Native Articular Cartilage Research Articles

Direct Human Cartilage Repair Using Three-Dimensional Bioprinting Technology

Current cartilage tissue engineering strategies cannot as yet fabricate new tissue that is indistinguishable from native cartilage with respect to zonal organization, extracellular matrix composition, and mechanical properties. Integration of implants with surrounding native tissues is crucial for long-term stability and enhanced functionality. In this study, we developed a bioprinting system with simultaneous photopolymerization capable for three-dimensional (3D) cartilage tissue engineering. Poly(ethylene glycol) dimethacrylate (PEGDMA) with human chondrocytes were printed to repair defects in osteochondral plugs (3D biopaper) in layer-by-layer assembly. Compressive modulus of printed PEGDMA was 395.73±80.40 kPa, which was close to the range of the properties of native human articular cartilage. Printed human chondrocytes maintained the initially deposited positions due to simultaneous photopolymerization of surrounded biomaterial scaffold, which is ideal in precise cell distribution for anatomic cartilage engineering. Viability of printed human chondrocytes increased 26% in simultaneous polymerization than polymerized after printing. Printed cartilage implant attached firmly with surrounding tissue and greater proteoglycan deposition was observed at the interface of implant and native cartilage in Safranin-O staining. This is consistent with the enhanced interface failure strength during the culture assessed by push-out testing. Printed cartilage in 3D biopaper had elevated glycosaminoglycan (GAG) content comparing to that without biopaper when normalized to DNA. These observations were consistent with gene expression results. This study indicates the importance of direct cartilage repair and promising anatomic cartilage engineering using 3D bioprinting technology.

Functional biomaterials for cartilage regeneration

The injury and degeneration of articular cartilage and associated arthritis are leading causes of disability worldwide. Cartilage tissue engineering as a treatment modality for cartilage defects has been investigated for over 20 years. Various scaffold materials have been developed for this purpose, but has yet to achieve feasibility and effectiveness for widespread clinical use. Currently, the regeneration of articular cartilage remains a formidable challenge, due to the complex physiology of cartilage tissue and its poor healing capacity. Although intensive research has been focused on the developmental biology and regeneration of cartilage tissue and a diverse plethora of biomaterials have been developed for this purpose, cartilage regeneration is still suboptimal, such as lacking a layered structure, mechanical mismatch with native cartilage and inadequate integration between native tissue and implanted scaffold. The ideal scaffold material should have versatile properties that actively contribute to cartilage regeneration. Functional scaffold materials may overcome the various challenges faced in cartilage tissue engineering by providing essential biological, mechanical, and physical/chemical signaling cues through innovative design. This review thus focuses on the complex structure of native articular cartilage, the critical properties of scaffolds required for cartilage regeneration, present strategies for scaffold design, and future directions for cartilage regeneration with functional scaffold materials.

Current Clinical Therapies for Cartilage Repair, their Limitation and the Role of Stem Cells

The management of osteochondral defects of articular cartilage, whether from trauma or degenerative disease, continues to be a significant challenge for Orthopaedic surgeons. Current treatment options such as abrasion arthroplasty procedures, osteochondral transplantation and autologous chondrocyte implantation fail to produce repair tissue exhibiting the same mechanical and functional properties of native articular cartilage. This results in repair tissue that inevitably fails as it is unable to deal with the mechanical demands of articular cartilage, and does not prevent further degeneration of the native cartilage. Mesenchymal stem cells have been proposed as a potential source of cells for cell-based cartilage repair due to their ability to self-renew and undergo multi-lineage differentiation. This proposed procedure has the advantage of not requiring harvesting of cells from the joint surface, and its associated donor site morbidity, as well as having multiple possible adult donor tissues such as bone marrow, adipose tissue and synovium. Mesenchymal stem cells have multi-lineage potential, but can be stimulated to undergo chondrogenesis in the appropriate culture medium. As the majority of work with mesenchymal stem cell-derived articular cartilage repair has been carried out in vitro and in animal studies, more work still has to be done before this technique can be used for clinical purposes. This includes realizing the ideal method of harvesting mesenchymal stem cells, the culture medium to stimulate proliferation and differentiation, appropriate choice of scaffold incorporating growth factors directly or with gene therapy and integration of repair tissue with native tissue.

