Cartilage engineering: a crucial combination of cells, biomaterials and biofactors

Preparation and characterization of collagen/PLA, chitosan/PLA, and collagen/chitosan/PLA hybrid scaffolds for cartilage tissue engineering

In this study, three-dimensional (3D) porous scaffolds were developed for the repair of articular cartilage defects. Novel collagen/polylactide (PLA), chitosan/PLA, and collagen/chitosan/PLA hybrid scaffolds were fabricated by combining freeze-dried natural components and synthetic PLA mesh, where the 3D PLA mesh gives mechanical strength, and the natural polymers, collagen and/or chitosan, mimic the natural cartilage tissue environment of chondrocytes. In total, eight scaffold types were studied: four hybrid structures containing collagen and/or chitosan with PLA, and four parallel plain scaffolds with only collagen and/or chitosan. The potential of these types of scaffolds for cartilage tissue engineering applications were determined by the analysis of the microstructure, water uptake, mechanical strength, and the viability and attachment of adult bovine chondrocytes to the scaffolds. The manufacturing method used was found to be applicable for the manufacturing of hybrid scaffolds with highly porous 3D structures. All the hybrid scaffolds showed a highly porous structure with open pores throughout the scaffold. Collagen was found to bind water inside the structure in all collagen-containing scaffolds better than the chitosan-containing scaffolds, and the plain collagen scaffolds had the highest water absorption. The stiffness of the scaffold was improved by the hybrid structure compared to plain scaffolds. The cell viability and attachment was good in all scaffolds, however, the collagen hybrid scaffolds showed the best penetration of cells into the scaffold. Our results show that from the studied scaffolds the collagen/PLA hybrids are the most promising scaffolds from this group for cartilage tissue engineering.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Nasal reconstruction using tissue engineered constructs: an update

Currently, the gold standard for reconstruction after rhinectomy or severe trauma to the nose, includes transposition of autologous mucosal flaps plus autologous cartilage grating and coverage using a skin flap. Difficulties with this approach arise where; cartilage and mucosa harvested from autologous donor sites is insufficient to achieve a passable aesthetic and functional reconstruction. Skin flaps are often bulky, poor color matches with hair follicles that reduce the aesthetic quality of the reconstruction. We suggest that tissue engineering could be a source of functional replacement tissues for nasal reconstructive surgery. However, the advancement of such an approach is dependent on the dissemination of scientific information into the clinical community, regarding the engineering of tissues such as mucosa, skin, and cartilage. This paper therefore reviews how the tissue engineering strategies available for producing clinically viable tissues could help resolve issues around reconstructing the human nose.

Effects of hydrostatic pressure on biosynthetic activity during chondrogenic differentiation of MSCs in hybrid scaffolds

The objective of this study was to determine the effects of hydrostatic pressure (HP) on the biochemical properties and gene expression of mesenchymal stem cells (MSCs) on scaffolds for cartilage tissue engineering composed of poly(caprolactone) (PCL) poly(vinyl alcohol) (PVA) gelatin (GEL) semi interpenetrating polymer network (semi-IPN). The MSCs were cultured on PCL-PVA-GEL semi-IPN scaffolds in two groups (A and B) for 7 and 21 days, respectively, and then loaded with hydrostatic pressure (5 MPa, 0.5 Hz) for 2 h per day for the period of 7 days and compared with two non-loaded groups (C and D) as controls. DMMB and real-time PCR analysis for assaying cartilage-specific extracellular matrix (ECM) gene markers were carried out. According to the results, there were no significant differences in GAG amounts between the loaded and non-loaded constructs were observed after 14 days. However, significant and considerable increases in the expression amount of type II collagen mRNA levels in group A ( from 2.43 × 10-4 ± 5.32 × 10-5 to 2.09 × 10-3 ± 1.07 × 10-4 time), and in group B (from 3.04 × 10-4 ± 4.31 × 10-5 to 2.08 × 10-3 ± 1.59 × 10-4 time) in comparison with non-loaded groups (C and D) were observed, respectively. Results showed the beneficial role of hydrostatic pressure on the increase of type II collagen mRNA levels in articular cartilage tissue engineering.

Effect of PRP and PPP on proliferation and migration of human chondrocytes and synoviocytes in vitro

Cartilage tissue engineering can provide substantial relief to people suffering from degenerative cartilage disease, such as osteoarthritis. The autologous platelet-rich plasma (PRP) application appears to improve cartilage healing due to its ability to positively influence cellular mechanisms, mainly in cells from synovium and cartilage. Primary cultures of human synovial fluid stem cells (synoviocytes, SCs) and chondrocytes (CCs) were exposed to various concentrations of non-activated PRP and plateletpoor plasma (PPP) prepared by apheresis. Cell proliferation and migration were evaluated in real-time with the non-invasive xCELLigence System. It was found that PRP had a similar effect on the growth of cells as fetal bovine serum (FBS). Surprisingly, our proliferation assay results indicated that 50% PPP had the largest effect on both cell types, with a statistically significant increase in cell number (P<0.001) compared to the (0% FBS) in vitro control. The migratory ability of SCs was significantly enhanced with 10% PRP and 0.8% hyaluronic acid (HA). HA also augmented migration of CCs. In summary, these results demonstrate that directed cell proliferation and migration are inducible in human articular CCs and SCs, and that both platelet-derived fractions may exert a positive effect and modulate several cell responses that are potentially involved in tissue integration during cartilage repair.

Current concepts: tissue engineering and regenerative medicine applications in the ankle joint

Tissue engineering and regenerative medicine (TERM) has caused a revolution in present and future trends of medicine and surgery. In different tissues, advanced TERM approaches bring new therapeutic possibilities in general population as well as in young patients and high-level athletes, improving restoration of biological functions and rehabilitation. The mainstream components required to obtain a functional regeneration of tissues may include biodegradable scaffolds, drugs or growth factors and different cell types (either autologous or heterologous) that can be cultured in bioreactor systems (in vitro) prior to implantation into the patient. Particularly in the ankle, which is subject to many different injuries (e.g. acute, chronic, traumatic and degenerative), there is still no definitive and feasible answer to ‘conventional’ methods. This review aims to provide current concepts of TERM applications to ankle injuries under preclinical and/or clinical research applied to skin, tendon, bone and cartilage problems. A particular attention has been given to biomaterial design and scaffold processing with potential use in osteochondral ankle lesions.

