Stem cells for tissue engineering of articular cartilage

Continuous Low-Intensity Ultrasound Preserves Chondrogenesis of Mesenchymal Stromal Cells in the Presence of Cytokines by Inhibiting NFκB Activation

Proinflammatory joint environment, coupled with impeded chondrogenic differentiation of mesenchymal stromal cells (MSCs), led to inferior cartilage repair outcomes. Nuclear translocation of phosphorylated-NFκB downregulates SOX9 and hinders the chondrogenesis of MSCs. Strategies that minimize the deleterious effects of NFκB, while promoting MSC chondrogenesis, are of interest. This study establishes the ability of continuous low-intensity ultrasound (cLIUS) to preserve MSC chondrogenesis in a proinflammatory environment. MSCs were seeded in alginate:collagen hydrogels and cultured for 21 days in an ultrasound-assisted bioreactor (5.0 MHz, 2.5 Vpp; 4 applications/day) in the presence of IL1β and evaluated by qRT-PCR and immunofluorescence. The differential expression of markers associated with the NFκB pathway was assessed upon a single exposure of cLIUS and assayed by Western blotting, qRT-PCR, and immunofluorescence. Mitochondrial potential was evaluated by tetramethylrhodamine methyl ester (TMRM) assay. The chondroinductive potential of cLIUS was noted by the increased expression of SOX9 and COLII. cLIUS extended its chondroprotective effects by stabilizing the NFκB complex in the cytoplasm via engaging the IκBα feedback mechanism, thus preventing its nuclear translocation. cLIUS acted as a mitochondrial protective agent by restoring the mitochondrial potential and the mitochondrial mRNA expression in a proinflammatory environment. Altogether, our results demonstrated the potential of cLIUS for cartilage repair and regeneration under proinflammatory conditions.

Tumor Formation of Adult Stem Cell Transplants in Rodent Arthritic Joints

PURPOSE

While imaging matrix-associated stem cell transplants aimed for cartilage repair in a rodent arthritis model, we noticed that some transplants formed locally destructive tumors. The purpose of this study was to determine the cause for this tumor formation in order to avoid this complication for future transplants.

PROCEDURES

Adipose-derived stem cells (ADSC) isolated from subcutaneous adipose tissue were implanted into 24 osteochondral defects of the distal femur in ten athymic rats and two immunocompetent control rats. All transplants underwent serial magnetic resonance imaging (MRI) up to 6 weeks post-transplantation to monitor joint defect repair. Nine transplants showed an increasing size over time that caused local bone destruction (group 1), while 11 transplants in athymic rats (group 2) and 4 transplants in immunocompetent rats did not. We compared the ADSC implant size and growth rate on MR images, macroscopic features, histopathologic features, surface markers, and karyotypes of these presumed neoplastic transplants with non-neoplastic ADSC transplants.

RESULTS

Implants in group 1 showed a significantly increased two-dimensional area at week 2 (p = 0.0092), 4 (p = 0.003), and 6 (p = 0.0205) compared to week 0, as determined by MRI. Histopathological correlations confirmed neoplastic features in group 1 with significantly increased size, cellularity, mitoses, and cytological atypia compared to group 2. Six transplants in group 1 were identified as malignant chondrosarcomas and three transplants as fibromyxoid sarcomas. Transplants in group 2 and immunocompetent controls exhibited normal cartilage features. Both groups showed a normal ADSC phenotype; however, neoplastic ADSC demonstrated a mixed population of diploid and tetraploid cells without genetic imbalance.

CONCLUSIONS

ADSC transplants can form tumors in vivo. Preventive actions to avoid in vivo tumor formations may include karyotyping of culture-expanded ADSC before transplantation. In addition, serial imaging of ADSC transplants in vivo may enable early detection of abnormally proliferating cell transplants.

