Tissue engineering of osteochondral constructs in vitro using bioreactors

Structure and Pathologies of Articular Cartilage

The aim of the review was to describe a complex microstructure and biomechanical properties of the articular cartilage as well as a current review of its pathologies encountered in veterinary practice. The articular cartilage with its unique features: complex microarchitecture, significant mechanical durability and elasticity, lacking blood, lymphatic vessels, and innervation, seems to stand in contradiction to the laws of biology. It can be involved in a vast majority of diseases, from osteoarthrosis as a result of natural aging process to more complex in nature like osteochondromatosis. The primary role of articular cartilage is to provide the surface for movement in any single joint in the body. Therefore, its diseases lead to physical impairment and deterioration of the quality of life. Treatment of articular cartilage poses a formidable challenge in both modern human and animal medicine.

Engineering of gradient osteochondral tissue: From nature to lab

The osteochondral tissue is an interface between two distinct tissues: articular cartilage and bone. These two tissues are significantly diverse with regard to their chemical compositions, mechanical properties, structure, electrical properties, and the amount of nutrient and oxygen consumption. Thus, transition from the surface of the articular cartilage to the subchondral bone needs to face several smooth gradients. These gradients are imperative to study to generate a scaffold suitable for the reconstruction of the cartilaginous and osseous layers of a defected osteochondral tissue, simultaneously. The aim of this review is to peruse the alternation of biochemical, biomechanical, structural, electrical, and metabolic properties of the osteochondral tissue moving from the surface of the articular cartilage to the subchondral bone. Moreover, this review also discusses currently developed approaches and ideal techniques with a focus on gradients present in the interface of the cartilage and bone. STATEMENT OF SIGNIFICANCE: The submitted review paper entitled as "Engineering of the gradient osteochondral tissue: from nature to lab" is a complete review with regard to the osteochondral tissue and transition of different properties between the cartilage and bone tissues. Moreover, previous studies on the osteochondral tissue engineering have been reviewed in this paper. This complete information can be a valuable and useful source for current and future researchers and scientists. Considering the scope of the submitted paper, Acta Biomaterialia would be a suitable journal for publishing this article.

Treatment of Articular Cartilage Defects: Focus on Tissue Engineering

The treatment of articular cartilage defects seems to be one of the greatest challenges in modern orthopaedics. From a medical point of view there are 3 main goals to achieve for cartilage trauma treatment: restoration of the joints motion, pain relief and elimination/delay of the onset of osteoarthritis. Treatment can be divided into conservative (including pharmacotherapy, arthrocentesis and physiotherapy) and surgical. The last comprises reparative techniques, regenerative methods and symptomatic treatment. While both are focused on reconstruction of the damaged cartilage, the difference lies in the type of filling tissue. Reparative techniques include: drilling of the subchondral bone, spongiolisation, abrasion, mictrofracture, and autologous matrix induced chondrogenesis (AMIC). Regenerative methods contain: periosteal and perichondral grafts, mosaicplasty, autologous chondrocyte implantation and matrix-induced autologous chondrocyte implantation (MACI). Nowadays tissue engineering, including gene therapy, is emerging as one of the key approaches to cartilage treatment and holds promises for new achievements and better outcomes of many cartilage diseases and traumas.

Osteochondral Repair Using Porous Three-dimensional Nanocomposite Scaffolds in a Rabbit Model

AIM

To evaluate the utility of a novel nanocomposite biomaterial consisting of poly-L/D-lactide, and hydroxyapatite bioceramics, enriched with sodium alginate in articular cartilage defect treatment.

MATERIALS AND METHODS

The biomaterial was prepared using the method of solvent casting and particle leaching. The study was conducted on 20 New Zealand White rabbits. Experimental osteochondral defects were created in the femoral trochlear grooves and filled with biomaterials. In control groups, the defects were left to spontaneously heal. The quality of newly-formed tissue was evaluated on the basis of macroscopic and histological assessment. Additionally the level of osteogenic and cartilage degradation markers were measured.

RESULTS

The majority of the defects from the treatment group were covered with tissue similar in structure and colour to healthy cartilage, whereas in the control group, tissue was uneven, and not integrated into the surrounding cartilage.

CONCLUSION

The results obtained validate the choice of biomaterial used in this study as well as the method of its application.

