Enhanced proliferation and differentiation of human articular chondrocytes when seeded at low cell densities in alginate in vitro

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Current Therapeutic Strategies for Stem Cell-Based Cartilage Regeneration

The process of cartilage destruction in the diarthrodial joint is progressive and irreversible. This destruction is extremely difficult to manage and frustrates researchers, clinicians, and patients. Patients often take medication to control their pain. Surgery is usually performed when pain becomes uncontrollable or joint function completely fails. There is an unmet clinical need for a regenerative strategy to treat cartilage defect without surgery due to the lack of a suitable regenerative strategy. Clinicians and scientists have tried to address this using stem cells, which have a regenerative potential in various tissues. Cartilage may be an ideal target for stem cell treatment because it has a notoriously poor regenerative potential. In this review, we describe past, present, and future strategies to regenerate cartilage in patients. Specifically, this review compares a surgical regenerative technique (microfracture) and cell therapy, cell therapy with and without a scaffold, and therapy with nonaggregated and aggregated cells. We also review the chondrogenic potential of cells according to their origin, including autologous chondrocytes, mesenchymal stem cells, and induced pluripotent stem cells.

Development of a 3D cell printed structure as an alternative to autologs cartilage for auricular reconstruction

Surgical technique using autologs cartilage is considered as the best treatment for cartilage tissue reconstruction, although the burdens of donor site morbidity and surgical complications still remain. The purpose of this study is to apply three-dimensional (3D) cell printing to fabricate a tissue-engineered graft, and evaluate its effects on cartilage reconstruction. A multihead tissue/organ building system is used to print cell-printed scaffold (CPS), then assessed the effect of the CPS on cartilage regeneration in a rabbit ear. The cell viability and functionality of chondrocytes were significantly higher in CPS than in cell-seeded scaffold (CSS) and cell-seeded hybrid scaffold (CSHS) in vitro. CPS was then implanted into a rabbit ear that had an 8 mm-diameter cartilage defect; at 3 months after implantation the CPS had fostered complete cartilage regeneration whereas CSS and autologs cartilage (AC) fostered only incomplete healing. This result demonstrates that cell printing technology can provide an appropriate environment in which encapsulated chondrocytes can survive and differentiate into cartilage tissue in vivo. Moreover, the effects of CPS on cartilage regeneration were even better than those of AC. Therefore, we confirmed the feasibility of CPS as an alternative to AC for auricular reconstruction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1016-1028, 2017.

Cellular response of chondrocytes to magnesium alloys for orthopedic applications

In the present study, the effects of Mg-Nd-Zn-Zr (JDBM), brushite (CaHPO₄·₂H₂O)-coated JDBM (C-JDBM), AZ31, WE43, pure magnesium (Mg) and Ti alloy (TC4) on rabbit chondrocytes were investigated in vitro. Adhesion experiments revealed the satisfactory morphology of chondrocytes on the surface of all samples. An indirect cytotoxicity test using MTT assay revealed that C-JDBM and TC4 exhibited results similar to those of the negative control, better than those obtained with JDBM, AZ31, WE43 and pure Mg (p<0.05). There were no statistically significant differences observed between the JDBM, AZ31, WE43 and pure Mg group (p>0.05). The results of indirect cell cytotoxicity and proliferation assays, as well as those of apoptosis assay, glycosaminoglycan (GAG) quantification, assessment of collagen II (Col II) levels and RT-qPCR revealed a similar a trend as was observed with MTT assay. These findings suggested that the JDBM alloy was highly biocompatible with chondrocytes in vitro, yielding results similar to those of AZ31, WE43 and pure Mg. Furthermore, CaHPO₄·₂H₂O coating significantly improved the biocompatibility of this alloy.

Adipose stem cell microbeads as production sources for chondrogenic growth factors

Microencapsulating stem cells in injectable microbeads can enhance delivery and localization, but their ability to act as growth factor production sources is still unknown. To address this concern, growth factor mRNA levels and production from alginate microbeads with encapsulated human adipose stem cells (ASC microbeads) cultured in both growth and chondrogenic media (GM and CM) were measured over a two week period. Human ASCs in microbeads were either commercially purchased (Lonza) or isolated from six human donors and compared to human ASCs on tissue culture polystyrene (TCPS). The effects of crosslinking and alginate compositions on growth factor mRNA levels and production were also determined. Secretion profiles of IGF-I, TGF-β3 and VEGF-A from commercial human ASC microbeads were linear and at a significantly higher rate than TCPS cultures over two weeks. For human ASCs derived from different donors, microencapsulation increased pthlh and both IGF-I and TGF-β3 secretion. CM decreased fgf2 and VEGF-A secretion from ASC microbeads derived from the same donor population. Crosslinking microbeads in BaCl₂ instead of CaCl₂ did not eliminate microencapsulation’s beneficial effects, but did decrease IGF-I production. Increasing the guluronate content of the alginate microbead increased IGF-I retention. Decreasing alginate molecular weight eliminated the effects microencapsulation had on increasing IGF-I secretion. This study demonstrated that microencapsulation can enhance chondrogenic growth factor production and that chondrogenic medium treatment can decrease angiogenic growth factor production from ASCs, making these cells a potential source for paracrine factors that can stimulate cartilage regeneration.

Evaluation of metabolomic changes as a biomarker of chondrogenic differentiation in 3D-cultured human mesenchymal stem cells using proton (1H) nuclear magnetic resonance spectroscopy

PURPOSE

The purpose of this study was to evaluate the metabolomic changes in 3D-cultured human mesenchymal stem cells (hMSCs) in alginate beads, so as to identify biomarkers during chondrogenesis using (1)H nuclear magnetic resonance (NMR) spectroscopy.

MATERIALS AND METHODS

hMSCs (2×10(6) cells/mL) were seeded into alginate beads, and chondrogenesis was allowed to progress for 15 days. NMR spectra of the chondrogenic hMSCs were obtained at 4, 7, 11, and 15 days using a 14.1-T (600-MHz) NMR with the water suppression sequence, zgpr. Real-Time polymerase chain reaction (PCR) was performed to confirm that that the hMSCs differentiated into chondrocytes and to analyze the metabolomic changes indicated by the NMR spectra.

