811

Biocompatibility of particulate pol~e~y~e~ac~late bone cements: a comparative study in vi&~ and in tivo L.A. Thomson, F.C. Law, K.H. James, CA. Matthew and N. Rushton University of Cambridge Orthopaedic Cambridge C62 200, UK

Research

Unit, Level E6, Addenbrooke’s

Hospital, Hills Road,

The biocompatibility of particles of four different commercial polymethy~methacrylate (PMMA) bone cements was evaluated by exposing human synovial fibroblasts and mouse peritoneal macrophages to particles of cement. Cell integrity and inflammatory potential were assessed using enzyme release and microscopical examination. Results suggested the occurrence of cell damage in both cell types and macrophage studies indicated inflammatory potential. The response in vivo was investigated by intra-articular injection of the particles into mouse knee joints. Clinical and histological evaluation was performed over 2-52 wk. Particles of all four cements were well tolerated in the joints. Keywords: Received

Bone cement, 10 October

PMMA,

1990; revised

toxicity,

11 December

that are implanted into the human body present a source of potentially toxic agents. Polymethylmethacrylate (PMMA) bone cement is used to fix orthopaedic prostheses, such as total joint replacements, in position. This can result in an accumulation of cement particles in the joint, from wear or from small particles of cement remaining in the joint following surgery. These particles may be hazardous to synovial fibroblasts or to macrophages which phagocytose particulate material. The response of joint tissues to foreign particles varies greatly depending on size and chemical composition. It is therefore essential to determine the tissue reaction to particles of different materials implanted in the body. When investigating the biological response to an implant material it is important to screen both for overt toxicity and the induction of other adverse reactions such as chronic inflammation with granuloma formation or neoplastic changes. The only practical way of studying the many facets of inflammatory and other chronic responses towards foreign materials is in laboratory animals. However, cells in culture can be used to screen for an overt toxic response and to study specific aspects of an inflammatory response. A combination of in vitro and in vivu screening of a material provides a sensitive method of revealing adverse reactions. Materials

Correspondence to L.A. Thomson, Orthopaedics, University of Aberdeen Aberdeen, AB9 2ZD, UK.

0 1992 Butterworth-Heinemann 0142-9612/92/12OSll-OS

Ltd

currently Medical

biocompatibility,

at Department of School, Foresterhill,

1990; accepted

tissue

culture

26 May 1991

Tissue culture techniques were used to monitor the effects of particulate bone cements on macrophages and normal human synovial fibroblasts. By monitoring the redistribution of marker enzymes after cells have been exposed to particles of experimental materials the extent and nature of any reaction can be revealed. Lactate dehydrogenase (LDH) is an enzyme found in the cell cytosol and its release indicates a loss of membrane integrity resulting in leakage of the cytosol. /3-N-acetylD-glucosaminidase [P-NAG) is a lysosomal enzyme and was used to give an indication of the inflammato~ potential of the test particles. Particles known to be inflammatory, such as zymosan or chrysotile asbestos, cause a specific release of lysosomal enzymes with little cell damage as measured with LDH release’. Severely damaging particles such as silica cause gross cell destruction and hence release of both LDH and lysosomal enzymes. Therefore, by investigating the pattern of enzyme release from cells in vitro exposed to an implant material, it is possible to predict the implant’s biocompatibility under clinical conditions. The in viva technique used in this investigation was developed in our Unit by Rushton and Rae’ and has been used to evaluate the biocompatibility of a variety of materials used in orthopaedics, including high-density polyethylene, carbon fibre and the resultant composite materia13, particles of pure titanium and titaniumaluminium-vanadium alloy4, starch glove powder5 and cross-linked high-density poIyethylene6. Using this Biomaterials

1992, Vol. 13 No. 12

Biocompatibiiity of PITA

812 technique, previous results have shown a good correlation with the effects of wear particles from many orthopaedic implants in man. MATERIALS Cements used were Paiacos R and PaIavit (both supplied by Schering Plough, Dardilly, France), CMW3 (CMW Laboratories Ltd, Blackpool, UK) and Surgical Simplex P (Howmedica Ltd, London, UK). All tissue culture requisites were supplied by Flow Laboratories Ltd, Rickmansworth, Herts, UK.

