System-Engineered Cartilage Using Poly(N-isopropylacrylamide)-Grafted Gelatin as in Situ-Formable Scaffold: In Vivo Performance

Semi-interpenetrating nanosilver doped polysaccharide hydrogel scaffolds for cutaneous wound healing

The extensive advancement with novel wound dressing materials functionalized with desirable properties, often touted as a panacea for cuts and burns afflicting various pathologies. However, it would indeed be a hard task to isolate any such material which perfectly fits the needs of any biomedical issue at hand. Biocompatibility, biodegradability as well as non-toxicity of natural polysaccharide served as a versatile and tunable platform for designing natural polysaccharide based scaffolds as an attractive tool in tissue engineering with a greater degree of acceptability. In this regard, we aimed to fabricate a semi interpenetrating hydrogel via exploiting the nontoxic and immune-stimulatory nature of galacto-xyloglucan (PST001) which was further doped with silver nanoparticles to formulate SNP@PST. The wound healing potential of SNP@PST was then studied both with in vitro and preclinical mice models. The current study gives a formulation for cost effective preparation of polysaccharide hydrogels using acrylamide crosslinking with improved biocompatibility and degradability. Wound healing studies in mice proved the efficiency of gels for the clinical application wherein the incorporation of nanosilver greatly enhanced the antimicrobial activity.

Injectable hydrogels: a new paradigm for osteochondral tissue engineering

Osteochondral tissue engineering has become a promising strategy for repairing focal chondral lesions and early osteoarthritis (OA), which account for progressive joint pain and disability in millions of people worldwide. Towards improving osteochondral tissue repair, injectable hydrogels have emerged as promising matrices due to their wider range of properties such as their high water content and porous framework, similarity to the natural extracellular matrix (ECM), ability to encapsulate cells within the matrix and ability to provide biological cues for cellular differentiation. Further, their properties such as those that facilitate minimally invasive deployment or delivery, and their ability to repair geometrically complex irregular defects have been critical for their success. In this review, we provide an overview of innovative approaches to engineer injectable hydrogels towards improved osteochondral tissue repair. Herein, we focus on understanding the biology of osteochondral tissue and osteoarthritis along with the need for injectable hydrogels in osteochondral tissue engineering. Furthermore, we discuss in detail different biomaterials (natural and synthetic) and various advanced fabrication methods being employed for the development of injectable hydrogels in osteochondral repair. In addition, in vitro and in vivo applications of developed injectable hydrogels for osteochondral tissue engineering are also reviewed. Finally, conclusions and future perspectives of using injectable hydrogels in osteochondral tissue engineering are provided.

Injectable thermosensitive hydrogel containing hyaluronic acid and chitosan as a barrier for prevention of postoperative peritoneal adhesion

Peritoneal adhesion is one of the common complications after abdominal surgery. Injectable thermosensitive hydrogel could serve as an ideal barrier to prevent this postoperative tissue adhesion. In this study, poly(N-isopropylacrylamide) (PNIPAm) was grafted to chitosan (CS) and the polymer was further conjugated with hyaluronic acid (HA) to form thermosensitive HA-CS-PNIPAm hydrogel. Aqueous solutions of PNIPAm and HA-CS-PNIPAm at 10%(w/v) are both free-flowing and injectable at room temperature and exhibit sol-gel phase transition around 31°C; however, HA-CS-PNIPAm shows less volume shrinkage after gelation and higher complex modulus than PNIPAm. Cell culture studies indicate both injectable hydrogel show barrier effects to reduce fibroblasts penetration while induce little cytotoxicity in vitro. From a sidewall defect-bowel abrasion model in rats, significant reduction of postoperative peritoneal adhesion was found for peritoneal defects treated with HA-CS-PNIPAm compared with those treated with PNIPAm and untreated controls from gross and histological evaluation. Furthermore, HA-CS-PNIPAm did not interfere with normal peritoneal tissue healing and did not elicit acute toxicity from blood analysis and tissue biopsy examination. By taking advantage of the easy handling and placement properties of HA-CS-PNIPAm during application, this copolymer hydrogel would be a potentially ideal injectable anti-adhesion barrier after abdominal surgeries.

