Helically-driven granular mobility and gravity-variant scaling relations

This study discusses the role and function of helical design as it relates to slippage during translation of a vehicle in glass bead media. We show discrete element method (DEM) and multi-body dynamics (MBD) simulations and experiments of a double-helix Archimedes screw propelled vehicle traveling in a bed of soda-lime glass beads. Utilizing granular parameters from the literature and a reduced Young''s modulus, we validate the set of granular parameters against experiments. The results suggest that MBD-DEM provides reliable dynamic velocity estimates. We provide the glass, ABS, and glass–ABS simulation parameters used to obtain these results. We also examine recently developed granular scaling laws for wheels applied to these shear-driven vehicles under three different simulated gravities. The results indicate that the system obeys gravity granular scaling laws for constant slip conditions but is limited in each gravity regime when slip begins to increase.

This study discusses the role and function of helical design as it relates to slippage during translation of a vehicle in glass bead media.     

Development of a composite degradable/nondegradable tissue-engineered vascular graft

The present study aimed to determine the feasibility of constructing a reinforced autologous vascular graft by combining the advantages of fibrin gel as an autologous cell carrier material with the inherent mechanical strength of an integrated mesh structure. It was hypothesized that the mesh and dynamic culture conditions could be combined to generate mechanically stable and implantable vascular grafts within a shorter cultivation period than traditional methods. A two-step moulding technique was developed to integrate a polyvinylidene fluoride (PVDF) mesh (pore size: 1-2 mm) in the wall of a fibrin-based vascular graft (I.D. 5 mm) seeded with carotid myofibroblasts. The graft was cultured under increasing physiological flow conditions for 2 weeks. Histology, burst strength, and suture retention strength were evaluated. Cell growth and tissue development was excellent within the fibrin gel matrix surrounding the PVDF fibers, and tissue structure demonstrated remarkable similarity to native tissue. The grafts were successfully subjected to physiological flow rates and pressure gradients from the outset, and mechanical properties were enhanced by the mesh structure. Mean suture retention strength of the graft tissue was 6.3 N and the burst strength was 236 mm Hg. Using the vascular composite graft technique, the production of tissue engineered, small-caliber vascular grafts with good mechanical properties within a conditioning period of 14 days is feasible.