Collagen scaffold for cartilage tissue engineering: the benefit of fibrin glue and the proper culture time in an infant cartilage model

This study (i) developed a scaffold made of collagen I designed for hosting the autologous chondrocytes, (ii) focused on the optimization of chondrocytes seeding by the addition of the fibrin glue, and (iii) investigated the culture time for the ideal scaffold maturation in vitro. In the first part of the study, fresh chondrocytes were isolated from infant swine articular cartilage, and immediately seeded onto the collagen sponges either in medium or in fibrinogen in order to show the contribute of fibrin glue in cell seeding and survival into the scaffold. In the second part of the study, chondrocytes were first expanded in vitro and then resuspended in fibrinogen, seeded in collagen sponges, and cultured for 1, 3, and 5 weeks in order to identify the optimal time for the rescue of cell phenotype and for the scaffold maturation into a tissue with chondral properties. The histological and immunohistochemical data from the first part of the study (study with primary chondrocytes) demonstrated that the presence of fibrin glue ameliorated cell distribution and survival into the chondral composites. The second part of this work (study with dedifferentiated chondrocytes) showed that the prolongation of the culture to 3 weeks promoted a significant restoration of the cell phenotype, resulting in a composite with proper morphological features, biochemical composition, and mechanical integrity. In conclusion, this study developed a collagenic-fibrin glue scaffold that was able to support chondrocyte survival and synthetic activity in a static culture; in particular, this model was able to turn the engineered samples into a tissue with chondral-like properties when cultured in vitro for at least 3 weeks.

Conditioned medium as a strategy for human stem cells chondrogenic differentiation

Paracrine signalling from chondrocytes has been reported to increase the synthesis and expression of cartilage extracellular matrix (ECM) by stem cells. The use of conditioned medium obtained from chondrocytes for stimulating stem cells chondrogenic differentiation may be a very interesting alternative for moving into the clinical application of these cells, as chondrocytes could be partially replaced by stem cells for this type of application. In the present study we aimed to achieve chondrogenic differentiation of two different sources of stem cells using conditioned medium, without adding growth factors. We tested both human bone marrow-derived mesenchymal stem cells (hBSMCs) and human Wharton's jelly-derived stem cells (hWJSCs). Conditioned medium obtained from a culture of human articular chondrocytes was used to feed the cells during the experiment. Cultures were performed in previously produced three-dimensional (3D) scaffolds, composed of a blend of 50:50 chitosan:poly(butylene succinate). Both types of stem cells were able to undergo chondrogenic differentiation without the addition of growth factors. Cultures using hWJSCs showed significantly higher GAGs accumulation and expression of cartilage-related genes (aggrecan, Sox9 and collagen type II) when compared to hBMSCs cultures. Conditioned medium obtained from articular chondrocytes induced the chondrogenic differentiation of MSCs and ECM formation. Obtained results showed that this new strategy is very interesting and should be further explored for clinical applications.

Exogenous bFGF promotes articular cartilage repair via up-regulation of multiple growth factors

OBJECTIVE

To investigate the roles of exogenous basic fibroblast growth factor (bFGF) on the repair of full-thickness articular cartilage defects in rabbits.

DESIGN

In the present study, a double-layered collagen membrane sandwiched with bFGF-loaded-nanoparticles between a dense layer and a loose layer was implanted into full-thickness articular cartilage defects in rabbits. By grafting the membrane in a different direction, the dense layer or the loose layer facing the surface of the subchondral bone, the effects of the released bFGF on the defects and the profiles of nine growth factors (GFs) in synovial fluid (SF) were investigated using histological methods and antibody arrays, respectively.

RESULTS

In the group with the loose layer facing the surface of the subchondral bone, fast release of bFGF was observed, and early high levels of endogenous transforming growth factor-β2 (TGF-β2), vascular endothelial growth factor (VEGF), bFGF, bone morphogenetic protein 2 (BMP-2), BMP-3, and BMP-4 in SF were detected by antibody arrays, especially on day 3. Chondrocyte-like cells were also observed in this group at an early stage. As a result, this group showed better levels of repair, as compared to the other groups in which low GF levels were detected at an early stage, and chondrocyte-like cells appeared much later.

CONCLUSIONS

Our study suggests that exogenous bFGF promotes articular cartilage repair by up-regulating the levels of multiple GFs, but administration at an early stage is required.

Chondrogenic differentiation of ATDC5 and hMSCs could be induced by a novel scaffold-tricalcium phosphate-collagen-hyaluronan without any exogenous growth factors in vitro

Application of chondrogenic growth factors is a routine strategy to induce chondrogenesis of hMSCs, but they have economic and safety problems in the long term. It is expected that scaffold material itself could play an important role in chondrogenesis of hMSCs. In this study we tested whether a novel tricalcium phosphate-collagen-hyaluronan scaffold (TCP-COL-HA) had inherent chondro-inductive capacity for chondrogenesis of both ATDC5 and hMSCs without any exogenous growth factors in vitro. hMSCs and ATDC5 were seeded onto TCP-COL-HA scaffolds and cultured in basal medium for 3 weeks to investigate whether the TCP-COL-HA scaffold itself had differentiation-inductive capacity in basal culture. With hMSCs-seeded scaffold in chondrogenic medium (including TGF-β1) as positive control, we then compared the chondrogenic induction of TCP-COL-HA in basal culture and in chondrogenic culture. The chondrogenic differentiation was evaluated by sulfated glycosaminoglycans (GAGs) quantification, type II collagen immunohistochemistry, and RT-PCR. Mechanical strength was evaluated by compression test and the cell death rate of hMSCs was assessed with TUNEL assay. The results showed TCP-COL-HA scaffold itself could efficiently induce chondrogenic differentiation of both ATDC5 and hMSCs after 3 weeks in basal culture. The accumulation of GAGs and the expression of chondrocyte marker genes were all significantly increased. In addition, hMSCs-seeded scaffold showed a significantly higher mechanical strength after 3 weeks in basal culture. The chondrogenic induction of TCP-COL-HA scaffolds in basal medium were almost similar to that in chondrogenic medium on hMSCs. The chondrogenesis-inducing capacity of TCP-COL-HA scaffold might help to improve cartilage tissue engineering with economic and safe benefits.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part I: recapitulation of native tissue healing and variables for the design of delivery systems

The potential of growth factors to stimulate tissue healing through the enhancement of cell proliferation, migration, and differentiation is undeniable. However, critical parameters on the design of adequate carriers, such as uncontrolled spatiotemporal presence of bioactive factors, inadequate release profiles, and supraphysiological dosages of growth factors, have impaired the translation of these systems onto clinical practice. This review describes the healing cascades for bone, cartilage, and osteochondral interface, highlighting the role of specific growth factors for triggering the reactions leading to tissue regeneration. Critical criteria on the design of carriers for controlled release of bioactive factors are also reported, focusing on the need to provide a spatiotemporal control over the delivery and presentation of these molecules.

