Recent technological advancements related to articular cartilage regeneration

Some treatments for full thickness defects of the articular cartilage, such as the transplantation of cultured chondrocytes have already been performed. However, in order to overcome osteoarthritis, we must further study the partial thickness defects of articular cartilage. It is much more difficult to repair a partial thickness defect because few repair cells can address such injured sites. We herein show that bioengineered and layered chondrocyte sheets using temperature-responsive culture dishes may be a potentially useful treatment for the repair of partial thickness defects. We also show that a chondrocyte-plate using a rotational culture system without the use of a scaffold may also be useful as a core cartilage of an articular cartilageous defect. We evaluated the properties of these sheets and plates using histological findings, scanning electrical microscopy, and photoacoustic measurement methods, which we developed to evaluate the biomechanical properties of tissue-engineered cartilage. In conclusion, the layered chondrocyte sheets and chondrocyte-plates were able to maintain the cartilageous phenotype, thus suggesting that they could be a new and potentially effective therapeutic product when attached to the sites of cartilage defects.     

Mesenchymal stem cell sheet encapsulated cartilage debris provides great potential for cartilage defects repair in osteoarthritis

The restoration of the degenerated articular cartilage in patients with osteoarthritis (OA) is still a challenge for researchers and clinicians. Drug interventions and surgical treatments have been widely attempted for cartilage regeneration in OA. However, the results were largely unsatisfactory. Autologous chondrocyte implantation (ACI) or matrix-induced autologous chondrocyte implantation (MACI) offers potential for the regeneration of cartilage over the long-term. However, due to the limitations and disadvantages of ACI, alternative therapies for cartilage regeneration are in need. The availability of large quantities of mesenchymal stem cells (MSCs) and the multilineage differentiation, especially their chondrogenic differentiation property, have made MSCs the most promising cell source for cartilage regeneration. In addition, MSCs have been shown the ability to undergo site-specific differentiation. MSCs can be obtained as MSC sheets using the temperature-responsive culture dish method. The MSC sheet can provide amounts of cells and extracellular matrix, which might provide the continuity between the implant and host cartilage, thus improving integrative cartilage repair. Moreover, OA is associated with progressive and often severe inflammation. MSCs not only have the ability to contribute structurally to tissue repair, but also possess potent immunomodulatory and anti-inflammatory effects. Taken together, these properties make MSC sheet promising candidate for cartilage repair in OA. We hypothesize that MSC sheet encapsulated cartilage debris can efficiently promote cartilage repair in OA patients. Chondrocytes can be obtained and cultured from small cartilage debris in vitro. Therefore, the chondrocytes may grow from the debris in cartilage defect and improve cartilage regeneration. MSC sheet provide amounts of cells, ECM and protein for cartilage regeneration and integration, and may play some roles of periosteum. The operation of MSC sheet encapsulated cartilage debris for cartilage repair is simple and practical. Moreover, the cell sheet/cartilage debris constructs can be easily shaped based on the size and shape of cartilage defects. The new method might have great potential in treating cartilage defects clinically, especially for OA patients.     

Optimization of allograft implantation using scaffold-free chondrocyte plates

If a tissue-engineered cartilage transplant is to succeed, it needs to integrate with the host tissue, to endure physiological loading, and to acquire the phenotype of the articular cartilage. Although there are many reported treatments for osteochondral defects of articular cartilage, problems remain with the use of artificial matrices (scaffolds) and the stage of implantation. We constructed scaffold-free three-dimensional tissue-engineered cartilage allografts using a rotational culture system and investigated the optimal stage of implantation and repair of the remodeling site. We evaluated the amounts of extracellular matrix and gene expression levels in scaffold-free constructs and transplanted the constructs for osteochondral defects using a rabbit model. Allografted 2-week constructs expressed high levels of proteoglycan and collagen per DNA content, integrated with the host cartilage successfully, and were able to counter physiological loads, and the chondrocyte plate contributed reparative mesenchymal stem cells to the final phenotype of the articular cartilage.     

