GB 23101.2-2025Implants for surgery - Hydroxyapatite - Part 2: Thermally sprayed coatings of hydroxyapatite (English PDF)

5.1 Overview

5.2 ~ 5.8 specify the minimum requirements for hydroxyapatite coatings.

Additional characterization tests described in A.2 ~ A.4 of Appendix A may also be required.

NOTE. in addition to the tests described in 5.2 ~ 5.8, regulatory authorities may require the tests in Appendix A to characterize hydroxyapatite coatings.

5.2 Calcium-to-phosphorus Atomic Ratio (Ca. P)

Before testing, the coating shall be stripped from the substrate.

The Ca. P ratio in hydroxyapatite ceramic coatings shall be determined in accordance with the provisions of GB/T 23101.3.

The Ca. P ratio shall be within the range of 1.61 ~ 1.76.

NOTE. the Ca. P ratio is generally unaffected by coating thickness.

5.3 Trace Elements

Before testing, the coating shall be stripped from the substrate. The sample volume required for chemical analysis depends on the chemical analysis technique used. The sample volume used shall be sufficient to achieve the appropriate limit of quantification. The coating stripping technique shall minimize the possibility of coating contamination. Care shall be taken to use appropriate tools and avoid contamination caused by substrate particles.

Trace element and heavy metal content shall be determined in accordance with the provisions of GB/T 23101.3.

The maximum permissible limits for specific trace elements and heavy metals in hydroxyapatite coatings are shown in Table 1.

All potential trace elements whose concentrations may exceed the manufacturer’s specified limit of 1,000 mg/kg shall be identified. Quantitative test of these trace elements shall be performed. If there are trace elements with concentrations exceeding 1,000 mg/kg, their impact on biocompatibility and bone healing shall be evaluated in accordance with GB/T 16886.1.

5.6 Morphology

The morphology (thickness, roughness and micromorphology) of the hydroxyapatite coating on the final device shall be evaluated. If morphological examination of the final device is not possible because the geometric structure of the device does not satisfy the requirements of this document, specimens may be used and shall be proven to be representative of the final device.

The average thickness and tolerance [in micrometers (µm)] shall be determined in accordance with the provisions of YY/T 0988.14.This document does not specify the acceptance criteria for average thickness. The acceptance criteria for the average thickness and tolerance of the hydroxyapatite coating for different regions of the implant shall be specified and documented for each implant.

Roughness (Ra or Rt) shall be determined [in micrometers (µm)] in accordance with the provisions of GB/T 10610.This document does not specify the acceptance criteria for roughness. The acceptance criteria for the roughness (Ra or Rt) and tolerance of the hydroxyapatite coating shall be specified and documented.

The surface and cross-section of the hydroxyapatite coating shall be observed using a scanning electron microscope (SEM) or optical microscope. This document does not specify the acceptance criteria for this test. This test is intended to qualitatively characterize the coating porosity and surface condition.

NOTE. data from surface and cross-section observations of the hydroxyapatite coating are used to assist in evaluating process changes or comparing two different types of hydroxyapatite coatings.

5.7 Coating / Substrate Interface Adhesion Strength

The test of static tensile adhesion strength or static shear adhesion strength shall be performed in accordance with the practical application. The static tensile adhesion strength test shall be conducted in accordance with the provisions of GB/T 23101.4, and the static shear adhesion strength test shall be conducted in accordance with the provisions of YY/T 0988.12.If the practical application requires both tensile and shear resistance properties, both tests shall be conducted.

If the static tensile adhesion strength test is performed, the average tensile adhesion strength of the coating shall be no less than 15 MPa, and individual results shall be no less than 10 MPa.

NOTE 1.GB/T 23101.4 provides the quantity and dimensional requirements for the specimens required for the tensile strength test.

If the static shear adhesion strength test is performed, the average shear adhesion strength of the coating shall be no less than 15 MPa, and individual results shall be no less than 10 MPa.

At least 10 valid results shall be obtained from the static shear adhesion strength test.

Coatings may affect the fatigue performance of implants. YY/T 0988.13 can be used to compare the fatigue performance of substrates before and after applying the coating. Implant fatigue performance studies shall be conducted using the final product.

NOTE 2.coating thickness may affect the test results of adhesion strength. Thicker coatings may reduce the results of adhesion strength. Therefore, during the process of verifying the adhesion performance of the coating and substrate, it may be reasonable to use specimens with coating thicknesses in the uppermost quarter of the specified thickness or higher.

NOTE 3.YY/T 0988.14 describes a method for evaluating coating thickness. Because this method requires the preparation of metallographic specimens, it is destructive. However, other non-destructive methods, for example, eddy current or micrometers, exist, but may lead to different test results.

5.8 Accuracy of Test Methods

The accuracy of the test methods shall be determined.

NOTE. GB/T 23101.3 provides accuracy requirements for the test methods of chemical analysis, impurity phase, crystallinity, and Ca. P.