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.     

Poly(lactic-co-glycolic acid) microspheres as an injectable scaffold for cartilage tissue engineering

Injectable scaffold has raised great interest for tissue regeneration in vivo, because it allows easy filling of irregularly shaped defects and the implantation of cells through minimally invasive surgical procedures. In this study, we evaluated poly(lactic-co-glycolic acid) (PLGA) microsphere as an injectable scaffold for in vivo cartilage tissue engineering. PLGA microspheres (30-80 microm in diameter) were injectable through various gauges of needles, as the microspheres did not obstruct the needles and microsphere size exclusion was not observed at injection. The culture of chondrocytes on PLGA microspheres in vitro showed that the microspheres were permissive for chondrocyte adhesion to the microsphere surface. Rabbit chondrocytes were mixed with PLGA microspheres and injected immediately into athymic mouse subcutaneous sites. Chondrocyte transplantation without PLGA microspheres and PLGA microsphere implantation without chondrocytes served as controls. Four and 9 weeks after implantation, chondrocytes implanted with PLGA microspheres formed solid, white cartilaginous tissues, whereas no gross evidence of cartilage tissue formation was noted in the control groups. Histological analysis of the implants by hematoxylin and eosin staining showed mature and well-formed cartilage. Alcian blue/safranin O staining and Masson's trichrome staining indicated the presence of highly sulfated glycosaminoglycans and collagen, respectively, both of which are the major extracellular matrices of cartilage. Immunohistochemical analysis showed that the collagen was mainly type II, the major collagen type in cartilage. This study demonstrates the feasibility of using PLGA microspheres as an injectable scaffold for in vivo cartilage tissue engineering. This scaffold may be useful to regenerate cartilaginous tissues through minimally invasive surgical procedures in orthopedic, maxillofacial, and urologic applications.     

Histological and biomechanical properties of regenerated articular cartilage using chondrogenic bone marrow stromal cells with a PLGA scaffold in vivo

The properties of regenerated cartilage using bone marrow-derived mesenchymal stem cells (MSCs) and poly lactic-co-glycolic acid (PLGA) scaffold composites pretreated with TGF-beta3 were investigated and compared to the non-TGF-beta3 treated MSCs/PLGA composites in a rabbit model. We prepared MSCs/PLGA scaffold composites and pretreated it with TGF-beta3 for 3 weeks prior to transplantation. Then, composites were transplanted to the osteochondral defect in the rabbit knee. After 12 weeks of transplantation, 10 of the 12 rabbits in which TGF-beta3 pretreated MSCs/PLGA scaffold composites were transplanted showed cartilaginous regeneration. In gross morphology, regenerated cartilage showed smooth, flush, and transparent features. In indentation test, this had about 80% of Young's modulus of normal articular cartilage. Histological examination demonstrated hyaline like cartilage structures with glycosaminoglycan and type II collagen expression. Histological scores were not statistically different to the normal articular cartilage. These results showed improvement of cartilage regeneration compared to the non-TGF-beta3 pretreated MSCs/PLGA scaffold composite transplanted group. Thus, we have successfully regenerated improved hyaline-like cartilage and determined the feasibility of treating damaged articular cartilage using MSCs/PLGA scaffold composite pretreated with TGF-beta3. Also, we suggest this treatment modality as another concept of cartilage tissue engineering.     

