A novel MSC‐seeded triphasic construct for the repair of osteochondral defects

Mesenchymal stem cells (MSC) are increasingly replacing chondrocytes in tissue engineering based research for treatment of osteochondral defects. The aim of this work was to determine whether repair of critical‐size chronic osteochondral defects in an ovine model using MSC‐seeded triphasic constructs would show results comparable to osteochondral autografting (OATS). Triphasic implants were engineered using a beta‐tricalcium phosphate osseous phase, an intermediate activated plasma phase, and a collagen I hydrogel chondral phase. Autologous MSCs were used to seed the implants, with chondrogenic predifferentiation of the cells used in the cartilage phase. Osteochondral defects of 4.0 mm diameter were created bilaterally in ovine knees (n = 10). Six weeks later, half of the lesions were treated with OATS and half with triphasic constructs. The knees were dissected at 6 or 12 months. With the chosen study design we were not able to demonstrate significant differences between the histological scores of both groups. Subcategory analysis of O'Driscoll scores showed superior cartilage bonding in the 6‐month triphasic group compared to the autograft group. The 12‐month autograft group showed superior cartilage matrix morphology compared to the 12‐month triphasic group. Macroscopic and biomechanical analysis showed no significant differences at 12 months. Autologous MSC‐seeded triphasic implants showed comparable repair quality to osteochondral autografts in terms of histology and biomechanical testing. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1586–1599, 2010     

Effect of chondroitinase ABC on adhesion and behavior of synovial membrane‐derived mesenchymal stem cells in rabbit partial‐thickness chondral defects

Transplanted cells may have difficulty attaching to the surface of partial‐thickness chondral lesions because of the anti‐adhesive properties of the proteoglycan rich matrix. Therefore, the current study attempts to evaluate the effect of chondroitinase ABC (chABC) on the adhesion and behavior of transplanted synovial membrane‐derived mesenchymal stem cells (SDSCs) in rabbit partial‐thickness chondral defects. In ex vivo adhesion experiments, chABC treatment (0.1 U/ml) was increased in SDSC attachment to the cartilage explants, and significantly diminished by pretreatment with neutralizing antibody against fibronectin. In the in vivo experiments, 1 day and 4 weeks after the chABC treatment (0.1 and 1 U/ml), the immunoreactivity (IR) against CS‐56 (intact chondroitin sulfate antibody) was markedly decreased; however, the IR of 2B6 (stub of the chondroitin 4‐sulfate chain), 3B3 (stub of the chondroitin 6‐sulfate chain), and fibronectin was increased. At 12 weeks, this IR returned to normal except in the high‐dose chABC‐treated group (1 U/ml). Furthermore, the attachment of SDSCs to the chondral defects after chABC treatment was increased at 7 days compared with that in the chondral defects pretreated with saline. However, the tissue repaired by SDSCs was negatively stained for type II collagen at 12 weeks. In conclusion, these results showed that the exposure to fibronectin by chABC treatment enhances the attachment of SDSCs to partial‐thickness chondral defects. However, the tissue regenerated by SDSCs showed lack of hyaline cartilage regeneration. Thus, to understand the fate of transplanted MSCs in cartilage defect is very important for successful cell therapies. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1293–1301, 2013     

Osteochondral regeneration using constructs of mesenchymal stem cells made by bio three‐dimensional printing in mini‐pigs

Osteoarthritis is a major joint disease that has been extensively investigated in humans and in model animals. In this study, we examined the regeneration of articular cartilage and subchondral bone using artificial scaffold‐free constructs composed of adipose tissue‐derived mesenchymal stem cells (AT‐MSCs) created using bio three‐dimensional (3D) printing with a needle‐array. Printed constructs were implanted into osteochondral defects created in the right femoral trochlear groove of six mini‐pigs, using femoral defects created in the left femurs as controls. Repair within the defects was evaluated at 3 and 6 months post‐implantation using computed tomography (CT) and magnetic resonance (MR) imaging. The radiolucent volume (RV, mm³) in the defects was calculated using multi‐planar reconstruction of CT images. MR images were evaluated based on a modified 2D‐ MOCART (magnetic resonance observation of cartilage repair tissue) grading system. Gross and microscopic pathology were scored according to the ICRS (International Cartilage Repair Society) scale at 6 months after implantation. The percentage RV at 3 months postoperation was significantly lower in the implanted defects than in the controls, whereas total scores based on the MOCART system were significantly higher in the implanted defects as compared with the controls. Although there were no statistical differences in the gross scores, the average histological scores were significantly higher in the implanted defects than in the controls. To our knowledge, this is the first report to suggest that artificial scaffold‐free 3D‐printed constructs of autologous AT‐MSCs can be aid in the osteochondral regeneration in pigs. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1398–1408, 2019.     