以羊膜为载体培养游离软骨细胞修复兔关节软骨缺损

目的：探讨膜结构为载体培养游离软骨细胞修复软骨缺损的可行性。方法：以兔羊膜为载体将体外培养的同种异体游离软骨细胞植于兔左侧股骨外踝软骨缺损区，分别于4、8、12周处死动物，整个膝关节被解剖，进行大体观察、组织学评价、电镜观察及SRY基因性别鉴定，并以兔体的右膝关节做为对照。结果：术后4、8、12周大体、组织学、电镜观察显示软骨缺损区新生了透明软骨，SRY基因性别鉴定证明新生的软骨来源于移植的同种异体软骨细胞；而对照组则仅见纤维组织样的修复组织。结论：以羊膜为载体进行同种异体软骨细胞移植能够修复关节软骨缺损。     

The use of poly(lactic-co-glycolic acid) microspheres as injectable cell carriers for cartilage regeneration in rabbit knees

The use of injectable scaffolding materials for in vivo tissue regeneration has raised great interest because it allows cell implantation through minimally invasive surgical procedures. Previously, we showed that poly(lactic-co-glycolic acid) (PLGA) microspheres can be used as an injectable scaffold to engineer cartilage in the subcutaneous space of athymic mice. The purpose of this study was to determine whether PLGA microspheres can be used as an injectable scaffold to regenerate hyaline cartilage in the osteochondral defects of rabbit knees. A full-thickness wound to the patellar groove of the articular cartilage was made in the knees of rabbits. Rabbit chondrocytes were mixed with PLGA microspheres and injected immediately into these osteochondral wounds. Both chondrocyte transplantations without PLGA microspheres and culture medium injections without chondrocytes served as controls. Sixteen weeks after implantation, chondrocytes implanted using the PLGA microspheres formed white cartilaginous tissues. Histological scores indicating the extent of the cartilaginous tissue repair and the absence of degenerative changes were significantly higher in the experimental group than in the control groups (P < 0.05). Histological analysis by a hematoxylin and eosin stain of the group transplanted with microspheres showed thicker and better-formed cartilage compared to the control groups. Alcian blue staining and Masson's trichrome staining indicated a higher content of the major extracellular matrices of cartilage, sulfated glycosaminoglycans and collagen in the group transplanted with microspheres than in the control groups. In addition, immunohistochemical analysis showed a higher content of collagen type II, the major collagen type in cartilage, in the microsphere transplanted group compared to the control groups. In the group transplanted without microspheres, the wounds were repaired with fibro-cartilaginous tissues. This study demonstrates the feasibility of using PLGA microspheres as an injectable scaffold for cartilage regeneration in a rabbit model of osteochondral wound repair.     

The use of poly(lactic-co-glycolic acid) microspheres as injectable cell carriers for cartilage regeneration in rabbit knees

The use of injectable scaffolding materials for in vivo tissue regeneration has raised great interest because it allows cell implantation through minimally invasive surgical procedures. Previously, we showed that poly(lactic-co-glycolic acid) (PLGA) microspheres can be used as an injectable scaffold to engineer cartilage in the subcutaneous space of athymic mice. The purpose of this study was to determine whether PLGA microspheres can be used as an injectable scaffold to regenerate hyaline cartilage in the osteochondral defects of rabbit knees. A full-thickness wound to the patellar groove of the articular cartilage was made in the knees of rabbits. Rabbit chondrocytes were mixed with PLGA microspheres and injected immediately into these osteochondral wounds. Both chondrocyte transplantations without PLGA microspheres and culture medium injections without chondrocytes served as controls. Sixteen weeks after implantation, chondrocytes implanted using the PLGA microspheres formed white cartilaginous tissues. Histological scores indicating the extent of the cartilaginous tissue repair and the absence of degenerative changes were significantly higher in the experimental group than in the control groups (P < 0.05). Histological analysis by a hematoxylin and eosin stain of the group transplanted with microspheres showed thicker and better-formed cartilage compared to the control groups. Alcian blue staining and Masson's trichrome staining indicated a higher content of the major extracellular matrices of cartilage, sulfated glycosaminoglycans and collagen in the group transplanted with microspheres than in the control groups. In addition, immunohistochemical analysis showed a higher content of collagen type II, the major collagen type in cartilage, in the microsphere transplanted group compared to the control groups. In the group transplanted without microspheres, the wounds were repaired with fibro-cartilaginous tissues. This study demonstrates the feasibility of using PLGA microspheres as an injectable scaffold for cartilage regeneration in a rabbit model of osteochondral wound repair.     

