Osteoarticular Regenerative Nanomedicine: Advances and Drawbacks in Articular Cartilage Regeneration Implants

Figure 1:  Cellular population and collagen orientation zones in the articular cartilage (reproduction from labrha.com).

The auricular cartilage is composed of different layers defined by the cell specificity: the superficial zone containing small and flat chondrocytes, the reserve zone containing spherical and bigger chondrocytes, the proliferation zone where chondrocytes are disposed in axial isogenic group and where they show an important mitotic activity, the mineralized hypertrophic zone containing hypertrophic chondrocytes, and the sub chondral bone. The collagen fibers are parallel to the articular surface in the superficial zone, oblique in the reserve zone and perpendicular to the articular surface in the proliferation and hypertrophic zones. This specific orientation gives cartilage its resistance to the compression forces.

Asymptomatic lesions in cartilage can degenerate into painful symptomatic chondral disease like osteoarthritis. Osteochondral lesions, which involve both cartilage and sub chondral bone, lead to fibro cartilage, which does not have the same biomechanical properties of hyaline cartilage, and cannot protect the sub chondral bone for further deterioration. Gaining functional repair is a big challenge, and the aim of cartilage repair is to restore the functional properties of the osteochondral unit [3].

Several surgical techniques are commonly used for the treatment of osteochondral lesions. We can cite joint debridement [4], micro fracture (alias chondroplasty) which is a marrow stimulation technique [5], and mosaicplasty (or osteochondral transplantation, or autologous osteochondral graft) which is a resurfacing technique [6]. Joint debridement only consists in eliminating lesion debris from the joint, to reduce pain. It is usually associated with either of the two other techniques. Bone marrow stimulation technique consists in penetrating the sub chondral bone to release progenitor cells from the bone marrow into the defect. These progenitor cells will transform into chondrocyte-like cells and produce some fibrocartilagenous repair tissue. In mosaicplasty, one removes cylindrical plugs of sane cartilage with its sub chondral bone, and implants them into the lesion like a mosaic pattern. These first generation treatments are aimed to relieve pain, recover function and inhibit cartilage lesion progress, but are not fully satisfactory, especially in the long term. Most of these surgical techniques mainly produce repair fibrocartilage, which will not last and does not resist compression and load demands as hyaline cartilage does.

Articular cartilage viability depends on chondrocytes ability in Synthesizing Extracellular Matrix (ECM) and restoring the different zones of hyaline cartilage. This is the aim of Autologous Chondrocyte Implantation (ACI) introduced more recently. ACI is a two-step procedure: first, collection by arthroscopy of a little piece of autologous cartilage, for chondrocyte culture; second, about one month later, surgical procedure of implantation of cultured chondrocytes. ACI has been the first cell engineering application in orthopedic surgery. The procedure was introduced by Peterson et al. in 1987 [7] and the first clinical use of this procedure was reported by Brittberg et al. in 1994 [8] and consisted in injecting autologous chondrocytes under a periosteal patch. ACI is indicated for large symptomatic lesions surrounded by non-osteoarthritic cartilage [9], whereas marrow-stimulating techniques or mosaicplasty are used for small lesions [3,10,11]. Good histological results on implantation sites after treatment were reported by various authors and lesion repair lasted several years [8,12-14]. An estimation of 10 000 patients worldwide having undergone an ACI was given by Brittberg in 2003 [15].

In order to obtain new tissue formation from the implanted cells, there is a need for a suitable environment at the lesion site, which might not be the case if there is extensive cartilage loss. This is why the early Brittberg procedure has been abandoned in favor of implanting cells in biodegradable three dimensional matrices, like collagen membranes, as provisional supportive ECM-like scaffolds. Therefore, new techniques implying tissue engineering have been developing for the last ten years [16-18].

Research to improve cartilage repair is focused on tissue engineering combining three axes: the presence of cells, tridimensional scaffolds mimicking ECM and various environmental factors (growth factors etc.). Tuning these parameters is really the challenge in cartilage repair.

