Human cell culture toxicity testing of medical devices and correlation to animal tests

Cell Culture in the Biological Evaluation of Dental Materials: A Review

Systematic research on dental materials began after World War I. For a long time the research was focused on the physical properties of the materials, and papers dealing with biological aspects were scarce. By the late 1950s a growing interest in biological responses to dental materials developed, and from the 1970s biological and physical evaluations were deemed equally important (1).

Mammalian cells have been maintained in vitro since the early years of this century, but the use of cultured cells to evaluate the effects of chemicals and drugs is a more recent occurrence. The first practical application of this technique was in pharmacological investigations (2), but applications in other fields soon followed, and in 1955 the first studies were reported where a cell culture technique had been applied to the biological evaluation of dental materials (3,4). Since then the use of cell culture systems in dental materials research has grown rapidly. The main application has been for the assessment of cytotoxic effects, and the purpose of this paper is to review different test methods and discuss some facets of the problems posed by the cytotoxicity testing of dental materials.

Human Bone Marrow Cell Culture: A Sensitive Method for Determination of the Biocompatibility of Implant Materials

The objective of this study was to develop a test method for determining the cytotoxicity and biocompatibility of various biomaterials that are used in orthopaedic surgery. This method is based on the use of a human bone marrow cell culture and was developed as an alternative to animal experiments. Human bone marrow cell culture has certain advantages over other cell culture models, as its results show a greater conformity with animal experimental results and clinical studies. Primary cell adherence, cell number, cell proliferation, production of extracellular matrix, cell viability and cell differentiation were used as indicative parameters of biocompatibility. After 2 weeks in culture, differences could be observed between the biomaterials with respect to these parameters. Cell numbers were greatest on the hydroxyapatite ceramic specimens, but were decreased on the titanium alloy specimens. Extracellular matrix hydroxyapatite production was high for ceramics, but reduced for titanium specimens. The polymers allowed only a few cells to adhere, and there were no signs of extracellular matrix production. The influence of biomaterials on differentiation of large numbers of cells was analysed by using flow cytophotometry. There were similar populations of T cells and monocytes on all specimens. However, extended B cell and granulocyte populations were observed with titanium and polyethylene.

Magnesium alloys: A stony pathway from intensive research to clinical reality. Different test methods and approval-related considerations

The first degradable implant made of a magnesium alloy, a compression screw, was launched to the clinical market in March 2013. Many different complex considerations are required for the marketing authorization of degradable implant materials. This review gives an overview of existing and proposed standards for implant testing for marketing approval. Furthermore, different common in vitro and in vivo testing methods are discussed. In some cases, animal tests are inevitable to investigate the biological safety of a novel medical material. The choice of an appropriate animal model is as important as subsequent histological examination. Furthermore, this review focuses on the results of various mechanical tests to investigate the stability of implants for temporary use. All the above aspects are examined in the context of development and testing of magnesium-based biomaterials and their progress them from bench to bedside. A brief history of the first market launch of a magnesium-based degradable implant is given. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 329-347, 2017.

Osteosynthese im Gesichtsschädelbereich

BACKGROUND

The favorable properties of silicon nitride (Si3N4) ceramic, such as high stability and biocompatibility suggest its biomedical use as an implant material. The aim of this study was to test its suitability for osteosynthesis.

MATERIALS AND METHODS

A Si3N4 prototype minifixation system was manufactured and implanted for osteosynthesis of artificial frontal bone defects in three minipigs. After 3 months, histological sections, CT and MRI scans were obtained. Finite element modeling (FEM) was used to simulate stresses and strains on Si3N4 miniplates and screws to calculate survival probabilities.

RESULTS

Si3N4 miniplates and screws showed satisfactory intraoperative workability. There was no implant loss, displacement or fracture. Bone healing was complete in all animals and formation of new bone was observed in direct contact to the implants.