Icariin Promotes the Migration of BMSCs In Vitro and In Vivo via the MAPK Signaling Pathway

Bone marrow-derived mesenchymal stem cells (BMSCs) are widely used in tissue engineering for regenerative medicine due to their multipotent differentiation potential. However, their poor migration ability limits repair effects. Icariin (ICA), a major component of the Chinese medical herb Herba Epimedii, has been reported to accelerate the proliferation, osteogenic, and chondrogenic differentiation of BMSCs. However, it remains unknown whether ICA can enhance BMSC migration, and the possible underlying mechanisms need to be elucidated. In this study, we found that ICA significantly increased the migration capacity of BMSCs, with an optimal concentration of 1 μmol/L. Moreover, we found that ICA stimulated actin stress fiber formation in BMSCs. Our work revealed that activation of the MAPK signaling pathway was required for ICA-induced migration and actin stress fiber formation. In vivo, ICA promoted the recruitment of BMSCs to the cartilage defect region. Taken together, these results show that ICA promotes BMSC migration in vivo and in vitro by inducing actin stress fiber formation via the MAPK signaling pathway. Thus, combined administration of ICA with BMSCs has great potential in cartilage defect therapy.

Influence of chitosan-chitin nanofiber composites on cytoskeleton structure and the proliferation of rat bone marrow stromal cells

Chitosan scaffolds have gained much attention in various tissue engineering applications, but the effect of their microstructure on cell-material spatial interactions remains unclear. Our objective was to evaluate the effect of chitosan-based matrices doping with chitin nano-whiskers (CNW) on adhesion, spreading, cytoskeleton structure, and proliferation of rat bone marrow stromal cells (BMSCs). The behavior of BMSCs during culture on chitosan-CNW films was determined by the molecular mass, hydrophobicity, porosity, crosslinking degree, protonation degree and molecular structure of the composite chitosan-CNW films. The shape, spreading area, cytoskeleton structure, and proliferation of BMSCs on chitosan matrices with a crystalline structure and high porosity were similar to that observed for BMSCs cultured on polystyrene tissue culture plates. The amorphous polymer structure and high swelling led to a decrease in the spreading area and cell proliferation. Thus, we can control the behavior of cells in culture (adhesion, spreading, and proliferation) by changing the physico-chemical properties of the chitosan-CNW films.

Periodontal ligament mesenchymal stromal cells increase proliferation and glycosaminoglycans formation of temporomandibular joint derived fibrochondrocytes

Objectives. Temporomandibular joint (TMJ) disorders are common disease in maxillofacial surgery. The aim of this study is to regenerate fibrocartilage with a mixture of TMJ fibrochondrocytes and periodontal ligament derived mesenchymal stem cells (PD-MSCs). Materials and Methods. Fibrochondrocytes and PD-MSC were cocultured (ratio 1 : 1) for 3 weeks. Histology and glycosaminoglycans (GAGs) assay were performed to examine the deposition of GAG. Green florescent protein (GFP) was used to track PD-MSC. Conditioned medium of PD-MSCs was collected to study the soluble factors. Gene expression of fibrochondrocytes cultured in conditioned medium was tested by quantitative PCR (qPCR). Results. Increased proliferation of TMJ-CH was observed in coculture pellets when compared to monoculture. Enhanced GAG production in cocultures was shown by histology and GAG quantification. Tracing of GFP revealed the fact that PD-MSC disappears after coculture with TMJ-CH for 3 weeks. In addition, conditioned medium of PD-MSC was also shown to increase the proliferation and GAG deposition of TMJ-CH. Meanwhile, results of qPCR demonstrated that conditioned medium enhanced the expression levels of matrix-related genes in TMJ-CH. Conclusions. Results from this study support the mechanism of MSC-chondrocyte interaction, in which MSCs act as secretor of soluble factors that stimulate proliferation and extracellular matrix deposition of chondrocytes.