Simultaneous anabolic and catabolic responses of human chondrocytes seeded in collagen hydrogels to long-term continuous dynamic compression

Cartilage repair strategies increasingly focus on the in vitro development of cartilaginous tissues that mimic the biological and mechanical properties of native articular cartilage. However, current approaches still face problems in the reproducible and standardized generation of cartilaginous tissues that are both biomechanically adequate for joint integration and biochemically rich in extracellular matrix constituents. In this regard, the present study investigated whether long-term continuous compressive loading would enhance the mechanical and biological properties of such tissues. Human chondrocytes were harvested from 8 knee joints (n=8) of patients having undergone total knee replacement and seeded into a collagen type I hydrogel at low density of 2×10(5)cells/ml gel. Cell-seeded hydrogels were cut to disks and subjected to mechanical stimulation for 28 days with 10% continuous cyclic compressive loading at a frequency of 0.3 Hz. Histological and histomorphometric evaluation revealed long-term mechanical stimulation to significantly increase collagen type II and proteoglycan staining homogenously throughout the samples as compared to unstimulated controls. Gene expression analyses revealed a significant increase in collagen type II, collagen type I and MMP-13 gene expression under stimulation conditions, while aggrecan gene expression was decreased and no significant changes were observed in the collagen type II/collagen type I mRNA ratio. Mechanical propertywise, the average value of elastic stiffness increased in the stimulated samples. In conclusion, long-term mechanical preconditioning of human chondrocytes seeded in collagen type I hydrogels considerably improves biological and biomechanical properties of the constructs, corroborating the clinical potential of mechanical stimulation in matrix-associated autologous chondrocyte transplantation (MACT) procedures.

Oriented cartilage extracellular matrix-derived scaffold for cartilage tissue engineering

The structure of a cartilage scaffold is required to mimic native articular cartilage, which has an oriented structure associated with its mechanical function. In this study, an oriented cartilage extracellular matrix (ECM)-derived scaffold was fabricated composed of microtubules arranged in parallel in vertical section. The mechanical property was higher than that of a typical non-oriented scaffold (p<0.05). Oriented and non-oriented scaffolds were seeded with chondrogenic-induced bone mesenchymal stem cells and cell-scaffold constructs were implanted subcutaneously in the dorsa of nude mice. At 4 weeks, all samples stained positive for safranin O, toluidine blue, and collagen type II, but negative for collagen type I. Oriented-structure constructs contained numerous parallel giant bundles of densely packed collagen fibers with chondrocyte-like cells aligned along the fibers. Total DNA, glycosaminoglycans and collagen contents increased with time and these values were similar in the two groups. Compared with the native articular cartilage, the Young's modulus of the tissue-engineered (TE) cartilage reached 42.9%, 23.0% in oriented and non-oriented scaffolds respectively, at 4 weeks. These results indicate that oriented ECM-derived scaffolds enhance the biomechanical property of TE cartilage and thus represent a promising approach to cartilage tissue engineering.

Depth and orientational dependencies of MRI T2 and T1ρ sensitivities towards trypsin degradation and Gd-DTPA2− presence in articular cartilage at microscopic resolution