CONCLUSIONS

Si3N4 ceramic showed a good biocompatibility outcome both in vitro and in vivo. This ceramic may serve as biomaterial for osteosynthesis, e.g. of the midface including reconstruction of the floor of the orbit and the skull base. Advantages compared to titanium are no risk of implantation to bone with mucosal attachment, no need for explantation, no interference with radiological imaging.

Comparison of different wound dressings on cultured human fibroblasts and collagen lattices

OBJECTIVE

We compared the effects on cultured human fibroblasts of a new non-adhesive wound dressing, Urgotul, with five other wound dressings. Urgotul is a hydrocolloid dressing; the comparator dressings included impregnated gauze and modern wound dressings.

METHOD

Cultures in monolayer were used to study the morphology and growth of fibroblasts. The Bell model of cultured dermis equivalents was used to investigate myofibroblast differentiation. These cultures were labelled a-SM actin and F-actin.

RESULTS

Two of the tested dressings induced cytotoxic effects. They were found to inhibit cell growth (greater than 60%) and to disturb cell shape and cytoskeletal differentiation. Urgotul and the remaining three dressings showed no effect on proliferation. However, some of them modified fibroblast morphology and affected F-actin distribution.

CONCLUSION

Depending on their nature and components, wound dressings may respect or affect fibroblast behaviour in vitro (proliferation, morphology and a-SM actin and F-actin distribution). The significance of these in vitro observed findings require further investigations.

Toxicity testing of polymer materials for dialysis equipment: reconsidering in vivo testing

The rationale for preclinical testing of plastic materials for medical devices is the protection of patients from leachable toxic substances. A controversial and costly part of this testing is the use of animal in vivo procedures. The objective of the present study was to analyse the importance of in vivo tests in relation to the decision to approve or not to approve materials for use. A total of 1044 plastic materials were analysed by employing chemical, in vitro and in vivo tests: 5708 in vivo tests were performed. In only one out of 2650 systemic injection tests on mice did a material fail. As that material also failed in chemical tests, the systemic injection test had no influence on the decision not to approve the material. Intradermal irritation (2644 tests), implantation (398 tests) and sensitivity (11 tests) procedures on rabbits and guinea-pigs were the other in vivo tests. However, in all except three cases, the same decision on whether or not to use a material would have been reached without any of these in vivo tests. Thus, little security appears to be gained from the in vivo tests, and abandoning them would save resources, probably without any additional risk.

Corrosion and cell culture evaluations of nickel-chromium dental casting alloys

In this study, the corrosion and surface properties of four commercially available nickel-chromium dental casting alloys, were evaluated using electrochemical corrision testing and Auger electron microscopy. The corrosion tests were conducted under cell culture conditions of 5% CO 2 humidified atmosphere at 37 degrees C in minimum essential medium (MEM) balanced salt solution, 95% MEM-5% FBS (fetal bovine serum) cell culture media, and in 95% MEM-5% FBS media after cold solution sterilization of test samples. The results of the surface and corrision analyses were correlated to cytotoxicity and metal ion release from the alloys using agarose overlay and direct contact cell culture tests. The surface and electrochemical corrision analyses demonstrated that the non-beryllium containing alloys were more resistant to accelerated corrosion processes as compared to the beryllium-containing alloys. All alloys demonstrated decreased corrision rates in cell culture solutions after cold solution sterilization treatment. The corrision products released from the nickel-based alloys failed to alter the cellular morphology and viability of human gingival fibroblasts, however they did cause reductions in cellular proliferation. The potential for accelerated corrision and the exposure of local and systemic tissues to elevated levels of corrision products raises concerns over the biocompatibility of these alloys.

