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Background:: Tissue defects in the annulus fibrosus (AF) due to intervertebral disc (IVD) degeneration or after nucleodiscectomy have little self-healing capacity. To prevent progressive degeneration of the IVD, the AF must be repaired. Biological closure has not yet been achieved and is a challenge for the research community. In this study, a scaffold made of absorbable poly (glycolic acid) (PGA) and hyaluronan (HA) that exhibit excellent biocompatibility and cell colonization properties was used to repair AF defects in an ovine model. Methods:: A partial resection was performed in AF in L3/4 or L4/5 of 10 sheep and PGA-HA scaffolds were implanted on the defects (n = 5), while defects in the control group were left untreated (n = 5). Three months post-operation, the lumbar discs were sectioned and stained with hematoxylin and eosin and safranin-O/fast-green. Histological features including proteoglycan content, annular structure, cellular morphology, blood vessel ingrowth and tear/cleft formation were scored using a modified scoring scheme by 3 investigators and evaluated by a pathologist independently. Results:: The treated AF exhibited significantly enhanced repair tissue structure with signs of proteoglycan formation compared to the untreated group. The median scores were 4.3 for the treated and 9.8 for the untreated group. Cystic degeneration, perivascular infiltration, inflammation and necrosis were only present in the untreated group. Blood vessel ingrowth and tear/cleft formation were increased, though not significant, in the untreated group while cell morphology was comparable in both groups. Conclusion:: PGA-HA scaffolds used for AF closure support repair tissue formation in an ovine lumbar disc defect model.

Objective The objective was to evaluate the proliferating, migratory and extracellular matrix (ECM) forming potential of annulus fibrosus cells derived from early (edAFC) or advanced (adAFC) degenerative tissue and their usability as a possible cell source for regenerative approaches for AF closure.Design EdAFC (n= 5 Pfirrman score of 2-3) and adAFC (n = 5 Pfirrman score of 4-5) were isolated from tissue of patients undergoing spine stabilizing surgery. Cell migration on stimulation with human serum (HS), platelet-rich plasma (PRP), and transforming growth factor β-3 (TGFB3) was assessed by migration assay and proliferation was assessed on stimulation with HS. Induction of ECM synthesis was evaluated by gene expression analysis of AF-related genes in three-dimensional scaffold cultures that have been stimulated with 5% PRP or 10 ng/mL TGFB3 and histologically by collagen type I, type II, alcian blue, and safranin-O staining.Results EdAFC and adAFC were significantly attracted by 10% HS and 5% PRP. Additionally, both cell groups proliferated under stimulation with HS. Stimulation with 10 ng/mL TGFB3 showed significant induction of gene expression of collagen type II and aggrecan, while 5% PRP decreased the expression of collagen type I. Both cell groups showed formation of AF-like ECM after stimulation with TGFB3, whereas stimulation with PRP did not.Conclusions Our study demonstrated that AF cells retain their potential for proliferation, migration, and ECM formation independent of the degeneration status of the tissue. Proliferation, migration, and ECM synthesis of the endogenous AF cells can be supported by different supplements. Hence, endogenous AF cells might be a suitable cell source for a regenerative repair approaches.