RESULTS

During chondrogenesis, changes were detected in several metabolomes as hMSC chondrogenesis biomarkers, e.g., fatty acids, alanine, glutamate, and phosphocholine. The metabolomic changes were compared with the Real-Time PCR results, and significant differences were determined using statistical analysis. We found that changes in metabolomes were closely related to biological reactions that occurred during the chondrogenesis of hMSCs.

CONCLUSIONS

In this study, we confirm that metabolomic changes detected by (1)H-NMR spectroscopy during chondrogenic differentiation of 3D-cultured hMSCs in alginate beads can be considered as biomarkers of stem cell differentiation.

Cell Seeding Densities in Autologous Chondrocyte Implantation Techniques for Cartilage Repair

Cartilage repair techniques have been among the most intensively investigated treatments in orthopedics for the past decade, and several different treatment modalities are currently available. Despite the extensive research effort within this field, the generation of hyaline cartilage remains a considerable challenge. There are many parameters attendant to each of the cartilage repair techniques that can affect the amount and types of reparative tissue generated in the cartilage defect, and some of the most fundamental of these parameters have yet to be fully investigated. For procedures in which in vitro-cultured autologous chondrocytes are implanted under a periosteal or synthetic membrane cover, or seeded onto a porous membrane or scaffold, little is known about how the number of cells affects the clinical outcome. Few published clinical studies address the cell seeding density that was employed. The principal objective of this review is to provide an overview of the cell seeding densities used in cell-based treatments currently available in the clinic for cartilage repair. Select preclinical studies that have informed the use of specific cell seeding densities in the clinic are also discussed.

Differentiation capacity of human chondrocytes embedded in alginate matrix

Healing capacity of cartilage is low. Thus, cartilage defects do not regenerate as hyaline but mostly as fibrous cartilage which is a major drawback since this tissue is not well adapted to the mechanical loading within the joint. During in vitro cultivation in monolayers, chondrocytes proliferate and de-differentiate to fibroblasts. In three-dimensional cell cultures, de-differentiated chondrocytes could re-differentiate toward the chondrogenic lineage and re-express the chondrogenic phenotype. The objective of this study was to characterize the mesenchymal stem cell (MSC) potential of human chondrocytes isolated from articular cartilage. Furthermore, the differentiation capacity of human chondrocytes in three-dimensional cell cultures was analyzed to target differentiation direction into hyaline cartilage. After isolation and cultivation of chondrogenic cells, the expression of the MSC-associated markers: cluster of differentiation (CD)166, CD44, CD105, and CD29 was performed by flow cytometry. The differentiation capacity of human chondrocytes was analyzed in alginate matrix cultured in Dulbecco?s modified eagle medium with (chondrogenic stimulation) and without (control) chondrogenic growth factors. Additionally, the expression of collagen type II, aggrecan, and glycosaminoglycans was determined. Cultivated chondrocytes showed an enhanced expression of the MSC-associated markers with increasing passages. After chondrogenic stimulation in alginate matrix, the chondrocytes revealed a significant increase of cell number compared with unstimulated cells. Further, a higher synthesis rate of glycosaminoglycans and a positive collagen type II and aggrecan immunostaining was detected in stimulated alginate beads. Human chondrocytes showed plasticity whilst cells were encapsulated in alginate and stimulated by growth factors. Stimulated cells demonstrated characteristics of chondrogenic re-differentiation due to collagen type II and aggrecan synthesis.

Combined 3D and hypoxic culture improves cartilage-specific gene expression in human chondrocytes

BACKGROUND AND PURPOSE

In vitro expansion of autologous chondrocytes is an essential part of many clinically used cartilage repair treatments. Native chondrocytes reside in a 3-dimensional (3D) network and are exposed to low levels of oxygen. We compared monolayer culture to combined 3D and hypoxic culture using quantitative gene expression analysis.

METHODS

Cartilage biopsies were collected from the intercondylar groove in the distal femur from 12 patients with healthy cartilage. Cells were used for either monolayer or scaffold culture. The scaffolds were clinically available MPEG-PLGA scaffolds (ASEED). After harvesting of cells for baseline investigation, the remainder was divided into 3 groups for incubation in conditions of normoxia (21% oxygen), hypoxia (5% oxygen), or severe hypoxia (1% oxygen). RNA extractions were performed 1, 2, and 6 days after the baseline time point, respectively. Quantitative RT-PCR was performed using assays for RNA encoding collagen types 1 and 2, aggrecan, sox9, ankyrin repeat domain-37, and glyceraldehyde-3-phosphate dehydrogenase relative to 2 hypoxia-stable housekeeping genes.

RESULTS

Sox9, aggrecan, and collagen type 2 RNA expression increased with reduced oxygen. On day 6, the expression of collagen type 2 and aggrecan RNA was higher in 3D culture than in monolayer culture.

INTERPRETATION

Our findings suggest that there was a combined positive effect of 3D culture and hypoxia on cartilage-specific gene expression. The positive effects of 3D culture alone were not detected until day 6, suggesting that seeding of chondrocytes onto a scaffold for matrix-assisted chondrocyte implantation should be performed earlier than 2 days before implantation.