Biocompatibility analysis of different biomaterials in human bone marrow cell cultures

A cell culture system for biocompatibility testing of hip implant materials is described. Human bone marrow cells have been chosen because these cells are in direct contact with the biomaterial after implantation in situ. The sensitivity of this method is evaluated for materials which are already being used as implants in humans and animal, e.g., hydroxyapatite (HA) ceramic, pure titanium, and ultra-high-molecular-weight polyethylene (UHMWPE). As indicative parameters of biocompatibility primary cell adherence, cell number, cell proliferation, production of extracellular matrix, cell vitality, and cell differentiation are described. After 2 weeks in culture, obvious differences between the biomaterials with respect to the indicative parameters could be observed. Cell numbers were greatest on the HA specimens. In the case of titanium alloys, we observed a decreased number of cells. The production of extracellular matrix was high for the HA ceramics but reduced for titanium specimens. The polymers allowed only a few adherent cells and showed no signs of extracellular matrix production. The results can be correlated astonishingly well to animal experiments and clinical experiences. Therefore, we suggest that this cell culture system seems to be a useful tool for biocompatibility testing of bone implantation materials. It also helps reduce animal experiments. With the help of flow cytophotometry, we analyzed the influence of biomaterials on large numbers of cells with respect to differentiation. There were similar populations of T cells and monocytes on all specimens tested. Extended B-cell and granulocyte populations, however, were observed with titanium and UHMWPE. Most osteocalcin-containing cells adhered to the HA ceramics.

Biocompatibility analysis of different biomaterials in human bone marrow cell cultures

A cell culture system for biocompatibility testing of hip implant materials is described. Human bone marrow cells have been chosen because these cells are in direct contact with the biomaterial after implantation in situ. The sensitivity of this method is evaluated for materials which are already being used as implants in humans and animal, e.g., hydroxyapatite (HA) ceramic, pure titanium, and ultra-high-molecular-weight polyethylene (UHMWPE). As indicative parameters of biocompatibility primary cell adherence, cell number, cell proliferation, production of extracellular matrix, cell vitality, and cell differentiation are described. After 2 weeks in culture, obvious differences between the biomaterials with respect to the indicative parameters could be observed. Cell numbers were greatest on the HA specimens. In the case of titanium alloys, we observed a decreased number of cells. The production of extracellular matrix was high for the HA ceramics but reduced for titanium specimens. The polymers allowed only a few adherent cells and showed no signs of extracellular matrix production. The results can be correlated astonishingly well to animal experiments and clinical experiences. Therefore, we suggest that this cell culture system seems to be a useful tool for biocompatibility testing of bone implantation materials. It also helps reduce animal experiments. With the help of flow cytophotometry, we analyzed the influence of biomaterials on large numbers of cells with respect to differentiation. There were similar populations of T cells and monocytes on all specimens tested. Extended B-cell and granulocyte populations, however, were observed with titanium and UHMWPE. Most osteocalcin-containing cells adhered to the HA ceramics.

Toxicity testing of polymer materials for dialysis equipment: is there any need for in vivo testing?

In an earlier work, slightly more than 650 plastic materials, intended for use in medical devices, were tested with a battery of chemical, as well as in vitro and in vivo biological tests. An analysis showed that only a limited number of the tests used were actually necessary to obtain the same pass or fail decision as that obtained using the full test battery. This prompted us to prescreen all new materials with a small test battery consisting of the two most discriminating chemical tests and an in vitro cell growth inhibition test. The present work is a report of our findings after testing another 155 materials using this prescreen system. For each single one of the 155 tested materials the same decision on whether or not to use the material in the intended medical device would have been reached without any in vivo testing. In no single case in a total of 851 in vivo tests did an eluate that had passed the in vitro cell test give rise to a reaction in vivo. Thus, among the tests on living systems, the cell test alone seems to be sensitive enough to provide sufficient information. Nothing appears to be gained from the in vivo animal tests. However, some of the materials that passed the prescreening tests later failed in one or several of the chemical tests. Both nonspecific chemical tests and tests for specific molecules seem to detect undesirable levels of leachable substances not detected by the prescreening system. Therefore these tests should not be abandoned. Abandoning unnecessary in vivo testing, on the other hand, would save considerable costs.