Preparation

of bone cements

Bone cements were mixed under sterile conditions according to the manufacturers’ instructions, formed into pellets and allowed to cure in sterile isotonic saline. Particles were generated from these pellets using a Spex freezer mill (Glen Creston Ltd, Stanmore, Middlesex, UK). Particles were milled for 3 min at high speed. After a 3 min rest period the cycle was repeated twice. After milling the bone cements were analysed for their content of methylmethacrylate, N,N-dimethyl-p-toluidine and terpinolene. The values obtained from these analyses are presented in 7$&le 1.

Isolation

of normal

human

synovial

fibroblasts

Primary monolayer cultures of human synovial fibroblasts were prepared from fresh samples of normal synovium as described by Rae7. Tissue was washed in sterile phosphate buffered saline, dissected to remove any fat and the synovium cut into 1 mm3 Qubes. These cubes were seeded out on to tissue culture plates in medium 199 containing 10% fetal calf serum and antibiotics (200 units/ml penicillin, 100 ,ug/ml streptomycin) and allowed to adhere. Medium was changed regularly and the plates maintained at 37°C in a humidified atmosphere of 5% CO,. After incubation for several days, cells were seen to have grown out of the explant. These were removed from the plate using trypsin-EDTA and placed in a small (25 cm’) tissue culture flask, Cells were subcultured at confluence and the medium changed twice per week. For each experiment, the cells were seeded into 24-well tissue culture plates (2 X lo4 cells/ml, 2 ml/well) and pre-incubated for 24 h (37% humidified 5% CO,). The medium was then removed and replaced with fresh medium containing test particles at concentrations of 0, 0.025,0.05,0.1 and 1.0 mglml. Homogeneous suspensions were obtained by sonication using an ultrasound probe. Cells were exposed to the particles for up to 7 d. Mouse peritoneal macrophages were isolated from freshly killed female To mice according to the method of Rae’. Briefly, mice were killed using chloroform Table 1

Composition of bone cements

followed by cervical dislocation. Medium (10 ml per mouse, medium 199 containing 5 units/ml heparin, 200 units/ml penicillin and 100 pg/ml streptomycin) was injected into the peritoneal cavity. The peritoneum was carefully punctured and the washings removed using a sterile siliconized Pasteur pipette, placed in a sterile container, centrifuged (lOOO+ rev min-I, 10 min) and the macrophage pellet resuspended in medium 199 containing 10% fetal calf serum and antibiotics. Cells were seeded on to sterile 24-well tissue culture plates (lo6cells/ml, 2 ml/well) and pre-incubated for 48 h (37”C, humidified 5% CO,). The medium was then changed for fresh medium containing cement particles as above.

Cell culture Six replicate wells were set up for each time point at each concentration and each cell type. Two of the wells contained sterile glass coverslips to which the cells attached. At the end of the experiment the medium was removed and retained for up to 3 d at 4°C before assay. Cells were lysed by adding Triton-PBS (0.5 ml, TritonXl00 0.5% in phosphate buffered saline) and allowed to stand for at least 2 h at 4’C to ensure complete lysis. Medium was removed from coverslip-containing wells, cells fixed in methanol and stained with May-Grunwald and Giemsa stain. The coverslips were then mounted on slides and examined microscopically.

Enzyme

assays

Samples from the macrophages were assayed for lactate dehydrogenase (EC 1.1.1.27) activity and /?-IV-acetyl-Dglucosaminidase (EC 3.2.1.30) activity, whereas samples from the fibroblasts were only assayed for LDH activity [as fibroblasts are not involved in the inflammatory response). LDH was measured using a kinetic assay based on the method of Wroblewski and La Due’. Medium (0.1 ml) was placed in a quartz cuvette with phosphate buffer containing NADH (2.8 ml, 0.1 M phosphate buffer, pH 7.6 containing 0.1 mM NADH). Pyruvate (0.1 ml, 0.02 M in phosphate buffer, as above) was added to start the reaction. The rate of decrease of absorbance at 340 nm was measured continually for 3 min in a spectrophotometer coupled to a BBC microcomputer at constant 37°C. Activity was expressed as percentage LDH in the medium. @-N-acetyl-D-glucosaminidase was assayed using a stopped spectrophotometric assay”‘. Samples of medium (0.1 ml) were incubated for 2-4 h with ~-nitrophenyl-~acetyl-~-D-glucosaminidase (0.1 ml, 2.2 mM in 0.1M citrate phosphate buffer, pH 4.5). GlycineiNaOH buffer (2.0 ml, pH 10.4,0.2 M) was added to stop the reaction and the absorbance at 400 nm was measured using a spectrophotometer. Absorbance at 400 nm due to release

used in the study

Cement

Methylmethacrylate (mglg)

~,~-dimethyl-p-toluidine

Paiavit Palaces R Surgical Simplex P GMW3

12.415 13.733 20.434 11.652

2625.43 2645.96 1339.25 191.64

Biomaterials 1992, Vol. 13 No. 12

bone cements: LA. Thomson etal.

