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

Self-assembly-peptide hydrogels as tissue-engineering scaffolds for three-dimensional culture of chondrocytes in vitro

The promising potential of a RAD-16 self-assembly-peptide hydrogel as a scaffold for tissue-engineered cartilage was investigated. Within 3 weeks of in vitro culture, chondrocytes within the hydrogel produced a high amount of GAG and type-II collagen, which are the components of cartilage-specific extracellular matrix (ECM). With the culture time increased, toluidine-blue staining for GAG and immuno-histochemistry staining for type-II collagen of the chondrocytes-hydrogel composites became more intense. Analysis of the gene expression of the ECM molecules also confirmed the chondrocytes in the peptide hydrogel maintained their phenotype within 3 weeks of in vitro culture.

Engineered cartilage covered ear implants for auricular cartilage reconstruction

Cartilage tissues are often required for auricular tissue reconstruction. Currently, alloplastic ear-shaped medical implants composed of silicon and polyethylene are being used clinically. However, the use of these implants is often associated with complications, including inflammation, infection, erosion, and dislodgement. To overcome these limitations, we propose a system in which tissue-engineered cartilage serves as a shell that entirely covers the alloplastic implants. This study investigated whether cartilage tissue, engineered with chondrocytes and a fibrin hydrogel, would provide adequate coverage of a commercially used medical implant. To demonstrate the in vivo stability of cell-fibrin constructs, we tested variations of fibrinogen and thrombin concentration as well as cell density. After implantation, the retrieved engineered cartilage tissue was evaluated by histo- and immunohistochemical, biochemical, and mechanical analyses. Histomorphological evaluations consistently showed cartilage formation over the medical implants with the maintenance of dimensional stability. An initial cell density was determined that is critical for the production of matrix components such as glycosaminoglycans (GAG), elastin, type II collagen, and for mechanical strength. This study shows that engineered cartilage tissues are able to serve as a shell that entirely covers the medical implant, which may minimize the morbidity associated with implant dislodgement.

Chitosan/poly(epsilon-caprolactone) blend scaffolds for cartilage repair

Chitosan (CHT)/poly(ɛ-caprolactone) (PCL) blend 3D fiber-mesh scaffolds were studied as possible support structures for articular cartilage tissue (ACT) repair. Micro-fibers were obtained by wet-spinning of three different polymeric solutions: 100:0 (100CHT), 75:25 (75CHT) and 50:50 (50CHT) wt.% CHT/PCL, using a common solvent solution of 100 vol.% of formic acid. Scanning electron microscopy (SEM) analysis showed a homogeneous surface distribution of PCL. PCL was well dispersed throughout the CHT phase as analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. The fibers were folded into cylindrical moulds and underwent a thermal treatment to obtain the scaffolds. μCT analysis revealed an adequate porosity, pore size and interconnectivity for tissue engineering applications. The PCL component led to a higher fiber surface roughness, decreased the scaffolds swelling ratio and increased their compressive mechanical properties. Biological assays were performed after culturing bovine articular chondrocytes up to 21 days. SEM analysis, live-dead and metabolic activity assays showed that cells attached, proliferated, and were metabolically active over all scaffolds formulations. Cartilaginous extracellular matrix (ECM) formation was observed in all formulations. The 75CHT scaffolds supported the most neo-cartilage formation, as demonstrated by an increase in glycosaminoglycan production. In contrast to 100CHT scaffolds, ECM was homogenously deposited on the 75CHT and 50CHT scaffolds. Although mechanical properties of the 50CHT scaffold were better, the 75CHT scaffold facilitated better neo-cartilage formation.