Repair of articular cartilage defect by cell transplantation

Full-thickness articular cartilage defects are a major clinical problem; however, at present there is no treatment that is widely accepted to regeneratively repair these lesions. The current therapeutic approach is to drill or abrade the base of the defect to expose the bone marrow with its cells and growth factors. This usually results in a repaired tissue of fibrocartilage that functions poorly in the loaded joint environment. Recently, autologous cultured chondrocyte transplantation and mosaic plasty were explored. We can repair small articular cartilage defects using these methods, although their effectiveness is still controversial. We have reported that transplantation of allogeneic chondrocytes embedded in collagen gels or allogeneic chondrocytes cultured in collagen gels could repair articular cartilage defect in a rabbit model. We also reported that autologous culture-expanded bone marrow mesenchymal cell transplantation could repair articular cartilage defect in a rabbit model. This procedure offers expedient clinical use, given that autologous bone marrow cells are easily obtained and can be culture-expanded. We transplanted autologous culture-expanded bone marrow cells into the cartilage defect of the osteoarthritic knee joint on 11 patients at the time of high tibial osteotomy. As early as 6.8 weeks after transplantation, the defect was covered with white soft tissue, in which slight metachromasia was histologically observed. Thirty-three weeks after transplantation, the repaired tissue had hardened. Histologically, repaired tissues showed stronger metachromasia and a partial hyaline cartilage-like appearance. This procedure may prove a promising method by which to repair articular cartilage defects.     

Treatment with Insulin-Like Growth Factor-1 Increases Chondrogenesis by Periosteum In Vitro

The repair of defects in articular cartilage with hyaline tissue that is resilient to wear is a challenging problem. Fibrocartilaginous tissue forms in response to injury through the articular surface and degenerates under mechanical load. Because periosteum contains cells, which are capable of synthesizing cartilage matrix proteins, it has been used to repair defects in articular surfaces. Treatment of periosteal grafts with growth factors, particularly those that elicit chondrocyte gene expression, may improve tissue regeneration. Gene expression by periosteal explants in vitro was measured. Expression of type II collagen and aggrecan mRNA was increased in response to treatment with IGF-I. Furthermore, IGF-I treatment caused an increase in type II collagen and aggrecan mRNA that was time and concentration dependent. The effect of short and long-term (continuous) incubations was compared to determine if a pretreatment could be used to condition a graft for subsequent surgical use. Short-term incubation in vitro with IGF-I followed by incubation without IGF-I was nearly as effective at increasing expression of type II collagen and aggrecan mRNA as incubation for the same length of time with IGF-I present continuously in the culture media. Treatment with IGF-I also produced cell clustering and nodule formation which are indicative of chondrogenesis. These results suggest that pretreatment with IGF-I in vitro may enhance the effectiveness of a graft to produce hyaline cartilage in vivo. Whether the cellular and molecular changes we have observed can lead to the formation of tissue that withstands the mechanical forces exerted by weight bearing remains to be determined.     

Treatment with insulin-like growth factor-1 increases chondrogenesis by periosteum in vitro

The repair of defects in articular cartilage with hyaline tissue that is resilient to wear is a challenging problem. Fibrocartilaginous tissue forms in response to injury through the articular surface and degenerates under mechanical load. Because periosteum contains cells, which are capable of synthesizing cartilage matrix proteins, it has been used to repair defects in articular surfaces. Treatment of periosteal grafts with growth factors, particularly those that elicit chondrocyte gene expression, may improve tissue regeneration. Gene expression by periosteal explants in vitro was measured. Expression of type II collagen and aggrecan mRNA was increased in response to treatment with IGF-I. Furthermore, IGF-I treatment caused an increase in type II collagen and aggrecan mRNA that was time and concentration dependent. The effect of short and long-term (continuous) incubations was compared to determine if a pretreatment could be used to condition a graft for subsequent surgical use. Short-term incubation in vitro with IGF-I followed by incubation without IGF-I was nearly as effective at increasing expression of type II collagen and aggrecan mRNA as incubation for the same length of time with IGF-I present continuously in the culture media. Treatment with IGF-I also produced cell clustering and nodule formation which are indicative of chondrogenesis. These results suggest that pretreatment with IGF-I in vitro may enhance the effectiveness of a graft to produce hyaline cartilage in vivo. Whether the cellular and molecular changes we have observed can lead to the formation of tissue that withstands the mechanical forces exerted by weight bearing remains to be determined.     

