ISO 10993-15:2019 pdf download – Biological evaluation of medicaldevices— Part 15: Identification and quantification of degradation products from metals and alloys
ISO 10993-15:2019 pdf download – Biological evaluation of medicaldevices— Part 15: Identification and quantification of degradation products from metals and alloys.
5.3.4 Sample surface condition
Since the surface condition of a material can affect its electrochemical behaviour, the surface condition
of the test sample shall be identical to the final medical device and shall be described in the test report.
6 Electrochemical tests
6.1.1 Test cells of borosilicate glass, in appropriate sizes, in accordance with ISO 3585, with a means of controlling the bath temperature within ii °C.
6.1.2 Scanning potentlostat with a potential range ±2 V and a current output range from iO A to 10’ A.
6.1.3 Potential-measuring instrument with a high input impedance (>1011 II) and a sensitivity and accuracy to detect a change of I mV over a potential range between ±2 V.
6.1.4 Current-measuring instrument capable of measuring a current to ±1 % of the absolute value over a current range between I 0- A and 10-i A.
6.1.5 WorkIng electrode (test sample).
6.1.6 Counter-electrode(s) such as platinum (grid. plate, or wire) or vitreous carbon with an area at least 10 times that of the working electrode.
6.1.7 Reference electrode which has a known electrode potential and is stable.
6.1.8 pH-meter with a sensitivity of ±0,1.
A schematic diagram of the electrochemical measurement circuit which can be used as a system with variable potential is given in AnnexE. EigureB1-
A schematic drawing of an electrolytic cell is given in Annex C.
6.2 Sample preparation
Mount the test sample In a watertight electrode holder so that only the test surface Is In contact with the electrolyte. Take care to avoid the creation of conditions where crevice corrosion can occur due to the formation of a crevice between the mounting and the sample. Before testing, clean the sample ultrasonically for 10 mm to 15 mm In ethanol. carefully rinse the sample with water of grade 2 In accordance with ISO 3696, and immediately transfer the sample into the test cell.
6.3 Test conditions
Fill the test cell with the test solution (electrolyte). If the electrochemical behavior is temperature sensitive In the range of 10 °C to 50 °C, maintain the electrolyte cell at (37 ± 1) C. Reduce the oxygen level in the electrolyte by bubbling oxygen-free nitrogen or argon at a rate of approximately 100 cm3/ mm for not less than 30 mm prior to the start of the test. The electrolyte shall 1w agitated either by the bubbling gas or mechanical means to avoid concentration gradients. If gas agitation Is used, take care not to have any gas bubbles adhering to the active test surface.
7.2 Sample preparation
The test sample shall be placed in a separate glass container. The size of the glass container should be selected so that an electrolyte volume of less than 1 ml/c& of sample surface shall completely cover the sample(s). The test sample shall be totally covered by the electrolyte.
Do not risk compromising long-term data through biological (e.g. bacterial. lungal) contamination. For example, the utilized containers may need to be sterile and electrolyte may need to be prepared under aseptic COnditiOnS.
The surface area and volume of electrolyte should be sufficient for the intended method of analysis (see Clause 8).
Care should be taken such that the samples do not touch the glass surface except in a minimum support line or point. If the test sample is small, the proper surface area/volume ratio might not he attainable with a single test sample. Therefore, If the test sample shall be made up of two or more pieces, the pieces shall not touch each other.
For test samples with roughened or Irregular shapes and therefore difficult to determine the surface area, the user is referred to the discussion in ISO 10993-12 and ISO/TR 10993-22 concerning how such differences can Impact the risk assessmenL
7.3 ImmersIon test procedure
Measure the pH of the electrolyte containing the test sample at the start of the test. Then tightly close the test cell to prevent evaporation and maintain at (37 ± 1) °C for (7 ± 0,1) d. Then remove the sample and measure the pH of the residual electrolyte. Certain materials can call for the use of tissue culture (i.e. sterile filtered) grade phosphate buffered saline as the immersion electrolyte.
It can be necessary to conduct immersion tests for a longer period of time if all of the following conditions apply:
a) the alloy Is used In a permanent implant
b) the alloy contains constituents that are soluble in the use environment
c) the soluble constituents are present at potentially hazardous levels within the device
d) no additional information exists to demonstrate the stability of the constituents of concern (e.g. established surface process and acceptable corrosion resistance)
For devices that meet the above criteria, the release of potentially hazardous constituents shall be quantified over time to determine what short- and long-term exposure to the alloy will present for consideration In the risk analysis. To quantify the time-dependent release rate, successive immersion testing shall be conducted on the same test sample. After each test interval, the immersion procedure should be repeated by removing the test sample from the container, sampling the electrolyte for analysis, and placing the test sample Into a container with fresh electrolyte.