1085th General Monthly Meeting
Spare Parts for Humans
Dr. John A.M. Ramshaw, CSIRO Molecular Science andProfessor I. Klineberg, Professor of Prosthodontics, University of Sydney
Date: Wednesday 6th October 1999
Time: 6 for 6.15 pm
Venue: Hallstrom Theatre, Australian Museum
ABSTRACTS
Collagen-Polymer Composites
Dr. John A.M. RamshawCSIRO Molecular Science
Extracellular matrix components, particularly collagens, have proved very successful as biomaterials in a range of medical devices used in the treatment of various tissue diseases and trauma recovery applications. An understanding of the in vivo performance of these devices is an essential step in development and further improvement.
We have conducted extensive pre-implant and explant analysis studies on a range of collagen-based devices, particularly vascular replacements intended for use in peripheral artery replacement. An example of these studies has been a collagen-polymer composite, the Omniflow Vascular Prosthesis (BioNova International, North Melbourne). This device has proved very successful for clinical management of arterial disease, performing significantly better than synthetic polymeric devices in femoral artery replacement. Our studies have characterised the collagen organisation in the device and have provided information on the biochemical nature of the blood contact surface. Studies on explants from animal models, up to 4 years from implant, and of clinical explants, up to 8 years from implant, have provided detailed information of the host's response to the device. Data show, for example, the important role of porosity in the composite material to allow integration of host tissue and show the differential incorporation of new, host derived connective tissue components into the implanted device.
Together, these and other data provide a better understanding of the in vivo performance of this device and allow for the development of strategies to further improve the device for new, more challenging applications, such as a small diameter device that would be effective for coronary artery applications.
Oral implants restoration and osseoperception
Professor I. KlinebergProfessor of Prosthodontics, University of Sydney
Teeth and supporting structures provide an exquisitely delicate mechanism for proprioceptive information on the degree and direction of bite force. Together with mechanoreceptor feed-back from muscles, ligaments, joints and skin, contribute to kinaesthetic perception and neuromuscular control. When teeth are lost, the loss of the delicate control mechanism is significant, as is the psychosocial implications of tooth loss. This state of dental deafferentation is particularly significant when all teeth are lost, and replacement prostheses are poor substitutes.
The use of bone-anchored implant-supported prostheses offers a new dimension to the restoration of oral function and psychosocial well being. Correct handling of tissues allows osseointegration of the implants and as well a return of proprioceptive discriminative abilities.
A New Man, Thanks to Polyurethane and Titanium
Report on the General Monthly Meetingby Dr Edmund Potter
The Society's President, Associate Professor Tony Baker, took the chair at the 1085th General Monthly Meeting at the Hallstrom Theatre in the Australian Museum on Wednesday evening, 6th October 1999, the theme being "Spare Parts for Humans". There were two speakers, first Dr John Ramshaw, (CSIRO Chief Research Scientist, Molecular Science), who covered "Collagen-Polymer Composites", followed by Professor I. Klineberg (Sydney University, Prosthodontics), addressing "Oral implants restoration and osseoperception".
Both speakers had been motivated in their separate ways by the quest to improve the performance and endurance of familiar body parts (blood vessels for Ramshaw and teeth for Klineberg) through taking advantage of modern materials (synthetic polymers for Ramshaw and metallic titanium for Klineberg).
By 1991 development in the "spare parts industry" had inspired international definition of a "biomaterial", a substance intended to interface with biological systems. Clearly, an acceptable biomaterial must exhibit long-term compatibility (chemical, physical, and mechanical) with the biological substrates the living body offers and imposes. Thus it would be futile if a synthetic polymer were gradually to lose strength and integrity on contact with pulsating blood, or if a metal were unstable in saline conditions and the accumulating corrosion products were poisonous.
Dr Ramshaw described the formation of composite tubular structures from naturally occurring collagens (essentially stringy proteins, as in the leather industry, for example) finely enmeshed in vivo with a tough, durable, synthetic polymer (like polyurethane or fluoropolymers, both familiar to us in quality paints, for example). A silicone-polymer tube is the starting point, and after about 12 weeks embedment in a sheep's back tissue, sufficient intergrowth with the animal's collagen has taken place to yield a composite, which, after purification, has a microscopic mesh texture like that of a typical garden hose. This semi-natural material has been used as an aortic bypass (in greyhounds actually), and an excellent performance without threat of blockage has extended out to 4 years so far, with 10 years expected.
Professor Klineberg recalled the 1965 pioneering work of Brnemark in Gothenberg on "osseointegration", where bone (initially the jaw, but later elbow, ankle and hip) was anchored with an inert metal (specifically precision-made titanium screws). An initial titanium/bone interaction stabilises after about 18 months, when it seems that biocompatibility has been established, presumably through the agency of a film of titanium dioxide, which is known to secure the passivity of titanium under otherwise corrosive conditions. The speaker emphasised the differing and sometimes-extreme sensory discrimination of teeth or (in default) the jawbone, and this creates an imperfectly understood but significant factor in the application of implants. We were reminded that amputees feels the limbs they no longer have, and the same can apply to teeth - hence the term "osseoperception".
Both speakers used slide illustrations most effectively. At question time, Dr Ramshaw commented that the surgery was more expensive than his composite materials, and Professor Klineberg conceded that teeth implants are awkward with growing children. The President proposed the vote of thanks to the speakers , and with others entertained them to dinner afterwards.