(mg/g)

lerpinolene (mglg) Not Not Not Not

detected detected detected detected

Biocompatibility

ofp-nitrophenol was expressed medium.

Administration

of PMMA bone cements:

was proportional as the percentage

of particles

L.A. Thomson

et al.

to enzyme activity and activity present in the

in viva

Particles were injected into the knee joints of female To mice using the technique described by Rushton and Rae’. Briefly, a length of sterile stainless steel wire was inserted into a sterile 25 G, 16 mm hypodermic needle until the end was visible at the bevel. The wire was retracted 4 mm and, under a dissection microscope, particulate material was loaded into the bevel of the needle using a manual tamping action until the cavity was firmly packed with cement. This gave a dose4 of 0.2 mg. Animals were lightly anaesthetized by inhalation of diethyl ether. The right knee joint was flexed to about 90’ and the needle inserted into the superficial soft tissue on the medial side of the patellar tendon. The needle was moved slightly laterally [thus displacing the patellar tendon) until it was in line with the intercondylar notch, inserted into the joint cavity and the contents deposited there by gently pushing the wire plunger down the needle. The contralateral knee was treated identically except no material was introduced into the joint, thus enabling the response due to the particles to be distinguished from that due to the procedure. Four groups of 30 mice were injected with particles from the four cements, each group receiving a different cement. Five animals from each group were killed at 24, 8, 16, 26 and 52 wk. Both hind limbs and the regional lymph nodes were removed and fixed in neutral buffered formal saline. Hind legs were cleaned of much of the surrounding tissue and were then decalcified in 5% trichloroacetic acid for 4-6 d. On fixation the limbs were placed in 90” of flexion, sections were cut in an anteriorposterior direction in the longitudinal direction of the tibia, All specimens were embedded in paraffin wax, 7pm sections cut, and stained with haematoxylin and eosin and Masson trichrome.

RESULTS

813

to particles of CMW3 bone cement caused no significant increase in LDH release up to 24 h. However, a statistically significant increase occurred after 24 h exposure to 0.1 mg/ml particles and this was repeated at concentrations of 0.05, 0.1 and 1.0 mg/ml after 48 h exposure. Results are expressed in Figure lc. Morphological examination showed many vacuoles in the cells after exposure to 0.1 mg/ml for 24 h and at all concentrations after 48 h. No significant enzyme release was recorded for exposure to particles of Surgical Simplex P cement at any time or for any concentration up to 48 h and 1 mg/ml respectively (Figure ld). Morphological examination of the coverslips revealed no changes.

Release of /3NAG from primary mouse peritoneal macrophages A highly significant increase in the percentage of PNAG released into the medium occurred following 48 h exposure of mouse peritoneal macrophages to 1 mg/ml Palaces R particles (Figure A). In contrast, statistically significant enzyme release resulted from exposure to Palavit particles under the following conditions: 1 mg/ml for 2 h, 0.05 and 0.1 mg/ml for 4 h, 0.1 and 1.0 mg/ml for 24 h and 1 mg/ml for 48 h. This indicates that particles of Palavit cement caused an inflammatory response after short periods of exposure at quite low doses (Figure Zb). Incubation with particles of CMW3 bone cement caused no statistically significant increase in the percentage of PNAG present in the medium after any of the treatment regimes. Results are expressed graphically in Figure 2c. Exposure to Surgical Simplex P particles caused no inflammatory response under any of the experimental conditions and no statistically significant increase in PNAG release occurred at any time [Figure 2d).

Release of LDH from normal fihroblasts of particles of release at

human R bone

human

synovial

synovial fibroblasts caused increase

to in

Results of the chemical tests performed by Schering Plough are shown in Table I. The particle size for the cements used was lo-100 pm.