The first point of interest is the development of tridimensional matrices, natural or synthetic, biocompatible and biodegradable, which serve as filling material for the lesion itself, as scaffolds for new cellular growth, and as reservoirs for the release of chondrogenic factors.

Then, one needs to define which are the best cell candidates to concentrate on, either chondrocytes, which are the native cartilage cell types, or stem cells for example Mesenchymal Stem Cells (MSC) from bone marrow. This choice is concerned with cell source requirements, cell adhesion and proliferation and cell efficiency.

The third topic of interest concerns the identification and implementation of specific adequate growth factors or signaling molecules, enabling both chondrocyte cell differentiation and phenotype preservation.

Combinations of these three parameters, as well as optimal implementation conditions are currently under investigation for tissue regeneration in cartilage lesions, both in animal models and clinic studies.

Analysis and Interpretation

Materials used in osteoarticular tissue engineering

Cell adhesion, growth and resulting tissue regeneration will depend on the first place on the scaffold properties. To mimic extracellular matrix, the scaffold must be biodegradable, biocompatible, favor cell adhesion, regulate cell expression, and be a suitable reservoir for bioactive molecules such as growth factors [19]. There have been extensive studies on potential biomaterials, natural, synthetic, ceramics or composite.

Matrices of natural origin

A few natural matrices have been investigated to date, in vitro and in vivo, mainly of protein or carbohydrate origin: collagen, fibrin, agarose, alginate, Hyaluronic Acid (HA), chitosan, cellulose [20].

Early interest has focused on collagen: type I gels and sponges [21,22] and type II sponges [23]. In second generation ACI, a collagen membrane has been used (for example, Chondro-Gide^®, from Geistlich, Switzerland) to replace perioste [24], to facilitate the second part of the treatment, which is the implantation of cultured autologous chondrocytes. In third generation ACI, the focus is made on the use of tridimensional scaffolds optimized for chondrocyte implantation, the so-called MACI (Matrix-assisted Autologous Chondrocyte Implantation) for example with Verigen (Leverkusen, Germany) or Genzyme (Boston, USA) [25].

The main drawback encountered with these materials concerns the type of repair tissue obtained: the best tissue obtained was hyaline-like, but still not identical to articular hyaline cartilage in terms of morphology or histo-chemistry, and could only be obtained in some cases. Often, only fibrocartilage was formed [26,27].

After collagen membranes [28], research has focused on HA derivatives as potential scaffold [29], see for example Hyalograft^® C (Fidia Advanced Biopolymers, Abano Terme, Italy), an esterified derivative of HA, which showed good results [30-32], namely cartilage function improvement among 91.5% of patients. This graft enables chondrocyte growth together with phenotype conservation [33] and resorbs without inflammatory reaction [34].

Films and sponges of chitosan, chitosan/HA and chitosan/ chondroitin sulfate were prepared by film deposition (films) or lyophilisation (sponges) and were shown to constitute good cell supports [35].

Hydrogels, such as alginate, also constitute a suitable scaffold for cell development and differentiation [36-38], however they display mechanical weaknesses. Agarose has been used as a matrix [39] and more recently in a layered manner, to produce depth-dependent in homogeneity in the scaffold [40]. Some hybrid agarose-alginate gel, Cartipatch^® (Lyon, France), has been used in vivo in an ACI case study on man. After two years, all patients showed clinical improvement and eight out of thirteen patients displayed hyaline cartilage restoration [41]. HA-based injectable hydrogels have been widely studied [42], often in combination with chitosan [43-45]. They enable chondrocyte survival and these retain their morphology [46]. New chitosan-based hydrogels have also been shown to enable chondrogenic differentiation of encapsulated MSCs [47]. GAG-augmented polysaccharide hydrogels have also been reported as suitable supports for chondrogenesis, based on chondroitin-sulfate and chitosan, a GAG-analog [48]. Chitosan, which is a polycationic repeating monosaccharide of β-1,4-linked glucosamine monomers with randomly located N-acetyl glucosamine units, may be combined with the polyanionic CSA resulting in hydrogel formation by ionic cross-linking.