Depth and orientational dependencies of microscopic magnetic resonance imaging (MRI) T2 and T1ρ sensitivities were studied in native and trypsin-degraded articular cartilage before and after being soaked in 1 mM Gd-DTPA2− solution. When the cartilage surface was perpendicular to B0, a typical laminar appearance was visible in T2-weighted images but not in T1ρ-weighted images, especially when the spin-lock field was high (2 kHz). At the magic angle (55°) orientation, neither T2- nor T1ρ-weighted image had a laminar appearance. Trypsin degradation caused a depth- and orientational-dependent T2 increase (4%–64%) and a more uniform T1ρ increase at a sufficiently high spin-lock field (55%–81%). The presence of the Gd ions caused both T2 and T1ρ to decrease significantly in the degraded tissue (6%–38% and 44%–49%, respectively) but less notably in the native tissue (5%–10% and 16%–28%, respectively). A quantity Sensitivity was introduced that combined both the percentage change and the absolute change in the relaxation analysis. An MRI experimental protocol based on two T1ρ measurements (without and with the presence of the Gd ions) was proposed to be a new imaging marker for cartilage degradation.

Engineering Lubrication in Articular Cartilage

Despite continuous progress toward tissue engineering of functional articular cartilage, significant challenges still remain. Advances in morphogens, stem cells, and scaffolds have resulted in enhancement of the bulk mechanical properties of engineered constructs, but little attention has been paid to the surface mechanical properties. In the near future, engineered tissues will be able to withstand and support the physiological compressive and tensile forces in weight-bearing synovial joints such as the knee. However, there is an increasing realization that these tissue-engineered cartilage constructs will fail without the optimal frictional and wear properties present in native articular cartilage. These characteristics are critical to smooth, pain-free joint articulation and a long-lasting, durable cartilage surface. To achieve optimal tribological properties, engineered cartilage therapies will need to incorporate approaches and methods for functional lubrication. Steady progress in cartilage lubrication in native tissues has pushed the pendulum and warranted a shift in the articular cartilage tissue-engineering paradigm. Engineered tissues should be designed and developed to possess both tribological and mechanical properties mirroring natural cartilage. In this article, an overview of the biology and engineering of articular cartilage structure and cartilage lubrication will be presented. Salient progress in lubrication treatments such as tribosupplementation, pharmacological, and cell-based therapies will be covered. Finally, frictional assays such as the pin-on-disk tribometer will be addressed. Knowledge related to the elements of cartilage lubrication has progressed and, thus, an opportune moment is provided to leverage these advances at a critical step in the development of mechanically and tribologically robust, biomimetic tissue-engineered cartilage. This article is intended to serve as the first stepping stone toward future studies in functional tissue engineering of articular cartilage that begins to explore and incorporate methods of lubrication.

The application of an optically switched dielectrophoretic (ODEP) force for the manipulation and assembly of cell-encapsulating alginate microbeads in a microfluidic perfusion cell culture system for bottom-up tissue engineering

This study reports the utilisation of an optically switched dielectrophoretic (ODEP) force for the manipulation and assembly of cell-encapsulating alginate microbeads in a microfluidic perfusion cell culture system for bottom-up tissue engineering. One of the key features of this system is the ODEP force-based mechanism, which allows a commercial projector to be coupled with a computer to manipulate and assemble cell-encapsulating microbeads in an efficient, manageable, and user-friendly manner. Another distinctive feature is the design of the microfluidic cell culture chip, which allows the patterned cell-encapsulating microbeads to be cultivated on site under culture medium perfusion conditions. For demonstrating its application in bottom-up cartilage tissue engineering, chondrocyte-encapsulating alginate microbeads varying in encapsulated cell densities were generated. The manipulation forces associated with operating the alginate microbeads were experimentally evaluated. The results revealed that the measured manipulation forces increased with increases in both the applied electric voltage and the number of cells in the alginate microbeads. Nevertheless, the observed manipulation force was found to be independent of the size of the cell-free alginate microbeads. It can be speculated that the friction force may influence the estimation of the ODEP force within the experimental conditions investigated. In this study, chondrocyte-encapsulating alginate microbeads with three different cell densities were manipulated and assembled in the proposed microfluidic system to form a compact sheet-like cell culture construct that imitates the cell distribution in the cross-section of native articular cartilage. Moreover, the demonstration case also showed that the cell viability of the cultured cells in the microfluidic system remained as high as 96 ± 2%. In this study, four sheet-like cell culture constructs were stacked to create a larger assembled cell culture construct. The cell distribution inside the cell culture construct was further confirmed by a confocal microscopy observation, which showed that the distribution was similar to that in native articular cartilage. As a whole, the proposed system holds great promise as a platform for engineering tissue constructs with easily tunable inner cell distributions.