Release of LDH from primary macrophages

mouse

peritoneal

Particles of Palaces R bone cement did not cause toxicity until macrophages were exposed to a concentration of 1 mg/ml for 48 h (Figure la). LDH release after 48 h exposure to 1 mg/ml was highly significant and morphological examination of the coverslips revealed a loss of cell number and vacuolization of the remaining cells. Exposure to Palavit particles caused significant release of LDH at a concentration of 1 mg/ml after 48 h (Figure lb). There was a considerable number of vacuoles within these cells when examined microscopically. Exposure of primary mouse peritoneal macrophages Biomaterials

1992, Vol. 13

No. 12

814

Biocompatibility

of PMMA bone cements:

L.A. Thomson

et al.

100

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Figure1 Graph showing the percentage release of lactate dehydrogenase (LDH) into the medium from mouse peritoneal macrophages exposed to cement particles for up to 48 h: a, Palaces R; b, Palavit; c, CMW3; d, Surgical Simplex P. 0 0 mg/ml; 0 0.025 mg/ml; A 0.05mg/ml; A 0.1 mg/ml; 0 1.0 mg/ml.

bone cements was studied over 2-52 wk. During this time none of the animals showed any clinical signs of discomfort in the knee area and no tumours were found at any site. Microscopical evaluation of sections of the knee joints and regional lymph nodes showed similar results for all four cements. Four weeks after injection, cement particles were found in a standard position - lying in the substance of the meniscus. No cement particles were associated with the patellar fat pad. Cartilage surrounding the injection site showed neither formation of granulation tissue nor hyperplasia. There was no synovial response in any knee and the tissue structure throughout appeared normal [Figure 4). After 8 wk the cement particles were more widely spaced with no changes in tissue structure. A slight increase in cellularity was noted in the knees that particulate

Biomaterials

1992, Vol. 13 No. 12

had received an injection of Palavit particles. No tissue reaction or damage was seen at the later time points with cement particles being located in the articular cartilage adjacent to the joint cavity at 16 wk and only small areas of particles located near the joint cavity at 26 and 52 wk (Figure 5). Apart from the slight increase in cellularity observed 8 wk after injection of particles of Palavit, particles of all four cements caused no tissue response in the mouse knee joint over a period of 1 yr with particles still present at this time. Four weeks after injection all cements were found in the lymph nodes of both treated and untreated knees. The tissue response, which was present from 2 to 26 wk, was characterized by lymphocytic depletion and formation of granulation tissue. There was a high frequency of macrophages present during the early stages and most of

BiocomDatibilitv -

of PMMA bone cements:

L.A. Thomson

et a/.

815

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Figure 2 Graph showing the percentage release of&N-acetyl-D-gtucosaminidase @NAG) into the medium from mouse peritoneal macrophages exposed to cement particles for up to 48 h: a, Palacos R; b, Palavit: c, CMW3; d, Surgical Simplex P. 0 0 mg/ml; 0 0.025 mgiml; A 0.05 mglml; A 0.1 mgtml; q 1.0 mglml.

them contained cement particles. This frequency at 26 and 52 wk.

decreased

DISCUSSION Evaluation of biocompatibility using in vitro techniques is well established as a valid initial step in the testing of biomaterials. Many different systems have been used& 11-15. The mouse peritoneal macrophage system used in this study was developed in our laboratory by Rae’ and has been used to evaluate the biocompatibility of a wide range of materials relevant to orthopaedics. Materials tested include cobalt-chromium alloy, cobalt, chromium, molybdenum, nickel and titanium’, barium sulphate”, titanium-aluminium-vanadium alloy17, starch glove

powder5, high-density polyethylene, carbon fibre and the cross-linked high-density polyresultant composite3, ethylene”, carbon fibre-reinforced epoxy resin, expanded polytetrafluoroethylene”, diamond-like carbon coating” and ceramic”. The macrophage is an eminently suitable cell for use in in vitro biocompatibility testing as this cell plays a major role in inflammation and the response to foreign bodies. One of the methods of assessing the inflammatory potential of a material is to measure the levels of the lysosomal enzyme ~-~-acetyl-D-glucosaminidase in culture medium following exposure of macrophages to the test material. Lysosomai enzymes are known to be released from macrophages during inflammation and hence increased lysosomal enzyme activity in the medium indicates that an inflammatory reaction has been elicited. Biomaterials 1992, Vol. 13 No. 12

Biocompatibility

816

of PMMA bone cements:

L.A. Thomson

et al.

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Figure3 Graph showing the percentage release of lactate dehydrogenase into the medium from human synovial fibroblasts exposed to cement particles for up to 7 d: a, Palaces R; b, Palavit; c, CMW3; d, Surgical Simplex P.0 0 mglml; 0 0.025 mglml; A 0.05 mglml;

A 0.1 mglml.

