Plastics in Medicine and Surgery

Enschede, The Netherlands, 21-22 June 1979

The third conference to be organised by the Plastics and Rubber Institute on the theme Plastics in Medicine and Surgery took place at Twente University of Technology. Approximately 160 delegates from 16 countries attended the meeting, testifying to the topicality of this subject.

As usual with any conference, there were some good points and some not-so-good points about the meeting and many of the remarks I made in the report on the Keele biomaterials conference (J. Biomed. Engng., 1, 1, 67) are equally applicable here. The primary raison d’itre of an international conference is the co-existence of delegates from different centres within one location, to discuss their work. This cannot be achieved if the delegates are scattered about in different hotels and their activities are constrained by coach departure times. It must be said that the fact that this situation existed at Enschede was no fault of the P.R.I. who had their room allocation on the campus decimated at a late stage. However, it did have a significant influence on the meeting.

The perennial parallel session problem arose yet again, the solution here being to hold concurrent sessions on the afternoon of one of the two days. Whilst again understanding the reasons for this, I do believe this is the wrong solution and that it is better to have greater selectivity in the papers rather than adopt parallel sessions to accommodate more speakers.

On the positive side, the preprinting of the papers in a booklet (available from PRI, 11 Hobart Place, London SW1 W OH L) is excellent, both in concept and practice. This is perhaps the best answer to the problem of publishing conference proceedings. When authors have to submit abstracts for a conference a year or so before the meeting, and then submit written papers at the time of the conference for a publication that will appear a year, or even years later, there is a considerable time lag between performing the work and seeing it in print. In the method adopted by the PRI the authors can spend the time between submitting the abstract and a few months prior to the conference writing up the paper, in camera-ready format so that all the papers are available at the time of the conference. Such a publication is invaluable, both for prior reading and subsequent reference. A few interleaved clear pages might be an added benefit to supplement with notes should any author want to update or retract any statements.

Forty papers were delivered during the two days of the conference which was opened by the chairman and host, Professor Bantjes. The first paper, by way of an introduction, was a review of the effects of implant morphology and compositions on the soft tissue response, given by Professor D.F. Gibbons of Cleveland, Ohio. He described the tissue response to implant in terms of the

ways in which the material reacts with the normal wound healing process. Professor Gibbons put forward the hypo- thesis that the soft tissue response is dependent upon the way in which two pleuripotential cells, the monocyte and the pericyte, differentiate. The wound without an implant stimulates a basically fibroblastic and macrophage redifferentiation of the monocyte while epithelial cells derive from pericytes. The presence of a foreign body in the wound increases the number of stimuli controlling redifferentiation and various ways were suggested on how this might occur. There is much in the literature on the phenomenology of the tissue response but only in the last few years have we begun to see some hypotheses on mechanisms evolving and this approach is certainly welcome.

Following in the same session were two papers on polymer degradation, two on Bioplast, two on polyvinyl- chloride catheters and one on intraocular lenses. Polymer degradation was first reviewed by Professor J. Leray of Paris and then discussed with specific reference to enzymes by Dr. D.F. Williams of Liverpool. Both papers on Bioplast originated in Hungary and were read by Dr. G. Kerenyi. PVC catheters have been around for a long time, of course, and many discussions have taken place on the problem of plasticizer leaching and toxicity. Dr. G. Hastings from Stoke-on-Trent discussed the possible link between the leaching of the di-2-ethylhexylphthalate from PVC catheters and necrotizing enterocolitis in neonates and urges that either alternative non-leachable or non-toxic plasticizers should be used or totally different polymers employed instead of PVC. M.S. Biggs, from British Industrial Plastics, described the development of a different plasticizer and speculated on the availability of a low extraction grade of PVC for medical use. Dr. Galin (New York Medical College) provided an informative and well-illustrated review of the use of polymethylmethacrylate for intraocular lenses. Although there are many problems associated with the removal of cataracts and the insertion of intraocular lenses, progress does appear to have been good and high long-term success rates are achieved.

The two parallel sessions in the afternoon concerned plastics in orthopaedics and sterilization and processing of plastics. There seems to be little of interest to report in the area of orthopaedic plastics at the moment. The discussion following a paper by Dr. Tunino of the Netherlands on the use of low modulus fracture plates showed there is still a lot of confusion concerning fracture fixation and I remain to be convinced of the need for plates of equivalent modulus to bone.

Concerning sterilization, Dr. Ouwerkerk from the Netherlands reviewed the use of gamma irradiation, R. Peterson (Utah, USA), discussed residual ethylene oxide and ethylene chlorohydrin after ethylene oxide sterilization,

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V. Handles from Denmark concentrated on formaldehyde- steam sterilization and Dr. Meakin, Unjversity of Bath discussed the chemical disinfection of contact lenses. All- in-all, these papers provided a usefuf summary of the status of these various methods.