This study evaluated whether intramyocardial injection of cardiac‐derived adherent proliferating cells (CardAPs) modulates cardiac fibrosis and hypertrophy in a mouse model of angiotensin II (Ang II)‐induced systolic heart failure and analyzed underlying mechanisms. Among other findings, results indicated that intramyocardial injection of CardAPs improved left ventricular (LV) function and reduced LV remodeling. These improvements were attributed to antifibrotic and antihypertrophic effects resulting from paracrine actions and immunomodulatory properties. Cardiac‐derived adherent proliferating cells (CardAPs) are cells derived from human endomyocardial biopsy specimens; they share several properties with mesenchymal stromal cells. The aims of this study were to evaluate whether intramyocardial injection of CardAPs modulates cardiac fibrosis and hypertrophy in a mouse model of angiotensin II (Ang II)‐induced systolic heart failure and to analyze underlying mechanisms. Intramyocardial application of 200,000 CardAPs improved left ventricular function. This was paralleled by a decline in left ventricular remodeling, as indicated by a reduction in cardiac fibrosis and hypertrophy. CardAPs reduced the ratio of the left ventricle to body weight and cardiac myosin expression (heavy chain), and decreased the Ang II‐induced phosphorylation state of the cardiomyocyte hypertrophy mediators Akt, extracellular‐signal regulated kinase (ERK) 1, and ERK2. In accordance with the antifibrotic and antihypertrophic effects of CardAPs shown in vivo, CardAP supplementation with cardiac fibroblasts decreased the Ang II‐induced reactive oxygen species production, α‐SMA expression, fibroblast proliferation, and collagen production. Coculture of CardAPs with HL‐1 cardiomyocytes downregulated the Ang II‐induced expression of myosin in HL‐1. All antifibrotic and antihypertrophic features of CardAPs were mediated in a nitric oxide‐ and interleukin (IL)‐10‐dependent manner. Moreover, CardAPs induced a systemic immunomodulation, as indicated by a decrease in the activity of splenic mononuclear cells and an increase in splenic CD4CD25FoxP3, CD4‐IL‐10, and CD8‐IL‐10 T‐regulatory cells in Ang II mice. Concomitantly, splenocytes from Ang II CardAPs mice induced less collagen in fibroblasts compared with splenocytes from Ang II mice. We conclude that CardAPs improve Ang II‐induced cardiac remodeling involving antifibrotic and antihypertrophic effects via paracrine actions and immunomodulatory properties. Despite effective pharmacological treatment with angiotensin II type I receptor antagonists or angiotensin II‐converting enzyme inhibitors, morbidity and mortality associated with heart failure are still substantial, prompting the search of novel therapeutic strategies. There is accumulating evidence supporting the use of cell therapy for cardiac repair. This study demonstrates that cells derived from human endomyocardial biopsies, cardiac‐derived adherent proliferating cells (CardAPs), have the potential to reduce angiotensin II‐induced cardiac remodeling and improve left ventricular function in angiotensin II mice. The mechanism involves antifibrotic and antihypertrophic effects via paracrine actions and immunomodulatory properties. These findings support the potential of CardAPs for the treatment of heart failure.

In vitro tissue models are useful tools for the development of novel therapy strategies in cartilage repair and care. The limited availability of human primary tissue and high costs of animal models hamper preclinical tests of innovative substances and techniques. In this study we tested the potential of porcine chondrocyte micromass cultures to mimic human articular cartilage and essential aspects of osteoarthritis (OA) in vitro. Primary chondrocytes were enzymatically isolated from porcine femoral condyles and were maintained in 96-multiwell format to establish micromass cultures in a high-throughput scale. Recombinant porcine tumor necrosis factor alpha (TNF-α) was used to induce OA-like changes documented on histological (Safranin O, collagen type II staining), biochemical (hydroxyproline assay, dimethylmethylene blue method), and gene expression level (Affymetrix porcine microarray, real time PCR) and were compared with published data from human articular cartilage and human micromass cultures. After 14 days in micromass culture, porcine primary chondrocytes produced ECM rich in proteoglycans and collagens. On gene expression level, significant correlations of detected genes with porcine cartilage (r= 0.90), human cartilage (r= 0.71), and human micromass culture (r= 0.75) were observed including 34 cartilage markers such as COL2A1, COMP, and aggrecan. TNF-α stimulation led to significant proteoglycan (−75%) and collagen depletion (−50%). Comparative expression pattern analysis revealed the involvement of catabolic enzymes (MMP1, -2, -13, ADAM10), chemokines (IL8, CCL2,CXCL2, CXCL12, CCXL14), and genes associated with cell death (TNFSF10, PMAIPI, AHR) and skeletal development (GPNMB, FRZB) including transcription factors (WIF1,DLX5, TWIST1) and growth factors (IGFBP1, -3, TGFB1) consistent with published data from human OA cartilage. Expression of genes related to cartilage ECM formation (COL2A1, COL9A1, COMP, aggrecan) as well as hypertrophic bone formation (COL1A1, COL10A1) was predominantly found decreased. These findings indicating significant parallels between human articular cartilage and the presented porcine micromass model and vice versa confirm the applicability of known cartilage marker and their characteristics in the porcine micromass model. TNF-α treatment enabled the initiation of typical OA reaction patterns in terms of extensive ECM loss, cell death, formation of an inflammatory environment through the induction of genes coding for chemokines and enzymes, and the modulation of genes involved in skeletal development such as growth factors, transcription factors, and cartilage ECM-forming genes. In conclusion, the porcine micromass model represents an alternative tissue platform for the evaluation of innovative substances and techniques for the treatment of OA.