Evaluation of an injectable thermoresponsive hyaluronan hydrogel in a rabbit osteochondral defect model

Articular cartilage displays very little self-healing capabilities, generating a major clinical need. Here, we introduce a thermoresponsive hyaluronan hydrogel for cartilage repair obtained by covalently grafting poly(N-isopropylacrylamide) to hyaluronan, to give a brush co-polymer HpN. The gel is fluid at room temperature and becomes gel at body temperature. In this pilot study HpN safety and repair response were evaluated in an osteochondral defect model in rabbit. Follow-up was of 1 week and 12 weeks and the empty defect served as a control, for a total of four experimental groups. At 12 weeks the defect sites were evaluated macroscopically and histologically. Local lymph nodes, spleen, liver, and kidneys were analyzed for histopathological evaluation. HpN could be easily injected and remained into the defect throughout the study. The macroscopic score was statistically superior for HpN versus empty. Histological score gave opposite trend but not statistically significant. A slight tissue reaction was observed around HpN, however, vascularization and subchondral bone formation were not impeded. An upper proteoglycans rich fibro-cartilaginous tissue with fairly good continuity and lateral integration into the existing articular cartilage was observed in all cases. No signs of local or systemic acute or subacute toxicity were observed. In conclusion, HpN is easily injectable, remains into an osteochondral defect within a moving synovial joint, is biocompatible and does not interfere with the intrinsic healing response of osteochondral defects in a rabbit model. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1469-1478, 2016.

Multi-Functional Macromers for Hydrogel Design in Biomedical Engineering and Regenerative Medicine

Contemporary biomaterials are expected to provide tailored mechanical, biological and structural cues to encapsulated or invading cells in regenerative applications. In addition, the degradative properties of the material also have to be adjustable to the desired application. Oligo- or polymeric building blocks that can be further cross-linked into hydrogel networks, here addressed as macromers, appear as the prime option to assemble gels with the necessary degrees of freedom in the adjustment of the mentioned key parameters. Recent developments in the design of multi-functional macromers with two or more chemically different types of functionalities are summarized and discussed in this review illustrating recent trends in the development of advanced hydrogel building blocks for regenerative applications.

A novel injectable thermoresponsive and cytocompatible gel of poly(N-isopropylacrylamide) with layered double hydroxides facilitates siRNA delivery into chondrocytes in 3D culture

Hybrid hydrogels composed of poly(N-isopropylacrylamide) (pNIPAAM) and layered double hydroxides (LDHs) are presented in this study as novel injectable and thermoresponsive materials for siRNA delivery, which could specifically target several negative regulators of tissue homeostasis in cartilaginous tissues. Effectiveness of siRNA transfection using pNIPAAM formulated with either MgAl-LDH or MgFe-LDH platelets was investigated using osteoarthritic chondrocytes. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used as an endogenous model gene to evaluate the extent of silencing. No significant adverse effects of pNIPAAM/LDH hydrogels on cell viability were noticed. Cellular uptake of fluorescently labeled siRNA was greatly enhanced (>75%) in pNIPAAM/LDH hydrogel constructs compared to alginate, hyaluronan and fibrin gels, and was absent in pNIPAAM hydrogel without LDH platelets. When using siRNA against GAPDH, 82-98% reduction of gene expression was found in both types of pNIPAAM/LDH hydrogel constructs after 6 days of culturing. In the pNIPAAM/MgAl-LDH hybrid hydrogel, 80-95% of GAPDH enzyme activity was reduced in parallel with gene. Our findings show that the combination of a cytocompatible hydrogel and therapeutic RNA oligonucleotides is feasible. Thus it might hold promise in treating degeneration of cartilaginous tissues by providing supporting scaffolds for cells and interference with locally produced degenerative factors.

Liposomal delivery of horseradish peroxidase for thermally triggered injectable hyaluronic acid–tyramine hydrogel scaffolds

A thermally triggered injectable scaffold was developed by utilizing thermoresponsive liposomes to segregate the crosslinking agent from a polymer.

