3D Printing of a Polymer Bioactive Glass Composite for Bone Repair

A major limitation of synthetic bone repair is insufficient vascularization of the interior region of the scaffold. In this study, we investigated the 3D printing of adipose derived mesenchymal stem cells (AD-MSCs) with polycaprolactone (PCL)/bioactive glass composite in a single process. This offered a three-dimensional environment for complex and dynamic interactions that govern the cell’s behavior in vivo. Borate based bioactive (13-93B3) glass of different concentrations (10 to 50 weight %) was added to a mixture of PCL and organic solvent to make an extrudable paste. AD-MSCs suspended in Matrigel was extruded as droplets using a second syringe. Scaffolds measuring 10x10x1 mm3 in overall dimensions with a filament width of ~500 μm and pore sizes ranging from 100 to 200 μm were fabricated. Strut formability dependence on paste viscosity, scaffold integrity, and printing parameters for droplets of ADMSCs suspended in Matrigel were investigated

On the History and Potentials of Evolutionary Metaphors in Urban Planning

This article looks at the history of evolutionary thought in urban planning. It classifies the use of evolutionary metaphors in three broad theoretical streams. The first stream of thought considers the existence of vital forces and energy flows (vitalism) in an urban form. The second stream provides a holistic-organic (organicism) perspective to the city. The third stream, contemporarily very popular in social sciences, is based on the natural evolutionary theories of Lamarck and Darwin to look at urban dynamics. It is suggested that the flexible-adaptive and self-regulatory nature of evolutionary metaphors can support a holistic-integrative perspective to urban and regional planning