Enzyme replacement in a human model of mucopolysaccharidosis IVA in vitro and its biodistribution in the cartilage of wild type mice

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is a lysosomal storage disorder caused by deficiency of N-acetylgalactosamine-6-sulfatase (GALNS), an enzyme that degrades keratan sulfate (KS). Currently no therapy for MPS IVA is available. We produced recombinant human (rh)GALNS as a potential enzyme replacement therapy for MPS IVA. Chinese hamster ovary cells stably overexpressing GALNS and sulfatase modifying factor-1 were used to produce active ( approximately 2 U/mg) and pure (>or=97%) rhGALNS. The recombinant enzyme was phosphorylated and was dose-dependently taken up by mannose-6-phosphate receptor (K(uptake) = 2.5 nM), thereby restoring enzyme activity in MPS IVA fibroblasts. In the absence of an animal model with a skeletal phenotype, we established chondrocytes isolated from two MPS IVA patients as a disease model in vitro. MPS IVA chondrocyte GALNS activity was not detectable and the cells exhibited KS storage up to 11-fold higher than unaffected chondrocytes. MPS IVA chondrocytes internalized rhGALNS into lysosomes, resulting in normalization of enzyme activity and decrease in KS storage. rhGALNS treatment also modulated gene expression, increasing expression of chondrogenic genes Collagen II, Collagen X, Aggrecan and Sox9 and decreasing abnormal expression of Collagen I. Intravenous administration of rhGALNS resulted in biodistribution throughout all layers of the heart valve and the entire thickness of the growth plate in wild-type mice. We show that enzyme replacement therapy with recombinant human GALNS results in clearance of keratan sulfate accumulation, and that such treatment ameliorates aberrant gene expression in human chondrocytes in vitro. Penetration of the therapeutic enzyme throughout poorly vascularized, but clinically relevant tissues, including growth plate cartilage and heart valve, as well as macrophages and hepatocytes in wild-type mouse, further supports development of rhGALNS as enzyme replacement therapy for MPS IVA.

Sox9 expression of alginate-encapsulated chondrocytes is stimulated by low cell density

Recent research in tissue engineering for the treatment of cartilage defects have demonstrated that matrix-biomaterial, cell culture conditions, and cytokine-related factors influence the chondrogenic differentiation pattern, especially for the expression of matrix genes. However, little is known about the impact of cell seeding density in a three-dimensional environment on the key chondrogenic transcription factor Sox9. Here we investigated, whether the cell concentration of alginate encapsulated chondrocytes influences the Sox9 expression. Dedifferentiated passage-4 porcine chondrocytes were encapsulated in alginate beads at two different concentrations (4 x 10(6) versus 7 x 10(7) cells/mL) and cultivated for up to 4 weeks under TGF-ss stimulation. The expression of Sox9, Collagen I, II, and X was assessed via quantitative RT-PCR and compared to those observed in the initial monolayer culture. Cellular viability, cell morphology, and the sulphated glycosaminoglycan-production were monitored. Interestingly Sox9 expression was significantly upregulated in the low-cell-density group, whereas no difference between high-cell-density and monolayer culture group could be observed. Furthermore, the cellular survival and the sulphated glycosaminoglycan production were higher in the low-cell-density group. Collagen I expression was downregulated in the low-cell-density group whereas it was upregulated in the high-cell-density one. Surprisingly, only the high-cell-density group showed the expression of Collagen II, although it appeared not significant. Collagen X expression was upregulated in the low-cell-density group. Taken together our data indicate that a low concentration of cell seeding in a three-dimensional environment is beneficial for the overall chondrogenic development. However, this article reveals discrepancies between Sox9 and the chondrogenic pathway in redifferentiating chondrocytes that should be addressed in further work.

Additive effects of hyperbaric oxygen and platelet-derived growth factor-BB in chondrocyte transplantation via up-regulation expression of platelet-derived growth factor-beta receptor

The present study investigated the effects of hyperbaric oxygen (HBO) and platelet-derived growth factor-BB (PDGF-BB) in chondrocyte transplantation. In vitro, chondrocytes were treated with HBO, PDGF-BB, and HBO combined with PDGF-BB (H+P). Cell growth was analyzed using cell counting, MTT assay, and FACS analysis. mRNA expression of the PDGF-alpha receptor (PDGFR-alpha) and beta receptor (PDGFR-beta) was detected by RT-PCR. Protein expression of PDGFR-beta was detected by Western blotting. In vivo, chondrocytes and PDGF-BB were suspended in alginate as a transplantation system. Cartilage defects were grafted with this system and with or without HBO treatment. Released PDGF-BB concentration was quantified by ELISA. After 8 weeks, animals were sacrificed and the repaired tissues were examined. In vitro data suggested that each treatment increased cell growth via the up-regulated mRNA expression of PDGFR-alpha and increased cell accumulation in the S-phase. The H+P treatment was more additive in cell growth and in mRNA and protein expression of PDGFR-beta than HBO or PDGF-BB. In vivo results suggested that PDGF-BB delivery lasted for more than 5 weeks. Scoring results showed that each treatment significantly increased the cartilage repair. Safranin-O and type II collagen staining confirmed the hyaline-like cartilage regeneration in the repaired tissues. In situ up-regulation of PDGFR-beta expression partially explains the additive effect of H+P treatment in cartilage repair. Accordingly, H+P offers a potential treatment method for cartilage repair.

Combined use of RGD-peptide modified PLGA and TGF-beta1 gene transfected MSCs to improve cell biobehaviors in vitro

In order to improve the surface properties of PLGA polymer for a better material/cell interface to modulate the cells behaviors, we prepared a novel three-block copolymer, PLGA-[ASP-PEG], and immobilized an RGD-containing peptide, Gly-Arg-Gly-Asp-Ser-Pro-Cys (GRGDSPC) on the surface of it. Transforming growth factor-beta1 (TGF-beta1) was transfected into bone marrow stromal cells (MSCs) employed as seeded cells. Cell adhesion, spreading, proliferation and differentiation on this material were investigated. The results showed that the cell adhesive ratio on RGD-modified materials was higher than on un-modified materials (P<0.05). The extent of cell spreading was also wider on RGD-modified materials than on un-modified materials. Cell proliferation indices of transfected MSCs were increased as compared with the un-transfected MSCs (P<0.05). The ALP activities in the MSCs cultured with RGD-modified materials were higher than on un-modified materials after 14 days (P<0.05), and those in transfected MSCs were higher than in un-transfected MSCs (P<0.05). It was suggested that the combined use of RGD-modification and TGF-beta gene transfection could improve the interaction of biomaterial and cells.

