Differential effects of eight metal ions on lymphocyte differentiation antigens in vitro

The Inflammatory Effects of Breast Implant Particulate Shedding: Comparison With Orthopedic Implants

Currently, there is a dearth of information regarding the degree of particle shedding from breast implants (BIs) and what are the general biological consequences of BI debris. Thus, it is unclear to what degree BI debris compromises the long-term biological performance of BIs. For orthopedic implants, it is well established that the severity of biological reactivity to implant debris governs long-term clinical performance. Orthopedic implant particulate debris is generally in the range of 0.01 to 100 μm in diameter. Implant debris-induced bioreactivity/inflammation is mostly a peri-implant phenomenon caused by local innate immune cells (eg, macrophages) that produce proinflammatory cytokines such as tumor necrosis factor-α, interleukin-1β, interleukin-6, and prostaglandin 2 (PGE2). In orthopedics, there have been few systemic concerns associated with polymeric implant debris (like silicone) other than documented dissemination to remote organs (eg, liver, spleen, etc.) with no known associated pathogenicity. This is not true of metal implant debris where normal (well-functioning) implants can induce systemic reactions such as delayed type hypersensitivity. Diagnostic analysis of orthopedic tissues has focused on innate (macrophage mediated) and adaptive (lymphocyte-mediated hypersensitivity) immune responses. Orthopedic implant debris-associated lymphocyte cancers have not been reported in over 40 years of orthopedic literature. Adaptive immune responses such as hypersensitivity reactions to orthopedic implant debris have been dominated by certain implant types that produce specific kinds of debris (eg, metal-on-metal total joint prostheses). Orthopedic hypersensitivity responses and atypical BI bioreactivity such as BI-associated anaplastic large cell lymphoma share crossover markers for diagnosis. Differentiating normal innate immune reactivity to particles from anaplastic large cell lymphoma reactions from delayed type hypersensitivity reactions to BI-associated implant debris remains unclear but vital to patients and surgeons.

Osteolysis and wear debris after total knee arthroplasty presenting with extra-articular metallosis in the calf

Component wear after total knee arthroplasty (TKA) with extruded metallosis in the extra-articular tissue of the calf secondary to a periprosthetic fracture is a rare complication. A 77-year-old man with a failed Insall-Burstein II TKA prosthesis presented with calf cellulitis after a fall. Radiologic evaluation revealed severe osteolysis and loosening of prosthetic components and an intramuscular abscess communicating with the medullary canal of the tibia through an undisplaced periprosthetic fracture. The patient developed rhabdomyolysis with acute renal failure. Drainage of the calf abscess showed staining of the muscles with wear debris and metallosis. The patient subsequently had debridement and excision of the infected TKA implant. Prompt diagnosis of this condition should be suspected in cases of failed arthroplasty with osteolysis and periprosthetic fracture.

Biocompatibility: a biomechanical and biological concept in total hip replacement

The insertion of any implant or prosthesis into bone usually changes the biomechanical environment and, thus, alters the stresses and strains applied to the bone. Both bone overload and excessive stress protection can result in bone resorption. The material and geometry of any implant should be designed to avoid excessive flexural mismatch. Incompatibility of materials may result in interface and mechanical failure, with the consequent generation of particulate debris, subsequent osteolysis and implant failure. Particulate debris can be generated from articulating surfaces and from any other modular or fixation interface. Larger particles are associated with a foreign body giant cell reaction. Polyethylene particles in the size range of 0.5 to 10 microm excite a cytochemical reaction that culminates in osteolysis. The precise pathogenesis of osteolysis has not been characterised, but it is probable that different pathogenetic mechanisms are involved in the different radiological types of osteolysis. A large number of very small metallic particles are released from metal-on-metal couples. These may cause mutagenic damage (chromatid breaks, chromosome translocations, aneuploidy, etc.). In defining implant biocompatibility it is essential to consider the biological response both to an altered mechanical environment and to the liberation of particulate debris.

