanical properties of HA-based engineered cartilage constructs. NIR spectral data were collected from control, unseeded constructs, and twice per week by fiber optic from constructs seeded with chondrocytes during their development over an 8-week period. Constructs were harvested at 2, 4, 6, and 8 weeks, collagen and sulfated glycosaminoglycan content measured using biochemical assays, and the mechanical properties of the constructs evaluated using unconfined compression tests. NIR absorbances associated with the scaffold material, water, and engineered cartilage matrix, were identified. The NIR-determined matrix absorbance plateaued after 4 weeks of culture, which was in agreement with the biochemical assay results. Similarly, the mechanical properties of the constructs also plateaued at 4 weeks. A multivariate partial least square model based on NIR spectral input was developed to predict the moduli of the constructs, which resulted in a prediction error of 10% and R value of 0.88 for predicted versus actual values of dynamic modulus. Furthermore, the maximum increase in moduli was calculated from the first derivative of the curve fit of NIR-predicted and actual moduli values over time, and both occurred at ∼2 weeks. Collectively, these data suggest that NIR spectral data analysis could be an alternative to destructive biochemical and mechanical methods for evaluation of HA-based engineered cartilage construct properties.

* Harnessing External Cues: Development and Evaluation of an In Vitro Culture System for Osteochondral Tissue Engineering

Over the last decade, engineered structures have been developed for osteochondral (OC) tissue regeneration. While the optimal structure design is yet to be determined, these scaffolds require in vitro evaluation before clinical use. However, the means by which complex scaffolds, such as OC scaffolds, can be tested are limited. Taking advantage of a mesenchymal stem cell's (MSC's) ability to respond to its surrounding we harness external cues, such as the cell's mechanical environment and delivered factors, to create an in vitro culture system for OC tissue engineering with a single cell source on a gradient yet integrated scaffold system. To do this, the effect of hydrogel stiffness on the expression of human MSCs (hMSCs) chondrogenic differentiation was studied using histological analysis. Additionally, hMSCs were also cultured in different combinations of chondrogenic and osteogenic media to develop a co-differentiation media suitable for OC lineage differentiation. A uniquely graded (density-gradient matrix) OC scaffold with a distal cartilage hydrogel phase specifically tailored to support chondrogenic differentiation was cultured using a newly developed "simulated in vivo culture method." The scaffold's culture in co-differentiation media models hMSC infiltration into the scaffold and subsequent differentiation into the distal cartilage and proximal bone layers. Cartilage and bone marker staining along with specific matrix depositions reveal the effect of external cues on the hMSC differentiation. As a result of these studies a model system was developed to study and culture OC scaffolds in vitro.

Cell-laden hydrogels for osteochondral and cartilage tissue engineering

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered artificial matrices that can replace the damaged regions and promote tissue regeneration. Hydrogels are emerging as a promising class of biomaterials for both soft and hard tissue regeneration. Many critical properties of hydrogels, such as mechanical stiffness, elasticity, water content, bioactivity, and degradation, can be rationally designed and conveniently tuned by proper selection of the material and chemistry. Particularly, advances in the development of cell-laden hydrogels have opened up new possibilities for cell therapy. In this article, we describe the problems encountered in this field and review recent progress in designing cell-hydrogel hybrid constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel type, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation matrices with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing technologies (e.g. molding, bioprinting, and assembly) for fabrication of hydrogel-based osteochondral and cartilage constructs with complex compositions and microarchitectures to mimic their native counterparts.

STATEMENT OF SIGNIFICANCE

Despite tremendous advances in the field of regenerative medicine, it still remains challenging to repair the osteochondral interface and full-thickness articular cartilage defects. This inefficiency largely originates from the lack of appropriate tissue-engineered biomaterials that replace the damaged regions and promote tissue regeneration. Cell-laden hydrogel systems have emerged as a promising tissue-engineering platform to address this issue. In this article, we describe the fundamental problems encountered in this field and review recent progress in designing cell-hydrogel constructs for promoting the reestablishment of osteochondral/cartilage tissues. Our focus centers on the effects of hydrogel composition, cell type, and growth factor delivery on achieving efficient chondrogenesis and osteogenesis. We give our perspective on developing next-generation hydrogel/inorganic particle/stem cell hybrid composites with improved physical and biological properties for osteochondral/cartilage tissue engineering. We also highlight recent advances in biomanufacturing and bioengineering technologies (e.g. 3D bioprinting) for fabrication of hydrogel-based osteochondral and cartilage constructs.