Figure 4 Photomicrograph of a section of a mouse knee 4 wk after injection of Palaces R particles. Original magnification x250, haematoxylin and eosin. Biomaterials 1992, Vol.

13 No. 12

Figure5 Photomicrograph of a section of a mouse knee 52 wk after injection of Palavit particles. Original magnification x400, haematoxylin and eosin.

Biocompatibility

of PMMA bone cements:

L.A. Thomson

The human synovial fibroblast assay system has a similar pedigree to that of the macrophage system. This system has been used to examine the biocompatibility of many materials including both particles and soluble salts of many orthopaedic metals7’17. Analysis of the results from these experiments shows variations in the toxicity ranking of the cement particles depending on the experiment performed. Exposure to mouse peritoneal macrophages revealed a toxicity ranking of CMW3 > Palaces R > Palavit > Surgical Simplex P as determined by release of LDH. There is no apparent link between the chemical composition of the particles as tabulated in Table 2 and LDH release. When release of P-NAG was measured, the order of the inflammatory potential altered to Palavit > Palaces R > CMW3 = Surgical Simplex P. This bears some relation to the composition of the particles, Palavit and Palaces R having the highest levels of N,N-dimethyltoluidine. These results demonstrate that a lack of gross toxicity does not necessarily indicate a lack of inflammatory potential. The toxicity data for human synovial fibroblasts was considerably different to that for the peritoneal macrophages. In this case the order of toxicity as determined by LDH release was Palaces R > CMW3 > Surgical Simplex P > Palavit. All rankings were assigned according to the statistical significance of results obtained. Differences in toxicity rankings between the two cell types are probably due to innate differences. Macrophages are the main scavenging cells within the body and as such have a high phagocytic capacity, readily engulfing foreign particles. However, although fibroblasts have some phagocytic capacity it is very limited and particles are rarely engulfed. Particles that have been phagocytosed are exposed to the complement of degradative enzymes in the lysosome and can cause toxicity via an intracellular route. This makes phagocytic cells more vulnerable to intracellular mechanisms of toxicity than non-phagocytic cells and offers one explanation for the results observed. Although the results show some toxicity and evidence of an inflammatory response, these effects are minor when compared with the positive controls included in the experiments, cobalt particles and zymosan. Zymosan is a well-known inflammatory agent that causes release of lysosomal enzymes without damage to the cell membrane. Cobalt particles are known to be toxic, causing an increased release of LDH into the medium. The mouse knee joint model for evaluation of the biocompatibility of particulate materials in viva was developed in Cambridge’ and has been used to investigate many particulate materials2-6. Results from these investigations have shown a good correlation with the effects of wear particles in man, thus validating the system. The benign nature of the response to particles of all four cements was not unexpected, as PMMA bone cements have been in clinical use for many years. However, changes in the exact nature and chemical composition can have drastic effects on biocompatibility. The system used in our investigation involves comparatively large volumes of particulate material being present in the joint, thus testing for the reaction to a worst-case scenario with total breakdown of the cement. Observations of lymphocyte depletion and granulation

817

et al.

tissue formation in the lymph nodes have not previously been reported in this system, but may be an important response to the presence of foreign material in the lymphatic system and warrant further investigation. It is also important to note that the particles were spread systematically, being found in both legs of the animal after 4 wk. However, no gross adverse responses were

detected. In conclusion, although slight toxicity was observed with these cement particles this was a relatively small effect and much less than that of the controls. Differences in reactions to the four different cements were small and all cements caused essentially similar responses. In viva, slight toxicity was observed with these cement particles but this was a relatively small effect and much less than that of known toxic materials. Differences in reactions to the four different cements were small and all cements caused similar, essentially benign, responses.

