Tissue engineering of cartilage

Mesenchymal stem cells: amazing remedies for bone and cartilage defects

Skeletal disorders are among the leading debilitating factors affecting millions of people worldwide. The use of stem cells for tissue repair has raised many promises in various medical fields, including skeletal disorders. Mesenchymal stem cells (MSCs) are multipotent stromal cells with mesodermal and neural crest origin. These cells are one of the most attractive candidates in regenerative medicine, and their use could be helpful in repairing and regeneration of skeletal disorders through several mechanisms including homing, angiogenesis, differentiation, and response to inflammatory condition. The most widely studied sources of MSCs are bone marrow (BM), adipose tissue, muscle, umbilical cord (UC), umbilical cord blood (UCB), placenta (PL), Wharton's jelly (WJ), and amniotic fluid. These cells are capable of differentiating into osteoblasts, chondrocytes, adipocytes, and myocytes in vitro. MSCs obtained from various sources have diverse capabilities of secreting many different cytokines, growth factors, and chemokines. It is believed that the salutary effects of MSCs from different sources are not alike in terms of repairing or reformation of injured skeletal tissues. Accordingly, differential identification of MSCs' secretome enables us to make optimal choices in skeletal disorders considering various sources. This review discusses and compares the therapeutic abilities of MSCs from different sources for bone and cartilage diseases.

Cell Viability of Porous Poly(d,l-lactic acid)/Vertically Aligned Carbon Nanotubes/Nanohydroxyapatite Scaffolds for Osteochondral Tissue Engineering

Treatment of articular cartilage lesions remains an important challenge. Frequently the bone located below the cartilage is also damaged, resulting in defects known as osteochondral lesions. Tissue engineering has emerged as a potential approach to treat cartilage and osteochondral defects. The principal challenge of osteochondral tissue engineering is to create a scaffold with potential to regenerate both cartilage and the subchondral bone involved, considering the intrinsic properties of each tissue. Recent nanocomposites based on the incorporation of nanoscale fillers into polymer matrix have shown promising results for the treatment of osteochondral defects. In this present study, it was performed using the recently developed methodologies (electrodeposition and immersion in simulated body fluid) to obtain porous superhydrophilic poly(d,l-lactic acid)/vertically aligned carbon nanotubes/nanohydroxyapatite (PDLLA/VACNT-O:nHAp) nanocomposite scaffolds, to analyze cell behavior and gene expression of chondrocytes, and then assess the applicability of this nanobiomaterial for osteochondral regenerative medicine. The results demonstrate that PDLLA/VACNT-O:nHAp nanocomposite supports chondrocytes adhesion and decreases type I Collagen mRNA expression. Therefore, these findings suggest the possibility of novel nanobiomaterial as a scaffold for osteochondral tissue engineering applications.

Tensile Biomechanical Properties of Human Nasal Septal Cartilage

Background

The biomechanical properties of human septal cartilage have yet to be fully defined and thereby limits our ability to compare tissue-engineered constructs to native tissue. In this study, we analyzed the tensile properties of human nasal septal cartilage with respect to axis of tension, age group, and gender.

Methods

Fifty-five tensile tests were run on human septal specimens obtained from 28 patients. Samples obtained in the vertical and anterior–posterior (both above and within the maxillary crest) axes were subjected to equilibrium and dynamic tensile testing.

Results

The average values for strength, failure strain, equilibrium modulus and dynamic modulus were not found to be significantly different with respect to axis of tension testing, age group, or gender. Tensile results for septal cartilage were as follows: equilibrium modulus 3.01 ± 0.39 MPa, dynamic modulus 4.99 ± 0.49 MPa, strength 1.90 ± 0.24 MPa, and failure strain 0.35 ± 0.03 mm/mm.

Conclusion

We confirm that septal cartilage has weaker tensile properties compared to articular cartilage and found no difference in strength with respect to age, gender, or axis of tension (isotropic).