Despite their ability for cell adhesion, proliferation, differentiation and subsequent ECM production, these natural gel matrices have several disadvantages, such as potential immunogenicity, possible transmission of animal pathogens, difficulty of processing, mechanical weakness often needing chemical modification, like cross-linking for stabilization and improvement of mechanical properties [49-51]. However, these cross-linking agents, like glutaraldehyde, are often toxic and to avoid possible complications due to these components, various groups have developed composite hydrogels which combine the hydrogel compound and structural proteins. For example, the composite hydrogel matrices fibrin/HA and HA/collagen type I display improved mechanical properties, promote cell development and ECM production [38,52].

Another way of approaching cartilage structure is based on the electro spinning technique to produce collagen fibers [53-57], fibrinogen fibers [58], or other protein fibers like elastin which support the growth of MSCs [59], or gelatin [60]. Some authors combined collagen for the fibrous scaffold and chitosan gel to model ECM proteoglycans [61], or electrospan collagen together with HA [62] or with chitosan [63]. Kim et al. have reported on fibrous electrospun HA hydrogels that direct MSCs chondrogenesis through mechanical (cross linking density) and adhesive (RGD motives density) characteristics [64].

To stabilize collagen based electrospun nanofibers, other groups have focused on the development of safer cross-linking processes, like photopolymerization based on the use of methacrylates [65,66] or rose Bengal [67]. These photo-cross linked matrices successfully encapsulate chondrocytes or MSCs [68,69]. Another approach consisted in inserting some thermo sensitive elements, like poly (N-isopropylacrylamide) in the structure. Upon a certain temperature modified HA chains undergo conformational changes which lead to self-assembly and stabilization of the hydrogel [70]. Self-assembly processes are currently widely explored, with a variety of peptidic building blocks (see next chapter). Jiang et al. have recently reported on the electro spinning of collagen fibers from a non-toxic solvent (ethanol-water) and gentle cross-linking system (citric acid with glycerol) [57]. Native collagen conformation was retained after electro spinning and water stability was enhanced after the cross-linking. Furthermore, cells showed better adhesion and growth than on glutaraldehyde cross-linked scaffolds.

Synthetic matrices

Synthetic materials have been widely used in tissue engineering due to their controllable properties. Various artificial biodegradable scaffolds are being investigated, based on Poly-Lactic Acid (PLA) [71], Poly-glycolic Acid (PGA) [72], and Copolymers (PLGA), Polycaprolactone (PCL), nanocarbon, Dacron^®, Teflon^® fibers or polymer hydrogels [20].

Based on the characteristics of hydrogels (biocompatibility, hydration and bioactive molecules reservoir capacity), ECM-mimicking matrices have been developed for example with designed peptides amphiphiles [73-75], elastin-like polymers [76,77]. A large number of studies are currently devoted to self-assembling peptides, for instance those developed by O'Leary et al., combining both high water content and structural robustness [78,79]. Amino-acid self-assembling β-sheet interaction has been used by Liu et al. to promote chondrocyte growth and hyaline cartilage formation [80], or chondrogenesis from bone marrow stem cells [81]. Some self-assembled nanofibers of peptides amphiphiles have been shown to display a large number of binding domains for TGF-β1, allowing chondrogenic differentiation of MSCs and cartilage repair in a rabbit chondral defect [82]. Although biocompatible, these polymers do not enable cell adhesion on their own, and sites for cell adhesion have to be added. Moreover, they can induce some local pH lowering upon hydrolysis, with possible inflammatory reaction [19].

Hydrogels based on PEG (polyethylene glycol) have attracted much attention [83,84], and were shown to promote cell adhesion [85], and serve as reservoirs with possible multiphase composition for bioactive molecules, like chondroitin sulfate and specific peptides [86-88].