Cardiovascular diseases are one of the main causes of morbidity and mortality worldwide. Cell-based therapies represent promising treatment options. We have identified a unique cell type, cardiac-derived adherent proliferating (CardAP) cells, which can be isolated and expanded from human endomyocardial biopsies. These cells show several cardioprotective features in vitro and in vivo and present a potential cell source for cardiac repair. Initial genome-wide gene expression profiling revealed that CardAP cells express a large number of genes involved in angiogenesis. Therefore, we expected that they support this process and the aim of this work was to investigate the angiogenic features of CardAP cells. First, we studied the direct angiogenic differentiation potential of CardAP cells in a functional in vitro Matrigel tube formation assay. Since also paracrine-mediated mechanism of angiogenesis for cell therapy in cardiac regeneration are known, we further investigated the pro-angiogenic potential of CardAP cells on human umbilical vein endothelial cells (HUVECs) by using conditioned medium (CM) in the tube formation assay. Finally, we studied the secretion of the proangiogenic factors VEGF and IL-8 during the cultivation of CardAP cells. The investigation of the angiogenic differentiation potential in tube formation assay revealed that CardAP cells showed endothelial structures but expression of endothelial markers could not be detected. Treating HUVECs with CM resulted in a significant up to a two-fold increase in total tube length and a up to a three fold increase in the number of branching points, indicating a pro-angiogenic effect of CardAP cells. Moreover, these cells secreted a mean of 576 ± 60 pg VEGF and a maximum mean of 99 ± 30 ng IL-8 per 105 cells. Our findings revealed that CardAP cells mediate a pro-angiogenic effect in a paracrine manner, which might bean underlying mechanism of the cardio protective features of CardAP cells.

It is generally accepted that after differentiation bone marrow mesenchymal stem cells (MSC) become lineage restricted and unipotent in an irreversible manner. However, current results imply that even terminally differentiated cells transdifferentiate across lineage boundaries and therefore act as a progenitor cells for other lineages. This leads to the questions that whether transdifferentiation occurs via direct cell-to-cell conversion or dedifferentiation to a progenitor cells and subsequent differentiation, and whether MSC potency decreases or increases during differentiation. To address these questions, MSC were differentiated into adipogenic lineage cells, followed by dedifferentiation. The process of dedifferentiation was also confirmed by single cell clonal analysis. Finally the dedifferentiated cells were used for adipogenesis, osteogenesis and chondrogenesis. Histology, FACS, qPCR and GeneChip analyses of undifferentiated MSC, adipogenic-differentiated and dedifferentiated cells were performed. Interestingly, gene profiling and bioinformatics demonstrated that upregulation (DHCR24, G0S2, MAP2K6, SESN3) and downregulation (DST, KAT2, MLL5, RB1, SMAD3, ZAK) of distinct genes have an association with cell cycle arrest in adipogenic-differentiated cells and perhaps narrow down the lineage potency. However, the upregulation (CCND1, CHEK, HGF, HMGA2, SMAD3) and downregulation (CCPG1, RASSF4, RGS2) of these genes have an association with cell cycle progression and maybe motivate dedifferentiation of adipogenic-differentiated cells. We found that dedifferentiated cells have a multilineage potency comparable to MSC, and also observed the associative role of proliferation genes with cell cycle arrest and progression. Concluded, our results indicate that transdifferentiation of adipogenic-differentiated cells into osteogenic- or chondrogenic-differentiated cells proceeds via dedifferentiation and correlates with cell cycle arresting and deriving genes. Regarding clinical use, the knowledge of potency and underlying mechanisms are prerequisites.