In vitro evaluation of dental materials

Biocompatibility has been described as the ability of a material to perform with an appropriate host response in a specific application. Appropriate host response means no (or a tolerable) adverse reaction of a living system to the presence of such a material. An adverse reaction may be due to the toxicity of a dental material. Therefore toxicity may be regarded as one reason for nonbiocompatibility of a dental material. The toxicity of a dental material can be evaluated by in vitro tests, animal experiments and clinical trials. There exists a variety of different in vitro test methods. The most widely used biological systems for toxicity screening of dental materials are cell cultures. Cell cultures for toxicity screening of dental materials are valuable tools for understanding their biological behavior, if the limitations of the methods are taken into consideration, especially concerning the interpretation of the results. Further research should concentrate on better simulations of the in vivo situation in cell cultures. In this review the applications of various cell culture methods to evaluate the cytotoxicity of a wide range of dental materials, e.g. metals, alloys, polymers and cements, are described.

Critical Evaluation of an Agarose Diffusion Method for the Assessment of Eye Irritancy

The agarose overlay method is often used to study the cytotoxicity of non-liquid products. However, diffusion through agarose is a limiting factor in some cases, and this reduces contact between the cells and the test material.

We have developed a new model aimed at reducing this phenomenon. In our technique, rather than being cultured in a monolayer, V79 cells are suspended in 1% agarose medium. We obtained a good linear correlation between this method and the usual L-929 cell monolayer technique (r = 0.95; n = 31). In addition, the new technique is more sensitive. In particular, the cytotoxicity of surfactants is apparent at lower concentrations.

Using this technique, we studied 115 miscellaneous raw materials and cosmetic products, for which in vivo historical ocular irritancy data were available. As expected, our method was unsuitable for the study of alkaline and acidic products, as well as water-alcohol-based lotions. We also adapted the method for testing mascaras and obtained a good ranking for eye irritancy.

For the other 93 products (surfactants, shampoos, lotions, gels, emulsions and miscellaneous products), the mean diameter of the lysis zone after contact for 18 hours was used as the endpoint for comparison with in vivo maximum average scores. There was a strong linear/rank correlation between the two parameters (r = 0.83/rho = 0.79). Furthermore, the concordance between the in vivo and in vitro data in a three-class ranking system was good (weighed kappa index = 0.81). These results suggest that the agarose diffusion method is a potentially useful screening tool for the ocular safety of the categories of products described above.

Cytotoxicity of retrofill materials

Dentin bonding agents reduce microleakage and enhance marginal adaption of composite resin restorations. These characteristics are advantages for their use as an endodontic retrofilling material. Because these materials will be in direct contact with vital tissues, their cytotoxic potential must be evaluated before clinical use. It was the purpose of this study to evaluate the cell cytotoxicity of amalgam, Caulk Universal Bond, Gluma, 35% HEMA, Morita Clearfil, Scotchbond 2, Super EBA, Tenure, and Tenure 5-4. VERO cells were grown in RPMI-1640 medium and cell monolayers were prepared by incubating 15 ml of the cell suspension in 60-mm culture dishes at 37 degrees C in 5% CO2. Twelve milliliters of a medium-agarose mixture containing 1% neutral red vital stain were overlayed onto the cell layer and allowed to solidify. The materials were directly exposed to the agarose overlays by inverting 6.0-mm diameter polypropylene capsules containing the cured and liquid sample materials either immediately (0 time) or after placement in phosphate-buffered saline with 1% gentamicin for 7, 15, or 30 days. Cytotoxicity was determined by measuring the zone of killed cells around the sample 24 h after placement on the agarose. Cytotoxicity was determined by measuring the zones of cell inhibition at 24 h and at 7, 15, and 30 days. Initially, all of the materials were found to be cytotoxic, except amalgam and the Tenure components. The dentin bonding primers showed a mean zone of inhibition of 13.2 mm and the cleansers a 40.0-mm zone. Amalgam demonstrated increasing cytotoxicity: 0.0 mm at 24 h to 12.0 mm at 30 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of two types of human oral fibroblast with a potential application to cellular toxicity studies: tooth pulp fibroblasts and buccal mucosa fibroblasts

Cultures of human oral buccal mucosa fibroblasts and human tooth pulp fibroblasts were established and grown under standard routine conditions. The biological characteristics of cell proliferation, growth pattern, cell morphology and enzyme release (lactate dehydrogenase and acid phosphatase) were studied. Under the same standard in vitro conditions the two cell types demonstrated different growth patterns and different levels of enzyme activity. It is suggested that differences in biological characteristics should be considered when selecting appropriate cells for toxicological studies of dental materials.

