Alumina: Implantable Bionics and Tissue Scaffolds

Abstract

This chapter has a two-fold focus: the first section focuses on the bionic application, and the second section focuses on the tissue scaffold application. Bionics: Alumina is an essential component of the hermetic encapsulation and electrical feedthrough system used in implantable bionics. This has been the case since 1970 when the transition was made from the rudimentary epoxy encapsulation systems used in the developmental era of implantable bionics, to the alumina/titanium hermetic electrical feedthrough system used for all implantable bionics since then. Implantable bionics is a global industry currently worth $25 billion per annum and growing rapidly. Thus, implantable bionics is one of the most important commercial applications for alumina advanced ceramics in the world today. The alumina/titanium hermetic feedthrough system for implantable bionics was invented in 1970 by Author Cowdery and has now become the standard hermetic encapsulation for all bionic implants in the global $25 Billion market. This chapter outlines the science and engineering underlying this feedthrough technology and explores its application in 3 key bionic implants (of the 14 or so types of bionic implants on the market): the pacemaker (Cowdery), bionic ear (Cowdery), and bionic eye (Ruys). Tissue Scaffolds: Alumina is a very strong ceramic, far superior to calcium phosphates, and has a high strength even at porosities of over 90%. It can be rendered bioactive by surface-doping with bioactivity-enhancing ions, such as calcium, phosphorous, magnesium and silicon. Authors Soh and Ruys pioneered a novel doped-porous-alumina tissue scaffold technology with an extremely high porosity of 94.4%, a high compressive strength of 384 MPa, with an average pore size of 300 microns, more than large enough for bone ingrowth. This chapter outlines the science and engineering underlying these developments.