Joint destruction occurs in both osteoarthritis and rheumatoid arthritis. Even in the era of biologic agents, this destruction can be delayed but not averted. As cartilage has limited ability to self-regenerate, joint arthroplasty is required. Here, we outline current tissue engineering procedures (including autologous chondrocyte implantation and in situ mesenchymal stem cell recruitment) that are routinely applied for the regenerative treatment of injured or early osteoarthritic cartilage. Potential future regenerative therapies, including administration of multipotent or pluripotent stem cells, are also discussed. In the future, cell-free, material-based (for cartilage lesions) or cell-free, factor-based (for osteoarthritic cartilage) therapies to facilitate the recruitment of repair cells and improve cartilage metabolism are likely to become more important. Moreover, delivery of anti-inflammatory factors or immunomodulatory cells could be a regenerative treatment option for rheumatoid arthritis. Tissue engineering faces a crucial phase to translate products into clinical routine and the regulatory framework for cell-based products in particular is an important issue.

Diseases such as degenerative or rheumatoid arthritis are accompanied by joint destruction. Clinically applied tissue engineering technologies like autologous chondrocyte implantation, matrix-assisted chondrocyte implantation, or in siturecruitment of bone marrow mesenchymal stem cells target the treatment of traumatic defects or of early osteoarthritis. Inflammatory conditions in the joint hamper the application of tissue engineering during chronic joint diseases. Here, most likely, cartilage formation is impaired and engineered neocartilage will be degraded. Based on the observations that mesenchymal stem cells (a) develop into joint tissues and (b) in vitroand in vivoshow immunosuppressive and anti-inflammatory qualities indicating a transplant-protecting activity, these cells are prominent candidates for future tissue engineering approaches for the treatment of rheumatic diseases. Tissue engineering also provides highly organized three-dimensional in vitroculture models of human cells and their extracellular matrix for arthritis research.

The 3-dimensional (3-D) pannus model for rheumatoid arthritis (RA) is based on the interactive co-culture of cartilage and synovial fibroblasts (SFs). Besides the investigation of the pathogenesis of RA, it can be used to analyze the active profiles of antirheumatic pharmaceuticals and other bioactive substances under in vitro conditions. For a potential application in the industrial drug-screening process as a transitional step between 2-dimensional (2-D) cell-based assays and in vivo animal studies, the pannus model was developed into an in vitro high-throughput screening (HTS) assay. Using the CyBi™-Disk workstation for parallel liquid handling, the main cell culture steps of cell seeding and cultivation were automated. Chondrocytes were isolated from articular cartilage and seeded directly into 96-well microplates in high-density pellets to ensure formation of cartilage-specific extracellular matrix (ECM). Cell seeding was performed automatically and manually to compare both processes regarding accuracy, reproducibility, consistency, and handling time. For automated cultivation of the chondrocyte pellet cultures, a sequential program was developed using the CyBio Control software to minimize shear forces and handling time. After 14 days of cultivation, the pannus model was completed by coating the cartilage pellets with a layer of human SFs. The effects due to automation in comparison to manual handling were analyzed by optical analysis of the pellets, histological and immunohistochemical staining, and real-time PCR. Automation of this in vitro model was successfully achieved and resulted in an improved quality of the generated pannus cultures by enhancing the formation of cartilage-specific ECM. In addition, automated cell seeding and media exchange increased the efficiency due to a reduction of labor intensity and handling time.

Nonbiological therapeutics are frequently used for the treatment of patients with rheumatoid arthritis (RA). Because the mechanisms of action of these therapeutics are unclear, the authors aimed to elucidate the molecular effects of typical antirheumatic drugs on the expression profile of RA-related genes expressed in activated synovial fibroblasts. For reasons of standardization and comparability, immortalized synovial fibroblasts derived from RA (RASF) and normal donors (NDSF) were treated with methotrexate, prednisolone, or diclofenac and used for gene expression profiling with oligonucleotide microarrays. The cytotoxicity of the antirheumatic drugs was tested in different concentrations by MTS tetrazolium assay. Genes that were differentially expressed in RASF compared to NDSF and reverted by treatment with antirheumatic drugs were verified by semiquantitative polymerase chain reaction and by chemiluminescent enzyme immunoassay. Treatment with methotrexate resulted in the reversion of the RA-related expression profile of genes associated with growth and apoptosis including insulin-like growth factor binding protein 3, retinoic acid induced 3, and caveolin 2 as well as in the re-expression of the cell adhesion molecule integrin α6. Prednisolone reverted the RA-related profile of genes that are known from inflammation and suppressed interleukins 1β and 8. Low or high doses of diclofenac had no effect on the expression profile of genes related to RA in synovial fibroblasts. These data give the first insight into the mechanisms of action of common antirheumatic drugs used for the treatment of arthritides. Synovial fibroblasts reflect the disease-related pathophysiology and are useful tools for screening putative antirheumatic compounds.