Spatial Engineering of Osteochondral Tissue Constructs Through Microfluidically Directed Differentiation of Mesenchymal Stem Cells

The development of tissue engineered osteochondral units has been slowed by a number of technical hurdles associated with recapitulating their heterogeneous nature ex vivo. Subsequently, numerous approaches with respect to cell sourcing, scaffolding composition, and culture media formulation have been pursued, which have led to high variability in outcomes and ultimately the lack of a consensus bioprocessing strategy. As such, the objective of this study was to standardize the design process by focusing on differentially supporting formation of cartilaginous and bony matrix by a single cell source in a spatially controlled manner within a single material system. A cell-polymer solution of bovine mesenchymal stem cells and agarose was cast against micromolds of a serpentine network and stacked to produce tissue constructs containing two independent microfluidic networks. Constructs were fluidically connected to two controlled flow loops and supplied with independently tuned differentiation parameters for chondrogenic and osteogenic induction, respectively. Constructs receiving inductive media showed differential gene expression of both chondrogenic and osteogenic markers in opposite directions along the thickness of the construct that was recapitulated at the protein level with respect to collagens I, II, and X. A control group receiving noninductive media showed homogeneous expression of these biomarkers measured in lower concentrations at both the mRNA and protein level. This work represents an important step in the rational design of engineered osteochondral units through establishment of an enabling technology for further optimization of scaffolding formulations and bioprocessing conditions toward the production of commercially viable osteochondral tissue products.

Intermittent hydrostatic pressure maintains and enhances the chondrogenic differentiation of cartilage progenitor cells cultivated in alginate beads

The objective of this study was to explore the effects of intermittent hydrostatic pressure (IHP) on the chondrogenic differentiation of cartilage progenitor cells (CPCs) cultivated in alginate beads. CPCs were isolated from the knee joint cartilage of rabbits, and infrapatellar fat pad-derived stem cells (FPSCs) and chondrocytes (CCs) were included as the control cell types. Cells embedded in alginate beads were treated with IHP at 5 Mpa and 0.5 Hz for 4 h/day for 1, 2, or 4 weeks. The cells' migratory and proliferative capacities were evaluated using the scratch and Live/Dead assays, respectively. Hematoxylin and eosin staining, safranin O staining, and immunohistochemical staining were performed to determine the effects of IHP on the synthesis of extracellular matrix (ECM) proteins. Real-time polymerase chain reaction analysis was performed to measure the expression of genes related to chondrogenesis. The scratch and Live/Dead assays revealed that IHP significantly promoted the migration and proliferation of FPSCs and CPCs to different extents. The staining experiments showed greater production of cartilage ECM components (glycosaminoglycans and collagen II) by cells exposed to IHP, and the gene expression analysis demonstrated that IHP stimulated the expression of chondrocyte-related genes. Importantly, these effects of IHP were more prominent in CPCs than in FPSCs and CCs. Considering all of our experimental results combined, we conclude that CPCs demonstrated a stronger chondrogenic differentiation capacity than the FPSCs and CCs under stimulation with IHP. Thus, the use of CPCs, combined with mechanical stimulation, may represent a valuable strategy for cartilage tissue engineering.

Positive effects of cell-free porous PLGA implants and early loading exercise on hyaline cartilage regeneration in rabbits

The regeneration of hyaline cartilage remains clinically challenging. Here, we evaluated the therapeutic effects of using cell-free porous poly(lactic-co-glycolic acid) (PLGA) graft implants (PGIs) along with early loading exercise to repair a full-thickness osteochondral defect. Rabbits were randomly allocated to a treadmill exercise (TRE) group or a sedentary (SED) group and were prepared as either a PGI model or an empty defect (ED) model. TRE was performed as a short-term loading exercise; SED was physical inactivity in a free cage. The knees were evaluated at 6 and 12 weeks after surgery. At the end of testing, none of the knees developed synovitis, formed osteophytes, or became infected. Macroscopically, the PGI-TRE group regenerated a smooth articular surface, with transparent new hyaline-like tissue soundly integrated with the neighboring cartilage, but the other groups remained distinct at the margins with fibrous or opaque tissues. In a micro-CT analysis, the synthesized bone volume/tissue volume (BV/TV) was significantly higher in the PGI-TRE group, which also had integrating architecture in the regeneration site. The thickness of the trabecular (subchondral) bone was improved in all groups from 6 to 12 weeks. Histologically, remarkable differences in the cartilage regeneration were visible. At week 6, compared with SED groups, the TRE groups manifested modest inflammatory cells with pro-inflammatory cytokines (i.e., TNF-α and IL-6), improved collagen alignment and higher glycosaminoglycan (GAG) content, particularly in the PGI-TRE group. At week 12, the PGI-TRE group had the best regeneration outcomes, showing the formation of hyaline-like cartilage, the development of columnar rounded chondrocytes that expressed enriched levels of collagen type II and GAG, and functionalized trabecular bone with osteocytes. In summary, the combination of implanting cell-free PLGA and performing an early loading exercise can significantly promote the full-thickness osteochondral regeneration in rabbit knee joint models.