A novel cylinder-type poly(L-lactic acid)-collagen hybrid sponge for cartilage tissue engineering

The development of porous scaffolds having both high porosity and strong mechanical strength for tissue engineering and regenerative medicine has been quite challenging. A novel hybrid poly(L-lactic acid) (PLLA)-collagen hybrid sponge was developed by enclosing collagen sponge in a cup-shaped PLLA sponge to meet the necessary requirements. Collagen sponge was formed in the center of the PLLA sponge cup, and collagen microsponges were formed in the pores of the PLLA sponge cup. The PLLA-collagen hybrid sponge showed higher mechanical strength than did those of the PLLA sponge cup and collagen sponge. The porosity of the PLLA-collagen hybrid sponge was greater than that of the PLLA sponge cup. The cup-shaped PLLA sponge skeleton provided the hybrid sponge with high mechanical strength and protected against cell leakage during cell seeding, while the central collagen sponge contributed to high porosity, and facilitated cell adhesion and distribution in the hybrid sponge. Cartilaginous tissue was successfully regenerated when chondrocytes were cultured in the hybrid sponge. This method of hybridization will provide a new technique for the preparation of functional porous scaffolds for tissue engineering.

The restoration of full-thickness cartilage defects with BMSCs and TGF-beta 1 loaded PLGA/fibrin gel constructs

Poly(lactide-co-glycolide) (PLGA) sponge was filled with fibrin gel, bone marrow mesenchymal stem cells (BMSCs) and transforming growth factor-β1 (TGF-β1) to obtain a construct for cartilage restoration in vivo. The PLGA sponge lost its weight steadily in vitro, but degraded much faster in the construct of PLGA/fibrin gel/BMSCs implanted in the full-thickness cartilage defects. The in vivo degradation of the fibrin gel inside the construct was prolonged to 12 wk too. The CM-DiI labeled allogenic BMSCs were detectable after transplantation (implantation) into the defects for 12 wk by small animal in vivo fluorescence imaging and confocal laser scanning microscopy. In vivo repair experiments were firstly performed by implantation of the PLGA/fibrin gel/BMSCs and PLGA/BMSCs constructs into full-thickness cartilage defects (3 mm in diameter and 4 mm in depth) of New Zealand white rabbits for 12 wk. The defects implanted with the PLGA/fibrin gel/BMSCs constructs were filled with cartilage-like tissue containing collagen type II and glycosaminoglycans (GAGs), while those by the PLGA/BMSCs constructs were filled with fibrous-like tissues. To repair the defects of larger size (4 mm in diameter), addition of growth factors was mandatory as exemplified here by further loading of TGF-β1. Implantation of the PLGA/fibrin gel/BMSCs/TGF-β1 constructs into the full-thickness cartilage defects for 12 wk resulted in full restoration of the osteochondral tissue. The neo-cartilage integrated well with its surrounding cartilage and subchondral bone. Immunohistochemical and GAGs staining confirmed the similar distribution of collagen type II and GAGs in the regenerated cartilage as that of hyaline cartilage. The quantitative reverse transcription-polymerase chain reaction (qRT-PCR) revealed that the cartilage special genes were significantly up-regulated compared with those of the TGF-β1 absent constructs.

Strategies for articular cartilage lesion repair and functional restoration

Injury of articular cartilage due to trauma or pathological conditions is the major cause of disability worldwide, especially in North America. The increasing number of patients suffering from joint-related conditions leads to a concomitant increase in the economic burden. In this review article, we focus on strategies to repair and replace knee joint cartilage, since knee-associated disabilities are more prevalent than any other joint. Because of inadequacies associated with widely used approaches, the orthopedic community has an increasing tendency to develop biological strategies, which include transplantation of autologous (i.e., mosaicplasty) or allogeneic osteochondral grafts, autologous chondrocytes (autologous chondrocyte transplantation), or tissue-engineered cartilage substitutes. Tissue-engineered cartilage constructs represent a highly promising treatment option for knee injury as they mimic the biomechanical environment of the native cartilage and have superior integration capabilities. Currently, a wide range of tissue-engineering-based strategies are established and investigated clinically as an alternative to the routinely used techniques (i.e., knee replacement and autologous chondrocyte transplantation). Tissue-engineering-based strategies include implantation of autologous chondrocytes in combination with collagen I, collagen I/III (matrix-induced autologous chondrocyte implantation), HYAFF 11 (Hyalograft C), and fibrin glue (Tissucol) or implantation of minced cartilage in combination with copolymers of polyglycolic acid along with polycaprolactone (cartilage autograft implantation system), and fibrin glue (DeNovo NT graft). Tissue-engineered cartilage replacements show better clinical outcomes in the short term, and with advances that have been made in orthopedics they can be introduced arthroscopically in a minimally invasive fashion. Thus, the future is bright for this innovative approach to restore function.