ACKNOWLEDGEMENT This work France.

was financed

by Schering

Plough,

Dardilly,

REFERENCES 1

Schorlemmer, H.U., Davis, P., Hylton, W., Gugis, M. and Allison, A.C., The selective release of lysosomal acid hydrolases from mouse peritoneal macrophages by stimuli of chronic inflammation, Br. J. Exp. Pat. 1977 58,

2

Rushton, N. and Rae, T., The intra-articular response to particulate carbon fibre reinforced high density polyethylene and its constituents: an experimental study in mice, Biomaterials 1984, 5, 352-356 Rae, T. and Rushton, N., Biocompatibility of carbon fibres, high density polyethylene and the resultant composite material, Proceedings of the International Conference on Biomedical Polymers (The Biological Engineering Society and The Plastics and Rubber Institute), 1982, pp 23-28 Rae, T., The biological response to titanium and titaniumaluminium-vanadium alloy particles. II. Long-term animal studies, Biomaterials 1986, 7, 37-40 Rae, T., McCormick-Thomson, L.A., Murray, D.W. and Rushton, N., The effect of starch glove powder on joint and other tissues, Ann. Roy. Coil. Surg. Eng. 1989, 71,

315-326

3

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361-365 6

7

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10

Rae, T., Rushton, N., Thomson, L.A., Lardner, A.L. and Martin, S.J., Biocompatibility studies of cross-linked polyethylene, J. Bone Joint Surg. 1988, 70B, 724 Rae, T., The toxicity of metals used in orthopaedic prostheses: an experimental study using cultured human synovial fibroblasts, J. Bone Joint Surg. 1961, 63B, 435 Rae, T., A study on the effects of particulate metals of orthopaedic interest on murine macrophages in vitro, J. Bone Joint Surg. 1975, 57B, 444-450 Wroblewski, F. and La Due, J.S., Lactic dehydrogenase activity in blood, Proc. Sot. Exp. Biol. Med. 1956, 91, 564 Bergmeyer,

H.U., Grassl, M. and Walter, H.E., Reagents for enzymatic analysis in Methods of Enzymatic Analysis (Ed. H.U. Bergmeyer], 3rd Edn, VCH, Weinheim, Germany, 1983, pp 130-131

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Sabelman, E.E., An organ culture model for screening of bone implant materials, ZYansactions 2nd World Congress of Biomaterials, Vol. 7,1964,Washington, USA Haustveit, G., Torheim, B., Fystro, D., Eidern, T. and Sandvik, M., Toxicity testing of medical device materials tested in human tissue cultures, Biomaterials 1964,5,75 Jessup, W. and Dean, R.T., Spontaneous lysosomal enzyme secretion by a murine macrophage-like cell line, Biocbem. J. 1980, 190,647 McCormick-Thomson, L.A., Sgouras, D. and Duncan, R., Poly(amino acid) copolymers as a potential soluble drug delivery system. 2. Body distribution and preliminary biocompatibility testing in vitro and in viva, 1. Bioactive Compatible Polymers 1969, 4, 252-266. McCormick, L.A., Biocompatibility of soluble synthetic polymers being developed as drug carriers, MSc Thesis, University of Keele, UK, 1966

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19

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Rae, T., Tolerance of mouse macrophages in vitro to barium sulphate used in orthopaedic bone cement, 1. Biomed. Mater. Res. 1977, 11,839-846 Rae, T., The biological response to titanium and titaniumaluminium-vanadium alloy particles. 1. Tissue culture studies, Biomaterials 1986, 7, 30-36 Thomson, L.A., Law, F.C., James, K.H. and Rushton, N., Biocompatibility of particles of GORE-TEX@ cruciate ligament prosthesis: an investigation both in vitro and in viva, Biomaterials 1991, 12,781-785 Thomson, L.A., Law, F.C., Franks, J, and Rushton, N., Biocompatibility of diamond-like carbon coating, Biomaterials 1991, 12,37-40 Rae, T., In vitro biocompatibility tests on particulate aluminium oxide, carbon fibre and titanium alloy based on lysosomal enzyme release, Proceedings 4th European Conference on Biomaterials, Leuven, 1983

7th International Conference on Polymers in Medicine and Surgery l-3 September

PiMS 1993

Leeuwenhorst Congress Centre, Noordwijkerhout The Netherlands This meeting is relevant to those involved in the manufacture, evaluation and clinical use of materials and devices, and the scope will include the following topics: 0 Blood-material interactions l

0 0

0

Development and design Development and design Development and design Membranes and sorbents

of new soft tissue implants of new orthopaedic implants of material and implants for the circulatory systems for biomedical applications

For further information please contact: MS D Schorer, Conference Department (C144), The Institute of Materials, 1 Carlton House Terrace, London, SWlY 5DB, UK. Tel: 071 839 4071 (direct line 071 976 1339) Fax: 071 839 3576 Telex: 8814813

Biomaterials

1992, Vol. 13 No. 12

et al.