羟基丁酸-羟基辛酸共聚体/胶原骨软骨一体化支架修复膝关节软骨损伤

BACKGROUND: Due to the complex physiological characteristics of the osteochondral tissue, the clinical repair of knee cartilage injury often has dissatisfied outcomes. Tissue engineering methods and tools provide a new idea for osteochondral repair. OBJECTIVE: To observe the effect of poly(hydroxybutyrate-co-hydroxyoctanoate/collagen) osteochondral tissue-engineered scaffold on the repair of articular cartilage injury in a rabbit. METHODS: The poly(hydroxybutyrate-co-hydroxyoctanoate/collagen) osteochondral tissue-engineered scaffold was prepared by solvent casting/particle leaching method. Then, seed cells were isolated and cultured on the scaffold. Twenty-four healthy New Zealand white rabbits, 4 weeks of age, were used for the study. Under balanced anesthesia, an articular cartilage defect (4.5 mm in diameter, 5 mm in depth) was created on the rabbit’s femoral condyle using a bone drill. After modeling, rabbits were randomized into three groups and given direct suture in blank group, pure scaffold implantation in control group and implantation of the scaffold-cell complex in experimental group. Femoral condyle of each rabbit was taken out for gross and histological observations at 8, 20 weeks after surgery. RESULTS AND CONCLUSION: At 8 weeks after surgery, transparent film-covered defects and small/irregular cells were found in the experimental group; the defects were filled with fibrous tissues in the control group; while there was no repair in the blank group. Until the 20th week, the defects were covered with hyaline cartilage-like tissues, accompanied by regular cell arrangement in the experimental group; in the control group, the defects were covered with white membranous tissues, and many chondrocytes were found at the basement and edge; in the blank group, some newborn tissues were visible at the defect region. These findings suggest that the poly (hydroxybutyrate-co- hydroxyoctanoate/collagen) osteochondral tissue-engineered scaffold carrying seed cells contributes to articular cartilage repair.     

Apatite-coated poly(lactic-co-glycolic acid) microspheres as an injectable scaffold for bone tissue engineering

Biodegradable polymer/ceramic composite scaffold could overcome limitations of biodegradable polymers or ceramics for bone regeneration. Injectable scaffold has raised great interest for bone regeneration in vivo, since it allows one for easy filling of irregularly shaped bone defects and implantation of osteogenic cells through minimally invasive surgical procedures The purpose of this study was to determine whether apatite-coated poly(lactic-co-glycolic acid) (PLGA) microspheres could be used as an injectable scaffold to regenerate bone in vivo. Apatite-coated PLGA microspheres were fabricated by incubating PLGA microspheres in simulated body fluid. The apatite that coated the PLGA microsphere surfaces was similar to apatite in natural bone, as demonstrated by scanning electron microscopy, X-ray diffraction spectra, energy-dispersive spectroscopy, and Fourier transformed-infrared spectroscopy analyses. Rat osteoblasts were mixed with apatite-coated PLGA microspheres and injected immediately into subcutaneous sites of athymic mice. Osteoblast transplantation with plain PLGA microspheres served as a control. Histological analysis of the implants at 6 weeks with hematoxylin and eosin staining, Masson's trichrome staining, and von Kossa staining revealed much better regeneration of bone in the apatite-coated PLGA microsphere group than the plain PLGA microsphere group. The new bone formation area and the calcium content of the implants were significantly higher in the apatite-coated PLGA microsphere group than in the plain PLGA microsphere group. This study demonstrates the feasibility of using apatite-coated PLGA microspheres as an injectable scaffold for in vivo bone tissue engineering. This scaffold may be useful for bone regeneration through minimally invasive surgical procedures in orthopedic applications.     

Novel composite hyaluronan/type I collagen/fibrin scaffold enhances repair of osteochondral defect in rabbit knee

A new composite scaffold containing type I collagen, hyaluronan, and fibrin was prepared with and without autologous chondrocytes and implanted into a rabbit femoral trochlea. The biophysical properties of the composite scaffold were similar to native cartilage. The macroscopic, histological, and immunohistochemical analysis of the regenerated tissue from cell-seeded scaffolds was performed 6 weeks after the implantation and predominantly showed formation of hyaline cartilage accompanied by production of glycosaminoglycans and type II collagen with minor fibro-cartilage production. Implanted scaffolds without cells healed predominantly as fibro-cartilage, although glycosaminoglycans and type II collagen, which form hyaline cartilage, were also observed. On the other hand, fibro-cartilage or fibrous tissue or both were only formed in the defects without scaffold. The new composite scaffold containing collagen type I, hyaluronan, and fibrin, seeded with autologous chondrocytes and implanted into rabbit femoral trochlea, was found to be highly effective in cartilage repair after only 6 weeks. The new composite scaffold can therefore enhance cartilage regeneration of osteochondral defects, by the supporting of the hyaline cartilage formation.     