A Novel Biomaterial for Cartilage Repair Generated by Self-Assembly: Creation of a Self-Organized Articular Cartilage-Like Tissue

Recently, attention has been drawn to tissue engineering and other novel techniques aimed at reconstruction of the joint. Regarding articular cartilage tissue engineering, three-dimensional materials created in vitro by cultivation of autologous chondrocytes or mesenchymal stem cells with a collagen gel have been implanted to replace defective parts of the articular cartilage in limited cases with the diseases such as trauma or arthritis. However, several passages of chondrocyte culture are required to obtain a sufficient number of cells for tissue engineering. Additionally, several other problems arise including dedifferentiation of chondrocytes during cell culture, which need to be solved from a viewpoint of cellular resources. The purpose of our study is to create a novel biomaterial possessing functions and structures comparable to native hyaline articular cartilage by utilizing the physicochemical properties of the cartilage matrix components themselves, in other words, employing a self-assembly technique instead of using chondrocytes to produce cartilage matrices eventually leading to articular cartilage tissue formation. We verified the conditions and accuracy of the self-organization process and analyzed the resulting micro structure using electron beam microscopy in order to study the technique involved in the self-organization which would be applicable to creation of cartilage-like tissue. We demonstrated that self-assembly of several cartilage components including type II collagen, proteoglycan and hyaluronic acid could construct self-assembled cartilage-like tissues characterized by nano composite structures comparable to human articular cartilage and by low friction coefficients as small as those of native cartilage.

The incorporation of a zone of calcified cartilage improves the interfacial shear strength between in vitro-formed cartilage and the underlying substrate

A major challenge for cartilage tissue engineering remains the proper integration of constructs with surrounding tissues in the joint. Biphasic osteochondral constructs that can be anchored in a joint through bone ingrowth partially address this requirement. In this study, a methodology was devised to generate a cell-mediated zone of calcified cartilage (ZCC) between the in vitro-formed cartilage and a porous calcium polyphosphate (CPP) bone substitute in an attempt to improve the mechanical integrity of that interface. To do so, a calcium phosphate (CaP) film was deposited on CPP by a sol–gel process to prevent the accumulation of polyphosphates and associated inhibition of mineralization as the substrate degrades. Cartilage formed in vitro on the top surface of CaP-coated CPP by deep-zone chondrocytes was histologically and biochemically comparable to that formed on uncoated CPP. Furthermore, the mineral in the ZCC was similar in crystal structure, morphology and length to that formed on uncoated CPP and native articular cartilage. The generation of a ZCC at the cartilage–CPP interface led to a 3.3-fold increase in the interfacial shear strength of biphasic constructs. Improved interfacial strength of these constructs may be critical to their clinical success for the repair of large cartilage defects.

Structural characteristics of the collagen network in human normal, degraded and repair articular cartilages observed in polarized light and scanning electron microscopies

