Tissue Engineering Cartilage with Aged Articular Chondrocytes In Vivo

Stochastic Resonance with Dynamic Compression Improves the Growth of Adult Chondrocytes in Agarose Gel Constructs

Dynamic mechanical stimulation has been an effective method to improve the growth of tissue engineering cartilage constructs derived from immature cells. However, when more mature cell populations are used, results are often variable due to the differing responses of these cells to external stimuli. This can be especially detrimental in the case of mechanical loading. In previous studies, multi-modal mechanical stimulation in the form of stochastic resonance was shown to be effective at improving the growth of young bovine chondrocytes. Thus, the aim of this study was to investigate the short-term and long-term effects of stochastic resonance on two groups of bovine chondrocytes, adult (> 30 month) and juvenile (~ 18 months). While the juvenile cells outperformed the adult cells in terms of their anabolic response to loading, combined mechanical loading for both age groups resulted in greater matrix synthesis compared to compressive loading alone. In the adult cells, potential pathological tissue formation was evident with the presence of cell clustering. However, the presence of broad-band mechanical vibrations (alone or with compressive loading) appeared to mitigate this response and allow these cells to attain a growth response similar to the juvenile, unstimulated cells. Therefore, the use of stochastic resonance appears to show promise as a method to improve the formation and properties of tissue engineered cartilage constructs, irrespective of cell age.

Properties of cartilage engineered from elderly human chondrocytes for articular surface repair

Numerous studies on engineering cartilage utilizing chondrocytes from juvenile animal sources have been reported. However, there are many unknown aspects of engineering cartilage using human chondrocytes-especially from middle-aged or elderly adults-which are critical for clinical application of tissue engineering in the field of orthopedic surgery. The primary aim of this study was to engineer neocartilage tissue from 50-60-year-old human chondrocytes in comparison to engineered cartilage made from juvenile swine chondrocytes (JSCs). Articular chondrocytes from middle-aged, nonarthritic humans and juvenile swine were isolated and placed in culture for expansion. The chondrocytes (passage 1) were mixed in fibrin gel at 40-60×10(6) cells/mL until polymerization. Cells/nodule constructs and devitalized cartilage-cells/hydrogel-devitalized cartilage constructs (three-layered model) were implanted into subcutaneous pockets of nude mice for 12, 18, and 24 weeks. The specimens were evaluated histologically, biochemically, and biomechanically. This allowed for direct comparison of the cartilage engineered from human versus swine cells. Histological analysis demonstrated that samples engineered utilizing chondrocytes from middle-aged adults accumulated basophilic, sulfated glycosaminoglycans (sGAG), and abundant type II collagen around the cells in a manner similar to that seen in samples engineered using JSCs at all time points. Biochemical analysis revealed that samples made with human cells had about 40%-60% of the amount hydroxyproline of native human cartilage, a trend parallel to that observed in the specimens made with swine chondrocytes. The amount of sGAG in the human chondrocyte specimens was about one-and-a-half times the amount in native human cartilage, whereas the amount in the samples made with swine chondrocytes was always less than native cartilage. The biomechanical analysis revealed that the stiffness and tensile of samples made with human cells were in a pattern similar to that seen with swine chondrocytes. This study demonstrates that chondrogenesis using articular chondrocytes from middle-aged adults can be achieved in a predictable and reliable manner similar to that shown in studies using cells from juvenile animals and can form the basis of engineering cartilage with degradable scaffolds in this patient population.

Genipin-crosslinked fibrin hydrogels as a potential adhesive to augment intervertebral disc annulus repair

Treatment of damaged intervertebral discs is a significant clinical problem and, despite advances in the repair and replacement of the nucleus pulposus, there are few effective strategies to restore defects in the annulus fibrosus. An annular repair material should meet three specifications: have a modulus similar to the native annulus tissue, support the growth of disc cells, and maintain adhesion to tissue under physiological strain levels. We hypothesized that a genipin crosslinked fibrin gel could meet these requirements. Our mechanical results showed that genipin crosslinked fibrin gels could be created with a modulus in the range of native annular tissue. We also demonstrated that this material is compatible with the in vitro growth of human disc cells, when genipin:fibrin ratios were 0.25:1 or less, although cell proliferation was slower and cell morphology more rounded than for fibrin alone. Finally, lap tests were performed to evaluate adhesion between fibrin gels and pieces of annular tissue. Specimens created without genipin had poor handling properties and readily delaminated, while genipin crosslinked fibrin gels remained adhered to the tissue pieces at strains exceeding physiological levels and failed at 15-30%. This study demonstrated that genipin crosslinked fibrin gels show promise as a gap-filling adhesive biomaterial with tunable material properties, yet the slow cell proliferation suggests this biomaterial may be best suited as a sealant for small annulus fibrosus defects or as an adhesive to augment large annulus repairs. Future studies will evaluate degradation rate, fatigue behaviors, and long-term biocompatibility.

