Quantitative cell culture biocompatibility testing of medical devices and correlation to animal tests

Tannic acid/Sr2+-coated silk/graphene oxide-based meniscus scaffold with anti-inflammatory and anti-ROS functions for cartilage protection and delaying osteoarthritis

Tissue engineering method provides a promising solution for meniscus repair and regeneration. However, the inflammatory environment that persists after meniscus injury in the knee joint impedes meniscus tissue regeneration. The purpose of this study was to investigate the applicability of silk/graphene oxide (GO)-based meniscus scaffold modified with tannic acid (TA)/Sr²⁺ coating for the elimination of inflammatory cytokines and reactive oxygen species (ROS) under osteoarthritis (OA) environment along with cartilage protection by using a rat model. The self-assembled coating composed of a series of TA-Sr²⁺ complex concentrations was formed by a facile, rapid, and efficient method on the scaffold. The phenolic hydroxyl groups on the coating endowed the meniscus scaffold with excellent anti-inflammatory and ROS scavenging capacities. We also found that the coating could promote cell migration in a mock wound model and could increase extracellular matrix secretion in vitro. Moreover, the coating components at a certain concentration played an effective role in delaying OA and providing cartilage protection in the rat model. The expression of inflammation cytokines (e.g., IL-6, IL-8, and MMPs) in rat knee tissue was significantly downregulated, and cartilage degeneration and OA damage were also inhibited according to tissue staining results and the OARSI (Osteoarthritis Research Society International) scoring system. Combining these performances, we suggest that this silk/GO-based scaffold modified with TA/Sr²⁺ coating could have broader application prospects by virtue of its effective and user-friendly properties. STATEMENT OF SIGNIFICANCE: The biological properties of the meniscus play a role in activating and regulating the metabolic and inflammatory responses that influence the homeostasis of joint health and ultimately lead to knee osteoarthritis (OA). The inflammation condition of the knee joint may exacerbate the degeneration of meniscus and cartilage. The present study aimed to develop a functional coating composed of tannic acid/Sr²⁺ complex on a silk/graphene oxide-based meniscus scaffold and to endow the scaffold with anti-inflammatory and ROS elimination capacities during the meniscus regeneration process to protect cartilage and delay OA development. The in vitro cytocompatibility study and the in vivo rat OA model study revealed that the coating was effective in promoting cell migration, facilitating ECM secretion, inhibiting inflammation, and delaying OA development.

In vitro cytocompatibility testing of oxidative degradation products

Implantable medical devices must undergo thorough evaluation to ensure safety and efficacy before use in humans. If a device is designed to degrade, it is critical to understand the rate of degradation and the degradation products that will be released. Oxidative degradation is typically modeled in vitro by immersing materials or devices in hydrogen peroxide, which can limit further analysis of degradation products in many cases. Here we demonstrate a novel approach for testing the cytocompatibility of degradation products for oxidatively-degradable biomaterials where the materials are exposed to hydrogen peroxide, and then catalase enzyme is used to convert the hydrogen peroxide to water and oxygen so that the resulting aqueous solution can be added to cell culture media. To validate our results, expected degradation products are also synthesized then added to cell culture media. We used these methods to evaluate the cytocompatibility of degradation products from an oxidatively-degradable shape memory polyurethane designed in our lab and found that the degradation of these polymers is unlikely to cause a cytotoxic response in vivo based on the guidance provided by ISO 10993-5. These methods may also be applicable to other biocompatibility tests such as tests for mutagenicity or systemic toxicity, and evaluations of cell proliferation, migration, or gene and protein expression.

The Application of In Vitro Cytotoxicity Assays to the Water Industry

This paper describes areas in which in vitro cytotoxicity assays may be of use to the water industry and reviews the studies that have already been published on water samples and water industry materials. In vitro cytotoxicity assays are useful in comparing aqueous samples and for testing of materials, but direct comparisons of test systems have not been carried out. At present, it is therefore unclear if any one method is particularly appropriate for use with water samples.

