Trajectories in nanotechnology: embracing complexity, seeking analogies.

This account comprises personal reflections on the field of nanosystems primarily designed for the delivery of biologically active agents. It emphasises the colloidal nature of nanoparticles obeying the same physical laws that dictate the behaviour of disperse systems. Research reveals not only intrinsic complexities but a variety of possible trajectories in vivo and ex vivo, issues of stability, interactions and behaviour in a range of often constrained environments. Such are the variations in the chemical and physical nature of the nanosystems and the active agents they carry, their putative "targets" and the many biological systems and models in which they are employed, it is not possible to generalise. Stochastic events may exclude precise prediction or extrapolation of outcomes, but embracing and studying complexity lead to new insights, often aided by consideration of analogies in cognate areas. This is part of the process of illumination. Unexpected results provide the true essence and excitement of scientific endeavour. Simplification is perhaps its antithesis.