Regenerating cartilages by engineered ASCs: prolonged TGF-β3/BMP-6 expression improved articular cartilage formation and restored zonal structure

Adipose-derived stem cells (ASCs) hold promise for cartilage regeneration but their chondrogenesis potential is inferior. Here, we used a baculovirus (BV) system that exploited FLPo/Frt-mediated transgene recombination and episomal minicircle formation to genetically engineer rabbit ASCs (rASCs). The BV system conferred prolonged and robust TGF-β3/BMP-6 expression in rASCs cultured in porous scaffolds, which critically augmented rASCs chondrogenesis and suppressed osteogenesis/hypertrophy, leading to the formation of cartilaginous constructs with improved maturity and mechanical properties in 2-week culture. Twelve weeks after implantation into full-thickness articular cartilage defects in rabbits, these engineered constructs regenerated neocartilages that resembled native hyaline cartilages in cell morphology, matrix composition and mechanical properties. The neocartilages also displayed cartilage-specific zonal structures without signs of hypertrophy and degeneration, and eventually integrated with host cartilages. In contrast, rASCs that transiently expressed TGF-β3/BMP-6 underwent osteogenesis/hypertrophy and resulted in the formation of inferior cartilaginous constructs, which after implantation regenerated fibrocartilages. These data underscored the crucial role of TGF-β3/BMP-6 expression level and duration in rASCs in the cell differentiation, constructs properties and in vivo repair. The BV-engineered rASCs that persistently express TGF-β3/BMP-6 improved the chondrogenesis, in vitro cartilaginous constructs production and in vivo hyaline cartilage regeneration, thus representing a remarkable advance in cartilage engineering.

Use of magnetic forces to promote stem cell aggregation during differentiation, and cartilage tissue modeling

Magnetic forces induce cell condensation necessary for stem cell differentiation into cartilage and elicit the formation of a tissue-like structure: Magnetically driven fusion of aggregates assembled by micromagnets results in the formation of a continuous tissue layer containing abundant cartilage matrix.

Effects of in vitro low oxygen tension preconditioning of adipose stromal cells on their in vivo chondrogenic potential: application in cartilage tissue repair

Purpose

Multipotent stromal cell (MSC)-based regenerative strategy has shown promise for the repair of cartilage, an avascular tissue in which cells experience hypoxia. Hypoxia is known to promote the early chondrogenic differentiation of MSC. The aim of our study was therefore to determine whether low oxygen tension could be used to enhance the regenerative potential of MSC for cartilage repair.

Methods

MSC from rabbit or human adipose stromal cells (ASC) were preconditioned in vitro in control or chondrogenic (ITS and TGF-β) medium and in 21 or 5% O₂. Chondrogenic commitment was monitored by measuring COL2A1 and ACAN expression (real-time PCR). Preconditioned rabbit and human ASC were then incorporated into an Si-HPMC hydrogel and injected (i) into rabbit articular cartilage defects for 18 weeks or (ii) subcutaneously into nude mice for five weeks. The newly formed tissue was qualitatively and quantitatively evaluated by cartilage-specific immunohistological staining and scoring. The phenotype of ASC cultured in a monolayer or within Si-HPMC in control or chondrogenic medium and in 21 or 5% O₂ was finally evaluated using real-time PCR.

Results/Conclusions

5% O₂ increased the in vitro expression of chondrogenic markers in ASC cultured in induction medium. Cells implanted within Si-HPMC hydrogel and preconditioned in chondrogenic medium formed a cartilaginous tissue, regardless of the level of oxygen. In addition, the 3D in vitro culture of ASC within Si-HPMC hydrogel was found to reinforce the pro-chondrogenic effects of the induction medium and 5% O₂. These data together indicate that although 5% O₂ enhances the in vitro chondrogenic differentiation of ASC, it does not enhance their in vivo chondrogenesis. These results also highlight the in vivo chondrogenic potential of ASC and their potential value in cartilage repair.

An interpenetrating HA/G/CS biomimic hydrogel via Diels-Alder click chemistry for cartilage tissue engineering

In order to mimic the natural cartilage extracellular matrix, a novel biological degradable interpenetrating network hydrogel was synthesized from the gelatin (G), hyaluronic acid (HA) and chondroitin sulfate (CS) by Diels-Alder "click" chemistry. HA was modified with furylamine and G was modified with furancarboxylic acid respectively. (1)H NMR spectra and elemental analysis showed that the substitution degrees of HA-furan and G-furan were 71.5% and 44.5%. Then the hydrogels were finally synthesized by cross-linking furan-modified HA and G derivatives with dimaleimide poly(ethylene glycol) (MAL-PEG-MAL). The mechanical and degradation properties of the hydrogels could be tuned simply through varying the molar ratio between furan and maleimide. Rheological, mechanical and degradation studies demonstrated that the Diels-Alder "click" chemistry is an efficient method for preparing high performance biological interpenetrating hydrogels. This biomimic hydrogel with improved mechanical properties could have great potential applications in cartilage tissue engineering.