多种特殊状态下关节软骨缺损修复的组织工程技术

文题释义： 生长板：是位于儿童长骨末端的软骨组织结构,生长板中的软骨细胞可不断增生、成熟、肥大并发生骨化过程,使长骨增长。当长骨生长至一定程度,生长板软骨逐渐被成熟骨组织取代,长骨至此也停止生长。 特殊状态：文章提及的特殊状态即指关节软骨缺损的临床治疗中常见的阻碍因素,即全层软骨缺损及骨软骨缺损、生长板缺损、负重区软骨缺损、炎症状态下(骨性关节炎、风湿性关节炎)的软骨缺损。 背景：应用组织工程学技术可获得良好的关节软骨再生,但多为生理状态下小面积缺损的单纯修复。然而临床上的软骨缺损常伴随骨性关节炎、类风湿性关节炎等基础疾病,且缺损的位置、范围、深度均不确定,给软骨组织修复带来了很大挑战。 目的：总结不同位置和炎症状态下软骨缺损的修复方式。 方法：检索PubMed数据库和CNKI数据库,英文检索词为“cartilage defect regeneration,osteochondral,growth plate,weight-bearing area,inflammatory”,中文检索词为“关节软骨缺损,骨软骨,生长板,负重区,炎症”,检索建库至2019年3月发表的相关文献。共检索到相关文献209篇,按照纳入与排除标准,最终纳入86篇文献进行总结。 结果与结论：针对各种特殊状态下的关节软骨缺损,其修复目标和策略是不同的：全层软骨和骨软骨结构缺损多采用具有多层结构的支架,旨在修复软骨特有的分层结构及软骨下骨结构,同时避免新生软骨内异位骨化的问题;生长板缺损的修复关键在于避免长骨成熟后发生畸形,因此在修复支架内应添加胰岛素样生长因子、骨发生形态蛋白7等生长因子,以持续刺激生长板的修复并发挥骨生长的生理功能;负重区软骨修复则需要修复支架具有良好的力学性能,负重时不会发生严重形变及结构破坏,同时新生的软骨组织具有足够的力学强度以支撑持续的纵向压力和磨损;炎症状态下的软骨缺损则要同时治疗炎症与软骨缺损,间充质干细胞的引入可同时发挥免疫调节及组织再生功能,以使疾病达到彻底治疗的目标。ORCID: 0000-0001-9443-8158(陈劲松) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

The synergistic effects of microfracture, perforated decalcified cortical bone matrix and adenovirus-bone morphogenetic protein-4 in cartilage defect repair

We reported a technique for articular cartilage repair, consisting of microfracture, a biomaterial scaffold of perforated decalcified cortical bone matrix (DCBM) and adenovirus-bone morphogenetic protein-4 (Ad-BMP4) gene therapy. In the present study, we evaluated its effects on the quality and quantity for induction of articular cartilage regeneration. Full-thickness defects were created in the articular cartilage of the trochlear groove of rabbits. Four groups were assigned: Ad-BMP4/perforated DCBM composite (group I); perforated DCBM alone without Ad-BMP4 (group II); DCBM without perforated (group III) and microfracture alone (group IV). Animals were sacrificed 6, 12 and 24 weeks postoperation. The harvested tissues were analyzed by magnetic resonance image, scanning electron microscope, histological examination and immunohistochemistry. Group I showed vigorous and rapid repair leading to regeneration of hyaline articular cartilage at 6 weeks and to complete repair of articular cartilage and subchondral bone at 12 weeks. Groups II and III completely repaired the defect with hyaline cartilage at 24 weeks, but group II was more rapid than group III in the regeneration of repair tissue. In group IV the defects were concave and filled with fibrous tissue at 24 weeks. These findings demonstrated that this composite biotechnology can rapidly repair large areas of cartilage defect with regeneration of native hyaline articular cartilage.     

