Silk fiber reinforcement modulates in vitro chondrogenesis in 3D composite scaffolds.

The limited self-regenerative capacity of adult cartilage has steered the upsurge in tissue engineered replacements to combat the problem of osteoarthritis. In the present study, the potential of fiber-reinforced silk composites from mulberry (Bombyx mori) and non-mulberry (Antheraea assamensis) silk has been investigated for cartilage tissue engineering. The fabricated composites were physico-chemically characterized and analyzed for cellular viability, proliferation, extracellular matrix formation and immunocompatibility. Both mulberry and non-mulberry silk composites showed effective swelling (25%-30%) and degradation (10%-30%) behavior, owing to their interconnected porous nature. The non-mulberry fiber-reinforced composite scaffolds showed slower degradation (∼90% mass remaining) than mulberry silk over a period of 28 days. The reinforcement of silk fibers within silk solution resulted in an increased compressive modulus and stiffness (nearly eight-fold). The biochemical analysis revealed significant increase in DNA content, sulphated glycosaminoglycan (sGAG) (∼1.5 fold) and collagen (∼1.4 fold) in reinforced composites as compared to pure solution scaffolds (p ≤ 0.01). Histological and immunohistochemical (IHC) staining corroborated enhanced deposition of sGAG and localization of collagen type II in fiber-reinforced composites. This was further substantiated by real time polymerase chain reaction studies, which indicated an up-regulation (∼1.5 fold) of cartilage-specific gene markers namely collagen type II, sox-9 and aggrecan. The minimal secretion of tumor necrosis factor-α (TNF-α) by murine macrophages further demonstrated in vitro immunocompatibility of the scaffolds. Taken together, the results signified the potential of silk fiber-reinforced composite (particularly non-mulberry, A. assamensis) scaffolds as viable alternative biomaterial for cartilage tissue engineering.

Reloadable Silk-Hydrogel Hybrid Scaffolds for Sustained and Targeted Delivery of Molecules.

Tunable repeated drug administration is often inevitable in a number of pathological cases. Reloadable 3D matrices for sustained drug delivery are predicted as a prospective avenue to realize this objective. This study was directed toward sonication-induced fabrication of novel reloadable Bombyx mori silk fibroin (SF) (4, 6, and 8 wt %) hydrogel, injected within 3D porous (8 wt %) scaffolds. The focus was to develop a dual-barrier reloadable depot system for sustained molecular cargo release. Both the varying SF concentration (4, 6, and 8 wt %) and the sonication time (30, 45, and 60 s) dictated the extent of cross-linking, ß-sheet content, and porosity (1-10 µm) influencing the release behavior of model molecules. Release studies of model molecules (trypan blue, TB, 961 Da and bovine serum albumin, BSA, 66 kDa) for 28 days attested that the variations in their molecular weight, the matrix cross-linking density, and the scaffold-hydrogel interactions dictated the release behavior. The Ritger and Peppas equation was further fitted into the release behavior of model molecules from various SF matrices. The hybrid constructs exhibited high compressive strength along with in vitro compatibility using primary porcine chondrocytes and tunable enzymatic degradation as assessed for 28 days. The aptness of the constructs was evinced as a reloadable model molecule (BSA and fluorescein isothiocyanate-inulin, 3.9 kDa) depot system through UV-visible and fluorescence spectroscopic analyses. The novel affordable platform developed using silk scaffold-hydrogel hybrid constructs could serve as a sustained and reloadable drug depot system for administration of multiple and repeated drugs.