Chronic inflammation during rheumatoid arthritis and degenerative processes during osteoarthritis eventually result in joint destruction. Anti-inflammatory therapies facilitate the inhibition or delay of progressing joint cartilage and bone loss, but do not regenerate these tissues. Surgical procedures are quite unsatisfactory in long-term evaluation and often lead to endoprothetic joint replacement. Present tissue engineering technologies offer new strategies for the treatment of cartilage and bone defects. Here, beyond implantation of cell suspensions, biomaterials combined with tissue-specific cells or mesenchymal stem cells are clinically applied. This review focusses on state-of-the-art and future in situmesenchymal stem cell-based tissue engineering approaches for joint repair in patients with rheumatic diseases.

In 1742, H.L. Duhamel published a report in which the osteogenic function of periosteum was described. In 1932 H.B. Fell was the first to successfully culture periosteum; Fell concluded that this tissue might have the capability to form mineralized tissue in vitro. In the 1990s the research group of A.L. Caplan pioneered work exploring the osteogenic potential of periosteal cells in the field of bone engineering. On the basis of these studies a number of research groups have developed hard tissue generation concepts that aim to repeat the clinical success of bone autografts by culturing cells from periosteum and seeding a sufficient quantity of those cells into scaffolds made of biomaterials of natural and synthetic origin. The highly porous matrices support the induction of bone regeneration by creating and maintaining a space that facilitates progenitor cell migration, proliferation, and differentiation as well as graft revascularization. In this way, a host tissue-scaffold cell interphase might be created that allows reproduction of the intrinsic properties of autogenous bone, including the ability to be incorporated into the surrounding host bone and to continue normal bone-remodeling processes. This review discusses the history and state of the art of bone tissue engineering from a periosteum and periosteal cell source point of view and attempts to indicate future research directions.

Abstract. The adult bone marrow stroma contains a subset of nonhematopoietic cells referred to as mesenchymal stem or mesenchymal progenitor cells (MSC). These cells have the capacity to undergo extensive replication in an undifferentiated state ex vivo. In addition, MSC have the potential to develop either in vitro or in vivo into distinct mesenchymal tissues, including bone, cartilage, fat, tendon, muscle, and marrow stroma, which suggest these cells as an attractive cell source for tissue engineering approaches. The interest in modern biological technologies such as tissue engineering has dramatically increased since it is feasible to isolate living, healthy cells from the body, expand them under cell culture conditions, combine them with biocompatible carrier materials and retransplant them into patients. Therefore, tissue engineering gives the opportunity to generate living substitutes for tissues and organs, which may overcome the drawbacks of classical tissue reconstruction: lacking quality and quantity of autologous grafts, immunogenicity of allogenic grafts and loosening of alloplastic implants. Due to the prerequisite for tissue engineering to ensure a sufficient number of tissue specific cells without donor site morbidity, much attention has been drawn to multipotential progenitor cells such as embryonic stem cells, periosteal cells and mesenchymal stem cells. In this report we review the state of the art in tissue engineering with mesenchymal stem and mesenchymal progenitor cells with emphasis on bone and cartilage reconstruction. Furthermore, several issues of importance, especially with regard to the clinical application of mesenchymal stem cells, are discussed.