Sox9-regulated miRNA-574-3p inhibits chondrogenic differentiation of mesenchymal stem cells

The aim of this study was to identify new microRNAs (miRNAs) that are modulated during the differentiation of mesenchymal stem cells (MSCs) toward chondrocytes. Using large scale miRNA arrays, we compared the expression of miRNAs in MSCs (day 0) and at early time points (day 0.5 and 3) after chondrogenesis induction. Transfection of premiRNA or antagomiRNA was performed on MSCs before chondrogenesis induction and expression of miRNAs and chondrocyte markers was evaluated at different time points during differentiation by RT-qPCR. Among miRNAs that were modulated during chondrogenesis, we identified miR-574-3p as an early up-regulated miRNA. We found that miR-574-3p up-regulation is mediated via direct binding of Sox9 to its promoter region and demonstrated by reporter assay that retinoid X receptor (RXR)α is one gene specifically targeted by the miRNA. In vitro transfection of MSCs with premiR-574-3p resulted in the inhibition of chondrogenesis demonstrating its role during the commitment of MSCs towards chondrocytes. In vivo, however, both up- and down-regulation of miR-574-3p expression inhibited differentiation toward cartilage and bone in a model of heterotopic ossification. In conclusion, we demonstrated that Sox9-dependent up-regulation of miR-574-3p results in RXRα down-regulation. Manipulating miR-574-3p levels both in vitro and in vivo inhibited chondrogenesis suggesting that miR-574-3p might be required for chondrocyte lineage maintenance but also that of MSC multipotency.

Preparation of an adipose-derived stem cell/fibrin–poly(d,l-lactic-co-glycolic acid) construct based on a rapid prototyping technique

Currently, large, thick, and complex tissue vascularization is one of the research focuses of tissue engineering. Numerous studies have proven that microvascular systems can be developed by cultivating endothelial cells in a hydrogel/scaffold structure. As the sources of adult endothelial cells are very limited and very easily degraded, it is better to induce stem cells into endothelial cells. In this article, a grid poly(d,l-lactic- co-glycolic acid) structure with defined internal channels was fabricated using a low-temperature deposition manufacturing technique under computer direction. In a fibrinogen mixture, an aqueous adipose-derived stem cell fibrinogen mixture was incorporated into the internal walls of the poly(d,l-lactic- co-glycolic acid) scaffold and stabilized with thrombin solution. After several days of in vitro culture, the adipose-derived stem cells immobilized in the fibrin hydrogel were induced into endothelial-like cells with endothelial growth factor and basic fibroblast growth factor. Morphological and biological properties of the composite cell/fibrin–poly(d,l-lactic- co-glycolic acid) construct were characterized.

Osteochondral tissue regeneration using a bilayered composite hydrogel with modulating dual growth factor release kinetics in a rabbit model

Biodegradable oligo(poly(ethylene glycol) fumarate) (OPF) composite hydrogels have been investigated for the delivery of growth factors (GFs) with the aid of gelatin microparticles (GMPs) and stem cell populations for osteochondral tissue regeneration. In this study, a bilayered OPF composite hydrogel that mimics the distinctive hierarchical structure of native osteochondral tissue was utilized to investigate the effect of transforming growth factor-β3 (TGF-β3) with varying release kinetics and/or insulin-like growth factor-1 (IGF-1) on osteochondral tissue regeneration in a rabbit full-thickness osteochondral defect model. The four groups investigated included (i) a blank control (no GFs), (ii) GMP-loaded IGF-1 alone, (iii) GMP-loaded IGF-1 and gel-loaded TGF-β3, and (iv) GMP-loaded IGF-1 and GMP-loaded TGF-β3 in OPF composite hydrogels. The results of an in vitro release study demonstrated that TGF-β3 release kinetics could be modulated by the GF incorporation method. At 12weeks post-implantation, the quality of tissue repair in both chondral and subchondral layers was analyzed based on quantitative histological scoring. All groups incorporating GFs resulted in a significant improvement in cartilage morphology compared to the control. Single delivery of IGF-1 showed higher scores in subchondral bone morphology as well as chondrocyte and glycosaminoglycan amount in adjacent cartilage tissue when compared to a dual delivery of IGF-1 and TGF-β3, independent of the TGF-β3 release kinetics. The results suggest that although the dual delivery of TGF-β3 and IGF-1 may not synergistically enhance the quality of engineered tissue, the delivery of IGF-1 alone from bilayered composite hydrogels positively affects osteochondral tissue repair and holds promise for osteochondral tissue engineering applications.

Fabrication of poly(lactide-co-glycolide) scaffold filled with fibrin gel, mesenchymal stem cells, and poly(ethylene oxide)-b-poly(L-lysine)/TGF-β1 plasmid DNA complexes for cartilage restoration in vivo

A poly (lactide-co-glycolide) (PLGA) scaffold filled with fibrin gel, mesenchymal stem cells (MSCs) and poly(ethylene oxide)-b-poly (L-lysine) (PEO-b-PLL)/pDNA-TGF-β1 complexes was fabricated and applied in vivo for synchronized regeneration of cartilage and subchondral bone. The PEO-b-PLL/pDNA-TGF-β1 complexes could transfect MSCs in vitro to produce TGF-β1 in situ and up regulate the expression of chondrogenesis-related genes in the construct. The expression of heterogeneous TGF-β1 in vivo declined along with the prolongation of implantation time, and lasted for 3 and 6 weeks in the mRNA and protein levels, respectively. The constructs (Experimental group) of PLGA/fibrin gel/MSCs/(PEO-b-PLL/pDNA-TGF-β1 complexes) were implanted into the osteochondral defects of rabbits to restore the functional cartilages, with gene-absent constructs as the Control. After 12 weeks, the Experimental group regenerated the neo-cartilage and subchondral bone with abundant deposition of glycosaminoglycans (GAGs) and type II collagen. The regenerated tissues had good integration with the host tissues too. By contrast, the defects were only partially repaired by the Control constructs. qRT-PCR results demonstrated that expression of the chondrogenesis-marker genes in the Experimental group was significantly higher than that of the Control group, and was very close to that of the normal cartilage tissue.

Scaffolds for cartilage repair of the ankle joint: The impact on surgical practice

BACKGROUND

Ideal management of osteochondral lesions in the ankle joint is still theme of debate. Scaffold-based repair is emerging as a new approach for regenerative treatment.

METHODS

Articles published in PubMed from 2000 to January 2012 addressing cartilage scaffold-based treatment were identified, including levels I-IV evidence clinical trials with measures of functional, clinical or imaging outcome.

RESULTS

The analysis showed a progressively increasing number of articles from 2000. The number of selected papers was 19:15 focusing on two-step and 4 on one-step procedures; no randomized studies, 3 comparative studies, 11 case series and 5 case reports were identified.

CONCLUSIONS

Regenerative surgical approach with scaffold-based procedures is emerging as a potential therapeutic option for the treatment of chondral lesions of the ankle. One step treatments simplify the procedure and the results reported are very close to the previous techniques. However, well-designed studies are lacking, and randomized long-term trials are necessary to confirm the potential of these techniques.