Development and Characterization of Acellular Extracellular Matrix Scaffolds from Porcine Menisci for Use in Cartilage Tissue Engineering

Given the growing number of arthritis patients and the limitations of current treatments, there is great urgency to explore cartilage substitutes by tissue engineering. In this study, we developed a novel decellularization method for menisci to prepare acellular extracellular matrix (ECM) scaffolds with minimal adverse effects on the ECM. Among all the acid treatments, formic acid treatment removed most of the cellular contents and preserved the highest ECM contents in the decellularized porcine menisci. Compared with fresh porcine menisci, the content of DNA decreased to 4.10%±0.03%, and there was no significant damage to glycosaminoglycan (GAG) or collagen. Histological staining also confirmed the presence of ECM and the absence of cellularity. In addition, a highly hydrophilic scaffold with three-dimensional interconnected porous structure was fabricated from decellularized menisci tissue. Human chondrocytes showed enhanced cell proliferation and synthesis of chondrocyte ECM including type II collagen and GAG when cultured in this acellular scaffold. Moreover, the scaffold effectively supported chondrogenesis of human bone marrow-derived mesenchymal stem cells. Finally, in vivo implantation was conducted in rats to assess the biocompatibility of the scaffolds. No significant inflammatory response was observed. The acellular ECM scaffold provided a native environment for cells with diverse physiological functions to promote cell proliferation and new tissue formation. This study reported a novel way to prepare decellularized meniscus tissue and demonstrated the potential as scaffolds to support cartilage repair.

Chondrogenic potential of bone marrow-derived mesenchymal stem cells on a novel, auricular-shaped, nanocomposite scaffold

Reconstruction of the human auricle remains a challenge to plastic surgeons, and current approaches are not ideal. Tissue engineering provides a promising alternative. This study aims to evaluate the chondrogenic potential of bone marrow-derived mesenchymal stem cells on a novel, auricular-shaped polymer. The proposed polyhedral oligomeric silsesquioxane-modified poly(hexanolactone/carbonate)urethane/urea nanocomposite polymer has already been transplanted in patients as the world's first synthetic trachea, tear duct and vascular bypass graft. The nanocomposite scaffold was fabricated via a coagulation/salt-leaching method and shaped into an auricle. Adult bone marrow-derived mesenchymal stem cells were isolated, cultured and seeded onto the scaffold. On day 21, samples were sent for scanning electron microscopy, histology and immunofluorescence to assess for neocartilage formation. Cell viability assay confirmed cytocompatability and normal patterns of cellular growth at 7, 14 and 21 days after culture. This study demonstrates the potential of a novel polyhedral oligomeric silsesquioxane-modified poly(hexanolactone/carbonate)urethane/urea scaffold for culturing bone marrow-derived mesenchymal stem cells in chondrogenic medium to produce an auricular-shaped construct. This is supported by scanning electron microscopy, histological and immunofluorescence analysis revealing markers of chondrogenesis including collagen type II, SOX-9, glycosaminoglycan and elastin. To the best of our knowledge, this is the first report of stem cell application on an auricular-shaped scaffold for tissue engineering purposes. Although many obstacles remain in producing a functional auricle, this is a promising step forward.

Preparation and characterization of macromolecule cross-linked collagen hydrogels for chondrocyte delivery

Collagen hydrogels are widely used in cartilage tissue engineering for their mimicked chondrogenic environment. Due to the rapid degradation nature and weak mechanical property, collagen hydrogels are often cross-linked in application. In this work, collagen hydrogels were soaked into oxidized alginate solution which used as macromolecular cross-linker to prepare the cross-linked hydrogels. Soaking method could retain the self-assemble property of collagen and also bring in a cross-linking network. The compressive modulus and degradation properties of collagen hydrogels were ameliorated after cross-linked, and chondrocytes encapsulated in the cross-linked hydrogels proliferated well and maintained the cell phenotype. This study implied that collagen hydrogels cross-linked by oxidized alginate may have a great potential for application in cartilage tissue engineering.

Bioengineering of articular cartilage: past, present and future

The treatment of cartilage defects poses a clinical challenge owing to the lack of intrinsic regenerative capacity of cartilage. The use of tissue engineering techniques to bioengineer articular cartilage is promising and may hold the key to the successful regeneration of cartilage tissue. Natural and synthetic biomaterials have been used to recreate the microarchitecture of articular cartilage through multilayered biomimetic scaffolds. Acellular scaffolds preserve the microarchitecture of articular cartilage through a process of decellularization of biological tissue. Although promising, this technique often results in poor biomechanical strength of the graft. However, biomechanical strength could be improved if biomaterials could be incorporated back into the decellularized tissue to overcome this limitation.