An important role in joint and cartilage homeostasis in adults has been demonstrated recently for morphogenetic factors of the transforming growth factor β family. Therefore, this study was undertaken to investigate the potential of bone morphogenetic proteins (BMPs) in chondrocyte differentiation using current technologies of tissue engineering. Complementary DNAs of recombinant human BMPs 2, 4, 5, 6, and 7 were transfected into primary bovine articular chondrocytes. Transgenic chondrocytes were assembled 3-dimensionally in alginate or in bioresorbable co-polymer fleeces of vicryl and polydioxanon embedded in low-melting-point agarose. Redifferentiation and formation of cartilage tissue in vitro or after subcutaneous transplantation into nude mice were assayed by semiquantitative reverse transcriptase–polymerase chain reaction, histology, and in situ hybridization, and findings were compared with those in unmodified or control-transfected primary chondrocytes. Compared with other BMPs and control vector, BMP-7 induced a decrease in type I collagen expression in artificial cartilage, while transcription of the cartilage-specific type II collagen remained stable. In transplantation experiments, BMP-7 transgenic cartilage revealed the greatest amount of matrix synthesis, and BMP-7 was the only morphogen to suppress the infiltrative response of mouse fibroblastic cells into engineered cartilage, thereby preventing transplant destruction. Cartilage differentiation and matrix maturation are promoted by BMPs in cartilage engineering. The inhibitory effect of BMP-7 on a nonspecific infiltrative response in immunocompromised nude mice further suggests that individual morphogens not only may contribute to cartilage maturation, but also may protect it from nonspecific inflammation and invasive destruction. These properties advance BMPs as promising tools for engineering of cartilaginous joint bioprostheses and as candidate biologic agents or genes for cartilage stabilization in arthritis.

Natural cartilage tissue has a limited self-regenerative capacity; thus, strategies to replenish the lost cartilage are desired in reconstructive and plastic surgery. Tissue-engineered cartilage using biodegradable polymeric scaffolds is one such approach gaining wide attention. We have earlier demonstrated the biocompatible nature and ability of chitosan-gelatin hydrogel to maintain differentiated populations of respiratory epithelial cells. The aim of the present study was to evaluate its suitability as a substratum for inducing chondrocyte growth and differentiation. Electron microscopic (SEM) analysis of freeze-dried hydrogels showed a highly porous morphology with interconnections as seen in cross section. Chondrocytes were observed to attach and exhibited a differentiated phenotype with proper cell-cell contact on three-dimensional freeze-dried hydrogels. When cultured on two-dimensional hydrogel films they showed higher growth rates (4–6%) compared with a polystyrene (TCPS) control until 6 days (p > 0.05), which slowed down after 10 days. Immunofluorescent microscopic studies revealed that chondrocytes on hydrogel films exhibited comparable expression of β1 integrin (CD29) to TCPS controls, indicating the ability of the hydrogel substrate to maintain normal expression of β1 integrin. RT-PCR analysis of chondrocytes grown on hydrogel films showed that chondrocytes express the mRNA for extracellular matrix proteins such as collagen type IIα1 (COL IIα1), COL III, COL IXα3. Expression of COL I was less prominent than COL II as indication of differentiation. Expression of COL X could not be detected, suggesting an absence of chondrocyte hypertrophy. Chondrocytes also showed weak mRNA expression of aggrecan, a cartilage-specific proteoglycan. All of these results point out the ability of the chitosan-gelatin hydrogel to induce the expression of mRNAs for cartilage-specific extracellular matrix proteins by nasal septal chondrocytes. This hydrogel needs to be further evaluated for its ability to support chondrocyte-specific marker expression to explore the possibility of forming a tissue resembling natural cartilage in vitro.

Extensive tracheal defect reconstruction is a major challenge in plastic and reconstructive surgery. The lack of an epithelial lining on the luminal surfaces of tracheal prostheses is among the major causes of their failure. Chitosan–gelatin hydrogels were synthesized for the development of biocompatible, growthsupportive substrata for respiratory epithelial cells. We employed J774 macrophages to test the immunocompatibility of this gel. The hydrogel did not exert a cytotoxic effect on macrophages, as confirmed by tetrazolium reduction and neutral red uptake assay. Flow cytometric analysis of macrophages cultured on the hydrogel showed a comparable expression of activation markers CD11bCD18, CD45, and CD14 to the control. Semiquantitative RTPCR results showed an absence of upregulation of interleukin6 IL6 and TNFα in these macrophages with respect to the controls. Primary human respiratory epithelial cells cultured on the hydrogel showed proper attachment, normal morphology, and growth. A small proportion of cells on the hydrogel showed synchronously beating cilia. RTPCR analysis showed that cells on the hydrogel expressed mucins 2 and 5 and cytokeratin 13, which are markers for secretory goblet and squamous cells, respectively. All these results demonstrate that the hydrogel supports the growth of a mixed population of differentiated epithelial cells. This hydrogel is suitable as a culture substratum for respiratory epithelial cells and could be used as a potential candidate for coating tracheal prostheses. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 120–127, 2001

The advances in biomedicine over the past decade have provided revolutionary insights into molecules that mediate cell proliferation and differentiation. Findings on the complex interplay of cells, growth factors, matrix molecules and cell adhesion molecules in the process of tissue patterning have vitalized the revolutionary approach of bioregenerative medicine and tissue engineering. Here we review the impact of recent work in this interdisciplinary field on the treatment of musculoskeletal disorders. This novel concept combines the transplantation of pluripotent stem cells, and the use of specifically tailored biomaterials, arrays of bioactive molecules and gene transfer technologies to direct the regeneration of pathologically altered musculoskeletal tissues.