Moutos et al. have reported on a tridimensional scaffold of specially woven microfibers of PGA impregnated with hydrogel (agarose or fibrin) containing chondrocytes, with tensile and compressive mechanical properties close to that of native cartilage [89]. This study was the first to use composite biomaterials to specifically target these biomechanical properties [90].

Bio seed^® (Bio Tissue Technologies, Freiburg, Germany) based on PGA derived matrix, in combination with fibrin gel, used in MACI, has shown promising results [91].

Synthetic electrospun nanofibers have also been studied for MACI: chondrocytes were associated with electrospun poly-lactic acid nanofibers [92], or for example co-electrospun fibers of poly-caprolactone (slow degrading polyester) and poly-ethylene glycol (hydro soluble polymer) forming an architecture with controlled porosity [93]. In general, chondrocytes as well as MSCs grow well on this type of nanofiber scaffold, and produce ECM components like collagen and proteoglycans, as shown for example by Li et al. with PCL scaffolds [94] in a mini-pig model [95] or Foroni et al. with electrospun poly(L-lactic) acid [96]. Recently, some authors have successfully developed specific zones in such nanofibrous scaffolds; based on different fiber organization, in a way to mimic the different cartilage layers [97]. Some others have introduced sacrificial polymer fibers in the scaffold to improve later cell colonization [98]. Wright et al. have developed scaffolds based on electrospun poly(D,L-lactide)/ poly(L-lactide) or poly (D,L-lactide)/polycaprolactone, with salt leached pores and embedded chitosan hydrogel [99] which enabled growth and ECM production by chondrocytes. The increase in the pore sizes to enhance cell infiltration has been investigated by Phipps et al. on a bone-mimetic electrospun scaffold of PCL, collagen I and hydroxyapatite, using three different techniques: limited protease digestion, decrease of fiber packing density during electro spinning, and inclusion of sacrificial fibers (water soluble PEO) [100]. The sacrificial fibers approach appeared to be the most effective. Schneider et al. have studied the influence of fiber orientation (random versus aligned) in electrospun synthetic polymer scaffolds (PDC, PPDO) on adhesion and differentiation of chondrocytes. SEM microscopy revealed a flattened chondrocyte shape on scaffolds with random fiber orientation and growth mainly restricted to the scaffold surface. On aligned fibers the chondrocytes exhibited a more spindle-shaped morphology with rougher cell surfaces but only a minority of the cells aligned according to the fibers [101].

Among ceramic materials, hydroxyapatite and tricalcium phosphate are known to induce the formation of a bony apatite layer when implanted. They have been widely investigated in the last decades in bone regeneration systems [102-105]. Bone and cartilage have very different properties and it is a real challenge to tune systems aiming at osteochondral lesion treatment. For sub chondral bone we are looking for stiffness, porosity and vascularization, to promote cell growth and the production of a bone matrix rich in type I collagen and hydroxyapatite. On the other hand, the cartilage is not vascularized, presents mainly a type II collagen matrix with an embedded proteoglycan hydrogel, allowing altogether resistance and elasticity. Some attempts have been made to mimic more closely this complex multi zone architecture, but few show good results in vivo. For example, I'm et al. have elaborated a multiphase scaffold combining HA and atelocollagen for chondral regeneration, and hydroxyapatite and tricalcium phosphate for the bone layer, and obtained good results in osteochondral regeneration upon implantation in the knee joint of a pig [106]. Promising results have been obtained with a ditopic combination of collagen and glycosaminoglycans on the one side, associated with calcium phosphate on the other side, with a soft interface between them. The physical properties achieved with this architecture are quite good, but further in vivo investigation is needed [107]. Jiang et al. have elaborated a multi-phase scaffold composed of agarose hydrogel and sintered microspheres of PLGA-bioactive glass, which successfully resulted in both osteoblasts and chondrocytes in the appropriate region of the scaffold, leading to the production of three tissues: cartilage, calcified cartilage and bone [108]. Stanishevsky et al. have studied the micro architecture of hydroxyapatite nanoparticle loaded collagen fiber composites [109]. Catledge et al. have elaborated an electrospun triphasic nanofibrous scaffold by electro spinning a mixture of PCL, type I collagen and hydroxyapatite nanoparticles [110]. Qu et al. have recently studied some composite bilayer scaffold of PVA/gelatin, nano-hydroxyapatite and polyamide-6, seeded with marrow MSCs, and have observed in rabbit neocartilage formation in the PVA layer, and sub chondral bone regeneration within the HA-PA6 layer [111].

