Toxicity evaluation contact method

M. E. Stern, H. F. Edelhauser, and J. W. Hiddemen, Methods of Evaluation of Corneal Epithelial and Endothelial Toxicity of Soft Contact Lens Preservatives. Presented at Contact Lens International Congress, Las Vegas, Nevada, March 1985. 

Substances when applied to human skin might exert a sensitizing potential on the skin and need, therefore, to be evaluated and classified for their possible toxicity. Every substance that provokes immunologically mediated cutaneous reactions (i.e., skin sensitization or allergic contact dermatitis) is referred to as skin sensitizer. Several tests are recommended, but no single method is able to identify all potential substances capable of inducing sensitization of human skin. Widely used test methods for the investigation of skin sensitization, the so-called adjuvant and nonadjuvant tests, are described below. 

Before implantation several in vitro tests were performed. For evaluation of a possible toxic reaction, we investigated the material and the whole devices in vitro with cell culture methods. Direct contact and extraction tests with a mouse fibroblasts cell line (L 929) and a neuroblastoma cell line (neuro-2-a) were performed according to the international standard ISO 10993 ( Biological Evaluation of Medical Devices ). The materials and devices showed no toxicity, i.e. no significant differences in membrane integrity of the cell membranes, mitochondrial activity and DNA synthesis rate. The neuro-2-a cell line is so sensitive that even small changes in process technology are detectable. The flexible polyimide structures proved to be non toxic. 

Other in vitro methods include evaluation of hemolytic properties of material extracts for blood-contacting polymers and evaluation of specific materials in their final form. An example of this is given in Table 10.1 for the standard evaluation of thermoplastic polyurethanes (PU). These standard evaluations have been developed for many commercially used biomaterials and include toxicity testing as well as me ods of final form assessment for other physical properties. 

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