Autologous chondrocyte implantation with collagen bioscaffold for the treatment of osteochondral defects in rabbits

Osteochondral injury is therapeutically irreversible within current treatment parameters. Autologous chondrocyte implantation (ACI) promises to regenerate hyaline articular cartilage, but conventional ACI is plagued by complications determined by periosteal grafting. Here we propose the utilization of collagen membrane in ACI as an effective bioscaffold for the regeneration of osteochondral lesions. Using a rabbit model of osteochondral injury, we have inoculated autologous chondrocytes onto a type I/III collagen scaffold [so-called matrix-induced ACI (MACI)] and implanted into 3-mm osteochondral knee defects. All untreated defect histology showed inferior fibrocartilage and/or fibrous tissue repair. In our time-course study, ACI with type I/III collagen membrane regenerated cartilage with healthy osteochondral architecture in osteochondral defects at 6 weeks. At 12 weeks, articular cartilage regeneration was maintained, with reduced thickness and proteoglycan compared with the adjacent cartilage. Both 6-week (p < 0.01) and 12-week (p < 0.05) ACI with collagen membrane showed significant improvement as compared with untreated controls. To further examine the efficacy of cartilage regeneration by ACI, we conducted a dose-response study, using chondrocytes at various cell densities between 10(4) and 10(6) cells/cm(2). The results showed that cell density had no effect on outcome histology, but all cell densities were significantly better than untreated controls (p < 0.01) and cell-free collagen membrane treatment (p < 0.05). In short, our data suggest that autologous chondrocyte-seeded type I/III collagen membrane is an effective method for the treatment of focal osteochondral knee injury in rabbits.     

Bioactive Stratified Polymer Ceramic-Hydrogel Scaffold for Integrative Osteochondral Repair

Due to the intrinsically poor repair potential of articular cartilage, injuries to this soft tissue do not heal and require clinical intervention. Tissue engineered osteochondral grafts offer a promising alternative for cartilage repair. The functionality and integration potential of these grafts can be further improved by the regeneration of a stable calcified cartilage interface. This study focuses on the design and optimization of a stratified osteochondral graft with biomimetic multi-tissue regions, including a pre-designed and pre-integrated interface region. Specifically, the scaffold based on agarose hydrogel and composite microspheres of polylactide-co-glycolide (PLGA) and 45S5 bioactive glass (BG) was fabricated and optimized for chondrocyte density and microsphere composition. It was observed that the stratified scaffold supported the region-specific co-culture of chondrocytes and osteoblasts which can lead to the production of three distinct yet continuous regions of cartilage, calcified cartilage and bone-like matrices. Moreover, higher cell density enhanced chondrogenesis and improved graft mechanical property over time. The PLGA-BG phase promoted chondrocyte mineralization potential and is required for the formation of a calcified interface and bone regions on the osteochondral graft. These results demonstrate the potential of the stratified scaffold for integrative cartilage repair and future studies will focus on scaffold optimization and in vivo evaluations.     

同种异体和异种来源骨髓间充质干细胞诱导成软骨修复喉软骨缺损

BACKGROUND: Because chondrocytes have no regeneration ability, to select suitable seed cells is the primary problem to repair cartilage defects. OBJECTIVE: To investigate the effect of allogeneic versus heterologous bone marrow mesenchymal stem cells (BMSCs) in repairing laryngeal cartilage defects after chondrogenic induction. METHODS: BMSCs from human and rabbits were isolated and cultured. Passage 3 cells were cultured in chondrogenic induction medium containing transforming transforming growth factor beta 1 and bone morphogenetic protein, and then were dropped onto a poly(lactic-co-glycolic acid) (PLGA) scaffold. Thirty New Zealand rabbits were randomly assigned into three groups: blank control group, human BMSCs group, rabbit BMSCs group. Animal models of laryngeal cartilage defects were made in the three groups. After modeling, saline-soaked PLGA scaffold, PLAG scaffold with human BMSCs or with rabbit BMSCs were implanted respectively into the rabbits in the normal blank, human BMSCs and rabbit BMSCs groups. The expression of type II collagen in the larynx and its surrounding tissues was detected by immunohistochemistry at 4 and 8 weeks postoperatively. RESULTS AND CONCLUSION: The animals in each group breathed normally with no presence of wheezing, and their eating and activity were good. Moreover, there was no purulency or infection in the three groups. At 4 and 8 weeks after operation, the positive rates of type II collagen in the two BMSCs groups were significantly higher than that in the blank control group (P < 0.05). There was no significant difference between two BMSCs groups (P > 0.05). These results show that both allogeneic and heterologous BMSCs have good therapeutic effects on the repair of laryngeal cartilage defects in rabbits.      

