The Influence of Cell-Matrix Attachment and Matrix Development on the Micromechanical Environment of the Chondrocyte in Tissue-Engineered Cartilage

Advanced gellan gum-based glycol chitosan hydrogel for cartilage tissue engineering biomaterial

Gellan gum (GG), a nature-derived polysaccharide, is one of the materials widely used in cartilage tissue engineering (TE). Glycol chitosan (GC), a derivative of chitosan, is a water-soluble natural polymer that has excellent biocompatibility and biodegradability as well as cell adhesion. Herein, GG was physically blended with GC to enhance the mechanical properties and microenvironment of the GG to apply in cartilage TE. The study was conducted with a hydrogel model which is similar to the extracellular matrix (ECM) of cartilage tissue. The physicochemical studies were carried out with morphological study, swelling ratio, weight loss, and sol fraction. The mechanical characterization was conducted with compression test and rheological study to confirm availability in cartilage TE material. Furthermore, in vitro studies such as morphology investigation, viability assay, GAG content, qRT-PCR, and histological study were performed to verify biocompatibility and chondrogenesis of the material. The mechanical and biological properties improved with a proper amount of GC. Overall results verify the potential of the material and can be further used for the cartilage TE.

Influence of the pericellular and extracellular matrix structural properties on chondrocyte mechanics

Understanding the mechanical factors that drive the biological responses of chondrocytes is central to our interpretation of the cascade of events that lead to osteoarthritic changes in articular cartilage. Chondrocyte mechanics is complicated by changes in tissue properties that can occur as osteoarthritis (OA) progresses and by the interaction between macro-scale, tissue level, properties, and micro-scale pericellular matrix (PCM) and local extracellular matrix (ECM) properties, both of which cannot be easily studied using in vitro systems. Our objective was to study the influence of macro- and micro-scale OA-associated structural changes on chondrocyte strains. We developed a multi-scale finite element model of articular cartilage subjected to unconfined loading, for the following three conditions: (i) normal articular cartilage, (ii) OA cartilage (where macro and micro-scale changes in collagen content, matrix modulus, and permeability were modeled), and (iii) early-stage OA cartilage (where only micro-scale changes in matrix modulus were modeled). In the macro-scale model, we found that a depth-dependent strain field was induced in both healthy and OA cartilage and that the middle and superficial zones of OA cartilage had increased tensile and compressive strains. At the micro-scale, chondrocyte shear strains were sensitive to PCM and local ECM properties. In the early-OA model, micro-scale spatial softening of PCM and ECM resulted in a substantial increase (30%) of chondrocyte shear strain, even with no structural changes in macro-scale tissue properties. Our study provides evidence that micromechanical changes at the cellular level may affect chondrocyte activities before macro-scale degradations at the tissue level become apparent. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:721-729, 2018.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

Improvement of In Vitro Three-Dimensional Cartilage Regeneration by a Novel Hydrostatic Pressure Bioreactor

In vitro three‐dimensional (3D) cartilage regeneration is a promising strategy for repair of cartilage defects. However, inferior mechanical strength and tissue homogeneity greatly restricted its clinical translation. Simulation of mechanical stress through a bioreactor is an important approach for improving in vitro cartilage regeneration. The current study developed a hydrostatic pressure (HP) bioreactor based on a novel pressure‐transmitting mode achieved by slight deformation of a flexible membrane in a completely sealed stainless steel device. The newly developed bioreactor efficiently avoided the potential risks of previously reported pressure‐transmitting modes and simultaneously addressed a series of important issues, such as pressure scopes, culture chamber sizes, sealability, contamination control, and CO₂ balance. The whole bioreactor system realized stable long‐term (8 weeks) culture under high HP (5–10 MPa) without the problems of medium leakage and contamination. Furthermore, the results of in vitro 3D tissue culture based on a cartilage regeneration model revealed that HP provided by the newly developed bioreactor efficiently promoted in vitro 3D cartilage formation by improving its mechanical strength, thickness, and homogeneity. Detailed analysis in cell proliferation, cartilage matrix production, and cross‐linking level of collagen macromolecules, as well as density and alignment of collagen fibers, further revealed the possible mechanisms that HP regulated in vitro cartilage regeneration. The current study provided a highly efficient and stable bioreactor system for improving in vitro 3D cartilage regeneration and thus will help to accelerate its clinical translation. Stem Cells Translational Medicine2017;6:982–991