Osteochondral differentiation factors

Many bioactive molecules intervene in the physiological process of maturation and differentiation of immature bone and cartilage cells. Most of these molecules are proteins (growth factors and cytokines). A major family is the Bone Morphogenetic Proteins (BMPs) [112,113], but there are other potential candidates for osteochondral induction. The differentiation factors tested in various in vitro or in vivo models are among various protein growth factor families: Epidermal Growth Factor (EGF), Fibroblast Growth Factor (FGF) [114], Transforming Growth Factor Beta (TGF-β) [115], Insulin-like Growth Factor (IGF), Vascular Endothelial Growth Factor (VEGF), and also among signaling and regulatory molecules such as Wnt ligands (wingless family) and Hh proteins (hedgehog family) [19,20]. The exploration of their use in MACI is expanding. Different ways are being explored for the controlled release of these growth factors. Limitations encountered concern problems of dose, factor efficiency and over-time delivery, and suitable spatial delivery.

The most common way of delivering these factors consists in direct injection at the lesion site or in direct contact with the implant scaffold, however due to the short half-life of these active protein factors, these methods require high doses for therapeutic effect and do not permit a controlled-time delivery [51].

In many studies the growth factors are delivered via the scaffold itself, by mixing them with the scaffold components during fabrication. In these cases the matrix characteristics such as porosity or cross-linking degree will modulate the protein delivery by diffusion. For example; growth factors like BMP-2 have been incorporated into chitosan and hyaluronan hydrogels, and induced bone formation in the quadriceps muscle of rats [116]. Kopesky et al. have shown sustained delivery of TGF-β1 from self-assembling peptide hydrogels, which induced chondrogenesis by encapsulated bone marrow stromal cells [117].

In other studies reporting microsphere-based scaffolds, TGF-β1, BMP-2 or IGF-1 were loaded in the microspheres (of PLGA, or PEG), resulting in good osteochondral regeneration [118-120]. These systems provide spatial controlled delivery of various growth factors [121], or even co-delivery of adipose derived stem cells and growth factors, as in the study of Sukarto et al. using loaded microspheres in RGD-grafted N-methacrylate glycol chitosan gels for focal chondral repair [122].

Simple Ionic bonding was used to load Insulin-like Growth Factor IGF-1 in a porous collagen-glycosaminoglycan scaffold and the adsorption and release characteristics were examined by the authors, which confirmed the bioactivity profile of the growth factor by the ECM component production from seeded chondrocytes [123]. Lee et al. exploited weak interactions to coat an electrospun poly(lactide-co-glycolic acid) PLGA nanofiber scaffold with polydopamine by immersion of the fibers in a dopamine solution under weakly basic conditions, and further immobilized Bone-forming Peptide 1 (BPF-1) derived from the immature region of Bone Morphogenetic Protein-7 (BMP-7) on the polydopamine-coated fibers, by similar immersion in the peptide solution [124]. These peptide-coated scaffolds acknowledged positive results in bone regeneration, and the same approach could be applied for cartilage tissue. Although this kind of material can control the spatial release of factor, the release in time cannot be controlled, leading to a massive release in the body.

