Mesoporous Biomaterials – multifunctional materials for future medical therapies and bioanalysis

Nanoscience and nanotechnology – the ability to not only fabricate precisely at the nanoscale, but also fully characterize and understand behaviour at these dimensions, is now having some profound influences on medicine. Richard Feynman is widely credited with prompting this era with his challenging 1959 lecture “There’s Plenty of Room at the Bottom”. When we look at how biomaterials have evolved over many centuries (Figure 1), they have moved from convenience (wooden replacement teeth) to resilience (stainless steel hip implants) to temporary forms (biodegradable implants and tissue engineering) that increasingly utilize nanotechnology. The relative number of new solid biomaterials appearing has also gradually declined at the expense of porous or “nanocomposite” ones, as the material approaches to assisting healing have become more and more biomimetic. Indeed, living organisms rely onpores to function to such an extent that our own bodies are highly porous over widely varying length scales. Blood perfusion around the body is based on conduits of hugely different diameters (arteries, arterioles, capillaries, venules and veins). Our bone remodelling relies on osteoclasts adapting its macroand mesoporosity in-vivo and sensing the local stress fields via fluid flow. At the tissue level, our skin relies on macropores for homeostasis. At the individual cell level we rely on membrane proteins that create micropores for moving molecules in and out. So, what pore sizes are needed for biomaterials? Biomaterial scaffolds for tissue engineering are a clear example where high levels of macroporosity and very large pores (pore diameters normally in excess of 100 microns) are essential for cellular infiltration, but additional mesoporosity can be very beneficial. Indeed, the so-called “hierarchical porosity” of very broad pore size range is increasingly used here. Biomaterials for immunoisolation on the other hand require tightly controlled mesoporosity Figure 1: Biomaterial evolution: more interactive, multifunctional, nanostructured and porous.