http://www.ncbi.nlm.nih.gov/pubmed/2577851 from 1988 starts:

> In recent years it has been shown that the structures of a wide variety of colloidal aggregates can be described in terms of the concepts of fractal geometry. The purpose of this review is to discuss some of the evidence for fractal geometry in experimental systems and indicate how fractal geometry can be used to develop a better understanding of their aggregation kinetics and physical properties.

so I think the answer is "many". Try https://scholar.google.com/scholar?q=fractal+material for some pointers.

Thank you so much for the pointers. So fascinating!

Google Scholar is a great resource for these sorts of research-oriented questions. I hope you continue to find it useful.