Increased chondrocyte seeding density has no positive effect on cartilage repair in an MPEG-PLGA scaffold

Autologous Minced Cartilage Implantation for Treatment of Chondral and Osteochondral Lesions in the Knee Joint: An Overview

Cartilage defects in the knee are being diagnosed with increased frequency and are treated with a variety of techniques. The aim of any cartilage repair procedure is to generate the highest tissue quality, which might correlate with improved clinical outcomes, return-to-sport, and long-term durability. Minced cartilage implantation (MCI) is a relatively simple and cost-effective technique to transplant autologous cartilage fragments in a single-step procedure. Minced cartilage has a strong biologic potential since autologous, activated non-dedifferentiated chondrocytes are utilized. It can be used both for small and large cartilage lesions, as well as for osteochondral lesions. As it is purely an autologous and homologous approach, it lacks a significant regulatory oversight process and can be clinically adopted without such limitations. The aim of this narrative review is to provide an overview of the current evidence supporting autologous minced cartilage implantation.

Human Articular Chondrocytes Retain Their Phenotype in Sustained Hypoxia While Normoxia Promotes Their Immunomodulatory Potential

OBJECTIVE

To assess the phenotype of human articular chondrocytes cultured in normoxia (21% O2) or continuous hypoxia (2% O2).

DESIGN

Chondrocytes were extracted from patients undergoing total knee replacement (n = 5) and cultured in ~21% (normoxic chondrocytes, NC) and 2% (hypoxic chondrocytes, HC) oxygen in both monolayer and 3-dimensional (3D) pellet culture and compared with freshly isolated chondrocytes (FC). Cells were assessed by flow cytometry for markers indicative of mesenchymal stromal cells (MSCs), chondrogenic-potency and dedifferentiation. Chondrogenic potency and immunomodulatory gene expression was assessed in NC and HC by reverse transcription quantitative polymerase chain reaction. Immunohistochemistry was used to assess collagen II production following 3D pellet culture.

RESULTS

NC were positive (>97%, n = 5) for MSC markers, CD73, CD90, and CD105, while HC demonstrated <90% positivity (n = 4) and FC (n = 5) less again (CD73 and CD90 <20%; CD105 <40%). The markers CD166 and CD151, indicative of chondrogenic de-differentiation, were significantly higher on NC compared with HC and lowest on FC. NC also produced the highest levels of CD106 and showed the greatest levels of IDO expression, following interferon-γ stimulation, indicating immunomodulatory potential. NC produced the highest levels of CD49c (>60%) compared with HC and FC in which production was <2%. Hypoxic conditions upregulated expression of SOX9, frizzled-related protein (FRZB), fibroblast growth factor receptor 3 (FGFR3), and collagen type II (COL2A1) and downregulated activin receptor-like kinase 1 (ALK1) in 3 out of 4 patients compared with normoxic conditions for monolayer cells.

CONCLUSIONS

Hypoxic conditions encourage retention of a chondrogenic phenotype with some immunomodulatory potential, whereas normoxia promotes dedifferentiation of chondrocytes toward an MSC phenotype with loss of chondrogenic potency but enhanced immunomodulatory capacity.

Chondrocyte Culture Parameters for Matrix-Assisted Autologous Chondrocyte Implantation Affect Catabolism and Inflammation in a Rabbit Model

