A sonication-induced silk-collagen hydrogel for functional cartilage regeneration.

Cartilage tissue has limited self-regeneration capacity and current treatment methods often result in fibrocartilage formation. Although collagen has shown the ability to induce chondrogenesis of mesenchymal stem cells (MSCs) and regenerate hyaline cartilage, the application of a pure collagen hydrogel is inherently limited by its fast degradation, poor mechanical properties and excessive cell-mediated shrinkage. To overcome this challenge, we developed a sonication-induced silk-collagen composite hydrogel (COL + SF(S)) and investigated its physicochemical and biological properties compared with a collagen hydrogel (COL) and a non-sonicated silk-collagen composite hydrogel (COL + SF(NS)). The results showed that the sonication treatment of silk fibroin induced antiparallel ß-sheet formation and a stronger negative charge on the silk fibroin molecule, which resulted in improved mechanical properties of the COL + SF(S) hydrogel. The COL + SF(S) hydrogel exhibited superior stability during cell culture and promoted the gene expression of SOX9 at the early stage and sulfated glycosaminoglycan (sGAG) deposition without any exogenous growth factor. Moreover, the cartilage regeneration capacity of the COL + SF(S) group was evaluated in rabbit knee defects. The COL + SF(S) group exhibited well-integrated articular hyaline cartilage closely resembling native articular cartilage after 6 months. Overall, the COL + SF(S) hydrogel holds great potential as a scaffold material to regenerate functional hyaline cartilage.

The Effect of Early and Delayed Harvest on Dynamics of Fermentation Profile, Chemical Composition, and Bacterial Community of King Grass Silage.

The objective of this study was to assess the effect of harvesting time on the fermentation characteristics, chemical composition, and microbial community of king grass silage. King grass was harvested at three growth periods of 90 days (KN90S), 110 days (KN110S), and 130 days (KN130S); chopped into 2-3-cm particle size; and ensiled in polyethylene bags (20 × 30 cm). The fermentation quality and chemical composition of silages were analyzed after 1, 3, 7, 14, 30, and 60 days of ensiling. Bacterial community of silage ensiled for 60 days was profiled using next generation sequencing (NGS) technology. The KN110S showed the most extensive lactic acid (LA) fermentation during 7 days of fermentation compared to KN90S and KN130S. After 60 days of fermentation, the KN110S showed the lowest pH and the highest lactic acid content among the three treatments. The butyric acid and ammonia nitrogen contents of KN90S and KN130S were significantly greater than those of KN110S (p < 0.05). After a timespan of 60 days of ensiling, the bacterial community of king grass silage was predominantly populated by Proteobacteria in phylum level, whereas unclassified Enterobacteriaceae genus remained dominant in all silages. A higher relative abundance of Clostridium was observed in KN90S and KN130S, but not in KN110S, and greater abundance of Lactococcus appeared in KN110S and KN130S silages than KN90S. It is concluded that harvesting time had an important effect on the fermentation quality and microbial community of king grass silage.

Progress in Preparation of Silk Fibroin Microspheres for Biomedical Applications.

As a natural biomaterial, silk fibroin (SF) holds great potential in biomedical applications with its broad availability, good biocompatibility, high mechanical strength, ease of fabrication, and controlled degradation. With emerging fabrication methods, nanoand microspheres made from SF have brought about unique opportunities in drug delivery, cell culture, and tissue engineering. For these applications, the size and distribution of silk fibroin particles (SFPs) are critical and require precise control during fabrication. Herein, we review common and emerging SFPs fabrication methods and their biomedical applications, and also the challenges and opportunities for SFPs in the near future. Lay Summary: The application of silk in textile has an extraordinarily long history and new biomedical applications emerged owing to the good biocompatibility and versatile fabrication options of its major protein component, silk fibroin. With the development of nanotechnology and microfabrication, silk fibroin has been fabricated into nano- or microspheres with precisely controlled shape and distribution. In this review, we summarize common and emerging silk fibroin particle fabrication methods and their biomedical applications, and also discuss their challenges and opportunities in the nearest future.

Role of N-Cadherin in a Niche-Mimicking Microenvironment for Chondrogenesis of Mesenchymal Stem Cells In Vitro.

During the development of natural cartilage, mesenchymal condensation is the starting event of chondrogenesis, and mesenchymal stem cells (MSCs) experienced a microenvironment transition from primarily cell-cell interactions to a later stage, where cell-extracellular matrix (ECM) interactions dominate. Although micromass pellet culture has been developed to mimic mesenchymal condensation in vitro, the molecular mechanism remains elusive, and the transition from cell-cell to cell-ECM interactions has been poorly recapitulated. In this study, we first constructed MSC microspheres (MMs) and investigated their chondrogenic differentiation with functional blocking of N-cadherin. The results showed that early cartilage differentiation and cartilage-specific matrix deposition of MSCs in the group with the N-cadherin antibody were significantly postponed. Next, poly(l-lysine) treatment was transiently applied to promote the expression of N-cadherin gene, CDH2, and the treatment-promoted MSC chondrogenesis. Upon one-day culture in MMs with established cell-cell adhesions, collagen hydrogel-encapsulated MMs (CMMs) were constructed to simulate the cell-ECM interactions, and the collagen microenvironment compensated the inhibitory effects from N-cadherin blocking. Surprisingly, chondrogenic-differentiated cell migration, which has important implications in cartilage repair and integration, was found in the CMMs without N-cadherin blocking. In conclusion, our study demonstrated that N-cadherin plays the critical role in early mesenchymal condensation, and the collagen hydrogel provides a supportive microenvironment for late chondrogenic differentiation. Therefore, sequential presentations of cell-cell adhesion and cell-ECM interaction in an engineered microenvironment seem to be a promising strategy to facilitate MSC chondrogenic differentiation.