Included in the sterilization and processing session, for some reason, was a paper by Dr. John Autian, University of Tennessee on the screening program that has been developed for the evaluation of biomaterials. The amount of work put into this project and the results obtained are impressive and it is to be hoped that some useful standard protocols wilt emerge. Also in this session was a paper on the use of antibiotics in silicone rubber catheters for use in hydrocephalus, by Mr. R. Bayston, of Sheffield.

Perhaps the most interesting session of the conference was that on blood compatibility, opened by a paper by Dr. Jan Feijen of Enschede on blood foreign surface contact phenomena. This was followed by discussions on protein absorption by Dr. Brash, McMaster University, Canada, and then by Dr. Andrade of Salt Lake City. The work reported

London, 4 October 1979

The possible disappearance from world markets of certain materials was a topic which caught the attention of manu- facturers and clinicians brought together at a recent day conference by the Plastics and Rubber Institute to consider recent developments in the use of polymers in dentistry. The particular properties required for denture bases, impression materials, and in reconstructive surgery, make gutta-percha an ideal material for which no adequate replacement has been found. The small batch requirements of consumers make such compounds uncommercial although some altruistic manufacturers do indeed oblige long-standing clients with small amounts.

Dr. Stafford (University of Wales at Cardiff) began the day with a clear and comprehensive survey of the various materials employed, and their special properties as denture bases; impression materials; restoratives and fillers; adhesives and tissue conditioners.

More detail of the actual polymers used and their advantages and faults was given by Dr. Brian Causton (London Hospital Medical College). A critical factor is the cost of preparing individual dies for each patient. At present, heat-cured PMMA is widely used; injection moulding is too capital intensive and has met with resistance from some technicians; for the future we look to pourable polymers.

The fatigue life of a hardened dental plate is important and has been studied using tiny strain gauges; deformation and fracture form a large part of the NHS repair bill! A badly fitted denture can even result in bone resorption and loss of the support bone. Miss A. Fletcher asked whether prolonging the life of a plate was really valuable since patients’ mouths changed and a perfect long-lasting material might cause more damage. Entanglement gels, used as tissue conditioners, and plasticized acrylics as soft linings, relieve

in these papers and others in this session contrasts strongly with some of the other work presented at the meeting for the experimental techniques used are more sophisticated and the scientific content of the work of far greater depth. Much of the work in other areas of biomaterials research seems a little naive in contrast. Comments were made from the floor about the clinical relevance of some of this work but how are we ever going to come to terms with the real situation in patients if we do not understand the funda- mental concepts in the first place. Certainly these papers on blood compatibility provided a very interesting and useful session.

The conference concluded with a session on mis- cellaneous topics among which were the immobilization of collagenase on millipore membranes (Dr. R. Sparks, Washington University, USA), elastomers for leaflet heart valves (Dr. W. Hoffacter, F.R. Germany) and controlled drug release (Prof. N. Graham, Strathclyde).

David Williams.

the pressure initially, but soon harden due to loss of plasticizer.

The teeth themselves must be aesthetically acceptable, and combination of this property with sufficient wear resistance is currently being investigated by several companies, to maintain a faceted ‘pearly’ look.

Mr. Conroy from Queen Mary’s Hospital, Roehampton gave a fascinating slide show of the use of different polymers in maxilla-facial surgery, to repair traumatic injury, congenital deformity or following disease or chronic infection. Depending on the degree of damage, prostheses which give rigid support may be needed, as well as elastomers such as silicone rubber, to replace soft tissue. Skull implants are now perforated to aid fibrous regeneration. While RTV silicones take a comparatively long time to cure, speeding the process by catalysis may introduce toxic additives, which may migrate causing physiological damage.

The afternoon was devoted to polymer chemistry. Professor Braden explained those aspects of physical chemistry which pertain to polymers in the oral environ- ment; his present interest is the uptake of water from solution. Dr. A. Wilson (Laboratory Government Chemist) predicted the increasing use of polyelectrolyte glasses as fillers since they show good adhesion and thus do not need a cement. A team from Revertex are developing an improved dental impression material by adaptation of an already proven commercial poly(butadiene).

During discussion the acceptability of carbon fibres was mentioned; they improve the modulus when used as filler and are biocompatible. The use of polyurethane in surgery was approached with caution; some results have been unreliable and since isocyanate is used in its manu- facture, caution was advised. The P.R.I. are to be thanked for the opportunity of some valuable discussion.

Mary Korndo~er

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