STATEMENT OF SIGNIFICANCE

Promoting effective hyaline cartilage regeneration rather than fibrocartilage scar tissue remains clinically challenging. To address the obstacle, we fabricated a spongy cell-free PLGA scaffold, and designed a reasonable exercise program to generate combined therapeutic effects. First, the implanting scaffold generates an affordable mechanical structure to bear the loading forces and bridge with the host to offer a space in the full-thickness osteochondral regeneration in rabbit knee joint. After implantation, rabbits were performed by an early treadmill exercise 15 min/day, 5 days/week for 2 weeks that directly exerts in situ endogenous growth factor and anti-inflammatory effects in the reparative site. The advanced therapeutic strategy showed that neo-hyaline cartilage formation with enriched collagen type II, higher glycosaminoglycan, integrating subchondral bone formation and modest inflammation.

Comparative assessment of bone regeneration by histometry and a histological scoring system / Evaluarea comparativă a regenerării osoase utilizând histometria și un scor de vindecare histologică

Objective: The aim of this research is to evaluate the value of the histological score based on a histological record compared to the histometry for monitoring cranial bone defect healing. Methods: We designed a case -control study with a control and a study group. For a number of 60 CD1 mice representing the study group, a bone defect in the cranial bone was surgically induced and grafted with bone grafts obtained by tissue engineering. Bone grafts were obtained using embryonic stem cells seeded on a scaffold obtained from the red deer antler, and osteogenic basal and complex medium was used as differentiation medium. For other 30 CD1 mice representing the control group, a bone defect in the cranial bone was induced and left to heal without grafts. The regeneration process was assessed after 2 and 4 months using the histological healing scoring system and histometry. Results: The healing score was statistically significantly correlated with the defect size obtained by means of histometry (p<0.001). The evaluation of the parameters comprised in the healing score shows that regeneration of the bone diastasis was the most advanced in the group sacrificed at 4 months after plasty, which employed embryonic stem cells, a complex osteogenic differentiation medium and deer antler as scaffold. Conclusion: histological method based on a histological score is a valuable quantification system of bone regeneration comparable to histometry. Clinical Relevance: This study proves that the presented histological score can help the clinician in the process of bone regeneration evaluation.

Influence of extremely low frequency, low energy electromagnetic fields and combined mechanical stimulation on chondrocytes in 3-D constructs for cartilage tissue engineering

Articular cartilage, once damaged, has very low regenerative potential. Various experimental approaches have been conducted to enhance chondrogenesis and cartilage maturation. Among those, non-invasive electromagnetic fields have shown their beneficial influence for cartilage regeneration and are widely used for the treatment of non-unions, fractures, avascular necrosis and osteoarthritis. One very well accepted way to promote cartilage maturation is physical stimulation through bioreactors. The aim of this study was the investigation of combined mechanical and electromagnetic stress affecting cartilage cells in vitro. Primary articular chondrocytes from bovine fetlock joints were seeded into three-dimensional (3-D) polyurethane scaffolds and distributed into seven stimulated experimental groups. They either underwent mechanical or electromagnetic stimulation (sinusoidal electromagnetic field of 1 mT, 2 mT, or 3 mT; 60 Hz) or both within a joint-specific bioreactor and a coil system. The scaffold-cell constructs were analyzed for glycosaminoglycan (GAG) and DNA content, histology, and gene expression of collagen-1, collagen-2, aggrecan, cartilage oligomeric matrix protein (COMP), Sox9, proteoglycan-4 (PRG-4), and matrix metalloproteinases (MMP-3 and -13). There were statistically significant differences in GAG/DNA content between the stimulated versus the control group with highest levels in the combined stimulation group. Gene expression was significantly higher for combined stimulation groups versus static control for collagen 2/collagen 1 ratio and lower for MMP-13. Amongst other genes, a more chondrogenic phenotype was noticed in expression patterns for the stimulated groups. To conclude, there is an effect of electromagnetic and mechanical stimulation on chondrocytes seeded in a 3-D scaffold, resulting in improved extracellular matrix production.