Characterization of colony-forming cells in adult human articular cartilage

Recent studies have shown that adult human articular cartilage contains stem-like cells within the native structure. In this study, we aimed to determine the localization of putative stem cell markers such as CD90, STRO-1, OCT-3/4, CD105 and CD166 in adult human articular cartilage tissue sections and demonstrate the expression of these markers within the expanded surface zone colony-forming (CF) cells and evaluate their differentiation potential. Biopsy samples were either fixed immediately for immunohistochemical analyses or processed for in vitro cell culture. Immunohistochemical and flow cytometry analyses were performed by using CD90, STRO-1, OCT-3/4, CD105 and CD166 antibodies. Isolated colony-forming (CF) cells were further stimulated, by using the appropriate growth factors in their pellet culture, to obtain cartilage, bone and adipose lineages. We observed that the expression of the stem cell markers were in various zones of the human adult cartilage. Flow cytometry results showed that in CF cells the expression of CD90 and CD166 was high, while OCT-3/4 was low. We also determined that CF cells could be stimulated towards cartilage, bone and adipose lineages. The results of this research support the idea that the resident stem-like cells in adult human articular cartilage express these putative stem cell markers, but further experimental investigations are needed to determine the precise localization of these cells.

Gene modification of mesenchymal stem cells and articular chondrocytes to enhance chondrogenesis

Current cell based treatment for articular cartilage and osteochondral defects are hampered by issues such as cellular dedifferentiation and hypertrophy of the resident or transplanted cells. The reduced expression of chondrogenic signalling molecules and transcription factors is a major contributing factor to changes in cell phenotype. Gene modification of chondrocytes may be one approach to redirect cells to their primary phenotype and recent advances in nonviral and viral gene delivery technologies have enabled the expression of these lost factors at high efficiency and specificity to regain chondrocyte function. This review focuses on the various candidate genes that encode signalling molecules and transcription factors that are specific for the enhancement of the chondrogenic phenotype and also how epigenetic regulators of chondrogenesis in the form of microRNA may also play an important role.

Scaffold-mediated lentiviral transduction for functional tissue engineering of cartilage

The ability to develop tissue constructs with matrix composition and biomechanical properties that promote rapid tissue repair or regeneration remains an enduring challenge in musculoskeletal engineering. Current approaches require extensive cell manipulation ex vivo, using exogenous growth factors to drive tissue-specific differentiation, matrix accumulation, and mechanical properties, thus limiting their potential clinical utility. The ability to induce and maintain differentiation of stem cells in situ could bypass these steps and enhance the success of engineering approaches for tissue regeneration. The goal of this study was to generate a self-contained bioactive scaffold capable of mediating stem cell differentiation and formation of a cartilaginous extracellular matrix (ECM) using a lentivirus-based method. We first showed that poly-L-lysine could immobilize lentivirus to poly(ε-caprolactone) films and facilitate human mesenchymal stem cell (hMSC) transduction. We then demonstrated that scaffold-mediated gene delivery of transforming growth factor β3 (TGF-β3), using a 3D woven poly(ε-caprolactone) scaffold, induced robust cartilaginous ECM formation by hMSCs. Chondrogenesis induced by scaffold-mediated gene delivery was as effective as traditional differentiation protocols involving medium supplementation with TGF-β3, as assessed by gene expression, biochemical, and biomechanical analyses. Using lentiviral vectors immobilized on a biomechanically functional scaffold, we have developed a system to achieve sustained transgene expression and ECM formation by hMSCs. This method opens new avenues in the development of bioactive implants that circumvent the need for ex vivo tissue generation by enabling the long-term goal of in situ tissue engineering.

Ferumoxytol: a new, clinically applicable label for stem-cell tracking in arthritic joints with MRI

AIM

To develop a clinically applicable MRI technique for tracking stem cells in matrix-associated stem-cell implants, using the US FDA-approved iron supplement ferumoxytol.