Differential lymphocyte reactivity to serum-derived metal-protein complexes produced from cobalt-based and titanium-based implant alloy degradation

The lymphocyte response to serum protein complexed with metal from implant alloy degradation was investigated in this in vitro study using primary human lymphocytes from healthy volunteers (n = 10). Cobalt chromium molybdenum alloy (Co-Cr-Mo, ASTM F-75) and titanium alloy (Ti-6Al-4V, ASTM F-136) beads (70 microm) were incubated in agitated human serum at 37 degrees C to simulate naturally occurring metal implant alloy degradation processes. Particulate free serum samples that had been incubated with metal were then separated into molecular weight based fractions. The amounts of soluble Cr and Ti within each serum fraction were measured and correlated with lymphocyte proliferation response to the individual serum fractions. Lymphocytes from each subject were cultured with 11 autologous molecular weight based serum fractions either with or without added metal. Two molecular weight ranges of human serum proteins were associated with the binding of Cr and Ti from Co-Cr-Mo and Ti implant alloy degradation (at <30 and 180-250 kDa). High molecular weight serum proteins ( approximately 180 kDa) demonstrated greater lymphocyte reactivity when complexed with Cr alloy and Ti alloy than low (5-30 kDa) and midrange (30-77 kDa) serum proteins. When the amount of lymphocyte stimulation was normalized to both the moles of metal and the moles of protein within each fraction (metal-protein complex reactivity index), Cr from Co-Cr-Mo alloy degradation demonstrated approximately 10-fold greater reactivity than Ti in the higher molecular weight serum proteins ( approximately 180 kDa). This in vitro study demonstrated a lymphocyte proliferative response to both Co-Cr-Mo and Ti alloy metalloprotein degradation products. This response was greatest when the metals were complexed with high molecular weight proteins, and with metal-protein complexes formed from Co-Cr-Mo alloy degradation.

Metal sensitivity in patients with orthopaedic implants

All metals in contact with biological systems undergo corrosion. This electrochemical process leads to the formation of metal ions, which may activate the immune system by forming complexes with endogenous proteins. Implant degradation products have been shown to be associated with dermatitis, urticaria, and vasculitis. If cutaneous signs of an allergic response appear after implantation of a metal device, metal sensitivity should be considered. Currently, there is no generally accepted test for the clinical determination of metal hypersensitivity to implanted devices. The prevalence of dermal sensitivity in patients with a joint replacement device, particularly those with a failed implant, is substantially higher than that in the general population. Until the roles of delayed hypersensitivity and humoral immune responses to metallic orthopaedic implants are more clearly defined, the risk to patients may be considered minimal. It is currently unclear whether metal sensitivity is a contributing factor to implant failure.

Sarcoma arising adjacent to a total hip arthroplasty

We present the case of a 79-year-old woman who developed a high grade spindle cell sarcoma adjacent to total hip arthroplasty 13 years after the index operation. MRI scan appeared to show a direct communication between the tumour and intra medullary canal through a breach in the femoral cortex.

Environmental immunogens and T-cell-mediated responses in fibromyalgia: evidence for immune dysregulation and determinants of granuloma formation

Thirty-nine patients with fibromyalgia syndrome (FMS) according to American College of Rheumatology criteria were studied for cell-mediated sensitivity to environmental chemicals. Lymphocytes were tested by standard [(3)H]thymidine incorporation in vitro for T cell memory to 11 chemical substances. Concanavalin A (Con A) was used to demonstrate T cell proliferation. Controls were 25 contemporaneous healthy adults and 252 other concurrent standard controls without any aspect of FMS. Significantly higher (P < 0.01) stimulation indexes (SI) were found in FMS for aluminum, lead, and platinum; borderline higher (0.05 > P > 0.02) SI were found for cadmium and silicon. FMS patients showed sporadic responses to the specific substances tested, with no high-frequency result (>50%) and no obvious pattern. Mitogenic responses to Con A indicated some suppression of T cell functionality in FMS. Possible links between mitogenicity and immunogenic T cell proliferation, certain electrochemical specifics of granuloma formation, maintenance of connective tissue, and the fundamental nature of FMS are considered.