Bone morphogenetic protein-7 promotes chondrogenesis in human amniotic epithelial cells

Bone morphogenetic proteins (BMPs) play important roles at multiple stages of chondrogenesis. This study was undertaken to investigate the potential role of bone morphogenetic protein-7 (BMP-7) in the differentiation of chondrocytes using tissue engineering techniques. The impact of BMP-7 on human amniotic epithelial cells (hAECs) was tested. The hAECs were treated either with recombinant human BMP-7 cDNA or with transforming growth factor beta 1 (TGF-β1) as a positive control for three weeks in vitro. Cartilaginous differentiation and proliferation were assayed by quantitative RT-PCR, histology, and in situ hybridization. Our results were such that hAECs treated with either BMP-7 or TGF-β1 expressed cartilage markers (aggrecan, Sox9, CEP-68, and type II and X collagens) within three weeks. Compared with a control vector, BMP-7 induced a decrease in type I collagen expression, while the transcription of the cartilage-specific type II collagen remained stable. In induction experiments, BMP-7 transgenic hAECs exhibited the largest amount of matrix synthesis. In conclusion, these data indicate that BMP-7 plays an important role in inducing the production of cartilage by hAECs in vitro. Cartilage differentiation and matrix maturation can be promoted by BMPs in a cartilage engineering paradigm. These properties make BMPs promising tools in the engineering of cartilaginous joint bio-prostheses and as candidate biological agents or genes for cartilage stabilisation.

Thiol-containing degradable poly(thiourethane-urethane)s for tissue engineering

Poly(thiourethane-urethane)s with varying amounts of sulphur were synthesised by a two-step polycondensation consisting of the sequential addition of 1,6-hexamethylene diisocyanate and bis(2-mercaptoethyl) ether in a poly(epsilon-caprolactone) diol solution. Polymers prepared had high weight-average molecular weight and typical microdomains separation, as shown by size-exclusion chromatography and thermal analysis. Polymer surfaces were characterized by X-ray photoelectron spectroscopy and atomic force microscopy. The quantification of thiol groups at the surface was assessed using a fluorescent assay. Thiol concentration ranged between 7 and 14 nmol/cm, and was directly related to the amount of sulphur introduced in the polymerization and the macromolecule chains orientation at the surfaces. A preliminary in vitro degradation study and a proliferation assay were performed. The poly(thiourethane-urethane)s may have important applications as biodegradable and biocompatible materials for cartilage and bone tissue engineering. The surface thiol groups add the prospect of further functionalization. This is an important benefit compared to biodegradable poly(urethane)s that usually present low biological activity.

Growth of human septal chondrocytes in fibrin scaffolds

BACKGROUND

Tissue engineering of nasal septal cartilage has been the focus of research owing to its superior structural rigidity and ease of harvest. In vitro constructs formed from septal chondrocytes using fibrin glue within a polyglycolic acid (PGA) scaffold have been shown to be viable, but their cellular growth and expression of differentiated features still have not been quantified. In this study, we evaluated cellular proliferation and production of cartilaginous extracellular matrix (ECM) components in fibrin glue preparations within a PGA scaffold.

METHODS

Human chondrocytes were expanded for one passage in monolayer in culture medium. The cells were then grown in (1) fibrinogen, (1/2)x-thrombin, (1/2)x (F/2:T/2); (2) fibrinogen, 1/10x-thrombin, 1/10x (F/10:T/10); (3) fibrinogen, 1x-thrombin, 1/100x (F/1:T/100).

RESULTS

Cellular proliferation and glycosaminoglycan (GAG) production per cell were highest in the F/2:T/2 preparations. Greater proliferation was seen in chondrocyte-fibrin composites seeded onto the PGA scaffold when compared with chondrocytes seeded onto the PGA scaffold alone. No significant difference in GAG production was seen.