Mesenchymal cells condensation-inducible mesh scaffolds for cartilage tissue engineering

Mesenchymal cells condensation is crucial in chondrogenic development. However current tissue-engineered scaffolds for chondrogenesis pay little attention to this phenomenon. In this study, we fabricate poly(l-lactide-co-glycolide) (PLGA)/poly(l-lactide) (PLLA) microfiber scaffolds and coat them with human fibroblast-derived matrix (hFDM) that is a decellularized extracellular matrix (ECM) obtained from in vitro cultured human lung fibroblasts (WI-38). Those scaffolds were then conjugated with heparin via EDC chemistry and subsequently immobilized with transforming growth factor (TGF)-β1. The amount of TGF-β1 was quantitatively measured and the release profile showed a continuous release of TGF-β1 for 4 weeks. Human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) were seeded in four different scaffolds; control, fibronectin (FN)-coated, hFDM-coated, hFDM/TGF-β1 and subjected to chondrogenic differentiation in vitro for up to 28 days. Both hFDM and hFDM/TGF-β1 groups exhibited significantly more synthesis of glycosaminoglycan (GAG) and much better upregulation of chondrogenic markers expression. Interestingly, MSCs condensation that led to cell aggregates was clearly observed with time in the two hFDM-coated groups and the quantitative difference was obvious compared to the control and FN group. A mechanistic study in gene and protein level indicated that focal adhesion kinase (FAK) was involved at the early stage of cell adhesion and cell-cell contact-related markers, N-cadherin and neural cell adhesion molecule (NCAM), were highly up-regulated at later time point. In addition histological analysis proved that hFDM/TGF-β1 group was the most effective in forming neocartilage tissue in a rabbit articular cartilage defect model. Taken together, this study demonstrates not only the positive effect of hFDM on chondrogenesis of MSCs and cartilage repair but also provides an important insight toward the significance of in vitro mesenchymal condensation on chondrogenic development of MSCs.

Time evolution of in vivo articular cartilage repair induced by bone marrow stimulation and scaffold implantation in rabbits

PURPOSE

Tissue engineering techniques were used to study cartilage repair over a 12-month period in a rabbit model.

METHODS

A full-depth chondral defect along with subchondral bone injury were originated in the knee joint, where a biostable porous scaffold was implanted, synthesized of poly(ethyl acrylate-co-hydroxyethyl acrylate) copolymer. Morphological evolution of cartilage repair was studied 1 and 2 weeks, and 1, 3, and 12 months after implantation by histological techniques. The 3-month group was chosen to compare cartilage repair to an additional group where scaffolds were preseeded with allogeneic chondrocytes before implantation, and also to controls, who underwent the same surgery procedure, with no scaffold implantation.

RESULTS

Neotissue growth was first observed in the deepest scaffold pores 1 week after implantation, which spread thereafter; 3 months later scaffold pores were filled mostly with cartilaginous tissue in superficial and middle zones, and with bone tissue adjacent to subchondral bone. Simultaneously, native chondrocytes at the edges of the defect started to proliferate 1 week after implantation; within a month those edges had grown centripetally and seemed to embed the scaffold, and after 3 months, hyaline-like cartilage was observed on the condylar surface. Preseeded scaffolds slightly improved tissue growth, although the quality of repair tissue was similar to non-preseeded scaffolds. Controls showed that fibrous cartilage was mainly filling the repair area 3 months after surgery. In the 12-month group, articular cartilage resembled the untreated surface.

CONCLUSIONS

Scaffolds guided cartilaginous tissue growth in vivo, suggesting their importance in stress transmission to the cells for cartilage repair.