The science behind making ocular and orthopaedic implants more biocompatible was described by Professor Andrew Lloyd (University of Brighton) in the Conference science medal lecture on September 11
Most of the biomaterials developed for use as surgical implants, such as intraocular
lenses or prosthetic hip joints, had been designed to have optimal physical
or optical properties, Professor Lloyd said, but their main reason for failure
was poor biocompatibility.
Although the population of the United Kingdom was expected to fall by about
2m over the next 50 years, the proportion of people aged over 60 years was predicted
to increase by half over the same period. Mobility and vision were prime determinants
of healthy aging, Professor Lloyd said. The development of hip and knee prostheses
and intraocular implants had helped but the limits of these technologies had
been reached. In addition, many prostheses were being implanted in younger patients
leading to a need for revision operations, each with a greater chance of failure.
One natural compound involved in biocompatibility was glycine betaine, a zwitterion.
Professor Lloyd’s early reseach had involved using betaine based compounds
as cryopreservatives for frozen blood. Initial research had shown glycine betaine
to be an effective cryopreservative at low concentrations, when it protected
against salt stresses, but not at high concentrations, when it had a damaging
osmotic effect.
Ocular implants
Visual degradation could be caused by cataracts, glaucoma or retinal detachment.
Ocular implants, lacrymal plugs, intraocular lenses, glaucoma filtration implants,
keratoprosthetics and scleral buckles had been developed to counteract these
problems, but the materials involved had been developed on the basis of their
physical properties, not their biocompatibility, Professor Lloyd said.
For example, the first implant to treat cataracts had been developed in 1949.
Since then foldable lenses had been produced which could be inserted via smaller
surgical incisions. However, 50 per cent of implants suffered from protein conditioning
and cellular adhesion which led to reductions in vision. Most postoperative
complications were due to poor biocompatibility, he said. The materials were
not bioinert.
Professor Lloyd had worked with Biocompatibles Plc to develop new intraocular
lenses with phosphotidylcholine based coatings. These had been shown to have
reduced protein and macrophage adhesion and reduced Staphylococcus epidermidus
adhesion.
He had also worked on an implantable ocular drain for the treatment of glaucoma.
As well as giving the drain better biocompatibility, his work had developed
a new, elliptical shape and a more precise, laser-drilled hole, only 30 microns
in diameter, for the drain.
Work was under way on an artificial cornea which had both a central optical
part and a peripheral skirt. It was a more challenging design issue than any
previous implant.
Orthopaedic implants
Professor Lloyd’s research had also covered the production of osteogenerative
materials which could be used to lengthen the life of orthopaedic implants.
These implants would bond better with patients’ bones after surgery. A
calcified porous titanium surface had been formed in in vitro experiments, he
said.