Pathophysiology of infections after internal fixation of fractures

Infection complicating internal fixation of fractures is a serious complication that is difficult to treat. Whenever metallic devices are implanted in vivo, successful biointegration requires that host cells colonize the highly reactive implant surface. Bacteria such as staphylococci can also become adherent to metallic or polymeric implants and will compete with host cells for colonization of the implant surface. Once adherent, these bacteria form a biofilm and undergo phenotypic changes that make them resistant to the normal host immune response as well as to antibiotics. Furthermore, metallic implants themselves cause specific deficits in the function of the local immune system that may render the host response to infection inadequate. Any associated soft-tissue injury causes even greater impairment of local immune function. Despite the potentially detrimental impact of internal fixation, fracture stability is of paramount importance in achieving fracture union and in preventing infection. It has been demonstrated in animal models that contaminated fractures without internal fixation develop clinical infection more commonly than similar fractures treated with internal fixation at the time of colonization. Because of the potential for infection whenever internal fixation is utilized, appropriate prophylactic antibiotic coverage for staphylococci and Gram-negative organisms should be provided. Open wounds and severely damaged soft tissues require aggressive management so that a viable soft-tissue envelope is maintained around the implant. Host factors such as smoking and malnourishment should be corrected. Early diagnosis and aggressive treatment of implant-related infection with antibiotics, debridement, and maintenance of stable internal fixation are essential to successful treatment.

Hypersensitivity to metallic biomaterials: a review of leukocyte migration inhibition assays

Metal hypersensitivity is a well-established phenomenon occurring in a variety of domestic and workplace settings. Degradation products of metallic biomaterials may mediate metal hypersensitivity. However, little is known about the short- and long-term pharmacodynamics and bioavailability of circulating metal degradation products in vivo. Mechanisms by which in vivo metal sensitivity reactions occur have not been well characterized and the degree to which metal sensitivity may be a predisposing factor for eliciting an overaggressive immune response remains clinically unpredictable. In vitro leukocyte migration inhibition assays have been used for investigating cell-mediated hypersensitivity reactions to biomaterial and biomaterial degradation products. This review provides a historical and technical summary of four in vitro techniques used for determination of leukocyte migration activity: (1) membrane migration or Boyden chamber, (2) capillary tube, (3) leukocyte migration using agarose technique, and (4) collagen gels. It is difficult to determine which, if any, of these techniques is singularly best suited for the investigation of suspected biomaterial-related symptoms in patients. However, Boyden chamber membrane migration testing is recommended for clinical investigations, principally because a high degree of standardized investigator independent materials and methodologies is necessary for compiling and comparing the results of patients tested at various times over the length of an extended study. Ultimately, in vitro migration inhibition testing has the potential to provide a reliable means for predicting some complications and thus enhancing the outcome for patients receiving metallic implants. Continuing improvements in migration inhibition testing methods, used alone or in combination with other immunologic assays, will likely improve assessment of patients susceptible to biomaterial antigen-induced delayed-type hypersensitivity responses.

Systemic metal-protein binding associated with total joint replacement arthroplasty

The distribution of titanium [Ti] and chromium [Cr] in serum protein fractions of patients with and without total joint replacements containing Cr and Ti was studied. Three groups were evaluated: 10 patients with cobalt-chromium [CoCr] alloy prostheses and known elevated levels of Cr; 10 patients with Ti containing implants and known elevated levels of Ti; and 10 age matched controls without prostheses. Metal-protein binding was also examined by adding various concentrations of Cr(+3) (CrCl(3)) to control serum. Cr and Ti were bound to serum proteins within specific molecular weight ranges in both patient groups. Two molecular weight ranges were found to bind Cr (at approximately 70 and approximately 180 kDa) in patients with CoCr alloy prostheses, whereas a single molecular weight range (at approximately 70 kDa) was found to bind Ti in patients with Ti alloy implants. This metal-protein binding was reproduced in vitro by adding CrCl(3) at concentrations of approximately 100 and 1000 ppb Cr, which is orders of magnitude higher than that contained in the serum of patients with CoCr alloy implants ( approximately 3 ppb Cr). This suggests that protein binding is initiated in the periprosthetic space where metal concentrations are typically 2-3 orders of magnitude higher than that observed systemically in the serum. In vitro, high molecular weight proteins including immunoglobulins demonstrated the highest affinity to Cr. Determination of specific protein carriers of metal degradation products is an essential component in the assessment of the long-term biological affects of total joint replacement devices.