MATERIALS & METHODS

Ferumoxytol-labeling of adipose-derived stem cells (ADSCs) was optimized in vitro. A total of 11 rats with osteochondral defects of both femurs were implanted with ferumoxytol- or ferumoxides-labeled or unlabeled ADSCs, and underwent MRI up to 4 weeks post matrix-associated stem-cell implant. The signal-to-noise ratio of different matrix-associated stem-cell implant was compared with t-tests and correlated with histopathology.

RESULTS

An incubation concentration of 500 µg iron/ml ferumoxytol and 10 µg/ml protamine sulfate led to significant cellular iron uptake, T2 signal effects and unimpaired ADSC viability. In vivo, ferumoxytol- and ferumoxides-labeled ADSCs demonstrated significantly lower signal-to-noise ratio values compared with unlabeled controls (p < 0.01). Histopathology confirmed engraftment of labeled ADSCs, with slow dilution of the iron label over time.

CONCLUSION

Ferumoxytol can be used for in vivo tracking of stem cells with MRI.

Emerging Frontiers in cartilage and chondrocyte biology

Articular cartilage is a uniquely ordered tissue that is designed to resist compression and redistribute load, but is poorly equipped for self-repair. The chondrocyte is the only resident cell type, responsible for maintaining a specialised and extensive matrix that is avascular and lacks innervation. These attributes, as well as the slow turnover rate of aggrecan and type II collagen in mature articular cartilage, present a considerable challenge to the tissue engineer. Similarly, those attempting to halt the progression of cartilage erosion must contend with these unusual characteristics. This review explores the gaps in our knowledge of cartilage biology and pathology, including what is known about the relative contribution of collagenases and aggrecanases to cartilage degradation, the need to regulate the chondrocytic phenotype and the putative role of chondrocyte hypertrophy in the pathogenesis of degenerative and rheumatic joint disease. Recent advances in cartilage tissue engineering are also reviewed.

Nanotechnology and mesenchymal stem cells with chondrocytes in prevention of partial growth plate arrest in pigs

INTRODUCTION

This study describes the results achieved using a combination of allogeneic mesenchymal stem cells (MSCs) with chondrocytes (CHC) and a new scaffold consisting of type-I collagen and chitosan nanofibers in the prevention of partial growth plate arrest after iatrogenic injury in pigs.

MATERIAL AND METHODS

The miniature pig was selected as an experimental model to compare the results in the left femoral bones (MSCs and CHC in scaffold transplantation into the iatrogenic partial distal growth plate defect) and right femoral bones (scaffold alone transplantation). The experimental group consisted of 10 animals. Bone marrow from os ilium as the source of MSCs was used. A porous cylinder consisting of 0.5% by weight type-I collagen and 30% by weight chitosan, was the optimal choice. The length of the bone and angular deformity of distal femur after the healing period was measured and the quality and structure of the newly formed cartilage was histologically examined.

RESULTS

Transplantation of the composite scaffold in combination with MSCs and chondrocytes led to the prevention of growth disorder and angular deformity in the distal epiphysis of the left femur. Compared to the right (control) femur, tissue similar to hyaline cartilage with signs of columnar organization typical of the growth plate occurred in most cases.

CONCLUSIONS

The promising results of this study reveal the new and effective means for the prevention of bone bridge formation after growth plate injury.

Osteochondral tissue engineering approaches for articular cartilage and subchondral bone regeneration

PURPOSE

Osteochondral defects (i.e., defects which affect both the articular cartilage and underlying subchondral bone) are often associated with mechanical instability of the joint and therefore with the risk of inducing osteoarthritic degenerative changes. This review addresses the current surgical treatments and most promising tissue engineering approaches for articular cartilage and subchondral bone regeneration.

METHODS

The capability to repair osteochondral or bone defects remains a challenging goal for surgeons and researchers. So far, most clinical approaches have been shown to have limited capacity to treat severe lesions. Current surgical repair strategies vary according to the nature and size of the lesion and the preference of the operating surgeon. Tissue engineering has emerged as a promising alternative strategy that essentially develops viable substitutes capable of repairing or regenerating the functions of damaged tissue.