The influence of fibrin based hydrogels on the chondrogenic differentiation of human bone marrow stromal cells

Mesenchymal Stem Cells (MSC) are frequently incorporated into osteochondral implants and cell seeding is often facilitated with hydrogels which exert a profound influence on the chondrogenic differentiation of MSC. An attempt was made to elucidate this effect by comparing the chondrogenic differentiation of Bone Marrow Stromal Cells (BMSC) in fibrin and fibrin alginate composites. A biphasic osteochondral model which simulated the native in vivo environment was employed in the study. In the first stage of the experiment, BMSC was encapsulated in fibrin, Fibrin Alginate 0.3% (FA0.3) and 0.6% (FA0.6). Chondrogenic differentiation within these cell-hydrogel pellets was compared against that of standard cell pellets under inductive conditions and the matrices which supported chondrogenesis were used in the cartilage phase of biphasic constructs. Neo-cartilage growth was monitored in these cocultures. It was observed that hydrogel encapsulation influenced mesenchymal condensation which preceded chondrogenic differentiation. Early cell agglomeration was observed in fibrin as compared to fibrin alginate composites. These fibrin encapsulated cells differentiated into chondrocytes which secreted aggrecan and collagen II. When the alginate content rose from 0.3 to 0.6%, chondrogenic differentiation declined with a reduction in the expression of collagen II and aggrecan. Fibrin and FA0.3 were tested in the cartilage phase of the biphasic osteochondral constructs and the former supported superior cartilage growth with higher cellularity, total Glycosaminoglycan (GAG) and collagen II levels. The FA0.3 cartilage phase was found to be fragmented and partially calcified. The use of fibrin for cartilage repair was advocated as it facilitated BMSC chondrogenesis and cartilaginous growth in an osteochondral environment.

DNA methylation analysis as novel tool for quality control in regenerative medicine

Cell-based regenerative medicine, including tissue engineering, is a novel approach to reconstituting tissues that do not spontaneously heal, such as damaged cartilage, and to curing diseases caused by malfunctioning cells. Typically, manufacturing processes to generate cartilage for replacement therapies involve isolation and expansion of cells from cartilage biopsies. A challenge in the field is potential contamination by other cell types (e.g., fibroblast-like cells), which can overgrow the desired cells during culturing and may ultimately compromise clinical efficacy. No standard analytical system has been absolutely effective in ensuring the identity of these cell-based products. Therefore, we tested deoxyribonucleic acid methylation analysis as a quality assessment tool, applying it to Genzyme's Carticel product, a chondrocyte implant that the Food and Drug Administration has approved. We identified 7 potent discriminators by assaying candidate genomic regions derived from methylation discovery approaches and literature searches regarding a functional role of genes in chondrocyte biology. Using a support vector machine, we trained an optimal cell type classifier that was absolutely effective in discriminating chondrocytes from synovial membrane derived cells, the major potential contaminant of chondrocyte cultures. The abundant marker availability and high quality of this assay format also suggest it as a potential quality control test for other cell types grown or manipulated in vitro.

Influence of culture conditions on metal-induced responses in a cultured rainbow trout gill epithelium

A primary culture technique for rainbow trout (Oncorhynchus mykiss) gill cells was optimized to better represent the intact gill in vivo in response to waterborne toxic metals. Modifications in cell seeding density and culture conditions resulted in a gill epithelial cell culture model, which displayed classic in vivo responses to toxic metals. Metallothionein-A (MTA), metallothionein-B (MTB), zinc transporter-1 (ZnT-1), glutathione-S-transferase (GST), and glucose-6-phosphate-dehydrogenase (G6PD) all showed dose-dependent increases in expression at the mRNA level in response to waterborne zinc. Of these genes, the change in zinc-induced expression relative to the control was greatest for MTA, MTB, and ZnT-1. MT expression was also induced by silver, lead, copper, and cadmium. Cells cultured with freshwater on the apical side maintained the net transepithelial influx of Ca2+ displayed by freshwater trout gills in vivo, and there was an active inward movement of Ca2+. Waterborne zinc applied to the apical compartment reduced the net uptake of Ca2+ by stimulating the efflux component. The use of endogenous metal-responsive gene expression and inhibition of ion transport in the developed cell culture system will facilitate studies of metal-gill interactions and may prove to have future practical applications within biomonitoring of natural waters.

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Effect of Stratified Culture Compared to Confluent Culture in Monolayer on Proliferation and Differentiation of Human Articular Chondrocytes

With conventional tissue culture of cells, it is generally assumed that when the available 2D substrate is fully occupied, growth ceases or is greatly reduced.However, in nature wound repair mostly involves proliferation of cells that are attracted to the defect site in a 3D environment.Hence, proliferation continues in 3D until the defect site is filled with cells contributing to repair tissue. With this in mind,we examined the growth behavior of human articular chondrocytes during stratified culture as opposed to routine culture to confluency. Additionally, we studied the influence of growth factors on proliferation during stratified culture and differentiation thereafter. Chondrocytes were cultured in monolayer on tissue culture plastic to confluency or stratified for an additional 7 days. Culture medium was based on DMEM with 10% serum and either supplemented with high concentrations of nonessential amino acids (NEAA) and ascorbic acid (AsAP), or instead with basic fibroblastic growth factor (bFGF), platelet-derived growth factor (PDBF-BB), and/or transforming growth factor beta1 (TGF-beta). After expansion, cells were harvested, counted, and their differentiation capacity was examined in pellet culture assay. It was shown that chondrocytes, cultured stratified proliferate exponentially for up to an additional 4 days and that cell yield increased 5-fold. Furthermore, during stratified culture the number of cells increased further in the presence of bFGF, PDBF-BB, and TGFbeta1 or high concentrations of NEAA and AsAP. Depending on donor variation and factors supplemented the cell yield ranged from 0.06 up to 1.1 million cells/cm2 at the second passage. During stratified culture in the presence of either bFGF and PDGF or high concentrations of NEAA and AsAP, exponential growth continued for up to 7 days. Finally, cells maintained their differentiation capacity when cultured stratified with or without growth factors (bFGF, TGF-beta, and PDGF), but not when cultured with high levels of AsAP and NEAA. In contrast to other 3D culture techniques like microcarrier or suspension culture, nutrient consumption remained the same as with conventional expansion. Because this allows culturing of clinically relevant amounts of chondrocytes without increasing the amount of serum, chondrocytes can be fully expanded in the presence autologous serum, avoiding the risk of viral and/or prion disease transmission associated with the use of animal-derived serum or serum replacers with animal-derived constituents.