组织工程化软骨细胞和骨髓间充质干细胞用于修复同种异体关节软骨缺损

背景：关节软骨几乎没有自身修复的能力,目前临床大多采用自体或异体软骨移植修复、软骨膜或骨膜移植修复、软骨细胞移植修复。由于自体软骨来源有限,异体软骨又存在慢性免疫排斥反应,最终可能导致预后不佳;软骨膜或骨膜移植修复的软骨易于退化,导致修复效果不佳。 目的：总结组织工程化软骨细胞、骨髓间充质干细胞及两者共培养对同种异体软骨缺损修复作用的研究现状。 方法：应用计算机检索PubMed 数据库及中国期刊网全文数据库1994-01/2012-01有关组织工程化软骨细胞和骨髓间充质干细胞用于修复同种异体关节软骨缺损方面的文章,英文检索词为“cartilage defect,allograft,chondrocyte,mesenchymal stem cells,bone marrow mesenchymal stem cells”,中文检索词为“软骨缺损,同种异体移植,软骨细胞,骨髓间充质干细胞”。排除重复性及非中英文语种研究,共保留35篇文献进行综述。 结果与结论：随着体外细胞培养方法的不断改进,现已能够把软骨细胞从坚韧的软骨中分离出来,并获得大量高纯度的软骨细胞并繁殖出新生软骨细胞。软骨细胞培养增殖能力低,传代培养容易引起老化和去分化;而成体骨髓中骨髓间充质干细胞含量少,随传代次数的增多成软骨潜能明显降低。骨髓间充质干细胞和软骨细胞共培养,两种细胞相互促进增殖和分化,作为种子细胞可减少软骨细胞增殖传代次数并节省软骨细胞数量,与组织工程支架材料复合能有效修复关节软骨缺损。     

Lack of oxygen in articular cartilage: consequences for chondrocyte biology

Controlling the chondrocytes phenotype remains a major issue for cartilage repair strategies. These cells are crucial for the biomechanical properties and cartilage integrity because they are responsible of the secretion of a specific matrix. But chondrocyte dedifferentiation is frequently observed in cartilage pathology as well as in tissue culture, making their study more difficult. Given that normal articular cartilage is hypoxic, chondrocytes have a specific and adapted response to low oxygen environment. While huge progress has been performed on deciphering intracellular hypoxia signalling the last few years, nothing was known about the particular case of the chondrocyte biology in response to hypoxia. Recent findings in this growing field showed crucial influence of the hypoxia signalling on chondrocytes physiology and raised new potential targets to repair cartilage and maintain tissue integrity. This review will thus focus on describing hypoxia‐mediated chondrocyte function in the native articular cartilage.     

Clinical potential and challenges of using genetically modified cells for articular cartilage repair

Articular cartilage defects do not regenerate. Transplantation of autologous articular chondrocytes, which is clinically being performed since several decades, laid the foundation for the transplantation of genetically modified cells, which may serve the dual role of providing a cell population capable of chondrogenesis and an additional stimulus for targeted articular cartilage repair. Experimental data generated so far have shown that genetically modified articular chondrocytes and mesenchymal stem cells (MSC) allow for sustained transgene expression when transplanted into articular cartilage defects in vivo. Overexpression of therapeutic factors enhances the structural features of the cartilaginous repair tissue. Combined overexpression of genes with complementary mechanisms of action is also feasible, holding promises for further enhancement of articular cartilage repair. Significant benefits have been also observed in preclinical animal models that are, in principle, more appropriate to the clinical situation. Finally, there is convincing proof of concept based on a phase I clinical gene therapy study in which transduced fibroblasts were injected into the metacarpophalangeal joints of patients without adverse events. To realize the full clinical potential of this approach, issues that need to be addressed include its safety, the choice of the ideal gene vector system allowing for a long-term transgene expression, the identification of the optimal therapeutic gene(s), the transplantation without or with supportive biomaterials, and the establishment of the optimal dose of modified cells. As safe techniques for generating genetically engineered articular chondrocytes and MSCs are available, they may eventually represent new avenues for improved cell-based therapies for articular cartilage repair. This, in turn, may provide an important step toward the unanswered question of articular cartilage regeneration.     