Cartilage defects represent an increasing pathology among active individuals that affects the ability to contribute to sports and daily life. Cell therapy, such as autologous chondrocyte implantation (ACI), is a widespread option to treat larger cartilage defects still lacking standardization of in vitro cell culture parameters. We hypothesize that mRNA expression of cytokines and proteases before and after ACI is influenced by in vitro parameters: cell-passage, cell-density and membrane-holding time. Knee joint articular chondrocytes, harvested from rabbits (n = 60), were cultured/processed under varying conditions: after three different cell-passages (P1, P3, and P5), cells were seeded on 3D collagen matrices (approximately 25 mm³) at three different densities (2 × 10⁵/matrix, 1 × 10⁶/matrix, and 3 × 10⁶/matrix) combined with two different membrane-holding times (5 h and two weeks) prior autologous transplantation. Those combinations resulted in 18 different in vivo experimental groups. Two defects/knee/animal were created in the trochlear groove (defect dimension: &empty; 4 mm × 2 mm). Four identical cell-seeded matrices (CSM) were assembled and grouped in two pairs: One pair giving pre-operative in vitro data (CSM-i), the other pair was implanted in vivo and harvested 12 weeks post-implantation (CSM-e). CSMs were analyzed for TNF-α, IL-1β, MMP-1, and MMP-3 via qPCR. CSM-i showed higher expression of IL-1β, MMP-1, and MMP-3 compared to CSM-e. TNF-α expression was higher in CSM-e. Linearity between CSM-i and CSM-e values was found, except for TNF-α. IL-1β expression was higher in CSM-i at higher passage and longer membrane-holding time. IL-1β expression decreased with prolonged membrane-holding time in CSM-e. For TNF-α, the reverse was true. Lower cell-passages and lower membrane-holding time resulted in stronger TNF-α expression. Prolonged membrane-holding time resulted in increased MMP levels among CSM-i and CSM-e. Cellular density was of no significant effect. We demonstrated cytokine and MMP expression levels to be directly influenced by in vitro culture settings in ACI. Linearity of expression-patterns between CSM-i and CSM-e may predict ACI regeneration outcome in vivo. Cytokine/protease interaction within the regenerate tissue could be guided via adjusting in vitro culture parameters, of which membrane-holding time resulted the most relevant one.

Repair of Osteochondral Defects in a Rabbit Model Using Bilayer Poly(Lactide-co-Glycolide) Scaffolds Loaded with Autologous Platelet-Rich Plasma

BACKGROUND To examine the effects of the addition of autologous platelet-rich plasma (PRP) into bilayer poly(lactide-co-glycolide) (PLGA) scaffolds on the reconstruction of osteochondral defects in a rabbit model. MATERIAL AND METHODS Porous PLGA scaffolds were prepared in a bilayered manner to reflect the structure of chondral and subchondral bone. Bone defects, measuring 4 mm in diameter and 4 mm in thickness, were created in both knee joints in 18 healthy New Zealand white rabbits, aged between 120-180 days old. Rabbits were randomly divided into three groups: rabbits with bone defects implanted with bilayer PLGA scaffolds (PLGA group) (N=6); or with bilayer PLGA and autologous PRP (PLGA/PRP group) (N=6); and the untreated group (control group) (N=6). The gross morphology, histology, and immunohistochemistry for the expression of collagen type II and aggrecan were observed at 12 weeks after surgery and compared using a scoring system. Micro-computed tomography (CT) imaging and relative expression of specific genes were also assessed. RESULTS The platelet concentrations in the PRP samples were found to be 4.9 times greater than that of whole blood samples. The total score on gross appearance and histology was greatest in the PLGA/PRP group, as was the expression of collagen II and aggrecan of the neo-tissue. Micro-CT imaging showed that more subchondral bone was formed in the PLGA/PRP group. CONCLUSIONS Bilayer PLGA scaffolds loaded with autologous PRP improve the reconstruction of osteochondral defects in the rabbit model.

Ex vivo model unravelling cell distribution effect in hydrogels for cartilage repair

The implantation of chondrocyte-laden hydrogels is a promising cartilage repair strategy. Chondrocytes can be spatially positioned in hydrogels and thus in defects, while current clinical cell therapies introduce chondrocytes in the defect depth. The main aim of this study was to evaluate the effect of spatial chondrocyte distribution on the reparative process. To reduce animal experiments, an ex vivo osteochondral plug model was used and evaluated. The role of the delivered and endogenous cells in the repair process was investigated.

Full thickness cartilage defects were created in equine osteochondral plugs. Defects were filled with (A) chondrocytes at the bottom of the defect, covered with a cell-free hydrogel, (B) chondrocytes homogeneously encapsulated in a hydrogel, and (C, D) combinations of A and B with different cell densities. Plugs were cultured for up to 57 days, after which the cartilage and repair tissues were characterized and compared to baseline samples. Additionally, at day 21, the origin of cells in the repair tissue was evaluated.

Best outcomes were obtained with conditions C and D, which resulted in well-integrated cartilage-like tissue that completely filled the defect, regardless of the initial cell density. A critical role of the spatial chondrocyte distribution in the repair process was observed. Moreover, the osteochondral plugs stimulated cartilage formation in the hydrogels when cultured in the defects. The resulting repair tissue originated from the delivered cells.

These findings confirm the potential of the osteochondral plug model for the optimization of the composition of cartilage implants and for studying repair mechanisms.