For cartilage engineering a variety of biomaterials were applied for 3dimensional chondrocyte embedding and transplantation. In order to find a suitable carrier for the in vitroculture of chondrocytes and the subsequent preparation of cartilage transplants we investigated the feasibility of a combination of the wellestablished matrices fibrin and alginate. In this work human articular chondrocytes were embedded and cultured either in alginate, a mixture of alginate and fibrin, or in a fibrin gel after the extraction of the alginate component porous fibrin gel over a period of 30 days. Histomorphological analysis, electron microscopy, and immunohistochemistry were performed to evaluate the phenotypic changes of the chondrocytes, as well as the quality of the newly formed cartilaginous matrix. Our experiments showed that a mixture of 0.6 alginate with 4.5 fibrin promoted sufficient chondrocyte proliferation and differentiation, resulting in the formation of a specific cartilage matrix. Alginate served as a temporary supportive matrix component during in vitroculture and can be easily removed prior to transplantation. The presented tissue engineering method on the basis of a mixed alginate–fibrin carrier offers the opportunity to create stable cartilage transplants for reconstructive surgery. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 49, 305–311, 2000.

Abstract A new field in biomedical science has been established. Cell biologists, engineers, and surgeons now work within a team. Artificial connective, epithelial, or neuronal tissues are being constructed using living cells and different kinds of biomaterials. Numerous companies and laboratories are presenting dynamic developments in this field. Prognoses predict that, at the beginning of the coming century, the industry of tissue engineering will reach the importance of the present genetic technology. An enormous demand for organ and tissue transplants motivates research activities and drives the acquisition of innovative techniques and creative solutions. At the front of this development is the creation of artificial skin for severely burned patients and the generation of artificial cartilage for implantation in articular joint diseases. Future challenges are the construction of liver organoids and the development of an artificial kidney on the basis of cultured cells. In this paper we show strategies, needs, tools, and equipment for tissue engineering. The presupposition for all projects is the induction, development, and maintenance of differentiation within the tissue under in vitro conditions. As experiments in conventional culture dishes continued to fail, new cell and tissue culture methods had to be developed. Tissues are cultured under conditions as close as possible to their natural environment. To optimize adherence or embedding, cells are grown on novel tissue carriers and on individually selected biomatrices or scaffolds. The tissues are subsequently transferred into different types of containers for permanent perfusion with fresh culture medium. This guarantees constant nutrition of the developing tissue and prevents the accumulation of harmful metabolites. An organo-typical environment for epithelial cells, for example, is obtained in gradient containers, which are permanently superfused at the apical and basal sides with different media. Long term experiments result in cultured tissues in a quality thus far unreached.

Autologous chondrocyte implantation is an established option for the treatment of full-thickness cartilage defects of the knee. Open implantation has a high morbidity. On a resorbable polymer fleece, autologous chondrocytes can be implanted arthroscopically. Transosseous anchoring assures high initial stability of the implant. Tibial defects can be addressed. The arthroscopic technique for the implantation of autologous chondrocytes eliminates a substantial amount of the side effects known to occur after open autologous chondrocyte implantation procedures.

Autologous chondrocyte transplantation (ACT) is a routine technique to regenerate focal cartilage lesions. However, patients with osteoarthritis (OA) are lacking an appropriate long-lasting treatment alternative, partly since it is not known if chondrocytes from OA patients have the same chondrogenic differentiation potential as chondrocytes from donors not affected by OA.

Rheumatoid arthritis (RA) leads to progressive destruction of articular cartilage. This study aimed to disclose major mechanisms of antirheumatic drug action on human chondrocytes and to reveal marker and pharmacological target genes that are involved in cartilage dysfunction and regeneration.