Repair of large osteochondral defects in rabbits using porous hydroxyapatite/collagen (HAp/Col) and fibroblast growth factor‐2 (FGF‐2)

Articular cartilage has a limited capacity for self‐renewal. This article reports the development of a porous hydroxyapatite/collagen (HAp/Col) scaffold as a bone void filler and a vehicle for drug administration. The scaffold consists of HAp nanocrystals and type I atelocollagen. The purpose of this study was to investigate the efficacy of porous HAp/Col impregnated with FGF‐2 to repair large osteochondral defects in a rabbit model. Ninety‐six cylindrical osteochondral defects 5 mm in diameter and 5 mm in depth were created in the femoral trochlear groove of the right knee. Animals were assigned to one of four treatment groups: porous HAp/Col impregnated with 50 µl of FGF‐2 at a concentration of 10 or 100 µg/ml (FGF10 or FGF100 group); porous HAp/Col with 50 µl of PBS (HAp/Col group); and no implantation (defect group). The defect areas were examined grossly and histologically. Subchondral bone regeneration was quantified 3, 6, 12, and 24 weeks after surgery. Abundant bone formation was observed in the HAp/Col implanted groups as compared to the defect group. The FGF10 group displayed not only the most abundant bone regeneration but also the most satisfactory cartilage regeneration, with cartilage presenting a hyaline‐like appearance. These findings suggest that porous HAp/Col with FGF‐2 augments the cartilage repair process. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:677–686, 2010     

Comparison of repair between cartilage and osteocartilage defects in rabbits using similarly manipulated scaffold-free cartilage-like constructs

Background

Articular cartilage has a limited capacity for spontaneous repair, and its repair remains a clinical challenge. The purpose of this study was to prepare scaffold-free cartilage-like constructs and evaluate the feasibility of their use for the treatment of cartilage and osteocartilage defects in vivo.

Methods

The scaffold-free constructs were prepared by chondrocytes isolated from the articular cartilage of rabbits using a high-density three-dimensional culture system. Two different defects, i.e., a chondral defect without oozing blood and an osteochondral defect with oozing blood, of 4-mm diameter, were created on the patellar groove of rabbits and forwarded to in vivo trials. In each defect, the constructs cut into 4-mm-diameter cylinders were grafted at the bottom of the defects. As a control, defects were only made on the contralateral knee joint in each rabbit. At 2, 4, 8 and 12 weeks after surgery, six rabbits in each group were evaluated macroscopically and histologically.

Results

In vitro, histological examination revealed that the constructs have the character of hyaline cartilage with a potential adhesiveness to surrounding tissue. In vivo, in two control groups, incomplete spontaneous cartilage repair was observed in the osteochondral defects, whereas no repair was observed in the chondral defects. In the two treated groups, the surviving constructs in chondral defects showed significantly better repair compared to those in osteochondral defects.

Conclusions

It is possible for a chondral defect to be repaired by scaffold-free constructs in certain conditions. Establishing the optimal environment suitable for cartilage repair is warranted.     

Cell-based treatment of osteochondral defects in the rabbit knee with natural and synthetic matrices: cellular seeding determines the outcome

