Article Text
PDF
Statistics from Altmetric.com
Ophthalmology has a long history of successful conventional biomaterial applications including viscoelastics, drug delivery vehicles, contact lenses, and a variety of implants. A myriad of further possibilities exists as the margins between conventional material concepts and natural tissues continue to blur, and biomaterials move closer to nature. Genetically engineered materials (for example, hyaluronic acid and fibrin tissue glues) harnessing the power and accuracy of biological systems in molecular synthesis are becoming commonplace. New synthetic surfaces capable of upregulating or downregulating biological responses at the tissue/material interface are starting to reach clinical application; and an emerging understanding of matrix/cell interactions may soon allow engineered replacement for a range of tissues in the eye.
Synthetic materials in ophthalmology
A basic classification divides materials according to their primary bonding structure into ceramics (ionic bonding), metals (metallic bonding), and polymers (covalent bonding). Modern ophthalmic implants are almost all fabricated from synthetic polymers.
Polymeric materials are composed of long chain molecules (polymers) synthesised from repeat units (monomers) whose chemical character and reactivity determine many bulk properties. Most polymer chains have a covalently bonded backbone of carbon atoms joined to a variety of pendant groups. For siloxanes (“silicone”), an important group of synthetic biomaterials, this backbone consists of alternating atoms of silicone and oxygen. Molecular chains vary in length and are irregularly intertwined, although areas of regular arrangement (crystallinity) may exist. Cross linkage density and the density of secondary bonding further determine bulk properties for a given polymeric material.1
Biological conditioning after implantation
Secondary bonding mechanisms (for example, hydrogen bonds, van der Waals forces) are particularly relevant to biological systems, and are thought to have an important role in modulating protein conditioning—the process by which relatively inert polymeric material surfaces are rendered biologically active by contact with the tissues or body fluids.2
Protein conditioning is partly determined by surface reactivity, which varies …