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Second European Conference on Biomaterials (II)
SecondEuropeanConference onBiomaterhls(II) Gothenburg, Sweden, 27-29 August, 1981 The second European conference on Biomateriafs was organized by the European Society for Biomaterials and the Laboratory for Experimental Biology of the University of Gothenburg, Sweden. There were some 135 ~rticipants, primarily from Europe. The delegates met at the nicely located school of medicine at Gothenburg. This second report highlights the emerging tendencies of this field as made clear by the more important contributions. The purpose of the meeting was to review the progress in basic understanding of the interface of orthopaedic, dental, maxillofacial and plastic surgical implants. Although the meeting reached at moments a high level of excellence, it may be wondered if the meaning of ‘basic understanding’ was not clear enough when proposed in the conference announ~ments, Too many presentations were too cursory; facts and observation were reported without attempting to understand the observed phenomena. As a result, it was repeatedly stated that a basic science approach is to be used if this field is going to progress. Mechanical aspects and mechanical stability of the interface were the first topics to be discussed. New evidence was presented that the direction of loading should preferably be perpendicular to the implant surface for hard tissue substitution. If not, there is not necessarily direct bone implant contact. Experimental analysis of the bone stressesafter total hip replacement arthroplasty with Ti-6 AI-4V and 316 L stainless steel stems showed that calcar unloading is 50% higher with stainless steel. This finding bears direct clinical relevance, since, it is suggested that calcar unloading may be one of the causes of calcar resorption. When considering the interface between porous coated implants and bone there are at least five different aspects which are subjected to evaluation and engineering design. These are the stressesand strength of the bone, the porous coating and the substrate metal and the stressesand strength at the bone-porous coating interface and substrateporous coating interface. If any of these parts fails, the whole system fails. A new porous coating made of pressure ‘sintered wire meshes was presented. Its use yields better mechani~l properties of the substrate metal and may improve coating to substrate and coating strength. Porous coated metal implants have a larger specific surface area than the presently used implants. Therefore it is of concern whether or not there is increased metal ion release from these implants. This effect may then well provoke as yet unknown systemic reactions. The present status was reviewed; when the ratio of the metal specific area to total body weight increases an increase in Ni release, but not of Cu is noted. Right now there are not sufficient data to comment on the fate of Ti. A thermal passivation procedure effectively reduces the metal ion release from stainless steel. However, it was wondered if this passivation treatment could possibly improve the spontaneous repassi-
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Biomaterials 1982, Vol3 April
vation -- another critical issue of this alloy. In vitro testing of metal ion release is carried out in different solutions. Since the extra cellular space of the internal milieu contains a multitude of proteins and enzymes in addition to electrolytes, experiments in solutions with added amounts of proteins and enzymes are of value. Without understanding why, it was observed that the addition of serum proteins had a profound effect on corrosion rates. It was added later on that it is as valuable to look at the effect of lipoproteins. Quite a few papers dealt with the concept and the experimental and clinical results of ‘osseo-integration’. A 5 to 9 year follow-up study with 2500 titanium dental implants on 370 patients was presented outlining the excellent functionality in patients. There was a 91% success rate in the mandible and a 81% in the maxilla; mobility: 0 mm, bone loss by radiography: O.t5 mm/year (mean); gingival health: mean plaque index 13.7% and mean gingival index 7.6%; pocket depth: 2.6 mm (mean). It is suggested that these results follow from a restrictive patientselection protocol, the careful operative procedure, the material choice and the optimum loading configuration by using threaded roots. Papers dealing with other dental materials considered alumina (AlzOa) and dense hydroxyapatite. Interesting work showed the direct correlation between animal experimentation and theoretical stress analysis: bone resorption was reported where stress peaks were computed. Work with hydroxyapatite showed that these dental implants yield a bone bond which is able to survive chewing forces. The transmu~osal site resembles the natural interface, but the implants as they are now, fracture within 4 months after implantation. A careful study into the behaviour of hydroxyapatite in viva was presented which showed that even with certain lattice substitutions and biphasic structures the apatite bonds to osseous tissue. At the same time elaborate techniques were used to complement LAMMA (Laser microprobe mass analyser) to this field of endeavour. More conventional techniques are used to study the effect of different bioglasseson the surrounding tissues. But the results are therefore not less important. Close to the glass surface a seam is observed with fibrils, remainder of osteoid tissue and encased with minerals. Provided there is no negative influence on the process of differentiation and mineralization such as by TiOz, ZnO or Tao, present in the glass, this seam further influences mineralization. For different glass types the tissue reaction is qualitatively the same, but quantitatively depend on the degradation rate of the implant material. Bioglass is also investigated for its use in bone cement. These studies are phenomenological in nature. Data presented at the meeting would indicate no untoward tissue reaction on wear particles of this composite cement. A histologicat study which provoked great interest was the one where the anterior cruciate ligament of the knee was replaced by carbon fibre strands. A migration of small graphite fibres (80 pm in size) to the lumbo-aortic lymph nodes was observed.