In vitro and in vivo evaluation of self-mineralization and biocompatibility of injectable, dual-gelling hydrogels for bone tissue engineering

In this study, we investigated the mineralization capacity and biocompatibility of injectable, dual-gelling hydrogels in a rat cranial defect as a function of hydrogel hydrophobicity from either the copolymerization of a hydrolyzable lactone ring or the hydrogel polymer content. The hydrogel system comprised a poly(N-isopropylacrylamide)-based thermogelling macromer (TGM) and a polyamidoamine crosslinker. The thermogelling macromer was copolymerized with (TGM/DBA) or without (TGM) a dimethyl-γ-butyrolactone acrylate (DBA)-containing lactone ring that modulated the lower critical solution temperature and thus, the hydrogel hydrophobicity, over time. Three hydrogel groups were examined: (1) 15wt.% TGM, (2) 15wt.% TGM/DBA, and (3) 20wt.% TGM/DBA. The hydrogels were implanted within an 8mm critical size rat cranial defect for 4 and 12weeks. Implants were harvested at each timepoint and analyzed for bone formation, hydrogel mineralization and tissue response using microcomputed tomography (microCT). Histology and fibrous capsule scoring showed a light inflammatory response at 4weeks that was mitigated by 12weeks for all groups. MicroCT scoring and bone volume quantification demonstrated a similar bone formation at 4weeks that was significantly increased for the more hydrophobic hydrogel formulations - 15wt.% TGM and 20wt.% TGM/DBA - from 4weeks to 12weeks. A complementary in vitro acellular mineralization study revealed that the hydrogels exhibited calcium binding properties in the presence of serum-containing media, which was modulated by the hydrogel hydrophobicity. The tailored mineralization capacity of these injectable, dual-gelling hydrogels with hydrolysis-dependent hydrophobicity presents an exciting property for their use in bone tissue engineering applications.

Supporting Biomaterials for Articular Cartilage Repair

Orthopedic surgeons and researchers worldwide are continuously faced with the challenge of regenerating articular cartilage defects. However, until now, it has not been possible to completely mimic the biological and biochemical properties of articular cartilage using current research and development approaches. In this review, biomaterials previously used for articular cartilage repair research are addressed. Furthermore, a brief discussion of the state of the art of current cell printing procedures mimicking native cartilage is offered in light of their use as future alternatives for cartilage tissue engineering. Inkjet cell printing, controlled deposition cell printing tools, and laser cell printing are cutting-edge techniques in this context. The development of mimetic hydrogels with specific biological properties relevant to articular cartilage native tissue will support the development of improved, functional, and novel engineered tissue for clinical application.

Injectable thermoreversible hyaluronan-based hydrogels for nucleus pulposus cell encapsulation

INTRODUCTION

Thermoreversible hydrogels have potential in spine research as they provide easy injectability and mild gelling mechanism (by physical cross-link). The purpose of this study was to assess the potential of thermoreversible hyaluronan-based hydrogels (HA-pNIPAM) (pNIPAM Mn = 10, 20, 35 × 10(3) g mol(-1)) as nucleus pulposus cells (NPC) carrier.

MATERIALS AND METHODS

Cytocompatibility (WST-1 assay), viability (trypan blue), morphology (toluidine blue), sulphated glycosaminoglycan synthesis (DMMB assay) and gene expression profile (real-time PCR) of bovine NPC cultured in HA-pNIPAM were followed for 1 week and compared to alginate gel bead cultures. The injectability and cell survival in a whole disc organ culture model were assessed up to day 7.