In vivo cultivation of human articular chondrocytes in a nude mouse-based contained defect organ culture model

The nude mouse model is an established method to cultivate and investigate tissue engineered cartilage analogues under in vivo conditions. One limitation of this common approach is the lack of appropriate surrounding articular tissues. Thus the bonding capacity of cartilage repair tissue cannot be evaluated. Widely applied surgical techniques in cartilage repair such as conventional and three-dimensional autologous chondrocyte implantation (ACI) based on a collagen gel matrix cannot be included into nude mouse studies, since their application require a contained defect. The aim of this study is to apply an organ culture defect model for the in vivo cultivation of different cell-matrix-constructs.Cartilage defects were created on osteochondral specimens which had been harvested from 10 human knee joints during total knee replacement. Autologous chondrocytes were isolated from the cartilage samples and cultivated in monolayer until passage 2. On each osteochondral block defects were treated either by conventional ACI or a collagen gel seeded with autologous chondrocytes, including a defect left empty as a control. The samples were implanted into the subcutaneous pouches of nude mice and cultivated for six weeks. After retrieval, the specimens were examined histologically, immunohistochemically and by cell morphology quantification.In both, ACI and collagen gel based defect treatment, a repair tissue was formed, which filled the defect and bonded to the adjacent tissues. The repair tissue was immature with low production of collagen type II. In both groups redifferentiation of chondrocytes remained incomplete. Different appearances of interface zones between the repair tissue and the adjacent cartilage were found.The presented contained defect organ culture model offers the possibility to directly compare different types of clinically applied biologic cartilage repair techniques using human articular tissues in a nude mouse model.     

组织工程支架材料修复关节软骨缺损

BACKGROUND: Articular cartilage repair has been a difficulty in the clinical setting, which is mainly treated with autologous or allogeneic osteochondral grafts, and cartilage periosteum or periosteum grafts. However, the limited source, secondary lesion and immunological rejection force some researchers to search for a novel treatment strategy, cartilage tissue engineering, that is of great significance for cartilage regeneration and repair. OBJECTIVE: To investigate the tissue-engineered scaffolds for the repair of articular cartilage defects. METHODS: The first author searched the PubMed and WanFang databases for the articles addressing tissue-engineered cartilage for articular cartilage defects published between 1991 and 2015 using the keywords “articular cartilage defect, scaffold, tissue engineered cartilage” in English and Chinese, respectively. The irrelative and repetitive literatures were excluded. RESULTS AND CONCLUSION: Finally 48 eligible literatures were enrolled based on the inclusion and exclusion criteria. Cartilage tissue engineering possesses the advantages of controllability, little damage to tissue itself, and biological repair of injured cartilage. Tissue-engineered scaffold material is a critical factor in tissue engineering construction; therefore, it should hold biodegradability and histocompatibility. The commonly used scaffold materials include natural macromolecule materials (collagen, silk fibroin and chitosan), and synthetic polymer materials (polylactic acid and tricalcium phosphate). It is necessary to prepare composite scaffolds with high bioactivity integrate advantages of each material. The tissue engineering is bound to be a hotspot in the field of articular cartilage repair.      

间充质干细胞向软骨分化及在软骨修复中应用的研究进展

关节软骨是一种负重结缔组织,常因肿瘤、运动、退行性变或老年性疾病造成损伤;然而关节软骨自身修复能力有限,给临床治愈软骨缺损造成了很大困难.近些年出现了多种治疗软骨缺损的方法,包括自体软骨细胞移植、微裂缝和镶嵌成形术,但这些方法各自都有其局限性.近年来,组织工程软骨成为软骨修复研究的新热点,间充质干细胞（MSCs）是其当前最有前景的种子细胞.就MSCs在体外诱导分化为软骨细胞的培养条件及MSCs在软骨修复中应用的研究进展进行综述.     

Repair of articular cartilage defect with layered chondrocyte sheets and cultured synovial cells