Chondrocytes, Mesenchymal Stem Cells, and Their Combination in Articular Cartilage Regenerative Medicine

Articular cartilage (AC) is a highly organized connective tissue lining, covering the ends of bones within articulating joints. Its highly ordered structure is essential for stable motion and provides a frictionless surface easing load transfer. AC is vulnerable to lesions and, because it is aneural and avascular, it has limited self-repair potential which often leads to osteoarthritis. To date, no fully successful treatment for osteoarthritis has been reported. Thus, the development of innovative therapeutic approaches is desperately needed. Autologous chondrocyte implantation, the only cell-based surgical intervention approved in the United States for treating cartilage defects, has limitations because of de-differentiation of articular chondrocytes (AChs) upon in vitro expansion. De-differentiation can be abated if initial populations of AChs are co-cultured with mesenchymal stem cells (MSCs), which not only undergo chondrogenesis themselves but also support chondrocyte vitality. In this review we summarize studies utilizing AChs, non-AChs, and MSCs and compare associated outcomes. Moreover, a comprehensive set of recent human studies using chondrocytes to direct MSC differentiation, MSCs to support chondrocyte re-differentiation and proliferation in co-culture environments, and exploratory animal intra- and inter-species studies are systematically reviewed and discussed in an innovative manner allowing side-by-side comparisons of protocols and outcomes. Finally, a comprehensive set of recommendations are made for future studies.

Optimal Seeding Densities for In Vitro Chondrogenesis of Two- and Three-Dimensional-Isolated and -Expanded Bone Marrow-Derived Mesenchymal Stromal Stem Cells Within a Porous Collagen Scaffold

Bone marrow-derived mesenchymal stromal stem cells (BMSCs) are a promising cell source for treating articular cartilage defects. The objective of this study was to assess the impact of cell seeding density within a collagen I scaffold on in vitro BMSC chondrogenesis following isolation and expansion in two-dimensional (2D) and three-dimensional (3D) environments. It was hypothesized that both expansion protocols would produce BMSCs capable of hyaline-like chondrogenesis with an optimal seeding density of 10 × 10(6) cells/cm(3). Ovine BMSCs were isolated in a 2D environment by plastic adherence, expanded to passage two in flasks containing an expansion medium, and seeded within collagen I scaffolds at densities of 50, 10, 5, 1, and 0.5 × 10(6) BMSCs/cm(3). For 3D isolation and expansion, aspirates containing known quantities of mononucleated cells (bone marrow-derived mononucleated cells [BMNCs]) were seeded on scaffolds at 50, 10, 5, 1, and 0.5 × 10(6) BMNCs/cm(3) and cultured in the expansion medium for an equivalent duration to 2D expansion. Constructs were differentiated in vitro in the chondrogenic medium for 21 days and assessed with reverse-transcription quantitative polymerase chain reaction, safranin O staining, histological scoring using the Bern Score, collagen immunofluorescence, and glycosaminoglycan (GAG) quantification. Two-dimensional-expanded BMSCs seeded at all densities were capable of proteoglycan production and displayed increased expressions of aggrecan and collagen II messenger RNA (mRNA) relative to predifferentiation controls. Collagen II deposition was apparent in scaffolds seeded at 0.5-10 × 10(6) BMSCs/cm(3). Chondrogenesis of 2D-expanded BMSCs was most pronounced in scaffolds seeded at 5-10 × 10(6) BMSCs/cm(3) based on aggrecan and collagen II mRNA, safranin O staining, Bern Score, total GAG, and GAG/deoxyribonucleic acid (DNA). For 3D-expanded BMSC-seeded scaffolds, increased aggrecan and collagen II mRNA expressions relative to controls were noted with all densities. Proteoglycan deposition was present in scaffolds seeded at 0.5-50 × 10(6) BMNCs/cm(3), while collagen II deposition occurred in scaffolds seeded at 10-50 × 10(6) BMNCs/cm(3). The highest levels of aggrecan and collagen II mRNA, Bern Score, total GAG, and GAG/DNA occurred with seeding at 50 × 10(6) BMNCs/cm(3). Within a collagen I scaffold, 2D- and 3D-expanded BMSCs are capable of hyaline-like chondrogenesis with optimal cell seeding densities of 5-10 × 10(6) BMSCs/cm(3) and 50 × 10(6) BMNCs/cm(3), respectively.