A simple model for evaluating relative toxicity of root filling materials in cultures of human oral fibroblasts

Standardized test tubes filled with freshly mixed root filling materials (AH26, CRCS, N2, Kloroperka NO, ZOE cement and 2 experimental cements, ECI and ECII) were transferred into tissue culture flasks. Normal human oral fibroblasts were seeded in the flasks. Morphological cell changes were studied up to 15 days after seeding. The size of cell-free zones around the test tubes and the total cell number per culture flask were calculated after 5, 10 and 15 days. The findings showed N2 cement to be by far the most toxic material at all observation periods, whereas no toxic reactions could be seen in relation to tubes filled with Kloroperka NO. Compared with the 5-day observation period, some cell recovery was observed around test tubes with AH26 and ECII, whereas almost full cell recovery was found around test tubes with CRCS, ZOE and ECI. It was concluded that the present model, which allows long-term observations of human cellular reactions to dental materials, can be used as a simple and relatively cheap screening test for initial toxicity testing of dental materials.

Comparison of in vitro bacterial bioluminescence and tissue culture bioassays and in vivo tests for evaluating acute toxicity of biomaterials

The sensitivity of a bacterial bioluminescent acute toxicity test was compared to the sensitivity of the USP mouse safety, rabbit intramuscular implantation, rabbit intracutaneous, mouse systemic injection, and the MEM elution tissue culture tests. A variety of industrial plastics were used to evaluate the comparative sensitivities. Additional tests were conducted on low-density polyethylene containing a range of dibutyltin dichloride or trans-cinnamic acid concentrations. The bacterial bioluminescent test was more sensitive than any of the in vivo acute toxicity tests. The luminescent bacterial test was generally more sensitive than the tissue culture acute toxicity assay. The bacterial bioluminescent test offers a sensitive, rapid, uncomplicated, and inexpensive means for preliminary compatibility evaluation of biomaterials.

Biocompatibility test procedures for materials evaluation in vitro. I. Comparative test system sensitivity

Relative sensitivity of in vitro biocompatibility test systems was explored. Cellular responses of 12 standardized cell lines to 20 materials representing a range of toxicity were measured. Each cell line and material combination was tested in duplicate using four different culture methods, and each culture plate was examined by two graders. Results of the tissue culture assays were compared to those obtained for the same materials in vivo using a 5-day rabbit intramuscular implant assay. Methods involving measurement of cellular growth (colony counts or percent of confluence) in serum-fortified media extracts of test samples were generally more sensitive and discriminating than those in which test materials were placed directly in cell cultures (measurement of zone of growth inhibition). There was good agreement between graders for all test methods. Antibiotics were not used in the test program. Based upon sensitivity, reproducibility, ability to discriminate materials, and grader agreement, 4 of the 12 cell lines and 2 of the 4 test methods appeared most suitable for screening and evaluation of materials. Agreement of results using these four cell lines with intramuscular implantation tests for the 30 materials ranged from 60 to 90%.

Biological evaluation of dental restorative materials--a comparison of different test methods

Three restorative materials--two composite resins and zinc oxide-eugenol cement--were subjected to three cytotoxicity tests--chromium release, millipore filter, and agar overlay--one implantation test, and a pulp study. In the cytotoxicity test the materials were evaluated freshly prepared and after storage at 37 degrees C for 24 h. In the implant test polyethylene tubes holding freshly prepared materials were inserted subcutaneously into rats. After 30 and 90 days the tissue response at the end of the tube and at a window site along the side of the tube was assessed. In the pulp study the materials were placed in cavities prepared in newly erupted monkey teeth. After 7 and 78 days the reaction of the pulp tissue was studied. Comparison of the results from the cytotoxicity tests revealed a varying degree of correlation, indicating that the three tests were not interchangeable. When data from the pulp study were compared to those of the cytotoxicity tests and implantation test, the correlation was not as good. This emphasizes that the final biological evaluation of dental restorative materials still has to be carried out as pulp studies.