Transplantation of autologous endothelial progenitor cells in porous PLGA scaffolds create a microenvironment for the regeneration of hyaline cartilage in rabbits

OBJECTIVE

Repairing articular cartilage is clinically challenging. We investigated a simple, effective and clinically feasible cell-based therapeutic approach using a poly(lactide-co-glycolide) (PLGA) scaffold seeded with autologous endothelial progenitor cells (EPC) to repair a full-thickness osteochondral defect in rabbits using a one-step surgery.

METHODS

EPC obtained by purifying a small amount of peripheral blood from rabbits were seeded into a highly porous, biocompatible PLGA scaffold, namely, EPC-PLGA, and implanted into the osteochondral defect in the medial femoral condyle. Twenty two rabbits were randomized into one of three groups: the empty defect group (ED), the PLGA-only group or the EPC-PLGA group. The defect sites were evaluated 4 and 12 weeks after implantation.

RESULTS

At the end of testing, only the EPC-PLGA group showed the development of new cartilage tissue with a smooth, transparent and integrated articular surface. Moreover, histological analysis showed obvious differences in cartilage regeneration. At week 4, the EPC-PLGA group showed considerably higher TGF-β2 and TGF-β3 expression, a greater amount of synthesized glycosaminoglycan (GAG) content, and a higher degree of osteochondral angiogenesis in repaired tissues. At week 12, the EPC-PLGA group showed enhanced hyaline cartilage regeneration with a normal columnar chondrocyte arrangement, higher SOX9 expression, and greater GAG and collagen type II (COLII) content. Moreover, the EPC-PLGA group showed organized osteochondral integration, the formation of vessel-rich tubercular bone and significantly higher bone volume per tissue volume and trabecular thickness (Tb.Th).

CONCLUSION

The present EPC-PLGA cell delivery system generates a suitable in situ microenvironment for osteochondral regeneration without the supplement of exogenous growth factors.

Enhanced migration of human bone marrow stromal cells in modified collagen hydrogels

PURPOSE

Collagen I hydrogels are widely used as scaffolds for regeneration of articular cartilage defects. We hypothesised that ingrowth might be improved by removing the superficial layer of a compressed hydrogel. The control group consisted of the original unmodified product.

METHODS

The migration of human bone marrow stromal cells (hBMSCs) into the hydrogel was evaluated by confocal microscopy. We quantified the DNA concentration of the hydrogel for each group and time point and evaluated the chondrogenic differentiation of cells.

RESULTS

After one week, the detectable amount of cells at the depth of 26-50 μm was significantly higher in the modified matrix (MM) than in the non-modified matrix (NM) (p = 0.011). The maximum depth of penetration was 75 μm (NM) and 200 μm (MM). After three weeks, the maximum depth of penetration was 175 μm (NM) and 200 μm (MM). Likewise, at a depth of 0-25 μm the amount of detectable cells was significantly higher in the MM group (p = 0.003). After 14 days, the concentration of DNA was significantly higher in the samples of the MM than in the control group (p = 0.000). Staining of histological sections and labelling with collagen II antibodies showed that a chondrogenic differentiation of cells in the scaffold can occur during in vitro cultivation.

CONCLUSIONS

Removing the superficial layer is essential to ensuring proper ingrowth of cells within the compressed hydrogel. Compressed hydrogels contribute better to cartilage regeneration after surface modification.

Progenitor cells from cartilage--no osteoarthritis-grade-specific differences in stem cell marker expression

Tissue engineering efforts for the fabrication of cartilage substitutes head toward applicability in osteoarthritis (OA). Progenitor cells can be harvested from the osteoarthritic joint itself, resembling multipotent mesenchymal stromal cells (MSC). Our objective was to analyze MSC characteristics of those cells in respect to the OA-related damage of their harvest site. OA cartilage was obtained from six patients during alloarthroplastic knee surgery, sample grading was done according to Outerbridge's classification. Upon enzymatic dissociation, primary chondrocytes were expanded in two-dimensional monolayer culture. At distinct cell passages, the process of dedifferentiation was phenotypically monitored; cell surface expression of classical MSC markers was analyzed by flow cytometry. Cells were subjected to chondrogenesis and osteogenesis after their fourth passage. At third passage, 95% of cells became positive for cluster of differentiation (CD)105 and further subclassification revealed that the majority of them were positive for both CD73 and CD90. CD105(+) CD73(+) CD90(+) phenotype meets thus the minimal surface antigen criteria for MSC definition. More than one-third of dedifferentiated chondrocytes displayed a coexpression of CD9(+) CD166(+) CD90(+) and to a lesser extent CD105(+) CD73(+) CD44(+) , irrespective of the stage of the original cartilage degradation. Finally, we could successfully demonstrate a redifferentiation of these progenitors into sulfated glycosaminoglycan producing cells. The basic level of alkaline phosphatase activity could not be enhanced upon osteogenic differentiation. In conclusion, chondrogenic progenitors derived from OA cartilages with low or high Outerbridge's grade can be seen as a potential cellular source for cartilage replacement.