Cell seeding density is a critical determinant for copolymer scaffolds-induced bone regeneration

Constructs intended for bone tissue engineering (TE) are influenced by the initial cell seeding density. Therefore, the objective of this study was to determine the effect of bone marrow stromal stem cells (BMSCs) density loaded onto copolymer scaffolds on bone regeneration. BMSCs were harvested from rat's bone marrow and cultured in media with or without osteogenic supplements. Cells were seeded onto poly(l‐lactide‐co‐ε‐caprolactone) [poly(LLA‐co‐CL)] scaffolds at two different densities: low density (1 × 10⁶ cells/scaffold) or high density (2 × 10⁶ cells/scaffold) using spinner modified flasks and examined after 1 and 3 weeks. Initial attachment and spread of BMSC onto the scaffolds was recorded by scanning electron microscopy. Cell proliferation was assessed by DNA quantification and cell differentiation by quantitative real‐time reverse transcriptase‐polymerized chain reaction analysis (qRT‐PCR). Five‐millimeter rat calvarial defects (24 defects in 12 rats) were implanted with scaffolds seeded with either low or high density expanded with or without osteogenic supplements. Osteogenic supplements significantly increased cell proliferation (p < 0.001). Scaffolds seeded at high cell density exhibited higher mRNA expressions of Runx2 p = 0.001, Col1 p = 0.001, BMP2 p < 0.001, BSP p < 0.001, and OC p = 0.013. More bone was formed in response to high cell seeding density (p = 0.023) and high seeding density with osteogenic medium (p = 0.038). Poly (LLA‐co‐CL) scaffolds could be appropriate candidates for bone TE. The optimal number of cells to be loaded onto scaffolds is critical for promoting Extracellular matrix synthesis and bone formation. Cell seeding density and osteogenic supplements may have a synergistic effect on the induction of new bone. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3649–3658, 2015.

Biodegradable PEG-Based Amphiphilic Block Copolymers for Tissue Engineering Applications

Biodegradable tissue engineering scaffolds have great potential for delivering cells/therapeutics and supporting tissue formation. Polyesters, the most extensively investigated biodegradable synthetic polymers, are not ideally suited for diverse tissue engineering applications due to limitations associated with their hydrophobicity. This review discusses the design and applications of amphiphilic block copolymer scaffolds integrating hydrophilic poly(ethylene glycol) (PEG) blocks with hydrophobic polyesters. Specifically, we highlight how the addition of PEG results in striking changes to the physical properties (swelling, degradation, mechanical, handling) and biological performance (protein & cell adhesion) of the degradable synthetic scaffolds in vitro. We then perform a critical review of how these in vitro characteristics translate to the performance of biodegradable amphiphilic block copolymer-based scaffolds in the repair of a variety of tissues in vivo including bone, cartilage, skin, and spinal cord/nerve. We conclude the review with recommendations for future optimizations in amphiphilic block copolymer design and the need for better-controlled in vivo studies to reveal the true benefits of the amphiphilic synthetic tissue scaffolds.

Experimental articular cartilage repair in the Göttingen minipig: the influence of multiple defects per knee

Background

A gold standard treatment for articular cartilage injuries is yet to be found, and a cost-effective and predictable large animal model is needed to bridge the gap between in vitro studies and clinical studies.

Ideally, the animal model should allow for testing of clinically relevant treatments and the biological response should be reproducible and comparable to humans. This allows for a reliable translation of results to clinical studies.This study aimed at verifying the Göttingen minipig as a pre-clinical model for articular cartilage repair by testing existing clinical cartilage repair techniques and evaluating the use of two defects per knee.

Methods

Sixteen fully mature Göttingen minipigs were used. The minipigs received bilateral trochlear osteochondral drill-hole defects or chondral defects (Ø 6 mm), either one defect per knee or two defects per knee. The defects were treated with one of the following: Matrix-induced autologous chondrocyte implantation (MACI), microfracture (MFx), autologous-dual-tissue transplantation (ADTT), autologous bone graft, autologous cartilage chips. Empty chondral and osteochondral defects were used as controls. MRI and CT were performed 3 and 6 month, histology was performed 6 month postoperative.

Results

The repair tissue varied in morphology from non-cartilaginous fibrous tissue to fibrocartilaginous tissue as seen on MRI, CT and histology at 6 month. The worst results were seen in the empty controls, while the best results were achieved with the MACI and ADTT treatment. The use of two defects per knee did not have any significant effect on the repair response.

