  Design - especially of physical objects - can be understood as creative acts
solving practical problems. In this paper we describe a biologically-inspired
developmental model as the basis of a generative form-finding system. Using
local interactions between cells in a two-dimensional environment, then
capturing the state of the system at every time step, complex three-dimensional
(3D) forms can be generated by the system. Unlike previous systems, our method
is capable of directly producing 3D printable objects, eliminating intermediate
transformations and manual manipulation often necessary to ensure the 3D form
is printable. We devise fitness measures for optimising 3D printability and
aesthetic complexity and use a Covariance Matrix Adaptation Evolutionary
Strategies algorithm (CMA-ES) to find 3D forms that are both aesthetically
interesting and physically printable using fused deposition modelling printing
techniques. We investigate the system's capabilities by evolving and 3D
printing objects at different levels of structural consistency, and assess the
quality of the fitness measures presented to explore the design space of our
generative system. We find that by evolving first for aesthetic complexity,
then evolving for structural consistency until the form is 'just printable',
gives the best results.