Morphology and function of ovine articular cartilage chondrocytes in 3-d hydrogel culture

Different cell- and biomaterial-based tissue engineering techniques are under investigation to restore damaged tissue. Strategies that use chondrogenic cells or tissues in combination with bioresorbable delivery materials are considered to be suitable to regenerate bio-artificial cartilage. Three-dimensional (3-D) cell embedding techniques can provide anchorage-independent cell growth and homogenous spatial cell arrangement, which play a key role in the maintenance of the characteristic phenotype and thus the formation of differentiated tissue. We developed a new injectable high water content (90%) hydrogel formulation with 5% sodium alginic acid and 5% gelatin as a temporary supportive intercellular matrix for 3-D cell culture. The objective was to determine whether the in vitro hydrogel culture of chondrocytes could preserve hyaline characteristics and thus could provide cartilage regeneration in vitro. Chondrocytes harvested from knee joints of skeletally mature sheep were cultured 3-D in hydrogel (7 x 10(6) cells/ml, 2.8-mul beads) for up to 10 weeks. Cell morphology and viability were evaluated with light microscopy, and proliferative activity was assessed with antibromodeoxyuridine immunofluorescence. Expression of collagens type I (COL1) and II (COL2), cartilage proteoglycans (PG) and hyaluronan synthases (HAS) were studied immunohistochemically. We observed that up to 36% of chondrocytes proliferated, while almost 100% presented a differentiated spheroidal phenotype. After an initial decrease at 2 weeks, cell density recovered to 85% of the initial absolute value at 10 weeks. Expression of hyaline matrix molecules resembled the in vivo pattern with increasing spatial deposition of PG and COL2. The proportion of PG-positive cells increased from initially 13 to 53% after 10 weeks, in contrast to consistently 100% COL2-positive cells. We conclude that 3-D hydrogel culture, even without mechanical stimulation or growth factor application, can keep chondrocytes in a differentiated state and provides a chondrogenic cell environment for in vitro cartilage regeneration for at least 10 weeks. Moreover, this hydrogel appears to be a suitable cell delivery material for subsequent in vivo implantation.

A self-assembling process in articular cartilage tissue engineering

Current therapies for articular cartilage defects often result in fibrocartilaginous tissue. To achieve regeneration with hyaline articular cartilage, tissue-engineering approaches employing cell-seeded scaffolds have been investigated. However, limitations of scaffolds include phenotypic alteration of cells, stress-shielding, hindrance of neotissue organization, and degradation product toxicity. This study employs a self-assembling process to produce tissue-engineered constructs over agarose in vitro without using a scaffold. Compared to past studies using various meshes and gels as scaffolding materials, the self-assembly method yielded constructs with comparable GAG and collagen content. By 12 weeks, the self-assembling process resulted in tissue-engineered constructs that were hyaline- like in appearance with histological, biochemical, and biomechanical properties approaching those of native articular cartilage. Overall, constructs contained two thirds more GAG per dry weight than calf articular cartilage. Collagen per dry weight reached more than one third the level of native tissue. IHC and gel electrophoresis showed collagen type II production and absence of collagen type I. More importantly, self-assembled constructs reached well over one third the stiffness of native tissue.

Probing the role of multicellular organization in three-dimensional microenvironments

Successful application of living cells in regenerative medicine requires an understanding of how tissue structure relates to organ function. There is growing evidence that presentation of extracellular cues in a three-dimensional (3D) context can fundamentally alter cellular responses. Thus, microenvironment studies that previously were limited to adherent two-dimensional (2D) cultures may not be appropriate for many cell types. Here we present a method for the rapid formation of reproducible, high-resolution 3D cellular structures within a photopolymerizable hydrogel using dielectrophoretic forces. We demonstrate the parallel formation of >20,000 cell clusters of precise size and shape within a thin 2-cm(2) hydrogel and the maintenance of high cell viability and differentiated cell markers over 2 weeks. By modulating cell-cell interactions in 3D clusters, we present the first evidence that microscale tissue organization regulates bovine articular chondrocyte biosynthesis. This platform permits investigation of tissue architecture in other multicellular processes, from embryogenesis to regeneration to tumorigenesis.

Pluronic F127 as a cell encapsulation material: utilization of membrane-stabilizing agents

Thermoreversible gelation of the copolymer Pluronic F127 (generic name, poloxamer 407) in water makes it a unique candidate for cell encapsulation applications, either alone or to promote cell seeding and attachment in tissue scaffolds. At concentrations of 15-20% (w/w), aqueous Pluronic F127 (F127) solutions gel at physiological temperatures. The effect of F127 on viability and proliferation of human liver carcinoma cells (HepG2) was determined for both liquid and gel formulations. Cell concentration and viability over a 5-day period were measured by the trypan blue assay via hemocytometry and results were confirmed in both the MTT and LDH assays. With 0.1-5% (w/w) F127 (liquid), cells proliferated and maintained high viability over 5 days. However, at 10% (w/w) F127 (liquid), there was a significant decrease in cell viability and no cell proliferation was evident. HepG2 cell encapsulation in F127 concentrations ranging from 15 to 20% (w/w) (gel) resulted in complete cell death by 5 days. This was also true for the HMEC-1 (endothelial) and L6 (muscle) cell lines evaluated. Cell-seeding density did not affect cell survival or proliferation. Membrane-stabilizing agents (hydrocortisone, glucose, and glycerol) were added to the F127 gel formulations to improve cell viability. The steroid hydrocortisone demonstrated the most significant improvement in viability, from <2% (in F127 alone) to >70% (with 60 nM hydrocortisone added). These results suggest that F127 formulations supplemented with membrane-stabilizing agents can serve as viable cell encapsulation materials. In addition, hydrocortisone may be generally useful in the promotion of cell viability for a wide range of encapsulation materials.