Conclusion

The outcomes of the applied treatments were consistent with the outcomes in clinical studies and it was possible to apply two defects per knee. The Göttingen minipig model was easy to handle, cost-effective and provided predictable outcome. Based on this study the use of two defects per knee, one in the medial and one in the lateral trochlear facet, in male Göttingen minipigs is recommended.

Pullulan: a new cytoadhesive for cell-mediated cartilage repair

Introduction

Local delivery of mesenchymal stem cells (MSCs) to the acutely injured or osteoarthritic joint retards cartilage destruction. However, in the absence of assistive materials the efficiency of engraftment of MSCs to either intact or fibrillated cartilage is low and localization is further reduced by natural movement of the joint surfaces. It is hypothesised that enhanced engraftment of the delivered MSCs at the cartilage surface will increase their reparative effect and that the application of a bioadhesive to the degraded cartilage surface will provide improved cell retention. Pullulan is a structurally flexible, non-immunogenic exopolysaccharide with wet-stick adhesive properties and has previously been used for drug delivery via the wet surfaces of the buccal cavity. In this study, the adhesive character of pullulan was exploited to enhance MSC retention on the damaged cartilage surface.

Methods

MSCs labeled with PKH26 were applied to pullulan-coated osteoarthritic cartilage explants to measure cell retention. Cytocompatability was assessed by measuring the effects of prolonged exposure to the bioadhesive on MSC viability and proliferation. The surface phenotype of the cells was assessed by flow cytometry and their multipotent nature by measuring osteogenic, adipogenic and chrondrogenic differentiation. Experiments were also carried out to determine expression of the C-type lectin Dectin-2 receptor.

Results

MSCs maintained a stable phenotype following exposure to pullulan in terms of metabolic activity, proliferation, differentiation and surface antigen expression. An increase in osteogenic activity and Dectin-2 receptor expression was seen in MSCs treated with pullulan. Markedly enhanced retention of MSCs was observed in explant culture of osteoarthritic cartilage.

Conclusions

Pullulan is a biocompatible and effective cytoadhesive material for tissue engraftment of MSCs. Prolonged exposure to pullulan has no negative impact on the phenotype, viability and differentiation potential of the cells. Pullulan dramatically improves the retention of MSCs at the fibrillated surface of osteoarthritic articular cartilage. Pullulan causes an upregulation in expression of the Dectin-2 C-type lectin transmembrane complex.

Scaffold-assisted cartilage tissue engineering using infant chondrocytes from human hip cartilage

OBJECTIVE

Studies about cartilage repair in the hip and infant chondrocytes are rare. The aim of our study was to evaluate the use of infant articular hip chondrocytes for tissue engineering of scaffold-assisted cartilage grafts.

METHOD

Hip cartilage was obtained from five human donors (age 1-10 years). Expanded chondrocytes were cultured in polyglycolic acid (PGA)-fibrin scaffolds. De- and re-differentiation of chondrocytes were assessed by histological staining and gene expression analysis of typical chondrocytic marker genes. In vivo, cartilage matrix formation was assessed by histology after subcutaneous transplantation of chondrocyte-seeded PGA-fibrin scaffolds in immunocompromised mice.

RESULTS

The donor tissue was heterogenous showing differentiated articular cartilage and non-differentiated tissue and considerable expression of type I and II collagens. Gene expression analysis showed repression of typical chondrocyte and/or mesenchymal marker genes during cell expansion, while markers were re-induced when expanded cells were cultured in PGA-fibrin scaffolds. Cartilage formation after subcutaneous transplantation of chondrocyte loaded PGA-fibrin scaffolds in nude mice was variable, with grafts showing resorption and host cell infiltration or formation of hyaline cartilage rich in type II collagen. Addition of human platelet rich plasma (PRP) to cartilage grafts resulted robustly in formation of hyaline-like cartilage that showed type II collagen and regions with type X collagen.

CONCLUSION

These results suggest that culture of expanded and/or de-differentiated infant hip cartilage cells in PGA-fibrin scaffolds initiates chondrocyte re-differentiation. The heterogenous donor tissue containing immature chondrocytes bears the risk of cartilage repair failure in vivo, which may be possibly overcome by the addition of PRP.