Osteochondral tissue engineering: current strategies and challenges

Osteochondral defect management and repair remain a significant challenge in orthopedic surgery. Osteochondral defects contain damage to both the articular cartilage as well as the underlying subchondral bone. In order to repair an osteochondral defect the needs of the bone, cartilage and the bone-cartilage interface must be taken into account. Current clinical treatments for the repair of osteochondral defects have only been palliative, not curative. Tissue engineering has emerged as a potential alternative as it can be effectively used to regenerate bone, cartilage and the bone-cartilage interface. Several scaffold strategies, such as single phase, layered, and recently graded structures have been developed and evaluated for osteochondral defect repair. Also, as a potential cell source, tissue specific cells and progenitor cells are widely studied in cell culture models, as well with the osteochondral scaffolds in vitro and in vivo. Novel factor strategies being developed, including single factor, multi-factor, or controlled factor release in a graded fashion, not only assist bone and cartilage regeneration, but also establish osteochondral interface formation. The field of tissue engineering has made great strides, however further research needs to be carried out to make this strategy a clinical reality. In this review, we summarize current tissue engineering strategies, including scaffold design, bioreactor use, as well as cell and factor based approaches and recent developments for osteochondral defect repair. In addition, we discuss various challenges that need to be addressed in years to come.

The effect of osteochondral regeneration using polymer constructs and continuous passive motion therapy in the lower weight-bearing zone of femoral trocheal groove in rabbits

Remedying patellofemoral osteochondral defects using clinical therapy remains challenging. Construct-based and cell-based regenerative medicine with in vitro physical stimuli has been progressively implemented. However, the effect of physical stimuli in situ in knee joints with degradable constructs is still not well-documented. Therefore, we studied whether it was practical to achieve articular cartilage repair using a poly(lactic-co-glycolic acid) (PLGA) construct in addition to early short-term continuous passive motion (CPM) for treatment of full-thickness osteochondral defects in the lower-weigh bearing (LWB) zone of the femoral trocheal groove. Twenty-six rabbits were randomly allocated into either intermittent active motion (IAM) or CPM treatment groups with or without PLGA constructs, termed PLGA construct-implanted (PCI) and empty defect knee models, respectively. Gross observation, histology, inflammatory cells, which were identified using H&E staining, total collagen and alignment, studied qualitatively using Masson's trichrome staining, glycosaminoglycan (GAG), identified using Alcian blue staining, and newly formed bone, observed using micro-CT, were evaluated at 4 and 12 weeks after surgery. Repair of osteochondral defects in the PCI-CPM group was more promising than all other groups. The better osteochondral defect repair in the PCI-CPM group corresponded to smooth cartilage surfaces, no inflammatory reaction, hyaline cartilaginous tissues composition, sound collagen alignment with positive collagen type II expression, higher GAG content, mature bone regeneration with osteocyte, clear tidemark formation, and better degradation of PLGA. In summary, the use of a simple PLGA construct coupled with passive motion promotes positive healing and may be a promising clinical intervention for osteochondral regeneration in LWB defects.

Engineered bone tissue associated with vascularization utilizing a rotating wall vessel bioreactor

Tissue-engineered bone has attracted much attention as an alternative material for bone grafting; however, implantable bone tissue of an appropriate size and shape for clinical use has not yet been developed due to a lack of vascularization, which results in necrosis of the seeded cells in vivo. This is the first report of bone tissue engineering associated with vascularization by co-culturing bone marrow mesenchymal stem cells (MSCs) with MSC-derived endothelial cells (ECs) within a porous scaffold using a rotating wall vessel (RWV) bioreactor. MSC-derived ECs were identified by immunofluorescence staining for von Willebrand factor (vWF) and by flow cytometry for CD31 expression. The tissue obtained was histochemically analyzed using toluidin blue, hematoxylin and eosin, anti-osteopontin antibody, anti-osteocalcin antibody, and tomato-lectin stain. Results showed that bone tissue containing vascular-like structures was generated. Three-dimensional culture condition created by medium flow in the RWV vessel and the interaction of MSCs with MSC-derived ECs might provide the cells an advantage in the construction of three-dimensional bone tissue with blood vessels.

