Detection of the cleaning effect of plastic surface biofilm with cleaning agents

Medical YongDetection of the cleaning effect of plastic surface biofilm with cleaning agents

The biofilm contamination on the plastic surface of medical equipment has become an invisible challenge for hospital infection prevention and control.

Compared with metal materials, plastic surfaces are more prone to forming stubborn biofilms due to their low surface energy and numerous micro pores. Research shows that the formation rate of biofilm on the surface of polyvinyl chloride (PVC) conduits is three times faster than that of stainless steel, and the difficulty of removal increases by 40%. According to data from the 2024 Chinese Journal of Hospital Infection, infections caused by residual biofilms on plastic instruments account forMedical equipment38% of the infections were related, with a biofilm detection rate of up to 57% in the ICU respiratory tract. Therefore, the detection of the cleaning effect of medical cleaning agents on plastic surface biofilms has become a key link in ensuring medical safety.

The International Organization for Standardization's ISO 15883-7:2024 "Cleaning and Disinfection Equipment - Part 7: Testing of Plastic Surface Biofilm Removal Effectiveness" established a specialized testing system in 2024, requiring that the biofilm removal rate of plastic instruments should reach a log value reduction of ≥ 4.0, and the weight loss rate in material compatibility testing should be ≤ 0.5%.

GB/T 38502-2020 "Evaluation Method for Antimicrobial Properties of Medical Equipment Biofilms" in China further specifies，

Using acrylonitrile butadiene styrene copolymer (ABS) as the standard carrier, the surface roughness Ra value is controlled at 1.6-3.2 μ m to simulate the surface characteristics of commonly used plastic instruments in clinical practice. YY/T 0734.5-2025 "Medical cleaning agents Part 5: Determination of biofilm removal on plastic surfaces" implemented in 2025 innovatively introduces the "dynamic flow addition culture method", which constructs a biofilm model closer to the in vivo environment by supplying nutrient matrix at a flow rate of 0.5mL/min. Its structural complexity is increased by 2 levels compared to static culture.

The detection of biofilm on plastic surfaces requires a three in one verification system of "material properties cleaning parameters removal effect". Firstly, pre-treatment of the carrier is carried out: the ABS standard test piece (50mm × 10mm × 2mm) is cleaned by ethanol ultrasonic cleaning, and the surface contact angle is adjusted to 65 °± 5 ° using plasma etching (power 30W, time 60s) to ensure consistency in biofilm formation. The biofilm preparation was carried out using the clinically common Pseudomonas aeruginosa PAO1 strain, which was dynamically cultured in TSB medium (containing 1% glucose) at 37 ℃ for 72 hours to form mature biofilms with a thickness of 25-35 μ m. The initial bacterial count was controlled at 6-7 log CFU/cm ².

The cleaning effect verification adopts a step-by-step detection process:

The first step is to use ATP bioluminescence method for rapid screening. A specialized plastic surface sampling rod (such as 3M Clean Track Swab) is used to wipe the 5cm ² area on the surface of the test piece in a "zigzag" shape. After sampling, the sample is immediately tested, and the results are expressed in relative light units (RLU). A threshold setting of ≤ 300 RLU is considered preliminary qualified. Step 2: Count the viable cells of ATP positive samples: Place the test piece in PBS buffer containing 0.1% Tween-80 and wash it with ultrasound (power 250W, frequency 40kHz)

Key cleaning parameter optimization needs to focus on plastic material compatibility:

In terms of temperature, polycarbonate (PC) instruments need to be controlled below 45 ℃ to avoid material deformation; The pH value should be maintained within the weakly alkaline range of 7.5-8.5 to prevent hydrolysis of polyamide (PA) materials. The ultrasonic cleaning parameters are optimized to a power of 300W and a frequency of 35kHz, at which point the cavitation effect on the plastic surface is the strongest and no micro cracks will be generated. A study in the 2024 Journal of Medical Equipment Materials showed that using pulsed ultrasound (working 30s/pause 10s) on PVC materials can increase biofilm removal rate by 27%, while controlling material weight loss rate below 0.3%. The recommended concentration of cleaning agent is 1.5% (1% for conventional metal instruments), and the action time is extended to 15 minutes to break the hydrogen bond between the EPS matrix of the biofilm and the plastic surface through the penetration of non-ionic surfactants.

The detection process requires strict control of interference factors:

When the scratch depth on the plastic surface exceeds 5 μ m, the biofilm removal rate will decrease by 50%. Therefore, the surface integrity of the test piece needs to be checked by a white light interferometer before use. Proteases in cleaning agents may cause discoloration of certain plastics, and a 24-hour immersion test is required. The color difference Δ E value should be ≤ 3.0. According to the 2024 capability verification results of the China National Institute for Food and Drug Control, only 8 out of 12 laboratories were able to pass both the clearance rate and material compatibility tests, and the main source of error was the failure to consider the interference of plastic adsorption on fluorescent dyes (ABS adsorption rate of SYTO 9 reached 18%).

In practical applications, differentiated testing plans need to be developed for different types of plastics: the disposable PVC transporter focuses on detecting the inner wall of the lumen (area with inner diameter<3mm), using the "ultrasound centrifugation" combined elution method (40kHz ultrasound for 10 minutes followed by centrifugation at 12000rpm for 5 minutes); Orthopedic PEEK implants require fatigue cycle pretreatment (1000 bending cycles, curvature radius 50mm) to simulate the residual micro cracks in biofilms after clinical use. The latest research shows that adding nano silica particles (with a particle size of 50nm) to cleaning agents can improve the removal rate of plastic surface biofilm by 1.8 log values through the "micro grinding effect", without damaging the material.

Detection of the cleaning effect of plastic surface biofilm with cleaning agents