CONCLUSION

The addition of fibrin glue to chondrocytes seeded onto a PGA scaffold results in increased cellular proliferation while maintaining production of ECM components. Long-term stable fibrin gels in combination with PGA scaffolds may facilitate generation of cartilaginous tissue for use in reconstructive surgery.

The application of atelocollagen gel in combination with porous scaffolds for cartilage tissue engineering and its suitable conditions

For improving the quality of tissue-engineered cartilage, we examined the in vivo usefulness of porous bodies as scaffolds combined with an atelocollagen hydrogel, and investigated the suitable conditions for atelocollagen and seeding cells within the engineered tissues. We made tissue-engineered constructs using a collagen sponge (CS) or porous poly(L-lactide) (PLLA) with human chondrocytes and 1% hydrogel, the concentration of which maximized the accumulation of cartilage matrices. The CS was soft with a Young's modulus of less than 1 MPa, whereas the porous PLLA was very rigid with a Young's modulus of 10 MPa. Although the constructs with the CS shrank to 50% in size after a 2-month subcutaneous transplantation in nude mice, the PLLA constructs maintained their original sizes. Both of the porous scaffolds contained some cartilage regeneration in the presence of the chondrocytes and hydrogel, but the PLLA counterpart significantly accumulated abundant matrices in vivo. Regarding the conditions of the chondrocytes, the cartilage regeneration was improved in inverse proportion to the passage numbers among passages 3-8, and was linear with the cell densities (10(6) to 10(8) cells/mL). Thus, the rigid porous scaffold can maintain the size of the tissue-engineered cartilage and realize fair cartilage regeneration in vivo when combined with 1% atelocollagen and some conditioned chondrocytes.

Farnesol-modified biodegradable polyurethanes for cartilage tissue engineering

A bifunctionalized 3,7,11-trimethyl-2,6,10-dodecatrien-1-diaminobutane amide (isoprenoid) was obtained from 3,7,11-trimethyl-2,6,10-dodecatrien-1-ol (farnesol) in a three-step synthesis. The bifunctionalized isoprenoid was characterized using infrared spectroscopy and (1)H and (13)C nuclear magnetic resonance spectroscopy and was covalently incorporated (0.12 mmol x g(-1)) into the biodegradable aliphatic polyurethane formed on the polycondensation reaction of poly(epsilon-caprolactone) diol, 1,4,3,6-dianhydro-D-sorbitol and 1,6-hexamethylene diisocyanate. Although the covalent incorporation of the isoprenoid molecule into the polyurethane chain modified the surface chemistry of the polymer, it did not affect the viability of attached chondrocytes. Porous 3D scaffolds were produced from the modified and unmodified biodegradable segmented polyurethanes by a salt leaching-phase-inverse technique. The scaffolds were seeded with bovine chondrocytes encapsulated in fibrin gel and cultured in vitro for 14 days. The incorporation of bifunctional isoprenoid into the polyurethane affected the morphology of the scaffolds produced, when compared with the morphology of the scaffolds produced using the same technique from the unmodified polyurethane. As a consequence, there was more uniform cell seeding and more homogeneous distribution of the synthesized extracellular matrix throughout the scaffold resulting in a reduced cell/tissue layer at the edges of the constructs. However, glycosaminoglycan (GAG), DNA content, and chondrocytes phenotype in the scaffolds produced from these two polyurethane formulations did not vary significantly. The findings suggest that the change of surface characteristics and the more open pore structure of the scaffolds produced from the isoprenoid-modified polyurethane are beneficial for the seeding efficiency and the homogeneity of the tissue engineered 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.