Surgical treatment of articular cartilage defects in the knee: are we winning?

Articular cartilage (AC) injury is a common disorder. Numerous techniques have been employed to repair or regenerate the cartilage defects with varying degrees of success. Three commonly performed techniques include bone marrow stimulation, cartilage repair, and cartilage regeneration. This paper focuses on current level of evidence paying particular attention to cartilage regeneration techniques.

Effect of chondroitin sulphate C on the in vitro and in vivo chondrogenesis of mesenchymal stem cells in crosslinked type II collagen scaffolds

This study evaluates the crosslinkage effect of chondroitin sulphate C (CSC) and type II collagen (COL II) on chondrogenesis of mesenchymal stem cells (MSCs) in vitro and in vivo. In the in vitro studies, our results show that the weight ratio CSC:COL II that reaches 1.2:100 (CSC1.2/100 -COL II scaffold) can provide an optimal microenvironment for MSC chondrogenesis. When MSCs are cultured in this CSC1.2/100 -COL II scaffold, the chondrogenic gene expression of cultured cells is upregulated, while the osteogenic gene expression of these is downregulated. In addition, MSCs cultivated in the CSC1.2/100 -COL II scaffold are found to express the highest glycosaminoglycans:DNA ratio as compared to those in scaffolds of other CSC:COL II ratios. Histological and immunohistological evidence also supports the result. In the in vivo study, our results show that MSCs cultivated in the CSC1.2/100 -COL II scaffold demonstrate a better repair ability on cartilage lesions than does the COL II scaffold. After 1 month in vivo, the injected MSCs in the CSC1.2/100 -COL II scaffold show lacuna structures and stimulate the formation of type II collagen at the defective sites. Six months after transplantation, the generated cells in the CSC1.2/100 -COL II group show higher gene expressions of type II collagen and aggrecan but lower gene expression of type I collagen at the defective sites than those in the COL II group. The results strongly suggest that CSC1.2/100 -COL II scaffold can serve as a potential candidate for cartilage repair and improve the chondrogenesis of MSCs in general.

General principles for the regeneration of bone and cartilage

For the regeneration of bone and cartilage, mesenchymal stem cells are currently used invitro and in-vivo. For bone, the existence of viable cells, scaffolds, mechanical environment, growth factors and vascularization are of paramount importance. Mesenchymal stem cells can be harvested from the bone marrow using minimally invasive techniques. Centrifugation can increase the number of transplanted cells per volume. The use of cell therapy is under current clinical investigation and the benefit from these systems has to be proven in level I studies. For cartilage, current techniques recruiting stem cells from the subchondral bone have been demonstrated to be nearly as effective as autologous chondrocyte transplantation, requiring less invasive surgery. The efficacy of mesenchymal stem cell concentrates remains to be proven. There is high potential for tissue engineered joint surfaces to become an option for joint surface defects and degeneration.

Physical stimulation of chondrogenic cells in vitro: a review

BACKGROUND

Mechanical stimuli are of crucial importance for the development and maintenance of articular cartilage. For conditioning of cartilaginous tissues, various bioreactor systems have been developed that have mainly aimed to produce cartilaginous grafts for tissue engineering applications. Emphasis has been on in vitro preconditioning, whereas the same devices could be used to attempt to predict the response of the cells in vivo or as a prescreening method before animal studies. As a result of the complexity of the load and motion patterns within an articulating joint, no bioreactor can completely recreate the in vivo situation.

QUESTIONS/PURPOSES

This article aims to classify the various loading bioreactors into logical categories, highlight the response of mesenchymal stem cells and chondrocytes to the various stimuli applied, and determine which data could be used within a clinical setting.

METHODS

We performed a Medline search using specific search terms, then selectively reviewed relevant research relating to physical stimulation of chondrogenic cells in vitro, focusing on cellular responses to the specific load applied.

RESULTS

There is much data pertaining to increases in chondrogenic gene expression as a result of controlled loading protocols. Uniaxial loading leads to selective upregulation of genes normally associated with a chondrogenic phenotype, whereas multiaxial loading results in a broader pattern of chondrogenic gene upregulation. The potential for the body to be used as an in vivo bioreactor is being increasingly explored.

CONCLUSIONS

Bioreactors are important tools for understanding the potential response of chondrogenic cells within the joint environment. However, to replicate the natural in vivo situation, more complex motion patterns are required to induce more physiological chondrogenic gene upregulation.

