Strategies for replicating anatomical cartilaginous tissue gradient in engineered intervertebral disc.

A critical challenge in fabricating a load bearing tissue, such as an intervertebral disc, is to simulate cellular and matrix alignment and anisotropy, as well as a specific biochemical gradient. Towards this goal, multilamellar silk fibroin scaffolds having criss-cross fibrous orientation were developed, where silk fibers in inner layers were crosslinked with bioactive molecule chondroitin sulfate. Upon culturing goat articular chondrocytes under static and dynamic conditions, lamellar scaffold architecture guided alignment of cells and the newly synthesized extracellular matrix (ECM) along the silk fibers. The dynamic culture conditions further improved the cellular metabolic rate and ECM production. Further the synergistic effect of chemical composition of scaffold and hydrodynamic environment of bioreactor contributed in developing a tissue gradient within the constructs, with an inner region rich in collagen II, glycosaminoglycan (GAG), and stiffer in compression, whereas an outer region rich in collagen I and stiffer in tension. Therefore, a unique combination of chemical and physical parameters of engineered constructs and dynamic culture conditions provides a promising starting point to further improve the system towards replicating the anatomical structure, composition gradient, and function of intervertebral disc tissue.

Enhanced redifferentiation of chondrocytes on microperiodic silk/gelatin scaffolds: toward tailor-made tissue engineering.

Direct-write assembly allows rapid fabrication of complex three-dimensional (3D) architectures, such as scaffolds simulating anatomical shapes, avoiding the need for expensive lithographic masks. However, proper selection of polymeric ink composition and tailor-made viscoelastic properties are critically important for smooth deposition of ink and shape retention. Deposition of only silk solution leads to frequent clogging due to shear-induced ß-sheet crystallization, whereas optimized viscoelastic property of silk-gelatin blends facilitate the flow of these blends through microcapillary nozzles of varying diameter. This study demonstrates that induction of controlled changes in scaffold surface chemistry, by optimizing silk-gelatin ratio, can govern cell proliferation and maintenance of chondrocyte morphology. Microperiodic silk-gelatin scaffolds can influence postexpansion redifferentiation of goat chondrocytes by enhancing Sox-9 gene expression, aggregation, and driving cartilage matrix production, as evidenced by upregulation of collagen type II and aggrecan expression. The strategy for optimizing redifferentiation of chondrocytes can offer valuable consideration in scaffold-based cartilage repair strategies.