RESULTS

All HA, HA-pNIPAM and their degradation products were cytocompatible to NPC. HA-pNIPAM hydrogels with no volume change upon gelling maintained NPC viability and characteristic rounded morphology. Glycosaminoglycan synthesis was similar in HA-pNIPAM and alginate gels. Following NPC expansion, both gels induced re-differentiation toward the NPC phenotype. Significant differences between the two gels were found for COLI, COLII, HAS1, HAS2 and ADAMTS4 but not for MMPs and TIMPs. Higher expression of hyaluronan synthases (HAS1, HAS2) and lower expression of COLI and COLII mRNA were noted in cells cultured in HA-pNIPAM (pNIPAM = 20 × 10(3)g mol(-1)). NPC suspension in HA-pNIPAM was injectable through a 22-G needle without loss of cell viability. Ex vivo, NPC viability was maintained in HA-pNIPAM for 1 week.

CONCLUSION

A HA-pNIPAM composition suitable for nucleus pulposus repair that provides an injectable carrier for NPC, maintains their phenotype and promotes extracellular matrix generation was identified.

Articular cartilage tissue engineering based on a mechano-active scaffold made of poly(L-lactide-co-epsilon-caprolactone): In vivo performance in adult rabbits

Our previous studies showed that a mechano-active scaffold made of poly(L-lactide-co-epsilon-caprolactone) (PLCL) exhibited a high potential to realize the formation of a functional, engineered cartilage in vitro. This animal study therefore was designed to investigate the feasibility of repairing on osteochondral defect with the use of bone marrow-derived mesenchymal stem cells (BMSCs) incorporated with a PLCL scaffold. Rabbit BMSCs, isolated and subsequently cultured in monolayer, were seeded into a porous PLCL scaffold sponge following an implantation onto a full-thickness osteochondral defect (diameter of 4.5 mm, depth of 5 mm) that was artificially created on the medial femoral condyles at a high load-bearing site on a rabbit's knee joint. Time-dependent healing of the defect was evaluated by macroscopic, histological examinations at both 3- and 6-month-implantations, respectively. A PLCL sponge incorporated with BMSCs exhibited sufficient structural support, resulting in new osteochondral tissue regeneration: a physiologically well-integrated subchondral bone formation, a hyaline cartilage-like morphology containing chondrocytes surrounded by abundant cartilaginous matrices. In addition, quantitative biochemical assays also demonstrated high potential for the synthesis of sulfated glycosaminoglycan and collagen, both of which are biomolecules essential to extracelluar matrix in normal cartilage tissue. In contrast, defects filled with cell-free PLCL scaffold or left empty showed a very limited potential for regeneration. Our findings suggest that a composite of PLCL-based sponge scaffold and BMSCs promote the repair of osteochondral defects at high load-bearing sites in adult rabbits.

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.

Biological cell detachment from poly(N-isopropyl acrylamide) and its applications

Over the past two decades, poly(N-isopropyl acrylamide) (pNIPAM) has become widely used for bioengineering applications. In particular, pNIPAM substrates have been used for the nondestructive release of biological cells and proteins. In this feature article, we review the applications for which pNIPAM substrates have been used to release biological cells, including for the study of the extracellular matrix (ECM), for cell sheet engineering and tissue transplantation, the formation of tumorlike spheroids, the study of bioadhesion and bioadsorption, and the manipulation or deformation of individual cells. The articles reviewed include submissions from our own group as well as from those performing research in the field worldwide.

Reversible hydrogel formation driven by protein-peptide-specific interaction and chondrocyte entrapment

We developed a hydrogel self-assembling method driven by the interaction between recombinant tax-interactive protein-1 (TIP1) with the PDZ domain in a molecule, which is fused to each end of the triangular trimeric CutA protein (CutA-TIP1), and a PDZ domain-recognizable peptide which is covalently bound to each terminus of four-armed poly(ethylene glycol) (PDZ-peptide-PEG). Genetic manipulation based on molecular-dynamic simulation generated a cell-adhesive RGD tripeptidyl sequence in the CutA loop region [CutA(RGD)-TIP1]. Spontaneous viscoelastic hydrogel formation occurred when either CutA-TIP1- or CutA(RGD)-TIP1-containing buffer solution and PDZ-peptide-PEG-containing buffer solutions were stoichiometrically mixed. Dynamic viscoelasticity measurement revealed shear stress-dependent reversible-phase transformation: a spontaneous viscoelastic hydrogel was formed at low shear stress, but it was transformed into a sol at high shear stress. Upon the cessation of shear, hydrogel was restored. When chondrocytes were pre-mixed with one of these two components containing buffer solutions, the stoichiometric mixed solution was also spontaneously gelled. Individual rounded cells and multicellular aggregates were entrapped within both hydrogels without substantial cellular impairment regardless of the presence or absence of RGD motif in the CutA-TIP1 molecule. The potential use of such a shear-sensitive hydrogel for injectable cell delivery into diseased or lost cartilage tissue is discussed.