Three-Dimensional Culture of Feline Articular Chondrocytes in Alginate Microspheres

Chondrocytes isolated from proximal femoral articular cartilage from 3 adult cat cadavers were expanded in monolayer culture and subsequently cultured in alginate microspheres for 24 days. Cell proliferation and production of proteoglycans in alginate microspheres were observed during day 18 and 24. Quantification of chondroitin sulfates (CS) by capillary electrophoresis revealed that cultured chondrocytes synthesized CS6 but not CS4. Three-dimensional culture using alginate microspheres is a useful in vitro technique to study proliferation and metabolism of chondrocytes; however, further modifications are needed to apply the technique to feline articular chondrocytes.

Cellular utilization determines viability and matrix distribution profiles in chondrocyte-seeded alginate constructs

The long-term success of any cellular construct used for cartilage tissue engineering is dependent on the maintenance of cell viability throughout the construct thickness. Furthermore, the cells must continue to be metabolically active in order to synthesize a mechanically functional extracellular matrix (ECM). In the present study, a live-dead staining technique and systematic profiling procedure enabled the spatial and temporal distribution of chondrocyte viability to be characterized within 4-mm-thick alginate scaffolds. ECM distribution after 14 days of culture is described both biochemically and histologically and the mechanical functionality of the constructs was assessed by an unconfined compression test. Parameters investigated included alginate permeability, cell-seeding density, and volume of culture medium. Nonhomogeneity of cell and matrix distribution was evident, with greater densities of both parameters in the periphery of the constructs. The culture time preceding central viability loss was inversely related to cell density but relatively independent of scaffold density. However, homogeneity could be attained with increasing medium volume, as evidenced with cell and matrix distribution for cultures in 6.4 mL of medium per 10(6) cells. Moreover, the mechanical properties of the construct were enhanced by culture in increasing volumes of medium. This work indicates that cellular utilization determines the nonhomogeneous nature of cartilage formation in three-dimensional constructs and presents a guide to nonlimiting medium volumes for static culture conditions.

Composite articular cartilage engineered on a chondrocyte-seeded aliphatic polyurethane sponge

To circumvent the reconstructive disadvantages inherent in resorbable polyglycolic acid (PGA)/polylactic acid (PLA) used in cartilage engineering, a nonresorbable, and nonreactive polyurethane sponge (Tecoflex sponge, TS) was studied as both a cell delivery device and as an internal support scaffolding. The in vitro viability and proliferation of porcine articular chondrocytes (PACs) in TS, and the in vivo generation of new articular cartilage and long-term resorption, were examined. The initial cell attachment rate was 40%, and cell density increased more than 5-fold after 12 days of culture in vitro. PAC-loaded TS blocks were implanted into nude mice, became opalescent, and resembled native cartilage at weeks 12 and 24 postimplantation. The mass and volume of newly formed cartilage were not significantly different at week 24 from samples harvested at week 6 or week 12. Safranin O-fast green staining revealed that the specimens from cell-loaded TS groups at week 12 and week 24 consisted of mature cartilage. Collagen typing revealed that type II collagen was present in all groups of tissue-engineered cartilage. In conclusion, the implantation of PAC-TS resulted in composite tissue-engineered articular cartilage with TS as an internal support. Long-term observation (24 weeks) of mass and volume showed no evidence of resorption.

Tissue engineering of articular cartilage under the influence of collagen I/III membranes and low oxygen tension

The objective of this study was to study the matrix production and phenotype stability of articular chondrocytes cultured on collagen I/III membranes (CM) under the influence of low oxygen tension (Po(2)). Primary bovine and osteoarthritic human chondrocytes were cultured for 2 weeks under 5-21% Po(2) on CM, in alginate, or as monolayers. Dedifferentiated cells were produced by 2-week monolayer culture under 21% Po(2). Collagen (Coll) type II and I expression was demonstrated immunohistochemically, by Western blotting (Coll II), and by semiquantitative RT-PCR; proteoglycan synthesis was demonstrated histochemically (toluidine blue); and biosynthetic activity was indicated by radiolabel incorporation ([(3)H]proline and [(35)S]sulfate). Bovine chondrocytes on CM showed an increase in Coll II expression and proteoglycan synthesis under low Po(2) conditions, whereas Coll I decreased. This oxygen-dependent phenotype-stabilizing effect was even more pronounced in alginate cultures. Biosynthesis of bovine and human chondrocytes was also increased by low Po(2), except for proline incorporation, which decreased in bovine CM cultures (low-oxygen effects were significantly higher in alginate than in CM cultures). Dedifferentiated chondrocytes reexpressed Coll II protein when cultured under low Po(2) on CM or in alginate only, but not under high Po(2) or in monolayer culture. We conclude that CM and, even more, alginate foster phenotype stability and cartilage-specific matrix production of bovine chondrocytes, especially when cultured under in vivo-like oxygen conditions.

A kinetic modeling of chondrocyte culture for manufacture of tissue-engineered cartilage

For repairing articular cartilage defects, innovative techniques based on tissue engineering have been developed and are now entering into the practical stage of clinical application by means of grafting in vitro cultured products. A variety of natural and artificial materials available for scaffolds, which permit chondrocyte cells to aggregate, have been designed for their ability to promote cell growth and differentiation. From the viewpoint of the manufacturing process for tissue-engineered cartilage, the diverse nature of raw materials (seeding cells) and end products (cultured cartilage) oblige us to design a tailor-made process with less reproducibility, which is an obstacle to establishing a production doctrine based on bioengineering knowledge concerning growth kinetics and modeling as well as designs of bioreactors and culture operations for certification of high product quality. In this article, we review the recent advances in the manufacturing of tissue-engineered cartilage. After outlining the manufacturing processes for tissue-engineered cartilage in the first section, the second and third sections, respectively, describe the three-dimensional culture of chondrocytes with Aterocollagen gel and kinetic model consideration as a tool for evaluating this culture process. In the final section, culture strategy is discussed in terms of the combined processes of monolayer growth (ex vivo chondrocyte cell expansion) and three-dimensional growth (construction of cultured cartilage in the gel).

