AMiCI (CA15114). Workshop for Early Career Investigators (ECIs) and Short Term Scientific Missions (STSM) Riga, Latvia, 7th of March 2019

1. Environmental Factors Affecting Drying
Time on Plastic and Potential Issues
Associated with Efficacy Testing of
Antimicrobial Surfaces
Methods Protoc. 2018, 1(4), 36; https://doi.org/10.3390/mps1040036
James Redfern, J.Redfern@mmu.ac.uk
Postdoctoral Research Associate,
Manchester Metropolitan University, UK

2. Scenario
Current test methods include JIS Z 2801 and BS ISO 22196:2011
• “Temperature of (35 ± 1) C and a relative humidity of not less than 90 % for
(24 ± 1) h.”
• Hospital wards are often between 30 H%-60RH%, 18C - 28C and with an
airflow of not more than 2m/s at a vent face (UK, Dept for Health, 2007)
• Other test methods have been developed that change the temperature and RH
to replicate the hospital environment.
Department of Health (2007). HTM 03-01: Specialised Ventilation for Healthcare Premises: Part A - Design and Validation. E. a. F. Division. Leeds, UK,
Department of Health.

3. Scenario
However,
Test chamber = 50%RH and 20C & 10ul inoculum = x drying time
Hospital room = 50%RH and 20C & 10ul inoculum = y drying time
Are the drying times the same??

4. Question
What is the variation of drying time within a test chamber
considering these environmental variables?
• Temperature
• Relative humidity
• Air flow

5. STSM
Saturated salts
Time taken for RH % to reach target of 43% (indicated by solid vertical line). Each
condition contained 75 g of potassium carbonate (K2CO3) mixed with 50 g of water (to
create a slurry) and evenly spread over either 64 cm2(condition 1), 128 cm2(condition 2),
192 cm2 (condition 3) or 256 cm2 (condition 4). Data points are every five minutes. Each
condition was repeated three times.

6. STSM
Saturated salts
Time taken for RH% to revert from the RH % achieved using potassium carbonate
(K2CO3) to the initial RH % after taking the lid off the glass chamber after condition 4
experiments. Data points are pooled from three repeats and error bars (where visible)
represent standard deviation.

7. STSM
Saturated salts
• In a test chamber, the surface area upon which the saturated salts
are spread is an important factor in the time taken for a RH%
target to be achieved
• If the lid of a test chamber is opened (for example to remove a
sample), the RH% is revert back to that of the local environment
very quickly
• If multiple samples in one chamber, they will receive varying
levels of RH% across an experiment

8. International
Biodeterioration
Research group
Drying time on plastic

9. IBRG
Drying time on plastic
A-C: 2μl
D-F: 5μl
G-I: 10μl
J-L: 20μl

10. IBRG
Drying time on plastic
• Samples of 2, 5 or 10 μl dried significantly (p<0.05) slower at a
temperature closer to hospital ward (20-22.9C)
• The absence of any airflow significantly (p<0.05) increased the
drying time across all volumes
• Higher RH% takes longer to dry

11. Specific examples
Volume
(ul)
Temp
(C)
RH% Drying
Time (m)
Airflow
(m/s)
Notes
5 25.8 52.7 45 0 50% increase in drying time for a 12% humidity
increase. The humidity of both points is still
within ‘normal’ range.5 25.5 40.6 29 0
2 25.8 37.3 10 1.3 70% decrease in drying time by introduction of
1.3m/s average airflow for comparable
temp/RH%.2 26.1 37.1 17 0
10 23.7 56.1 74 1.3 17.5% decrease in drying time for an 8%
increase in temperature.
10 25.7 55.9 61 1.3

13. If you know temperature,
humidity, sample size and
airflow, the model will
calculate drying time

14. If you have a target drying
time, know the humidity of
your room and intended
sample size, the model can
suggest test variables

15. Thanks
Manchester Met
- Jake Tucker (electrical engineer)
- Joanna Verran (microbiologist)
- Lisa Simmons (physics)
Bundesanstalt für Materialforschung und -prüfung (BAM)
- Ina Stephan
- Thomas Dimke
Industrial Microbiology Services Ltd (IMSL)
- Peter Askew
International Biodeterioration Research Group (IBRG)
COST AMiCI (anti-microbial coating innovations to prevent
infectious diseases) programme
Methods Protoc. 2018, 1(4),
36; https://doi.org/10.3390/mps1040036