Transplantation of chondrocytes seeded on collagen-based scaffold in cartilage defects in rabbits

Recent success in tissue engineering by restoring cartilage defects by transplanting autologous chondrocyte cells on a three-dimensional scaffold has prompted the improvement of this therapeutic strategy. Here we describe a new approach investigating the healing of rabbit cartilage by means of autologous chondrocytes seeded on a biomaterial made of an equine collagen type I-based scaffold. Full-thickness defects were created bilaterally in the weight-bearing surface of the medial femoral condyle of both femora of New Zealand male rabbits. The wounds were then repaired by using both chondrocytes seeded on the biomaterial and biomaterial alone. Controls were similarly treated but received either no treatment or implants of the delivery substance. Histological examination of the reconstructed tissues at 1, 3, 6, and 12 months after transplantation showed that at 1 and 3 months there was no formation of reconstructed tissue in any of the groups evaluated; after 6 months there was evidence of a newly regenerated tissue with some fibrocartilaginous features only in the group treated with biomaterial-seeded cells, and at 12 months a more organized tissue was evident in the same group. With regards to the group transplanted with biomaterial alone and the untreated control group, there was no evidence of new tissue production. These results advocate the use of this collagen-based scaffold for further in vivo studies on large size animals and, finally, in human clinical trials for the treatment of knee cartilage defects.     

The combined effects of continuous passive motion treatment and acellular PLGA implants on osteochondral regeneration in the rabbit

We investigated the active role of clinical rehabilitation in osteochondral regeneration using continuous passive motion (CPM) treatment together with acellular PLGA implants. CPM treatment was performed and compared with immobilization (Imm) treatment and intermittent active motion (IAM) treatment upon full-thickness osteochondral defects either with or without an PLGA implant in the PI (PLGA-implanted) and ED (empty defect) models. The PI and ED tests were performed in 38 rabbits for 4 and 12 weeks. At the end of testing, the PI-CPM group had the best regeneration with nearly normal articular surfaces and no joint contracture or inflammatory reaction. In contrast, degenerated joints, abrasion cartilage surfaces and synovitis were observed in the Imm and IAM groups. The achieved bone volume/tissue volume (BV/TV) ratio, which was measured using micro-CT, was significantly higher in the CPM group compared with the Imm and IAM groups; in particular, the performance of the PI-CPM group exceeds that of the ED-CPM group. The thickness of the trabecular (subchondral) bone was visibly increased in all of the groups from 4 through 12 weeks of testing. However, a histological analysis revealed differences in cartilage regeneration. At week 4, compared with the ED samples, all of the PI groups exhibited better collagen alignment and higher GAG content in the core of their repaired tissues, particularly in the PI-CPM group. At week 12, sound osteochondral repair and hyaline cartilaginous regeneration was observed in the PI-CPM group, and this was marked by type II collagen expression, osteocyte maturation, and trabecular boney deposition. In contrast, the PI-Imm and PI-IAM groups exhibited fibrocartilaginous tissues that had modest GAG content. In summary, this study demonstrates that early CPM treatment together with acellular PLGA implantation has significant positive effects on osteochondral regeneration in rabbit knee joint models.     

羟基乙酸负载软骨细胞组织工程软骨修复喉软骨缺损

BACKGROUND: A three-dimensional biodegradable scaffold is important for tissue-engineered cartilage construction, and it that can provide conditions for cell attachment and proliferation. OBJECTIVE: To observe the treatment outcomes of glycolic acid loaded with chondrocytes in laryngeal cartilage repair. METHODS: Sixty New Zealand white rabbits were enrolled and randomly divided into control and experimental groups. Laryngeal cartilage defect models were established in each group, followed by implanted with glycolic acid loaded with chondrocytes and glycolic acid, respectively. Gross and histological observations were conducted at 4 and 8 weeks after implantation. RESULTS AND CONCLUSION: Gross observation showed that at 4 weeks after implantation, a deep red wound with an obvious boundary was seen in the control group; the dark red and smooth defect parallel to the surrounding tissue was found in the experimental group. Toluidine blue staining revealed that at 8 weeks after implantation, the laryngeal defect site showed no obvious inflammation and cartilage collapse, with numerous newly-formed chondrocytes in the experimental group; in contrast, mild inflammation and cartilage collapse were found in the defect region of the control group, and few newly-formed chondrocytes appeared. The positive areas of glycosaminoglycan and type II collagen in the experimental group were significantly larger than those in the control group at 4 and 8 weeks after implantation (P < 0.05). These results indicate that glycolic acid loaded with chondrocytes contributes to the repair of laryngeal cartilage defects.     

