A 3D, Dynamically Loaded Hydrogel Model of the Osteochondral Unit to Study Osteocyte Mechanobiology

Abstract

Osteocytes are mechanosensitive cells that orchestrate signaling in bone and cartilage across the osteochondral unit. The mechanisms by which osteocytes regulate osteochondral homeostasis and degeneration in response to mechanical cues remain unclear. This study introduces a novel 3D hydrogel bilayer composite designed to support osteocyte differentiation and bone matrix deposition in a bone-like layer and to recapitulate key aspects of the osteochondral unit's complex loading environment. The bilayer hydrogel is fabricated with a soft cartilage-like layer overlaying a stiff bone-like layer. The bone-like layer contains a stiff 3D-printed hydrogel structure infilled with a soft, degradable, cellular hydrogel. The IDG-SW3 cells embedded within the soft hydrogel mature into osteocytes and produce a mineralized collagen matrix. Under dynamic compressive strains, near-physiological levels of strain are achieved in the bone layer (≤ 0.08%), while the cartilage layer bears the majority of the strains (>99%). Under loading, the model induces an osteocyte response, measured by prostaglandin E2, that is frequency, but not strain, dependent: a finding attributed to altered fluid flow within the composite. Overall, this new hydrogel platform provides a novel approach to study osteocyte mechanobiology in vitro in an osteochondral tissue-mimetic environment. Osteocytes are mechanosensitive cells that help to orchestrate signaling in bone and cartilage across the osteochondral unit. Yet the mechanisms by which osteocytes regulate osteochondral

Modeling early changes associated with cartilage trauma using human-cell-laden hydrogel cartilage models

“…Mechanical loads have been to date difficult to apply to synovial joint MPS, including traumatic loads, the causative event in the development of PTOA and responsible A review of studies on chondrocyte construct loading reveals the use of dynamic cyclic compression with physiological loading frequencies with rest periods replicating daily activity and continued exercise over multiple days. In the existing synovial joint MPS [29][30][31][32][33][34][35][36], the mechanical stimulation used has a strain of 0-35% at a frequency of 0.2-1 Hz [51]. These conditions are good for establishing joint tissue homeostasis and possibly modeling chronic overload as a cause of OA under the right (to be determined) conditions.…”

Hydrogels and Bioprinting in Bone Tissue Engineering: Creating Artificial Stem‐Cell Niches for In Vitro Models

“…Development of osteochondral models employing bioprinting approaches with functional hydrogels [156][157][158][159][160] to study osteoarthritis has been achieved. The hydrogels, paired with extrusion bioprinting, enhanced the potential of the construct as cell behavior and fate during osteoarthritis onset could be mimicked accurately, demonstrating the power of BTE approach employing hydrogels and bioprinting.…”

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

“…Nowadays, these materials are obtained using colonization of hydrogels [252] or three-dimensional printed constructs [253], or by cell encapsulation in hydrogels [254,255] with tuneable mechanical properties [252,256,257], three-dimensional printed gels [258] or microbeads [259]. Moreover, recent bioinspired scaffolds based on cell encapsulation in hydrogels have enabled to model angiogenesis [260], the osteochondral environment [261], bone [262], brain [263], gastric mucosa [264], and the liver [265]. The constant evolution of the materials processing techniques will continue to expand the cellularization pathways available to design new, more relevant healthy tissue models.…”