Abstract
The concept of biphasic or multi-layered compound scaffolds has been explored within numerous studies in the context of cartilage and osteochondral regeneration. To date, no system has been identified that stands out in terms of superior chondrogenesis, osteogenesis or the formation of a zone of calcified cartilage (ZCC). Herein we present a 3D plotted scaffold, comprising an alginate and hydroxyapatite paste, cast within a photocrosslinkable hydrogel made of gelatin methacrylamide (GelMA), or GelMA with hyaluronic acid methacrylate (HAMA). We hypothesized that this combination of 3D plotting and hydrogel crosslinking would form a high fidelity, cell supporting structure that would allow localization of hydroxyapatite to the deepest regions of the structure whilst taking advantage of hydrogel photocrosslinking. We assessed this preliminary design in terms of chondrogenesis in culture with human articular chondrocytes, and verified whether the inclusion of hydroxyapatite in the form presented had any influence on the formation of the ZCC. Whilst the inclusion of HAMA resulted in a better chondrogenic outcome, the effect of HAP was limited. We overall demonstrated that formation of such compound structures is possible, providing a foundation for future work. The development of cohesive biphasic systems is highly relevant for current and future cartilage tissue engineering.
Highlights
Articular cartilage is a complex tissue, organized into a zonal structure with varied biochemical and biomechanical properties throughout each zone
Four groups were chosen for the study (Figure 1), comprising HAP-containing (GelMA-alginate and hydroxyapatite paste (ALG/HAP), gelatin methacrylamide (GelMA)/hyaluronic acid methacrylate (HAMA)-ALG/HAP) and HAP-free (GelMA-ALG, GelMA/HAMA-ALG) constructs
Whilst hydrogels widely widely appear appear to givetothe most desired inofterms of hypoxia, high fluidease content, ease of and diffusivity andmechanical tailorable desired matrixmatrix in terms hypoxia, high fluid content, of diffusivity tailorable mechanical there properties, thereconsensus is no clear what type of material is most desirable for properties, is no clear onconsensus what typeon of material is most desirable for osteochondral osteochondral regeneration
Summary
Articular cartilage is a complex tissue, organized into a zonal structure with varied biochemical and biomechanical properties throughout each zone. The zones of cartilage vary with depth, with collagen fiber orientation and chondrocyte morphology changing throughout the tissue, from the superficial layer (fibers parallel to surface, flattened cell morphology), to the transitional layer (fibers randomly oriented, rounded cell morphology) and the deep layer (fibers perpendicular to surface, columnar cell alignment). Is found beyond the deepest part of cartilage, linking the cartilage to the subchondral bone. The ZCC varies considerably from the cartilage, for instance in collagen II content: ~60% dry weight in cartilage versus ~20% in the ZCC [2]. The percentage of hydroxyapatite (HAP) in the ZCC by dry weight is ~65%, comparable with that of subchondral bone at ~86% [2]. The ZCC is rich in collagen X, Materials 2016, 9, 285; doi:10.3390/ma9040285 www.mdpi.com/journal/materials
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