The tissue-engineered auricle: past, present, and future

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitro and in vivo conditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

Hyperosmolarity and hypoxia induce chondrogenesis of adipose-derived stem cells in a collagen type 2 hydrogel

Apart from soluble growth factors, various other biophysicochemical cues are known to promote chondrogenesis. Under physiological conditions, cartilage in the joint comprises a hyperosmotic and hypoxic environment. Therefore, in this study, we examined the inductive effects of hyperosmotic and/or hypoxic conditions on adipose stem cells (ASCs) and compared them with conventional TGFβ1-induction. After encapsulation in collagen type II hydrogels and specific induction, ASCs were assessed for viability, proliferation, morphology and chondrogenic differentiation potential. Viability was similar under all conditions, with low proliferative activity. After 4 days, hypoxia and/or hyperosmolarity did not affect round cell morphology, while cells were mainly stretched in the TGFβ1-induced group. At 21 days, the TGFß1-treated group had aggregated into a cell nodule. Hyperosmolarity mimicked this aggregation to a lesser extent, whereas cells under hypoxia stretched out after 21 days, with a combined effect in the hypoxic/hyperosmotic group. Both individual and combined hyperosmotic and/or hypoxic conditions significantly upregulated SOX5, SOX9, COMP and Link-p gene expression compared with the non-induced group, and to similar levels as the TGFβ1-induced group. GAG synthesis in both hydrogel and medium was increased under hypoxic conditions, whereas hyperosmolarity decreased GAG formation in the hydrogels, but increased GAG formation in the medium. We conclude that in a joint mimicking the three-dimensional (3D) micro-environment, a combination of hyperosmolarity and hypoxia is able to induce chondrogenesis to the same extent as TGFβ1. This might lead to an interesting alternative when considering short-term triggering in a one-step surgical procedure for the treatment of cartilaginous defects.

Mesenchymal stem cell therapy regenerates the native bone-tendon junction after surgical repair in a degenerative rat model

Background

The enthesis, which attaches the tendon to the bone, naturally disappears with aging, thus limiting joint mobility. Surgery is frequently needed but the clinical outcome is often poor due to the decreased natural healing capacity of the elderly. This study explored the benefits of a treatment based on injecting chondrocyte and mesenchymal stem cells (MSC) in a new rat model of degenerative enthesis repair.

Methodology

The Achilles' tendon was cut and the enthesis destroyed. The damage was repaired by classical surgery without cell injection (group G1, n = 52) and with chondrocyte (group G2, n = 51) or MSC injection (group G3, n = 39). The healing rate was determined macroscopically 15, 30 and 45 days later. The production and organization of a new enthesis was assessed by histological scoring of collagen II immunostaining, glycoaminoglycan production and the presence of columnar chondrocytes. The biomechanical load required to rupture the bone-tendon junction was determined.

Principal Findings

The spontaneous healing rate in the G1 control group was 40%, close to those observed in humans. Cell injection significantly improved healing (69%, p = 0.0028 for G2 and p = 0.006 for G3) and the load-to-failure after 45 days (p<0.05) over controls. A new enthesis was clearly produced in cell-injected G2 and G3 rats, but not in the controls. Only the MSC-injected G3 rats had an organized enthesis with columnar chondrocytes as in a native enthesis 45 days after surgery.

Conclusions

Cell therapy is an efficient procedure for reconstructing degenerative entheses. MSC treatment produced better organ regeneration than chondrocyte treatment. The morphological and biomechanical properties were similar to those of a native enthesis.

Osteoblast adhesion, proliferation and growth on polyelectrolyte complex-hydroxyapatite nanocomposites

In this work, we have investigated osteoblast adhesion, proliferation and differentiation on nanocomposites of chitosan, polygalacturonic acid (PgA) and hydroxyapatite. These studies were done on both two- and three-dimensional (scaffold) samples. Atomic force microscopy experiments showed nanostructuring of film samples. Scaffolds were prepared by freeze-drying methods. The mechanical response and porosity of the scaffolds were also determined. The compressive elastic modulus and compressive strength were determined to be around 0.9 and 0.023 MPa, respectively, and the porosity of these scaffolds was found to be around 97 per cent. Human osteoblast cells were used to study their adhesion, proliferation and differentiation. Optical images were collected after different intervals of time of seeding cells. This study indicated that chitosan/PgA/hydroxyapatite nanocomposite films and scaffolds promote cellular adhesion, proliferation and differentiation. The formation of bone-like nodules was observed after 7 days of seeding cells. The nodule size continues to increase with time, and after 20 days the size of some nodules was around 735 microm. Scanning electron microscope images of nodules showed the presence of extracellular matrix. The alizarin red S staining technique was used to confirm mineralization of these nodules.