Introduction: Matrix-associated transplantation of cartilage constructs is an appealing method in cartilage repair. Three different matrices seeded with allogenic chondrocytes were compared in an osteochondral defect model in the rabbit. An investigation was conducted to identify the best matrix for cell-based treatment of osteochondral defects in the rabbit knee joint. Materials and methods: Osteochondral defects (diameter 3 mm) were created in the trochlea and the femoral condyles of 33 New Zealand White rabbits, which were then treated with bioartificial cartilage constructs. The cartilage constructs were created in vitro using three different resorbable carrier materials (two fleece matrices: one of PLLA, and one composite of polydioxanon/polyglactin, as well as one consisting of lyophilized dura) cultured with isolated allogenic chondrocytes. The defects were evaluated macroscopically, by histological and immunhistological techniques, and by scanning electron microscopy after 6 weeks, 6 months, and 12 months. The chondrocyte-seeded constructs were compared to defects treated with carrier material alone as well as to untreated control defects. Results: There was a significant improvement in defect repair quality in the transport materials, which were cultured with chondrocytes prior to implantation (P<0.0005). No significant differences were observed between the three carrier matrices, and no significant differences were seen between the unseeded matrices and the untreated control defects. Conclusion: There is no difference in the outcome between the three tested matrices in the treatment of osteochondral defects in the rabbit knee. The results of this in vitro experiment are promising and with refinement may lead to useful clinical therapies.     

Repair of superficial osteochondral defects with an autologous scaffold-free cartilage construct in a caprine model: implantation method and short-term results

OBJECTIVE: To compare four different implantation modalities for the repair of superficial osteochondral defects in a caprine model using autologous, scaffold-free, engineered cartilage constructs, and to describe the short-term outcome of successfully implanted constructs. METHODS: Scaffold-free, autologous cartilage constructs were implanted within superficial osteochondral defects created in the stifle joints of nine adult goats. The implants were distributed between four 6-mm-diameter superficial osteochondral defects created in the trochlea femoris and secured in the defect using a covering periosteal flap (PF) alone or in combination with adhesives (platelet-rich plasma (PRP) or fibrin), or using PRP alone. Eight weeks after implantation surgery, the animals were killed. The defect sites were excised and subjected to macroscopic and histopathologic analyses. RESULTS: At 8 weeks, implants that had been held in place exclusively with a PF were well integrated both laterally and basally. The repair tissue manifested an architecture similar to that of hyaline articular cartilage. However, most of the implants that had been glued in place in the absence of a PF were lost during the initial 4-week phase of restricted joint movement. The use of human fibrin glue (FG) led to massive cell infiltration of the subchondral bone. CONCLUSIONS: The implantation of autologous, scaffold-free, engineered cartilage constructs might best be performed beneath a PF without the use of tissue adhesives. Successfully implanted constructs showed hyaline-like characteristics in adult goats within 2 months. Long-term animal studies and pilot clinical trials are now needed to evaluate the efficacy of this treatment strategy.     

Effect of tenascin‐C on the repair of full‐thickness osteochondral defects of articular cartilage in rabbits

The purpose of this study was to examine the effect of tenascin‐C (TNC) on the repair of full‐thickness osteochondral defects of articular cartilage in vivo. We used a gellan–gellan–sulfate sponge (Gellan–GS) to maintain a TNC‐rich environment in the cartilage defects. We implanted Gellan‐GS soaked in PBS only (Group 1), Gellan‐GS soaked in 10 µg/ml of TNC (Group 2), and Gellan‐GS soaked in 100 µg/ml of TNC (Group 3) into a full‐thickness osteochondral defect of the patellar groove of rabbits. The defect area was examined grossly and histologically 4–12 weeks after surgery. Sections of synovium were also immunohistochemically investigated. Histologically as well as macroscopically, the defects in Group 2 showed better repair than the other groups at 8 and 12 weeks after surgery. Inflammation of the synovium tended to diminish over time in all groups, and the degree of synovitis was the same for all three groups at each time point. In conclusion, Gellan–GS soaked in TNC can be used as a novel scaffold for the repair of articular cartilage defects. This study also indicates that TNC promotes the repair of full‐thickness osteochondral defects in vivo. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:563–571, 2015.     

Orderly osteochondral regeneration in a sheep model using a novel nano‐composite multilayered biomaterial