RESULTS

An overview of novel and most promising osteochondroconductive scaffolds, osteochondroinductive signals, osteochondrogenic precursor cells, and scaffold fixation approaches are presented addressing advantages, drawbacks, and future prospectives for osteochondral regenerative medicine.

CONCLUSION

Tissue engineering has emerged as an excellent approach for the repair and regeneration of damaged tissue, with the potential to circumvent all the limitations of autologous and allogeneic tissue repair.

LEVEL OF EVIDENCE

Systematic review, Level III.

A human embryonic stem cell-derived clonal progenitor cell line with chondrogenic potential and markers of craniofacial mesenchyme

AIMS

We screened 100 diverse human embryonic stem-derived progenitor cell lines to identify novel lines with chondrogenic potential.

MATERIALS & METHODS

The 4D20.8 cell line was compared with mesenchymal stem cells and dental pulp stem cells by assessing osteochondral markers using immunohistochemical methods, gene expression microarrays, quantitative real-time PCR and in vivo repair of rat articular condyles.

RESULTS

4D20.8 expressed the site-specific gene markers LHX8 and BARX1 and robustly upregulated chondrocyte markers upon differentiation. Differentiated 4D20.8 cells expressed relatively low levels of COL10A1 and lacked IHH and CD74 expression. Transplantation of 4D20.8 cells into experimentally induced defects in the femoral condyle of athymic rats resulted in cartilage and bone differentiation approximating that of the original tissue architecture. Relatively high COL2A1 and minimal COL10A1 expression occurred during differentiation in HyStem-C hydrogel with TGF-β3 and GDF-5.

CONCLUSION

Human embryonic stem cell-derived embryonic progenitor cell lines may provide a novel means of generating purified site-specific osteochondral progenitor cell lines that are useful in research and therapy.

Cartilage fragments from osteoarthritic knee promote chondrogenesis of mesenchymal stem cells without exogenous growth factor induction

Extracellular matrix (ECM) is thought to participate significantly in guiding the differentiation process of mesenchymal stem cells (MSCs). In this study, we hypothesized that cartilage fragments from osteoarthritic knee could promote chondrogenesis of MSCs. Nonworn parts of cartilage tissues were obtained during total knee arthroplasty (TKA) surgery. Cartilage fragments and MSCs were wrapped into fibrin glue; and the constructs were implanted subcutaneously into nude mice. Histological analysis showed neocartilage-like structure with positive Alcian blue staining in the cartilage fragment-fibrin-MSC constructs. However, constructs with only MSCs in fibrin showed condensed appearance like MSCs in the pellet culture. Gene expression of type II collagen in the constructs with 60 mg cartilage fragments were significantly elevated after 4 weeks of implantation. Conversely, the constructs without cartilage fragments failed to express type II collagen, which indicated MSCs did not differentiate into a chondrogenic lineage. In conclusion, we demonstrated the effect of cartilage fragments from osteoarthritic knee in promoting chondrogenic differentiation of MSCs. This may be a favorable strategy for MSC chondrogenesis without exogenous growth factor induction.

Catabolic factors and osteoarthritis-conditioned medium inhibit chondrogenesis of human mesenchymal stem cells