Immunological effects can also be induced by metals. Stainless steel and cobalt chomium alloys produce leucocyte migration inhibition in rabbits sensitized by nickel or cobalt. Various polymers were reported to be successful when used as vehicles for drugs, as vascular prostheses or as a guiding structure for nerve regeneration. Cement free HDPE hip prostheses provided functionally satisfactory results, despite wear, cup deformation and giant cell reaction. An analysis of various failure modes of polymeric percutaneous devices showed that the main reason for failure are infection, interfacial stressing and incompatibility of the materials. A thermodynamic model was proposed to predict platelet adhesion. Experimental evidence of plateletbacteria interactions supported the theory. A panel debate concluded the meeting. The topics addressed varied immensely. Therefore one cannot single out major tendencies or problems with regard to the study of the interfaces. However, a few issues were repeatedly stressed and it is therefore of value to record them here.
There is a need for more basic science, not just descriptions of results. This holds not just for clinical reports, but for histological, mechanical and materials work as well. There is also a need for more and better biomaterials; this is to say many more materials should be developed for potential biomedical usage. Right now designing an implant device is seriously hindered by the scarcity of available materials. It was also stressed that the European Society for Biomaterials should help to organize highly specialized meetings to define the state-of-the-art in some problem areas or areas of great potential. To end with a personal note, it has been a delight to us to be hosted with such friendliness and to have had the opportunity to interact with the excellent and efficient conference organizers, led by Per-l ngvar Branemark and successfully assisted by Tomas Albrektsson.
Paul Ducheyne, Berton Rahn
Twelfthneural prosthesis workshox, National Institutes of Health, Bethesda, Maryland, 5-6 November, 1981
USA,
The Twelfth Neural Prosthesis Workshop sponsored by the National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health (NIH), was held under the Chairmanship of Dr. F. Terry Hambrecht of the N I H. As was the last year’s Conference (that I reported in Biomaterials, 1981, 2, 125-126), this meeting was a highly successful one especially because of its informality and ample time for questions from the audience. Although most of the papers fall in the province of rehabilitation engineering, there were a number of papers that directly relate to biomedical materials and biocompatibility. The Neural Prosthesis Program of the NIH is administered by extramural grants and contracts. A good account of the Development of Neural Prosthesis at the Ranch0 Los Amigos Rehabilitation Center was presented by Dr. D. McNeal. It focused on alleviating some of the problems of stroke and spinal cord injury victims, as well as the treatment of spinal deformities, such as scoliosis and kyphosis. In the case of spinal cord injury, stimulation of the perineal nerve causes massive response permitting the raising of the foot, and enabling the assisted walking of the patient. With scoliosis (20’ to 45” deformities), it has been shown that electrode placement on either side of the spine and therapy over a period of six months lead to a success rate of approximately 87%. No side effects were observed other than minor skin rash due to the surface electrodes. Even with kyphosis, it was possible to achieve a certain amount of correction. A paper on Prosthetic Control (University of Alberta, Canada) was presented by Dr. R. Stein who showed a dramatic film in an amputee with implanted neural electrodes emerging from the stump through a percutaneous bottom. Although excessive fibrosis developed, the electric signals remained stable for the duration of the experiment. Nevertheless, the patient, equipped with an artificial plastic hand and arm (in contrast to the excessively used hook device in the U.S.), was able to drink champagne without spilling. A preliminary report on Multichannel Multiplex In tracortical Recording Electrodes was presented by Dr. K. Wise (University of
Michigan)., Among the requirements were the need for biocompatible materials, recording sites spaced 100 pm apart in depth, chronic implantation and testing in vivo over a period of one year or longer, a reliable percutaneous plug, and small size of the device. An outline of another new project for this year concerned Insulating Materials and their Adhesion (Hughes Aircraft Company) directed by Drs. D.I. Basiulis and A. Naselow. The paper was presented by Dr. Basiulis and outlined the project in terms of selection of insulating films, metallic substrates, adhesion studies, and testing methodologies. No experimental results were given because the project has just commenced. As continuation of their previous work, Drs. A. Hahn and H. Yasuda (University of Missouri) reported on the use of Plasma Polymer Biomaterials. They discussed the application of parylenes (polyp-xylylene, Union Carbide) to platinum macroelectrodes in conjunction with glow discharge polymers of methane and siloxanes. They pointed out the effect of water on adhesion, the strength of which was studied by cyclic voltammetry. Urinary Bladder Control was the subject of a paper by Drs. E. Tanagho and E. Schmidt (University of California, San Francisco). Initial experiments with dogs were followed by human studies in which current of 50 Hz with 50 milliseconds on and 100 milliseconds off was applied to the sacral segments nos. 2 and 3 of the pudental nerves. After a period of several weeks, good results were obtained with one young male patient when the initial electric stimulus was a 6 hours/day, with further improvements when the stimulation was extended to 15 hours/day. The development of Miniature Capacitor Stimulating Electrodes was the subject of a paper by Dr. H. Lerner (Giner, Inc.) who outlined his work on porous electrodes (diameter = 0.19 mm + 5%; length = 0.55 mm ? 