No abstract

Cartilage loss is a leading cause of disability among adults and effective therapy remains elusive. Neonatal chondrocytes (NChons) are an attractive allogeneic cell source for cartilage repair, but their clinical translation has been hindered by scarce donor availability. Here we examine the potential for catalyzing cartilage tissue formation using a minimal number of NChons by co-culturing them with adipose-derived stem cells (ADSCs) in 3D hydrogels. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation are dependent on the intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and resulted in the formation of large neocartilage nodules. This work raises the potential of utilizing stem cells to catalyze tissue formation by neonatal chondrocytes via paracrine signaling, and highlights the importance of controlling cell distribution in 3D matrices to achieve optimal synergy.C artilage loss is a leading cause of disability among adults and represents a huge socio-economical burden.Articular cartilage has limited self-repair potential and damage is often irreversible 1 . Conventional cellbased therapy utilizes autologous chondrocytes for cartilage repair, which is associated with several shortcomings including donor site morbidity and the need for in vitro expansion and multiple surgeries 2 . Furthermore, the ability of autologous chondrocytes to regenerate cartilage tissue declines rapidly with patient age and in vitro expansion 3,4 , making them a suboptimal cell source for cartilage repair. Unlike autologous adult chondrocytes, allogeneic neonatal chondrocytes (NChons) are highly proliferative, immune-privileged, and can readily produce abundant cartilage matrix 3,5,6 . However, donor availability for NChons is scarce, which greatly hinders their broad application.In addition to chondrocytes, adult mesenchymal stem cells (MSCs) are an alternative cell source for cartilage repair 7 . Adipose-derived stem cells (ADSCs), in particular, are an attractive candidate due to their ease of isolation, relative abundance, and chondrogenic potential 8,9 . While stem cells are widely known for their potential to promote tissue regeneration through lineage-specific differentiation, emerging evidence suggests that paracrine signals secreted by stem cells may also contribute to tissue repair 10,11 . Several studies have examined the interactions between articular chondrocytes and MSCs; however, the reported results have been contradictory. While some studies indicated that MSCs inhibit cartilage production by chondrocytes 12,13 , others showed that MSCs stimulate chondrocyte proliferation and cartilage matrix production [14][15][16][17][18] . The discrepant findings may be due to the differences in various parameters in these studies such as co-culture models, medium composition (i.e. serum or other growth factor supplementation), and donor age or disease phenoty...

No abstract

Adipose-derived stromal cells (ADSCs) are attractive autologous cell sources for cartilage repair given their relative abundance and ease of isolation. Previous studies have demonstrated the potential of extracellular matrix (ECM) molecules as three-dimensional (3D) scaffolds for promoting chondrogenesis. However, few studies have compared the effects of varying types or doses of ECM molecules on chondrogenesis of ADSCs in 3D. Furthermore, increasing ECM molecule concentrations often result in simultaneous changes in the matrix stiffness, which makes it difficult to elucidate the relative contribution of biochemical cues or matrix stiffness on stem cell fate. Here we report the development of an ECM-containing hydrogel platform with largely decoupled biochemical and mechanical cues by modulating the degree of methacrylation of ECM molecules. Specifically, we incorporated three types of ECM molecules that are commonly found in the cartilage matrix, including chondroitin sulfate (CS), hyaluronic acid (HA), and heparan sulfate (HS). To elucidate the effects of interactive biochemical and mechanical signaling on chondrogenesis, ADSCs were encapsulated in 39 combinatorial hydrogel compositions with independently tunable ECM types (CS, HA, and HS), concentrations (0.5%, 1.25%, 2.5%, and 5% [w/v]), and matrix stiffness (3, 30, and 90 kPa). Our results show that the effect of ECM composition on chondrogenesis is dependent on the matrix stiffness of hydrogels, suggesting that matrix stiffness and biochemical cues interact in a nonlinear manner to regulate chondrogenesis of ADSCs in 3D. In soft hydrogels (~3 kPa), increasing HA concentrations resulted in substantial upregulation of aggrecan and collagen type II expression in a dose-dependent manner. This trend was reversed in HA-containing hydrogels with higher stiffness (~90 kPa). The platform reported herein could provide a useful tool for elucidating how ECM biochemical cues and matrix stiffness interact together to regulate stem cell fate, and for rapidly optimizing ECM-containing scaffolds to support stem cell differentiation and tissue regeneration.

SUMMARYResearch on the adhesive locomotion of terrestrial gastropods is gaining renewed interest as it provides a source of guidance for the design of soft biomimetic robots that can perform functions currently not achievable by conventional rigid vehicles. The locomotion of terrestrial gastropods is driven by a train of periodic muscle contractions (pedal waves) and relaxations (interwaves) that propagate from their tails to their heads. These ventral waves interact with a thin layer of mucus secreted by the animal that transmits propulsive forces to the ground. The exact mechanism by which these propulsive forces are generated is still a matter of controversy. Specifically, the exact role played by the complex rheological and adhesive properties of the mucus is not clear. To provide quantitative data that could shed light on this question, we use a newly developed technique to measure, with high temporal and spatial resolution, the propulsive forces that terrestrial gastropods generate while crawling on smooth flat surfaces. The traction force measurements demonstrate the importance of the finite yield stress of the mucus in generating thrust and are consistent with the surface of the ventral foot being lifted with the passage of each pedal wave. We also show that a forward propulsive force is generated beneath each stationary interwave and that this net forward component is balanced by the resistance caused by the outer rim of the ventral foot, which slides at the speed of the center of mass of the animal. Simultaneously, the animal pulls the rim laterally inward. Analysis of the traction forces reveals that the kinematics of the pedal waves is far more complex than previously thought, showing significant spatial variation (acceleration/deceleration) as the waves move from the tail to the head of the animal. Supplementary material available online at