Focal articular cartilage (AC) defects, if left untreated, can lead to debilitating diseases such as osteoarthritis. While several tissue engineering strategies have been developed to promote cartilage regeneration, it is still challenging to generate functional AC capable of sustaining high load‐bearing environments. Here, a new class of cartilage extracellular matrix (cECM)‐functionalized alginate bioink is developed for the bioprinting of cartilaginous tissues. The bioinks are 3D‐printable, support mesenchymal stem cell (MSC) viability postprinting and robust chondrogenesis in vitro, with the highest levels of COLLII and ACAN expression observed in bioinks containing the highest concentration of cECM. Enhanced chondrogenesis in cECM‐functionalized bioinks is also associated with progression along an endochondral‐like pathway, as evident by increases in RUNX2 expression and calcium deposition in vitro. The bioinks loaded with MSCs and TGF‐β3 are also found capable of supporting robust chondrogenesis, opening the possibility of using such bioinks for direct “print‐and‐implant” cartilage repair strategies. Finally, it is demonstrated that networks of 3D‐printed polycaprolactone fibers with compressive modulus comparable to native AC can be used to mechanically reinforce these bioinks, with no loss in cell viability. It is envisioned that combinations of such biomaterials can be used in multiple‐tool biofabrication strategies for the bioprinting of biomimetic cartilaginous implants.

Abstract:The drainage of particulate foams is studied under conditions where the particles are not trapped individually by constrictions of the interstitial pore space. The drainage velocity decreases continuously as the particle volume fraction increases. The suspensions jam -and therefore drainage stops -for values which reveal a strong effect of the particle size.In accounting for the particular geometry of the foam, we show that accounts for unusual confinement effects when the particles pack into the foam network. We model quantitatively the overall behavior of the suspension -from flow to jamming -by taking into account explicitly the divergence of its effective viscosity at . Beyond the scope of drainage, the reported jamming transition is expected to have a deep significance for all aspects related to particulate foams, from aging to mechanical properties.

Foam-based materials are promising micro-structured materials with interesting thermal and acoustical properties. The control of the material morphology requires counteracting all the destabilizing mechanisms during their production, starting with the drainage process, which remains to be understood in the case of the complex fluids that are commonly used to be foamed. Here we perform measurements for the drainage velocity of aqueous foams made with granular suspensions of hydrophilic monodisperse particles and we show that the effect of the particles can be accounted by two parameters: the volume fraction of particles in the suspension (φp) and the confinement parameter (λ), that compares the particle size to the size of passage through constrictions in the foam network. We report data over wide ranges for those two parameters and we identify all the regimes and transitions occurring in the φp-λ diagram. In particular, we highlight a transition which refers to the included/excluded configuration of the particles with respect to the foam network, and makes the drainage velocity evolve from its minimal value (fully included particles) to its maximal one (fully excluded particles). We also determine the conditions (φp,λ) leading to the arrest of the drainage process.