Evaluating osteochondral defect repair potential of autologous rabbit bone marrow cells on type II collagen scaffold

The feasibility of using genipin cross-linked type II collagen scaffold with rabbit bone marrow mesenchymal stem cells (RBMSCs) to repair cartilage defect was herein studied. Induction of RBMSCs into chondrocytic phenotype on type II collagen scaffold in vitro was conducted using TGF-β 3 containing medium. After 3-weeks of induction, chondrocytic behavior, including marker genes expression and specific extracellular matrix (ECM) secretion, was observed. In the in vivo evaluation experiment, the scaffolds containing RBMSCs without prior induction were autologous implanted into the articular cartilage defects made by subchondral drilling. The repairing ability was evaluated. After 2 months, chondrocyte-like cells with lacuna structure and corresponding ECM were found in the repaired sites without apparent inflammation. After 24 weeks, we could easily find cartilage structure the same with normal cartilage in the repair site. In conclusion, it was shown that the scaffolds in combination of in vivo conditions can induce RBMSCs into chondrocytes in repaired area and would be a possible method for articular cartilage repair in clinic and cartilage tissue engineering.

Cartilage repair: A review of Stanmore experience in the treatment of osteochondral defects in the knee with various surgical techniques

Articular cartilage damage in the young adult knee, if left untreated, it may proceed to degenerative osteoarthritis and is a serious cause of disability and loss of function. Surgical cartilage repair of an osteochondral defect can give the patient significant relief from symptoms and preserve the functional life of the joint. Several techniques including bone marrow stimulation, cartilage tissue based therapy, cartilage cell seeded therapies and osteotomies have been described in the literature with varying results. Established techniques rely mainly on the formation of fibro-cartilage, which has been shown to degenerate over time due to shear forces. The implantation of autologous cultured chondrocytes into an osteochondral defect, may replace damaged cartilage with hyaline or hyaline-like cartilage. This clinical review assesses current surgical techniques and makes recommendations on the most appropriate method of cartilage repair when managing symptomatic osteochondral defects of the knee. We also discuss the experience with the technique of autologous chondrocyte implantation at our institution over the past 11 years.

No effect in combining chondrogenic predifferentiation and mechanical cyclic compression on osteochondral constructs stimulated in a bioreactor

Traumatic and degenerative osteochondral lesions are a common problem in orthopaedic surgery. The concept of tissue engineering represents the possibility of a promising therapeutical approach. The purpose of this study has been to improve the characteristics of osteochondral grafts consisting of a human certified collagen I-bone hybrid matrix seeded with human bone marrow stromal cells and stimulated in a custom-made biomechanoreactor. This study was undertaken as a follow-up to our prior studies. Based on our established system, we added chondrogenic growth factors (IGF-1 and TGF-beta(2)) and evaluated their effect on chondrogenic differentiation. Constructs were stimulated for 14, 21 and 28 days respectively by different protocols, including cyclic mechanical stimulation, hormonal stimulation or a combination of both. More than 70% of the cells were viable throughout the entire experimental period. Histological analysis revealed a homogeneous distribution of cells in a cartilage-like matrix organization. Immunohistological collagen II staining was positive irrespective of stimulation manner and time. Levels of DNA and glycosaminoglycans, having been normalized to DNA, did not change. Analysis of the biomechanical stiffness after 14 days showed increased stiffness in the hormonally and mechanically stimulated group compared to the static group. Stimulation time did not have a significant influence. The media supplements to foster the quality of the tissue tested here did not show any progress in our system. We conclude that cyclic compression enhances matrix stiffness, but stimulation time should be kept short and growth factors should be left out in this system with regard to clinical applicability and financial concerns.

Effects of low-amplitude, high-frequency vibrations on proliferation and differentiation of SAOS-2 human osteogenic cell line

The aim of the work was to understand the consequences of low-amplitude, high-frequency vibrations on proliferation and differentiation of SAOS-2 cells (sarcoma osteogenetic), an osteoblastic and tumorigenic cell line. We realized a bioreactor composed of an eccentric motor that produces a displacement of 11 mm at frequencies between 1 and 120 Hz on a plate connected to the motor. The cultures of SAOS-2 cells were fixed on the plate, and the linear acceleration provoked by the motor to the cultures was measured. We used 30 Hz as stimulating frequency after a preliminary test on the effect of different frequencies on differentiation of cells. Afterward, SAOS-2 cells were stimulated with 30 Hz for different durations, every day for 4 days. The expression of some genes involved in the differentiation process was analyzed first with a reverse transcriptase-polymerase chain reaction and afterward with a real-time polymerase chain reaction on the most expressed genes. Moreover, the proliferation of cells was evaluated. The results suggest a strong increase in the expression of the genes involved in tissue differentiation in the treated groups with respect to the controls. On the other hand, the proliferation seems to be slowed down, so probably the acceleration perceived by the mechanosensors of the cells changes the cellular cycle by blocking the duplication to early differentiate toward bone tissue.