Toxicity of 20 Chemicals from the MEIC Programme Determined by Growth Inhibition of L-929 Fibroblast-like Cells

The Multicentre Evaluation of In vitro Cytotoxicity (MEIC) programme is an international project aimed at evaluating the relevance of in vitro tests in predicting human toxicity. We have screened 20 chemicals (MEIC codes 31-50) from the programme, by using a cytotoxicity test based on growth inhibition of the mouse fibroblast-like L-929 cell line. Inhibition of cell growth was determined by the neutral red uptake method, which is well established and is used for screening the cytotoxicity of chemicals and plastics for pharmaceuticals and medical devices. The concentrations causing 50% inhibition of cell growth after a 72-hour exposure period varied from 3.1μM for hexachlorophene, to 1.4mM for caffeine. This is within the same range as results recently obtained with five other cell models. However, with some chemicals (chloroform, carbon tetrachloride and dichloromethane), no reliable results were obtained. These substances could not be dissolved in a reproducible way in any of the solvents used and, furthermore, they were highly volatile, which led to difficulties in maintaining the concentrations.

Validation of In Vitro Cytotoxicity Tests — Past and Present Strategies

In recent years, conventional toxicity testing in animals has been reinforced by in vitro methods. As a result, toxicity testing in some sectors has become more effective and at the same time more ethical. This trend is probably only at its beginning, as many of the newly-developed methods have not yet won general acceptance as a basis for the large-scale replacement and reduction of animal experimentation. What limits the wider use of these methods is validation, i.e. the evaluation of their reliability and relevance. The present paper is a short review of the validation efforts made hitherto, including projects being planned and under discussion. Our own MEIC approach is compared with other strategies. Finally, our opinion on the effectiveness of one large consensus project relative to several different smaller validation programmes is expressed — we advocate the latter strategy, because it will save time and reduce costs.

Preparation, Characterization and Properties of Alginate/Poly(γ-glutamic acid) Composite Microparticles

Alginate (Alg) is a renewable polymer with excellent hemostatic properties and biocapability and is widely used for hemostatic wound dressing. However, the swelling properties of alginate-based wound dressings need to be promoted to meet the requirements of wider application. Poly(γ-glutamic acid) (PGA) is a natural polymer with high hydrophility. In the current study, novel Alg/PGA composite microparticles with double network structure were prepared by the emulsification/internal gelation method. It was found from the structure characterization that a double network structure was formed in the composite microparticles due to the ion chelation interaction between Ca²⁺ and the carboxylate groups of Alg and PGA and the electrostatic interaction between the secondary amine group of PGA and the carboxylate groups of Alg and PGA. The swelling behavior of the composite microparticles was significantly improved due to the high hydrophility of PGA. Influences of the preparing conditions on the swelling behavior of the composites were investigated. The porous microparticles could be formed while compositing of PGA. Thermal stability was studied by thermogravimetric analysis method. Moreover, in vitro cytocompatibility test of microparticles exhibited good biocompatibility with L929 cells. All results indicated that such Alg/PGA composite microparticles are a promising candidate in the field of wound dressing for hemostasis or rapid removal of exudates.

Current Problems in Devices Evaluation: Some Solutions

Medical devices and their component materials are potential sources of toxins that may produce undesirable local or systemic effects when used clinically. Federal regulations thus require manufacturers to establish the safety of their products. Until 1987, FDA provided few specific guidelines for testing medical devices, although many standardized testing methods had been placed in use by industry. Now, proposed guidelines exist, but device manufacturers still face significant problems that are similar to those encountered when testing drugs and chemicals: (1) a strategy for testing must be established to make best use of screening methods, to develop parallel information about various families of products, and to make best use of resources, (2) test articles must be selected to represent finished products, not prototype formulations, (3) sample preparation must be appropriate and relate to product use conditions, (4) test methods that are inappropriate based on end use of a product must be avoided, (5) all potential sources of toxins must be taken into account, including raw materials, processing and manufacturing aids, and sterilization processes, and (6) Good Laboratory Practices must receive appropriate attention. In vitro alternatives to animal test methods are used widely for primary evaluation of biocompatibility, but suitable animal models are not yet available for preclinical evaluation of some devices.