Articular cartilage has a very limited intrinsic repair capacity leading to progressive joint damage. Therapies involving tissue engineering depend on chondrogenic differentiation of progenitor cells. This chondrogenic differentiation will have to survive in a diseased joint. We postulate that catabolic factors in this environment inhibit chondrogenesis of progenitor cells. We investigated the effect of a catabolic environment on chondrogenesis in pellet cultures of human mesenchymal stem cells (hMSCs). We exposed chondrogenically differentiated hMSC pellets, to interleukin (IL)-1α, tumor necrosis factor (TNF)-α or conditioned medium derived from osteoarthritic synovium (CM-OAS). IL-1α and TNF-α in CM-OAS were blocked with IL-1Ra or Enbrel, respectively. Chondrogenesis was determined by chondrogenic markers collagen type II, aggrecan, and the hypertrophy marker collagen type X on mRNA. Proteoglycan deposition was analyzed by safranin o staining on histology. IL-1α and TNF-α dose-dependently inhibited chondrogenesis when added at onset or during progression of differentiation, IL-1α being more potent than TNF-α. CM-OAS inhibited chondrogenesis on mRNA and protein level but varied in extent between patients. Inhibition of IL-1α partially overcame the inhibitory effect of the CM-OAS on chondrogenesis whereas the TNF-α contribution was negligible. We show that hMSC chondrogenesis is blocked by either IL-1α or TNF-α alone, but that there are additional factors present in CM-OAS that contribute to inhibition of chondrogenesis, demonstrating that catabolic factors present in OA joints inhibit chondrogenesis, thereby impairing successful tissue engineering.

Chondrogenesis by chemotactic homing of synovium, bone marrow, and adipose stem cells in vitro

Cell transplantation has been well explored for cartilage regeneration. We recently showed that the entire articular surface of a synovial joint can regenerate by endogenous cell homing and without cell transplantation. However, the sources of endogenous cells that regenerate articular cartilage remain elusive. Here, we studied whether cytokines not only chemotactically recruit adipose stem cells (ASCs), mesenchymal stem cells (MSCs), and synovium stem cells (SSCs) but also induce chondrogenesis of the recruited cells. Recombinant human transforming growth factor-β3 (TGF-β3; 100 ng) and/or recombinant human stromal derived factor-1β (SDF-1β; 100 ng) was control released into an acellular collagen sponge cube with underlying ASCs, MSCs, or SSCs in monolayer culture. Although all cell types randomly migrated into the acellular collagen sponge cube, TGF-β3 and/or SDF-1β recruited significantly more cells than the cytokine-free control group. In 6 wk, TGF-β3 alone recruited substantial numbers of ASCs (558±65) and MSCs (302±52), whereas codelivery of TGF-β3 and SDF-1β was particularly chemotactic to SSCs (400±120). Proliferation of the recruited cells accounted for some, but far from all, of the observed cellularity. TGF-β3 and SDF-1β codelivery induced significantly higher aggrecan gene expression than the cytokine-free group for ASCs, MSCs, and SSCs. Type II collagen gene expression was also significantly higher for ASCs and SSCs by SDF-1 and TGF-β3 codelivery. Remarkably, the expression of aggrecan and type II collagen was detected among all cell types. Thus, homing of multiple stem/progenitor cell populations may potentially serve as an alternative or adjunctive approach to cell transplantation for cartilage regeneration.

Musculoskeletal tissue engineering with human umbilical cord mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSCs) hold tremendous promise for tissue engineering and regenerative medicine, yet with so many sources of MSCs, what are the primary criteria for selecting leading candidates? Ideally, the cells will be multipotent, inexpensive, lack donor site morbidity, donor materials should be readily available in large numbers, immunocompatible, politically benign and expandable in vitro for several passages. Bone marrow MSCs do not meet all of these criteria and neither do embryonic stem cells. However, a promising new cell source is emerging in tissue engineering that appears to meet these criteria: MSCs derived from Wharton's jelly of umbilical cord MSCs. Exposed to appropriate conditions, umbilical cord MSCs can differentiate in vitro along several cell lineages such as the chondrocyte, osteoblast, adipocyte, myocyte, neuronal, pancreatic or hepatocyte lineages. In animal models, umbilical cord MSCs have demonstrated in vivo differentiation ability and promising immunocompatibility with host organs/tissues, even in xenotransplantation. In this article, we address their cellular characteristics, multipotent differentiation ability and potential for tissue engineering with an emphasis on musculoskeletal tissue engineering.