Cytotoxic and genotoxic effects of matrices for cartilage tissue engineering

Customizing auricles with biodegradable polyurethane colonized with autologous chondrocytes as an approach for tissue engineering cartilage transplants has been suggested for the reconstruction of the external ear to repair auricular deformities. Dextrose, triethanolamine and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) are matrices of an open-pored polyurethane three-dimensional scaffold. After release from the polymer, these compounds can be absorbed into the human organism. Therefore, cytotoxic effects on human chondrocytes and lymphocytes and genotoxic effects on human lymphocytes were determined. Propidium iodide and fluoresceine diacetate staining as well as quantitative proliferations testing with EZ4U served to detect cytotoxic effects on chondrocytes. In lymphocytes cytotoxicity was checked by trypan blue staining and the alkaline single cell microgel electrophoresis (Comet) assay was used to study genotoxic effects. Dose-dependent cytotoxicity and genotoxicity of the matrices could be shown. Concentrations up to 4.25mg/ml for dextrose, 0.15 mg/ml for PEG-PPG-PEG and 0.9 mg/ml for triethanolamine did not show cytotoxic effects in chondrocytes or genotoxic effects in lymphocytes. These data suggest that dextrose, triethanolamine and PEG-PPG-PEG could be safely used if scaffolds made of open-pored polyurethane do not release these compounds at a rate giving higher concentrations at the site of implantation or in body fluids, respectively.

In vivo biocompatibility and vascularization of biodegradable porous polyurethane scaffolds for tissue engineering

Scaffolds for tissue engineering should be biocompatible and stimulate rapid blood vessel ingrowth. Herein, we analyzed in vivo the biocompatibility and vascularization of three novel types of biodegradable porous polyurethane scaffolds. The polyurethane scaffolds, i.e., PU-S, PU-M and PU-F, were implanted into dorsal skinfold chambers of BALB/c mice. Using intravital fluorescence microscopy we analyzed vascularization of the implants and venular leukocyte-endothelial cell interaction in the surrounding host tissue over a 14 day period. Incorporation of the scaffolds was analyzed by histology, and a WST-1 assay was performed to evaluate their cell biocompatibility in vitro. Our results indicate that none of the polyurethane scaffolds was cytotoxic. Accordingly, rolling and adherent leukocytes in venules of the dorsal skinfold chamber were found in a physiological range after scaffold implantation and did not significantly differ between the groups, indicating a good in vivo biocompatibility. However, the three scaffolds induced a weak angiogenic response with a microvessel density of only approximately 47-60 and approximately 3-10cm/cm(2) in the border and centre zones of the scaffolds at day 14 after implantation. Histology demonstrated that the scaffolds were incorporated in a granulation tissue, which exhibited only a few blood vessels and inflammatory cells. In conclusion, PU-S, PU-M and PU-F scaffolds may be used to generate tissue constructs which do not induce a strong inflammatory reaction after implantation into patients. However, the scaffolds should be further modified or conditioned in order to accelerate and improve the process of vascularization.

Novel injectable gel (system) as a vehicle for human articular chondrocytes in cartilage tissue regeneration

We developed a novel injectable carrageenan/fibrin/hyaluronic acid-based hydrogel with in situ gelling properties to be seeded with chondrogenic cells and used for cartilage tissue engineering applications. We first analysed the distribution within the hydrogel construct and the phenotype of human articular chondrocytes (HACs) cultured for 3 weeks in vitro. We observed a statistically significant increase in the cell number during the first 2 weeks and maintenance of cell viability throughout the cell culture, together with the deposition/formation of a cartilage-specific extracellular matrix (ECM). Taking advantage of a new in vivo model that allows the integration between newly formed and preexisting cartilage in immunodeficient mice to be investigated, we showed that injectable hydrogel seeded with human articular chondrocytes was able to regenerate and repair an experimentally made lesion in bovine articular cartilage, thus demonstrating the potential of this novel cell delivery system for cartilage tissue engineering.

Morphogenetic and regulatory mechanisms during developmental chondrogenesis: new paradigms for cartilage tissue engineering

Cartilage is the first skeletal tissue to be formed during embryogenesis leading to the creation of all mature cartilages and bones, with the exception of the flat bones in the skull. Therefore, errors occurring during the process of chondrogenesis, the formation of cartilage, often lead to severe skeletal malformations such as dysplasias. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of some remains more elusive than of others. Many efforts have aimed at understanding the morphogenetic event of chondrogenesis in normal individuals, of which the main morphogenetic and regulatory mechanisms will be reviewed here. For instance, many signaling molecules that guide chondrogenesis--for example, transforming growth factor-beta, bone morphogenetic proteins, fibroblast growth factors, and Wnts, as well as transcriptional regulators such as the Sox family--have already been identified. Moreover, extracellular matrix components also play an important role in this developmental event, as evidenced by the promotion of the chondrogenic potential of chondroprogenitor cells caused by collagen II and proteoglycans like versican. The growing evidence of the elements that control chondrogenesis and the increasing number of different sources of progenitor cells will, hopefully, help to create tissue engineering platforms that could overcome many developmental or degenerative diseases associated with cartilage defects.