Highly sensitive pyrogen detection on medical devices by the monocyte activation test

Pyrogens are components of microorganisms, like bacteria, viruses or fungi, which can induce a complex inflammatory response in the human body. Pyrogen contamination on medical devices prior operation is still critical and associated with severe complications for the patients. The aim of our study was to develop a reliable test, which allows detection of pyrogen contamination on the surface of medical devices. After in vitro pyrogen contamination of different medical devices and incubation in a rotation model, the human whole blood monocyte activation test (MAT), which is based on an IL-1β-specific ELISA, was employed. Our results show that when combining a modified MAT protocol and a dynamic incubation system, even smallest amounts of pyrogens can be directly detected on the surface of medical devices. Therefore, screening of medical devices prior clinical application using our novel assay, has the potential to significantly reduce complications associated with pyrogen-contaminated medical devices.

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.

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.

Comparative studies by cell culture and in vivo implantation test on the toxicity of natural rubber latex materials

Colony assay using V79 cells, the agar diffusion assay with L929 cells, and the 7-day rabbit muscle implantation test were employed to evaluate the cytotoxicity and tissue toxicity of natural rubber latex (NRL) materials. The in vivo implantation test showed that, among 13 histological parameters, thickness of inflammatory layer was the most useful index to evaluate tissue responses quantitatively. A comparison of the in vivo and in vitro parameters revealed the following correlations between the thickness of the inflammatory layer and cytotoxicity indices: Colony assay of the extracts, IC50: r = 0.80; Agar diffusion assay, Zone index: r = 0.73; Lysis index: r = 0.61. From these results, it appears that the colony assay provides a more reliable prediction of the tissue response than the agar diffusion assay.

Biocompatibility of a prolonged-action antialcohol preparation

Acid and alkaline phosphatase activities in liver lysosomes and liver mitochondria, respectively, as well as in connective tissue capsule were studied for an antialcohol preparation (polyurethane carrier and disulfiram at 150, 300 and 625 mg/kg body weight) implanted subcutaneously. Increased acid phosphatase activity was observed in connective tissue capsule on days 14, 30 and 90 after implantation and in liver lysosome fraction on days 14 and 30 with preparation containing disulfiram at 300 and 625 mg/kg body weight. Alkaline phosphatase activity increased both in connective tissue capsule and in liver mitochondria up to day 30 only when sample with maximal disulfiram dose was implanted. Acid phosphatase activity is an adequate indicator for biocompatibility of prolonged-action medicine preparations. The data obtained show that the suggested medical form containing disulfiram 150 mg/kg body weight is biocompatible. Interaction between acid and alkaline phosphatase activity changes and biocompatibility and destruction of polymer implants is discussed.

Testing of Polymer Materials: What Methods Should be Used?

Tests, performed over a ten-year period, on 653 polymers intended for use in extracorporeal renal replacement therapy, were evaluated. The test battery used included animal tests, in vitro tests and chemical tests. Some tests were found to have a very low sensitivity. Thus, acute systemic toxicity testing in mice with sodium chloride, ethanol or paraffin oil as extractants was performed on a total of 806 occasions. Only two of these resulted in a “fail” decision. The final outcome of the tests for the majority of materials could be predicted by the results of the UV absorption, chloride, inhibition of cell growth, and tin tests. Of the materials that passed these four tests, less than 2% were not approved on the basis of the whole test battery. The experiments show that only a limited number of tests have to be performed when testing polymers intended for use in extracorporeal renal replacement therapy.

Bioimplant surfaces: binding of fibronectin and fibroblast adhesion

The adhesion of baby hamster kidney 21C/13 fibroblasts to surfaces of passivated titanium, carbon fibers, bioactive glasses B5 and B6, fibronectin-precoated passivated titanium, and fibronectin-precoated B6 was quantified. The order of adhesive cell avidity for the uncoated surfaces was passivated titanium (greatest), B6 and carbon fibers (intermediate), and B5 (least). Precoating with fibronectin enhanced the adhesive characteristics of fibroblasts on passivated titanium and B6 by 74% and 118%, respectively.

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.