Effect of prosthetic titanium wear debris on mitogen-induced monocyte and lymphoid activation

Wear debris generated by joint implant components has been reported to activate inflammatory and immune cells. Particulate debris derived from prosthetic material induces monocytes/macrophages, lymphocytes, synoviocytes, and fibroblasts to secrete cellular products, such as cytokines, which mediate inflammation. It has been speculated that degradation products impair the ability of inflammatory and immune cells to mount a protective response against noxious agents and infectious organisms by interfering with cell activation. Recent in vitro studies suggest that soluble metal ions inhibit T and B cell activation, but it is not known whether insoluble metal particles generated by prosthetic wear in tissue have the same effect. The purpose of the present study was to determine whether titanium wear debris retrieved from periprosthetic tissues surrounding a failed knee prosthesis suppresses activation of human monocytic and lymphoid cells. Peripheral blood monocytes and lymphocytes were incubated with the nonspecific activator pokeweed mitogen (PWM) in the presence or absence of titanium particles. Cell proliferative capacity and production of interleukins IL-1beta and IL-2 were determined as measures of activation. Titanium wear debris induced monocyte secretion of IL-1beta at levels comparable to those induced by PWM alone. In combination with PWM, titanium wear debris stimulated monocytes to secrete higher concentrations of IL-1beta than is stimulated by titanium itself or by PWM alone. Titanium wear debris did not activate lymphocytes, as indicated by marginal changes in DNA synthesis and IL-2 secretion, nor did it suppress the PWM-induced stimulation of DNA synthesis and IL-2 secretion. Our study suggests that nonspecific mitogen activators in spite of exposure to titanium wear debris can stimulate monocytic and lymphoid cells.

Metal release in patients who have had a primary total hip arthroplasty. A prospective, controlled, longitudinal study

There is an increasing recognition that, in the long term, total joint replacement may be associated with adverse local and remote tissue responses that are mediated by the degradation products of prosthetic materials. Particular interest has centered on the metal-degradation products of total joint replacements because of the known toxicities of the metal elements that make up the alloys used in the implants. We measured the concentrations of titanium, aluminum, cobalt, and chromium in the serum and the concentration of chromium in the urine of seventy-five patients during a three-year prospective, longitudinal study. Twenty patients had had a so-called hybrid total hip replacement (insertion of a modular cobalt-alloy femoral stem and head with cement and a titanium acetabular cup without cement), fifteen had had insertion of an extensively porous-coated cobalt-alloy stem with a cobalt-alloy head and a titanium-alloy socket without cement, and twenty had had insertion of a proximally porous-coated titanium-alloy stem with a cobalt-alloy head and a titanium socket without cement. The remaining twenty patients did not have an implant and served as controls. The results of our study showed that, thirty-six months postoperatively, patients who have a well functioning prosthesis with components containing titanium have as much as a threefold increase in the concentration of titanium in the serum and those who have a well functioning prosthesis with cobalt-alloy components have as much as a fivefold and an eightfold increase in the concentrations of chromium in the serum and urine, respectively. The predominant source of the disseminated chromium-degradation products is probably the modular head-neck junction and may be a function of the geometry of the coupling. Passive dissolution of extensively porous-coated cobalt-alloy stems was not found to be a dominant mode of metal release.

CLINICAL RELEVANCE

Increased concentrations of circulating metal-degradation products derived from orthopaedic implants may have deleterious biological effects over the long term that warrant investigation. This is a particularly timely concern because of recent clinical trends, including the reintroduction of metal-on-metal bearing surfaces and the increasing popularity of extensively porous-coated devices with large surface areas of exposed metal. Accurate monitoring of the concentrations of metal in the serum and urine after total hip replacement also can provide insights into the mechanisms of metal release. Our findings suggest that fretting corrosion at the head-neck coupling is an important source of metal release that can lead to increased concentrations of chromium in the serum. Determinations of the concentrations of metal in the serum and urine may be useful in the diagnosis of patients who are symptomatic after a total joint replacement as increased levels are indicative of at least one mode of mechanical dysfunction (for example, fretting corrosion) of the device.

Fluorescent microplate assay for respiratory burst of PMNs challenged in vitro with orthopedic metals

This report describes a simple, rapid, automated microassay for measuring in vitro changes of oxidative burst of phagocytes following challenge with metals for orthopedic devices. The production of reactive oxygen species (ROS) by polymorphonuclear leukocytes (PMNs) was measured using 2',7'-dichlorofluorescin-diacetate (DCFH-DA) as fluorescent probe. DCFH-DA enters the cells and is oxidized by ROS to fluorescent DCF. The DCF generated was directly proportional to ROS produced intracellularly: The fluorescence intensity was read and converted to an index of ROS production by cells. In our experimental system, granulocytes (PMNs) were isolated from normal human blood and seeded in microplates. To verify if metals could influence ROS production, chromium, cobalt, nickel, molybdenum, titanium, aluminum, and vanadium prepared as aqueous extracts in phosphate-buffered saline were tested onto PMNs using phorbolmyristate acetate (PMA) as positive control. Molybdenum, aluminum, and vanadium increased ROS generation by PMNs, while signals not different from unstimulated PMNs were recorded for chromium, cobalt, nickel, and titanium. The DCFH-DA microplate-based assay provides an in vitro tool for the detection of oxygen-reactive species generated by PMNs as a response to metals.