Peptide-functionalized starPEG/heparin hydrogels direct mitogenicity, cell morphology and cartilage matrix distribution in vitro and in vivo

Cell-based tissue engineering is a promising approach for treating cartilage lesions, but available strategies still provide a distinct composition of the extracellular matrix and an inferior mechanical property compared to native cartilage. To achieve fully functional tissue replacement more rationally designed biomaterials may be needed, introducing bioactive molecules which modulate cell behavior and guide tissue regeneration. This study aimed at exploring the impact of cell-instructive, adhesion-binding (GCWGGRGDSP called RGD) and collagen-binding (CKLER/CWYRGRL) peptides, incorporated in a tunable, matrixmetalloprotease (MMP)-responsive multi-arm poly(ethylene glycol) (starPEG)/heparin hydrogel on cartilage regeneration parameters in vitro and in vivo. MMP-responsive-starPEG-conjugates with cysteine termini and heparin-maleimide, optionally pre-functionalized with RGD, CKLER, CWYRGRL or control peptides, were cross-linked by Michael type addition to embed and grow mesenchymal stromal cells (MSC) or chondrocytes. While starPEG/heparin-hydrogel strongly supported chondrogenesis of MSC according to COL2A1, BGN and ACAN induction, MMP-degradability enhanced cell viability and proliferation. RGD-modification of the gels promoted cell spreading with intense cell network formation without negative effects on chondrogenesis. However, CKLER and CWYRGRL were unable to enhance the collagen content of constructs. RGD-modification allowed more even collagen type II distribution by chondrocytes throughout the MMP-responsive constructs, especially in vivo. Collectively, peptide-instruction via heparin-enriched MMP-degradable starPEG allowed adjustment of self-renewal, cell morphology and cartilage matrix distribution in order to guide MSC and chondrocyte-based cartilage regeneration towards an improved outcome. Copyright © 2017 John Wiley & Sons, Ltd.

* Constrained Cage Culture Improves Engineered Cartilage Functional Properties by Enhancing Collagen Network Stability

When cultured with sufficient nutrient supply, engineered cartilage synthesizes proteoglycans rapidly, producing an osmotic swelling pressure that destabilizes immature collagen and prevents the development of a robust collagen framework, a hallmark of native cartilage. We hypothesized that mechanically constraining the proteoglycan-induced tissue swelling would enhance construct functional properties through the development of a more stable collagen framework. To test this hypothesis, we developed a novel "cage" growth system to mechanically prevent tissue constructs from swelling while ensuring adequate nutrient supply to the growing construct. The effectiveness of constrained culture was examined by testing constructs embedded within two different scaffolds: agarose and cartilage-derived matrix hydrogel (CDMH). Constructs were seeded with immature bovine chondrocytes and cultured under free swelling (FS) conditions for 14 days with transforming growth factor-β before being placed into a constraining cage for the remainder of culture. Controls were cultured under FS conditions throughout. Agarose constructs cultured in cages did not expand after the day 14 caging while FS constructs expanded to 8 × their day 0 weight after 112 days of culture. In addition to the physical differences in growth, by day 56, caged constructs had higher equilibrium (agarose: 639 ± 179 kPa and CDMH: 608 ± 257 kPa) and dynamic compressive moduli (agarose: 3.4 ± 1.0 MPa and CDMH 2.8 ± 1.0 MPa) than FS constructs (agarose: 193 ± 74 kPa and 1.1 ± 0.5 MPa and CDMH: 317 ± 93 kPa and 1.8 ± 1.0 MPa for equilibrium and dynamic properties, respectively). Interestingly, when normalized to final day wet weight, cage and FS constructs did not exhibit differences in proteoglycan or collagen content. However, caged culture enhanced collagen maturation through the increased formation of pyridinoline crosslinks and improved collagen matrix stability as measured by α-chymotrypsin solubility. These findings demonstrate that physically constrained culture of engineered cartilage constructs improves functional properties through improved collagen network maturity and stability. We anticipate that constrained culture may benefit other reported engineered cartilage systems that exhibit a mismatch in proteoglycan and collagen synthesis.

Regeneration of meniscus tissue using adipose mesenchymal stem cells-chondrocytes co-culture on a hybrid scaffold: In vivo study