In this study, we investigate the effects of treatment with layered chondrocyte sheets and synovial cell transplantation. An osteochondral defect was created of 48 Japanese white rabbits. In order to determine the effects of treatment, the following 6 groups were produced: (A) synovial cells (1.8 × 10(6) cells), (B)layered chondrocyte sheets (1.7 × 10(6) cells), (C) synovial cells (3.0 × 10(5) cells) + layered chondrocyte sheets, (D)synovial cells (6.0 × 10(5) cells) + layered chondrocyte sheets, (E)synovial cells (1.2 × 10(6) cells) + layered chondrocyte sheets, (F) osteochondral defect. Layered chondrocyte sheets and synovial cells were transplanted, sacrificed four and 12 weeks postoperatively. An incapacitance tester (Linton) was used to find trends in the weight distribution ratio of the damaged limbs after surgery. Sections were stained with Safranin-O. Repair sites were evaluated using ICRS grading system. In groups (A) to (E), the damaged limb weight distribution ratio had improved. The repair tissue stained positively with Safranin-O. Four and 12 weeks after surgery, groups (A) to (E) exhibited significantly higher scores than group (F), and groups (D) and (E) exhibited significantly higher scores than groups (A) and (B). This suggests the efficacy of combining layered chondrocyte sheets with synovial cells.     

Repair of osteochondral defects in rabbits with ectopically produced cartilage

Cartilage has poor regenerative capacity. Donor site morbidity and interference with joint homeostasis should be considered when applying the autologous chondrocyte transplantation technique. The use of ectopically produced cartilage, derived from periosteum, might be a novel method to heal cartilage defects. Ectopic cartilage was produced by dissecting a piece of periosteum from the tibia of rabbits. After 14 days the reactive tissue at the dissection site was harvested and a graft was cored out and press-fit implanted in an osteochondral defect in the medial condyle of the femur with or without addition of hyaluronan. After 3 weeks and 3 months the repair reaction was evaluated by histology. Thionine- and collagen type II-stained sections were evaluated for graft viability, ingrowth of the graft, and joint surface repair. Empty defects remained empty 3 weeks after implantation, ectopic cartilage filled the defect to the level of the surrounding cartilage. Histologically, the grafts were viable, consisting mainly of cartilage, and showed a variable pattern of ingrowth. Three months after implantation empty defects with or without hyaluronan were filled primarily with fibrocartilaginous tissue. Defects treated with ectopic cartilage contained mixtures of fibrocartilaginous and hyaline cartilage. Sometimes a tidemark was observed in the new articular cartilage and the orientation of the cells resembled that of healthy articular cartilage. Subchondral bone repair was excellent. The modified O'Driscoll scores for empty defects without and with hyaluronan were 12.7 +/- 6.4 and 15.3 +/- 3.2; for treated defects scores were better (15.4 +/- 3.9 and 18.2 +/- 2.9). In this conceptual study the use of ectopic cartilage derived from periosteum appears to be a promising novel method for joint surface repair in rabbits.     

Phenotypic Variations in Chondrocyte Subpopulations and Their Response to <Emphasis Type="Italic">In Vitro</Emphasis> Culture and External Stimuli

Articular cartilage defects have limited capacity to self-repair, and cost society up to 60 billion dollars annually in both medical treatments and loss of working days. Recent developments in cartilage tissue engineering have resulted in many new products coming to market or entering clinical trials. However, there is a distinct lack of treatments which aim to recreate the complex zonal organization of articular cartilage. Cartilage tissue withstands repetitive strains throughout an individual’s lifetime and provides frictionless movement between joints. The structure and composition of its intricately organized extracellular matrix varies with tissue depth to provide optimal resistance to loading, ensure ease of movement, and integrate with the subchondral bone. Each tissue zone is specially designed to resist the load it experiences, and maximize the tissue properties needed for its location. It is unlikely that a homogenous solution to tissue repair will be able to optimally restore the function of such a heterogeneous tissue. For zonal engineering of articular cartilage to become practical, maintenance of phenotypically stable zonal cell populations must be achieved. The chondrocyte phenotype varies considerably by zone, and it is the activity of these cells that help achieve the structural organization of the tissue. This review provides an examination of literature which has studied variations in cellular phenotype between cartilage zones. By doing so, we have identified critical differences between cell populations and highlighted areas of research which show potential in the field. Current research has made the morphological and metabolic variations between these cell populations clear, but an ideal way of maintaining these differences in vitro culture is yet to be established. Combinations of delivered growth factors, mechanical loading, and layered three-dimensional culture systems all show potential for achieving this goal. Furthermore, differentiation of progenitor cell populations into chondrocyte subpopulations may also hold promise for achieving large numbers of zonal chondrocytes. Success of the field lies in establishing methods of retaining phenotypically stable cell populations for in vitro culture.