Neovascularization and free microsurgical transfer of in vitro cartilage-engineered constructs

Cartilage tissue engineering shows to have tremendous potential for the reconstruction of three-dimensional cartilage defects. To ensure survival, shape, and function, in vitro cartilage-engineered constructs must be revascularized. This article presents an effective method for neovascularization and free microsurgical transfer of these in vitro constructs. Twelve female Chinchilla Bastard rabbits were used. Cartilage-engineered constructs were created by isolating chondrocytes from auricular biopsies, amplifying in monolayer culture, and then seeding them onto polycaprolactone scaffolds. In each prefabricated skin flap, three in vitro cartilage-engineered constructs (2 x 2 x 0.5 cm) and one construct without cells (served as the control) were implanted beneath an 8 x 15 cm random-pattern skin flap, neovascularized by implantation of an arteriovenous vascular pedicle with maximal blood flow. Six weeks later, the neovascularized flaps with embedded cartilage-engineered constructs were completely removed based on the newly implanted vascular pedicle, and then freely retransferred into position using microsurgery. Macroscopic observation, selective microangiography, histology, and immunohistochemistry were performed to determine the construct vitality, neovascularization, and new cartilage formation. The results showed that all neovascularized skin flaps with embedded constructs were successfully free-transferred as free flaps. The implanted constructs were well integrated and protected within the flap. All constructs were well neovascularized and showed histologically stability in both size and form. Immunohistology showed the existence of cartilage-like tissue with extracellular matrix neosynthesis.

Plasma-fibroblast gel as scaffold for islet transplantation

The transplant of pancreatic islets into the liver can restore normal blood glucose levels in patients with type I diabetes. However, long-term results have indicated that the site and method of transplantation still need to be optimized to improve islet engraftment. This study was designed to assess the efficiency of the use of clotted blood plasma containing fibroblasts ("plasma-fibroblast gel") as a scaffold for subcutaneous islet transplantation in diabetic athymic mice. Islets embedded in the plasma-fibroblast gel were able to resolve hyperglycemia in transplanted mice, restoring normoglycemia over a 60-day period and allowing gradual body weight recovery. Glucose clearances were significantly improved when compared to those recorded in diabetic animals and similar to those observed in the control group (free islets transplanted beneath the kidney capsule). Histological evaluation revealed functional islets within a subcutaneous tissue rich in collagen fibers that was well vascularized, with blood vessels observed around and inside the islets. These findings suggest that this approach could be used as an alternative option for the treatment of type I diabetes in human clinical practice.

Chitosan gel as an in situ-forming scaffold for rat bone marrow mesenchymal stem cells in vivo

We herein formulated and characterized an in situ-forming chitosan gel consisting of chitosan and glycerol phosphate (GP) disodium salt, and examined its use as an in vivo scaffold for rat bone marrow mesenchymal stem cells (rBMSCs). First, the phase transition behaviors of chitosan solutions formulated with and without GP were characterized as a function of temperature. Chitosan solutions containing > 20 wt % GP became a gel at 37 degrees C and maintained this form for 28 days in vitro and in vivo. Next, we examined whether the chitosan gel could act as a suitable biocompatible substrate for the attachment and proliferation of rBMSCs. Immunohistochemistry clearly demonstrated that rBMSCs survived well on the scaffold created by in situ-forming chitosan gel in rats. Injection of chitosan gel alone induced macrophage accumulation in the host tissue and at the edge of the chitosan, whereas injection of chitosan gel containing rBMSCs was associated with decreased macrophage accumulation, indicating immunosuppression by the transplanted rBMSCs. Our results collectively show for the first time that chitosan gel could serve as an in situ-forming gel scaffold for entrapped rBMSCs in vivo.

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.