Synthesis and characterization of injectable, thermally and chemically gelable, amphiphilic poly(N-isopropylacrylamide)-based macromers

In this study, we synthesized and characterized a series of macromers based on poly( N-isopropylacrylamide) that undergo thermally induced physical gelation and, following chemical modification, can be chemically cross-linked. Macromers with number average molecular weights typically ranging from 2000-3500 Da were synthesized via free radical polymerization from, in addition to N-isopropylacrylamide, pentaerythritol diacrylate monostearate, a bifunctional monomer containing a long hydrophobic chain, acrylamide, a hydrophilic monomer, and hydroxyethyl acrylate, a hydrophilic monomer used to provide hydroxyl groups for further chemical modification. Results indicated that the hydrophobic-hydrophilic balance achieved by varying the relative concentrations of comonomers used during synthesis was an important parameter in controlling the transition temperature of the macromers in solution and stability of the resultant gels. Storage moduli of the macromers increased over 4 orders of magnitude once gelation occurred above the transition temperature. Furthermore, chemical cross-linking of these macromers resulted in gels with increased stability compared to uncross-linked controls. These results demonstrate the feasibility of synthesizing poly( N-isopropylacrylamide)-based macromers that undergo tandem gelation and establish key criteria relating to the transition temperature and stability of these materials. The data suggest that these materials may be attractive substrates for tissue engineering and cellular delivery applications as the combination of mechanistically independent gelation techniques used in tandem may offer superior materials with regard to gelation kinetics and stability.

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

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

Hydrogels as Extracellular Matrices for Skeletal Tissue Engineering: State-of-the-Art and Novel Application in Organ Printing

Organ printing, a novel approach in tissue engineering, applies layered computer-driven deposition of cells and gels to create complex 3-dimensional cell-laden structures. It shows great promise in regenerative medicine, because it may help to solve the problem of limited donor grafts for tissue and organ repair. The technique enables anatomical cell arrangement using incorporation of cells and growth factors at predefined locations in the printed hydrogel scaffolds. This way, 3-dimensional biological structures, such as blood vessels, are already constructed. Organ printing is developing fast, and there are exciting new possibilities in this area. Hydrogels are highly hydrated polymer networks used as scaffolding materials in organ printing. These hydrogel matrices are natural or synthetic polymers that provide a supportive environment for cells to attach to and proliferate and differentiate in. Successful cell embedding requires hydrogels that are complemented with biomimetic and extracellular matrix components, to provide biological cues to elicit specific cellular responses and direct new tissue formation. This review surveys the use of hydrogels in organ printing and provides an evaluation of the recent advances in the development of hydrogels that are promising for use in skeletal regenerative medicine. Special emphasis is put on survival, proliferation and differentiation of skeletal connective tissue cells inside various hydrogel matrices.

Cell Sorting Technique Based on Thermoresponsive Differential Cell Adhesiveness

Cell sorting of specific target cells from a mixture of different cell types is a prerequisite for development of functional engineered tissues based on stem-cell and tissue engineering. This paper presents a new method of cell sorting that uses a mixture of thermoresponsive cell-adhesive and non-cell-adhesive substances. The former substance is poly(N-isopropylacrylamide)-grafted gelatin (PNIPAM-gelatin) and the latter is PNIPAM. Graded cell adhesion, produced by mixed coating of these thermoresponsive substances at an appropriate mixing ratio, clearly differentiated the adhesive potentials of two bovine vascular cell types (endothelial cell and smooth muscle cell). The sequential procedures of detachment at room temperature and subsequent replating at 37 degrees C on dishes coated with a mixed coating with the same composition as that employed previously yielded remarkably pure target cells, as determined using confocal laser scanning fluorescence microscopy. This method, leading to harvesting of target cells, is characteristic of simple manipulation with no cell damage. Such advantages are expected to facilitate stem-cell and tissue engineering.