LEVEL OF EVIDENCE

Review - IV.

Nanostructured 3D constructs based on chitosan and chondroitin sulphate multilayers for cartilage tissue engineering

Nanostructured three-dimensional constructs combining layer-by-layer technology (LbL) and template leaching were processed and evaluated as possible support structures for cartilage tissue engineering. Multilayered constructs were formed by depositing the polyelectrolytes chitosan (CHT) and chondroitin sulphate (CS) on either bidimensional glass surfaces or 3D packet of paraffin spheres. 2D CHT/CS multi-layered constructs proved to support the attachment and proliferation of bovine chondrocytes (BCH). The technology was transposed to 3D level and CHT/CS multi-layered hierarchical scaffolds were retrieved after paraffin leaching. The obtained nanostructured 3D constructs had a high porosity and water uptake capacity of about 300%. Dynamical mechanical analysis (DMA) showed the viscoelastic nature of the scaffolds. Cellular tests were performed with the culture of BCH and multipotent bone marrow derived stromal cells (hMSCs) up to 21 days in chondrogenic differentiation media. Together with scanning electronic microscopy analysis, viability tests and DNA quantification, our results clearly showed that cells attached, proliferated and were metabolically active over the entire scaffold. Cartilaginous extracellular matrix (ECM) formation was further assessed and results showed that GAG secretion occurred indicating the maintenance of the chondrogenic phenotype and the chondrogenic differentiation of hMSCs.

Fabrication and characterization of multiscale electrospun scaffolds for cartilage regeneration

Recently, scaffolds for tissue regeneration purposes have been observed to utilize nanoscale features in an effort to reap the cellular benefits of scaffold features resembling extracellular matrix (ECM) components. However, one complication surrounding electrospun nanofibers is limited cellular infiltration. One method to ameliorate this negative effect is by incorporating nanofibers into microfibrous scaffolds. This study shows that it is feasible to fabricate electrospun scaffolds containing two differently scaled fibers interspersed evenly throughout the entire construct as well as scaffolds containing fibers composed of two discrete materials, specifically fibrin and poly(ε-caprolactone). In order to accomplish this, multiscale fibrous scaffolds of different compositions were generated using a dual extrusion electrospinning setup with a rotating mandrel. These scaffolds were then characterized for fiber diameter, porosity and pore size and seeded with human mesenchymal stem cells to assess the influence of scaffold architecture and composition on cellular responses as determined by cellularity, histology and glycosaminoglycan (GAG) content. Analysis revealed that nanofibers within a microfiber mesh function to maintain scaffold cellularity under serum-free conditions as well as aid the deposition of GAGs. This supports the hypothesis that scaffolds with constituents more closely resembling native ECM components may be beneficial for cartilage regeneration.

Repair of large animal partial-thickness cartilage defects through intraarticular injection of matrix-rejuvenated synovium-derived stem cells

Cartilage defects have a limited ability to self-heal. Stem cell treatment is a promising approach; however, replicative senescence is a challenge to acquiring large-quantity and high-quality stem cells for cartilage regeneration. Synovium-derived stem cells (SDSCs) are a tissue-specific stem cell for cartilage regeneration. Our recent findings suggest that decellularized stem cell matrix (DSCM) can rejuvenate expanded SDSCs in cell proliferation and chondrogenic potential. In this study, we were investigating (1) whether transforming growth factor (TGF)-β1 and TGF-β3 played a similar role in chondrogenic induction of SDSCs after expansion on either DSCM or plastic flasks (plastic), and (2) whether DSCM-expanded SDSCs had an enhanced capacity in repairing partial-thickness cartilage defects in a minipig model. SDSCs were isolated from synovium in two 3-month-old pigs and DSCM was prepared using SDSCs. Passage 2 SDSCs were expanded on either DSCM or plastic for one passage. The expanded cells were evaluated for cell morphology, chondrogenic capacity, and related mechanisms. TGF-β1 and TGF-β3 were compared for their role in chondrogenesis of SDSCs after expansion on either DSCM or plastic. The chondrogenic induction medium without TGF-β served as a control. In 13 minipigs, we intraarticularly injected DSCM- or plastic-expanded SDSCs or saline into knee partial-thickness cartilage defects and assessed their repair using histology and immunohistochemistry. We found DSCM-expanded SDSCs were small, had a fibroblast-like shape, and grew quickly in a three-dimensional format with concomitant up-regulation of phosphocyclin D1 and TGF-β receptor II. Plastic-expanded SDSCs exhibited higher mRNA levels of chondrogenic markers when incubated with TGF-β3, while DSCM-expanded SDSCs displayed comparable chondrogenic potential when treated with either TGF-β isotype. In the minipig model, DSCM-expanded SDSCs were better than plastic-expanded SDSCs in enhancing collagen II and sulfated glycosaminoglycan expression in repair of partial-thickness cartilage defects, but both groups were superior to the saline control group. Our observations suggested that DSCM is a promising cell expansion system that can promote cell proliferation and enhance expanded cell chondrogenic potential in vitro and in vivo. Our approach could lead to a tissue-specific cell expansion system providing large-quantity and high-quality stem cells for the treatment of cartilage defects.

Extracellular matrix scaffolds for cartilage and bone regeneration

Regenerative medicine approaches based on decellularized extracellular matrix (ECM) scaffolds and tissues are rapidly expanding. The rationale for using ECM as a natural biomaterial is the presence of bioactive molecules that drive tissue homeostasis and regeneration. Moreover, appropriately prepared ECM is biodegradable and does not elicit adverse immune responses. Successful clinical application of decellularized tissues has been reported in cardiovascular, gastrointestinal, and breast reconstructive surgery. At present, the use of ECM for osteochondral tissue engineering is attracting interest. Recent data underscore the great promise for future application of decellularized ECM for osteochondral repair. This review describes the rationale for using ECM-based approaches for different regenerative purposes and details the application of ECM for cartilage or osteochondral repair.