The meniscus has poor intrinsic regenerative capacity and its damage inevitably leads to articular cartilage degeneration. We focused on evaluating the effects of Polyvinyl alcohol/Chitosan (PVA/Ch) scaffold seeded by adipose-derived mesenchymal stem cell (ASC) and articular chondrocytes (AC) in meniscus regeneration. The PVA/Ch scaffolds with different molar contents of Ch (Ch1, Ch2, Ch4 and Ch8) were cross-linked by pre-polyurethane chains. By increasing amount of Ch tensile modulus was increased from 83.51 MPa for Ch1 to 110 MPa for Ch8 while toughness showed decrease from 0.33 mJ/mm³ in Ch1 to 0.11 mJ/mm³ in Ch8 constructs. Moreover, swelling ratio and degradation rate increased with an increase in Ch amount. Scanning electron microscopy imaging was performed for pore size measurement and cell attachment. At day 21, Ch4 construct seeded by AC showed the highest expression with 24.3 and 22.64 folds increase in collagen II and aggrecan (p ≤ 0.05), respectively. Since, the mechanical properties, water uptake and degradation rate of Ch4 and Ch8 compositions had no statistically significant differences, Ch4 was selected for in vivo study. New Zealand rabbits were underwent unilateral total medial meniscectomy and AC/scaffold, ASC/scaffold, AC-ASC (co-culture)/scaffold and cell-free scaffold were engrafted. At 7 months post-implantation, macroscopic, histologic, and immunofluorescent studies for regenerated meniscus revealed better results in AC/scaffold group followed by AC-ASC/scaffold and ASC/scaffold groups. In the cell-free scaffold group, there was no obvious meniscus regeneration. Articular cartilages were best preserved in AC/scaffold group. The best histological score was observed in AC/scaffold group. Our results support that Ch4 scaffold seeded by AC alone can successfully regenerate meniscus in tearing injury and ASC has no significant contribution in the healing process.

Effect of hydrogel material composition on hBMSC differentiation into zone-specific neo-cartilage: engineering human articular cartilage-like tissue with spatially varying properties

Material composition alone can be used to direct human bone marrow stromal cells into distinct, zone-specific cell phenotypes and spatially-varying, multi-layered material scaffolds can generate complex, patterned tissue structures.

Timing of mesenchymal stem cell delivery impacts the fate and therapeutic potential in intervertebral disc repair

Cell-based therapies offer a promising approach to treat intervertebral disc (IVD) degeneration. The impact of the injury microenvironment on treatment efficacy has not been established. This study used a rat disc stab injury model with administration of mesenchymal stromal cells (MSCs) at 3, 14, or 30 days post injury (DPI) to evaluate the impact of interventional timing on IVD biochemistry and biomechanics. We also evaluated cellular localization within the disc with near infrared imaging to track the time and spatial profile of cellular migration after in vivo delivery. Results showed that upon injection into a healthy disc, MSCs began to gradually migrate outwards over the course of 14 days, as indicated by decreased signal intensity from the disc space and increased signal within the adjacent vertebrae. Cells administered 14 or 30 DPI also tended to migrate out 14 days after injection but cells injected 3 DPI were retained at a significantly higher amount versus the other groups (p < 0.05). Correspondingly the 3 DPI group, but not 14 or 30 DPI groups, had a higher GAG content in the MSC injected discs (p = 0.06). Enrichment of MSCs and increased GAG content in 3 DPI group did not lead to increased compressive biomechanical properties. Findings suggest that cell therapies administered at an early stage of injury/disease progression may have greater chances of mitigating matrix loss, possibly through promotion of MSC activity by the inflammatory microenvironment associated with injury. Future studies will evaluate the mode and driving factors that regulate cellular migration out of the disc. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:32-40, 2017.

The direction of human mesenchymal stem cells into the chondrogenic lineage is influenced by the features of hydrogel carriers

Low back pain is a major public health issue in the Western world, one main cause is believed to be intervertebral disc (IVD) degeneration. To halt/diminish IVD degeneration, cell therapy using different biomaterials e.g. hydrogels as cell carriers has been suggested. In this study, two different hydrogels were examined (in vitro) as potential cell carriers for human mesenchymal stem cells (hMSCs) intended for IVD transplantation. The aim was to investigate cell-survival and chondrogenic differentiation of hMSCs when cultured in hydrogels Puramatrix^® or Hydromatrix^® and potential effects of stimulation with growth hormone (GH). hMSCs/hydrogel cultures were investigated for cell-viability, attachment, gene expression of chondrogenic markers SOX9, COL2A1, ACAN and accumulation of extracellular matrix (ECM). In both hydrogel types, hMSCs were viable for 28days, expressed integrin β1 which indicates adhesion of hMSCs. Differentiation was observed into chondrocyte-like cells, in a higher extent in hMSCs/Hydromatrix^® cultures when compared to hMSCs/Puramatrix^® hydrogel cultures. Gene expression analyses of chondrogenic markers verified results. hMSCs/hydrogel cultures stimulated with GH displayed no significant effects on chondrogenesis. In conclusion, both hydrogels, especially Hydromatrix^® was demonstrated as a promising cell carrier in vitro for hMSCs, when directed into chondrogenesis. This knowledge could be useful in biological approaches for regeneration of degenerated human IVDs.