Radially oriented collagen scaffold with SDF-1 promotes osteochondral repair by facilitating cell homing

The migration of cells from the side and the bottom of the defect is important in osteochondral defect healing. Here, we designed a novel collagen scaffold that possessed channels in both the horizontal and the vertical directions, along with stromal cell-derived factor-1 (SDF-1) to enhance osteochondral regeneration by facilitating cell homing. Firstly we fabricated the radially oriented and random collagen scaffolds, then tested their properties. The radially oriented collagen scaffold had better mechanical properties than the random scaffold, but both supported cell proliferation well. Then we measured the migration of BMSCs in the scaffolds in vitro. The radially oriented collagen scaffold effectively promoted their migration, and this effect was further facilitated by addition of SDF-1. Moreover, we created osteochondral defects in rabbits, and implanted them with random or oriented collagen scaffolds with or without SDF-1, and evaluated cartilage and subchondral bone regeneration at 6 and 12 weeks after surgery. Cartilage regeneration with both the radially oriented scaffold and SDF-1 effectively promoted repair of the cartilage defect. Our results confirmed that the implantation of the radially oriented channel collagen scaffold with SDF-1 could be a promising strategy for osteochondral repair.     

The use of de-differentiated chondrocytes delivered by a heparin-based hydrogel to regenerate cartilage in partial-thickness defects

Partial-thickness cartilage defects, with no subchondral bone injury, do not repair spontaneously, thus there is no clinically effective treatment for these lesions. Although the autologous chondrocyte transplantation (ACT) is one of the promising approaches for cartilage repair, it requires in vitro cell expansion to get sufficient cells, but chondrocytes lose their chondrogenic phenotype during expansion by monolayer culture, leading to de-differentiation. In this study, a heparin-based hydrogel was evaluated and optimized to induce cartilage regeneration with de-differentiated chondrocytes. First, re-differentiation of de-differentiated chondrocytes encapsulated in heparin-based hydrogels was characterized in vitro with various polymer concentrations (from 3 to 20 wt.%). Even under a normal cell culture condition (no growth factors or chondrogenic components), efficient re-differentiation of cells was observed with the optimum at 10 wt.% hydrogel, showing the complete re-differentiation within a week. Efficient re-differentiation and cartilage formation of de-differentiated cell/hydrogel construct were also confirmed in vivo by subcutaneous implantation on the back of nude mice. Finally, excellent cartilage regeneration and good integration with surrounding, similar to natural cartilage, was also observed by delivering de-differentiated chondrocytes using the heparin-based hydrogel in partial-thickness defects of rabbit knees whereas no healing was observed for the control defects. These results demonstrate that the heparin-based hydrogel is very efficient for re-differentiation of expanded chondrocytes and cartilage regeneration without using any exogenous inducing factors, thus it could serve as an injectable cell-carrier and scaffold for cartilage repair. Excellent chondrogenic nature of the heparin-based hydrogel might be associated with the hydrogel characteristic that can secure endogenous growth factors secreted from chondrocytes, which then can promote the chondrogenesis, as suggested by the detection of TGF-β1 in both in vitro and in vivo cell/hydrogel constructs.     

