In vitro mechanical tests

In vitro mechanical tests should also focus on the dynamic behavior of a given polymer scaffold, which is very crucial for applications like knee/hip joint repair and vascular grafts. Certain polymers like polypropylene show creep behavior, i.e., exhibit dimensional changes nnder continuous load and cannot be used to make vascular grafts [15]. 

It should be noted that the in vitro mechanical test methods most often used to date suffer from end artifacts [35-37], errors due to platen-specimen friction and machining-related damage of the specimen ends, which compromise the accuracy of most of the data. Modulus values are underestimated by at least 20% [36-38], with the error possibly depending... 

Due to the nature of the test method, quality by design is an important qualification aspect for in vitro disolution test equipment. The suitability of the apparatus for the dissolu-tion/drug-release testing depends on both the physical and chemical calibrations which qualifies the equipment for further analysis. Besides the geometrical and dimensional accuracy and precision, as described in USP 27 and Ph.Eur., any irregularities such as vibration or undesired agitation by mechanical imperfection are to be avoided. Temperature of the test medium, rotation speed/flow rate, volume, sampling probes, and procedures need to be monitored periodically. 

Positive results from the in vitro micronucleus test indicate that the test substance induces chromosome damage and/or damage to the cell division apparams, in cultured mammahan somatic cells. Immunochemical labehng (FISH fluorescence in sim hybridization) of kinetochores, or hybridization with general or chromosome specific centromeric/telomeric probes can provide useful information on the mechanism of micronucleus formation. Use of cytokinesis block facilitates the acquisition of the additional mechanistic information (e.g., chromosome nondisjunction) that can be obtained by FISH techniques. The micronucleus assay has a number of advantages over metaphase analysis performed to measure chromosome aberrations (see OECD TG 487 draft). 

In chapter 3 one of these specific mechanism-based in vitro toxicity tests was studied in more detail. 

Specific mechanism-based in vitro toxicity testing... 

Trevisan, A., Meneghetti, P, Maso, S. Troso, O. (1993) In vitro mechanisms of 1,2-dichloropropane nephrotoxicity using the renal cortical slice model. Hum. exp. Toxicol., 12,117-121 von der Hude, W., Scheutwinkel, M., Gramlich, U., Fissler, B. Easier, A. (1987) Genotoxicity of three-carbon compounds evaluated in the SCE test in vitro. Environ. Mutagen., 9.401-410... 

Genotoxicity. Neither in vitro nor in vivo genotoxicity studies have been located for radium. A battery of in vitro genotoxicity tests may provide useful information on the mechanism of carcinogenicity for radium. 

Investigation of coagulation is more easily carried out in vitro. Although the two processes are similar, it is necessary to be cautious in comparing in vivo and in vitro mechanisms. The clot formed in a test tube is different from that formed in the vascular system. Coagulation in vitro consists of a fibrin net in which there exist white and red cells and a small number of platelets. In vivo, the clots consist of large amorphous masses of platelets surrounded by white cells and very few red cells. 

The stepwise procedure usually starts with the determination of the LD50, a short term repeated exposure test in rodents and the evaluation of genotoxicity by an in vitro bacterial test system (Ames-test) and for cytogenicity in mammalian cells. In case of indication for genotoxicity the results are verified in vivo usually by the mouse bone marrow micronucleus test. For further evaluation the compound additional tests including studies on toxicokinetics or the toxic mechanisms will follow. Such information provides information on the reactivity of the test compound, its... 

Posner, G. H. Oh, C. H. Wang, D. Gerena, L. Milhous, W. K. Meshnick, S. R. Asawamahasadka, W. Mechanism-based design, synthesis, and in vitro antimalarial testing of new 4-methylated trioxanes structurally related to artemisinin The importance of a carbon-centered radical for antimalarial activity. J. Med Chem., 1994, 37(9) 1256-1258. 

Garriott ML, Phelps JB, Hoffman WP. A protocol for the in vitro micronucleus test. I. Contributions to the development of a protocol suitable for regulatory submissions from an examination of 16 chemicals with different mechanisms of action and different levels of activity. Mutat Res 2002 517 123-34. 

Phototoxicity or chemical phototoxicity is the term used for an acute reaction that can be induced by a single treatment with a chemical and UV or visible radiation. The basic mechanism of phototoxicity can be described as an increase in toxicity of a chemical induced by exposure to UV or visible radiation. Therefore the phototoxic potential of a chemical can be measured as an increase in cytotoxicity after exposure to UV or visible light. The 3T3 NRU PT test is a validated and robust in vitro phototoxicity test according to the criteria laid down by the ECVAM Workshop on practical aspects of the validation of toxicity test procedures and the conclusion of the ECVAM/COLIPA validation study [72], Owing to the convincing performance of the 3T3 NRU PT test, the test is now established and in use in industry laboratories to screen... 

Cardiomyocyte-like cells derived from hESCs or human-induced pluripotent stem cells (hiPSCs) recapitulate genomic, biochemical, mechanical, and electrophysiological behaviors of human cardiomyocytes [77, 78] and thus provide an amenable source of cells for in vitro cardiotoxicity testing [79-85],... 

As in the case of chemical or pharmaceutical substances, the results from in vitro toxicity testing of NMs are dependent upon many factors, such as the cell types used, exposure time, dosing regimen, and exposure conditions. However, what makes toxicology of NMs so complex as compared to chemical products is the large number of physicochemical properties that are essential to know for proper toxicity assessment. The toxicity mechanisms are multiple and depend strongly on the characteristics of the studied NMs and the conditions of the test. Several aspects may affect the... 

---