High fidelity visualization of cell-to-cell variation and temporal dynamics in nascent extracellular matrix formation

Extracellular matrix dynamics are key to tissue morphogenesis, homeostasis, injury, and repair. The spatiotemporal organization of this matrix has profound biological implications, but is challenging to monitor using standard techniques. Here, we address these challenges by using noncanonical amino acid tagging to fluorescently label extracellular matrix synthesized in the presence of bio-orthogonal methionine analogs. This strategy labels matrix proteins with high resolution, without compromising their distribution or mechanical function. We demonstrate that the organization and temporal dynamics of the proteinaceous matrix depend on the biophysical features of the microenvironment, including the biomaterial scaffold and the niche constructed by cells themselves. Pulse labeling experiments reveal that, in immature constructs, nascent matrix is highly fibrous and interdigitates with pre-existing matrix, while in more developed constructs, nascent matrix lacks fibrous organization and is retained in the immediate pericellular space. Inhibition of collagen crosslinking increases matrix synthesis, but compromises matrix organization. Finally, these data demonstrate marked cell-to-cell heterogeneity amongst both chondrocytes and mesenchymal stem cells undergoing chondrogenesis. Collectively, these results introduce fluorescent noncanonical amino acid tagging as a strategy to investigate spatiotemporal matrix organization, and demonstrate its ability to identify differences in phenotype, microenvironment, and matrix assembly at the single cell level.

Anatomic Mesenchymal Stem Cell-Based Engineered Cartilage Constructs for Biologic Total Joint Replacement

Cartilage has a poor healing response, and few viable options exist for repair of extensive damage. Hyaluronic acid (HA) hydrogels seeded with mesenchymal stem cells (MSCs) polymerized through UV crosslinking can generate functional tissue, but this crosslinking is not compatible with indirect rapid prototyping utilizing opaque anatomic molds. Methacrylate-modified polymers can also be chemically crosslinked in a cytocompatible manner using ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED). The objectives of this study were to (1) compare APS/TEMED crosslinking with UV crosslinking in terms of functional maturation of MSC-seeded HA hydrogels; (2) generate an anatomic mold of a complex joint surface through rapid prototyping; and (3) grow anatomic MSC-seeded HA hydrogel constructs using this alternative crosslinking method. Juvenile bovine MSCs were suspended in methacrylated HA (MeHA) and crosslinked either through UV polymerization or chemically with APS/TEMED to generate cylindrical constructs. Minipig porcine femoral heads were imaged using microCT, and anatomic negative molds were generated by three-dimensional printing using fused deposition modeling. Molded HA constructs were produced using the APS/TEMED method. All constructs were cultured for up to 12 weeks in a chemically defined medium supplemented with TGF-β3 and characterized by mechanical testing, biochemical assays, and histologic analysis. Both UV- and APS/TEMED-polymerized constructs showed increasing mechanical properties and robust proteoglycan and collagen deposition over time. At 12 weeks, APS/TEMED-polymerized constructs had higher equilibrium and dynamic moduli than UV-polymerized constructs, with no differences in proteoglycan or collagen content. Molded HA constructs retained their hemispherical shape in culture and demonstrated increasing mechanical properties and proteoglycan and collagen deposition, especially at the edges compared to the center of these larger constructs. Immunohistochemistry showed abundant collagen type II staining and little collagen type I staining. APS/TEMED crosslinking can be used to produce MSC-seeded HA-based neocartilage and can be used in combination with rapid prototyping techniques to generate anatomic MSC-seeded HA constructs for use in filling large and anatomically complex chondral defects or for biologic joint replacement.

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.

Seaweed polysaccharide-based hydrogels used for the regeneration of articular cartilage

This manuscript provides an overview of the in vitro and in vivo studies reported in the literature focusing on seaweed polysaccharides based hydrogels that have been proposed for applications in regenerative medicine, particularly, in the field of cartilage tissue engineering. For a better understanding of the main requisites for these specific applications, the main aspects of the native cartilage structure, as well as recognized diseases that affect this tissue are briefly described. Current available treatments are also presented to emphasize the need for alternative techniques. The following part of this review is centered on the description of the general characteristics of algae polysaccharides, as well as relevant properties required for designing hydrogels for cartilage tissue engineering purposes. An in-depth overview of the most well known seaweed polysaccharide, namely agarose, alginate, carrageenan and ulvan biopolymeric gels, that have been proposed for engineering cartilage is also provided. Finally, this review describes and summarizes the translational aspect for the clinical application of alternative systems emphasizing the importance of cryopreservation and the commercial products currently available for cartilage treatment.