Bi-layer collagen/microporous electrospun nanofiber scaffold improves the osteochondral regeneration

An optimal scaffold is crucial for osteochondral regeneration. Collagen and electrospun nanofibers have been demonstrated to facilitate cartilage and bone regeneration, respectively. However, the effect of combining collagen and electrospun nanofibers on osteochondral regeneration has yet to be evaluated. Here, we report that the combination of collagen and electrospun poly-l-lactic acid nanofibers synergistically promotes osteochondral regeneration. We first fabricated bi-layer microporous scaffold with collagen and electrospun poly-l-lactic acid nanofibers (COL-nanofiber). Mesenchymal stem cells were cultured on the bi-layer scaffold and their adhesion, proliferation and differentiation were examined. Moreover, osteochondral defects were created in rabbits and implanted with COL-nanofiber scaffold. Cartilage and subchondral bone regeneration were evaluated at 6 and 12 weeks after surgery. Compared with COL scaffold, cells on COL-nanofiber scaffold exhibited more robust osteogenic differentiation, indicated by higher expression levels of OCN and runx2 genes as well as the accumulation of calcium nodules. Furthermore, implantation of COL-nanofiber scaffold seeded with cells induced more rapid subchondral bone emergence, and better cartilage formation, which led to better functional repair of osteochondral defects as manifested by histological staining, biomechanical test and micro-computed tomography data. Our study underscores the potential of using the bi-layer microporous COL-nanofiber scaffold for the treatment of deep osteochondral defects.     

Use of a biphasic graft constructed with chondrocytes overlying a beta-tricalcium phosphate block in the treatment of rabbit osteochondral defects

To evaluate the ability of a biphasic construct to repair osteochondral defects in articular cartilage, plugs made of chondrocytes in collagen gel overlying a resorbable porous beta-tricalcium phosphate (TCP) block were implanted into defects in rabbit knees. The repair tissue was evaluated at 8, 12, and 30 weeks. Eight weeks after implantation of the biphasic construct, histologic examination showed hyaline-like cartilage formation that was positive for safranin O and type II collagen. At 12 weeks, most of the beta-TCP was replaced by bone, with a small amount remaining in the underlying cartilage. In the cell-seeded layer, the newly formed middle and deep cartilage adjacent to the subchondral bone stained with safranin O, but no staining was observed in the superficial layer. In addition, cell morphology was distinctly different from the deep levels of the reparative cartilage, with hypertrophic cells at the bottom of the cartilaginous layer. At 30 weeks, beta-TCP had completely resorbed and a tidemark was observed in some areas. In contrast, controls (defects filled with a beta-TCP block alone) showed no cartilage formation but instead had subchondral bone formation. These findings indicate that beta-TCP-supported chondrocytes in collagen gel can partially repair isolated articular cartilage osteochondral defects.     

Highly open porous biodegradable microcarriers: in vitro cultivation of chondrocytes for injectable delivery

Injectable cell therapy would provide a patient-friendly procedure for treatment of degenerated or wounded tissue. Biodegradable injectable porous microspheres were fabricated to use as dual-purpose microcarriers for cell culture and injectable scaffold for tissue regeneration. Gas foaming in a water-in-oil-in-water double emulsion was performed for fabricating the well-interconnected porous microcarriers using poly(lactic-co-glycolic acid) (PLGA). The gas foaming conditions were finely tuned to control the structural and morphological characteristics. Porous microcarriers with a mean size of approximately 175 microm and an average pore diameter of approximately 29 microm were produced for cell cultivation and injectable delivery. To promote cell seeding, amine-functionalized porous microcarriers were prepared by blending amine-functionalized PLGA with unreacted PLGA. To assess the porous microcarriers for chondrocyte cultivation, bovine articular chondrocytes were seeded and cultured in vitro in spinner flasks for 4 weeks. Visualization and biochemical analyses of the microcarrier-cell constructs were performed to demonstrate cell proliferation and phenotypic expression. Quantification of deoxyribonucleic acid, glycosaminoglycan, and collagen content showed that much greater cell proliferation and expression of cartilage-specific phenotype were observed for cultures in the following order: amine-functionalized porous microcarriers, porous microcarriers, nonporous microcarriers, and monolayer culture.     

Cartilage regeneration using mesenchymal stem cells and a three-dimensional poly-lactic-glycolic acid (PLGA) scaffold

Cartilage engineered from mesenchymal stem cells (MSCs) requires a scaffold to keep the cells in the cartilage defect and to act as a support for inducing hyaline cartilage formation. We developed a novel three-dimensional special poly-lactic-glycolic acid (PLGA) scaffold that provided structural support and stimulated repair. Three-dimensional PLGA scaffolds seeded with cultured MSCs were transplanted into large defects in rabbit knees and analyzed histologically at 4 and 12 weeks after the operation. Our findings showed that in the engineered cartilage with the PLGA scaffold, the defects were filled with smooth, shiny white tissue macroscopically and hyaline-like cartilage histologically at 12 weeks after the transplantation. The structure of the novel PLGA scaffolds provided architectural support for the differentiation of progenitor cells and demonstrated successful induction of in vivo chondrogenesis.     