This study characterizes collagen organization (CO) in human normal (n=6), degraded (n=6) and repair (n=22) cartilages, using polarized light (PLM) and scanning electron (SEM) microscopies. CO was assessed using a recently developed PLM-CO score (Changoor etal. Osteoarthritis Cartilage 2011;19:126-35), and zonal proportions measured. SEM images were captured from locations matched to PLM. Fibre orientations were assessed in SEM and compared to those observed in PLM. CO was also assessed in individual SEM images and combined to generate a SEM-CO score for overall CO analogous to PLM-CO. Fibre diameters were measured in SEM. PLM-CO and SEM-CO scores were correlated, r=0.786 (P<0.00001, n=32), after excluding two outliers. Orientation observed in PLM was validated by SEM since PLM/SEM correspondence occurred in 91.6% of samples. Proportions of the deep (DZ), transitional (TZ) and superficial (SZ) zones averaged 74.0±9.1%, 18.6±7.0%, and 7.3±1.2% in normal, and 45.6±10.7%, 47.2±10.1% and 9.5±3.4% in degraded cartilage, respectively. Fibre diameters in normal cartilage increased with depth from the articular surface [55.8±9.4nm (SZ), 87.5±1.8nm (TZ) and 108.2±1.8nm (DZ)]. Fibre diameters were smaller in repair biopsies [60.4±0.7nm (SZ), 63.2±0.6nm (TZ) and 67.2±0.8nm (DZ)]. Degraded cartilage had wider fibre diameter ranges and bimodal distributions, possibly reflecting new collagen synthesis and remodelling or collagen fibre unravelling. Repair tissues revealed the potential of microfracture-based repair procedures to produce zonal CO resembling native articular cartilage structure. Values are reported as mean±95% confidence interval. This detailed assessment of collagen architecture could benefit the development of cartilage repair strategies intended to recreate functional collagen architecture.

Finite element study of a tissue-engineered cartilage transplant in human tibiofemoral joint

Most tissue-engineered cartilage constructs are more compliant than native articular cartilage (AC) and are poorly integrated to the surrounding tissue. To investigate the effect of an implanted tissue-engineered construct (TEC) with these inferior properties on the mechanical environment of both the engineered and adjacent native tissues, a finite element study was conducted. Biphasic swelling was used to model tibial cartilage and an implanted TEC with the material properties of either native tissue or a decreased elastic modulus and fixed charged density. Creep loading was applied with a rigid impermeable indenter that represented the femur. In comparison with an intact joint, compressive strains in the transplant, surface contact stress in the adjacent native AC and load partitioning between different phases of cartilage were affected by inferior properties of TEC. Results of this study may lead to a better understanding of the complex mechanical environment of an implanted TEC.

Friction and wear behaviour of bacterial cellulose against articular cartilage

Bacterial cellulose (BC) is a natural and biocompatible material with unique properties, such as high water holding capacity, ultra-fine fibre network and high strength that makes it an attractive material for the repair of articular cartilage lesions. However, data on the tribological properties of BC is very scarce, particularly if natural articular cartilage is involved in the contact. In this work, unmodified BC pellicles were grown from Gluconacetobacter xylinus in order to be used as tribological samples against bovine articular cartilage (BAC) in the presence of phosphate buffered saline (PBS). The tribological assessment of the sliding pairs was accomplished using reciprocating pin-on-flat tests at 37 °C. The reciprocating sliding frequency and stroke length were kept constant at 1 Hz and 8 mm, respectively. Contact pressures ranging from 0.80 to 2.40 MPa were applied. The friction coefficient evolution was continuously monitored during the tests and the release of total carbohydrates into the lubricating solution was followed by means of the phenol–H2SO4 method as an attempt to evaluate wear losses. The morphology of worn surfaces was characterized by SEM/EDS and the main wear mechanisms were identified. Low friction coefficient values (∼0.05) combined with the preservation of the mating surfaces (BC and BAC) indicate the potential of BC to be used as artificial cartilage for articular joints.

