Catalog of Regulatory Science Tools to Help Assess New Medical Devices
This regulatory science tool presents a laboratory method to evaluate the barrier effectiveness of PPE materials against viral surrogate or liquid (artificial blood) penetration. Please see appendix.
Technical Description
The Modified Dot-Blot Method to Evaluate Personal Protective Equipment (PPE) is a peer-reviewed method to test the barrier performance of PPE materials against viral surrogate or liquid (artificial blood) penetration. The physical equipment components needed to execute this method comprise:
- a Dot-Blot Apparatus (for example, Whatman Schleicher & Schuell Minifold I) modified as described in Appendix A,
- PPE materials (such as, gowns and drapes) and
- clinically relevant artificial test soils.
For a visual depiction of the apparatus, refer to Appendix A.
For step-by-step protocols for testing of PPE materials, refer to Appendix B.
Intended Purpose
The intended purpose of the Modified Dot-Blot Method to Evaluate PPE is to serve as a screening method to evaluate the barrier effectiveness of Level 4 PPE (surgical gowns and surgical drapes) against penetration by
- bacteriophage ΦΧ174 (universal viral surrogate) or
- clinically relevant test soils.
If the PPE fails preliminary screening by this method, it may eliminate the need for evaluation by FDA-recognized standards ASTM F1671/ F1671M-13 (Standard Test Method For Resistance Of Materials Used In Protective Clothing To Penetration By Blood-Borne Pathogens Using Phi-X174 Bacteriophage Penetration As A Test System) or ASTM F1670/F1670M-17a (Standard Test Method For Resistance Of Materials Used In Protective Clothing To Penetration By Synthetic Blood), which are more resource-intensive.
As will be described in more detail in subsequent sections, the method consists of securing a cut piece of PPE into the modified Dot-Blot apparatus, exposing the PPE to bacteriophage ΦΧ174 or artificial blood for a set time, and applying vacuum for a set time to test the ability of the PPE to resist penetration.
Note: The ASTM methods use a common apparatus that serves as a comparator for the modified Dot-Blot apparatus described here.
Testing
The Modified Dot-Blot Method’s utility in informing the decision whether to evaluate PPE using ASTM F1671/ F1671M-13 is demonstrated in the publication Comparing ASTM F1671 with a Modified Dot-Blot Method to Evaluate Personal Protective Materials. Materials, test organism, and equivalent pressures were identical between the two methods, and the results were essentially equivalent.
The Modified Dot-Blot Method’s utility in informing the decision whether to evaluate PPE using ASTM F1670/F1670M-17a is demonstrated in the publication Evaluation of Apparatus Used to Test Liquid through Protective Materials: Comparison of a Modified Dot-Blot Apparatus to the ASTM Penetration Cell. Pressures, materials, and artificial test soils were identical between the two methods, and the results were essentially equivalent
After evaluating the equivalence of the Modified Dot-Blot Method (as it pertains to artificial blood) to the ASTM F1670 test method, the Modified Dot-Blot Method was used to evaluate several additional clinically relevant test soils representing urine, vomit, and feces. Note: ASTM F1670 does not contain provisions for these test soils. When the Modified Dot-Blot method was used with these test soils, increased failure rates of PPE were observed, as described in the publication Using Clinically Relevant Test Soils to Evaluate Personal Protective Materials. These observations underscore the need for careful consideration of the chemical nature of test soils and their respective effects on PPE.
Limitations
The Modified Dot-Blot Method does not replace or alter the recognition of currently FDA-recognized standards used to evaluate PPE, such as ASTM F1671/ F1671M-13 and ASTM F1670/F1670M-17a. Rather, the Modified Dot-Blot Method can be used to decide whether it is appropriate to undertake these more resource-intensive evaluations. If a PPE device passes screening with the Modified Dot-Blot Method, evaluation using the resource-intensive methods may be necessary.
Limitations of using the Modified Dot-Blot Method as it relates to ASTM F1671 (FDA-recognized standard for evaluating viral penetration of Level 4 gowns) include that the Modified Dot-Blot Method:
- does not directly detect viable bacteriophage ΦΧ174; it detects antigenic proteins of the bacteriophage. There is a possibility of artifactual detection (false positive).
- tests a smaller surface area than the ASTM F1671 method. A greater number of tests are needed with the Modified Dot-Blot to assess the same sample surface area.
More details on the difference between F1671 and The Modified Dot-Blot method can be found in the publication Comparing ASTM F1671 with a Modified Dot-Blot Method to Evaluate Personal Protective Materials.
The limitations of using the Modified Dot-Blot Method as it relates to ASTM F1670 (FDA-recognized standard for evaluating liquid penetration of Level 4 drapes) include that the Modified Dot-Blot Method:
- uses a smaller surface area than the ASTM F1670 method. A greater number of tests are needed with the Modified Dot-Blot to assess the same sample surface area.
More details on the difference between F1670 and The Modified Dot-Blot method can be found in the publication Evaluation of Apparatus Used to Test Liquid through Protective Materials: Comparison of a Modified Dot-Blot Apparatus to the ASTM Penetration Cell
Supporting Documentation
The Materials and Methods sections of the following peer-reviewed publications contain the appropriate level of detail needed to execute the Modified Dot-Blot Method to Evaluate PPE.
The paper Comparing ASTM F1671 with a Modified Dot-Blot Method to Evaluate Personal Protective Materials describes using the Modified Dot-Blot Method with bacteriophage, in direct comparison to the FDA-recognized ASTM standard method.
The paper Evaluation of Apparatus Used to Test Liquid through Protective Materials: Comparison of a Modified Dot-Blot Apparatus to the ASTM Penetration Cell describes using the Modified Dot-Blot Method with blood, in direct comparison to the FDA-recognized ASTM standard method.
The paper Using Clinically Relevant Test Soils to Evaluate Personal Protective Materials describes using the Modified Dot-Blot Method with test soils not covered by any FDA-recognized PPE evaluation standard.
Contact
Tool Reference
- In addition to citing relevant publications please reference the use of this tool using RST24MC03.01