Biological evaluation of calcium alginate microspheres as a vehicle for the localized delivery of a therapeutic enzyme

Gaucher disease (GD) is caused by the decreased activity and/or stability of the lysosomal enzyme glucocerebrosidase (GCR). The available treatment consists in the intravenous administration of exogenous GCR, and is effective in reverting most of the symptoms. However, in terms of bone pathology, which is among the most disabling manifestations, a slow and incomplete response is observed, indicating that adjuvant therapies are necessary to consistently restore GCR activity in bone and accelerate regeneration. In this study, calcium alginate microspheres were analyzed as a vehicle for localized GCR delivery to bone. Results demonstrated that the entrapped enzyme retained full activity and exhibited a broader pH-dependent activity profile, compared to that of free-GCR, with improved stability at physiological pH. GCR release profile was established, and it was demonstrated that GCR could be released in a sustained manner. The biological behavior of the system was evaluated by analyzing the uptake of released GCR by GCR-deficient cells from GD patients, using different techniques: GCR activity measurements, radiolabeling, and cellulose acetate electrophoresis. Results demonstrated that GCR was internalized by cells significantly enhancing the residual enzymatic activity. To achieve an activity reconstitution level comparable to that obtained using free-GCR, only half of the dose was required with entrapped-GCR.

Adhesion and Growth of Bone Marrow Stromal Cells on Modified Alginate Hydrogels

Alginate is a biodegradable, immunocompatible biopolymer that is capable of immobilizing viable cells and bioactive factors. Few investigations have analyzed the efficacy of alginate gels as substrata for cell attachment and proliferation. Here we have compared the adhesion and subsequent growth of human and rat bone marrow stromal fibroblastic cells on unmodified alginate hydrogel surfaces. It was found that, in contrast to rat cells, human cells did not readily attach or proliferate on unmodified alginates. In attempts to enhance these features, or collagen type I was incorporated into the gels, with no significant improvements in prolonged human cell adherence. However, alginate gels containing both collagen type I and beta-tricalcium phosphate were found to enhance human cell adherence and proliferation. Furthermore, interactions between the collagen and beta-tricalcium phosphate prevented loss of the protein from the hydrogels. These results indicate that alginate gels containing collagen have potential uses as vehicles for delivery of adherent cells to a tissue site. In addition, gels containing beta-tricalcium phosphate, with or without collagen type I incorporation, have potential to support cell growth and differentiation in vitro before implantation. This study emphasizes the limitations of the uses of cells derived from experimental animals in certain model studies relating to human tissue engineering.

Attachment, proliferation, and migration of marrow stromal osteoblasts cultured on biomimetic hydrogels modified with an osteopontin-derived peptide

We prepared oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels modified with a rat osteopontin-derived peptide (ODP), Asp-Val-Asp-Val-Pro-Asp-Gly-Arg-Gly-Asp-Ser-Leu-Ala-Try-Gly (DVDVPDGRGDSLAYG), as well as Gly-Arg-Gly-Asp-Ser (GRGDS) and investigated the modulation of marrow stromal osteoblast function on the peptide-modified hydrogels. Osteoblast attachment was competitively inhibited by a soluble peptide suggesting that the interaction of osteoblasts with the hydrogel was ligand specific. The proliferation index of osteoblasts relative to the initial seeding density was similar on the hydrogels modified with ODP (1.18+/-0.13) and GRGDS (1.27+/-0.12). However, fibroblasts proliferated faster on GRGDS-modified hydrogels than on ODP-modified hydrogels as evidenced by the proliferation indices of 4.89+/-0.03 and 2.42+/-0.16, respectively. A megacolony migration assay conducted for 3 days with a seeding density of 53,000 cells/cm(2) showed that osteoblasts migrated to a longer distance on ODP-modified hydrogels (0.23+/-0.06 mm/day) than on hydrogels modified with GRGDS (0.15+/-0.02 mm/day). In addition, osteoblasts migrated faster than fibroblasts seeded at the same density on ODP-modified hydrogels (0.15+/-0.11 mm/day). The migration of osteoblasts on the peptide-modified hydrogels was dependent on the peptide concentration of the hydrogels resulting in an increased migration distance with increasing the peptide concentration for the concentrations tested. These results show that OPF-based biomimetic hydrogels hold promise for modulating cell proliferation and migration for specific applications by altering the specific ligand and its concentration in the hydrogels.

The use of debrided human articular cartilage for autologous chondrocyte implantation: maintenance of chondrocyte differentiation and proliferation in type I collagen gels

Autologous chondrocyte implantation (ACI) is the most promising surgical treatment for large full thickness knee joint articular cartilage (AC) defects where cells from healthy non-weight bearing area AC are multiplied in vitro and implanted into such defects. In the routine surgical procedure for symptomatic knee full thickness AC defects, damaged AC surrounding the edge and the base of such defects is usually debrided and discarded. The purpose of this study was to examine if chondrocytes from this 'debrided' AC can proliferate, synthesize a cartilage specific matrix and thus can be used for ACI.

METHODS

Biopsies were retrieved from 12 patients (debrided articular cartilage: DAC, aged 35-61) and from two autopsies (normal articular cartilage: NAC, aged 21 and 25). Chondrocytes were isolated, seeded at low density in type I collagen gels and as monolayer cultures for 4 weeks without passage.

RESULTS

After 4 weeks cultures in type I collagen gels, cell proliferation from DAC (18.34 +/- 1.95 fold) was similar to cells from NAC (11.24 +/- 1.02 fold). Syntheses of proteoglycan and collagen in DAC were also similar to NAC. Newly synthesized matrices in gel cultures consisted predominantly of type II collagen as shown by immuno-labelling and SDS-PAGE followed by fluorography. Chondrocytes from 'debrided human AC' cultured at low density in type I collagen gels may be used for the ACI procedure as they provide sufficient viable cell numbers for ACI and maintain their chondrocyte phenotype as they synthesize a cartilage-like matrix.