Cellular immune responses to orthopaedic implant materials following cemented total joint replacement

In vitro cellular immune responses to metallic and polymeric implant materials in particulate form were measured preoperatively in 185 patients. The patients were candidates for either primary total joint replacement (n = 65) or revision arthroplasty (n = 120). Proliferative cellular responses to polymethylmethacrylate particles in patients with osteoarthritis at revision surgery for aseptic loosening were significantly higher than the responses of patients with osteoarthritis at either primary surgery or surgical revision for mechanical failure of the prosthesis or sepsis. The responses to particles of cobalt-chromium alloy at revision surgery were also higher than the responses at primary surgery. The responses were reevaluated in 32 patients after a minimum of 10 months following surgery to correlate individual changes in the biological responses with clinical progress. Reevaluation at early follow-up of patients who had undergone primary surgery revealed significantly elevated proliferative responses and in vitro cytokine production in response to polymethylmethacrylate and cobalt-chromium alloy particles compared with their preoperative responses. In contrast, the response at follow-up to polymethylmethacrylate was significantly reduced in patients who had undergone revision surgery, and this reduction corresponded with a marked improvement in pain, joint motion, and function following revision surgery. These data suggest that specific cellular responses to polymethylmethacrylate or cobalt-chromium alloy particles, or both, may be associated with loose or painful prostheses.

Prosthetic metals impair murine immune response and cytokine release in vivo and in vitro

This study was designed to investigate whether prosthetic metals adversely affect immune responses and the release of immunoregulatory cytokines in vivo and in vitro. Titanium and cobalt-chromium alloy were injected into the peritoneal cavity of female mice. At 5, 8, and 12 weeks after the injection, the levels of cobalt and chromium in the blood were significantly increased compared with the levels in control mice; the level of titanium was not significantly changed until 12 weeks. The release of interleukin-2 was significantly inhibited by cobalt-chromium particles after 3 weeks; titanium particles did not have the same effect until 8 and 12 weeks. The release of interleukin-4 was significantly inhibited by cobalt-chromium particles after 3 weeks but was not significantly inhibited by titanium particles until 12 weeks. The release of interferon-gamma was significantly inhibited by cobalt-chromium particles only at 12 weeks and was not inhibited by titanium particles. The proliferation of T cells was significantly inhibited by cobalt-chromium particles at 3 weeks and by titanium particles at 8 and 12 weeks, and the proliferation of B cells was significantly inhibited by cobalt-chromium particles after 3 weeks but was not inhibited by titanium particles. The production of immunoglobulin by lipopolysaccharide-stimulated B cells was also significantly reduced by cobalt-chromium particles after 3 weeks and by titanium particles at 8 and 12 weeks. The cytokine release by lymphocytes, proliferation of T and B cells, and immunoglobulin production by B cells were also significantly inhibited by titanium and cobalt-chromium particles, as well as by titanium, cobalt, and chromium ions in vitro, whereas these metals are not cytotoxic to murine lymphocytes in vitro. The data indicate that the metal-induced immunosuppression may be another important factor in the development of implant-associated infection in patients with a prosthesis.

Inhibition of T and B cell proliferation by titanium, cobalt, and chromium: role of IL-2 and IL-6