Toxicity testing of urinary catheters

The tissue toxicity of 23 urinary catheter batches (6 latex and 2 non-latex brands) was tested in vitro and in vivo. In vitro, a human T-cell leukemia line (JM) was cultured in the presence of different concentrations of eluates made from the catheters. The cytotoxicity of the eluates was assessed from their ability to inhibit DNA synthesis measured by incorporation of 3H-thymidine. In vivo, two methods were used. Strips of catheters were implanted into the rabbit dorsal muscle and pieces of catheters were implanted into the rat peritoneal cavity. After four days, the foreign body reaction, type of inflammation and necrosis were quantified macroscopically and by light microscopy. The results of the in vitro cytotoxicity test were correlated with those of in vivo methods. The rat peritoneal implantation test correlated better with the cell culture test (P less than 0.01) than with the rabbit muscle implantation test (P less than 0.05). Based on the clinical experience of urethral stricture complications caused by urinary catheters, catheters yielding eluate which at 30% dilution inhibited 50% DNA synthesis were regarded as toxic. According to this, the rabbit muscle implantation test was not reliable in testing the tissue toxicity of urinary catheters, while the cell culture test was quantitative and seemed to correlate with both the rat peritoneal implantation test and with the clinical complications observed.

Rat peritoneal implantation test. A new method for tissue toxicity testing of urinary catheters

Severe urethral inflammatory reactions followed by strictures have been reported after short-term catheterisation with latex catheters since 1982. In this study a new method for assessing tissue toxicity is presented. It is based on the degree of inhibition of rat peritoneal foreign body reaction. Because the results are easier to interpret and more quantitative than those of the rabbit muscle implantation test, the rat peritoneal implantation test is recommended as a standard in vivo toxicity test.

A method for toxicological evaluation of biomaterials based on colony formation of V79 cells

This report describes a method for cytotoxicity screening of biomaterials based on colony formation of V79 cells. For this test, two metals (titanium and nickel), two ceramics (alumina ceramic and tricalcium phosphate), and two types of polymeric material [high density polyethylene (HDP) and polyvinylchloride (PVC)] were used. Each metal and ceramic was cast into a disk and semidisk 49 mm in diameter and 1 to 2 mm thick. The HDP was molded into a petri dish and PVC was used as a thin film. The materials were sterilized by heating or with ethylene oxide and placed in plastic petri dishes, after which 8 ml cell suspension containing 100 cells were added to each dish. After 1 week, the colonies formed on the materials were fixed, stained, and then the number of colonies was counted. Titanium, alumina ceramic, and HDP showed no differences from the controls in terms of colonies. On the disks and the semidisks of nickel and tricalcium phosphate and on the thin disks of PVC, however, no colonies were detected. The V79 cells used in this experiment showed a rapid and logarithmically stable growth curve and such a high rate of colony formation as to form visible noticeable colonies, and were therefore suitable cells for screening test the cytotoxicity of biomaterials. Unlike other previously reported methods of in vitro cytotoxicity testing, this method permits assay of colonies formed from a single cell after proliferation directly on the materials. Moreover, the test with semidisks permits simple screening to assess the cytotoxicity is caused by either the chemical substances or the physical properties of the materials.(ABSTRACT TRUNCATED AT 250 WORDS)

On the application of cultured neuroblastoma cells in chemical toxicity screening

The acute toxic action of a number of common chemicals was tested by their ability to cause detachment of cultured mouse neuroblastoma C1300 cells. A TD25 value was obtained by graphic estimation of the concentration needed to cause 25% of the total cell number to detach. These TD25 values were compared with LD50 values obtained from the literature, and they were found to correlate with a coefficient of 0.86. For six of the tested substances-diuron, butylated hydroxytoluene, benzidine, cyclophosphamide, Na2SeO3, and KCN-a very poor correlation was obtained. These diverging results could be ascribed to deficiencies in the neuroblastoma cell detachment test and emphasize the necessity for combined in vitro test procedures.

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%.

Cellular toxicity of urinary catheters

The cellular compatibility of each of several brands of urinary catheters available on the Australian market was measured by means of cell-culture methods, a rabbit intramuscular implant test, and the traditional mouse systemic toxicity test. Good agreement was obtained between the in-vitro tests and the rabbit implant tests (although the cell-culture tests were simpler, more rapid, more sensitive, and quantitative). The mouse systemic toxicity test was insensitive, and detected no toxic samples. The cell-culture and rabbit-implant test results indicated that some urinary catheters can release substances harmful to mammalian cells. Such substances may contribute to the clinical reactions of urethritis and strictures after urethral catheterization.