Mesenchymal stem cell-collagen microspheres for articular cartilage repair: Cell density and differentiation status

Mesenchymal stem cells (MSC) hold promise for cartilage repair. A microencapsulation technique was previously established to entrap MSC in collagen microspheres, and the collagen fibrous meshwork was found to be an excellent scaffold for supporting MSC survival, growth and differentiation. This study investigates the importance of cell density and differentiation status of MSC–collagen microspheres in cartilage repair. MSC were isolated from rabbit bone marrow and encapsulated in collagen microspheres. The effects of pre-differentiating the encapsulated MSC into chondrogenic lineages and different cell densities on cartilage repair were investigated in rabbits. Implantation of undifferentiated collagen–MSC microspheres formed hyaline-like cartilage rich in type II collagen and glycosaminoglycans (GAG) at 1 month post-implantation. By 6 months, hyaline cartilage rich in type II collagen and GAG, but negative for type I collagen, and partial zonal organization were found in both undifferentiated and chondrogenically differentiated groups in the high cell density group. The undifferentiated group and high cell density group significantly improved the O’Driscoll histological score. Moreover, the undifferentiated group significantly increased the GAG content. The mechanically differentiated group showed stiffer but thinner cartilage, while the undifferentiated group showed thicker but softer cartilage compared with their respective contra-lateral controls. This work suggests that a higher local cell density favors cartilage regeneration, regardless of the differentiation status of MSC, while the differentiation status of MSC does significantly affect regeneration outcomes.     

The use of absorbable co-polymer pads with alginate and cells for articular cartilage repair in rabbits

PURPOSE: To determine the effect of polyglycolic acid (PGA)-polylactic acid (PLA) co-polymer pads with calcium alginate on chondrogenic gene expression for chondrocytes cultured in vitro. We also evaluated the ability of these absorbable pads with alginate to deliver chondrocytes and influence osteochondral defect repair in vivo in immature rabbit knees. METHODS: Rabbit rib chondrocytes were suspended in calcium alginate and co-polymer pads composed of either 47.5/52.5 PGA-PLA or 90/10 PGA-PLA at two different cell concentrations and cultured in vitro for 1, 3, and 5 days. Analysis was performed using RT-PCR for chondrogenic gene expression of aggrecan, type II collagen, and type I collagen. Cells labeled with a traceable green fluorescent protein (GFP) marker in vitro were suspended within the pads to analyze for dispersion and attachment to the pad. An in vivo study was performed in which full-thickness (3x4mm(2)) osteochondral defects were made in 60 rabbit knees. The study comprised four treatment groups based on the type of implant into the defect (empty, alginate alone, or either type of co-polymer pad) and harvested at either 6 or 12 weeks. Two independent blinded observers analyzed and scored the defects grossly and histologically. RESULTS: In vitro analysis of the chondrocytes after 1, 3, and 5 days in culture showed no statistical differences between the types of PGA/PLA co-polymer pad with regard to expression of aggrecan, type II collagen, or type I collagen. However, although statistically insignificant, the expression of aggrecan and type II collagen was found to be greater than that for type I collagen in both types of pads, confirming the chondrogenic effect of suspension culture for this system. The addition of alginate to polymer pads allowed costal chondrocytes to be implanted in vivo, as evidenced by the attachment of the cells to the fibers and the uniform dispersion of the GFP-labeled cells through the pad as seen on fluorescent microscopy. Histologic results showed improved scores for the 47.5/52.5 PGA-PLA group (21.3) and the 90/10 PGA-PLA group (18.3) when compared to empty (15.3) or alginate alone (15.1) defects at 12 weeks. CONCLUSION: The addition of calcium alginate to the co-polymer pads offers a new approach to deliver cells to an osteochondral defect and may enhance cartilage regeneration. Future application of this model may allow for an arthroscopic delivery system to assist the healing of cartilage defects.