Influence of tissue- and cell-scale extracellular matrix distribution on the mechanical properties of tissue-engineered cartilage

The insufficient load-bearing capacity of today's tissue- engineered (TE) cartilage limits its clinical application. Generally, cartilage TE studies aim to increase the extracellular matrix (ECM) content, as this is thought to determine the load-bearing properties of the cartilage. However, there are apparent inconsistencies in the literature regarding the correlation between ECM content and mechanical properties of TE constructs. In addition to the amount of ECM, the spatial inhomogeneities in ECM distribution at the tissue scale as well as at the cell scale may affect the mechanical properties of TE cartilage. The relative importance of such structural inhomogeneities on mechanical behavior of TE cartilage is unknown. The aim of the present study was, therefore, to theoretically elucidate the influence of these inhomogeneities on the mechanical behavior of chondrocyte-agarose TE constructs. A validated non-linear fiber-reinforced poro-elastic swelling cartilage model that can accommodate for effects of collagen reinforcement and swelling by proteoglycans was used. At the tissue scale, ECM was gradually varied from predominantly localized in the periphery of the TE construct toward an ECM-rich inner core. The effect of these inhomogeneities in relation to the total amount of ECM was also evaluated. At the cell scale, ECM was gradually varied from localized in the pericellular area, toward equally distributed throughout the interterritorial area. Results from the tissue-scale model indicated that localization of ECM in either the construct periphery or in the inner core may reduce construct stiffness compared with that of constructs with homogeneous ECM. Such effects are more significant at high ECM amounts. At the cell scale, localization of ECM around the cells significantly reduced the overall stiffness, even at low ECM amounts. The compressive stiffness gradually increased when ECM distribution became more homogeneous and the osmotic swelling pressure in the interterritorial area increased. We conclude that for the same amount of ECM content in TE cartilage constructs, superior mechanical properties can be achieved with more homogeneous ECM distribution at both tissue and cell scale. Inhomogeneities at the cell scale are more important than those at the tissue scale.

Transient serum exposure regimes to support dual differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs), which can generate both osteoblasts and chondrocytes, represent an ideal resource for orthopaedic repair using tissue-engineering approaches. One major difficulty for the development of osteochondral constructs using undifferentiated MSCs is that serum is typically used in culture protocols to promote differentiation of the osteogenic component, whereas existing chondrogenic differentiation protocols rely on the use of serum-free conditions. In order to define conditions which could be compatible with both chondrogenic and osteogenic differentiation in a single bioreactor, we have analysed the efficiency of new biphasic differentiation regimes based on transient serum exposure followed by serum-free treatment. MSC differentiation was assessed either in serum-free medium or with a range of transient exposure to serum, and compared to continuous serum-containing treatment. Although osteogenic differentation was not supported in the complete absence of serum, marker expression and extensive mineralization analyses established that 5 days of transient exposure triggered a level of differentiation comparable to that observed when serum was present throughout. This initial phase of serum exposure was further shown to support the successful chondrogenic differentiation of MSCs, comparable to controls maintained in serum-free conditions throughout. This study indicates that a culture based on temporal serum exposure followed by serum-free treatment is compatible with both osteogenic and chondrogenic differentiation of MSCs. These results will allow the development of novel strategies for osteochondral tissue engineering approaches using MSCs for regenerative medicine.

Human induced pluripotent stem cells differentiated into chondrogenic lineage via generation of mesenchymal progenitor cells

Human induced pluripotent stem cells (hiPSCs) exhibit pluripotency, proliferation capability, and gene expression similar to those of human embryonic stem cells (hESCs). hESCs readily form cartilaginous tissues in teratomas in vivo; despite extensive effort, however, to date no efficient method for inducing mature chondrocytes in vitro has been established. hiPSCs can also differentiate into cartilage in vivo by teratoma formation, but as with hESCs, no reliable system for in vitro chondrogenic differentiation of hiPSCs has yet been reported. Here, we examined the chondrogenic differentiation capability of hiPSCs using a multistep culture method consisting of embryoid body (EB) formation, cell outgrowth from EBs, monolayer culture of sprouted cells from EBs, and 3-dimensional pellet culture. In this culture process, the cell density of monolayer culture was critical for cell viability and subsequent differentiation capability. Monolayer-cultured cells exhibited fibroblast-like morphology and expressed markers for mesenchymal stem cells. After 2-3 weeks of pellet culture, cells in pellets exhibited a spherical morphology typical of chondrocytes and were surrounded by extracellular matrix that contained acidic proteoglycans. The expression of type II collagen and aggrecan in pellets progressively increased. Histological analysis revealed that over 70% of hiPSC-derived pellets successfully underwent chondrogenic differentiation. Using the same culture method, hESCs showed similar histological changes and gene expression, but differentiated slightly faster and more efficiently than hiPSCs. Our study demonstrates that hiPSCs can be efficiently differentiated into the chondrogenic lineage in vitro via generation of mesenchymal progenitor cells, using a simplified, multistep culture method.

Endogenous regeneration of critical-size chondral defects in immunocompromised rat xiphoid cartilage using decellularized human bone matrix scaffolds

Clinical efforts to repair cartilage defects delivering cells or engineered cartilage implants into the lesions have met with limited success. This study used a critical-size chondral defect model in immunocompromised rat xiphoid cartilage to test whether endogenous chondrogenesis could be achieved using human bone matrix scaffolds to deliver human cartilage particles and/or a variant isoform of fibroblast growth factor-2 (FGF2-variant). Seventy-two male athymic RNU rats were enrolled in this study with eight rats per experimental group. Decellularized and demineralized human bone matrix scaffolds loaded with human articular cartilage particles or heat-inactivated cartilage particles were combined with different doses of the FGF2-variant. Scaffolds were implanted into 3-mm-diameter critical-size defects prepared using a biopsy punch through the center of the xiphoid. The samples were evaluated 28 days postsurgery using X-ray, equilibrium partitioning of ionic contrast microcomputed tomography, and safranin O-stained histological sagittal sections. Scaffolds containing cartilage particles plus the FGF2-variant induced dose-dependent increases in the formation of neocartilage (p<0.05), which was distributed homogeneously throughout the defects in comparison to scaffolds containing only the FGF2-variant. These effects were less pronounced when scaffolds with heat-inactivated cartilage particles were used. These results demonstrate that endogenous repair of chondral defects can be achieved in the absence of exogenous cells or bone marrow, suggesting that a similar approach may be successful for treating chondral lesions clinically.

