Mimicking Cartilage Tissue Zonal Organization by Engineering Tissue-Scale Gradient Hydrogels as 3D Cell Niche

Abstract

Zonal organization plays an important role in cartilage structure and function, whereas most tissue-engineering strategies developed to date have only allowed the regeneration of cartilage with homogeneous biochemical and mechanical cues. To better restore tissue structure and function, there is a strong need to engineer materials with biomimetic gradient niche cues that recapitulate native tissue organization. To address this critical unmet need, in this study, we report a method for rapid formation of tissue-scale gradient hydrogels as a three-dimensional (3D) cell niche with tunable biochemical and physical properties. When encapsulated in stiffness gradient hydrogels, both chondrocytes and mesenchymal stem cells demonstrated zone-specific response and extracellular deposition that mimics zonal organization of articular cartilage. Blocking cell mechanosensing using blebbistatin abolished the zonal response of chondrocytes in 3D hydrogels with a stiffness gradient. Such tissue-scale gradient hydrogels can provide a 3D artificial cell niche to enable tissue engineering of various tissue types with zonal organizations or tissue interfaces.

Mimicking nature: Fabrication of 3D anisotropic electrospun polycaprolactone scaffolds for cartilage tissue engineering applications

“…In this way, mimicking cartilage requires the design and fabrication of anisotropic scaffolds capable of simulating the hierarchical biochemical, biophysical and geometric depth dependent arrangement of the cartilaginous tissue. Recent studies have reported that advanced hydrogels, including both injectable 18 and stimuli responsive 19 , are promising biomimetic platforms for regenerating cartilage since they can guarantee zonal-specific cell responses, for example, by introduction of stiffness gradients 20 or by assembly different layers with specific gelation formulations that consequently ensure particular properties 21 . Additionally, new designs have already overcome some limitations related with the reduced nutrient exchange in the inte rna l regions of tri-layered hydrogels by introducing porous hollow fibres to transport nutrient/waste across the scaffold with the purpose of supporting an optimized and uniform cell behaviour 22 .…”

Recent advances on gradient hydrogels in biomimetic cartilage tissue engineering

“…The chondrocytes were more hypertrophic as the stiffness increased from zone 1 to zone 5. Increasing matrix stiffness led to a stiffness-dependent increase in cartilage-specific gene expression by hMSCs, and there was a two- to three-fold higher expression of the genes encoding aggrecan and type II collagen in the stiffer zone (zone 5) compared with the softer zone (zone 1) 30 . More details on the gradient stiffness hydrogel fabrication methods and mechanical property tests can be found in a recent review by Xia et al .…”

“…proposed a hypothesis that stiffness gradient can induce a zonal-specific response of encapsulated cells in 3D, where the newly deposited tissues in gradient hydrogels will mimic the zonal organization of native articular cartilage 30 . To test this hypothesis, they used a tissue-scale, photo-cross-linkable, multi-arm PEG hydrogel system as a backbone and chondroitin sulfate methacrylate, mixed with two cell-containing precursor solutions: neonatal bovine chondrocytes or human mesenchymal stromal cells (hMSCs).…”

“…Up to now, the most promising approach for generating dual large-scale (that is, tissue-scale) gradient hydrogels in the context of cartilage TE is the method (described above) by Zhu et al . 30 .…”

Mimetic Hierarchical Approaches for Osteochondral Tissue Engineering

“…They used photocrosslinkable, multi-arm PEG hydrogel system as a backbone and chondroitin sulfate methacrylate, mixed with two cellcontaining precursor solutions (chondrocytes and hMSCs), which, upon exposure to light, quickly formed insoluble cell-laden gradient hydrogels mimicking zonal structure of the native cartilage. The method enabled rapid (~2 min) formation of tissue-scale hydrogels (3 cm × 1 cm × 3 mm) with stiffness and/or ECM molecule gradient cues, while enabling homogeneous cell encapsulation in 3D [66].…”