10%; capacitance = 0.095 PFD f 15%; leakage current = 1.5 f 0.6 NA; charge storage density = 40 /.X/cm*). The electrodes were etched tantalum, niobium/niobium oxide, and titanium. Although possible tissue damage by porous vs. smooth electrodes was not fully investigated as yet, this does not appear to be a problem. The Electrochemistry of
Biomaterials
1982,
Vol3
April
125
124
Biomaterials 1982, Vol3 April
vation -- another critical issue of this alloy. In vitro testing of metal ion release is carried out in different solutions. Since the extra cellular space of the internal milieu contains a multitude of proteins and enzymes in addition to electrolytes, experiments in solutions with added amounts of proteins and enzymes are of value. Without understanding why, it was observed that the addition of serum proteins had a profound effect on corrosion rates. It was added later on that it is as valuable to look at the effect of lipoproteins. Quite a few papers dealt with the concept and the experimental and clinical results of ‘osseo-integration’. A 5 to 9 year follow-up study with 2500 titanium dental implants on 370 patients was presented outlining the excellent functionality in patients. There was a 91% success rate in the mandible and a 81% in the maxilla; mobility: 0 mm, bone loss by radiography: O.t5 mm/year (mean); gingival health: mean plaque index 13.7% and mean gingival index 7.6%; pocket depth: 2.6 mm (mean). It is suggested that these results follow from a restrictive patientselection protocol, the careful operative procedure, the material choice and the optimum loading configuration by using threaded roots. Papers dealing with other dental materials considered alumina (AlzOa) and dense hydroxyapatite. Interesting work showed the direct correlation between animal experimentation and theoretical stress analysis: bone resorption was reported where stress peaks were computed. Work with hydroxyapatite showed that these dental implants yield a bone bond which is able to survive chewing forces. The transmu~osal site resembles the natural interface, but the implants as they are now, fracture within 4 months after implantation. A careful study into the behaviour of hydroxyapatite in viva was presented which showed that even with certain lattice substitutions and biphasic structures the apatite bonds to osseous tissue. At the same time elaborate techniques were used to complement LAMMA (Laser microprobe mass analyser) to this field of endeavour. More conventional techniques are used to study the effect of different bioglasseson the surrounding tissues. But the results are therefore not less important. Close to the glass surface a seam is observed with fibrils, remainder of osteoid tissue and encased with minerals. Provided there is no negative influence on the process of differentiation and mineralization such as by TiOz, ZnO or Tao, present in the glass, this seam further influences mineralization. For different glass types the tissue reaction is qualitatively the same, but quantitatively depend on the degradation rate of the implant material. Bioglass is also investigated for its use in bone cement. These studies are phenomenological in nature. Data presented at the meeting would indicate no untoward tissue reaction on wear particles of this composite cement. A histologicat study which provoked great interest was the one where the anterior cruciate ligament of the knee was replaced by carbon fibre strands. A migration of small graphite fibres (80 pm in size) to the lumbo-aortic lymph nodes was observed.
Immunological effects can also be induced by metals. Stainless steel and cobalt chomium alloys produce leucocyte migration inhibition in rabbits sensitized by nickel or cobalt. Various polymers were reported to be successful when used as vehicles for drugs, as vascular prostheses or as a guiding structure for nerve regeneration. Cement free HDPE hip prostheses provided functionally satisfactory results, despite wear, cup deformation and giant cell reaction. An analysis of various failure modes of polymeric percutaneous devices showed that the main reason for failure are infection, interfacial stressing and incompatibility of the materials. A thermodynamic model was proposed to predict platelet adhesion. Experimental evidence of plateletbacteria interactions supported the theory. A panel debate concluded the meeting. The topics addressed varied immensely. Therefore one cannot single out major tendencies or problems with regard to the study of the interfaces. However, a few issues were repeatedly stressed and it is therefore of value to record them here.