Another way to improve the biodisponibility of the growth factor can be used. In another approach, growth factors have been successfully delivered through innovative nanoreservoirs based on the layer-by-layer technology, on electrospun PCL nanofibrous scaffolds or collagen membranes, resulting in efficient cell response for bone regeneration, process which may easily apply to cartilage tissue regeneration [125,126].

A recent study by Lim et al. [127] has described the development of a new bio functionalized electrospun Poly (L-lactide) scaffold for cartilage differentiation: latent transforming growth factor LTGF-β1 was anchored to the scaffold via surface chemical modification. Both random and orientated bio functionalized scaffolds were tested in vitro and in vivo in rats, and proved chondrocyte differentiation and collagen II production. Jeong et al. have also performed some chemical modification to attach BMP-2 on a 3D PCL scaffold [128]. The authors found that these chemically conjugated BMP-2 PCL scaffolds promote significantly greater cartilage regeneration from seeded chondrocytes, in vitro and in vivo, compared to untreated scaffolds.

Recently magnetic scaffolds have been elaborated, based on biocompatible magnetic nanoparticles, which enable continuous and controlled loading of growth factors by the means of an external magnetic field [129-131].

Gene therapy is an alternative to the direct delivery of proteins, as the delivery of genes encoding for specific factors leads to the synthesis of these factors directly by the cells [132-135]. Among various vectors, the non-pathogenic human Adeno-associated Virus (AAV) is most promising, as recombinant AAV vectors allow the transduction of most relevant tissues and cells involved in cartilage repair, and it has been successfully tested in vivo in a rabbit osteochondral defect, using the FGF-2 gene sequence [133,136]. Moreover, although viral gene vectors are subject to safety considerations, rAAV has recently been recommended for clinical use in the treatment of pancreatitis. The group of Lu et al has recently described porous chitosan scaffolds with embedded HA/chitosan/plasmid-DNA nanoparticles encoding for TGF-β1 which induces DNA controlled release, transfect chondrocytes and promote cell proliferation [137]. Chen et al. have produced simultaneous regeneration of articular cartilage and sub chondral bone in vivo using MSCs by the use of a spatially controlled gene delivery system in bilayered osteochondral scaffolds, consisting of plasmid TGF-β1-activated chitosan-gelatin scaffold for chondrogenic layer and plasmid BMP-2-activated hydroxyapatite/ chitosan-gelatin scaffold for osteogenic layer. The results showed that spatially controlled and localized gene delivery system in the bilayered integrated scaffolds could induce the mesenchymal stem cells in different layers to differentiate into chondrocytes and osteoblasts in vitro, respectively, and simultaneously support the articular cartilage and sub chondral bone regeneration in the rabbit knee osteochondral defect model [138] (Figure: 2).

Figure 2:  Examples of scaffolds potentially used for osteoarticular regeneration.
(A) Solorio et al.[121] reported a polymeric 3-D nanofibrous microspheres scaffold used in cartilage engineering to improve the naturally round form of the
chondrogenic cells.
(B) SEM micrograph of hydroxyapatite mineralized collagen-I synthetic scaffold, representing structure and composition close to extracellular bone matrix by
Bernhardt et al.[104] for bone regeneration.
(C) SEM micrograph showing PCL electrospun nanofibers containing nanoreservoirs of BSA added by the layer-by-layer technology. This kind of nanofunctionalized
scaffold can also contain osteogenic or chondrogenic growth factors for osteochondral repair (Eap et al).