Perfusion and cyclic compression of mesenchymal cell-loaded and clinically applicable osteochondral grafts

Osteochondral lesions are often seen in orthopedics, but the available treatment strategies are limited in success. Regenerative medicine provides novel concepts for curing them. The purpose of this study was to test the effects of perfusion and cyclic compression on cell differentiation and mechanical properties using a custom-made biomechanoreactor in a recently established system of human bone marrow stromal cells (hBMSC) cultured in a 3-D collagen I-bone hybrid matrix out of commercially available and separately in human-certified products. Seeded hBMSC were viable for 88 +/- 8.9% during the entire experimental period in the constructs. GAG and DNA levels did not change. Perfusion induced collagen II and cyclic compression increased collagen X expression. Matrix stiffness was significantly increased after 28 days of cyclic compression. Cyclic compression of cell-loaded hybrid constructs enhanced chondrocyte differentiation and matrix stiffness. This system is a promising tool with a view to a later clinical application.

Polytrauma management - a single centre experience

The management of polytraumatised patients remains challenging in spite of advances and improvements in trauma care in recent decades. Trauma systems require enormous staff resources as well as technical equipment. Internal and external quality management processes are necessary to identify weak points and improve treatment quality. Continuous training of all professionals involved in trauma care is necessary to assure high quality, up-to-date therapy in patients with multiple injuries. Standard operating procedures such as prehospital trauma algorithms and clinical management protocols (ie, ATLS) can help to standardise and compare treatment of patients suffering from major trauma. In this overview, we describe the development and current state of our trauma department. Differences in our cohort of polytraumatised patients compared to other facilities and current strategies for initial treatment of these patients are also discussed.

Articular cartilage tissue engineering

Articular cartilage repair remains a challenge to surgeons and basic scientists. The field of tissue engineering allows the simultaneous use of material scaffolds, cells and signalling molecules to attempt to modulate the regenerative tissue. This review summarises the research that has been undertaken to date using this approach, with a particular emphasis on those techniques that have been introduced into clinical practice, via in vitro and preclinical studies.

Cells and biomaterials in cartilage tissue engineering

Cartilage defects are notoriously difficult to repair and owing to the long-term prognosis of osteoarthritis, and a rapidly aging population, a need for new therapies is pressing. Cell-based therapies for cartilage regeneration were introduced into patients in the early 1990s. Since that time the technology has developed from a simple cell suspension to more complex 3D structures. Cells, both chondrocytes and stem cells, have been incorporated into scaffold material with the aim to better recreate the natural environment of the cell, while providing more structural support to withstand the large forces applied on the de novo tissue. This review aims to provide an overview of potential cell sources and different scaffold materials, which are in development for cartilage tissue engineering.

MOSAICPLASTY WITH PERIOSTEAL GRAFT FOR RESURFACING LOCAL FULL-THICKNESS CHONDRAL DEFECTS OF THE KNEE

Introduction and Objectives: Clinical and functional assessment comparing cases of full-thickness chondral defects (OC) treated with mosaicplasty or mosaicplasty covered with periosteum (mosaicambium). Methods: 20 knees with chondral defect, (10 mosaicplasty/10 mosaicambium) were operated between 1999 and 2005. All patients were clinically assessed preoperatively using the ICRS scale, VAS scale, X-ray and MRI. During 2008, we reviewed patients using the same protocol. For statistical purposes, the patients were divided into two groups, according to the surgical technique. Statistical analysis was performed with EPI2000 program, using chi-squared test and Student's t test, with a significance level of 0.05. Results: Preoperatively, all patients were in group C/D (ICRS scale). In 2008, 18 cases were in groups A and B according to the ICRS scale (12 in A). Between groups, there were no statistical differences. The X-ray study revealed no changes in 55% of cases. Discussion: With no differences, why mosaicambium option? Morbidity on graft donor zones is not negligible. Mosaicambium uses less chondral grafts, reducing the potential for morbidity at graft donor zones. Conclusion: The mosaicambium technique is an excellent alternative for chondral defects greater than 2 cm2.

“… articular cartilage defects are a troublesome thing … they don't heal …”. William Hunter (1718-1783).