Photo-iniferter-based thermoresponsive block copolymers composed of poly(ethylene glycol) and poly(N-isopropylacrylamide) and chondrocyte immobilization

A series of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM)-poly(ethylene glycol) (PEG) block copolymers with various PNIPAM contents and copolymer architectures, such as linear, four-armed and eight-armed configurations, were prepared by iniferter-based photopolymerization of dithiocarbamylated PEGs (DC-PEGs) under ultraviolet (UV)-light irradiation. The increase in monomer/DC-PEG feed ratio resulted in an increase in both the molecular weight and PNIPAM content of copolymers. The measurement of the optical transmittances of aqueous solutions of PNIPAM-PEG block copolymers determined the lower critical solution temperatures (LCSTs) of block copolymers, which ranged from 31.3 to 34.0 degrees C. LCST decreased with increasing block length of PNIPAM and with the formation of a branched architecture. Rabbit chondrocytes were immobilized and cultured in a three-dimensional (3D) gel composed of PNIPAM-PEG block copolymer at 37 degrees C. Gels prepared from copolymers with higher PNIPAM contents at higher concentrations appeared to exhibit a minimal decrease in both cell number and cell viability during a 7-day culture. Cell viability dependencies on material and formulation parameters and the potential use of PNIPAM-PEG block copolymers as an in situ formable scaffold for an engineered cartilage tissue were discussed.

Evaluation of cartilage repair tissue after biomaterial implantation in rat patella by using T2 mapping

To evaluate the ability of MR T2 mapping (8.5 T) to characterize ex vivo longitudinally, morphologically and quantitatively, alginate-based tissue engineering in a rat model of patellar cartilage chondral focal defect. Calibrated rat patellar cartilage defects (1.3 mm) were created at day 0 (D0) and alginate sponge with (Sp/C+) or without (Sp/C-) autologous chondrocytes were implanted. Animals were sacrificed sequentially at D20, D40 and D60 after surgery and dissected patellae underwent MRI exploration (8.5 T). T2 values were calculated from eight SE images by using nonlinear least-squares curve fitting on a pixel-by-pixel basis (constant repetition time of 1.5 s, eight different echo times: 5.5, 7.5, 10.5, 12.5, 15.0, 20.0, 25.0 and 30.0 ms). On the T2 map, acquired in a transversal plane through the repair zone, global T2 values and zonal variation of T2 values of repair tissue were evaluated versus control group and compared with macroscopic score and histological studies (toluidine blue, sirius red and hematoxylin-eosin). "Partial", "total" and "hypertrophic" repair patterns were identified. At D40 and D60, Sp/C+ group was characterized by a higher proportion of "total" repair in comparison to Sp/C- group. At D60, the proportion of "hypertrophic" repair was two fold in Sp/C- group versus Sp/C+ group. As confirmed morphologically and histologically, the T2 map also permitted the distinction of three types of repair tissue: "total", "partial" and "hypertrophic". "Total" repair tissue was characterized by high T2 values versus normal cartilage (p<0.05). Zonal variation, reflecting the collagen network organization, appeared only at D60 for Sp/C+ group (p<0.05). "Hypertrophic" tissue, mainly observed at D60, presented high T2 global values without zonal variation with cartilage depth. These results confirm the potency of the MR T2 map (8.5 T) to characterize macroscopically and microscopically the patterns of the scaffold guided-tissue repair of a focal chondral lesion in the rat patella ("total", "partial" and "hypertrophic"). On T2 map, three parameters (i.e. MRI macroscopic pattern, T2 global values and zonal variation of T2 values) permit to characterize chondral repair tissue, as a virtual biopsy.