A novel recirculating flow-perfusion bioreactor for periosteal chondrogenesis

Previous research indicated that engineered cartilage was soft and fragile due to less extracellular matrix than native articular cartilage. Consequently, the focus of this study was mostly confined to application in vitro function. In order to generate 3D engineered cartilage resembling native articular cartilage, we developed a recirculating flow-perfusion bioreactor to simulate the motion of a native diarthrodial joint by offering shear stress and hydrodynamic pressure simultaneously. The bioreactor we developed offers steady oscillating laminar flow (maximum shear stress of 250 dyne/cm(2)) and hydrodynamic pressure (increased from 0 to 15 psi) simultaneously. The periosteal explants were harvested from the proximal medial tibiae of rabbits and fixed onto PCL scaffold with four corner sutures and cambium layer facing upward, then these periosteal composites (periosteum/ PCL) were placed into the culture chamber of our bioreactor for six weeks in vitro culture. The cartilage yield in our recirculating bioreactor was 75-85%. The outcome was better than the 65-75% in the spinner flask bioreactor (shear stress only) and 17% in static culture. In addition, there was a significant difference in the cell morphology and zonal organisation among the three methods of culture; the engineered cartilage in the recirculating bioreactor presented many more characteristics of native articular cartilage. If the environment of culture provides the shear stress and hydrodynamic pressure simultaneously, the composition of the engineered cartilage resembles native articular cartilage, including their ECM composition, cell distribution, zonal organisation and mechanical properties.

Modulation of collagen II fiber formation in 3-D porous scaffold environments

Collagen II, a major extracellular matrix component in cartilaginous tissues, undergoes fibrillogenesis under physiological conditions. The present study explored collagen II fiber formation in solution and in two- (coverslip) and three-dimensional (scaffold) environments under different incubation conditions. These conditions include variations in adsorption buffers, the presence of 1-ethyl-3-(3-dimenthylaminopropyl) carbodiimide/N-hydroxysuccinimide crosslinker and the nature of the material surfaces. We extend our observations of collagen II fiber formation in two dimensions to develop an approach for the formation of a fibrillar collagen II network throughout surface-modified polylactide-co-glycolide porous scaffolds. Morphologically, the collagen II network is similar to that present in native articular cartilage. Biological validation of the resultant optimized functional scaffold, using rat bone marrow-derived mesenchymal stem cells, shows appreciable cell infiltration throughout the scaffold with enhanced cell spreading at 24 h post-seeding. This economic and versatile approach is thus believed to have significant potential in cartilage tissue engineering applications.

NEL-like molecule-1-modified bone marrow mesenchymal stem cells/poly lactic-co-glycolic acid composite improves repair of large osteochondral defects in mandibular condyle

Articular cartilage of the mandibular condyle has limited ability to regenerate itself after injury. This study was to investigate whether osteochondral defects in mandibular condyle could be repaired by NELL-1(NEL-like molecule-1)-modified autogenous bone marrow mesenchymal stem cells (BMMSCs) and poly lactic-co-glycolic acid (PLGA) composite. Osteochondral defects of 3mm-diameter × 5mm-depth were created unilaterally in the central part of the condyle in 50 adult goats. The injury sites were treated with NELL-1-modified BMMSCs/PLGA, BMMSCs/PLGA, PLGA alone, or left empty. The defect area was monitored using gross examination, histology, immunohistochemistry, and micro-computed tomography (μ-CT). Implanted BMMSCs were tracked using Adeno-LacZ labeling. The NELL-1-modified BMMSCs/PLGA group showed vigorous and rapid repair leading to regeneration of fibrocartilage at 6 weeks and to complete repair of native articular cartilage and subchondral bone at 24 weeks. The BMMSCs/PLGA group also completely repaired the defect with fibrocartilage at 24 weeks, but the cartilage in the BMMSCs/PLGA group was less well-organized than the NELL-1-modified BMMSCs/PLGA. The osteochondral defects in the PLGA and empty defect groups were poorly repaired, and no cartilage in the empty defect group or only small portion of cartilage in the PLGA group was found. In vivo viability of implanted cells was demonstrated by the retention for 6 weeks in the defects. These findings demonstrated that NELL-1-modified BMMSCs/PLGA composite can rapidly repair large osteochondral defect in the mandibular condyle with regeneration of native fibrocartilage and subchondral bone.