The effect of an external magnetic force on cell adhesion and proliferation of magnetically labeled mesenchymal stem cells

BACKGROUND

As the strategy for tissue regeneration using mesenchymal stem cells (MSCs) for transplantation, it is necessary that MSCs be accumulated and kept in the target area. To accumulate MSCs effectively, we developed a novel technique for a magnetic targeting system with magnetically labeled MSCs and an external magnetic force. In this study, we examined the effect of an external magnetic force on magnetically labeled MSCs in terms of cell adhesion and proliferation.

METHODS

Magnetically labeled MSCs were plated at the bottom of an insert under the influence of an external magnetic force for 1 hour. Then the inserts were turned upside down for between 1 and 24 hours, and the number of MSCs which had fallen from the membrane was counted. The gene expression of MSCs affected magnetic force was analyzed with microarray. In the control group, the same procedure was done without the external magnetic force.

RESULTS

At 1 hour after the inserts were turned upside down, the average number of fallen MSCs in the magnetic group was significantly smaller than that in the control group, indicating enhanced cell adhesion. At 24 hours, the average number of fallen MSCs in the magnetic group was also significantly smaller than that in control group. In the magnetic group, integrin alpha2, alpha6, beta3 BP, intercellular adhesion molecule-2 (ICAM-2), platelet/endothelial cell adhesion molecule-1 (PECAM-1) were upregulated. At 1, 2 and 3 weeks after incubation, there was no statistical significant difference in the numbers of MSCs in the magnetic group and control group.

CONCLUSIONS

The results indicate that an external magnetic force for 1 hour enhances cell adhesion of MSCs. Moreover, there is no difference in cell proliferation after using an external magnetic force on magnetically labeled MSCs.

Macromolecular Monomers for the Synthesis of Hydrogel Niches and Their Application in Cell Encapsulation and Tissue Engineering

Hydrogels formed from the photoinitiated, solution polymerization of macromolecular monomers present distinct advantages as cell delivery materials and are enabling researchers to three-dimensionally encapsulate cells within diverse materials that mimic the extracellular matrix and support cellular viability. Approaches to synthesize gels with biophysically and biochemically controlled microenvironments are becoming increasingly important, and require strategies to control gel properties (e.g., degradation rate and mechanism) on multiple time and size scales. Furthermore, biological responses of gel-encapsulated cells can be promoted by hydrogel degradation products, as well as by the release of tethered biologically relevant molecules.

Chondrocyte signaling and artificial matrices for articular cartilage engineering

Chondrocytes depend on their environment to aid in their expression of appropriate proteins. It has been found that the interaction of integrin receptors with chondrocytes effects the production of extracellular molecules such as type II collagen and aggrecan. Additionally, the presence of growth factors such as IGF-1, TGF-beta1 and BMP-7 induce various signaling pathways that also aid in transducing phenotypic expressions by chondrocytes. Natural and synthetic polymers have been used to act as a scaffold for chondrocytes. The production of extracellular matrix proteins by chondrocytes has been studied. As tissue engineers, it is advantageous to explore the possibility of how altering biomaterial properties affect the signaling cascades by activation of receptors and transduction through the cytoplasm. This vital information will be able to aid in the future of engineering an appropriate biomaterial that can incorporate chondrocytes to act as a scaffold for articular cartilage.

Bone tissue engineering with human mesenchymal stem cell sheets constructed using magnetite nanoparticles and magnetic force

An in vitro reconstruction of three-dimensional (3D) tissues without the use of scaffolds may be an alternative strategy for tissue engineering. We have developed a novel tissue engineering strategy, termed magnetic force-based tissue engineering (Mag-TE), in which magnetite cationic liposomes (MCLs) with a positive charge at the liposomal surface, and magnetic force were used to construct 3D tissue without scaffolds. In this study, human mesenchymal stem cells (MSCs) magnetically labeled with MCLs were seeded onto an ultra-low attachment culture surface, and a magnet (4000 G) was placed on the reverse side. The MSCs formed multilayered sheet-like structures after a 24-h culture period. MSCs in the sheets constructed by Mag-TE maintained an in vitro ability to differentiate into osteoblasts, adipocytes, or chondrocytes after a 21-day culture period using each induction medium. Using an electromagnet, MSC sheets constructed by Mag-TE were harvested and transplanted into the bone defect in the crania of nude rats. Histological observation revealed that new bone surrounded by osteoblast-like cells was formed in the defect area 14 days after transplantation with MSC sheets, whereas no bone formation was observed in control rats without the transplant. These results indicated that Mag-TE could be used for the transplantation of MSC sheets using magnetite nanoparticles and magnetic force, providing novel methodology for bone tissue engineering.