The objective of this article was to investigate the safety and regenerative potential of a newly developed biomimetic scaffold when applied to osteochondral defects in an animal model. A new multilayer gradient nano‐composite scaffold was obtained by nucleating collagen fibrils with hydroxyapatite nanoparticles. In the femoral condyles of 12 sheep, 24 osteochondral lesions were created. Animals were randomized into three treatment groups: scaffold alone, scaffold colonized in vitro with autologous chondrocytes and empty defects. Six months after surgery, the animals were sacrificed and the lesions were histologically evaluated. Histologic and gross evaluation of specimens showed good integration of the chondral surface in all groups except for the control group. Significantly better bone regeneration was observed both in the group receiving the scaffold alone and in the group with scaffold loaded with autologous chondrocytes. No difference in cartilage surface reconstruction and osteochondral defect filling was noted between cell‐seeded and cell‐free groups. In the control group, no bone or cartilage defect healing occurred, and the defects were filled with fibrous tissue. Quantitative macroscopic and histological score evaluations confirmed the qualitative trends observed. The results of the present study showed that this novel osteochondral scaffold is safe and easy to use, and may represent a suitable matrix to direct and coordinate the process of bone and hyaline‐like cartilage regeneration. The comparable regeneration process observed with or without autologous chondrocytes suggests that the main mode of action of the scaffold is based on the recruitment of local cells. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:116–124, 2010     

Tissue engineering‐based cartilage repair with mesenchymal stem cells in a porcine model

This in vivo pilot study explored the use of mesenchymal stem cell (MSC) containing tissue engineering constructs in repair of osteochondral defects. Osteochondral defects were created in the medial condyles of both knees of 16 miniature pigs. One joint received a cell/collagen tissue engineering construct with or without pretreatment with transforming growth factor β (TGF‐β) and the other joint from the same pig received no treatment or the gel scaffold only. Six months after surgery, in knees with no treatment, all defects showed contracted craters; in those treated with the gel scaffold alone, six showed a smooth gross surface, one a hypertrophic surface, and one a contracted crater; in those with undifferentiated MSCs, five defects had smooth, fully repaired surfaces or partially repaired surfaces, and one defect poor repair; in those with TGF‐β‐induced differentiated MSCs, seven defects had smooth, fully repaired surfaces or partially repaired surfaces, and three defects showed poor repair. In Pineda score grading, the group with undifferentiated MSC, but not the group with TGF‐β‐induced differentiated MSCs, had significantly lower subchondral, cell morphology, and total scores than the groups with no or gel‐only treatment. The compressive stiffness was larger in cartilage without surgical treatment than the treated area within each group. In conclusion, this preliminary pilot study suggests that using undifferentiated MSCs might be a better approach than using TGF‐β‐induced differentiated MSCs for in vivo tissue engineered treatment of osteochondral defects. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1874–1880, 2011     

Combination therapy with intra‐articular injection of mesenchymal stem cells and articulated joint distraction for repair of a chronic osteochondral defect in the rabbit

The present study investigated intra‐articular injection of bone‐marrow‐derived mesenchymal stem cells (MSCs) combined with articulated joint distraction as treatment for osteochondral defects. Large osteochondral defects were created in the weight‐bearing area of the medial femoral condyle in rabbit knees. Four weeks after defect creation, rabbits were divided into six groups: control group, MSC group, distraction group, distraction + MSC group, temporary distraction group, and temporary distraction + MSC group. Groups with MSC received intra‐articular injection of MSCs. Groups with distraction underwent articulated distraction arthroplasty. Groups with temporary distraction discontinued the distraction after 4 weeks. The rabbits were euthanized at 4, 8, and 12 weeks after treatment except temporary distraction groups which were euthanized at only 12 weeks. Histological scores in the distraction + MSC group were significantly better than in the control, MSC group or distraction group at 4 and 8 weeks, but showed no further improvement. At 12 weeks, the temporary distraction + MSC group showed the best results, demonstrating hyaline cartilage repair with regeneration of the osteochondral junction. In conclusion, joint distraction with intra‐articular injection of MSCs promotes early cartilage repair, and compressive loading of the repair tissue after temporary distraction stimulates articular cartilage regeneration. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1466–1473, 2015.     

Marrow stimulation and chondrocyte transplantation using a collagen matrix for cartilage repair

