Spatial patterning of phenotypically distinct microtissues to engineer osteochondral grafts for biological joint resurfacing.

Engineered Biomaterials to Guide Spheroid Formation, Function, and Fabrication into 3D Tissue Constructs.

Osteochondral injuries can lead to osteoarthritis (OA). OA is characterized by the progressive degradation of the cartilage tissue together with bone tissue turnover. Consequently, joint pain, inflammation, and stiffness are common, with joint immobility and dysfunction being the most severe symptoms. The increase in the age of the population, along with the increase in risk factors such as obesity, has led OA to the forefront of disabling diseases. In addition, it not only has an increasing prevalence, but is also an economic burden for health systems. Current treatments are focused on relieving pain and inflammation, but they become ineffective as the disease progresses. Therefore, new therapeutic approaches, such as tissue engineering and 3D bioprinting, have emerged. In this review, the advantages of using 3D bioprinting techniques for osteochondral regeneration are described. Furthermore, the biomaterials, cell types, and active molecules that are commonly used for these purposes are indicated. Finally, the most recent promising results for the regeneration of cartilage, bone, and/or the osteochondral unit through 3D bioprinting technologies are considered, as this could be a feasible therapeutic approach to the treatment of OA.

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Progress in 3D Bioprinting Technology for Osteochondral Regeneration

Bioprinting of structurally organized meniscal tissue within anisotropic melt electrowritten scaffolds.

Scaffold-free tissue engineering strategies aim to recapitulate key aspects of normal developmental processes as a means of generating highly biomimetic grafts. Cartilage and fibrocartilaginous tissues have successfully been engineered by bringing together large numbers of cells, cellular aggregates or microtissues and allowing them to self-assemble or self-organize into a functional graft. Despite the promise of such approaches, considerable challenges still remain, such as engineering scaled-up tissues with predefined geometries, ensuring robust fusion between adjacent cellular aggregates or microtissues, and directing the (re)modelling of such biological building blocks into a unified scaled-up graft with hierarchical matrix organisation mimetic of the native tissue. In this study, we first demonstrate the benefits of engineering cartilage via the fusion of multiple cartilage microtissues compared to conventional scaffold-free approaches where (millions of) individual cells are allowed to aggregate and generate a cartilaginous graft. Key advantages include the engineering of a tissue with a richer extracellular matrix, a more hyaline-like cartilage phenotype and a final graft which better matched the intended geometry. A major drawback associated with this approach is that individual microtissues did not completely (re)model and remnants of their initial architectures where still evident throughout the macrotissue. In an attempt to address this limitation, the enzyme chondroitinase ABC (cABC) was employed to accelerate structural (re)modelling of the engineered tissue. Temporal enzymatic treatment supported robust fusion between adjacent microtissues, enhanced microtissue (re)modelling and supported the development of a more biomimetic tissue with a zonally organised collagen architecture. Additionally, we observed that cABC treatment modulated matrix composition (rebalancing the collagen:glycosaminoglycans ratio), tissue phenotype, and to a lesser extent, tissue mechanics. Ultimately, this work demonstrates that microtissue self-organisation is an effective method for engineering scaled-up cartilage grafts with a pre-defined geometry and near-native levels of ECM accumulation. Importantly we have demonstrated that key limitations associated with tissue engineering using multiple cellular aggregates, microtissues or organoids can be alleviated by temporal enzymatic treatment during graft development.

/pdf/temporal-enzymatic-treatment-to-enhance-the-remodelling-of-i6xw2vgq.pdf

Temporal enzymatic treatment to enhance the remodelling of multiple cartilage microtissues into a structurally organised tissue

Despite sustained efforts, engineering truly biomimetic articular cartilage (AC) via traditional top-down approaches remains challenging. Emerging biofabrication strategies, from 3D bioprinting to scaffold-free approaches that leverage principles of cellular self-organisation, are generating significant interest in the field of cartilage tissue engineering as a means of developing biomimetic tissue analoguesin vitro.Although such strategies have advanced the quality of engineered cartilage, recapitulation of many key structural features of native AC, in particular a collagen network mimicking the tissue's 'Benninghoff arcade', remains elusive. Additionally, a complete solution to fixating engineered cartilagesin situwithin damaged synovial joints has yet to be identified. This study sought to address both of these key challenges by engineering biomimetic AC within a device designed to anchor the tissue within a synovial joint defect. We first designed and fabricated a fixation device capable of anchoring engineered cartilage into the subchondral bone. Next, we developed a strategy for inkjet printing porcine mesenchymal stem/stromal cells (MSCs) into this supporting fixation device, which was also designed to provide instructive cues to direct the self-organisation of MSC condensations towards a stratified engineered AC. We found that a higher starting cell-density supported the development of a more zonally defined collagen network within the engineered tissue. Dynamic culture was implemented to further enhance the quality of this engineered tissue, resulting in an approximate 3 fold increase in glycosaminoglycan and collagen accumulation. Ultimately this strategy supported the development of AC that exhibited near-native levels of glycosaminoglycan accumulation (>5% WW), as well as a biomimetic collagen network organisation with a perpendicular to a parallel fibre arrangement (relative to the tissue surface) from the deep to superficial zones via arcading fibres within the middle zone of the engineered tissue. Collectively, this work demonstrates the successful convergence of novel biofabrication methods, bioprinting strategies and culture regimes to engineer a hybrid implant suited to resurfacing AC defects.

Farhad Chariyev-Prinz

Papers

Bioprinting of biomimetic self-organised cartilage with a supporting joint fixation device.