A model culture system with human gingival fibroblasts for evaluating the cytotoxicity of dental materials

A model experimental culture system and protocol are described to screen polymerized dental materials for diffusible toxic products. The system employs cultures of human gingival fibroblasts grown in plates containing immobilized samples of polymerized resins. Comparative cytoxicity is evaluated by counting viable cells with the aid of phase optics at several time periods up to 48 h. To achieve adequate statistical sampling, multiple counts are made in four different zones at 90 degrees angles from each sample and at three distances from the centers of samples. The most significant data were generated during a 24 to 48 h test period in climate. This cytotoxicity test measured cell death as a function of time of exposure and distance from the sample (24 h, 0 to 3 mm; 48 h, 3 to 6 mm) and permitted a calculation of the relative cytoxicity for each material, which is termed the viability index (VI). This can be expressed as a percentage related to the control, which is called the time-distance cytotoxicity index (TDCI). This method is simple to carry out because it used basic laboratory equipment, is rapid, and has a sound scientific basis. It focuses on times and distances when or where, or both, the greatest cellular changes are taking place. Some data illustrated are based on the screening of eight different restorative resins. The literature of cell culture testing of dental materials is reviewed. It is concluded that biotoxicity studies ideally should employ diploid human target cells from the oral cavity because the cells retain specialized features. Secondary cultures or strains of human diploid gingival fibroblasts, which are relatively easy to obtain and maintain, are recommended as cells of choice for screening dental restorative materials in vitro.

Altered activity in cultured cells caused by contaminants in tubes widely used for blood collection and serum preparation

Cell culture has been recognized as an extremely sensitive system for measuring the toxicity of various materials. A study was done to determine whether the type of tube used to collect blood or store human serum might affect results in experiments requiring blood drawn into such tubes. In order to test tubes for contaminants that might alter cellular activity, a variety of commercially available tubes used for collection of blood and storage of serum were shaken while containing culture medium with fetal bovine serum. The medium was then applied to 3T3 fibroblasts in culture. Measuring incorporation of tritiated thymidine into DNA in log phase cells as an index of cellular proliferation, it was found that medium containing serum preincubated in tubes routinely used for blood collection could be extremely toxic. The same types of tube were also used to prepare human serum. When serum from some of the tubes was applied to 3T3 fibroblasts, a stimulatory effect was observed, perhaps caused by selective adsorption of inhibitory components of the blood or serum by various tubes. It is, therefore, crucial in a properly controlled experiment using serum in vitro to collect blood in tubes that exert no toxic or stimulatory effects in the assay or, at least, to be consistent in one's choice of tube. None of the tubes used for storage of serum showed significant effects in our assay.

Polypropylene

Polypropylene is a polymer widely used in lens implantation, both as a loop material and as an intracameral suture. The chemistry and qualities of this material are discussed. Predicated on its usage in other types of surgery, it appears to be resistant to degradation. However, reports have suggested that it may degrade when exposed to high levels of ultraviolet radiation. This would not be a consideration in internal organs, but the eye is a unique case, and the matter should be studied further.

Bioevaluation of plasma polymerized films in skeletal muscle

Plasma polymerized ethylene (PPE), styrene (PPS), and chlorotrifluoroethylene (PPCTFE) were synthesized by exposing the monomeric gases to an inductively coupled radio frequency "glow-discharge" field. The polymer films were deposited on poly(dimethyl) siloxane (medical grade Silastic), which was then surgically implanted in rat paravertebral muscle for periods up to 84 weeks. The biocompatibility of the plasma deposited films and uncoated Silastic was evaluated by qualitative (graded inflammatory cell response) and quantitative (connnective tissue capsule thickness) techniques as a function of time. The morphological features of the connective tissue capsule and the plasma polymerized films were examined by SEM after 75 weeks of implantation. Results showed that the acute inflammatory cell migration around PPS and PPCTFE was at a maximum in 2 weeks, decaying to control levels in 4 to 8 weeks. The PPE response was judged as less than the control response up to 4 weeks. After 8 weeks no qualitative difference could be detected between the plasma polymerized films and Silastic. On the other hand, a quantifiable change in fibrous capsule response as a function of time and material was noted until 24 weeks. From these data we conclude that these types of films do not elicit an untoward foreign body reaction at a skeletal muscle implant site in rats.