OBJECTIVE: The purpose of the study was to determine whether the implantation of a scaffold would facilitate cartilage repair after microfracture in sheep over a period of 12 months. Furthermore, we investigated the effect of additional autologous cell augmentation of the implanted constructs. METHODS: Two chondral defects were produced in the medial femoral condyle of sheep without penetrating the subchondral bone. Twenty-seven sheep were divided into the following groups: seven served as untreated controls (Group 1), microfracture was created in 20 animals, seven of them without further treatment (Group 2), in six sheep the defects were additionally covered with a porcine collagen matrix (Group 3), and in seven animals the matrix was augmented with cultured autologous chondrocytes (Group 4). After 4 (11 sheep) and 12 months (16 sheep), the filling of the defects, tissue types, and semiquantitative scores were determined. RESULTS: The untreated defects revealed the least amount of defect fill. Defects treated with microfractures achieved better defect fill, while the additional use of the matrix did not increase the defect fill. The largest quantity of reparative tissue was found in the cell-augmented group. Semiquantitative scores were best in the cell-augmented group. CONCLUSION: Microfracture treatment was observed to enhance the healing response. The implantation of a cell-seeded matrix further improved the outcome. The implantation of a collagen matrix alone did not enhance repair. Autologous cell implantation appears to be a very important aspect of the tissue engineering approach to cartilage defects.     

Sizable Scaffold‐Free Tissue‐Engineered Articular Cartilage Construct for Cartilage Defect Repair

This study introduces an implantable scaffold‐free cartilage tissue construct (SF) that is composed of chondrocytes and their self‐produced extracellular matrix (ECM). Chondrocytes were grown in vitro for up to 5 weeks and subjected to various assays at different time points (1, 7, 21, and 35 days). For in vivo implantation, full‐thickness defects (n = 5) were manually created on the trochlear groove of the both knees of rabbits (16‐week old) and 3 week‐cultured SF construct was implanted as an allograft for a month. The left knee defects were implanted with 1, 7, and 21 days in vitro cultured scaffold‐free engineered cartilages. (group 2, 3, and 4, respectively). The maturity of the engineered cartilages was evaluated by histological, chemical and mechanical assays. The repair of damaged cartilages was also evaluated by gross images and histological observations at 4, 8, and 12 weeks postsurgery. Although defect of groups 1, 2, and 3 were repaired with fibrocartilage tissues, group 4 (21 days) showed hyaline cartilage in the histological observation. In particular, mature matrix and columnar organization of chondrocytes and highly expressed type II collagen were observed only in 21 days in vitro cultured SF cartilage (group 4) at 12 weeks. As a conclusion, cartilage repair with maturation was recapitulated when implanted the 21 day in vitro cultured scaffold‐free engineered cartilage. When implanting tissue‐engineered cartilage, the maturity of the cartilage tissue along with the cultivation period can affect the cartilage repair.     

Cartilage repair: A review of Stanmore experience in the treatment of osteochondral defects in the knee with various surgical techniques

Articular cartilage damage in the young adult knee, if left untreated, it may proceed to degenerative osteoarthritis and is a serious cause of disability and loss of function. Surgical cartilage repair of an osteochondral defect can give the patient significant relief from symptoms and preserve the functional life of the joint. Several techniques including bone marrow stimulation, cartilage tissue based therapy, cartilage cell seeded therapies and osteotomies have been described in the literature with varying results. Established techniques rely mainly on the formation of fibro-cartilage, which has been shown to degenerate over time due to shear forces. The implantation of autologous cultured chondrocytes into an osteochondral defect, may replace damaged cartilage with hyaline or hyaline-like cartilage. This clinical review assesses current surgical techniques and makes recommendations on the most appropriate method of cartilage repair when managing symptomatic osteochondral defects of the knee. We also discuss the experience with the technique of autologous chondrocyte implantation at our institution over the past 11 years.     

Osteochondral repair using an acellular dermal matrix—pilot in vivo study in a rabbit osteochondral defect model

The aim of this pilot project was to introduce a novel use of acellular dermal matrix (ADM) in combination with infrapatellar fat pad mesenchymal stromal cells (IPFP‐MSCs) to effect repair in a rabbit osteochondral defect model. ADM, in a range of surgical procedures, has been shown to promote remodelling of tissue at the site of implantation. Rabbit‐derived ADM (rabADM) was prepared from the skin of donor rabbits. Autologous IPFP‐MSCs were obtained at the time of knee surgery. Osteochondral defects (4 mm cartilage outer/2 mm central bone defect) were drilled into distal femoral condyles of 12 New Zealand White rabbits. Treatments groups: (i) defect only; (ii) rabADM alone; (iii) IPFP‐MSCs alone; and (iv) rabADM with IPFP‐MSCs. Condyles were harvested at 12 weeks, and analyzed using histology, immunohistochemistry (types I and II collagen) and histomorphometry to evaluate osteochondral repair. The rabADM only group achieved the highest ratio of type II to non‐type II collagen (77.3%) using areal measures (similar to normal cartilage), which indicated a higher quality of cartilage repair. The addition of IPFP‐MSCs, with or without rabADM, formed a fibrous collagen cap above the lesion site not seen with rabADM alone. Macroscopically, there was no joint erosion, inflammation, swelling or deformity, and all animals maintained full range of motion. Conclusions: RabADM alone resulted in neocartilage formation similar to native cartilage. IPFP‐MSCs limited osteochondral repair and contributed to fibrosis, even in combination with the rabADM. Further studies using ADM for osteochondral repair are warranted in a more appropriate pre‐clinical model of osteochondral repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1919–1928, 2018.