Regenerative medicine: learning from past examples

Regenerative medicine products have characteristically shown great therapeutic potential, but limited market success. Learning from the past attempts at capturing value is critical for new and emerging regenerative medicine therapies to define and evolve their business models as new therapies emerge and others mature. We propose a framework that analyzes technological developments along with alternative business models and illustrates how to use both strategically to map value capture by companies in regenerative medicine. We analyze how to balance flexibility of the supply chain and clarity in the regulatory pathway for each business model and propose the possible pathways of evolution between business models. We also drive analogies between cell-based therapies and other healthcare products such as biologicals and medical devices and suggest how to strategically evolve from these areas into the cell therapy space.

Enhanced cartilage formation by inhibiting cathepsin K expression in chondrocytes expanded in vitro

Although engineered cartilage has great potential in cartilage regeneration and reconstruction, dedifferentiation of chondrocytes during in vitro expansion remains a technical bottleneck in the clinical application. To overcome the problem, a gene modification approach was developed to knock-down the key gene involving dedifferentiation of human chondrocytes. A microarray assay revealed 84 up-regulated genes and 56 down-regulated genes in passage 4 (dedifferentiated) human chondrocytes compared to passage 1 cells. Among them, cathepsin K (CTSK) was the key gene (with 28 folds of increased gene expression), which was further confirmed by RT-PCR and Western-Blot. Furthermore, over-expression of CTSK led to reduced matrix production in cultured human chondrocytes in vitro and poor formation of engineered cartilage in vivo. In contrast, CTSK knock-down could better maintain the chondrogenic phenotype of in vitro expanded cells with increased gene and protein expression of collagen II and aggrecan when compared to control cells. More importantly, after 6 passages, the knock-down cells formed much better engineered cartilage than the control cells after in vivo implantation with 30% Pluronic F127 for 8 weeks as the experimental group formed much bigger sized cartilages with significantly increased weight and glycosaminoglycan content (p < 0.05) than the control group. Histologically, the knock-down cells formed a more homogenous cartilage structure with enhanced production of collagen II and proteoglycans. Overall, these results suggest that CTSK knock-down may provide a feasible way to expand functional human chondrocytes in vitro for engineering good quality human cartilage and thus may have its great potential in the clinical translation of engineered cartilage in the future, given the fact that biosafe RNA interference techniques are already available.

Comparative evaluation of MSCs from bone marrow and adipose tissue seeded in PRP-derived scaffold for cartilage regeneration

The aims of this study were to (1) determine whether platelet-rich plasma (PRP) could be prepared as a bioactive scaffold capable of endogenous growth factor release for cartilage repair; (2) compare the chondrogenic differentiation ability of mesenchymal stem cells (MSCs) from bone marrow (BMSC) and from adipose (ADSC) seeded within the PRP scaffold; and (3) test the efficacy of ADSC-PRP construct in cartilage regeneration in vivo. In vitro evaluation showed that a 3-dimensional scaffold with a mesh-like microstructure was formed from PRP, with the capability of endogenous growth factor release and ready cell incorporation. Upon seeding in the PRP scaffold, BMSC showed higher proliferation rate, and higher expression of cartilage-specific genes and proteins than ADSC. In an osteochondral defect model in rabbits, implanted BMSC seeded within PRP scaffold also exhibited better gross appearance and histological and immunohistochemical characteristics, higher cartilage-specific gene and protein expression as well as subchondral bone regeneration. ADSC seeded constructs developed into functional chondrocytes secreting cartilaginous matrix in rabbits at 9 weeks post-implantation. Our findings suggest that PRP is a candidate bioactive scaffold capable of releasing endogenous growth factors and that BMSC and ADSC seeded within the PRP scaffold differentiate into chondrocytes and may be suitable for cell-based cartilage repair.

Hybrid matrix grafts to favor tissue regeneration in rabbit femur bone lesions

At present, typical approaches employed to repair fractures and other bone lesions tend to use matrix grafts to promote tissue regeneration. These grafts act as templates, which promote cellular adhesion, growth and proliferation, osteoconduction, and even osteoinduction, which commonly results in de novo osteogenesis. The present work aimed to study the bone-repairing ability of hybrid matrixes (HM) prepared with polyvinyl alcohol (PVA) and bioactive glass in an experimental rabbit model. The HM were prepared by combining 30% bioactive glass (nominal composition of 58% SiO2 -33 % CaO - 9% P2O5) and 70% PVA. New Zealand rabbits were randomly divided into the control group (C group) and two groups with bone lesions, in which one received a matrix implant HM (Implant group), while the other did not (no Implant group). Clinical monitoring showed no altered parameters from either the Implant or the no Implant groups as compared to the control group, for the variables of diet grades, day and night temperatures and hemograms. In the Implant group, radiologic and tomographic studies showed implanted areas with clean edges in femoral non-articular direction, and radio-dense images that suggest incipient integration. Minimum signs of phlogosis could be observed, whereas no signs of rejection at this imaging level could be identified. Histological analysis showed evidence of osteo-integration, with the formation of a trabecular bone within the implant. Together, these results show that implants of hybrid matrixes of bioactive glass are capable of promoting bone regeneration.

A comparative study of aggrecan synthesis between natural articular chondrocytes and differentiated chondrocytes from adipose derived stem cells in 3D culture

Introduction:

The main obstacle for tissue engineering is to find the most appropriate cell which is able to produce extracellular matrix (ECM) similar or better than natural chondrocytes in vitro. This study compared aggrecan synthesis's potential between differentiated chondrocytes (DCs) from adipose-derived stem cells (ADSCs) and natural articular chondrocytes (NCs) in 3D culture in vitro.

Materials and Methods:

Human ADSCs were isolated from sub-cutaneous adipose tissue and then the surface markers including CD 14, 45 CD105, CD90, CD44 were analyzed by flow cytometry. Also human articular chondrocytes were yielded of non-weight bearing area of Knee cartilage. Both types of the cells were encapsulated in alginate scaffolds and cultured in chondrogenic medium with and without TGFβ3 for 3 weeks. Then the extent of aggercan (AGC) production was evaluated by ELISA on days 14 and 21.

Results:

Our findings indicated that differentiated chondrocytes (DCs) with and without TGFβ3 synthesized more AGC than natural chondrocytes (NCs) on day 14. But DCs without TGFβ3 had higher production than other groups on day 21. Application of TGFβ3 resulted in an increase of amount of AGC in DCs on day 14 but a decrease on day 21 than same group.

Conclusion:

Since, aggrecan is an important chondrogenic marker, it was concluded that ADSCs can be possible reliable alternative cell source for cartilage tissue engineering in future.