Coculture of Human Mesenchymal Stem Cells and Articular Chondrocytes Reduces Hypertrophy and Enhances Functional Properties of Engineered Cartilage

Mesenchymal stem cells (MSCs) are being recognized as a viable cell source for cartilage repair; however, it still remains a challenge to recapitulate the functional properties of native articular cartilage using only MSCs. Additionally, MSCs may exhibit a hypertrophic phenotype under chondrogenic induction, resulting in calcification after ectopic transplantation. With this in mind, the objective of this study was to assess whether the addition of chondrocytes to MSC cultures influences the properties of tissue-engineered cartilage and MSC hypertrophy when cultured in hyaluronic acid hydrogels. Mixed cell populations (human MSCs and human chondrocytes at a ratio of 4:1) were encapsulated in the hydrogels and exhibited significantly higher Young's moduli, dynamic moduli, glycosaminoglycan levels, and collagen content than did constructs seeded with only MSCs or chondrocytes. Furthermore, the deposition of collagen X, a marker of MSC hypertrophy, was significantly lower in the coculture constructs than in the constructs seeded with MSCs alone. When MSCs and chondrocytes were cultured in distinct gels, but in the same wells, there was no improvement in biomechanical and biochemical properties of the engineered tissue, implying that a close proximity is essential. This approach can be used to improve the properties and prevent calcification of engineered cartilage formed from MSC-seeded hydrogels with the addition of lower fractions of chondrocytes, leading to improved clinical outcomes.

Contact Pressure Comparison of Proud Osteochondral Autograft Plugs Versus Proud Synthetic Plugs

Osteochondral autograft transfer is an accepted treatment for chondral and osteochondral defects of the knee. Synthetic plugs may eventually be used for primary treatment of defects. Currently they are largely used for osteochondral donor site backfill. Placement of osteochondral or synthetic plugs proud leads to articulating surface incongruity, increases in contact pressure, and potential for both plug and opposing surface degenerative change. We conducted a biomechanical study of human cadaver knees to determine whether differences exist in the contact pressure of osteochondral autograft plugs placed proud versus synthetic plugs placed proud. Ten human cadaveric knees were used (20 condyles). Contact pressure was measured with Tekscan sensor technology (South Boston, Massachusetts) with both static and cyclical loads (of 250 and 500 cycles) created by an MTS Bionix system (Eden Prairie, Minnesota) under the following conditions: native articular cartilage, surgically created defect (7-mm diameter), 1-mm proud osteochondral autograft, and 1-mm proud synthetic graft. Proud osteochondral autograft plugs resulted in a 21.4% increase in peak contact pressure over surrounding native articular cartilage versus a 4.9% increase with proud synthetic plugs. Synthetic plugs compressed their structure and subsided versus subchondral bone collapse with compressive load in osteochondral autograft plugs. Proud osteochondral autograft plugs have significantly higher peak contact pressures than proud synthetic plugs when placed for treatment of chondral and osteochondral defects in the knee.

On the Horizon From the ORS.

On the Horizon From the ORS.

Chondrogenic differentiation of human bone marrow mesenchymal stem cells in chitosan-based scaffolds using a flow-perfusion bioreactor

Native articular cartilage is subjected to synovial fluid flow during normal joint function. Thus, it is believed that the morphogenesis of articular cartilage may be positively regulated by the application of similar stimulation in vitro. In the present study, the effect of fluid flow over the chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) was investigated. We intended to find out whether the shear stress caused by perfusion of the medium through the constructs was capable of augmenting the differentiation process. Human BMSCs were isolated from bone marrow aspirates and were characterized by flow cytometry. After expansion, hBM-MSCs were seeded statically onto fibre mesh scaffolds, consisting of a blend of 50:50 chitosan:poly(butylene terephthalate adipate) (CPBTA). Constructs were cultured in a flow-perfusion bioreactor for 28 days, using complete medium for chondrogenesis supplemented by TGFβ3. An enhanced ECM deposition and collagen type II production was observed in the bioreactor samples when compared to the static controls. Moreover, it was observed that hBM-MSCs, in static cultures, take longer to differentiate. ECM accumulation in these samples is lower than in the bioreactor sections, and there is a significant difference in the expression of collagen type I. We found that the flow-induced shear stress has a beneficial effect on the chondrogenic differentiation of hMSCs.