There is a need for more basic science, not just descriptions of results. This holds not just for clinical reports, but for histological, mechanical and materials work as well. There is also a need for more and better biomaterials; this is to say many more materials should be developed for potential biomedical usage. Right now designing an implant device is seriously hindered by the scarcity of available materials. It was also stressed that the European Society for Biomaterials should help to organize highly specialized meetings to define the state-of-the-art in some problem areas or areas of great potential. To end with a personal note, it has been a delight to us to be hosted with such friendliness and to have had the opportunity to interact with the excellent and efficient conference organizers, led by Per-l ngvar Branemark and successfully assisted by Tomas Albrektsson.
Paul Ducheyne, Berton Rahn
Twelfthneural prosthesis workshox, National Institutes of Health, Bethesda, Maryland, 5-6 November, 1981
USA,
The Twelfth Neural Prosthesis Workshop sponsored by the National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health (NIH), was held under the Chairmanship of Dr. F. Terry Hambrecht of the N I H. As was the last year’s Conference (that I reported in Biomaterials, 1981, 2, 125-126), this meeting was a highly successful one especially because of its informality and ample time for questions from the audience. Although most of the papers fall in the province of rehabilitation engineering, there were a number of papers that directly relate to biomedical materials and biocompatibility. The Neural Prosthesis Program of the NIH is administered by extramural grants and contracts. A good account of the Development of Neural Prosthesis at the Ranch0 Los Amigos Rehabilitation Center was presented by Dr. D. McNeal. It focused on alleviating some of the problems of stroke and spinal cord injury victims, as well as the treatment of spinal deformities, such as scoliosis and kyphosis. In the case of spinal cord injury, stimulation of the perineal nerve causes massive response permitting the raising of the foot, and enabling the assisted walking of the patient. With scoliosis (20’ to 45” deformities), it has been shown that electrode placement on either side of the spine and therapy over a period of six months lead to a success rate of approximately 87%. No side effects were observed other than minor skin rash due to the surface electrodes. Even with kyphosis, it was possible to achieve a certain amount of correction. A paper on Prosthetic Control (University of Alberta, Canada) was presented by Dr. R. Stein who showed a dramatic film in an amputee with implanted neural electrodes emerging from the stump through a percutaneous bottom. Although excessive fibrosis developed, the electric signals remained stable for the duration of the experiment. Nevertheless, the patient, equipped with an artificial plastic hand and arm (in contrast to the excessively used hook device in the U.S.), was able to drink champagne without spilling. A preliminary report on Multichannel Multiplex In tracortical Recording Electrodes was presented by Dr. K. Wise (University of
Michigan)., Among the requirements were the need for biocompatible materials, recording sites spaced 100 pm apart in depth, chronic implantation and testing in vivo over a period of one year or longer, a reliable percutaneous plug, and small size of the device. An outline of another new project for this year concerned Insulating Materials and their Adhesion (Hughes Aircraft Company) directed by Drs. D.I. Basiulis and A. Naselow. The paper was presented by Dr. Basiulis and outlined the project in terms of selection of insulating films, metallic substrates, adhesion studies, and testing methodologies. No experimental results were given because the project has just commenced. As continuation of their previous work, Drs. A. Hahn and H. Yasuda (University of Missouri) reported on the use of Plasma Polymer Biomaterials. They discussed the application of parylenes (polyp-xylylene, Union Carbide) to platinum macroelectrodes in conjunction with glow discharge polymers of methane and siloxanes. They pointed out the effect of water on adhesion, the strength of which was studied by cyclic voltammetry. Urinary Bladder Control was the subject of a paper by Drs. E. Tanagho and E. Schmidt (University of California, San Francisco). Initial experiments with dogs were followed by human studies in which current of 50 Hz with 50 milliseconds on and 100 milliseconds off was applied to the sacral segments nos. 2 and 3 of the pudental nerves. After a period of several weeks, good results were obtained with one young male patient when the initial electric stimulus was a 6 hours/day, with further improvements when the stimulation was extended to 15 hours/day. The development of Miniature Capacitor Stimulating Electrodes was the subject of a paper by Dr. H. Lerner (Giner, Inc.) who outlined his work on porous electrodes (diameter = 0.19 mm + 5%; length = 0.55 mm ? 10%; capacitance = 0.095 PFD f 15%; leakage current = 1.5 f 0.6 NA; charge storage density = 40 /.X/cm*). The electrodes were etched tantalum, niobium/niobium oxide, and titanium. Although possible tissue damage by porous vs. smooth electrodes was not fully investigated as yet, this does not appear to be a problem. The Electrochemistry of
Biomaterials
1982,
Vol3
April
125