Tissue engineering of the synovial joint: the role of cell density

The ultimate goal in the tissue engineering of the synovial joint is to fabricate biologically derived analogues that can replace severely degenerated or traumatized synovial joint components. A number of challenges must be addressed before reaching this ultimate goal. In this report, the relevance of cell seeding density in the synthesis of chondrogenic and osteogenic matrices from human mesenchymal stem cells is explored. Human mesenchymal stem cells (hMSCs) were differentiated into chondrogenic cells and osteogenic cells ex vivo and encapsulated in poly(ethylene glycol) diacrylate (PEGDA) hydrogel at densities of 5 x 106 cells/ml, 40 x 10(6) cells/ml, and 80 x 10(6) cells/ml, in addition to a cell-free poly(ethylene glycol) (PEG) control group (0 x 10(6) cells/ml). Cell-seeded or cell-free PEG constructs were separately incubated in vitro for 4 weeks or implanted in vivo in the dorsum of immunodeficient rats for 4 weeks. In-vitro data demonstrated that hMSC-derived chondrocytes or hMSC-derived osteoblasts maintained their lineages per Safranin O and von Kossa staining after incubation for 4 weeks. The general pattern of initial cell seeding densities of 5 x 10(6) cells/ml, 40 x 10(6) cells/ml, and 80 x 10(6) cells/ml were preserved following in-vitro cultivation. Similarly, in-vivo data revealed that hMSC-derived chondrocytes and hMSC-derived osteoblasts maintained their respective lineages and the pattern of cell-seeding densities. An attempt was made to fabricate a composite construct with PEGDA hydrogel and polycaprolactone (PCL) with designed internal porosity for an osteochondral graft. Various cell-seeding densities as delineated in this report can be realized in the composite PEG-PCL graft. The findings demonstrate that cell-seeding density is likely a key parameter to consider in tissue-engineering design. The source of cells can either be transplanted cells or internally recruited cells.

Tissue Engineering the Mandibular Condyle

Tissue engineering provides the revolutionary possibility for curing temporomandibular joint (TMJ) disorders. Although characterization of the mandibular condyle has been extensively studied, tissue engineering of the mandibular condyle is still in an inchoate stage. The purpose of this review is to provide a summary of advances relevant to tissue engineering of mandibular cartilage and bone, and to serve as a reference for future research in this field. A concise anatomical overview of the mandibular condyle is provided, and the structure and function of the mandibular condyle are reviewed, including the cell types, extracellular matrix (ECM) composition, and biomechanical properties. Collagens and proteoglycans are distributed heterogeneously (topographically and zonally). The complexity of collagen types (including types I, II, III, and X) and cell types (including fibroblast-like cells, mesenchymal cells, and differentiated chondrocytes) indicates that mandibular cartilage is an intermediate between fibrocartilage and hyaline cartilage. The fibrocartilaginous fibrous zone at the surface is separated from hyaline-like mature and hypertrophic zones below by a thin and highly cellular proliferative zone. Mechanically, the mandibular condylar cartilage is anisotropic under tension (stiffer anteroposteriorly) and heterogeneous under compression (anterior region stiffer than posterior). Tissue engineering of mandibular condylar cartilage and bone is reviewed, consisting of cell culture, growth factors, scaffolds, and bioreactors. Ideal engineered constructs for mandibular condyle regeneration must involve two distinct yet integrated stratified layers in a single osteochondral construct to meet the different demands for the regeneration of cartilage and bone tissues. We conclude this review with a brief discussion of tissue engineering strategies, along with future directions for tissue engineering the mandibular condyle.

Developing an alginate/chitosan hybrid fiber scaffold for annulus fibrosus cells

A fibrous scaffold made of alginate or alginate/chitosan was fabricated for annulus fibrosus (AF) cell culture using a wet-spinning and lyophilization technique. The scaffolds were evaluated using several in vitro tests. Scanning electron microscopy showed the scaffold fibers generally aligned in one direction with individual fiber diameters varying between 40-100 microm. The alginate/chitosan hybrid scaffold exhibited a slower degradation rate, while both scaffold types did not display any cyto-toxicity to 3T3 fibroblasts and could maintain canine AF cell growth. The AF cells retained their spherical shape within the fibrous scaffold at the beginning of the culture period and formed into cell clusters at later times. Specific extracellular matrix molecules, including collagen I, collagen II, and aggrecan, could be detected in the AF cell clusters. These results demonstrate the feasibility of using this hybrid alginate/chitosan scaffold for AF cell culture, and the potential application for intervertebral disc tissue engineering.