Porous poly(vinyl alcohol)-alginate gel hybrid construct for neocartilage formation using human nasoseptal cells

BACKGROUND

Limited options exist for the restoration of craniofacial cartilage. Autologous tissue or porous polyethylene is currently used for nasal and auricular reconstruction. Both options are associated with drawbacks, including donor site morbidity and implant extrusion. Poly(vinyl alcohol) (PVA) is a non-degradable flexible biocompatible polymer than can be engineered to mimic the properties of cartilage. The goal of this study was to engineer a biosynthetic hybrid construct using a combination of PVA-alginate hydrogels and human nasal septum chondrocytes.

MATERIALS AND METHODS

Chondrocytes isolated from human nasal septum cartilage were expanded and mixed with 2% sodium alginate hydrogel. The chondrocyte-alginate mix was injected into a non-degradable porous PVA hydrogel, creating biosynthetic constructs. A group of these constructs were implanted into the subcutaneous environment of nude mice, while the other group was cultured in a spinner flask bioreactor system for 10 d and then implanted. After 6 wk in vivo, the histologic, biochemical, and biomechanical properties were examined.

RESULTS

Histological analysis demonstrated sulfated glycosaminoglycans and deposition of collagen type II in constructs from both groups. Constructs cultured in the bioreactor system prior in vivo implantation demonstrated higher levels of DNA, glycosaminoglycans, and hydroxyproline. An increase of 22% in the compressive strength of the engineered constructs exposed to the bioreactor was also observed.

CONCLUSION

A novel porous PVA-alginate gel hybrid was used to successfully engineer human cartilage in vivo. A 10-d period of bioreactor culturing increased levels of DNA, glycosaminoglycans, hydroxyproline, and the compressive modulus of the constructs.

Fibrin: a versatile scaffold for tissue engineering applications

Tissue engineering combines cell and molecular biology with materials and mechanical engineering to replace damaged or diseased organs and tissues. Fibrin is a critical blood component responsible for hemostasis, which has been used extensively as a biopolymer scaffold in tissue engineering. In this review we summarize the latest developments in organ and tissue regeneration using fibrin as the scaffold material. Commercially available fibrinogen and thrombin are combined to form a fibrin hydrogel. The incorporation of bioactive peptides and growth factors via a heparin-binding delivery system improves the functionality of fibrin as a scaffold. New technologies such as inkjet printing and magnetically influenced self-assembly can alter the geometry of the fibrin structure into appropriate and predictable forms. Fibrin can be prepared from autologous plasma, and is available as glue or as engineered microbeads. Fibrin alone or in combination with other materials has been used as a biological scaffold for stem or primary cells to regenerate adipose tissue, bone, cardiac tissue, cartilage, liver, nervous tissue, ocular tissue, skin, tendons, and ligaments. Thus, fibrin is a versatile biopolymer, which shows a great potential in tissue regeneration and wound healing.

A novel rat tail collagen type-I gel for the cultivation of human articular chondrocytes in low cell density

Collagen type-I matrix systems have gained growing importance as a cartilage repair device. However, most of the established matrix systems use collagen type-I of bovine origin seeded in high cell densities. Here we present a novel collagen type-I gel system made of rat tail collagen for the cultivation of human chondrocytes in low cell densities. Rat tail collagen type-I gel (CaReS, Arthro Kinetics, Esslingen, Germany) was seeded with human passage 2 chondrocytes in different cell densities to evaluate the optimal cell number. In vitro, the proliferation factor of low density cultures was more than threefold higher compared with high density cultures. After 6 weeks of in vitro cultivation, freshly prepared chondrocytes with an initial cell density of 2x10(5) cells/mL showed a proliferation factor of 33. A cell density of 2x10(5) cells/mL was chosen for in vitro and in vivo cultivation using the common nude mouse model as an in vivo system. Chondrocytes stayed viable as a Live/Dead fluorescence assay and TUNEL staining revealed. During in vitro cultivation, passage 0 cells partly dedifferentiated morphologically. In vivo, passage 0 cells maintained the chondrocyte phenotype and demonstrated an increased synthesis of collagen type-II protein and gene expression compared to passage 2 cells. Passage 2 cells did not redifferentiate in vivo. Cultivating a cell-seeded collagen gel of bovine origin as a control (AtelocollagenTM, Koken, Tokyo, Japan) did not lead to superior results with regard to cell morphology, col-II protein production and col-II gene expression. With the CaReS collagen gel system the best quality of repair tissue was obtained by seeding freshly isolated chondrocytes.