Toxicity evaluation of a novel filler free silicone rubber biomaterial by cell culture techniques

Cytotoxicity of a novel filler free silicone rubber (FFSR) was evaluated by studying its effect on mouse L929 cells. Silastic and a laboratory rubber tubing (RT) were used as control materials. Three different experimental methods were used. In method A, after six days of cell culturing in the sample extracts, there were 95, 80, and 50% of control viable cells for FFSR, Silastic, and RT, respectively. Similarly, in method B, after six days of direct contact between samples and the cells, there were 80, 40, and 20% of control viable cells for FFSR, Silastic, and RT, respectively. For the Agar Overlay Test, method C, the cells under the FFSR samples were normal and healthy compared to those under Silastic and RT. From these studies it was concluded that FFSR had the least cytotoxicity of the three materials studied.

A critical evaluation of the acute systemic toxicity test for dental alloys using histopathologic criteria

The A.D.A. acute systemic test for type II, class 11 materials defines compliance on the basis of fewer than 50% mortality at 2 weeks. Histopathologic criteria were developed from pilot study data to evaluate the effects of these materials. In this double blind study, the frequency of histopathological changes in lung, liver, small intestine, and kidney were rated at 2 and 5 weeks, for six dental crown and bridge alloys ranging from 44% to 97% (Au, Pt, and Pd). Two positive 360 mg/kg and 1 g/kg of cadmium and two negative, a blank capsule and untreated control groups were used. There was significant difference (chi square test, X2 = 0.95) between the positive and negative controls at 2 and 5 weeks. The lung, liver, kidney showed the highest level of histopathological changes. Significant changes occurred in the four tissues for all alloys at two and five weeks. At five weeks, alloys with a lower noble metal content (44-62%, Au, Pd, and Pt) elicited significant chronic changes, while higher noble metal content (78-97%) showed healing and no significant difference from the negative controls. Applying histopathologic criteria and statistical parameters independent examiners can examine experimental animals and arrive at conclusive and reproducible results.

Biological evaluation of root canal antiseptics using in vitro and in vivo methods

Five antiseptics commonly used in endodontic treatment were evaluated with regard to cytotoxicity and initial tissue irritating effect. The cytotoxicity was evaluated in a cell culture system using HeLa cells and the initial tissue irritating effect was assessed by application of the antiseptics onto an intact nonepithelialized tissue surface. The cell response was assessed by registering changes in the DNA synthesis of the cells and the tissue response was assessed by registering changes in the oxidoreductase enzyme activity of the tissue. To evaluate the ability of the cells and the tissue to overcome an induced damage, one part of the study included a recovery period before the condition of the cells and the tissue was assessed. The most severe cell and tissue reactions were caused by 5% Chloramine-T whereas no differences in toxicity or tissue irritating effect were found between 0.04% Jodopax, 0.1% Biosept, 0.1% Hibitane, or 0.5% sodium hypochlorite. The HeLa cells showed the best recovery after having been influenced by Jodopax, Chloramine-T or sodium hypochlorite solutions, whereas the best tissue recovery was observed in the experiments with Biosept and Hibitane.

Biocompatibility testing of polymers: in vitro studies with in vivo correlation

An in vitro method has been developed for screening of candidate biomaterials in an early phase of their development. The test is based on L-929 mouse fibroblast cultures and their response to powdered polymer samples. It applies microscopic observation for the detection of morphological changes, uses dye exclusion testing for cell viability determination, and utilizes estimation of population doublings as an end point. The test is shown to be reliable and reproducible and is compared to in vivo implantation studies in rats, previously reported.