Protein-releasing polymeric scaffolds induce fibrochondrocytic differentiation of endogenous cells for knee meniscus regeneration in sheep

Abstract

Regeneration of complex tissues, such as kidney, liver, and cartilage, continues to be a scientific and translational challenge. Survival of ex vivo cultured, transplanted cells in tissue grafts is among one of the key barriers. Meniscus is a complex tissue consisting of collagen fibers and proteoglycans with gradient phenotypes of fibrocartilage and functions to provide congruence of the knee joint, without which the patient is likely to develop arthritis. Endogenous stem/progenitor cells regenerated the knee meniscus upon spatially released human connective tissue growth factor (CTGF) and transforming growth factor–β3 (TGFβ3) from a three-dimensional (3D)–printed biomaterial, enabling functional knee recovery. Sequentially applied CTGF and TGFβ3 were necessary and sufficient to propel mesenchymal stem/progenitor cells, as a heterogeneous population or as single-cell progenies, into fibrochondrocytes that concurrently synthesized procollagens I and IIα. When released from microchannels of 3D–printed, human meniscus scaffolds, CTGF and TGFβ3 induced endogenous stem/progenitor cells to differentiate and synthesize zone-specific type I and II collagens. We then replaced sheep meniscus with anatomically correct, 3D–printed scaffolds that incorporated spatially delivered CTGF and TGFβ3. Endogenous cells regenerated the meniscus with zone-specific matrix phenotypes: primarily type I collagen in the outer zone, and type II collagen in the inner zone, reminiscent of the native meniscus. Spatiotemporally delivered CTGF and TGFβ3 also restored inhomogeneous mechanical properties in the regenerated sheep meniscus. Survival and directed differentiation of endogenous cells in a tissue defect may have implications in the regeneration of complex (heterogeneous) tissues and organs.

Harnessing endogenous stem/progenitor cells for tendon regeneration

“…For example, synovial joint condyles were successfully regenerated in rabbits by recruiting BM and synovium mesenchymal stem cells into implanted scaffolds incorporated with growth factors (6). With a similar approach, a complex multiphase knee meniscus was regenerated in sheep by recruiting endogenous stem/progenitor cells (9). In another study, endogenous latent transforming growth factor-β1 (TGF-β1) activated by a low-power laser successfully promoted dental pulp regeneration by differentiating endogenous stem cells (1).…”

“…Accordingly, a second potential therapeutic approach has been suggested by recent works showing the existence of endogenous stem cells with regenerative capacity (1,3,6). We and others reported promising findings that healing, repair, or regeneration can be achieved by recruiting, activating, and/or differentiating either tissue-resident or circulating stem cells, instead of stem cell transplantation necessitating ex vivo manipulation (1,3,6,9). For example, synovial joint condyles were successfully regenerated in rabbits by recruiting BM and synovium mesenchymal stem cells into implanted scaffolds incorporated with growth factors (6).…”

Cartilage-Bone Interface Features, Scaffold and Cell Options for Regeneration

“…Cell recruitment represents a more recent development in the regenerative engineering, and is seen as a promising approach. This method was successfully used with 3D printed polycaprolactone (PCL) scaffolds in a sheep model for mensiscus regeneration [16]. However, cell recruitment has not been utilized in the regeneration attempts for cartilage-bone interface at a scale of 100-200µm thickness.…”

Current progresses of 3D bioprinting based tissue engineering

“…In another trial, Chang H. Lee and colleagues replaced the sheep native meniscus with a PCL-printed scaffold carrying connective tissue growth factor (CTGF) and transforming Smooth muscle cell [40] Epithelial cell [24] growth factor-β3 (TGF-β). These factors stimulated endogenous cells to reconstruct ECM (collagen) and enabled sheep to resume walking capacity about 12 weeks after surgery [14].…”