Effects of FGF-2 on human adipose tissue derived adult stem cells morphology and chondrogenesis enhancement in Transwell culture

Injured cartilage is difficult to repair due to its poor vascularisation. Cell based therapies may serve as tools to more effectively regenerate defective cartilage. Both adult mesenchymal stem cells (MSCs) and human adipose derived stem cells (hADSCs) are regarded as potential stem cell sources able to generate functional cartilage for cell transplantation. Growth factors, in particular the TGF-b superfamily, influence many processes during cartilage formation, including cell proliferation, extracellular matrix synthesis, maintenance of the differentiated phenotype, and induction of MSCs towards chondrogenesis. In the current study, we investigated the effects of FGF-2 on hADSC morphology and chondrogenesis in Transwell culture. hADSCs were obtained from patients undergoing elective surgery, and then cultured in expansion medium alone or in the presence of FGF-2 (10 ng/ml). mRNA expression levels of SOX-9, aggrecan and collagen type II and type X were quantified by real-time polymerase chain reaction. The morphology, doubling time, trypsinization time and chondrogenesis of hADSCs were also studied. Expression levels of SOX-9, collagen type II, and aggrecan were all significantly increased in hADSCs expanded in presence of FGF-2. Furthermore FGF-2 induced a slender morphology, whereas doubling time and trypsinization time decreased. Our results suggest that FGF-2 induces hADSCs chondrogenesis in Transwell culture, which may be beneficial in cartilage tissue engineering.

In vivo cartilage repair using adipose-derived stem cell-loaded decellularized cartilage ECM scaffolds

We have previously reported a natural, human cartilage ECM (extracellular matrix)-derived three-dimensional (3D) porous acellular scaffold for in vivo cartilage tissue engineering in nude mice. However, the in vivo repair effects of this scaffold are still unknown. The aim of this study was to further explore the feasibility of application of cell-loaded scaffolds, using autologous adipose-derived stem cells (ADSCs), for cartilage defect repair in rabbits. A defect 4 mm in diameter was created on the patellar groove of the femur in both knees, and was repaired with the chondrogenically induced ADSC-scaffold constructs (group A) or the scaffold alone (group B); defects without treatment were used as controls (group C). The results showed that in group A all defects were fully filled with repair tissue and at 6 months post-surgery most of the repair site was filled with hyaline cartilage. In contrast, in group B all defects were partially filled with repair tissue, but only half of the repair tissue was hyaline cartilage. Defects were only filled with fibrotic tissue in group C. Indeed, histological grading score analysis revealed that an average score in group A was higher than in groups B and C. GAG and type II collagen content and biomechanical property detection showed that the group A levels approached those of normal cartilage. In conclusion, ADSC-loaded cartilage ECM scaffolds induced cartilage repair tissue comparable to native cartilage in terms of mechanical properties and biochemical components.

Compaction enhances extracellular matrix content and mechanical properties of tissue-engineered cartilaginous constructs

Many cell-based tissue-engineered cartilaginous constructs are mechanically softer than native tissue and have low content and abnormal proportions of extracellular matrix (ECM) constituents. We hypothesized that the load-bearing mechanical properties of cartilaginous constructs improve with the inclusion of collagen (COL) and proteoglycan (PG) during assembly. The objectives of this work were to determine (1) the effect of addition of PG, COL, or COL+PG on compressive properties of 2% agarose constructs and (2) the ability of mechanical compaction to concentrate matrix content and improve the compressive properties of such constructs. The inclusion of COL+PG improved the compressive properties of hydrogel constructs compared with PG or COL alone. Mechanical compaction increased the PG and COL concentrations in and compressive stiffness of the constructs. Chondrocytes included in the constructs maintained high viability after compaction. These results support the concepts that the assembly of cartilaginous constructs with COL+PG and application of mechanical compaction enhance the ECM content and compressive properties of engineered cartilaginous constructs.

Culture of human septal chondrocytes in a rotary bioreactor

OBJECTIVES

(1) To show that extracellular matrix deposition in 3-dimensional culture of human septal chondrocytes cultured in a rotary bioreactor is comparable to the deposition achieved under static culture conditions. (2) To demonstrate that the biomechanical properties of human septal chondrocytes cultured in a bioreactor are enhanced with time and are analogous to beads cultured under static culture.

STUDY DESIGN

Prospective, basic science.

SETTING

Research laboratory.

METHODS

Human septal chondrocytes from 9 donors were expanded in monolayer and seeded in alginate beads. The beads were cultured in a rotary bioreactor for 21 days in media supplemented with growth factors and human serum, using static culture as the control. Biochemical and biomechanical properties of the beads were measured.

RESULTS

Glycosaminoglycan (GAG) accumulation significantly increased during 2 measured time intervals, 0 to 21 days and 10 to 21 days (P < .01). No significant difference was seen between the static and bioreactor conditions. Substantial type II collagen production was demonstrated in the beads terminated at day 21 of culture in both conditions. In addition, the biomechanical properties of the beads were significantly improved at 21 days in comparison to beads from day 0.

CONCLUSION

Human septal chondrocytes cultured in alginate beads exhibit significant matrix deposition and improved biomechanical properties after 21 days. Alginate bead diameter and stiffness positively correlated with GAG and type II collagen accretion. Matrix production in beads is supported by the use of a rotary bioreactor.

Chitosan, hyaluronan and chondroitin sulfate in tissue engineering for cartilage regeneration: a review

Injection of hyaluronan into osteoarthritic joints restores the viscoelasticity, augments the flow of joint fluid, normalizes endogenous hyaluronan synthesis, and improves joint function. Chitosan easily forms polyelectrolyte complexes with hyaluronan and chondroitin sulfate. Synergy of chitosan with hyaluronan develops enhanced performances in regenerating hyaline cartilage, typical results being structural integrity of the hyaline-like neocartilage, and reconstitution of the subchondral bone, with positive cartilage staining for collagen-II and GAG in the treated sites. Chitosan qualifies for the preparation of scaffolds intended for the regeneration of cartilage: it yields mesoporous cryogels; it provides a friendly environment for chondrocytes to propagate, produce typical ECM, and assume the convenient phenotype; it is a good carrier for growth factors; it inactivates metalloproteinases thus preventing collagen degradation; it is suitable for the induction of the chondrogenic differentiation of mesenchymal stem cells; it is a potent means for hemostasis and platelet delivery.