Differential Behavior Between Isolated and Aggregated Rabbit Auricular Chondrocytes on Plastic Surfaces

A knowledge of the behavior of chondrocytes in culture is relevant for tissue engineering. Chondrocytes dedifferentiate to a fibroblast-like phenotype on plastic surfaces. Dedifferentiation is reversible if these cells are then cultured in suspension. In this report a description is given of how when chondrocyte aggregates formed in suspension are next seeded on plastic, most of them attach as round or polygonal cells. This morphological differentiation, with synthesis of type II collagen, is stable for long culture periods. This simple method can be of use as a model for studies of chondrocyte behavior on plastic. The results indicate that in addition to culture conditions, such as cell isolation method or cell density, chondrocyte behavior on plastic depends on the presence of aggregates.

Effects of cell density on proliferation and matrix synthesis of chondrocytes embedded in atelocollagen gel

The effects of cell density on the proliferation and chondroitin sulfate synthesis of chondrocytes embedded in Atelocollagen gel were examined. Chondrocytes of 21 10-week-old Japanese white rabbits isolated by collagenase digestion were embedded in Atelocollagen gel and cultured in Dulbecco's modified Eagles medium at cell densities of 2 x 105 cells/ml (105 group), 2 x 106 cells/ml (106 group), and 2 x 107 cells/ml (107 group) for 4 weeks. Chondrocytes in the 105 group gradually proliferated more than the other two groups. In contrast, most chondrocytes in the 107 group showed increased capability to produce chondroitin 6-sulfate. Cartilage-like tissue was produced from high-density cultures (107 cells/ml), although a decrease in cell number was seen. Even in three-dimensional cultures, the proliferation and chondroitin sulfate synthesis of chondrocytes were influenced by the cell density. These results are informative for the clinical application of chondrocyte transplantation in three-dimensional cultures for cartilage repair.

Human septal chondrocyte redifferentiation in alginate, polyglycolic acid scaffold, and monolayer culture

OBJECTIVES/HYPOTHESIS

Tissue engineering laboratories are attempting to create neocartilage that could serve as an implant material for structural support during reconstructive surgery. One approach to forming such tissue is to proliferate chondrocytes in monolayer culture and then seed the expanded cell population onto biodegradable scaffolds. However, chondrocytes are known to dedifferentiate after this type of monolayer growth and, as a result, decrease their production of cartilaginous extracellular matrix components such as sulfated glycosaminoglycans. The resultant tissue lacks the biomechanical properties characteristic of cartilage. The objective of the study was to determine whether different culture systems could induce monolayer-expanded human septal chondrocytes to redifferentiate and form extracellular matrix.

STUDY DESIGN

Laboratory research.

METHODS

Chondrocytes were isolated from human nasal septal cartilage of five donor patients (age, 35.8 +/- 9.3 y). Cell populations were seeded at low density (30,000 cells/cm2) into monolayer culture and expanded for 4 to 6 days. Following trypsin release, chondrocytes were placed into three different systems for neocartilage formation: alginate beads, polyglycolic acid scaffolds, and monolayer. After 7 and 14 days of growth, neocartilage was analyzed using histological and quantitative biochemical assessment of cellularity (Hoechst 33258 assay) and sulfated glycosaminoglycan content (dimethyl methylene blue assay).

RESULTS

Histologically, alginate beads contained spherical chondrocytes surrounded by dense extracellular matrix, an appearance similar to that of native cartilage. In contrast, polyglycolic acid scaffolds and monolayer cultures contained elongated cells with scant staining for matrix sulfated glycosaminoglycans, which are features that are characteristic of dedifferentiated chondrocytes. Biochemical analysis demonstrated a lower level of cell proliferation (P <.001) in scaffolds (+52% over baseline) and alginate (+96% over baseline) than in monolayer (+366% over baseline), as well as a higher content of sulfated glycosaminoglycans per cell (P <.001), after 14 days of growth in alginate culture than in either polyglycolic acid scaffolds (19-fold difference) or monolayer (98-fold difference).

CONCLUSIONS

Of the systems compared, monolayer-expanded human septal chondrocytes demonstrated the greatest accumulation of sulfated glycosaminoglycans per cell when grown in alginate beads. Future research on cartilage tissue engineering may use alginate culture for reverting dedifferentiated cells back to the chondrocytic phenotype.

Differential expression of multiple genes during articular chondrocyte redifferentiation

Articular chondrocytes undergo a rapid change in phenotype and gene expression, termed dedifferentiation, when isolated from cartilage tissue and cultured on tissue culture plastic. On the other hand, "redifferentiation" of articular chondrocytes in suspension culture is characterized by decreased cellular proliferation and the reinitiation of synthesis of hyaline articular cartilage extracellular matrix molecules. The molecular triggers for these events have yet to be defined. Subtracted cDNA libraries representing genes involved in the early events of adult human articular chondrocyte redifferentiation were generated from human articular chondrocytes that were first cultured in monolayer, and subsequently transferred to suspension culture at 10(6) cells/ml for redifferentiation. Differential regulation of genes involved in cellular organization, nuclear structure, cellular growth regulation, and extracellular matrix deposition and remodeling were observed within 48 hr of this transfer. Many of these genes had not been previously identified in the chondrocyte differentiation pathway and a number of the isolated cDNAs did not have homologies to sequences in the public data banks. Genes involved in IL-6 signal transduction including acute phase response factor (APRF), Mn superoxide dismutase, and IL-6 itself were up-regulated in suspension culture. Membrane glycoprotein gp130, a component of the IL-6 receptor, was down-regulated. Other genes involved in cell polarity, cell adherence, apoptosis, and possibly TGF-beta signaling were differentially regulated. The differential regulation of the cytokine connective tissue growth factor (CTGF) during the early stages of articular chondrocyte redifferentiation, decreasing within 48 hours of transfer to suspension culture, was particularly interesting given its reported role in the stimulation of cellular proliferation. CTGF was highly expressed in proliferative monolayer culture, and then greatly reduced by redifferentiation in standard high-density suspension culture. When articular chondrocytes were seeded in suspension at low-density (10(4) cells/ml), however, high levels of CTGF were observed along with increased levels of mature articular cartilage extracellular matrix protein RNAs, such as type II collagen and aggrecan. Although the role of CTGF in articular cartilage biology remains to be elucidated, the results described here demonstrate the potential utility of subtractive hybridization in understanding the process of articular chondrocyte redifferentiation.