Effect of construct properties on encapsulated chondrocyte expression of insulin-like growth factor-1

Hydrogels are a promising type of biomaterial for articular cartilage constructs since they have been shown to enable encapsulated chondrocytes to express their predominant phenotypic marker, type II collagen. Endogenously expressed signaling molecules, such as insulin-like growth factor-1 (IGF-1), are also known to facilitate the retention of this chondrocytic phenotype. Recent investigations have attempted to enhance the ability of encapsulated chondrocytes to regenerate cartilage through delivery of exogenous signaling molecules. However, we hypothesize that by altering construct properties, such as cell density and polymer concentration, we can augment the expression of endogenous IGF-1 in chondrocytes. To this end, bovine articular chondrocytes were encapsulated within alginate hydrogels at two different cell densities (25,000 and 100,000 cells/bead) and various alginate concentrations (0.8%, 1.2%, and 2.0% w/v). These parameters were chosen to simultaneously investigate cell-to-cell distance on paracrine signaling and water content on IGF-1 diffusion by chondrocytes. At 1, 4, and 8d, chondrocytes were analyzed for protein and mRNA expression of IGF-1 as well as type II collagen. Results suggest that cell density and alginate concentration at high cell density can significantly affect the endogenous IGF-1 expression by chondrocytes. Therefore, these results indicate that construct properties can impact chondrocyte gene expression and should be considered in order to create a proper engineered articular cartilage construct.

Mechanical Interlocking of Engineered Cartilage to an Underlying Polymeric Substrate: Towards a Biohybrid Tissue Equivalent

This study investigates the feasibility of engineering a biohybrid cartilage equivalent (BCE) with the long-term goal of restoring the mechanical integrity and interfacial characteristics of severely damaged cartilage. The BCE depends on the successful adhesion, via mechanical interlocking, of a cartilage layer to a nondegradable composite scaffold or prosthesis. The model scaffold, consisting of a nonwoven mesh bonded to a solid core, was seeded with bovine articular chondrocytes. High molecular weight poly(L-lactic acid), which has a slow degradation time, was used to model the nondegradable polymer. Biochemical and histological analysis demonstrate that the BCE can support the growth of a cartilaginous matrix for at least 6 weeks in culture. Mechanical testing of the BCE showed cartilage adhesion strength increased from 19.27+/-1.62 to 43.79+/-3.88 kPa between 35 and 50 days in culture. Nonmechanically interlocked cartilage achieved less than 5% of this adhesion strength. For the first time, atomic force microscopy (AFM) was used to characterize surface topography of tissue-engineered cartilage. Surface roughness of constructs after 8 and 10 weeks ranged from 153 to 171 nm, falling within the range of native cartilage (100-600 nm). This study demonstrates the feasibility of creating a biohybrid cartilage equivalent by mechanically interlocking a cartilaginous layer to an underlying polymeric matrix.

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.

Stem-cell-driven regeneration of synovial joints

Mammalian skeletal motion is made possible by synovial joints. Widespread suffering from arthritis and joint injuries has motivated recent effort to regenerate a stem-cell-driven synovial joint condyle implantable in total joint replacement. A single adult stem cell lineage, mesenchymal stem cells, differentiate to form all components of a synovial joint. Whereas localized joint lesions may be repaired by either cell-based or cell-free approaches, regeneration of the entire articular condyle of the synovial joint is unattainable without tissue-forming cells. A series of experiments are presented here to describe our initial attempts to regenerate a synovial joint condyle in the shape and dimensions of a human mandibular condyle, with both cartilaginous and osseous components derived from a single population of rat mesenchymal stem cells. Upcoming challenges are along several intertwining fronts including structural integrity, tissue maturation, mechanical strength and host integration. The synovial joint condyle may turn out to be one of the first 'human body parts' or organs truly regeneratable by stem-cell-derived approaches. Current approaches to regenerate the synovial joint condyle from stem-cell-derived multiple cell lineages may also offer clues for engineering complex organs such as the kidney or liver.