The effect of type II collagen coating of chitosan fibrous scaffolds on mesenchymal stem cell adhesion and chondrogenesis

The biocompatibility of chitosan and its similarity to glycosaminoglycans (GAG) make it attractive for cartilage tissue engineering. We have previously reported improved chondrogenesis but limited cell adhesion on chitosan scaffolds. Our objectives were to produce chitosan scaffolds coated with different densities of type II collagen and to evaluate the effect of this coating on mesenchymal stem cell (MSC) adhesion and chondrogenesis. Chitosan fibrous scaffolds were obtained by a wet spinning method and coated with type II collagen at two different densities. A polyglycolic acid mesh served as a reference group. The scaffolds were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and type II collagen content. Constructs were analyzed after MSCs seeding via live/dead assay, weight and DNA evaluations, SEM, and TEM. Constructs were cultured in chondrogenic medium for 21 days prior to quantitative analysis (weight, DNA, and GAG), SEM, TEM, histology, immunohistochemistry, and quantitative real time polymerase chain reaction. The cell attachment and distribution after seeding correlated with the density of type II collagen. The cell number, the matrix production, and the expression of genes specific for chondrogenesis were improved after culture in collagen coated chitosan constructs. These findings encourage the use of type II collagen for coating chitosan scaffolds to improve MSCs adhesion and chondrogenesis, and confirm the importance of biomimetic scaffolds for tissue engineering.

The restoration of full-thickness cartilage defects with BMSCs and TGF-beta 1 loaded PLGA/fibrin gel constructs

Poly(lactide-co-glycolide) (PLGA) sponge was filled with fibrin gel, bone marrow mesenchymal stem cells (BMSCs) and transforming growth factor-β1 (TGF-β1) to obtain a construct for cartilage restoration in vivo. The PLGA sponge lost its weight steadily in vitro, but degraded much faster in the construct of PLGA/fibrin gel/BMSCs implanted in the full-thickness cartilage defects. The in vivo degradation of the fibrin gel inside the construct was prolonged to 12 wk too. The CM-DiI labeled allogenic BMSCs were detectable after transplantation (implantation) into the defects for 12 wk by small animal in vivo fluorescence imaging and confocal laser scanning microscopy. In vivo repair experiments were firstly performed by implantation of the PLGA/fibrin gel/BMSCs and PLGA/BMSCs constructs into full-thickness cartilage defects (3 mm in diameter and 4 mm in depth) of New Zealand white rabbits for 12 wk. The defects implanted with the PLGA/fibrin gel/BMSCs constructs were filled with cartilage-like tissue containing collagen type II and glycosaminoglycans (GAGs), while those by the PLGA/BMSCs constructs were filled with fibrous-like tissues. To repair the defects of larger size (4 mm in diameter), addition of growth factors was mandatory as exemplified here by further loading of TGF-β1. Implantation of the PLGA/fibrin gel/BMSCs/TGF-β1 constructs into the full-thickness cartilage defects for 12 wk resulted in full restoration of the osteochondral tissue. The neo-cartilage integrated well with its surrounding cartilage and subchondral bone. Immunohistochemical and GAGs staining confirmed the similar distribution of collagen type II and GAGs in the regenerated cartilage as that of hyaline cartilage. The quantitative reverse transcription-polymerase chain reaction (qRT-PCR) revealed that the cartilage special genes were significantly up-regulated compared with those of the TGF-β1 absent constructs.

Effect of collagen II coating on mesenchymal stem cell adhesion on chitosan and on reacetylated chitosan fibrous scaffolds

The biocompatibility and biomimetic properties of chitosan make it attractive for tissue engineering but its use is limited by its cell adhesion properties. Our objectives were to produce and characterize chitosan and reacetylated-chitosan fibrous scaffolds coated with type II collagen and to evaluate the effect of these chemical modifications on mesenchymal stem cell (MSC) adhesion. Chitosan and reacetylated-chitosan scaffolds obtained by a wet spinning method were coated with type II collagen. Scaffolds were characterized prior to seeding with MSCs. The constructs were analyzed for cell binding kinetics, numbers, distribution and viability. Cell attachment and distribution were improved on chitosan coated with type II collagen. MSCs adhered less to reacetylated-chitosan and collagen coating did not improve MSCs attachment on those scaffolds. These findings are promising and encourage the evaluation of the differentiation of MSCs in collagen-coated chitosan scaffolds. However, the decreased cell adhesion on reacetylated chitosan scaffold seems difficult to overcome and will limit its use for tissue engineering.