Engineering cartilage tissue

Cartilage tissue engineering is emerging as a technique for the regeneration of cartilage tissue damaged due to disease or trauma. Since cartilage lacks regenerative capabilities, it is essential to develop approaches that deliver the appropriate cells, biomaterials, and signaling factors to the defect site. The objective of this review is to discuss the approaches that have been taken in this area, with an emphasis on various cell sources, including chondrocytes, fibroblasts, and stem cells. Additionally, biomaterials and their interaction with cells and the importance of signaling factors on cellular behavior and cartilage formation will be addressed. Ultimately, the goal of investigators working on cartilage regeneration is to develop a system that promotes the production of cartilage tissue that mimics native tissue properties, accelerates restoration of tissue function, and is clinically translatable. Although this is an ambitious goal, significant progress and important advances have been made in recent years.

A novel injectable scaffold for cartilage tissue engineering using adipose-derived adult stem cells

Articular cartilage has a limited self-regenerative capacity. Thus, treatment of cartilage lesions is a major challenge. Tissue engineering using a variety of biomaterials is a promising solution to the problem of cartilage damage. In this in vitro study, we investigated the effect of the presence of cartilage-tissue chondroitin-sulfate (CS) in a fibrin scaffold on the differentiation of adipose-derived adult stem cells (ADAS cells) into chondrocytes. Isolated rabbit ADAS cells were cultured in fibrin matrices with and without CS for up to 14 days. ADAS cells differentiated into chondrocytes in both matrices, but cell proliferation, glycoaminoglycans content, and type II collagen expression were significantly higher in the fibrin-CS matrices than those in the fibrin matrices alone. Histological examination and scanning electronic microscopy revealed the fibrin-CS matrices exceeded in inducing differentiation of ADAS cells into chondrocytes in terms of tissue morphological characteristics. We concluded that the fibrin-CS matrices mimicking native cartilage extracellular matrix could act as a three-dimensional scaffold for cartilage tissue engineering and have the potential for promoting ADAS cells differentiation into chondrocytes.

In VitroandIn VivoCartilage Engineering Using a Combination of Chondrocyte-Seeded Long-Term Stable Fibrin Gels and Polycaprolactone-Based Polyurethane Scaffolds

The use of either a hydrogel or a solid polymeric scaffold alone is often associated with distinct drawbacks in many tissue engineering applications. Therefore, in this study, we investigated the potential of a combination of long-term stable fibrin gels and polyurethane scaffolds for cartilage engineering. Primary bovine chondrocytes were suspended in fibrin gel and subsequently injected into a polycaprolactone-based polyurethane scaffold. Cells were homogeneously distributed within this composite system and produced high amounts of cartilage-specific extracellular matrix (ECM) components, namely glycosaminoglycans (GAGs) and collagen type II, within 4 weeks of in vitro culture. In contrast, cells seeded directly onto the scaffold without fibrin resulted in a lower seeding efficiency and distinctly less homogeneous matrix distribution. Cell-fibrin-scaffold constructs implanted into the back of nude mice promoted the formation of adequate engineered cartilaginous tissue within the scaffold after 1, 3, and 6 months in vivo, containing evenly distributed ECM components, such as GAGs and collagen. Again, in constructs seeded without fibrin, histology showed an inhomogeneous and, thus, not adequate ECM distribution compared to seeding with fibrin, even after 6 months in vivo. Strikingly, a precultivation for 1 week in vitro elicited similar results in vivo compared to precultivation for 4 weeks; that is, a precultivation for longer than 1 week did not enhance tissue development. The presented composite system is suggested as a promising alternative toward clinical application of engineered cartilaginous tissue for plastic and reconstructive surgery.

Methodological models for in vitro amplification and maintenance of human articular chondrocytes from elderly patients

Articular cartilage defects, an exceedingly common problem closely correlated with advancing age, is characterized by lack of spontaneous resolution because of the limited regenerative capacity of adult articular chondrocytes. Medical and surgical therapies yield unsatisfactory short-lasting results. Recently, cultured autologous chondrocytes have been proposed as a source to promote repair of deep cartilage defects. Despite encouraging preliminary results, this approach is not yet routinely applicable in clinical practice, but for young patients. One critical points is the isolation and ex vivo expansion of large enough number of differentiated articular chondrocytes. In general, human articular chondrocytes grown in monolayer cultures tend to undergo dedifferentiation. This reversible process produces morphological changes by which cells acquire fibroblast-like features, loosing typical functional characteristics, such as the ability to synthesize type II collagen. The aim of this study was to isolate human articular chondrocytes from elderly patients and to carefully characterize their morphological, proliferative, and differentiative features. Cells were morphologically analyzed by optic and transmission electron microscopy (TEM). Production of periodic acid-schiff (PAS)-positive cellular products and of type II collagen mRNA was monitored at different cellular passages. Typical chondrocytic characteristics were also studied in a suspension culture system with cells encapsulated in alginate-polylysine-alginate (APA) membranes. Results showed that human articular chondrocytes can be expanded in monolayers for several passages, and then microencapsulated, retaining their morphological and functional characteristics. The results obtained could contribute to optimize expansion and redifferentiation sequences for applying cartilage tissue engineering in the elderly patients.