     

Repair of experimentally induced large osteochondral defects in rabbit knee with various concentrations of Escherichia coli-derived recombinant human bone morphogenetic protein-2

Effective therapies for the regeneration of large osteochondral defects are still lacking; however, various approaches have been used. We evaluated the efficacy of Escherichia coli-derived dimeric recombinant human BMP-2 (E-rhBMP-2) for the repair of large osteochondral defects in a rabbit model. Osteochondral defects made in the femoral patellar groove of the knee were treated by transplanting gelatin sponges onto which no or various doses of E-rhBMP-2 were loaded. The outcomes were compared with those of an untreated control group four, 12 and 24 weeks after transplantation. At early time points, the cartilage tissue was repaired in a dose-dependent manner, and bone repair was accelerated in the defects treated with high doses of E-rhBMP-2. At 24 weeks, the repair of cartilage tissue was better with E-rhBMP-2 treatment, even at low doses, than without E-rhBMP-2 treatment. Our findings suggest that the use of E-rhBMP-2 improves and accelerates the repair of osteochondral defects in a rabbit model.     

Repair of Osteochondral Defects in a Rabbit Model Using a Porous Hydroxyapatite Collagen Composite Impregnated With Bone Morphogenetic Protein‐2

Articular cartilage has a limited capacity for spontaneous repair, and an effective method to repair damaged articular cartilage has not yet been established. The purpose of this study was to evaluate the effect of transplantation of porous hydroxyapatite collagen (HAp/Col) impregnated with bone morphogenetic protein‐2 (BMP‐2). To evaluate the characteristics of porous HAp/Col as a drug delivery carrier of recombinant human BMP‐2 (rhBMP‐2), the rhBMP‐2 adsorption capacity and release kinetics of porous HAp/Col were analyzed. Porous HAp/Col impregnated with different amounts of rhBMP‐2 (0, 5, and 25 μg) was implanted into osteochondral defects generated in the patellar groove of Japanese white rabbits to evaluate the effect on osteochondral defect regeneration. At 3, 6, 12, and 24 weeks after operation, samples were harvested and subjected to micro‐computed tomography analysis and histological evaluation of articular cartilage and subchondral bone repair. The adsorption capacity was 329.4 μg of rhBMP‐2 per cm³ of porous HAp/Col. Although 36% of rhBMP‐2 was released within 24 h, more than 50% of the rhBMP‐2 was retained in the porous HAp/Col through the course of the experiment. Defects treated with 5 μg of rhBMP‐2 showed the most extensive subchondral bone repair and the highest histological regeneration score, and differences against the untreated defect group were significant. The histological regeneration score of defects treated with 25 μg of rhBMP‐2 increased up to 6 weeks after implantation, but then decreased. Porous HAp/Col, therefore, is an appropriate carrier for rhBMP‐2. Implantation of porous HAp/Col impregnated with rhBMP‐2 is effective for rigid subchondral bone repair, which is important for the repair of the smooth articular surface.     

Repair of porcine articular cartilage defect with a biphasic osteochondral composite.