The mechanism by which an increased risk of prosthetic infection is induced in patients with total joint arthroplasties is poorly understood. The adverse effects of metallic corrosion products of a prosthesis on host defense mechanisms, particularly immune response and release of immunoregulatory cytokines, remain largely unknown. Titanium, cobalt, and chromium are the materials most often used for joint implantation. Therefore, this study was aimed at investigating the cytotoxicity of titanium, cobalt, and chromium and whether these metals affect T and B cell proliferation and the release of cytokines by human peripheral blood mononuclear cells (PBMC) in vitro. Metal cytotoxicity was not observed judging by cell viability and cell injury after PBMC was extensively exposed to the metals. Phytohemagglutinin (PHA)-induced T cell proliferation and lipopolysaccharide-induced B cell proliferation were significantly inhibited by titanium, chromium, and cobalt. The release of IL-2 and IL-6 by PHA-stimulated PBMC was significantly inhibited by titanium, chromium, and cobalt. Titanium did not alter IFN-gamma production, whereas chromium and cobalt significantly reduced IFN-gamma release by PHA-stimulated PBMC. The addition of IL-2 and IL-6 significantly restored the metal-induced inhibition of T cell and B cell proliferation, respectively. This study sheds light on how the metals impair immune response and cytokine release, suggesting that patients with an extensive exposure to the metals may develop immune dysfunctions. The compromised immune response induced by the metals might significantly contribute to an increased risk of infection in patients with joint prostheses.

The immune response to implant materials in humans

The etiology of aseptic loosening of prosthetic joint replacement components is unclear. Implant materials have been considered biologically inert, but recently studies indicate that inflammatory reactions directed against the implanted materials may contribute to aseptic loosening. Data suggesting a progression from a simple inflammatory reaction to complex immune responses against the biomaterials are reviewed. The cellular responses to particles of polymethylmethacrylate, ultrahigh molecular weight polyethylene, and alloys of cobalt-chromium and titanium were assayed in vitro to determine cell proliferation in patients with underlying diagnoses of osteoarthrosis, rheumatoid arthritis, and avascular necrosis who had joint replacement. Control populations were provided by patients with similar diagnoses who were preoperative surgical candidates. The underlying diagnoses did not seem to influence responses to particle stimulation. Elevated responses to both acrylic and cobalt-chromium were observed in patients with aseptically loosened prostheses. These findings suggest that the development of a cellular response to particulate debris may be significant in the pathogenesis of aseptic loosening.

Adhesion of human peripheral lymphocytes on biomaterials preadsorbed with fibronectin and vitronectin

The adhesion of human peripheral lymphocytes (HPL) was studied after preadsorption of fibronectin (FN) and vitronectin (VN) on hydrophilic glass and hydrophobic octadecyl glass. The adhesion of HPL was shown to be dependent not only on the wettability but also on the protein preadsorbed. Vitronectin expressed not only a higher extent of adhesion under static conditions but also a stronger interaction with HPL, indicated by the low detachment under shear stress. The flow experiments also demonstrated that FN adsorbed on octadecyl glass may undergo conformational changes because HPL could be easily removed. Scanning electron microscopy revealed that HPL on both FN- and VN-coated glass spread well whereas particularly on FN-coated octadecyl glass less cell spreading was observed; moreover, some round cells were detected. The typing of adherent HPL by immunofluorescence microscopy showed that on FN- and VN-coated glass about 70% of all HPL were T-cells (CD 3+). However, on octadecyl glass, particularly on VN, a smaller percentage of CD 3+ cell was observed. The testing for the beta 1 integrin--the receptor for FN and the alpha v integrin--the receptor for VN demonstrated that about 70% of all cells on FN-coated glass were positive for the beta 1 integrin. On VN-coated glass, however, only 5% of HPL were positive for the beta 1 integrin. Although on VN a high adhesion and strong binding of HPL was observed, no presence of the alpha v integrin was detected.

Use of microelectrodes as electrochemical sensors of metal ions released from biomaterials

In vitro studies to determine Fe3+ levels in mice liver samples were performed using platinum microelectrodes and atomic absorption spectrophotometry. Microelectrodes have been shown to be useful for quantitative analysis of metal ions released during the biodegradation process that occurs on implanted metallic biomaterials.

Cell culture methods for testing biocompatibility

Cell culture systems may be of value in testing the biocompatibility of prosthetic materials before they are introduced into clinical use. In recent years, in vitro methods for assaying biomaterials have gained in importance owing to the growing concern over the use of animals for biomaterials testing. Significant effort is therefore being focused toward developing predictive and quantitative, but also simple and reliable, methods of testing using cultured cells. At present, a number of methods for measuring both the cytotoxicity and the specific cytocompatibility of different materials are available. The usefulness of these systems is no longer confined to screening new materials; they can be used to study the mechanisms of action of various materials during tissue/material interaction. This paper reviews the published literature on the use of cell culture models in evaluating biocompatibility and reports on the personal experience of the authors, who have been using cell culture systems for many years and for different purposes.