  

    
Product
    
Company
    
Composition
    
Website
  
  

    
BST-CarGel
    
Biosyntech Inc., Laval, QC, Canada
    
Chitosan-Beta glycerolphosphate-based medical device
    
www.biosyntech.com 
      
 
  
  

    
ChonDux
    
Biomet Inc., Warsaw, IN, USA
    
Hydrogel made of polyethylene glycol and a bioadhesive to keep the    hydrogel in place after injection
    
www.biomet.com 
      
 
  
  

    
Gelrin C
    
Regentis, Haifa, Israel
    
Cellular implant made of polyethyleneglycol diacrylate

      (PEG-DA) covalently conjugated with a structural backbone of denatured    fibrinogen chains. The

      device comes in a liquid form, injected into the lesion site and polymerizes    in situ into a stable hydrogel solid matrix.
    
www.regentis.co.il 
      
 
  
  

    
Salucartilage
    
SaluMedica, Smyrna, GA, USA
    
Cylindrical    implant based on polyvinyl-alcohol     hydrogel
    
www.salumedia.com 
      
 
  
  

    
Chondromimetic
    
TiGenix NV    (Leuven, Belgium) 
    
Bi-layer Collagen-based implant (upper layer: collagen/GAG; bottom    layer: collagen/GAG/calcium phosphate
    
www.tigenix.com 
      
 
  
  

    
TrueFit Plug
    
OsteoBiologics/Smith & Newphew, Andover, MA, USA
    
Synthetic mosaicplasty plugs
    
www.smith-nephew.com 
      
 
  
  

    
OrthoGlide
    
Advanced Biosurfaces, Minnetonka, MN, USA
    
Interposition arthroplasty for the knee:  comprises a dished, disc-shaped cobalt    chrome component which is inserted into the medial compartment of the knee in    a minimally invasive fashion. The device has a lip which locks over the    posterior aspect of the tibial plateau.
    
www.advbiosurf.com 
      
 
  
  

    
Carticel, MACI
    
Genzyme Inc,    Cambridge, MA, USA
    
Autologous    cultured chondrocytes on bovine collagen membrane
    
www.genzyme.com 
      
 
  
  

    
ChondroGide
    
Geistlich Biomaterials, Wolhausen, Switzerland
    
Bilayer collagen membrane
    
www.geistlich.ch 
  
  

    
CaReS
    
Arthro Kinetics, Esslingen, Germany
    
Autologous chondrocytes embedded in a collagen matrix
    
www.arthro-kinetics.com 
  
  

    
Hyalograft-C
    
Fidia Advanced Biopolymers, Abano Terma, Italy
    
Autologous chondrocytes seeded on a hyaluronan-based scaffold
    
www.?diapharma.com
  
  

    
NeoCart, VeriCart
    
Histogenics, Waltham, MA, USA
    
NeoCart™ : autologous chondrocytes embedded in proprietary    type I collagen scaffold
      
VeriCart™ :a single-step, cell-free collagen scaffold    uniquely designed to be used in conjunction with the patient's own stem cells    to repair small cartilage defects
    
www.histogenics.com 
  
  

    
ACT 3D/ARTROcell 3D
    
Co.don AG/OrmedGmbH, Teltow, Germany
    
Autologous chondrocytes transplantation using chondrospheres (tissue    engineered chondrocytes without matrix, 3D culture)
    
www.codon.de 
  
  

    
Chondrotissue
      
Bioseed-C
    
BioTissue Technologies, Freiburg, Germany
      
BioTissue Technologies, Freiburg, Germany
    
1-step, cell-free implant used to treat traumatic or degenerative    cartilage defects in combination with marrow stimulating techniques. Patented    3D matrix of synthetic polymer (PGLA) and a hyaluronic acid.
      
Autologous 3D chondrocyte graft based on polymer matrix and fibrin
    
www.biotissue.de 
  
  

    
Novocart 3D
    
TETEC AG/B.Braun-Aescalap, Tuttlingen, Germany
    
A combination of autologous cartilage cells in a biphasic,    three-dimensional collagen-based matrix
    
www.tetec-ag.de 
  

Table 1: Commercial products in cartilage engineering [196].

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Citation: Schwinté P, Keller L, Eap S, Mainard D and Benkirane-Jessel N. Osteoarticular Regenerative Nanomedicine: Advances and Drawbacks in Articular Cartilage Regeneration Implants. Austin J Nanomed Nanotechnol. 2014;2(4): 1025. ISSN:2381-8956

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