Autologous chondrocyte implantation (ACI) has been recently used to treat cartilage defects. Partly because of the success of mosaicplasty, a procedure that involves the implantation of native osteochondral plugs, it is of potential significance to consider the application of ACI in the form of biphasic osteochondral composites. To test the clinical applicability of such composite construct, we repaired osteochondral defect with ACI at low cell-seeding density on a biphasic scaffold, and combined graft harvest and implantation in a single surgery. We fabricated a biphasic cylindrical porous plug of DL-poly-lactide-co-glycolide, with its lower body impregnated with beta-tricalcium phosphate as the osseous phase. Osteochondral defects were surgically created at the weight-bearing surface of femoral condyles of Lee-Sung mini-pigs. Autologous chondrocytes isolated from the cartilage were seeded into the upper, chondral phase of the plug, which was inserted by press-fitting to fill the defect. Defects treated with cell-free plugs served as control. Outcome of repair was examined 6 months after surgery. In the osseous phase, the biomaterial retained in the center and cancellous bone formed in the periphery, integrating well with native subchondral bone with extensive remodeling, as depicted on X-ray roentgenography by higher radiolucency. In the chondral phase, collagen type II immunohistochemistry and Safranin O histological staining showed hyaline cartilage regeneration in the experimental group, whereas only fibrous tissue formed in the control group. On the International Cartilage Repair Society Scale, the experimental group had higher mean scores in surface, matrix, cell distribution, and cell viability than control, but was comparable with the control group in subchondral bone and mineralization. Tensile stress-relaxation behavior determined by uni-axial indentation test revealed similar creep property between the surface of the experimental specimen and native cartilage, but not the control specimen. Implanted autologous chondrocytes could survive and could yield hyaline-like cartilage in vivo in the biphasic biomaterial construct. Pre-seeding of osteogenic cells did not appear to be necessary to regenerate subchondral bone.     

Use of a guanidine extract of demineralized bone in the treatment of osteochondral defects of articular cartilage

In order to evaluate the ability of a guanidine extract of demineralized bone to repair osteochondral defects in articular cartilage, plugs made of this extract were implanted into defects in rabbit knees. The repair tissue was examined macroscopically, histologically, and immunohistochemically at 4, 8, 12 and 30 weeks. Controls (defects that were left empty) showed no cartilage formation. Four weeks after implantation of a guanidine extract plug, histological examination showed a nonhomogeneous metachromatically stained region extending from the surface of the repair tissue down to cancellous bone. This region also was labeled by an anti-type-II collagen antibody, indicating that cartilage-like tissue had been induced. At 8 weeks, the newly formed cartilage in the subchondral and cancellous bone had been partially replaced by bone. At 12 weeks, the thickness of the newly formed cartilage layer had decreased, and most of the newly formed cartilage in the subchondral and cancellous bone had been replaced by bone. In addition, a tidemark was observed. At 30 weeks, the repair tissue was a mixture of cartilage and fibrocartilage, and there was severe degeneration of the cartilage surrounding the repaired defects. These findings indicate that osteochondral defects of articular cartilage can be partially repaired by the implantation of a guanidine extract and that the newly formed cartilage-like tissue is not permanent.     

Porous tantalum and poly‐ε‐caprolactone biocomposites for osteochondral defect repair: Preliminary studies in rabbits

Currently, various techniques are in use for the repair of osteochondral defects, none of them being truly satisfactory and they are often two step procedures. Comorbidity due to cancellous bone harvest from the iliac crest further complicates the procedure. Our previous in vitro studies suggest that porous tantalum (TM) or poly‐ε‐caprolactone scaffolds (PCL) in combination with periosteal grafts could be used for osteochondral defect repair. In this in vivo study, cylindrical osteochondral defects were created on the medial and lateral condyles of 10 rabbits and filled with TM/periosteum or PCL/periosteum biosynthetic composites (n = 8 each). The regenerated osteochondral tissue was then analyzed histologically, and evaluated in an independent and blinded manner by five different observers using a 30‐point histological score. The overall histological score for PCL/periosteum was significantly better than for TM/periosteum. However, most of the regenerates were well integrated with the surrounding bone (PCL/periosteum, n = 6.4; TM/periosteum, n = 7) along with partial restoration of the tidemark (PCL/periosteum, n = 4.4; TM/periosteum, n = 5.6). A cover of hyaline‐like morphology was found after PCL/periosteum treatment (n = 4.8), yet the cartilage yields were inconsistent. In conclusion, the applied TM and PCL scaffolds promoted excellent subchondral bone regeneration. Neo‐cartilage formation from periosteum supported by a scaffold was inconsistent. This is the first study to show in vivo results of both PCL and TM scaffolds for a novel approach to osteochondral defect repair. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:141–148, 2010