Comparison of articular and auricular cartilage as a cell source for the autologous chondrocyte implantation

Articular (medial femoral condyle) and auricular cartilage (anithelix) was compared as a cell source for the autologous joint repair. Cells isolated from five human cadaveric donors were cultured parallel in the monolayer cultures and in the 3D alginate hydrogel constructs for 1 week. Cell morphology was controlled by the fluorescent microscopy and gene expressions of type I collagen (COL1), type II collagen (COL2), aggrecan (AGR), versican (VER), and elastin (ELS) were analyzed by the real-time polymerase chain reaction. COL1 and ELS, predominant in the phenotype of auricular biopsy, were statistically lower in the articular biopsies. Even though COL2 and AGR decreased in monolayers of both cell sources, the dedifferentiation process affected auricular cells intensely. Cells embedded in the alginate hydrogel directly after the isolation did not exhibit the dedifferentiated phenotype. Additionally, COL1, COL2, AGR, and VER were comparable between the two sources. ELS however, remained higher in the auricular cells regardless of the culture type. The study indicates that auricular chondrocytes cultured in a 3D environment immediately after the isolation have a neo-cartilage potential for the articular surface reconstruction.

Cavernous nerve regeneration using acellular nerve grafts

INTRODUCTION

The restoration of erectile function following complete transection of nerve tissue during surgery remains challenging. Recently, graft procedures using sural nerve grafts during radical prostatectomy have had favorable outcomes, and this has rekindled interest in the applications of neural repair in a urologic setting. Although nerve repair using autologous donor graft is the gold standard of treatment currently, donor nerve availability and the associated donor site morbidity remain a problem. In this study, we investigated whether an "off-the-shelf" acellular nerve graft would serve as a viable substitute. We examined the capacity of acellular nerve scaffolds to facilitate the regeneration of cavernous nerve in a rodent model.

MATERIALS AND METHODS

Acellular nerve matrices, processed from donor rat corporal nerves, were interposed across nerve gaps. A total of 80 adult male Sprague-Dawley rats were divided into four groups. A 0.5-cm segment of cavernosal nerve was excised bilaterally in three of the four groups. In the first group, acellular nerve segments were inserted bilaterally at the defect site. The second group underwent autologous genitofemoral nerve grafts at the same site, and the third group had no repair. The fourth group underwent a sham procedure. Serial cavernosal nerve function assessment was performed using electromyography (EMG) at 1 and 3 months following initial surgery. Histological and immunocytochemical analyses were performed to identify the extent of nerve regeneration.

RESULTS

Animals implanted with acellular nerve grafts demonstrated a significant recovery in erectile function when compared with the group that received no repair, both at 1 and 3 months. EMG of the acellular nerve grafts demonstrated adequate intracavernosal pressures by 3 months (87.6% of the normal non-injured nerves). Histologically, the retrieved regenerated nerve grafts demonstrated the presence of host cell infiltration within the nerve sheaths. Immunohistochemically, antibodies specific to axons and Schwann cells demonstrated an increase in nerve regeneration across the grafts over time. No organized nerve regeneration was observed when the cavernous nerve was not repaired.

CONCLUSION

These findings show that the use of nerve guidance channel systems allow for accelerated and precise cavernosal nerve regeneration. Acellular nerve grafts represent a viable alternative to fresh autologous grafts in a rodent model of erectile dysfunction.